1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.3 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
156 @section Option Summary
158 Here is a summary of all the options, grouped by type. Explanations are
159 in the following sections.
162 @item Overall Options
163 @xref{Overall Options,,Options Controlling the Kind of Output}.
164 @gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol
165 -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
167 --version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
168 -fdump-ada-spec@r{[}-slim@r{]} -fdump-go-spec=@var{file}}
170 @item C Language Options
171 @xref{C Dialect Options,,Options Controlling C Dialect}.
172 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
173 -aux-info @var{filename} @gol
174 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
175 -fhosted -ffreestanding -fopenmp -fms-extensions -fplan9-extensions @gol
176 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
177 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
178 -fsigned-bitfields -fsigned-char @gol
179 -funsigned-bitfields -funsigned-char}
181 @item C++ Language Options
182 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
183 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
184 -fconserve-space -fconstexpr-depth=@var{n} -ffriend-injection @gol
185 -fno-elide-constructors @gol
186 -fno-enforce-eh-specs @gol
187 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
188 -fno-implicit-templates @gol
189 -fno-implicit-inline-templates @gol
190 -fno-implement-inlines -fms-extensions @gol
191 -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol
192 -fno-optional-diags -fpermissive @gol
193 -fno-pretty-templates @gol
194 -frepo -fno-rtti -fstats -ftemplate-depth=@var{n} @gol
195 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
196 -fno-default-inline -fvisibility-inlines-hidden @gol
197 -fvisibility-ms-compat @gol
198 -Wabi -Wconversion-null -Wctor-dtor-privacy @gol
199 -Wnoexcept -Wnon-virtual-dtor -Wreorder @gol
200 -Weffc++ -Wstrict-null-sentinel @gol
201 -Wno-non-template-friend -Wold-style-cast @gol
202 -Woverloaded-virtual -Wno-pmf-conversions @gol
205 @item Objective-C and Objective-C++ Language Options
206 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
207 Objective-C and Objective-C++ Dialects}.
208 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
209 -fgnu-runtime -fnext-runtime @gol
210 -fno-nil-receivers @gol
211 -fobjc-abi-version=@var{n} @gol
212 -fobjc-call-cxx-cdtors @gol
213 -fobjc-direct-dispatch @gol
214 -fobjc-exceptions @gol
217 -fobjc-std=objc1 @gol
218 -freplace-objc-classes @gol
221 -Wassign-intercept @gol
222 -Wno-protocol -Wselector @gol
223 -Wstrict-selector-match @gol
224 -Wundeclared-selector}
226 @item Language Independent Options
227 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
228 @gccoptlist{-fmessage-length=@var{n} @gol
229 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
230 -fno-diagnostics-show-option}
232 @item Warning Options
233 @xref{Warning Options,,Options to Request or Suppress Warnings}.
234 @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -pedantic @gol
235 -pedantic-errors @gol
236 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
237 -Wno-attributes -Wno-builtin-macro-redefined @gol
238 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
239 -Wchar-subscripts -Wclobbered -Wcomment @gol
240 -Wconversion -Wcoverage-mismatch -Wno-cpp -Wno-deprecated @gol
241 -Wno-deprecated-declarations -Wdisabled-optimization @gol
242 -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol
243 -Wno-endif-labels -Werror -Werror=* @gol
244 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
245 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
246 -Wformat-security -Wformat-y2k @gol
247 -Wframe-larger-than=@var{len} -Wjump-misses-init -Wignored-qualifiers @gol
248 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
249 -Winit-self -Winline @gol
250 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
251 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
252 -Wlogical-op -Wlong-long @gol
253 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
254 -Wmissing-format-attribute -Wmissing-include-dirs @gol
256 -Wno-multichar -Wnonnull -Wno-overflow @gol
257 -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
258 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
259 -Wpointer-arith -Wno-pointer-to-int-cast @gol
260 -Wredundant-decls @gol
261 -Wreturn-type -Wsequence-point -Wshadow @gol
262 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
263 -Wstrict-aliasing -Wstrict-aliasing=n @gol
264 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
265 -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{]} @gol
266 -Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
267 -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol
268 -Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol
269 -Wunsuffixed-float-constants -Wunused -Wunused-function @gol
270 -Wunused-label -Wunused-parameter -Wno-unused-result -Wunused-value @gol
271 -Wunused-variable -Wunused-but-set-parameter -Wunused-but-set-variable @gol
272 -Wvariadic-macros -Wvla -Wvolatile-register-var -Wwrite-strings}
274 @item C and Objective-C-only Warning Options
275 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
276 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
277 -Wold-style-declaration -Wold-style-definition @gol
278 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
279 -Wdeclaration-after-statement -Wpointer-sign}
281 @item Debugging Options
282 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
283 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
284 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
285 -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
286 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
287 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
288 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
289 -fdump-statistics @gol
291 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
295 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
298 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
299 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
300 -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
301 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
302 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
303 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
304 -fdump-tree-nrv -fdump-tree-vect @gol
305 -fdump-tree-sink @gol
306 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
307 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
308 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
309 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
310 -ftree-vectorizer-verbose=@var{n} @gol
311 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
312 -fdump-final-insns=@var{file} @gol
313 -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
314 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
315 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
316 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
317 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
318 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
319 -fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol
320 -fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol
321 -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
322 -ggdb -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
323 -gvms -gxcoff -gxcoff+ @gol
324 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
325 -fdebug-prefix-map=@var{old}=@var{new} @gol
326 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
327 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
328 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
329 -print-multi-directory -print-multi-lib -print-multi-os-directory @gol
330 -print-prog-name=@var{program} -print-search-dirs -Q @gol
331 -print-sysroot -print-sysroot-headers-suffix @gol
332 -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
334 @item Optimization Options
335 @xref{Optimize Options,,Options that Control Optimization}.
336 @gccoptlist{-falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
337 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
338 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
339 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
340 -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol
341 -fcompare-elim -fcprop-registers -fcrossjumping @gol
342 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
343 -fcx-limited-range @gol
344 -fdata-sections -fdce -fdce -fdelayed-branch @gol
345 -fdelete-null-pointer-checks -fdse -fdevirtualize -fdse @gol
346 -fearly-inlining -fipa-sra -fexpensive-optimizations -ffast-math @gol
347 -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
348 -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
349 -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
350 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
351 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
352 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg @gol
353 -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference @gol
354 -fira-algorithm=@var{algorithm} @gol
355 -fira-region=@var{region} @gol
356 -fira-loop-pressure -fno-ira-share-save-slots @gol
357 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
358 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
359 -floop-block -floop-flatten -floop-interchange -floop-strip-mine @gol
360 -floop-parallelize-all -flto -flto-compression-level @gol
361 -flto-partition=@var{alg} -flto-report -fmerge-all-constants @gol
362 -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
363 -fmove-loop-invariants fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg @gol
364 -fno-default-inline @gol
365 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
366 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
367 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
368 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
369 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
370 -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
371 -fprefetch-loop-arrays @gol
372 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
373 -fprofile-generate=@var{path} @gol
374 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
375 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
376 -freorder-blocks-and-partition -freorder-functions @gol
377 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
378 -frounding-math -fsched2-use-superblocks -fsched-pressure @gol
379 -fsched-spec-load -fsched-spec-load-dangerous @gol
380 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
381 -fsched-group-heuristic -fsched-critical-path-heuristic @gol
382 -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
383 -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
384 -fschedule-insns -fschedule-insns2 -fsection-anchors @gol
385 -fselective-scheduling -fselective-scheduling2 @gol
386 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
387 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
388 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
389 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
391 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
392 -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol
393 -ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol
394 -ftree-loop-if-convert-stores -ftree-loop-im @gol
395 -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol
396 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
397 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-pta -ftree-reassoc @gol
398 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
399 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
400 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
401 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
402 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
403 -fwhole-program -fwpa -fuse-linker-plugin @gol
404 --param @var{name}=@var{value}
405 -O -O0 -O1 -O2 -O3 -Os -Ofast}
407 @item Preprocessor Options
408 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
409 @gccoptlist{-A@var{question}=@var{answer} @gol
410 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
411 -C -dD -dI -dM -dN @gol
412 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
413 -idirafter @var{dir} @gol
414 -include @var{file} -imacros @var{file} @gol
415 -iprefix @var{file} -iwithprefix @var{dir} @gol
416 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
417 -imultilib @var{dir} -isysroot @var{dir} @gol
418 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
419 -P -fworking-directory -remap @gol
420 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
421 -Xpreprocessor @var{option}}
423 @item Assembler Option
424 @xref{Assembler Options,,Passing Options to the Assembler}.
425 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
428 @xref{Link Options,,Options for Linking}.
429 @gccoptlist{@var{object-file-name} -l@var{library} @gol
430 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
431 -s -static -static-libgcc -static-libstdc++ -shared @gol
432 -shared-libgcc -symbolic @gol
433 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
436 @item Directory Options
437 @xref{Directory Options,,Options for Directory Search}.
438 @gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol
439 -iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol
442 @item Machine Dependent Options
443 @xref{Submodel Options,,Hardware Models and Configurations}.
444 @c This list is ordered alphanumerically by subsection name.
445 @c Try and put the significant identifier (CPU or system) first,
446 @c so users have a clue at guessing where the ones they want will be.
449 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
450 -mabi=@var{name} @gol
451 -mapcs-stack-check -mno-apcs-stack-check @gol
452 -mapcs-float -mno-apcs-float @gol
453 -mapcs-reentrant -mno-apcs-reentrant @gol
454 -msched-prolog -mno-sched-prolog @gol
455 -mlittle-endian -mbig-endian -mwords-little-endian @gol
456 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
457 -mfp16-format=@var{name}
458 -mthumb-interwork -mno-thumb-interwork @gol
459 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
460 -mstructure-size-boundary=@var{n} @gol
461 -mabort-on-noreturn @gol
462 -mlong-calls -mno-long-calls @gol
463 -msingle-pic-base -mno-single-pic-base @gol
464 -mpic-register=@var{reg} @gol
465 -mnop-fun-dllimport @gol
466 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
467 -mpoke-function-name @gol
469 -mtpcs-frame -mtpcs-leaf-frame @gol
470 -mcaller-super-interworking -mcallee-super-interworking @gol
472 -mword-relocations @gol
473 -mfix-cortex-m3-ldrd}
476 @gccoptlist{-mmcu=@var{mcu} -mno-interrupts @gol
477 -mcall-prologues -mtiny-stack -mint8}
479 @emph{Blackfin Options}
480 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
481 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
482 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
483 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
484 -mno-id-shared-library -mshared-library-id=@var{n} @gol
485 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
486 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
487 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
491 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
492 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
493 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
494 -mstack-align -mdata-align -mconst-align @gol
495 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
496 -melf -maout -melinux -mlinux -sim -sim2 @gol
497 -mmul-bug-workaround -mno-mul-bug-workaround}
499 @emph{Darwin Options}
500 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
501 -arch_only -bind_at_load -bundle -bundle_loader @gol
502 -client_name -compatibility_version -current_version @gol
504 -dependency-file -dylib_file -dylinker_install_name @gol
505 -dynamic -dynamiclib -exported_symbols_list @gol
506 -filelist -flat_namespace -force_cpusubtype_ALL @gol
507 -force_flat_namespace -headerpad_max_install_names @gol
509 -image_base -init -install_name -keep_private_externs @gol
510 -multi_module -multiply_defined -multiply_defined_unused @gol
511 -noall_load -no_dead_strip_inits_and_terms @gol
512 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
513 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
514 -private_bundle -read_only_relocs -sectalign @gol
515 -sectobjectsymbols -whyload -seg1addr @gol
516 -sectcreate -sectobjectsymbols -sectorder @gol
517 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
518 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
519 -segprot -segs_read_only_addr -segs_read_write_addr @gol
520 -single_module -static -sub_library -sub_umbrella @gol
521 -twolevel_namespace -umbrella -undefined @gol
522 -unexported_symbols_list -weak_reference_mismatches @gol
523 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
524 -mkernel -mone-byte-bool}
526 @emph{DEC Alpha Options}
527 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
528 -mieee -mieee-with-inexact -mieee-conformant @gol
529 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
530 -mtrap-precision=@var{mode} -mbuild-constants @gol
531 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
532 -mbwx -mmax -mfix -mcix @gol
533 -mfloat-vax -mfloat-ieee @gol
534 -mexplicit-relocs -msmall-data -mlarge-data @gol
535 -msmall-text -mlarge-text @gol
536 -mmemory-latency=@var{time}}
538 @emph{DEC Alpha/VMS Options}
539 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
542 @gccoptlist{-msmall-model -mno-lsim}
545 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
546 -mhard-float -msoft-float @gol
547 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
548 -mdouble -mno-double @gol
549 -mmedia -mno-media -mmuladd -mno-muladd @gol
550 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
551 -mlinked-fp -mlong-calls -malign-labels @gol
552 -mlibrary-pic -macc-4 -macc-8 @gol
553 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
554 -moptimize-membar -mno-optimize-membar @gol
555 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
556 -mvliw-branch -mno-vliw-branch @gol
557 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
558 -mno-nested-cond-exec -mtomcat-stats @gol
562 @emph{GNU/Linux Options}
563 @gccoptlist{-mglibc -muclibc -mbionic -mandroid @gol
564 -tno-android-cc -tno-android-ld}
566 @emph{H8/300 Options}
567 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
570 @gccoptlist{-march=@var{architecture-type} @gol
571 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
572 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
573 -mfixed-range=@var{register-range} @gol
574 -mjump-in-delay -mlinker-opt -mlong-calls @gol
575 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
576 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
577 -mno-jump-in-delay -mno-long-load-store @gol
578 -mno-portable-runtime -mno-soft-float @gol
579 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
580 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
581 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
582 -munix=@var{unix-std} -nolibdld -static -threads}
584 @emph{i386 and x86-64 Options}
585 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
586 -mfpmath=@var{unit} @gol
587 -masm=@var{dialect} -mno-fancy-math-387 @gol
588 -mno-fp-ret-in-387 -msoft-float @gol
589 -mno-wide-multiply -mrtd -malign-double @gol
590 -mpreferred-stack-boundary=@var{num} @gol
591 -mincoming-stack-boundary=@var{num} @gol
592 -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mvzeroupper @gol
593 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
594 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfused-madd @gol
595 -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlwp @gol
596 -mthreads -mno-align-stringops -minline-all-stringops @gol
597 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
598 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
599 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
600 -mveclibabi=@var{type} -mvect8-ret-in-mem @gol
601 -mpc32 -mpc64 -mpc80 -mstackrealign @gol
602 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
603 -mcmodel=@var{code-model} -mabi=@var{name} @gol
604 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
605 -msse2avx -mfentry -m8bit-idiv}
607 @emph{i386 and x86-64 Windows Options}
608 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
609 -mnop-fun-dllimport -mthread @gol
610 -municode -mwin32 -mwindows -fno-set-stack-executable}
613 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
614 -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
615 -mconstant-gp -mauto-pic -mfused-madd @gol
616 -minline-float-divide-min-latency @gol
617 -minline-float-divide-max-throughput @gol
618 -mno-inline-float-divide @gol
619 -minline-int-divide-min-latency @gol
620 -minline-int-divide-max-throughput @gol
621 -mno-inline-int-divide @gol
622 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
623 -mno-inline-sqrt @gol
624 -mdwarf2-asm -mearly-stop-bits @gol
625 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
626 -mtune=@var{cpu-type} -milp32 -mlp64 @gol
627 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
628 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
629 -msched-spec-ldc -msched-spec-control-ldc @gol
630 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
631 -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
632 -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
633 -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
635 @emph{IA-64/VMS Options}
636 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
639 @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
640 -msign-extend-enabled -muser-enabled}
642 @emph{M32R/D Options}
643 @gccoptlist{-m32r2 -m32rx -m32r @gol
645 -malign-loops -mno-align-loops @gol
646 -missue-rate=@var{number} @gol
647 -mbranch-cost=@var{number} @gol
648 -mmodel=@var{code-size-model-type} @gol
649 -msdata=@var{sdata-type} @gol
650 -mno-flush-func -mflush-func=@var{name} @gol
651 -mno-flush-trap -mflush-trap=@var{number} @gol
655 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
657 @emph{M680x0 Options}
658 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
659 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
660 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
661 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
662 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
663 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
664 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
665 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
669 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
670 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
671 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
672 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
673 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
676 @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
677 -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
678 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
679 -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
682 @emph{MicroBlaze Options}
683 @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol
684 -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol
685 -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol
686 -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol
687 -mxl-mode-@var{app-model}}
690 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
691 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
692 -mips64 -mips64r2 @gol
693 -mips16 -mno-mips16 -mflip-mips16 @gol
694 -minterlink-mips16 -mno-interlink-mips16 @gol
695 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
696 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
697 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
698 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
699 -mfpu=@var{fpu-type} @gol
700 -msmartmips -mno-smartmips @gol
701 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
702 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
703 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
704 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
705 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
706 -membedded-data -mno-embedded-data @gol
707 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
708 -mcode-readable=@var{setting} @gol
709 -msplit-addresses -mno-split-addresses @gol
710 -mexplicit-relocs -mno-explicit-relocs @gol
711 -mcheck-zero-division -mno-check-zero-division @gol
712 -mdivide-traps -mdivide-breaks @gol
713 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
714 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
715 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
716 -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol
717 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
718 -mflush-func=@var{func} -mno-flush-func @gol
719 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
720 -mfp-exceptions -mno-fp-exceptions @gol
721 -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
722 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address}
725 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
726 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
727 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
728 -mno-base-addresses -msingle-exit -mno-single-exit}
730 @emph{MN10300 Options}
731 @gccoptlist{-mmult-bug -mno-mult-bug @gol
732 -mno-am33 -mam33 -mam33-2 -mam34 @gol
733 -mtune=@var{cpu-type} @gol
734 -mreturn-pointer-on-d0 @gol
735 -mno-crt0 -mrelax -mliw -msetlb}
737 @emph{PDP-11 Options}
738 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
739 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
740 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
741 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
742 -mbranch-expensive -mbranch-cheap @gol
743 -munix-asm -mdec-asm}
745 @emph{picoChip Options}
746 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol
747 -msymbol-as-address -mno-inefficient-warnings}
749 @emph{PowerPC Options}
750 See RS/6000 and PowerPC Options.
752 @emph{RS/6000 and PowerPC Options}
753 @gccoptlist{-mcpu=@var{cpu-type} @gol
754 -mtune=@var{cpu-type} @gol
755 -mcmodel=@var{code-model} @gol
756 -mpower -mno-power -mpower2 -mno-power2 @gol
757 -mpowerpc -mpowerpc64 -mno-powerpc @gol
758 -maltivec -mno-altivec @gol
759 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
760 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
761 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
762 -mfprnd -mno-fprnd @gol
763 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
764 -mnew-mnemonics -mold-mnemonics @gol
765 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
766 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
767 -malign-power -malign-natural @gol
768 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
769 -msingle-float -mdouble-float -msimple-fpu @gol
770 -mstring -mno-string -mupdate -mno-update @gol
771 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
772 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
773 -mstrict-align -mno-strict-align -mrelocatable @gol
774 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
775 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
776 -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol
777 -mprioritize-restricted-insns=@var{priority} @gol
778 -msched-costly-dep=@var{dependence_type} @gol
779 -minsert-sched-nops=@var{scheme} @gol
780 -mcall-sysv -mcall-netbsd @gol
781 -maix-struct-return -msvr4-struct-return @gol
782 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
783 -mblock-move-inline-limit=@var{num} @gol
784 -misel -mno-isel @gol
785 -misel=yes -misel=no @gol
787 -mspe=yes -mspe=no @gol
789 -mgen-cell-microcode -mwarn-cell-microcode @gol
790 -mvrsave -mno-vrsave @gol
791 -mmulhw -mno-mulhw @gol
792 -mdlmzb -mno-dlmzb @gol
793 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
794 -mprototype -mno-prototype @gol
795 -msim -mmvme -mads -myellowknife -memb -msdata @gol
796 -msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol
797 -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
798 -mno-recip-precision @gol
799 -mveclibabi=@var{type} -mfriz -mno-friz}
802 @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
804 -mbig-endian-data -mlittle-endian-data @gol
807 -mas100-syntax -mno-as100-syntax@gol
809 -mmax-constant-size=@gol
811 -msave-acc-in-interrupts}
813 @emph{S/390 and zSeries Options}
814 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
815 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
816 -mlong-double-64 -mlong-double-128 @gol
817 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
818 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
819 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
820 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
821 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
824 @gccoptlist{-meb -mel @gol
828 -mscore5 -mscore5u -mscore7 -mscore7d}
831 @gccoptlist{-m1 -m2 -m2e @gol
832 -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
834 -m4-nofpu -m4-single-only -m4-single -m4 @gol
835 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
836 -m5-64media -m5-64media-nofpu @gol
837 -m5-32media -m5-32media-nofpu @gol
838 -m5-compact -m5-compact-nofpu @gol
839 -mb -ml -mdalign -mrelax @gol
840 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
841 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
842 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
843 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
844 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
845 -maccumulate-outgoing-args -minvalid-symbols}
847 @emph{Solaris 2 Options}
848 @gccoptlist{-mimpure-text -mno-impure-text @gol
852 @gccoptlist{-mcpu=@var{cpu-type} @gol
853 -mtune=@var{cpu-type} @gol
854 -mcmodel=@var{code-model} @gol
855 -m32 -m64 -mapp-regs -mno-app-regs @gol
856 -mfaster-structs -mno-faster-structs @gol
857 -mfpu -mno-fpu -mhard-float -msoft-float @gol
858 -mhard-quad-float -msoft-quad-float @gol
860 -mstack-bias -mno-stack-bias @gol
861 -munaligned-doubles -mno-unaligned-doubles @gol
862 -mv8plus -mno-v8plus -mvis -mno-vis}
865 @gccoptlist{-mwarn-reloc -merror-reloc @gol
866 -msafe-dma -munsafe-dma @gol
868 -msmall-mem -mlarge-mem -mstdmain @gol
869 -mfixed-range=@var{register-range} @gol
871 -maddress-space-conversion -mno-address-space-conversion @gol
872 -mcache-size=@var{cache-size} @gol
873 -matomic-updates -mno-atomic-updates}
875 @emph{System V Options}
876 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
879 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
880 -mprolog-function -mno-prolog-function -mspace @gol
881 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
882 -mapp-regs -mno-app-regs @gol
883 -mdisable-callt -mno-disable-callt @gol
886 -mv850e1 -mv850es @gol
891 @gccoptlist{-mg -mgnu -munix}
893 @emph{VxWorks Options}
894 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
895 -Xbind-lazy -Xbind-now}
897 @emph{x86-64 Options}
898 See i386 and x86-64 Options.
900 @emph{Xstormy16 Options}
903 @emph{Xtensa Options}
904 @gccoptlist{-mconst16 -mno-const16 @gol
905 -mfused-madd -mno-fused-madd @gol
907 -mserialize-volatile -mno-serialize-volatile @gol
908 -mtext-section-literals -mno-text-section-literals @gol
909 -mtarget-align -mno-target-align @gol
910 -mlongcalls -mno-longcalls}
912 @emph{zSeries Options}
913 See S/390 and zSeries Options.
915 @item Code Generation Options
916 @xref{Code Gen Options,,Options for Code Generation Conventions}.
917 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
918 -ffixed-@var{reg} -fexceptions @gol
919 -fnon-call-exceptions -funwind-tables @gol
920 -fasynchronous-unwind-tables @gol
921 -finhibit-size-directive -finstrument-functions @gol
922 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
923 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
924 -fno-common -fno-ident @gol
925 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
926 -fno-jump-tables @gol
927 -frecord-gcc-switches @gol
928 -freg-struct-return -fshort-enums @gol
929 -fshort-double -fshort-wchar @gol
930 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
931 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
932 -fno-stack-limit -fsplit-stack @gol
933 -fleading-underscore -ftls-model=@var{model} @gol
934 -ftrapv -fwrapv -fbounds-check @gol
935 -fvisibility -fstrict-volatile-bitfields}
939 * Overall Options:: Controlling the kind of output:
940 an executable, object files, assembler files,
941 or preprocessed source.
942 * C Dialect Options:: Controlling the variant of C language compiled.
943 * C++ Dialect Options:: Variations on C++.
944 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
946 * Language Independent Options:: Controlling how diagnostics should be
948 * Warning Options:: How picky should the compiler be?
949 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
950 * Optimize Options:: How much optimization?
951 * Preprocessor Options:: Controlling header files and macro definitions.
952 Also, getting dependency information for Make.
953 * Assembler Options:: Passing options to the assembler.
954 * Link Options:: Specifying libraries and so on.
955 * Directory Options:: Where to find header files and libraries.
956 Where to find the compiler executable files.
957 * Spec Files:: How to pass switches to sub-processes.
958 * Target Options:: Running a cross-compiler, or an old version of GCC.
961 @node Overall Options
962 @section Options Controlling the Kind of Output
964 Compilation can involve up to four stages: preprocessing, compilation
965 proper, assembly and linking, always in that order. GCC is capable of
966 preprocessing and compiling several files either into several
967 assembler input files, or into one assembler input file; then each
968 assembler input file produces an object file, and linking combines all
969 the object files (those newly compiled, and those specified as input)
970 into an executable file.
972 @cindex file name suffix
973 For any given input file, the file name suffix determines what kind of
978 C source code which must be preprocessed.
981 C source code which should not be preprocessed.
984 C++ source code which should not be preprocessed.
987 Objective-C source code. Note that you must link with the @file{libobjc}
988 library to make an Objective-C program work.
991 Objective-C source code which should not be preprocessed.
995 Objective-C++ source code. Note that you must link with the @file{libobjc}
996 library to make an Objective-C++ program work. Note that @samp{.M} refers
997 to a literal capital M@.
1000 Objective-C++ source code which should not be preprocessed.
1003 C, C++, Objective-C or Objective-C++ header file to be turned into a
1004 precompiled header (default), or C, C++ header file to be turned into an
1005 Ada spec (via the @option{-fdump-ada-spec} switch).
1008 @itemx @var{file}.cp
1009 @itemx @var{file}.cxx
1010 @itemx @var{file}.cpp
1011 @itemx @var{file}.CPP
1012 @itemx @var{file}.c++
1014 C++ source code which must be preprocessed. Note that in @samp{.cxx},
1015 the last two letters must both be literally @samp{x}. Likewise,
1016 @samp{.C} refers to a literal capital C@.
1020 Objective-C++ source code which must be preprocessed.
1022 @item @var{file}.mii
1023 Objective-C++ source code which should not be preprocessed.
1027 @itemx @var{file}.hp
1028 @itemx @var{file}.hxx
1029 @itemx @var{file}.hpp
1030 @itemx @var{file}.HPP
1031 @itemx @var{file}.h++
1032 @itemx @var{file}.tcc
1033 C++ header file to be turned into a precompiled header or Ada spec.
1036 @itemx @var{file}.for
1037 @itemx @var{file}.ftn
1038 Fixed form Fortran source code which should not be preprocessed.
1041 @itemx @var{file}.FOR
1042 @itemx @var{file}.fpp
1043 @itemx @var{file}.FPP
1044 @itemx @var{file}.FTN
1045 Fixed form Fortran source code which must be preprocessed (with the traditional
1048 @item @var{file}.f90
1049 @itemx @var{file}.f95
1050 @itemx @var{file}.f03
1051 @itemx @var{file}.f08
1052 Free form Fortran source code which should not be preprocessed.
1054 @item @var{file}.F90
1055 @itemx @var{file}.F95
1056 @itemx @var{file}.F03
1057 @itemx @var{file}.F08
1058 Free form Fortran source code which must be preprocessed (with the
1059 traditional preprocessor).
1064 @c FIXME: Descriptions of Java file types.
1070 @item @var{file}.ads
1071 Ada source code file which contains a library unit declaration (a
1072 declaration of a package, subprogram, or generic, or a generic
1073 instantiation), or a library unit renaming declaration (a package,
1074 generic, or subprogram renaming declaration). Such files are also
1077 @item @var{file}.adb
1078 Ada source code file containing a library unit body (a subprogram or
1079 package body). Such files are also called @dfn{bodies}.
1081 @c GCC also knows about some suffixes for languages not yet included:
1092 @itemx @var{file}.sx
1093 Assembler code which must be preprocessed.
1096 An object file to be fed straight into linking.
1097 Any file name with no recognized suffix is treated this way.
1101 You can specify the input language explicitly with the @option{-x} option:
1104 @item -x @var{language}
1105 Specify explicitly the @var{language} for the following input files
1106 (rather than letting the compiler choose a default based on the file
1107 name suffix). This option applies to all following input files until
1108 the next @option{-x} option. Possible values for @var{language} are:
1110 c c-header cpp-output
1111 c++ c++-header c++-cpp-output
1112 objective-c objective-c-header objective-c-cpp-output
1113 objective-c++ objective-c++-header objective-c++-cpp-output
1114 assembler assembler-with-cpp
1116 f77 f77-cpp-input f95 f95-cpp-input
1122 Turn off any specification of a language, so that subsequent files are
1123 handled according to their file name suffixes (as they are if @option{-x}
1124 has not been used at all).
1126 @item -pass-exit-codes
1127 @opindex pass-exit-codes
1128 Normally the @command{gcc} program will exit with the code of 1 if any
1129 phase of the compiler returns a non-success return code. If you specify
1130 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1131 numerically highest error produced by any phase that returned an error
1132 indication. The C, C++, and Fortran frontends return 4, if an internal
1133 compiler error is encountered.
1136 If you only want some of the stages of compilation, you can use
1137 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1138 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1139 @command{gcc} is to stop. Note that some combinations (for example,
1140 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1145 Compile or assemble the source files, but do not link. The linking
1146 stage simply is not done. The ultimate output is in the form of an
1147 object file for each source file.
1149 By default, the object file name for a source file is made by replacing
1150 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1152 Unrecognized input files, not requiring compilation or assembly, are
1157 Stop after the stage of compilation proper; do not assemble. The output
1158 is in the form of an assembler code file for each non-assembler input
1161 By default, the assembler file name for a source file is made by
1162 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1164 Input files that don't require compilation are ignored.
1168 Stop after the preprocessing stage; do not run the compiler proper. The
1169 output is in the form of preprocessed source code, which is sent to the
1172 Input files which don't require preprocessing are ignored.
1174 @cindex output file option
1177 Place output in file @var{file}. This applies regardless to whatever
1178 sort of output is being produced, whether it be an executable file,
1179 an object file, an assembler file or preprocessed C code.
1181 If @option{-o} is not specified, the default is to put an executable
1182 file in @file{a.out}, the object file for
1183 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1184 assembler file in @file{@var{source}.s}, a precompiled header file in
1185 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1190 Print (on standard error output) the commands executed to run the stages
1191 of compilation. Also print the version number of the compiler driver
1192 program and of the preprocessor and the compiler proper.
1196 Like @option{-v} except the commands are not executed and arguments
1197 are quoted unless they contain only alphanumeric characters or @code{./-_}.
1198 This is useful for shell scripts to capture the driver-generated command lines.
1202 Use pipes rather than temporary files for communication between the
1203 various stages of compilation. This fails to work on some systems where
1204 the assembler is unable to read from a pipe; but the GNU assembler has
1209 Print (on the standard output) a description of the command line options
1210 understood by @command{gcc}. If the @option{-v} option is also specified
1211 then @option{--help} will also be passed on to the various processes
1212 invoked by @command{gcc}, so that they can display the command line options
1213 they accept. If the @option{-Wextra} option has also been specified
1214 (prior to the @option{--help} option), then command line options which
1215 have no documentation associated with them will also be displayed.
1218 @opindex target-help
1219 Print (on the standard output) a description of target-specific command
1220 line options for each tool. For some targets extra target-specific
1221 information may also be printed.
1223 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1224 Print (on the standard output) a description of the command line
1225 options understood by the compiler that fit into all specified classes
1226 and qualifiers. These are the supported classes:
1229 @item @samp{optimizers}
1230 This will display all of the optimization options supported by the
1233 @item @samp{warnings}
1234 This will display all of the options controlling warning messages
1235 produced by the compiler.
1238 This will display target-specific options. Unlike the
1239 @option{--target-help} option however, target-specific options of the
1240 linker and assembler will not be displayed. This is because those
1241 tools do not currently support the extended @option{--help=} syntax.
1244 This will display the values recognized by the @option{--param}
1247 @item @var{language}
1248 This will display the options supported for @var{language}, where
1249 @var{language} is the name of one of the languages supported in this
1253 This will display the options that are common to all languages.
1256 These are the supported qualifiers:
1259 @item @samp{undocumented}
1260 Display only those options which are undocumented.
1263 Display options which take an argument that appears after an equal
1264 sign in the same continuous piece of text, such as:
1265 @samp{--help=target}.
1267 @item @samp{separate}
1268 Display options which take an argument that appears as a separate word
1269 following the original option, such as: @samp{-o output-file}.
1272 Thus for example to display all the undocumented target-specific
1273 switches supported by the compiler the following can be used:
1276 --help=target,undocumented
1279 The sense of a qualifier can be inverted by prefixing it with the
1280 @samp{^} character, so for example to display all binary warning
1281 options (i.e., ones that are either on or off and that do not take an
1282 argument), which have a description the following can be used:
1285 --help=warnings,^joined,^undocumented
1288 The argument to @option{--help=} should not consist solely of inverted
1291 Combining several classes is possible, although this usually
1292 restricts the output by so much that there is nothing to display. One
1293 case where it does work however is when one of the classes is
1294 @var{target}. So for example to display all the target-specific
1295 optimization options the following can be used:
1298 --help=target,optimizers
1301 The @option{--help=} option can be repeated on the command line. Each
1302 successive use will display its requested class of options, skipping
1303 those that have already been displayed.
1305 If the @option{-Q} option appears on the command line before the
1306 @option{--help=} option, then the descriptive text displayed by
1307 @option{--help=} is changed. Instead of describing the displayed
1308 options, an indication is given as to whether the option is enabled,
1309 disabled or set to a specific value (assuming that the compiler
1310 knows this at the point where the @option{--help=} option is used).
1312 Here is a truncated example from the ARM port of @command{gcc}:
1315 % gcc -Q -mabi=2 --help=target -c
1316 The following options are target specific:
1318 -mabort-on-noreturn [disabled]
1322 The output is sensitive to the effects of previous command line
1323 options, so for example it is possible to find out which optimizations
1324 are enabled at @option{-O2} by using:
1327 -Q -O2 --help=optimizers
1330 Alternatively you can discover which binary optimizations are enabled
1331 by @option{-O3} by using:
1334 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1335 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1336 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1339 @item -no-canonical-prefixes
1340 @opindex no-canonical-prefixes
1341 Do not expand any symbolic links, resolve references to @samp{/../}
1342 or @samp{/./}, or make the path absolute when generating a relative
1347 Display the version number and copyrights of the invoked GCC@.
1351 Invoke all subcommands under a wrapper program. The name of the
1352 wrapper program and its parameters are passed as a comma separated
1356 gcc -c t.c -wrapper gdb,--args
1359 This will invoke all subprograms of @command{gcc} under
1360 @samp{gdb --args}, thus the invocation of @command{cc1} will be
1361 @samp{gdb --args cc1 @dots{}}.
1363 @item -fplugin=@var{name}.so
1364 Load the plugin code in file @var{name}.so, assumed to be a
1365 shared object to be dlopen'd by the compiler. The base name of
1366 the shared object file is used to identify the plugin for the
1367 purposes of argument parsing (See
1368 @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
1369 Each plugin should define the callback functions specified in the
1372 @item -fplugin-arg-@var{name}-@var{key}=@var{value}
1373 Define an argument called @var{key} with a value of @var{value}
1374 for the plugin called @var{name}.
1376 @item -fdump-ada-spec@r{[}-slim@r{]}
1377 For C and C++ source and include files, generate corresponding Ada
1378 specs. @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn,
1379 GNAT User's Guide}, which provides detailed documentation on this feature.
1381 @item -fdump-go-spec=@var{file}
1382 For input files in any language, generate corresponding Go
1383 declarations in @var{file}. This generates Go @code{const},
1384 @code{type}, @code{var}, and @code{func} declarations which may be a
1385 useful way to start writing a Go interface to code written in some
1388 @include @value{srcdir}/../libiberty/at-file.texi
1392 @section Compiling C++ Programs
1394 @cindex suffixes for C++ source
1395 @cindex C++ source file suffixes
1396 C++ source files conventionally use one of the suffixes @samp{.C},
1397 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1398 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1399 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1400 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1401 files with these names and compiles them as C++ programs even if you
1402 call the compiler the same way as for compiling C programs (usually
1403 with the name @command{gcc}).
1407 However, the use of @command{gcc} does not add the C++ library.
1408 @command{g++} is a program that calls GCC and treats @samp{.c},
1409 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1410 files unless @option{-x} is used, and automatically specifies linking
1411 against the C++ library. This program is also useful when
1412 precompiling a C header file with a @samp{.h} extension for use in C++
1413 compilations. On many systems, @command{g++} is also installed with
1414 the name @command{c++}.
1416 @cindex invoking @command{g++}
1417 When you compile C++ programs, you may specify many of the same
1418 command-line options that you use for compiling programs in any
1419 language; or command-line options meaningful for C and related
1420 languages; or options that are meaningful only for C++ programs.
1421 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1422 explanations of options for languages related to C@.
1423 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1424 explanations of options that are meaningful only for C++ programs.
1426 @node C Dialect Options
1427 @section Options Controlling C Dialect
1428 @cindex dialect options
1429 @cindex language dialect options
1430 @cindex options, dialect
1432 The following options control the dialect of C (or languages derived
1433 from C, such as C++, Objective-C and Objective-C++) that the compiler
1437 @cindex ANSI support
1441 In C mode, this is equivalent to @samp{-std=c90}. In C++ mode, it is
1442 equivalent to @samp{-std=c++98}.
1444 This turns off certain features of GCC that are incompatible with ISO
1445 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1446 such as the @code{asm} and @code{typeof} keywords, and
1447 predefined macros such as @code{unix} and @code{vax} that identify the
1448 type of system you are using. It also enables the undesirable and
1449 rarely used ISO trigraph feature. For the C compiler,
1450 it disables recognition of C++ style @samp{//} comments as well as
1451 the @code{inline} keyword.
1453 The alternate keywords @code{__asm__}, @code{__extension__},
1454 @code{__inline__} and @code{__typeof__} continue to work despite
1455 @option{-ansi}. You would not want to use them in an ISO C program, of
1456 course, but it is useful to put them in header files that might be included
1457 in compilations done with @option{-ansi}. Alternate predefined macros
1458 such as @code{__unix__} and @code{__vax__} are also available, with or
1459 without @option{-ansi}.
1461 The @option{-ansi} option does not cause non-ISO programs to be
1462 rejected gratuitously. For that, @option{-pedantic} is required in
1463 addition to @option{-ansi}. @xref{Warning Options}.
1465 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1466 option is used. Some header files may notice this macro and refrain
1467 from declaring certain functions or defining certain macros that the
1468 ISO standard doesn't call for; this is to avoid interfering with any
1469 programs that might use these names for other things.
1471 Functions that would normally be built in but do not have semantics
1472 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1473 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1474 built-in functions provided by GCC}, for details of the functions
1479 Determine the language standard. @xref{Standards,,Language Standards
1480 Supported by GCC}, for details of these standard versions. This option
1481 is currently only supported when compiling C or C++.
1483 The compiler can accept several base standards, such as @samp{c90} or
1484 @samp{c++98}, and GNU dialects of those standards, such as
1485 @samp{gnu90} or @samp{gnu++98}. By specifying a base standard, the
1486 compiler will accept all programs following that standard and those
1487 using GNU extensions that do not contradict it. For example,
1488 @samp{-std=c90} turns off certain features of GCC that are
1489 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1490 keywords, but not other GNU extensions that do not have a meaning in
1491 ISO C90, such as omitting the middle term of a @code{?:}
1492 expression. On the other hand, by specifying a GNU dialect of a
1493 standard, all features the compiler support are enabled, even when
1494 those features change the meaning of the base standard and some
1495 strict-conforming programs may be rejected. The particular standard
1496 is used by @option{-pedantic} to identify which features are GNU
1497 extensions given that version of the standard. For example
1498 @samp{-std=gnu90 -pedantic} would warn about C++ style @samp{//}
1499 comments, while @samp{-std=gnu99 -pedantic} would not.
1501 A value for this option must be provided; possible values are
1507 Support all ISO C90 programs (certain GNU extensions that conflict
1508 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1510 @item iso9899:199409
1511 ISO C90 as modified in amendment 1.
1517 ISO C99. Note that this standard is not yet fully supported; see
1518 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1519 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1522 ISO C1X, the draft of the next revision of the ISO C standard.
1523 Support is limited and experimental and features enabled by this
1524 option may be changed or removed if changed in or removed from the
1529 GNU dialect of ISO C90 (including some C99 features). This
1530 is the default for C code.
1534 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1535 this will become the default. The name @samp{gnu9x} is deprecated.
1538 GNU dialect of ISO C1X. Support is limited and experimental and
1539 features enabled by this option may be changed or removed if changed
1540 in or removed from the standard draft.
1543 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1547 GNU dialect of @option{-std=c++98}. This is the default for
1551 The working draft of the upcoming ISO C++0x standard. This option
1552 enables experimental features that are likely to be included in
1553 C++0x. The working draft is constantly changing, and any feature that is
1554 enabled by this flag may be removed from future versions of GCC if it is
1555 not part of the C++0x standard.
1558 GNU dialect of @option{-std=c++0x}. This option enables
1559 experimental features that may be removed in future versions of GCC.
1562 @item -fgnu89-inline
1563 @opindex fgnu89-inline
1564 The option @option{-fgnu89-inline} tells GCC to use the traditional
1565 GNU semantics for @code{inline} functions when in C99 mode.
1566 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1567 is accepted and ignored by GCC versions 4.1.3 up to but not including
1568 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1569 C99 mode. Using this option is roughly equivalent to adding the
1570 @code{gnu_inline} function attribute to all inline functions
1571 (@pxref{Function Attributes}).
1573 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1574 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1575 specifies the default behavior). This option was first supported in
1576 GCC 4.3. This option is not supported in @option{-std=c90} or
1577 @option{-std=gnu90} mode.
1579 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1580 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1581 in effect for @code{inline} functions. @xref{Common Predefined
1582 Macros,,,cpp,The C Preprocessor}.
1584 @item -aux-info @var{filename}
1586 Output to the given filename prototyped declarations for all functions
1587 declared and/or defined in a translation unit, including those in header
1588 files. This option is silently ignored in any language other than C@.
1590 Besides declarations, the file indicates, in comments, the origin of
1591 each declaration (source file and line), whether the declaration was
1592 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1593 @samp{O} for old, respectively, in the first character after the line
1594 number and the colon), and whether it came from a declaration or a
1595 definition (@samp{C} or @samp{F}, respectively, in the following
1596 character). In the case of function definitions, a K&R-style list of
1597 arguments followed by their declarations is also provided, inside
1598 comments, after the declaration.
1602 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1603 keyword, so that code can use these words as identifiers. You can use
1604 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1605 instead. @option{-ansi} implies @option{-fno-asm}.
1607 In C++, this switch only affects the @code{typeof} keyword, since
1608 @code{asm} and @code{inline} are standard keywords. You may want to
1609 use the @option{-fno-gnu-keywords} flag instead, which has the same
1610 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1611 switch only affects the @code{asm} and @code{typeof} keywords, since
1612 @code{inline} is a standard keyword in ISO C99.
1615 @itemx -fno-builtin-@var{function}
1616 @opindex fno-builtin
1617 @cindex built-in functions
1618 Don't recognize built-in functions that do not begin with
1619 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1620 functions provided by GCC}, for details of the functions affected,
1621 including those which are not built-in functions when @option{-ansi} or
1622 @option{-std} options for strict ISO C conformance are used because they
1623 do not have an ISO standard meaning.
1625 GCC normally generates special code to handle certain built-in functions
1626 more efficiently; for instance, calls to @code{alloca} may become single
1627 instructions that adjust the stack directly, and calls to @code{memcpy}
1628 may become inline copy loops. The resulting code is often both smaller
1629 and faster, but since the function calls no longer appear as such, you
1630 cannot set a breakpoint on those calls, nor can you change the behavior
1631 of the functions by linking with a different library. In addition,
1632 when a function is recognized as a built-in function, GCC may use
1633 information about that function to warn about problems with calls to
1634 that function, or to generate more efficient code, even if the
1635 resulting code still contains calls to that function. For example,
1636 warnings are given with @option{-Wformat} for bad calls to
1637 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1638 known not to modify global memory.
1640 With the @option{-fno-builtin-@var{function}} option
1641 only the built-in function @var{function} is
1642 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1643 function is named that is not built-in in this version of GCC, this
1644 option is ignored. There is no corresponding
1645 @option{-fbuiltin-@var{function}} option; if you wish to enable
1646 built-in functions selectively when using @option{-fno-builtin} or
1647 @option{-ffreestanding}, you may define macros such as:
1650 #define abs(n) __builtin_abs ((n))
1651 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1656 @cindex hosted environment
1658 Assert that compilation takes place in a hosted environment. This implies
1659 @option{-fbuiltin}. A hosted environment is one in which the
1660 entire standard library is available, and in which @code{main} has a return
1661 type of @code{int}. Examples are nearly everything except a kernel.
1662 This is equivalent to @option{-fno-freestanding}.
1664 @item -ffreestanding
1665 @opindex ffreestanding
1666 @cindex hosted environment
1668 Assert that compilation takes place in a freestanding environment. This
1669 implies @option{-fno-builtin}. A freestanding environment
1670 is one in which the standard library may not exist, and program startup may
1671 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1672 This is equivalent to @option{-fno-hosted}.
1674 @xref{Standards,,Language Standards Supported by GCC}, for details of
1675 freestanding and hosted environments.
1679 @cindex OpenMP parallel
1680 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1681 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1682 compiler generates parallel code according to the OpenMP Application
1683 Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option
1684 implies @option{-pthread}, and thus is only supported on targets that
1685 have support for @option{-pthread}.
1687 @item -fms-extensions
1688 @opindex fms-extensions
1689 Accept some non-standard constructs used in Microsoft header files.
1691 In C++ code, this allows member names in structures to be similar
1692 to previous types declarations.
1701 Some cases of unnamed fields in structures and unions are only
1702 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1703 fields within structs/unions}, for details.
1705 @item -fplan9-extensions
1706 Accept some non-standard constructs used in Plan 9 code.
1708 This enables @option{-fms-extensions}, permits passing pointers to
1709 structures with anonymous fields to functions which expect pointers to
1710 elements of the type of the field, and permits referring to anonymous
1711 fields declared using a typedef. @xref{Unnamed Fields,,Unnamed
1712 struct/union fields within structs/unions}, for details. This is only
1713 supported for C, not C++.
1717 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1718 options for strict ISO C conformance) implies @option{-trigraphs}.
1720 @item -no-integrated-cpp
1721 @opindex no-integrated-cpp
1722 Performs a compilation in two passes: preprocessing and compiling. This
1723 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1724 @option{-B} option. The user supplied compilation step can then add in
1725 an additional preprocessing step after normal preprocessing but before
1726 compiling. The default is to use the integrated cpp (internal cpp)
1728 The semantics of this option will change if "cc1", "cc1plus", and
1729 "cc1obj" are merged.
1731 @cindex traditional C language
1732 @cindex C language, traditional
1734 @itemx -traditional-cpp
1735 @opindex traditional-cpp
1736 @opindex traditional
1737 Formerly, these options caused GCC to attempt to emulate a pre-standard
1738 C compiler. They are now only supported with the @option{-E} switch.
1739 The preprocessor continues to support a pre-standard mode. See the GNU
1740 CPP manual for details.
1742 @item -fcond-mismatch
1743 @opindex fcond-mismatch
1744 Allow conditional expressions with mismatched types in the second and
1745 third arguments. The value of such an expression is void. This option
1746 is not supported for C++.
1748 @item -flax-vector-conversions
1749 @opindex flax-vector-conversions
1750 Allow implicit conversions between vectors with differing numbers of
1751 elements and/or incompatible element types. This option should not be
1754 @item -funsigned-char
1755 @opindex funsigned-char
1756 Let the type @code{char} be unsigned, like @code{unsigned char}.
1758 Each kind of machine has a default for what @code{char} should
1759 be. It is either like @code{unsigned char} by default or like
1760 @code{signed char} by default.
1762 Ideally, a portable program should always use @code{signed char} or
1763 @code{unsigned char} when it depends on the signedness of an object.
1764 But many programs have been written to use plain @code{char} and
1765 expect it to be signed, or expect it to be unsigned, depending on the
1766 machines they were written for. This option, and its inverse, let you
1767 make such a program work with the opposite default.
1769 The type @code{char} is always a distinct type from each of
1770 @code{signed char} or @code{unsigned char}, even though its behavior
1771 is always just like one of those two.
1774 @opindex fsigned-char
1775 Let the type @code{char} be signed, like @code{signed char}.
1777 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1778 the negative form of @option{-funsigned-char}. Likewise, the option
1779 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1781 @item -fsigned-bitfields
1782 @itemx -funsigned-bitfields
1783 @itemx -fno-signed-bitfields
1784 @itemx -fno-unsigned-bitfields
1785 @opindex fsigned-bitfields
1786 @opindex funsigned-bitfields
1787 @opindex fno-signed-bitfields
1788 @opindex fno-unsigned-bitfields
1789 These options control whether a bit-field is signed or unsigned, when the
1790 declaration does not use either @code{signed} or @code{unsigned}. By
1791 default, such a bit-field is signed, because this is consistent: the
1792 basic integer types such as @code{int} are signed types.
1795 @node C++ Dialect Options
1796 @section Options Controlling C++ Dialect
1798 @cindex compiler options, C++
1799 @cindex C++ options, command line
1800 @cindex options, C++
1801 This section describes the command-line options that are only meaningful
1802 for C++ programs; but you can also use most of the GNU compiler options
1803 regardless of what language your program is in. For example, you
1804 might compile a file @code{firstClass.C} like this:
1807 g++ -g -frepo -O -c firstClass.C
1811 In this example, only @option{-frepo} is an option meant
1812 only for C++ programs; you can use the other options with any
1813 language supported by GCC@.
1815 Here is a list of options that are @emph{only} for compiling C++ programs:
1819 @item -fabi-version=@var{n}
1820 @opindex fabi-version
1821 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1822 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1823 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1824 the version that conforms most closely to the C++ ABI specification.
1825 Therefore, the ABI obtained using version 0 will change as ABI bugs
1828 The default is version 2.
1830 Version 3 corrects an error in mangling a constant address as a
1833 Version 4 implements a standard mangling for vector types.
1835 Version 5 corrects the mangling of attribute const/volatile on
1836 function pointer types, decltype of a plain decl, and use of a
1837 function parameter in the declaration of another parameter.
1839 See also @option{-Wabi}.
1841 @item -fno-access-control
1842 @opindex fno-access-control
1843 Turn off all access checking. This switch is mainly useful for working
1844 around bugs in the access control code.
1848 Check that the pointer returned by @code{operator new} is non-null
1849 before attempting to modify the storage allocated. This check is
1850 normally unnecessary because the C++ standard specifies that
1851 @code{operator new} will only return @code{0} if it is declared
1852 @samp{throw()}, in which case the compiler will always check the
1853 return value even without this option. In all other cases, when
1854 @code{operator new} has a non-empty exception specification, memory
1855 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1856 @samp{new (nothrow)}.
1858 @item -fconserve-space
1859 @opindex fconserve-space
1860 Put uninitialized or runtime-initialized global variables into the
1861 common segment, as C does. This saves space in the executable at the
1862 cost of not diagnosing duplicate definitions. If you compile with this
1863 flag and your program mysteriously crashes after @code{main()} has
1864 completed, you may have an object that is being destroyed twice because
1865 two definitions were merged.
1867 This option is no longer useful on most targets, now that support has
1868 been added for putting variables into BSS without making them common.
1870 @item -fconstexpr-depth=@var{n}
1871 @opindex fconstexpr-depth
1872 Set the maximum nested evaluation depth for C++0x constexpr functions
1873 to @var{n}. A limit is needed to detect endless recursion during
1874 constant expression evaluation. The minimum specified by the standard
1877 @item -fno-deduce-init-list
1878 @opindex fno-deduce-init-list
1879 Disable deduction of a template type parameter as
1880 std::initializer_list from a brace-enclosed initializer list, i.e.
1883 template <class T> auto forward(T t) -> decltype (realfn (t))
1890 forward(@{1,2@}); // call forward<std::initializer_list<int>>
1894 This option is present because this deduction is an extension to the
1895 current specification in the C++0x working draft, and there was
1896 some concern about potential overload resolution problems.
1898 @item -ffriend-injection
1899 @opindex ffriend-injection
1900 Inject friend functions into the enclosing namespace, so that they are
1901 visible outside the scope of the class in which they are declared.
1902 Friend functions were documented to work this way in the old Annotated
1903 C++ Reference Manual, and versions of G++ before 4.1 always worked
1904 that way. However, in ISO C++ a friend function which is not declared
1905 in an enclosing scope can only be found using argument dependent
1906 lookup. This option causes friends to be injected as they were in
1909 This option is for compatibility, and may be removed in a future
1912 @item -fno-elide-constructors
1913 @opindex fno-elide-constructors
1914 The C++ standard allows an implementation to omit creating a temporary
1915 which is only used to initialize another object of the same type.
1916 Specifying this option disables that optimization, and forces G++ to
1917 call the copy constructor in all cases.
1919 @item -fno-enforce-eh-specs
1920 @opindex fno-enforce-eh-specs
1921 Don't generate code to check for violation of exception specifications
1922 at runtime. This option violates the C++ standard, but may be useful
1923 for reducing code size in production builds, much like defining
1924 @samp{NDEBUG}. This does not give user code permission to throw
1925 exceptions in violation of the exception specifications; the compiler
1926 will still optimize based on the specifications, so throwing an
1927 unexpected exception will result in undefined behavior.
1930 @itemx -fno-for-scope
1932 @opindex fno-for-scope
1933 If @option{-ffor-scope} is specified, the scope of variables declared in
1934 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1935 as specified by the C++ standard.
1936 If @option{-fno-for-scope} is specified, the scope of variables declared in
1937 a @i{for-init-statement} extends to the end of the enclosing scope,
1938 as was the case in old versions of G++, and other (traditional)
1939 implementations of C++.
1941 The default if neither flag is given to follow the standard,
1942 but to allow and give a warning for old-style code that would
1943 otherwise be invalid, or have different behavior.
1945 @item -fno-gnu-keywords
1946 @opindex fno-gnu-keywords
1947 Do not recognize @code{typeof} as a keyword, so that code can use this
1948 word as an identifier. You can use the keyword @code{__typeof__} instead.
1949 @option{-ansi} implies @option{-fno-gnu-keywords}.
1951 @item -fno-implicit-templates
1952 @opindex fno-implicit-templates
1953 Never emit code for non-inline templates which are instantiated
1954 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1955 @xref{Template Instantiation}, for more information.
1957 @item -fno-implicit-inline-templates
1958 @opindex fno-implicit-inline-templates
1959 Don't emit code for implicit instantiations of inline templates, either.
1960 The default is to handle inlines differently so that compiles with and
1961 without optimization will need the same set of explicit instantiations.
1963 @item -fno-implement-inlines
1964 @opindex fno-implement-inlines
1965 To save space, do not emit out-of-line copies of inline functions
1966 controlled by @samp{#pragma implementation}. This will cause linker
1967 errors if these functions are not inlined everywhere they are called.
1969 @item -fms-extensions
1970 @opindex fms-extensions
1971 Disable pedantic warnings about constructs used in MFC, such as implicit
1972 int and getting a pointer to member function via non-standard syntax.
1974 @item -fno-nonansi-builtins
1975 @opindex fno-nonansi-builtins
1976 Disable built-in declarations of functions that are not mandated by
1977 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1978 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1981 @opindex fnothrow-opt
1982 Treat a @code{throw()} exception specification as though it were a
1983 @code{noexcept} specification to reduce or eliminate the text size
1984 overhead relative to a function with no exception specification. If
1985 the function has local variables of types with non-trivial
1986 destructors, the exception specification will actually make the
1987 function smaller because the EH cleanups for those variables can be
1988 optimized away. The semantic effect is that an exception thrown out of
1989 a function with such an exception specification will result in a call
1990 to @code{terminate} rather than @code{unexpected}.
1992 @item -fno-operator-names
1993 @opindex fno-operator-names
1994 Do not treat the operator name keywords @code{and}, @code{bitand},
1995 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1996 synonyms as keywords.
1998 @item -fno-optional-diags
1999 @opindex fno-optional-diags
2000 Disable diagnostics that the standard says a compiler does not need to
2001 issue. Currently, the only such diagnostic issued by G++ is the one for
2002 a name having multiple meanings within a class.
2005 @opindex fpermissive
2006 Downgrade some diagnostics about nonconformant code from errors to
2007 warnings. Thus, using @option{-fpermissive} will allow some
2008 nonconforming code to compile.
2010 @item -fno-pretty-templates
2011 @opindex fno-pretty-templates
2012 When an error message refers to a specialization of a function
2013 template, the compiler will normally print the signature of the
2014 template followed by the template arguments and any typedefs or
2015 typenames in the signature (e.g. @code{void f(T) [with T = int]}
2016 rather than @code{void f(int)}) so that it's clear which template is
2017 involved. When an error message refers to a specialization of a class
2018 template, the compiler will omit any template arguments which match
2019 the default template arguments for that template. If either of these
2020 behaviors make it harder to understand the error message rather than
2021 easier, using @option{-fno-pretty-templates} will disable them.
2025 Enable automatic template instantiation at link time. This option also
2026 implies @option{-fno-implicit-templates}. @xref{Template
2027 Instantiation}, for more information.
2031 Disable generation of information about every class with virtual
2032 functions for use by the C++ runtime type identification features
2033 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
2034 of the language, you can save some space by using this flag. Note that
2035 exception handling uses the same information, but it will generate it as
2036 needed. The @samp{dynamic_cast} operator can still be used for casts that
2037 do not require runtime type information, i.e.@: casts to @code{void *} or to
2038 unambiguous base classes.
2042 Emit statistics about front-end processing at the end of the compilation.
2043 This information is generally only useful to the G++ development team.
2045 @item -fstrict-enums
2046 @opindex fstrict-enums
2047 Allow the compiler to optimize using the assumption that a value of
2048 enumeration type can only be one of the values of the enumeration (as
2049 defined in the C++ standard; basically, a value which can be
2050 represented in the minimum number of bits needed to represent all the
2051 enumerators). This assumption may not be valid if the program uses a
2052 cast to convert an arbitrary integer value to the enumeration type.
2054 @item -ftemplate-depth=@var{n}
2055 @opindex ftemplate-depth
2056 Set the maximum instantiation depth for template classes to @var{n}.
2057 A limit on the template instantiation depth is needed to detect
2058 endless recursions during template class instantiation. ANSI/ISO C++
2059 conforming programs must not rely on a maximum depth greater than 17
2060 (changed to 1024 in C++0x).
2062 @item -fno-threadsafe-statics
2063 @opindex fno-threadsafe-statics
2064 Do not emit the extra code to use the routines specified in the C++
2065 ABI for thread-safe initialization of local statics. You can use this
2066 option to reduce code size slightly in code that doesn't need to be
2069 @item -fuse-cxa-atexit
2070 @opindex fuse-cxa-atexit
2071 Register destructors for objects with static storage duration with the
2072 @code{__cxa_atexit} function rather than the @code{atexit} function.
2073 This option is required for fully standards-compliant handling of static
2074 destructors, but will only work if your C library supports
2075 @code{__cxa_atexit}.
2077 @item -fno-use-cxa-get-exception-ptr
2078 @opindex fno-use-cxa-get-exception-ptr
2079 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
2080 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
2081 if the runtime routine is not available.
2083 @item -fvisibility-inlines-hidden
2084 @opindex fvisibility-inlines-hidden
2085 This switch declares that the user does not attempt to compare
2086 pointers to inline methods where the addresses of the two functions
2087 were taken in different shared objects.
2089 The effect of this is that GCC may, effectively, mark inline methods with
2090 @code{__attribute__ ((visibility ("hidden")))} so that they do not
2091 appear in the export table of a DSO and do not require a PLT indirection
2092 when used within the DSO@. Enabling this option can have a dramatic effect
2093 on load and link times of a DSO as it massively reduces the size of the
2094 dynamic export table when the library makes heavy use of templates.
2096 The behavior of this switch is not quite the same as marking the
2097 methods as hidden directly, because it does not affect static variables
2098 local to the function or cause the compiler to deduce that
2099 the function is defined in only one shared object.
2101 You may mark a method as having a visibility explicitly to negate the
2102 effect of the switch for that method. For example, if you do want to
2103 compare pointers to a particular inline method, you might mark it as
2104 having default visibility. Marking the enclosing class with explicit
2105 visibility will have no effect.
2107 Explicitly instantiated inline methods are unaffected by this option
2108 as their linkage might otherwise cross a shared library boundary.
2109 @xref{Template Instantiation}.
2111 @item -fvisibility-ms-compat
2112 @opindex fvisibility-ms-compat
2113 This flag attempts to use visibility settings to make GCC's C++
2114 linkage model compatible with that of Microsoft Visual Studio.
2116 The flag makes these changes to GCC's linkage model:
2120 It sets the default visibility to @code{hidden}, like
2121 @option{-fvisibility=hidden}.
2124 Types, but not their members, are not hidden by default.
2127 The One Definition Rule is relaxed for types without explicit
2128 visibility specifications which are defined in more than one different
2129 shared object: those declarations are permitted if they would have
2130 been permitted when this option was not used.
2133 In new code it is better to use @option{-fvisibility=hidden} and
2134 export those classes which are intended to be externally visible.
2135 Unfortunately it is possible for code to rely, perhaps accidentally,
2136 on the Visual Studio behavior.
2138 Among the consequences of these changes are that static data members
2139 of the same type with the same name but defined in different shared
2140 objects will be different, so changing one will not change the other;
2141 and that pointers to function members defined in different shared
2142 objects may not compare equal. When this flag is given, it is a
2143 violation of the ODR to define types with the same name differently.
2147 Do not use weak symbol support, even if it is provided by the linker.
2148 By default, G++ will use weak symbols if they are available. This
2149 option exists only for testing, and should not be used by end-users;
2150 it will result in inferior code and has no benefits. This option may
2151 be removed in a future release of G++.
2155 Do not search for header files in the standard directories specific to
2156 C++, but do still search the other standard directories. (This option
2157 is used when building the C++ library.)
2160 In addition, these optimization, warning, and code generation options
2161 have meanings only for C++ programs:
2164 @item -fno-default-inline
2165 @opindex fno-default-inline
2166 Do not assume @samp{inline} for functions defined inside a class scope.
2167 @xref{Optimize Options,,Options That Control Optimization}. Note that these
2168 functions will have linkage like inline functions; they just won't be
2171 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
2174 Warn when G++ generates code that is probably not compatible with the
2175 vendor-neutral C++ ABI@. Although an effort has been made to warn about
2176 all such cases, there are probably some cases that are not warned about,
2177 even though G++ is generating incompatible code. There may also be
2178 cases where warnings are emitted even though the code that is generated
2181 You should rewrite your code to avoid these warnings if you are
2182 concerned about the fact that code generated by G++ may not be binary
2183 compatible with code generated by other compilers.
2185 The known incompatibilities in @option{-fabi-version=2} (the default) include:
2190 A template with a non-type template parameter of reference type is
2191 mangled incorrectly:
2194 template <int &> struct S @{@};
2198 This is fixed in @option{-fabi-version=3}.
2201 SIMD vector types declared using @code{__attribute ((vector_size))} are
2202 mangled in a non-standard way that does not allow for overloading of
2203 functions taking vectors of different sizes.
2205 The mangling is changed in @option{-fabi-version=4}.
2208 The known incompatibilities in @option{-fabi-version=1} include:
2213 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
2214 pack data into the same byte as a base class. For example:
2217 struct A @{ virtual void f(); int f1 : 1; @};
2218 struct B : public A @{ int f2 : 1; @};
2222 In this case, G++ will place @code{B::f2} into the same byte
2223 as@code{A::f1}; other compilers will not. You can avoid this problem
2224 by explicitly padding @code{A} so that its size is a multiple of the
2225 byte size on your platform; that will cause G++ and other compilers to
2226 layout @code{B} identically.
2229 Incorrect handling of tail-padding for virtual bases. G++ does not use
2230 tail padding when laying out virtual bases. For example:
2233 struct A @{ virtual void f(); char c1; @};
2234 struct B @{ B(); char c2; @};
2235 struct C : public A, public virtual B @{@};
2239 In this case, G++ will not place @code{B} into the tail-padding for
2240 @code{A}; other compilers will. You can avoid this problem by
2241 explicitly padding @code{A} so that its size is a multiple of its
2242 alignment (ignoring virtual base classes); that will cause G++ and other
2243 compilers to layout @code{C} identically.
2246 Incorrect handling of bit-fields with declared widths greater than that
2247 of their underlying types, when the bit-fields appear in a union. For
2251 union U @{ int i : 4096; @};
2255 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2256 union too small by the number of bits in an @code{int}.
2259 Empty classes can be placed at incorrect offsets. For example:
2269 struct C : public B, public A @{@};
2273 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2274 it should be placed at offset zero. G++ mistakenly believes that the
2275 @code{A} data member of @code{B} is already at offset zero.
2278 Names of template functions whose types involve @code{typename} or
2279 template template parameters can be mangled incorrectly.
2282 template <typename Q>
2283 void f(typename Q::X) @{@}
2285 template <template <typename> class Q>
2286 void f(typename Q<int>::X) @{@}
2290 Instantiations of these templates may be mangled incorrectly.
2294 It also warns psABI related changes. The known psABI changes at this
2300 For SYSV/x86-64, when passing union with long double, it is changed to
2301 pass in memory as specified in psABI. For example:
2311 @code{union U} will always be passed in memory.
2315 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2316 @opindex Wctor-dtor-privacy
2317 @opindex Wno-ctor-dtor-privacy
2318 Warn when a class seems unusable because all the constructors or
2319 destructors in that class are private, and it has neither friends nor
2320 public static member functions.
2322 @item -Wnoexcept @r{(C++ and Objective-C++ only)}
2324 @opindex Wno-noexcept
2325 Warn when a noexcept-expression evaluates to false because of a call
2326 to a function that does not have a non-throwing exception
2327 specification (i.e. @samp{throw()} or @samp{noexcept}) but is known by
2328 the compiler to never throw an exception.
2330 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2331 @opindex Wnon-virtual-dtor
2332 @opindex Wno-non-virtual-dtor
2333 Warn when a class has virtual functions and accessible non-virtual
2334 destructor, in which case it would be possible but unsafe to delete
2335 an instance of a derived class through a pointer to the base class.
2336 This warning is also enabled if -Weffc++ is specified.
2338 @item -Wreorder @r{(C++ and Objective-C++ only)}
2340 @opindex Wno-reorder
2341 @cindex reordering, warning
2342 @cindex warning for reordering of member initializers
2343 Warn when the order of member initializers given in the code does not
2344 match the order in which they must be executed. For instance:
2350 A(): j (0), i (1) @{ @}
2354 The compiler will rearrange the member initializers for @samp{i}
2355 and @samp{j} to match the declaration order of the members, emitting
2356 a warning to that effect. This warning is enabled by @option{-Wall}.
2359 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2362 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2365 Warn about violations of the following style guidelines from Scott Meyers'
2366 @cite{Effective C++} book:
2370 Item 11: Define a copy constructor and an assignment operator for classes
2371 with dynamically allocated memory.
2374 Item 12: Prefer initialization to assignment in constructors.
2377 Item 14: Make destructors virtual in base classes.
2380 Item 15: Have @code{operator=} return a reference to @code{*this}.
2383 Item 23: Don't try to return a reference when you must return an object.
2387 Also warn about violations of the following style guidelines from
2388 Scott Meyers' @cite{More Effective C++} book:
2392 Item 6: Distinguish between prefix and postfix forms of increment and
2393 decrement operators.
2396 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2400 When selecting this option, be aware that the standard library
2401 headers do not obey all of these guidelines; use @samp{grep -v}
2402 to filter out those warnings.
2404 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2405 @opindex Wstrict-null-sentinel
2406 @opindex Wno-strict-null-sentinel
2407 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2408 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2409 to @code{__null}. Although it is a null pointer constant not a null pointer,
2410 it is guaranteed to be of the same size as a pointer. But this use is
2411 not portable across different compilers.
2413 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2414 @opindex Wno-non-template-friend
2415 @opindex Wnon-template-friend
2416 Disable warnings when non-templatized friend functions are declared
2417 within a template. Since the advent of explicit template specification
2418 support in G++, if the name of the friend is an unqualified-id (i.e.,
2419 @samp{friend foo(int)}), the C++ language specification demands that the
2420 friend declare or define an ordinary, nontemplate function. (Section
2421 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2422 could be interpreted as a particular specialization of a templatized
2423 function. Because this non-conforming behavior is no longer the default
2424 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2425 check existing code for potential trouble spots and is on by default.
2426 This new compiler behavior can be turned off with
2427 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2428 but disables the helpful warning.
2430 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2431 @opindex Wold-style-cast
2432 @opindex Wno-old-style-cast
2433 Warn if an old-style (C-style) cast to a non-void type is used within
2434 a C++ program. The new-style casts (@samp{dynamic_cast},
2435 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2436 less vulnerable to unintended effects and much easier to search for.
2438 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2439 @opindex Woverloaded-virtual
2440 @opindex Wno-overloaded-virtual
2441 @cindex overloaded virtual function, warning
2442 @cindex warning for overloaded virtual function
2443 Warn when a function declaration hides virtual functions from a
2444 base class. For example, in:
2451 struct B: public A @{
2456 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2464 will fail to compile.
2466 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2467 @opindex Wno-pmf-conversions
2468 @opindex Wpmf-conversions
2469 Disable the diagnostic for converting a bound pointer to member function
2472 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2473 @opindex Wsign-promo
2474 @opindex Wno-sign-promo
2475 Warn when overload resolution chooses a promotion from unsigned or
2476 enumerated type to a signed type, over a conversion to an unsigned type of
2477 the same size. Previous versions of G++ would try to preserve
2478 unsignedness, but the standard mandates the current behavior.
2483 A& operator = (int);
2493 In this example, G++ will synthesize a default @samp{A& operator =
2494 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2497 @node Objective-C and Objective-C++ Dialect Options
2498 @section Options Controlling Objective-C and Objective-C++ Dialects
2500 @cindex compiler options, Objective-C and Objective-C++
2501 @cindex Objective-C and Objective-C++ options, command line
2502 @cindex options, Objective-C and Objective-C++
2503 (NOTE: This manual does not describe the Objective-C and Objective-C++
2504 languages themselves. @xref{Standards,,Language Standards
2505 Supported by GCC}, for references.)
2507 This section describes the command-line options that are only meaningful
2508 for Objective-C and Objective-C++ programs, but you can also use most of
2509 the language-independent GNU compiler options.
2510 For example, you might compile a file @code{some_class.m} like this:
2513 gcc -g -fgnu-runtime -O -c some_class.m
2517 In this example, @option{-fgnu-runtime} is an option meant only for
2518 Objective-C and Objective-C++ programs; you can use the other options with
2519 any language supported by GCC@.
2521 Note that since Objective-C is an extension of the C language, Objective-C
2522 compilations may also use options specific to the C front-end (e.g.,
2523 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2524 C++-specific options (e.g., @option{-Wabi}).
2526 Here is a list of options that are @emph{only} for compiling Objective-C
2527 and Objective-C++ programs:
2530 @item -fconstant-string-class=@var{class-name}
2531 @opindex fconstant-string-class
2532 Use @var{class-name} as the name of the class to instantiate for each
2533 literal string specified with the syntax @code{@@"@dots{}"}. The default
2534 class name is @code{NXConstantString} if the GNU runtime is being used, and
2535 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2536 @option{-fconstant-cfstrings} option, if also present, will override the
2537 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2538 to be laid out as constant CoreFoundation strings.
2541 @opindex fgnu-runtime
2542 Generate object code compatible with the standard GNU Objective-C
2543 runtime. This is the default for most types of systems.
2545 @item -fnext-runtime
2546 @opindex fnext-runtime
2547 Generate output compatible with the NeXT runtime. This is the default
2548 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2549 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2552 @item -fno-nil-receivers
2553 @opindex fno-nil-receivers
2554 Assume that all Objective-C message dispatches (@code{[receiver
2555 message:arg]}) in this translation unit ensure that the receiver is
2556 not @code{nil}. This allows for more efficient entry points in the
2557 runtime to be used. This option is only available in conjunction with
2558 the NeXT runtime and ABI version 0 or 1.
2560 @item -fobjc-abi-version=@var{n}
2561 @opindex fobjc-abi-version
2562 Use version @var{n} of the Objective-C ABI for the selected runtime.
2563 This option is currently supported only for the NeXT runtime. In that
2564 case, Version 0 is the traditional (32-bit) ABI without support for
2565 properties and other Objective-C 2.0 additions. Version 1 is the
2566 traditional (32-bit) ABI with support for properties and other
2567 Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If
2568 nothing is specified, the default is Version 0 on 32-bit target
2569 machines, and Version 2 on 64-bit target machines.
2571 @item -fobjc-call-cxx-cdtors
2572 @opindex fobjc-call-cxx-cdtors
2573 For each Objective-C class, check if any of its instance variables is a
2574 C++ object with a non-trivial default constructor. If so, synthesize a
2575 special @code{- (id) .cxx_construct} instance method that will run
2576 non-trivial default constructors on any such instance variables, in order,
2577 and then return @code{self}. Similarly, check if any instance variable
2578 is a C++ object with a non-trivial destructor, and if so, synthesize a
2579 special @code{- (void) .cxx_destruct} method that will run
2580 all such default destructors, in reverse order.
2582 The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct}
2583 methods thusly generated will only operate on instance variables
2584 declared in the current Objective-C class, and not those inherited
2585 from superclasses. It is the responsibility of the Objective-C
2586 runtime to invoke all such methods in an object's inheritance
2587 hierarchy. The @code{- (id) .cxx_construct} methods will be invoked
2588 by the runtime immediately after a new object instance is allocated;
2589 the @code{- (void) .cxx_destruct} methods will be invoked immediately
2590 before the runtime deallocates an object instance.
2592 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2593 support for invoking the @code{- (id) .cxx_construct} and
2594 @code{- (void) .cxx_destruct} methods.
2596 @item -fobjc-direct-dispatch
2597 @opindex fobjc-direct-dispatch
2598 Allow fast jumps to the message dispatcher. On Darwin this is
2599 accomplished via the comm page.
2601 @item -fobjc-exceptions
2602 @opindex fobjc-exceptions
2603 Enable syntactic support for structured exception handling in
2604 Objective-C, similar to what is offered by C++ and Java. This option
2605 is required to use the Objective-C keywords @code{@@try},
2606 @code{@@throw}, @code{@@catch}, @code{@@finally} and
2607 @code{@@synchronized}. This option is available with both the GNU
2608 runtime and the NeXT runtime (but not available in conjunction with
2609 the NeXT runtime on Mac OS X 10.2 and earlier).
2613 Enable garbage collection (GC) in Objective-C and Objective-C++
2614 programs. This option is only available with the NeXT runtime; the
2615 GNU runtime has a different garbage collection implementation that
2616 does not require special compiler flags.
2618 @item -fobjc-nilcheck
2619 @opindex fobjc-nilcheck
2620 For the NeXT runtime with version 2 of the ABI, check for a nil
2621 receiver in method invocations before doing the actual method call.
2622 This is the default and can be disabled using
2623 @option{-fno-objc-nilcheck}. Class methods and super calls are never
2624 checked for nil in this way no matter what this flag is set to.
2625 Currently this flag does nothing when the GNU runtime, or an older
2626 version of the NeXT runtime ABI, is used.
2628 @item -fobjc-std=objc1
2630 Conform to the language syntax of Objective-C 1.0, the language
2631 recognized by GCC 4.0. This only affects the Objective-C additions to
2632 the C/C++ language; it does not affect conformance to C/C++ standards,
2633 which is controlled by the separate C/C++ dialect option flags. When
2634 this option is used with the Objective-C or Objective-C++ compiler,
2635 any Objective-C syntax that is not recognized by GCC 4.0 is rejected.
2636 This is useful if you need to make sure that your Objective-C code can
2637 be compiled with older versions of GCC.
2639 @item -freplace-objc-classes
2640 @opindex freplace-objc-classes
2641 Emit a special marker instructing @command{ld(1)} not to statically link in
2642 the resulting object file, and allow @command{dyld(1)} to load it in at
2643 run time instead. This is used in conjunction with the Fix-and-Continue
2644 debugging mode, where the object file in question may be recompiled and
2645 dynamically reloaded in the course of program execution, without the need
2646 to restart the program itself. Currently, Fix-and-Continue functionality
2647 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2652 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2653 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2654 compile time) with static class references that get initialized at load time,
2655 which improves run-time performance. Specifying the @option{-fzero-link} flag
2656 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2657 to be retained. This is useful in Zero-Link debugging mode, since it allows
2658 for individual class implementations to be modified during program execution.
2659 The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")}
2660 regardless of command line options.
2664 Dump interface declarations for all classes seen in the source file to a
2665 file named @file{@var{sourcename}.decl}.
2667 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2668 @opindex Wassign-intercept
2669 @opindex Wno-assign-intercept
2670 Warn whenever an Objective-C assignment is being intercepted by the
2673 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2674 @opindex Wno-protocol
2676 If a class is declared to implement a protocol, a warning is issued for
2677 every method in the protocol that is not implemented by the class. The
2678 default behavior is to issue a warning for every method not explicitly
2679 implemented in the class, even if a method implementation is inherited
2680 from the superclass. If you use the @option{-Wno-protocol} option, then
2681 methods inherited from the superclass are considered to be implemented,
2682 and no warning is issued for them.
2684 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2686 @opindex Wno-selector
2687 Warn if multiple methods of different types for the same selector are
2688 found during compilation. The check is performed on the list of methods
2689 in the final stage of compilation. Additionally, a check is performed
2690 for each selector appearing in a @code{@@selector(@dots{})}
2691 expression, and a corresponding method for that selector has been found
2692 during compilation. Because these checks scan the method table only at
2693 the end of compilation, these warnings are not produced if the final
2694 stage of compilation is not reached, for example because an error is
2695 found during compilation, or because the @option{-fsyntax-only} option is
2698 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2699 @opindex Wstrict-selector-match
2700 @opindex Wno-strict-selector-match
2701 Warn if multiple methods with differing argument and/or return types are
2702 found for a given selector when attempting to send a message using this
2703 selector to a receiver of type @code{id} or @code{Class}. When this flag
2704 is off (which is the default behavior), the compiler will omit such warnings
2705 if any differences found are confined to types which share the same size
2708 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2709 @opindex Wundeclared-selector
2710 @opindex Wno-undeclared-selector
2711 Warn if a @code{@@selector(@dots{})} expression referring to an
2712 undeclared selector is found. A selector is considered undeclared if no
2713 method with that name has been declared before the
2714 @code{@@selector(@dots{})} expression, either explicitly in an
2715 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2716 an @code{@@implementation} section. This option always performs its
2717 checks as soon as a @code{@@selector(@dots{})} expression is found,
2718 while @option{-Wselector} only performs its checks in the final stage of
2719 compilation. This also enforces the coding style convention
2720 that methods and selectors must be declared before being used.
2722 @item -print-objc-runtime-info
2723 @opindex print-objc-runtime-info
2724 Generate C header describing the largest structure that is passed by
2729 @node Language Independent Options
2730 @section Options to Control Diagnostic Messages Formatting
2731 @cindex options to control diagnostics formatting
2732 @cindex diagnostic messages
2733 @cindex message formatting
2735 Traditionally, diagnostic messages have been formatted irrespective of
2736 the output device's aspect (e.g.@: its width, @dots{}). The options described
2737 below can be used to control the diagnostic messages formatting
2738 algorithm, e.g.@: how many characters per line, how often source location
2739 information should be reported. Right now, only the C++ front end can
2740 honor these options. However it is expected, in the near future, that
2741 the remaining front ends would be able to digest them correctly.
2744 @item -fmessage-length=@var{n}
2745 @opindex fmessage-length
2746 Try to format error messages so that they fit on lines of about @var{n}
2747 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2748 the front ends supported by GCC@. If @var{n} is zero, then no
2749 line-wrapping will be done; each error message will appear on a single
2752 @opindex fdiagnostics-show-location
2753 @item -fdiagnostics-show-location=once
2754 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2755 reporter to emit @emph{once} source location information; that is, in
2756 case the message is too long to fit on a single physical line and has to
2757 be wrapped, the source location won't be emitted (as prefix) again,
2758 over and over, in subsequent continuation lines. This is the default
2761 @item -fdiagnostics-show-location=every-line
2762 Only meaningful in line-wrapping mode. Instructs the diagnostic
2763 messages reporter to emit the same source location information (as
2764 prefix) for physical lines that result from the process of breaking
2765 a message which is too long to fit on a single line.
2767 @item -fno-diagnostics-show-option
2768 @opindex fno-diagnostics-show-option
2769 @opindex fdiagnostics-show-option
2770 By default, each diagnostic emitted includes text which indicates the
2771 command line option that directly controls the diagnostic (if such an
2772 option is known to the diagnostic machinery). Specifying the
2773 @option{-fno-diagnostics-show-option} flag suppresses that behavior.
2775 @item -Wcoverage-mismatch
2776 @opindex Wcoverage-mismatch
2777 Warn if feedback profiles do not match when using the
2778 @option{-fprofile-use} option.
2779 If a source file was changed between @option{-fprofile-gen} and
2780 @option{-fprofile-use}, the files with the profile feedback can fail
2781 to match the source file and GCC can not use the profile feedback
2782 information. By default, this warning is enabled and is treated as an
2783 error. @option{-Wno-coverage-mismatch} can be used to disable the
2784 warning or @option{-Wno-error=coverage-mismatch} can be used to
2785 disable the error. Disable the error for this warning can result in
2786 poorly optimized code, so disabling the error is useful only in the
2787 case of very minor changes such as bug fixes to an existing code-base.
2788 Completely disabling the warning is not recommended.
2792 @node Warning Options
2793 @section Options to Request or Suppress Warnings
2794 @cindex options to control warnings
2795 @cindex warning messages
2796 @cindex messages, warning
2797 @cindex suppressing warnings
2799 Warnings are diagnostic messages that report constructions which
2800 are not inherently erroneous but which are risky or suggest there
2801 may have been an error.
2803 The following language-independent options do not enable specific
2804 warnings but control the kinds of diagnostics produced by GCC.
2807 @cindex syntax checking
2809 @opindex fsyntax-only
2810 Check the code for syntax errors, but don't do anything beyond that.
2812 @item -fmax-errors=@var{n}
2813 @opindex fmax-errors
2814 Limits the maximum number of error messages to @var{n}, at which point
2815 GCC bails out rather than attempting to continue processing the source
2816 code. If @var{n} is 0 (the default), there is no limit on the number
2817 of error messages produced. If @option{-Wfatal-errors} is also
2818 specified, then @option{-Wfatal-errors} takes precedence over this
2823 Inhibit all warning messages.
2828 Make all warnings into errors.
2833 Make the specified warning into an error. The specifier for a warning
2834 is appended, for example @option{-Werror=switch} turns the warnings
2835 controlled by @option{-Wswitch} into errors. This switch takes a
2836 negative form, to be used to negate @option{-Werror} for specific
2837 warnings, for example @option{-Wno-error=switch} makes
2838 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2841 The warning message for each controllable warning includes the
2842 option which controls the warning. That option can then be used with
2843 @option{-Werror=} and @option{-Wno-error=} as described above.
2844 (Printing of the option in the warning message can be disabled using the
2845 @option{-fno-diagnostics-show-option} flag.)
2847 Note that specifying @option{-Werror=}@var{foo} automatically implies
2848 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2851 @item -Wfatal-errors
2852 @opindex Wfatal-errors
2853 @opindex Wno-fatal-errors
2854 This option causes the compiler to abort compilation on the first error
2855 occurred rather than trying to keep going and printing further error
2860 You can request many specific warnings with options beginning
2861 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2862 implicit declarations. Each of these specific warning options also
2863 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2864 example, @option{-Wno-implicit}. This manual lists only one of the
2865 two forms, whichever is not the default. For further,
2866 language-specific options also refer to @ref{C++ Dialect Options} and
2867 @ref{Objective-C and Objective-C++ Dialect Options}.
2869 When an unrecognized warning option is requested (e.g.,
2870 @option{-Wunknown-warning}), GCC will emit a diagnostic stating
2871 that the option is not recognized. However, if the @option{-Wno-} form
2872 is used, the behavior is slightly different: No diagnostic will be
2873 produced for @option{-Wno-unknown-warning} unless other diagnostics
2874 are being produced. This allows the use of new @option{-Wno-} options
2875 with old compilers, but if something goes wrong, the compiler will
2876 warn that an unrecognized option was used.
2881 Issue all the warnings demanded by strict ISO C and ISO C++;
2882 reject all programs that use forbidden extensions, and some other
2883 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2884 version of the ISO C standard specified by any @option{-std} option used.
2886 Valid ISO C and ISO C++ programs should compile properly with or without
2887 this option (though a rare few will require @option{-ansi} or a
2888 @option{-std} option specifying the required version of ISO C)@. However,
2889 without this option, certain GNU extensions and traditional C and C++
2890 features are supported as well. With this option, they are rejected.
2892 @option{-pedantic} does not cause warning messages for use of the
2893 alternate keywords whose names begin and end with @samp{__}. Pedantic
2894 warnings are also disabled in the expression that follows
2895 @code{__extension__}. However, only system header files should use
2896 these escape routes; application programs should avoid them.
2897 @xref{Alternate Keywords}.
2899 Some users try to use @option{-pedantic} to check programs for strict ISO
2900 C conformance. They soon find that it does not do quite what they want:
2901 it finds some non-ISO practices, but not all---only those for which
2902 ISO C @emph{requires} a diagnostic, and some others for which
2903 diagnostics have been added.
2905 A feature to report any failure to conform to ISO C might be useful in
2906 some instances, but would require considerable additional work and would
2907 be quite different from @option{-pedantic}. We don't have plans to
2908 support such a feature in the near future.
2910 Where the standard specified with @option{-std} represents a GNU
2911 extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a
2912 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2913 extended dialect is based. Warnings from @option{-pedantic} are given
2914 where they are required by the base standard. (It would not make sense
2915 for such warnings to be given only for features not in the specified GNU
2916 C dialect, since by definition the GNU dialects of C include all
2917 features the compiler supports with the given option, and there would be
2918 nothing to warn about.)
2920 @item -pedantic-errors
2921 @opindex pedantic-errors
2922 Like @option{-pedantic}, except that errors are produced rather than
2928 This enables all the warnings about constructions that some users
2929 consider questionable, and that are easy to avoid (or modify to
2930 prevent the warning), even in conjunction with macros. This also
2931 enables some language-specific warnings described in @ref{C++ Dialect
2932 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2934 @option{-Wall} turns on the following warning flags:
2936 @gccoptlist{-Waddress @gol
2937 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2939 -Wchar-subscripts @gol
2940 -Wenum-compare @r{(in C/Objc; this is on by default in C++)} @gol
2941 -Wimplicit-int @r{(C and Objective-C only)} @gol
2942 -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
2945 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2946 -Wmissing-braces @gol
2952 -Wsequence-point @gol
2953 -Wsign-compare @r{(only in C++)} @gol
2954 -Wstrict-aliasing @gol
2955 -Wstrict-overflow=1 @gol
2958 -Wuninitialized @gol
2959 -Wunknown-pragmas @gol
2960 -Wunused-function @gol
2963 -Wunused-variable @gol
2964 -Wvolatile-register-var @gol
2967 Note that some warning flags are not implied by @option{-Wall}. Some of
2968 them warn about constructions that users generally do not consider
2969 questionable, but which occasionally you might wish to check for;
2970 others warn about constructions that are necessary or hard to avoid in
2971 some cases, and there is no simple way to modify the code to suppress
2972 the warning. Some of them are enabled by @option{-Wextra} but many of
2973 them must be enabled individually.
2979 This enables some extra warning flags that are not enabled by
2980 @option{-Wall}. (This option used to be called @option{-W}. The older
2981 name is still supported, but the newer name is more descriptive.)
2983 @gccoptlist{-Wclobbered @gol
2985 -Wignored-qualifiers @gol
2986 -Wmissing-field-initializers @gol
2987 -Wmissing-parameter-type @r{(C only)} @gol
2988 -Wold-style-declaration @r{(C only)} @gol
2989 -Woverride-init @gol
2992 -Wuninitialized @gol
2993 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2994 -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2997 The option @option{-Wextra} also prints warning messages for the
3003 A pointer is compared against integer zero with @samp{<}, @samp{<=},
3004 @samp{>}, or @samp{>=}.
3007 (C++ only) An enumerator and a non-enumerator both appear in a
3008 conditional expression.
3011 (C++ only) Ambiguous virtual bases.
3014 (C++ only) Subscripting an array which has been declared @samp{register}.
3017 (C++ only) Taking the address of a variable which has been declared
3021 (C++ only) A base class is not initialized in a derived class' copy
3026 @item -Wchar-subscripts
3027 @opindex Wchar-subscripts
3028 @opindex Wno-char-subscripts
3029 Warn if an array subscript has type @code{char}. This is a common cause
3030 of error, as programmers often forget that this type is signed on some
3032 This warning is enabled by @option{-Wall}.
3036 @opindex Wno-comment
3037 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
3038 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
3039 This warning is enabled by @option{-Wall}.
3042 @r{(C, Objective-C, C++, Objective-C++ and Fortran only)}
3044 Suppress warning messages emitted by @code{#warning} directives.
3046 @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
3047 @opindex Wdouble-promotion
3048 @opindex Wno-double-promotion
3049 Give a warning when a value of type @code{float} is implicitly
3050 promoted to @code{double}. CPUs with a 32-bit ``single-precision''
3051 floating-point unit implement @code{float} in hardware, but emulate
3052 @code{double} in software. On such a machine, doing computations
3053 using @code{double} values is much more expensive because of the
3054 overhead required for software emulation.
3056 It is easy to accidentally do computations with @code{double} because
3057 floating-point literals are implicitly of type @code{double}. For
3061 float area(float radius)
3063 return 3.14159 * radius * radius;
3067 the compiler will perform the entire computation with @code{double}
3068 because the floating-point literal is a @code{double}.
3073 @opindex ffreestanding
3074 @opindex fno-builtin
3075 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
3076 the arguments supplied have types appropriate to the format string
3077 specified, and that the conversions specified in the format string make
3078 sense. This includes standard functions, and others specified by format
3079 attributes (@pxref{Function Attributes}), in the @code{printf},
3080 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
3081 not in the C standard) families (or other target-specific families).
3082 Which functions are checked without format attributes having been
3083 specified depends on the standard version selected, and such checks of
3084 functions without the attribute specified are disabled by
3085 @option{-ffreestanding} or @option{-fno-builtin}.
3087 The formats are checked against the format features supported by GNU
3088 libc version 2.2. These include all ISO C90 and C99 features, as well
3089 as features from the Single Unix Specification and some BSD and GNU
3090 extensions. Other library implementations may not support all these
3091 features; GCC does not support warning about features that go beyond a
3092 particular library's limitations. However, if @option{-pedantic} is used
3093 with @option{-Wformat}, warnings will be given about format features not
3094 in the selected standard version (but not for @code{strfmon} formats,
3095 since those are not in any version of the C standard). @xref{C Dialect
3096 Options,,Options Controlling C Dialect}.
3098 Since @option{-Wformat} also checks for null format arguments for
3099 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
3101 @option{-Wformat} is included in @option{-Wall}. For more control over some
3102 aspects of format checking, the options @option{-Wformat-y2k},
3103 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
3104 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
3105 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
3108 @opindex Wformat-y2k
3109 @opindex Wno-format-y2k
3110 If @option{-Wformat} is specified, also warn about @code{strftime}
3111 formats which may yield only a two-digit year.
3113 @item -Wno-format-contains-nul
3114 @opindex Wno-format-contains-nul
3115 @opindex Wformat-contains-nul
3116 If @option{-Wformat} is specified, do not warn about format strings that
3119 @item -Wno-format-extra-args
3120 @opindex Wno-format-extra-args
3121 @opindex Wformat-extra-args
3122 If @option{-Wformat} is specified, do not warn about excess arguments to a
3123 @code{printf} or @code{scanf} format function. The C standard specifies
3124 that such arguments are ignored.
3126 Where the unused arguments lie between used arguments that are
3127 specified with @samp{$} operand number specifications, normally
3128 warnings are still given, since the implementation could not know what
3129 type to pass to @code{va_arg} to skip the unused arguments. However,
3130 in the case of @code{scanf} formats, this option will suppress the
3131 warning if the unused arguments are all pointers, since the Single
3132 Unix Specification says that such unused arguments are allowed.
3134 @item -Wno-format-zero-length @r{(C and Objective-C only)}
3135 @opindex Wno-format-zero-length
3136 @opindex Wformat-zero-length
3137 If @option{-Wformat} is specified, do not warn about zero-length formats.
3138 The C standard specifies that zero-length formats are allowed.
3140 @item -Wformat-nonliteral
3141 @opindex Wformat-nonliteral
3142 @opindex Wno-format-nonliteral
3143 If @option{-Wformat} is specified, also warn if the format string is not a
3144 string literal and so cannot be checked, unless the format function
3145 takes its format arguments as a @code{va_list}.
3147 @item -Wformat-security
3148 @opindex Wformat-security
3149 @opindex Wno-format-security
3150 If @option{-Wformat} is specified, also warn about uses of format
3151 functions that represent possible security problems. At present, this
3152 warns about calls to @code{printf} and @code{scanf} functions where the
3153 format string is not a string literal and there are no format arguments,
3154 as in @code{printf (foo);}. This may be a security hole if the format
3155 string came from untrusted input and contains @samp{%n}. (This is
3156 currently a subset of what @option{-Wformat-nonliteral} warns about, but
3157 in future warnings may be added to @option{-Wformat-security} that are not
3158 included in @option{-Wformat-nonliteral}.)
3162 @opindex Wno-format=2
3163 Enable @option{-Wformat} plus format checks not included in
3164 @option{-Wformat}. Currently equivalent to @samp{-Wformat
3165 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
3167 @item -Wnonnull @r{(C and Objective-C only)}
3169 @opindex Wno-nonnull
3170 Warn about passing a null pointer for arguments marked as
3171 requiring a non-null value by the @code{nonnull} function attribute.
3173 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
3174 can be disabled with the @option{-Wno-nonnull} option.
3176 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
3178 @opindex Wno-init-self
3179 Warn about uninitialized variables which are initialized with themselves.
3180 Note this option can only be used with the @option{-Wuninitialized} option.
3182 For example, GCC will warn about @code{i} being uninitialized in the
3183 following snippet only when @option{-Winit-self} has been specified:
3194 @item -Wimplicit-int @r{(C and Objective-C only)}
3195 @opindex Wimplicit-int
3196 @opindex Wno-implicit-int
3197 Warn when a declaration does not specify a type.
3198 This warning is enabled by @option{-Wall}.
3200 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
3201 @opindex Wimplicit-function-declaration
3202 @opindex Wno-implicit-function-declaration
3203 Give a warning whenever a function is used before being declared. In
3204 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
3205 enabled by default and it is made into an error by
3206 @option{-pedantic-errors}. This warning is also enabled by
3209 @item -Wimplicit @r{(C and Objective-C only)}
3211 @opindex Wno-implicit
3212 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
3213 This warning is enabled by @option{-Wall}.
3215 @item -Wignored-qualifiers @r{(C and C++ only)}
3216 @opindex Wignored-qualifiers
3217 @opindex Wno-ignored-qualifiers
3218 Warn if the return type of a function has a type qualifier
3219 such as @code{const}. For ISO C such a type qualifier has no effect,
3220 since the value returned by a function is not an lvalue.
3221 For C++, the warning is only emitted for scalar types or @code{void}.
3222 ISO C prohibits qualified @code{void} return types on function
3223 definitions, so such return types always receive a warning
3224 even without this option.
3226 This warning is also enabled by @option{-Wextra}.
3231 Warn if the type of @samp{main} is suspicious. @samp{main} should be
3232 a function with external linkage, returning int, taking either zero
3233 arguments, two, or three arguments of appropriate types. This warning
3234 is enabled by default in C++ and is enabled by either @option{-Wall}
3235 or @option{-pedantic}.
3237 @item -Wmissing-braces
3238 @opindex Wmissing-braces
3239 @opindex Wno-missing-braces
3240 Warn if an aggregate or union initializer is not fully bracketed. In
3241 the following example, the initializer for @samp{a} is not fully
3242 bracketed, but that for @samp{b} is fully bracketed.
3245 int a[2][2] = @{ 0, 1, 2, 3 @};
3246 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
3249 This warning is enabled by @option{-Wall}.
3251 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
3252 @opindex Wmissing-include-dirs
3253 @opindex Wno-missing-include-dirs
3254 Warn if a user-supplied include directory does not exist.
3257 @opindex Wparentheses
3258 @opindex Wno-parentheses
3259 Warn if parentheses are omitted in certain contexts, such
3260 as when there is an assignment in a context where a truth value
3261 is expected, or when operators are nested whose precedence people
3262 often get confused about.
3264 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3265 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3266 interpretation from that of ordinary mathematical notation.
3268 Also warn about constructions where there may be confusion to which
3269 @code{if} statement an @code{else} branch belongs. Here is an example of
3284 In C/C++, every @code{else} branch belongs to the innermost possible
3285 @code{if} statement, which in this example is @code{if (b)}. This is
3286 often not what the programmer expected, as illustrated in the above
3287 example by indentation the programmer chose. When there is the
3288 potential for this confusion, GCC will issue a warning when this flag
3289 is specified. To eliminate the warning, add explicit braces around
3290 the innermost @code{if} statement so there is no way the @code{else}
3291 could belong to the enclosing @code{if}. The resulting code would
3308 Also warn for dangerous uses of the
3309 ?: with omitted middle operand GNU extension. When the condition
3310 in the ?: operator is a boolean expression the omitted value will
3311 be always 1. Often the user expects it to be a value computed
3312 inside the conditional expression instead.
3314 This warning is enabled by @option{-Wall}.
3316 @item -Wsequence-point
3317 @opindex Wsequence-point
3318 @opindex Wno-sequence-point
3319 Warn about code that may have undefined semantics because of violations
3320 of sequence point rules in the C and C++ standards.
3322 The C and C++ standards defines the order in which expressions in a C/C++
3323 program are evaluated in terms of @dfn{sequence points}, which represent
3324 a partial ordering between the execution of parts of the program: those
3325 executed before the sequence point, and those executed after it. These
3326 occur after the evaluation of a full expression (one which is not part
3327 of a larger expression), after the evaluation of the first operand of a
3328 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3329 function is called (but after the evaluation of its arguments and the
3330 expression denoting the called function), and in certain other places.
3331 Other than as expressed by the sequence point rules, the order of
3332 evaluation of subexpressions of an expression is not specified. All
3333 these rules describe only a partial order rather than a total order,
3334 since, for example, if two functions are called within one expression
3335 with no sequence point between them, the order in which the functions
3336 are called is not specified. However, the standards committee have
3337 ruled that function calls do not overlap.
3339 It is not specified when between sequence points modifications to the
3340 values of objects take effect. Programs whose behavior depends on this
3341 have undefined behavior; the C and C++ standards specify that ``Between
3342 the previous and next sequence point an object shall have its stored
3343 value modified at most once by the evaluation of an expression.
3344 Furthermore, the prior value shall be read only to determine the value
3345 to be stored.''. If a program breaks these rules, the results on any
3346 particular implementation are entirely unpredictable.
3348 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3349 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3350 diagnosed by this option, and it may give an occasional false positive
3351 result, but in general it has been found fairly effective at detecting
3352 this sort of problem in programs.
3354 The standard is worded confusingly, therefore there is some debate
3355 over the precise meaning of the sequence point rules in subtle cases.
3356 Links to discussions of the problem, including proposed formal
3357 definitions, may be found on the GCC readings page, at
3358 @uref{http://gcc.gnu.org/@/readings.html}.
3360 This warning is enabled by @option{-Wall} for C and C++.
3363 @opindex Wreturn-type
3364 @opindex Wno-return-type
3365 Warn whenever a function is defined with a return-type that defaults
3366 to @code{int}. Also warn about any @code{return} statement with no
3367 return-value in a function whose return-type is not @code{void}
3368 (falling off the end of the function body is considered returning
3369 without a value), and about a @code{return} statement with an
3370 expression in a function whose return-type is @code{void}.
3372 For C++, a function without return type always produces a diagnostic
3373 message, even when @option{-Wno-return-type} is specified. The only
3374 exceptions are @samp{main} and functions defined in system headers.
3376 This warning is enabled by @option{-Wall}.
3381 Warn whenever a @code{switch} statement has an index of enumerated type
3382 and lacks a @code{case} for one or more of the named codes of that
3383 enumeration. (The presence of a @code{default} label prevents this
3384 warning.) @code{case} labels outside the enumeration range also
3385 provoke warnings when this option is used (even if there is a
3386 @code{default} label).
3387 This warning is enabled by @option{-Wall}.
3389 @item -Wswitch-default
3390 @opindex Wswitch-default
3391 @opindex Wno-switch-default
3392 Warn whenever a @code{switch} statement does not have a @code{default}
3396 @opindex Wswitch-enum
3397 @opindex Wno-switch-enum
3398 Warn whenever a @code{switch} statement has an index of enumerated type
3399 and lacks a @code{case} for one or more of the named codes of that
3400 enumeration. @code{case} labels outside the enumeration range also
3401 provoke warnings when this option is used. The only difference
3402 between @option{-Wswitch} and this option is that this option gives a
3403 warning about an omitted enumeration code even if there is a
3404 @code{default} label.
3406 @item -Wsync-nand @r{(C and C++ only)}
3408 @opindex Wno-sync-nand
3409 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3410 built-in functions are used. These functions changed semantics in GCC 4.4.
3414 @opindex Wno-trigraphs
3415 Warn if any trigraphs are encountered that might change the meaning of
3416 the program (trigraphs within comments are not warned about).
3417 This warning is enabled by @option{-Wall}.
3419 @item -Wunused-but-set-parameter
3420 @opindex Wunused-but-set-parameter
3421 @opindex Wno-unused-but-set-parameter
3422 Warn whenever a function parameter is assigned to, but otherwise unused
3423 (aside from its declaration).
3425 To suppress this warning use the @samp{unused} attribute
3426 (@pxref{Variable Attributes}).
3428 This warning is also enabled by @option{-Wunused} together with
3431 @item -Wunused-but-set-variable
3432 @opindex Wunused-but-set-variable
3433 @opindex Wno-unused-but-set-variable
3434 Warn whenever a local variable is assigned to, but otherwise unused
3435 (aside from its declaration).
3436 This warning is enabled by @option{-Wall}.
3438 To suppress this warning use the @samp{unused} attribute
3439 (@pxref{Variable Attributes}).
3441 This warning is also enabled by @option{-Wunused}, which is enabled
3444 @item -Wunused-function
3445 @opindex Wunused-function
3446 @opindex Wno-unused-function
3447 Warn whenever a static function is declared but not defined or a
3448 non-inline static function is unused.
3449 This warning is enabled by @option{-Wall}.
3451 @item -Wunused-label
3452 @opindex Wunused-label
3453 @opindex Wno-unused-label
3454 Warn whenever a label is declared but not used.
3455 This warning is enabled by @option{-Wall}.
3457 To suppress this warning use the @samp{unused} attribute
3458 (@pxref{Variable Attributes}).
3460 @item -Wunused-parameter
3461 @opindex Wunused-parameter
3462 @opindex Wno-unused-parameter
3463 Warn whenever a function parameter is unused aside from its declaration.
3465 To suppress this warning use the @samp{unused} attribute
3466 (@pxref{Variable Attributes}).
3468 @item -Wno-unused-result
3469 @opindex Wunused-result
3470 @opindex Wno-unused-result
3471 Do not warn if a caller of a function marked with attribute
3472 @code{warn_unused_result} (@pxref{Variable Attributes}) does not use
3473 its return value. The default is @option{-Wunused-result}.
3475 @item -Wunused-variable
3476 @opindex Wunused-variable
3477 @opindex Wno-unused-variable
3478 Warn whenever a local variable or non-constant static variable is unused
3479 aside from its declaration.
3480 This warning is enabled by @option{-Wall}.
3482 To suppress this warning use the @samp{unused} attribute
3483 (@pxref{Variable Attributes}).
3485 @item -Wunused-value
3486 @opindex Wunused-value
3487 @opindex Wno-unused-value
3488 Warn whenever a statement computes a result that is explicitly not
3489 used. To suppress this warning cast the unused expression to
3490 @samp{void}. This includes an expression-statement or the left-hand
3491 side of a comma expression that contains no side effects. For example,
3492 an expression such as @samp{x[i,j]} will cause a warning, while
3493 @samp{x[(void)i,j]} will not.
3495 This warning is enabled by @option{-Wall}.
3500 All the above @option{-Wunused} options combined.
3502 In order to get a warning about an unused function parameter, you must
3503 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3504 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3506 @item -Wuninitialized
3507 @opindex Wuninitialized
3508 @opindex Wno-uninitialized
3509 Warn if an automatic variable is used without first being initialized
3510 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3511 warn if a non-static reference or non-static @samp{const} member
3512 appears in a class without constructors.
3514 If you want to warn about code which uses the uninitialized value of the
3515 variable in its own initializer, use the @option{-Winit-self} option.
3517 These warnings occur for individual uninitialized or clobbered
3518 elements of structure, union or array variables as well as for
3519 variables which are uninitialized or clobbered as a whole. They do
3520 not occur for variables or elements declared @code{volatile}. Because
3521 these warnings depend on optimization, the exact variables or elements
3522 for which there are warnings will depend on the precise optimization
3523 options and version of GCC used.
3525 Note that there may be no warning about a variable that is used only
3526 to compute a value that itself is never used, because such
3527 computations may be deleted by data flow analysis before the warnings
3530 These warnings are made optional because GCC is not smart
3531 enough to see all the reasons why the code might be correct
3532 despite appearing to have an error. Here is one example of how
3553 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3554 always initialized, but GCC doesn't know this. Here is
3555 another common case:
3560 if (change_y) save_y = y, y = new_y;
3562 if (change_y) y = save_y;
3567 This has no bug because @code{save_y} is used only if it is set.
3569 @cindex @code{longjmp} warnings
3570 This option also warns when a non-volatile automatic variable might be
3571 changed by a call to @code{longjmp}. These warnings as well are possible
3572 only in optimizing compilation.
3574 The compiler sees only the calls to @code{setjmp}. It cannot know
3575 where @code{longjmp} will be called; in fact, a signal handler could
3576 call it at any point in the code. As a result, you may get a warning
3577 even when there is in fact no problem because @code{longjmp} cannot
3578 in fact be called at the place which would cause a problem.
3580 Some spurious warnings can be avoided if you declare all the functions
3581 you use that never return as @code{noreturn}. @xref{Function
3584 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3586 @item -Wunknown-pragmas
3587 @opindex Wunknown-pragmas
3588 @opindex Wno-unknown-pragmas
3589 @cindex warning for unknown pragmas
3590 @cindex unknown pragmas, warning
3591 @cindex pragmas, warning of unknown
3592 Warn when a #pragma directive is encountered which is not understood by
3593 GCC@. If this command line option is used, warnings will even be issued
3594 for unknown pragmas in system header files. This is not the case if
3595 the warnings were only enabled by the @option{-Wall} command line option.
3598 @opindex Wno-pragmas
3600 Do not warn about misuses of pragmas, such as incorrect parameters,
3601 invalid syntax, or conflicts between pragmas. See also
3602 @samp{-Wunknown-pragmas}.
3604 @item -Wstrict-aliasing
3605 @opindex Wstrict-aliasing
3606 @opindex Wno-strict-aliasing
3607 This option is only active when @option{-fstrict-aliasing} is active.
3608 It warns about code which might break the strict aliasing rules that the
3609 compiler is using for optimization. The warning does not catch all
3610 cases, but does attempt to catch the more common pitfalls. It is
3611 included in @option{-Wall}.
3612 It is equivalent to @option{-Wstrict-aliasing=3}
3614 @item -Wstrict-aliasing=n
3615 @opindex Wstrict-aliasing=n
3616 @opindex Wno-strict-aliasing=n
3617 This option is only active when @option{-fstrict-aliasing} is active.
3618 It warns about code which might break the strict aliasing rules that the
3619 compiler is using for optimization.
3620 Higher levels correspond to higher accuracy (fewer false positives).
3621 Higher levels also correspond to more effort, similar to the way -O works.
3622 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3625 Level 1: Most aggressive, quick, least accurate.
3626 Possibly useful when higher levels
3627 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3628 false negatives. However, it has many false positives.
3629 Warns for all pointer conversions between possibly incompatible types,
3630 even if never dereferenced. Runs in the frontend only.
3632 Level 2: Aggressive, quick, not too precise.
3633 May still have many false positives (not as many as level 1 though),
3634 and few false negatives (but possibly more than level 1).
3635 Unlike level 1, it only warns when an address is taken. Warns about
3636 incomplete types. Runs in the frontend only.
3638 Level 3 (default for @option{-Wstrict-aliasing}):
3639 Should have very few false positives and few false
3640 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3641 Takes care of the common pun+dereference pattern in the frontend:
3642 @code{*(int*)&some_float}.
3643 If optimization is enabled, it also runs in the backend, where it deals
3644 with multiple statement cases using flow-sensitive points-to information.
3645 Only warns when the converted pointer is dereferenced.
3646 Does not warn about incomplete types.
3648 @item -Wstrict-overflow
3649 @itemx -Wstrict-overflow=@var{n}
3650 @opindex Wstrict-overflow
3651 @opindex Wno-strict-overflow
3652 This option is only active when @option{-fstrict-overflow} is active.
3653 It warns about cases where the compiler optimizes based on the
3654 assumption that signed overflow does not occur. Note that it does not
3655 warn about all cases where the code might overflow: it only warns
3656 about cases where the compiler implements some optimization. Thus
3657 this warning depends on the optimization level.
3659 An optimization which assumes that signed overflow does not occur is
3660 perfectly safe if the values of the variables involved are such that
3661 overflow never does, in fact, occur. Therefore this warning can
3662 easily give a false positive: a warning about code which is not
3663 actually a problem. To help focus on important issues, several
3664 warning levels are defined. No warnings are issued for the use of
3665 undefined signed overflow when estimating how many iterations a loop
3666 will require, in particular when determining whether a loop will be
3670 @item -Wstrict-overflow=1
3671 Warn about cases which are both questionable and easy to avoid. For
3672 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3673 compiler will simplify this to @code{1}. This level of
3674 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3675 are not, and must be explicitly requested.
3677 @item -Wstrict-overflow=2
3678 Also warn about other cases where a comparison is simplified to a
3679 constant. For example: @code{abs (x) >= 0}. This can only be
3680 simplified when @option{-fstrict-overflow} is in effect, because
3681 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3682 zero. @option{-Wstrict-overflow} (with no level) is the same as
3683 @option{-Wstrict-overflow=2}.
3685 @item -Wstrict-overflow=3
3686 Also warn about other cases where a comparison is simplified. For
3687 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3689 @item -Wstrict-overflow=4
3690 Also warn about other simplifications not covered by the above cases.
3691 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3693 @item -Wstrict-overflow=5
3694 Also warn about cases where the compiler reduces the magnitude of a
3695 constant involved in a comparison. For example: @code{x + 2 > y} will
3696 be simplified to @code{x + 1 >= y}. This is reported only at the
3697 highest warning level because this simplification applies to many
3698 comparisons, so this warning level will give a very large number of
3702 @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{]}
3703 @opindex Wsuggest-attribute=
3704 @opindex Wno-suggest-attribute=
3705 Warn for cases where adding an attribute may be beneficial. The
3706 attributes currently supported are listed below.
3709 @item -Wsuggest-attribute=pure
3710 @itemx -Wsuggest-attribute=const
3711 @itemx -Wsuggest-attribute=noreturn
3712 @opindex Wsuggest-attribute=pure
3713 @opindex Wno-suggest-attribute=pure
3714 @opindex Wsuggest-attribute=const
3715 @opindex Wno-suggest-attribute=const
3716 @opindex Wsuggest-attribute=noreturn
3717 @opindex Wno-suggest-attribute=noreturn
3719 Warn about functions which might be candidates for attributes
3720 @code{pure}, @code{const} or @code{noreturn}. The compiler only warns for
3721 functions visible in other compilation units or (in the case of @code{pure} and
3722 @code{const}) if it cannot prove that the function returns normally. A function
3723 returns normally if it doesn't contain an infinite loop nor returns abnormally
3724 by throwing, calling @code{abort()} or trapping. This analysis requires option
3725 @option{-fipa-pure-const}, which is enabled by default at @option{-O} and
3726 higher. Higher optimization levels improve the accuracy of the analysis.
3729 @item -Warray-bounds
3730 @opindex Wno-array-bounds
3731 @opindex Warray-bounds
3732 This option is only active when @option{-ftree-vrp} is active
3733 (default for @option{-O2} and above). It warns about subscripts to arrays
3734 that are always out of bounds. This warning is enabled by @option{-Wall}.
3736 @item -Wno-div-by-zero
3737 @opindex Wno-div-by-zero
3738 @opindex Wdiv-by-zero
3739 Do not warn about compile-time integer division by zero. Floating point
3740 division by zero is not warned about, as it can be a legitimate way of
3741 obtaining infinities and NaNs.
3743 @item -Wsystem-headers
3744 @opindex Wsystem-headers
3745 @opindex Wno-system-headers
3746 @cindex warnings from system headers
3747 @cindex system headers, warnings from
3748 Print warning messages for constructs found in system header files.
3749 Warnings from system headers are normally suppressed, on the assumption
3750 that they usually do not indicate real problems and would only make the
3751 compiler output harder to read. Using this command line option tells
3752 GCC to emit warnings from system headers as if they occurred in user
3753 code. However, note that using @option{-Wall} in conjunction with this
3754 option will @emph{not} warn about unknown pragmas in system
3755 headers---for that, @option{-Wunknown-pragmas} must also be used.
3758 @opindex Wtrampolines
3759 @opindex Wno-trampolines
3760 Warn about trampolines generated for pointers to nested functions.
3762 A trampoline is a small piece of data or code that is created at run
3763 time on the stack when the address of a nested function is taken, and
3764 is used to call the nested function indirectly. For some targets, it
3765 is made up of data only and thus requires no special treatment. But,
3766 for most targets, it is made up of code and thus requires the stack
3767 to be made executable in order for the program to work properly.
3770 @opindex Wfloat-equal
3771 @opindex Wno-float-equal
3772 Warn if floating point values are used in equality comparisons.
3774 The idea behind this is that sometimes it is convenient (for the
3775 programmer) to consider floating-point values as approximations to
3776 infinitely precise real numbers. If you are doing this, then you need
3777 to compute (by analyzing the code, or in some other way) the maximum or
3778 likely maximum error that the computation introduces, and allow for it
3779 when performing comparisons (and when producing output, but that's a
3780 different problem). In particular, instead of testing for equality, you
3781 would check to see whether the two values have ranges that overlap; and
3782 this is done with the relational operators, so equality comparisons are
3785 @item -Wtraditional @r{(C and Objective-C only)}
3786 @opindex Wtraditional
3787 @opindex Wno-traditional
3788 Warn about certain constructs that behave differently in traditional and
3789 ISO C@. Also warn about ISO C constructs that have no traditional C
3790 equivalent, and/or problematic constructs which should be avoided.
3794 Macro parameters that appear within string literals in the macro body.
3795 In traditional C macro replacement takes place within string literals,
3796 but does not in ISO C@.
3799 In traditional C, some preprocessor directives did not exist.
3800 Traditional preprocessors would only consider a line to be a directive
3801 if the @samp{#} appeared in column 1 on the line. Therefore
3802 @option{-Wtraditional} warns about directives that traditional C
3803 understands but would ignore because the @samp{#} does not appear as the
3804 first character on the line. It also suggests you hide directives like
3805 @samp{#pragma} not understood by traditional C by indenting them. Some
3806 traditional implementations would not recognize @samp{#elif}, so it
3807 suggests avoiding it altogether.
3810 A function-like macro that appears without arguments.
3813 The unary plus operator.
3816 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3817 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3818 constants.) Note, these suffixes appear in macros defined in the system
3819 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3820 Use of these macros in user code might normally lead to spurious
3821 warnings, however GCC's integrated preprocessor has enough context to
3822 avoid warning in these cases.
3825 A function declared external in one block and then used after the end of
3829 A @code{switch} statement has an operand of type @code{long}.
3832 A non-@code{static} function declaration follows a @code{static} one.
3833 This construct is not accepted by some traditional C compilers.
3836 The ISO type of an integer constant has a different width or
3837 signedness from its traditional type. This warning is only issued if
3838 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3839 typically represent bit patterns, are not warned about.
3842 Usage of ISO string concatenation is detected.
3845 Initialization of automatic aggregates.
3848 Identifier conflicts with labels. Traditional C lacks a separate
3849 namespace for labels.
3852 Initialization of unions. If the initializer is zero, the warning is
3853 omitted. This is done under the assumption that the zero initializer in
3854 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3855 initializer warnings and relies on default initialization to zero in the
3859 Conversions by prototypes between fixed/floating point values and vice
3860 versa. The absence of these prototypes when compiling with traditional
3861 C would cause serious problems. This is a subset of the possible
3862 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3865 Use of ISO C style function definitions. This warning intentionally is
3866 @emph{not} issued for prototype declarations or variadic functions
3867 because these ISO C features will appear in your code when using
3868 libiberty's traditional C compatibility macros, @code{PARAMS} and
3869 @code{VPARAMS}. This warning is also bypassed for nested functions
3870 because that feature is already a GCC extension and thus not relevant to
3871 traditional C compatibility.
3874 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3875 @opindex Wtraditional-conversion
3876 @opindex Wno-traditional-conversion
3877 Warn if a prototype causes a type conversion that is different from what
3878 would happen to the same argument in the absence of a prototype. This
3879 includes conversions of fixed point to floating and vice versa, and
3880 conversions changing the width or signedness of a fixed point argument
3881 except when the same as the default promotion.
3883 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3884 @opindex Wdeclaration-after-statement
3885 @opindex Wno-declaration-after-statement
3886 Warn when a declaration is found after a statement in a block. This
3887 construct, known from C++, was introduced with ISO C99 and is by default
3888 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3889 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3894 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3896 @item -Wno-endif-labels
3897 @opindex Wno-endif-labels
3898 @opindex Wendif-labels
3899 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3904 Warn whenever a local variable or type declaration shadows another variable,
3905 parameter, type, or class member (in C++), or whenever a built-in function
3906 is shadowed. Note that in C++, the compiler will not warn if a local variable
3907 shadows a struct/class/enum, but will warn if it shadows an explicit typedef.
3909 @item -Wlarger-than=@var{len}
3910 @opindex Wlarger-than=@var{len}
3911 @opindex Wlarger-than-@var{len}
3912 Warn whenever an object of larger than @var{len} bytes is defined.
3914 @item -Wframe-larger-than=@var{len}
3915 @opindex Wframe-larger-than
3916 Warn if the size of a function frame is larger than @var{len} bytes.
3917 The computation done to determine the stack frame size is approximate
3918 and not conservative.
3919 The actual requirements may be somewhat greater than @var{len}
3920 even if you do not get a warning. In addition, any space allocated
3921 via @code{alloca}, variable-length arrays, or related constructs
3922 is not included by the compiler when determining
3923 whether or not to issue a warning.
3925 @item -Wunsafe-loop-optimizations
3926 @opindex Wunsafe-loop-optimizations
3927 @opindex Wno-unsafe-loop-optimizations
3928 Warn if the loop cannot be optimized because the compiler could not
3929 assume anything on the bounds of the loop indices. With
3930 @option{-funsafe-loop-optimizations} warn if the compiler made
3933 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
3934 @opindex Wno-pedantic-ms-format
3935 @opindex Wpedantic-ms-format
3936 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3937 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3938 depending on the MS runtime, when you are using the options @option{-Wformat}
3939 and @option{-pedantic} without gnu-extensions.
3941 @item -Wpointer-arith
3942 @opindex Wpointer-arith
3943 @opindex Wno-pointer-arith
3944 Warn about anything that depends on the ``size of'' a function type or
3945 of @code{void}. GNU C assigns these types a size of 1, for
3946 convenience in calculations with @code{void *} pointers and pointers
3947 to functions. In C++, warn also when an arithmetic operation involves
3948 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3951 @opindex Wtype-limits
3952 @opindex Wno-type-limits
3953 Warn if a comparison is always true or always false due to the limited
3954 range of the data type, but do not warn for constant expressions. For
3955 example, warn if an unsigned variable is compared against zero with
3956 @samp{<} or @samp{>=}. This warning is also enabled by
3959 @item -Wbad-function-cast @r{(C and Objective-C only)}
3960 @opindex Wbad-function-cast
3961 @opindex Wno-bad-function-cast
3962 Warn whenever a function call is cast to a non-matching type.
3963 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3965 @item -Wc++-compat @r{(C and Objective-C only)}
3966 Warn about ISO C constructs that are outside of the common subset of
3967 ISO C and ISO C++, e.g.@: request for implicit conversion from
3968 @code{void *} to a pointer to non-@code{void} type.
3970 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3971 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3972 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3973 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3977 @opindex Wno-cast-qual
3978 Warn whenever a pointer is cast so as to remove a type qualifier from
3979 the target type. For example, warn if a @code{const char *} is cast
3980 to an ordinary @code{char *}.
3982 Also warn when making a cast which introduces a type qualifier in an
3983 unsafe way. For example, casting @code{char **} to @code{const char **}
3984 is unsafe, as in this example:
3987 /* p is char ** value. */
3988 const char **q = (const char **) p;
3989 /* Assignment of readonly string to const char * is OK. */
3991 /* Now char** pointer points to read-only memory. */
3996 @opindex Wcast-align
3997 @opindex Wno-cast-align
3998 Warn whenever a pointer is cast such that the required alignment of the
3999 target is increased. For example, warn if a @code{char *} is cast to
4000 an @code{int *} on machines where integers can only be accessed at
4001 two- or four-byte boundaries.
4003 @item -Wwrite-strings
4004 @opindex Wwrite-strings
4005 @opindex Wno-write-strings
4006 When compiling C, give string constants the type @code{const
4007 char[@var{length}]} so that copying the address of one into a
4008 non-@code{const} @code{char *} pointer will get a warning. These
4009 warnings will help you find at compile time code that can try to write
4010 into a string constant, but only if you have been very careful about
4011 using @code{const} in declarations and prototypes. Otherwise, it will
4012 just be a nuisance. This is why we did not make @option{-Wall} request
4015 When compiling C++, warn about the deprecated conversion from string
4016 literals to @code{char *}. This warning is enabled by default for C++
4021 @opindex Wno-clobbered
4022 Warn for variables that might be changed by @samp{longjmp} or
4023 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
4026 @opindex Wconversion
4027 @opindex Wno-conversion
4028 Warn for implicit conversions that may alter a value. This includes
4029 conversions between real and integer, like @code{abs (x)} when
4030 @code{x} is @code{double}; conversions between signed and unsigned,
4031 like @code{unsigned ui = -1}; and conversions to smaller types, like
4032 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
4033 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
4034 changed by the conversion like in @code{abs (2.0)}. Warnings about
4035 conversions between signed and unsigned integers can be disabled by
4036 using @option{-Wno-sign-conversion}.
4038 For C++, also warn for confusing overload resolution for user-defined
4039 conversions; and conversions that will never use a type conversion
4040 operator: conversions to @code{void}, the same type, a base class or a
4041 reference to them. Warnings about conversions between signed and
4042 unsigned integers are disabled by default in C++ unless
4043 @option{-Wsign-conversion} is explicitly enabled.
4045 @item -Wno-conversion-null @r{(C++ and Objective-C++ only)}
4046 @opindex Wconversion-null
4047 @opindex Wno-conversion-null
4048 Do not warn for conversions between @code{NULL} and non-pointer
4049 types. @option{-Wconversion-null} is enabled by default.
4052 @opindex Wempty-body
4053 @opindex Wno-empty-body
4054 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
4055 while} statement. This warning is also enabled by @option{-Wextra}.
4057 @item -Wenum-compare
4058 @opindex Wenum-compare
4059 @opindex Wno-enum-compare
4060 Warn about a comparison between values of different enum types. In C++
4061 this warning is enabled by default. In C this warning is enabled by
4064 @item -Wjump-misses-init @r{(C, Objective-C only)}
4065 @opindex Wjump-misses-init
4066 @opindex Wno-jump-misses-init
4067 Warn if a @code{goto} statement or a @code{switch} statement jumps
4068 forward across the initialization of a variable, or jumps backward to a
4069 label after the variable has been initialized. This only warns about
4070 variables which are initialized when they are declared. This warning is
4071 only supported for C and Objective C; in C++ this sort of branch is an
4074 @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
4075 can be disabled with the @option{-Wno-jump-misses-init} option.
4077 @item -Wsign-compare
4078 @opindex Wsign-compare
4079 @opindex Wno-sign-compare
4080 @cindex warning for comparison of signed and unsigned values
4081 @cindex comparison of signed and unsigned values, warning
4082 @cindex signed and unsigned values, comparison warning
4083 Warn when a comparison between signed and unsigned values could produce
4084 an incorrect result when the signed value is converted to unsigned.
4085 This warning is also enabled by @option{-Wextra}; to get the other warnings
4086 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
4088 @item -Wsign-conversion
4089 @opindex Wsign-conversion
4090 @opindex Wno-sign-conversion
4091 Warn for implicit conversions that may change the sign of an integer
4092 value, like assigning a signed integer expression to an unsigned
4093 integer variable. An explicit cast silences the warning. In C, this
4094 option is enabled also by @option{-Wconversion}.
4098 @opindex Wno-address
4099 Warn about suspicious uses of memory addresses. These include using
4100 the address of a function in a conditional expression, such as
4101 @code{void func(void); if (func)}, and comparisons against the memory
4102 address of a string literal, such as @code{if (x == "abc")}. Such
4103 uses typically indicate a programmer error: the address of a function
4104 always evaluates to true, so their use in a conditional usually
4105 indicate that the programmer forgot the parentheses in a function
4106 call; and comparisons against string literals result in unspecified
4107 behavior and are not portable in C, so they usually indicate that the
4108 programmer intended to use @code{strcmp}. This warning is enabled by
4112 @opindex Wlogical-op
4113 @opindex Wno-logical-op
4114 Warn about suspicious uses of logical operators in expressions.
4115 This includes using logical operators in contexts where a
4116 bit-wise operator is likely to be expected.
4118 @item -Waggregate-return
4119 @opindex Waggregate-return
4120 @opindex Wno-aggregate-return
4121 Warn if any functions that return structures or unions are defined or
4122 called. (In languages where you can return an array, this also elicits
4125 @item -Wno-attributes
4126 @opindex Wno-attributes
4127 @opindex Wattributes
4128 Do not warn if an unexpected @code{__attribute__} is used, such as
4129 unrecognized attributes, function attributes applied to variables,
4130 etc. This will not stop errors for incorrect use of supported
4133 @item -Wno-builtin-macro-redefined
4134 @opindex Wno-builtin-macro-redefined
4135 @opindex Wbuiltin-macro-redefined
4136 Do not warn if certain built-in macros are redefined. This suppresses
4137 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
4138 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
4140 @item -Wstrict-prototypes @r{(C and Objective-C only)}
4141 @opindex Wstrict-prototypes
4142 @opindex Wno-strict-prototypes
4143 Warn if a function is declared or defined without specifying the
4144 argument types. (An old-style function definition is permitted without
4145 a warning if preceded by a declaration which specifies the argument
4148 @item -Wold-style-declaration @r{(C and Objective-C only)}
4149 @opindex Wold-style-declaration
4150 @opindex Wno-old-style-declaration
4151 Warn for obsolescent usages, according to the C Standard, in a
4152 declaration. For example, warn if storage-class specifiers like
4153 @code{static} are not the first things in a declaration. This warning
4154 is also enabled by @option{-Wextra}.
4156 @item -Wold-style-definition @r{(C and Objective-C only)}
4157 @opindex Wold-style-definition
4158 @opindex Wno-old-style-definition
4159 Warn if an old-style function definition is used. A warning is given
4160 even if there is a previous prototype.
4162 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
4163 @opindex Wmissing-parameter-type
4164 @opindex Wno-missing-parameter-type
4165 A function parameter is declared without a type specifier in K&R-style
4172 This warning is also enabled by @option{-Wextra}.
4174 @item -Wmissing-prototypes @r{(C and Objective-C only)}
4175 @opindex Wmissing-prototypes
4176 @opindex Wno-missing-prototypes
4177 Warn if a global function is defined without a previous prototype
4178 declaration. This warning is issued even if the definition itself
4179 provides a prototype. The aim is to detect global functions that fail
4180 to be declared in header files.
4182 @item -Wmissing-declarations
4183 @opindex Wmissing-declarations
4184 @opindex Wno-missing-declarations
4185 Warn if a global function is defined without a previous declaration.
4186 Do so even if the definition itself provides a prototype.
4187 Use this option to detect global functions that are not declared in
4188 header files. In C++, no warnings are issued for function templates,
4189 or for inline functions, or for functions in anonymous namespaces.
4191 @item -Wmissing-field-initializers
4192 @opindex Wmissing-field-initializers
4193 @opindex Wno-missing-field-initializers
4197 Warn if a structure's initializer has some fields missing. For
4198 example, the following code would cause such a warning, because
4199 @code{x.h} is implicitly zero:
4202 struct s @{ int f, g, h; @};
4203 struct s x = @{ 3, 4 @};
4206 This option does not warn about designated initializers, so the following
4207 modification would not trigger a warning:
4210 struct s @{ int f, g, h; @};
4211 struct s x = @{ .f = 3, .g = 4 @};
4214 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
4215 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
4217 @item -Wmissing-format-attribute
4218 @opindex Wmissing-format-attribute
4219 @opindex Wno-missing-format-attribute
4222 Warn about function pointers which might be candidates for @code{format}
4223 attributes. Note these are only possible candidates, not absolute ones.
4224 GCC will guess that function pointers with @code{format} attributes that
4225 are used in assignment, initialization, parameter passing or return
4226 statements should have a corresponding @code{format} attribute in the
4227 resulting type. I.e.@: the left-hand side of the assignment or
4228 initialization, the type of the parameter variable, or the return type
4229 of the containing function respectively should also have a @code{format}
4230 attribute to avoid the warning.
4232 GCC will also warn about function definitions which might be
4233 candidates for @code{format} attributes. Again, these are only
4234 possible candidates. GCC will guess that @code{format} attributes
4235 might be appropriate for any function that calls a function like
4236 @code{vprintf} or @code{vscanf}, but this might not always be the
4237 case, and some functions for which @code{format} attributes are
4238 appropriate may not be detected.
4240 @item -Wno-multichar
4241 @opindex Wno-multichar
4243 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
4244 Usually they indicate a typo in the user's code, as they have
4245 implementation-defined values, and should not be used in portable code.
4247 @item -Wnormalized=<none|id|nfc|nfkc>
4248 @opindex Wnormalized=
4251 @cindex character set, input normalization
4252 In ISO C and ISO C++, two identifiers are different if they are
4253 different sequences of characters. However, sometimes when characters
4254 outside the basic ASCII character set are used, you can have two
4255 different character sequences that look the same. To avoid confusion,
4256 the ISO 10646 standard sets out some @dfn{normalization rules} which
4257 when applied ensure that two sequences that look the same are turned into
4258 the same sequence. GCC can warn you if you are using identifiers which
4259 have not been normalized; this option controls that warning.
4261 There are four levels of warning that GCC supports. The default is
4262 @option{-Wnormalized=nfc}, which warns about any identifier which is
4263 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
4264 recommended form for most uses.
4266 Unfortunately, there are some characters which ISO C and ISO C++ allow
4267 in identifiers that when turned into NFC aren't allowable as
4268 identifiers. That is, there's no way to use these symbols in portable
4269 ISO C or C++ and have all your identifiers in NFC@.
4270 @option{-Wnormalized=id} suppresses the warning for these characters.
4271 It is hoped that future versions of the standards involved will correct
4272 this, which is why this option is not the default.
4274 You can switch the warning off for all characters by writing
4275 @option{-Wnormalized=none}. You would only want to do this if you
4276 were using some other normalization scheme (like ``D''), because
4277 otherwise you can easily create bugs that are literally impossible to see.
4279 Some characters in ISO 10646 have distinct meanings but look identical
4280 in some fonts or display methodologies, especially once formatting has
4281 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
4282 LETTER N'', will display just like a regular @code{n} which has been
4283 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
4284 normalization scheme to convert all these into a standard form as
4285 well, and GCC will warn if your code is not in NFKC if you use
4286 @option{-Wnormalized=nfkc}. This warning is comparable to warning
4287 about every identifier that contains the letter O because it might be
4288 confused with the digit 0, and so is not the default, but may be
4289 useful as a local coding convention if the programming environment is
4290 unable to be fixed to display these characters distinctly.
4292 @item -Wno-deprecated
4293 @opindex Wno-deprecated
4294 @opindex Wdeprecated
4295 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
4297 @item -Wno-deprecated-declarations
4298 @opindex Wno-deprecated-declarations
4299 @opindex Wdeprecated-declarations
4300 Do not warn about uses of functions (@pxref{Function Attributes}),
4301 variables (@pxref{Variable Attributes}), and types (@pxref{Type
4302 Attributes}) marked as deprecated by using the @code{deprecated}
4306 @opindex Wno-overflow
4308 Do not warn about compile-time overflow in constant expressions.
4310 @item -Woverride-init @r{(C and Objective-C only)}
4311 @opindex Woverride-init
4312 @opindex Wno-override-init
4316 Warn if an initialized field without side effects is overridden when
4317 using designated initializers (@pxref{Designated Inits, , Designated
4320 This warning is included in @option{-Wextra}. To get other
4321 @option{-Wextra} warnings without this one, use @samp{-Wextra
4322 -Wno-override-init}.
4327 Warn if a structure is given the packed attribute, but the packed
4328 attribute has no effect on the layout or size of the structure.
4329 Such structures may be mis-aligned for little benefit. For
4330 instance, in this code, the variable @code{f.x} in @code{struct bar}
4331 will be misaligned even though @code{struct bar} does not itself
4332 have the packed attribute:
4339 @} __attribute__((packed));
4347 @item -Wpacked-bitfield-compat
4348 @opindex Wpacked-bitfield-compat
4349 @opindex Wno-packed-bitfield-compat
4350 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
4351 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
4352 the change can lead to differences in the structure layout. GCC
4353 informs you when the offset of such a field has changed in GCC 4.4.
4354 For example there is no longer a 4-bit padding between field @code{a}
4355 and @code{b} in this structure:
4362 @} __attribute__ ((packed));
4365 This warning is enabled by default. Use
4366 @option{-Wno-packed-bitfield-compat} to disable this warning.
4371 Warn if padding is included in a structure, either to align an element
4372 of the structure or to align the whole structure. Sometimes when this
4373 happens it is possible to rearrange the fields of the structure to
4374 reduce the padding and so make the structure smaller.
4376 @item -Wredundant-decls
4377 @opindex Wredundant-decls
4378 @opindex Wno-redundant-decls
4379 Warn if anything is declared more than once in the same scope, even in
4380 cases where multiple declaration is valid and changes nothing.
4382 @item -Wnested-externs @r{(C and Objective-C only)}
4383 @opindex Wnested-externs
4384 @opindex Wno-nested-externs
4385 Warn if an @code{extern} declaration is encountered within a function.
4390 Warn if a function can not be inlined and it was declared as inline.
4391 Even with this option, the compiler will not warn about failures to
4392 inline functions declared in system headers.
4394 The compiler uses a variety of heuristics to determine whether or not
4395 to inline a function. For example, the compiler takes into account
4396 the size of the function being inlined and the amount of inlining
4397 that has already been done in the current function. Therefore,
4398 seemingly insignificant changes in the source program can cause the
4399 warnings produced by @option{-Winline} to appear or disappear.
4401 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4402 @opindex Wno-invalid-offsetof
4403 @opindex Winvalid-offsetof
4404 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4405 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4406 to a non-POD type is undefined. In existing C++ implementations,
4407 however, @samp{offsetof} typically gives meaningful results even when
4408 applied to certain kinds of non-POD types. (Such as a simple
4409 @samp{struct} that fails to be a POD type only by virtue of having a
4410 constructor.) This flag is for users who are aware that they are
4411 writing nonportable code and who have deliberately chosen to ignore the
4414 The restrictions on @samp{offsetof} may be relaxed in a future version
4415 of the C++ standard.
4417 @item -Wno-int-to-pointer-cast
4418 @opindex Wno-int-to-pointer-cast
4419 @opindex Wint-to-pointer-cast
4420 Suppress warnings from casts to pointer type of an integer of a
4421 different size. In C++, casting to a pointer type of smaller size is
4422 an error. @option{Wint-to-pointer-cast} is enabled by default.
4425 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4426 @opindex Wno-pointer-to-int-cast
4427 @opindex Wpointer-to-int-cast
4428 Suppress warnings from casts from a pointer to an integer type of a
4432 @opindex Winvalid-pch
4433 @opindex Wno-invalid-pch
4434 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4435 the search path but can't be used.
4439 @opindex Wno-long-long
4440 Warn if @samp{long long} type is used. This is enabled by either
4441 @option{-pedantic} or @option{-Wtraditional} in ISO C90 and C++98
4442 modes. To inhibit the warning messages, use @option{-Wno-long-long}.
4444 @item -Wvariadic-macros
4445 @opindex Wvariadic-macros
4446 @opindex Wno-variadic-macros
4447 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4448 alternate syntax when in pedantic ISO C99 mode. This is default.
4449 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4454 Warn if variable length array is used in the code.
4455 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4456 the variable length array.
4458 @item -Wvolatile-register-var
4459 @opindex Wvolatile-register-var
4460 @opindex Wno-volatile-register-var
4461 Warn if a register variable is declared volatile. The volatile
4462 modifier does not inhibit all optimizations that may eliminate reads
4463 and/or writes to register variables. This warning is enabled by
4466 @item -Wdisabled-optimization
4467 @opindex Wdisabled-optimization
4468 @opindex Wno-disabled-optimization
4469 Warn if a requested optimization pass is disabled. This warning does
4470 not generally indicate that there is anything wrong with your code; it
4471 merely indicates that GCC's optimizers were unable to handle the code
4472 effectively. Often, the problem is that your code is too big or too
4473 complex; GCC will refuse to optimize programs when the optimization
4474 itself is likely to take inordinate amounts of time.
4476 @item -Wpointer-sign @r{(C and Objective-C only)}
4477 @opindex Wpointer-sign
4478 @opindex Wno-pointer-sign
4479 Warn for pointer argument passing or assignment with different signedness.
4480 This option is only supported for C and Objective-C@. It is implied by
4481 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4482 @option{-Wno-pointer-sign}.
4484 @item -Wstack-protector
4485 @opindex Wstack-protector
4486 @opindex Wno-stack-protector
4487 This option is only active when @option{-fstack-protector} is active. It
4488 warns about functions that will not be protected against stack smashing.
4491 @opindex Wno-mudflap
4492 Suppress warnings about constructs that cannot be instrumented by
4495 @item -Woverlength-strings
4496 @opindex Woverlength-strings
4497 @opindex Wno-overlength-strings
4498 Warn about string constants which are longer than the ``minimum
4499 maximum'' length specified in the C standard. Modern compilers
4500 generally allow string constants which are much longer than the
4501 standard's minimum limit, but very portable programs should avoid
4502 using longer strings.
4504 The limit applies @emph{after} string constant concatenation, and does
4505 not count the trailing NUL@. In C90, the limit was 509 characters; in
4506 C99, it was raised to 4095. C++98 does not specify a normative
4507 minimum maximum, so we do not diagnose overlength strings in C++@.
4509 This option is implied by @option{-pedantic}, and can be disabled with
4510 @option{-Wno-overlength-strings}.
4512 @item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
4513 @opindex Wunsuffixed-float-constants
4515 GCC will issue a warning for any floating constant that does not have
4516 a suffix. When used together with @option{-Wsystem-headers} it will
4517 warn about such constants in system header files. This can be useful
4518 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
4519 from the decimal floating-point extension to C99.
4522 @node Debugging Options
4523 @section Options for Debugging Your Program or GCC
4524 @cindex options, debugging
4525 @cindex debugging information options
4527 GCC has various special options that are used for debugging
4528 either your program or GCC:
4533 Produce debugging information in the operating system's native format
4534 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4537 On most systems that use stabs format, @option{-g} enables use of extra
4538 debugging information that only GDB can use; this extra information
4539 makes debugging work better in GDB but will probably make other debuggers
4541 refuse to read the program. If you want to control for certain whether
4542 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4543 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4545 GCC allows you to use @option{-g} with
4546 @option{-O}. The shortcuts taken by optimized code may occasionally
4547 produce surprising results: some variables you declared may not exist
4548 at all; flow of control may briefly move where you did not expect it;
4549 some statements may not be executed because they compute constant
4550 results or their values were already at hand; some statements may
4551 execute in different places because they were moved out of loops.
4553 Nevertheless it proves possible to debug optimized output. This makes
4554 it reasonable to use the optimizer for programs that might have bugs.
4556 The following options are useful when GCC is generated with the
4557 capability for more than one debugging format.
4561 Produce debugging information for use by GDB@. This means to use the
4562 most expressive format available (DWARF 2, stabs, or the native format
4563 if neither of those are supported), including GDB extensions if at all
4568 Produce debugging information in stabs format (if that is supported),
4569 without GDB extensions. This is the format used by DBX on most BSD
4570 systems. On MIPS, Alpha and System V Release 4 systems this option
4571 produces stabs debugging output which is not understood by DBX or SDB@.
4572 On System V Release 4 systems this option requires the GNU assembler.
4574 @item -feliminate-unused-debug-symbols
4575 @opindex feliminate-unused-debug-symbols
4576 Produce debugging information in stabs format (if that is supported),
4577 for only symbols that are actually used.
4579 @item -femit-class-debug-always
4580 Instead of emitting debugging information for a C++ class in only one
4581 object file, emit it in all object files using the class. This option
4582 should be used only with debuggers that are unable to handle the way GCC
4583 normally emits debugging information for classes because using this
4584 option will increase the size of debugging information by as much as a
4589 Produce debugging information in stabs format (if that is supported),
4590 using GNU extensions understood only by the GNU debugger (GDB)@. The
4591 use of these extensions is likely to make other debuggers crash or
4592 refuse to read the program.
4596 Produce debugging information in COFF format (if that is supported).
4597 This is the format used by SDB on most System V systems prior to
4602 Produce debugging information in XCOFF format (if that is supported).
4603 This is the format used by the DBX debugger on IBM RS/6000 systems.
4607 Produce debugging information in XCOFF format (if that is supported),
4608 using GNU extensions understood only by the GNU debugger (GDB)@. The
4609 use of these extensions is likely to make other debuggers crash or
4610 refuse to read the program, and may cause assemblers other than the GNU
4611 assembler (GAS) to fail with an error.
4613 @item -gdwarf-@var{version}
4614 @opindex gdwarf-@var{version}
4615 Produce debugging information in DWARF format (if that is
4616 supported). This is the format used by DBX on IRIX 6. The value
4617 of @var{version} may be either 2, 3 or 4; the default version is 2.
4619 Note that with DWARF version 2 some ports require, and will always
4620 use, some non-conflicting DWARF 3 extensions in the unwind tables.
4622 Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
4623 for maximum benefit.
4625 @item -gstrict-dwarf
4626 @opindex gstrict-dwarf
4627 Disallow using extensions of later DWARF standard version than selected
4628 with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
4629 DWARF extensions from later standard versions is allowed.
4631 @item -gno-strict-dwarf
4632 @opindex gno-strict-dwarf
4633 Allow using extensions of later DWARF standard version than selected with
4634 @option{-gdwarf-@var{version}}.
4638 Produce debugging information in VMS debug format (if that is
4639 supported). This is the format used by DEBUG on VMS systems.
4642 @itemx -ggdb@var{level}
4643 @itemx -gstabs@var{level}
4644 @itemx -gcoff@var{level}
4645 @itemx -gxcoff@var{level}
4646 @itemx -gvms@var{level}
4647 Request debugging information and also use @var{level} to specify how
4648 much information. The default level is 2.
4650 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4653 Level 1 produces minimal information, enough for making backtraces in
4654 parts of the program that you don't plan to debug. This includes
4655 descriptions of functions and external variables, but no information
4656 about local variables and no line numbers.
4658 Level 3 includes extra information, such as all the macro definitions
4659 present in the program. Some debuggers support macro expansion when
4660 you use @option{-g3}.
4662 @option{-gdwarf-2} does not accept a concatenated debug level, because
4663 GCC used to support an option @option{-gdwarf} that meant to generate
4664 debug information in version 1 of the DWARF format (which is very
4665 different from version 2), and it would have been too confusing. That
4666 debug format is long obsolete, but the option cannot be changed now.
4667 Instead use an additional @option{-g@var{level}} option to change the
4668 debug level for DWARF.
4672 Turn off generation of debug info, if leaving out this option would have
4673 generated it, or turn it on at level 2 otherwise. The position of this
4674 argument in the command line does not matter, it takes effect after all
4675 other options are processed, and it does so only once, no matter how
4676 many times it is given. This is mainly intended to be used with
4677 @option{-fcompare-debug}.
4679 @item -fdump-final-insns@r{[}=@var{file}@r{]}
4680 @opindex fdump-final-insns
4681 Dump the final internal representation (RTL) to @var{file}. If the
4682 optional argument is omitted (or if @var{file} is @code{.}), the name
4683 of the dump file will be determined by appending @code{.gkd} to the
4684 compilation output file name.
4686 @item -fcompare-debug@r{[}=@var{opts}@r{]}
4687 @opindex fcompare-debug
4688 @opindex fno-compare-debug
4689 If no error occurs during compilation, run the compiler a second time,
4690 adding @var{opts} and @option{-fcompare-debug-second} to the arguments
4691 passed to the second compilation. Dump the final internal
4692 representation in both compilations, and print an error if they differ.
4694 If the equal sign is omitted, the default @option{-gtoggle} is used.
4696 The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
4697 and nonzero, implicitly enables @option{-fcompare-debug}. If
4698 @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
4699 then it is used for @var{opts}, otherwise the default @option{-gtoggle}
4702 @option{-fcompare-debug=}, with the equal sign but without @var{opts},
4703 is equivalent to @option{-fno-compare-debug}, which disables the dumping
4704 of the final representation and the second compilation, preventing even
4705 @env{GCC_COMPARE_DEBUG} from taking effect.
4707 To verify full coverage during @option{-fcompare-debug} testing, set
4708 @env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden},
4709 which GCC will reject as an invalid option in any actual compilation
4710 (rather than preprocessing, assembly or linking). To get just a
4711 warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
4712 not overridden} will do.
4714 @item -fcompare-debug-second
4715 @opindex fcompare-debug-second
4716 This option is implicitly passed to the compiler for the second
4717 compilation requested by @option{-fcompare-debug}, along with options to
4718 silence warnings, and omitting other options that would cause
4719 side-effect compiler outputs to files or to the standard output. Dump
4720 files and preserved temporary files are renamed so as to contain the
4721 @code{.gk} additional extension during the second compilation, to avoid
4722 overwriting those generated by the first.
4724 When this option is passed to the compiler driver, it causes the
4725 @emph{first} compilation to be skipped, which makes it useful for little
4726 other than debugging the compiler proper.
4728 @item -feliminate-dwarf2-dups
4729 @opindex feliminate-dwarf2-dups
4730 Compress DWARF2 debugging information by eliminating duplicated
4731 information about each symbol. This option only makes sense when
4732 generating DWARF2 debugging information with @option{-gdwarf-2}.
4734 @item -femit-struct-debug-baseonly
4735 Emit debug information for struct-like types
4736 only when the base name of the compilation source file
4737 matches the base name of file in which the struct was defined.
4739 This option substantially reduces the size of debugging information,
4740 but at significant potential loss in type information to the debugger.
4741 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4742 See @option{-femit-struct-debug-detailed} for more detailed control.
4744 This option works only with DWARF 2.
4746 @item -femit-struct-debug-reduced
4747 Emit debug information for struct-like types
4748 only when the base name of the compilation source file
4749 matches the base name of file in which the type was defined,
4750 unless the struct is a template or defined in a system header.
4752 This option significantly reduces the size of debugging information,
4753 with some potential loss in type information to the debugger.
4754 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4755 See @option{-femit-struct-debug-detailed} for more detailed control.
4757 This option works only with DWARF 2.
4759 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4760 Specify the struct-like types
4761 for which the compiler will generate debug information.
4762 The intent is to reduce duplicate struct debug information
4763 between different object files within the same program.
4765 This option is a detailed version of
4766 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4767 which will serve for most needs.
4769 A specification has the syntax@*
4770 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4772 The optional first word limits the specification to
4773 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4774 A struct type is used directly when it is the type of a variable, member.
4775 Indirect uses arise through pointers to structs.
4776 That is, when use of an incomplete struct would be legal, the use is indirect.
4778 @samp{struct one direct; struct two * indirect;}.
4780 The optional second word limits the specification to
4781 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4782 Generic structs are a bit complicated to explain.
4783 For C++, these are non-explicit specializations of template classes,
4784 or non-template classes within the above.
4785 Other programming languages have generics,
4786 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4788 The third word specifies the source files for those
4789 structs for which the compiler will emit debug information.
4790 The values @samp{none} and @samp{any} have the normal meaning.
4791 The value @samp{base} means that
4792 the base of name of the file in which the type declaration appears
4793 must match the base of the name of the main compilation file.
4794 In practice, this means that
4795 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4796 but types declared in other header will not.
4797 The value @samp{sys} means those types satisfying @samp{base}
4798 or declared in system or compiler headers.
4800 You may need to experiment to determine the best settings for your application.
4802 The default is @samp{-femit-struct-debug-detailed=all}.
4804 This option works only with DWARF 2.
4806 @item -fno-merge-debug-strings
4807 @opindex fmerge-debug-strings
4808 @opindex fno-merge-debug-strings
4809 Direct the linker to not merge together strings in the debugging
4810 information which are identical in different object files. Merging is
4811 not supported by all assemblers or linkers. Merging decreases the size
4812 of the debug information in the output file at the cost of increasing
4813 link processing time. Merging is enabled by default.
4815 @item -fdebug-prefix-map=@var{old}=@var{new}
4816 @opindex fdebug-prefix-map
4817 When compiling files in directory @file{@var{old}}, record debugging
4818 information describing them as in @file{@var{new}} instead.
4820 @item -fno-dwarf2-cfi-asm
4821 @opindex fdwarf2-cfi-asm
4822 @opindex fno-dwarf2-cfi-asm
4823 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4824 instead of using GAS @code{.cfi_*} directives.
4826 @cindex @command{prof}
4829 Generate extra code to write profile information suitable for the
4830 analysis program @command{prof}. You must use this option when compiling
4831 the source files you want data about, and you must also use it when
4834 @cindex @command{gprof}
4837 Generate extra code to write profile information suitable for the
4838 analysis program @command{gprof}. You must use this option when compiling
4839 the source files you want data about, and you must also use it when
4844 Makes the compiler print out each function name as it is compiled, and
4845 print some statistics about each pass when it finishes.
4848 @opindex ftime-report
4849 Makes the compiler print some statistics about the time consumed by each
4850 pass when it finishes.
4853 @opindex fmem-report
4854 Makes the compiler print some statistics about permanent memory
4855 allocation when it finishes.
4857 @item -fpre-ipa-mem-report
4858 @opindex fpre-ipa-mem-report
4859 @item -fpost-ipa-mem-report
4860 @opindex fpost-ipa-mem-report
4861 Makes the compiler print some statistics about permanent memory
4862 allocation before or after interprocedural optimization.
4865 @opindex fstack-usage
4866 Makes the compiler output stack usage information for the program, on a
4867 per-function basis. The filename for the dump is made by appending
4868 @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
4869 the output file, if explicitly specified and it is not an executable,
4870 otherwise it is the basename of the source file. An entry is made up
4875 The name of the function.
4879 One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
4882 The qualifier @code{static} means that the function manipulates the stack
4883 statically: a fixed number of bytes are allocated for the frame on function
4884 entry and released on function exit; no stack adjustments are otherwise made
4885 in the function. The second field is this fixed number of bytes.
4887 The qualifier @code{dynamic} means that the function manipulates the stack
4888 dynamically: in addition to the static allocation described above, stack
4889 adjustments are made in the body of the function, for example to push/pop
4890 arguments around function calls. If the qualifier @code{bounded} is also
4891 present, the amount of these adjustments is bounded at compile-time and
4892 the second field is an upper bound of the total amount of stack used by
4893 the function. If it is not present, the amount of these adjustments is
4894 not bounded at compile-time and the second field only represents the
4897 @item -fprofile-arcs
4898 @opindex fprofile-arcs
4899 Add code so that program flow @dfn{arcs} are instrumented. During
4900 execution the program records how many times each branch and call is
4901 executed and how many times it is taken or returns. When the compiled
4902 program exits it saves this data to a file called
4903 @file{@var{auxname}.gcda} for each source file. The data may be used for
4904 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4905 test coverage analysis (@option{-ftest-coverage}). Each object file's
4906 @var{auxname} is generated from the name of the output file, if
4907 explicitly specified and it is not the final executable, otherwise it is
4908 the basename of the source file. In both cases any suffix is removed
4909 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4910 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4911 @xref{Cross-profiling}.
4913 @cindex @command{gcov}
4917 This option is used to compile and link code instrumented for coverage
4918 analysis. The option is a synonym for @option{-fprofile-arcs}
4919 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4920 linking). See the documentation for those options for more details.
4925 Compile the source files with @option{-fprofile-arcs} plus optimization
4926 and code generation options. For test coverage analysis, use the
4927 additional @option{-ftest-coverage} option. You do not need to profile
4928 every source file in a program.
4931 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4932 (the latter implies the former).
4935 Run the program on a representative workload to generate the arc profile
4936 information. This may be repeated any number of times. You can run
4937 concurrent instances of your program, and provided that the file system
4938 supports locking, the data files will be correctly updated. Also
4939 @code{fork} calls are detected and correctly handled (double counting
4943 For profile-directed optimizations, compile the source files again with
4944 the same optimization and code generation options plus
4945 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4946 Control Optimization}).
4949 For test coverage analysis, use @command{gcov} to produce human readable
4950 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4951 @command{gcov} documentation for further information.
4955 With @option{-fprofile-arcs}, for each function of your program GCC
4956 creates a program flow graph, then finds a spanning tree for the graph.
4957 Only arcs that are not on the spanning tree have to be instrumented: the
4958 compiler adds code to count the number of times that these arcs are
4959 executed. When an arc is the only exit or only entrance to a block, the
4960 instrumentation code can be added to the block; otherwise, a new basic
4961 block must be created to hold the instrumentation code.
4964 @item -ftest-coverage
4965 @opindex ftest-coverage
4966 Produce a notes file that the @command{gcov} code-coverage utility
4967 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4968 show program coverage. Each source file's note file is called
4969 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4970 above for a description of @var{auxname} and instructions on how to
4971 generate test coverage data. Coverage data will match the source files
4972 more closely, if you do not optimize.
4974 @item -fdbg-cnt-list
4975 @opindex fdbg-cnt-list
4976 Print the name and the counter upper bound for all debug counters.
4978 @item -fdbg-cnt=@var{counter-value-list}
4980 Set the internal debug counter upper bound. @var{counter-value-list}
4981 is a comma-separated list of @var{name}:@var{value} pairs
4982 which sets the upper bound of each debug counter @var{name} to @var{value}.
4983 All debug counters have the initial upper bound of @var{UINT_MAX},
4984 thus dbg_cnt() returns true always unless the upper bound is set by this option.
4985 e.g. With -fdbg-cnt=dce:10,tail_call:0
4986 dbg_cnt(dce) will return true only for first 10 invocations
4987 and dbg_cnt(tail_call) will return false always.
4989 @item -d@var{letters}
4990 @itemx -fdump-rtl-@var{pass}
4992 Says to make debugging dumps during compilation at times specified by
4993 @var{letters}. This is used for debugging the RTL-based passes of the
4994 compiler. The file names for most of the dumps are made by appending
4995 a pass number and a word to the @var{dumpname}, and the files are
4996 created in the directory of the output file. Note that the pass
4997 number is computed statically as passes get registered into the pass
4998 manager. Thus the numbering is not related to the dynamic order of
4999 execution of passes. In particular, a pass installed by a plugin
5000 could have a number over 200 even if it executed quite early.
5001 @var{dumpname} is generated from the name of the output file, if
5002 explicitly specified and it is not an executable, otherwise it is the
5003 basename of the source file. These switches may have different effects
5004 when @option{-E} is used for preprocessing.
5006 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
5007 @option{-d} option @var{letters}. Here are the possible
5008 letters for use in @var{pass} and @var{letters}, and their meanings:
5012 @item -fdump-rtl-alignments
5013 @opindex fdump-rtl-alignments
5014 Dump after branch alignments have been computed.
5016 @item -fdump-rtl-asmcons
5017 @opindex fdump-rtl-asmcons
5018 Dump after fixing rtl statements that have unsatisfied in/out constraints.
5020 @item -fdump-rtl-auto_inc_dec
5021 @opindex fdump-rtl-auto_inc_dec
5022 Dump after auto-inc-dec discovery. This pass is only run on
5023 architectures that have auto inc or auto dec instructions.
5025 @item -fdump-rtl-barriers
5026 @opindex fdump-rtl-barriers
5027 Dump after cleaning up the barrier instructions.
5029 @item -fdump-rtl-bbpart
5030 @opindex fdump-rtl-bbpart
5031 Dump after partitioning hot and cold basic blocks.
5033 @item -fdump-rtl-bbro
5034 @opindex fdump-rtl-bbro
5035 Dump after block reordering.
5037 @item -fdump-rtl-btl1
5038 @itemx -fdump-rtl-btl2
5039 @opindex fdump-rtl-btl2
5040 @opindex fdump-rtl-btl2
5041 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
5042 after the two branch
5043 target load optimization passes.
5045 @item -fdump-rtl-bypass
5046 @opindex fdump-rtl-bypass
5047 Dump after jump bypassing and control flow optimizations.
5049 @item -fdump-rtl-combine
5050 @opindex fdump-rtl-combine
5051 Dump after the RTL instruction combination pass.
5053 @item -fdump-rtl-compgotos
5054 @opindex fdump-rtl-compgotos
5055 Dump after duplicating the computed gotos.
5057 @item -fdump-rtl-ce1
5058 @itemx -fdump-rtl-ce2
5059 @itemx -fdump-rtl-ce3
5060 @opindex fdump-rtl-ce1
5061 @opindex fdump-rtl-ce2
5062 @opindex fdump-rtl-ce3
5063 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
5064 @option{-fdump-rtl-ce3} enable dumping after the three
5065 if conversion passes.
5067 @itemx -fdump-rtl-cprop_hardreg
5068 @opindex fdump-rtl-cprop_hardreg
5069 Dump after hard register copy propagation.
5071 @itemx -fdump-rtl-csa
5072 @opindex fdump-rtl-csa
5073 Dump after combining stack adjustments.
5075 @item -fdump-rtl-cse1
5076 @itemx -fdump-rtl-cse2
5077 @opindex fdump-rtl-cse1
5078 @opindex fdump-rtl-cse2
5079 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
5080 the two common sub-expression elimination passes.
5082 @itemx -fdump-rtl-dce
5083 @opindex fdump-rtl-dce
5084 Dump after the standalone dead code elimination passes.
5086 @itemx -fdump-rtl-dbr
5087 @opindex fdump-rtl-dbr
5088 Dump after delayed branch scheduling.
5090 @item -fdump-rtl-dce1
5091 @itemx -fdump-rtl-dce2
5092 @opindex fdump-rtl-dce1
5093 @opindex fdump-rtl-dce2
5094 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
5095 the two dead store elimination passes.
5098 @opindex fdump-rtl-eh
5099 Dump after finalization of EH handling code.
5101 @item -fdump-rtl-eh_ranges
5102 @opindex fdump-rtl-eh_ranges
5103 Dump after conversion of EH handling range regions.
5105 @item -fdump-rtl-expand
5106 @opindex fdump-rtl-expand
5107 Dump after RTL generation.
5109 @item -fdump-rtl-fwprop1
5110 @itemx -fdump-rtl-fwprop2
5111 @opindex fdump-rtl-fwprop1
5112 @opindex fdump-rtl-fwprop2
5113 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
5114 dumping after the two forward propagation passes.
5116 @item -fdump-rtl-gcse1
5117 @itemx -fdump-rtl-gcse2
5118 @opindex fdump-rtl-gcse1
5119 @opindex fdump-rtl-gcse2
5120 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
5121 after global common subexpression elimination.
5123 @item -fdump-rtl-init-regs
5124 @opindex fdump-rtl-init-regs
5125 Dump after the initialization of the registers.
5127 @item -fdump-rtl-initvals
5128 @opindex fdump-rtl-initvals
5129 Dump after the computation of the initial value sets.
5131 @itemx -fdump-rtl-into_cfglayout
5132 @opindex fdump-rtl-into_cfglayout
5133 Dump after converting to cfglayout mode.
5135 @item -fdump-rtl-ira
5136 @opindex fdump-rtl-ira
5137 Dump after iterated register allocation.
5139 @item -fdump-rtl-jump
5140 @opindex fdump-rtl-jump
5141 Dump after the second jump optimization.
5143 @item -fdump-rtl-loop2
5144 @opindex fdump-rtl-loop2
5145 @option{-fdump-rtl-loop2} enables dumping after the rtl
5146 loop optimization passes.
5148 @item -fdump-rtl-mach
5149 @opindex fdump-rtl-mach
5150 Dump after performing the machine dependent reorganization pass, if that
5153 @item -fdump-rtl-mode_sw
5154 @opindex fdump-rtl-mode_sw
5155 Dump after removing redundant mode switches.
5157 @item -fdump-rtl-rnreg
5158 @opindex fdump-rtl-rnreg
5159 Dump after register renumbering.
5161 @itemx -fdump-rtl-outof_cfglayout
5162 @opindex fdump-rtl-outof_cfglayout
5163 Dump after converting from cfglayout mode.
5165 @item -fdump-rtl-peephole2
5166 @opindex fdump-rtl-peephole2
5167 Dump after the peephole pass.
5169 @item -fdump-rtl-postreload
5170 @opindex fdump-rtl-postreload
5171 Dump after post-reload optimizations.
5173 @itemx -fdump-rtl-pro_and_epilogue
5174 @opindex fdump-rtl-pro_and_epilogue
5175 Dump after generating the function pro and epilogues.
5177 @item -fdump-rtl-regmove
5178 @opindex fdump-rtl-regmove
5179 Dump after the register move pass.
5181 @item -fdump-rtl-sched1
5182 @itemx -fdump-rtl-sched2
5183 @opindex fdump-rtl-sched1
5184 @opindex fdump-rtl-sched2
5185 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
5186 after the basic block scheduling passes.
5188 @item -fdump-rtl-see
5189 @opindex fdump-rtl-see
5190 Dump after sign extension elimination.
5192 @item -fdump-rtl-seqabstr
5193 @opindex fdump-rtl-seqabstr
5194 Dump after common sequence discovery.
5196 @item -fdump-rtl-shorten
5197 @opindex fdump-rtl-shorten
5198 Dump after shortening branches.
5200 @item -fdump-rtl-sibling
5201 @opindex fdump-rtl-sibling
5202 Dump after sibling call optimizations.
5204 @item -fdump-rtl-split1
5205 @itemx -fdump-rtl-split2
5206 @itemx -fdump-rtl-split3
5207 @itemx -fdump-rtl-split4
5208 @itemx -fdump-rtl-split5
5209 @opindex fdump-rtl-split1
5210 @opindex fdump-rtl-split2
5211 @opindex fdump-rtl-split3
5212 @opindex fdump-rtl-split4
5213 @opindex fdump-rtl-split5
5214 @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2},
5215 @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and
5216 @option{-fdump-rtl-split5} enable dumping after five rounds of
5217 instruction splitting.
5219 @item -fdump-rtl-sms
5220 @opindex fdump-rtl-sms
5221 Dump after modulo scheduling. This pass is only run on some
5224 @item -fdump-rtl-stack
5225 @opindex fdump-rtl-stack
5226 Dump after conversion from GCC's "flat register file" registers to the
5227 x87's stack-like registers. This pass is only run on x86 variants.
5229 @item -fdump-rtl-subreg1
5230 @itemx -fdump-rtl-subreg2
5231 @opindex fdump-rtl-subreg1
5232 @opindex fdump-rtl-subreg2
5233 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
5234 the two subreg expansion passes.
5236 @item -fdump-rtl-unshare
5237 @opindex fdump-rtl-unshare
5238 Dump after all rtl has been unshared.
5240 @item -fdump-rtl-vartrack
5241 @opindex fdump-rtl-vartrack
5242 Dump after variable tracking.
5244 @item -fdump-rtl-vregs
5245 @opindex fdump-rtl-vregs
5246 Dump after converting virtual registers to hard registers.
5248 @item -fdump-rtl-web
5249 @opindex fdump-rtl-web
5250 Dump after live range splitting.
5252 @item -fdump-rtl-regclass
5253 @itemx -fdump-rtl-subregs_of_mode_init
5254 @itemx -fdump-rtl-subregs_of_mode_finish
5255 @itemx -fdump-rtl-dfinit
5256 @itemx -fdump-rtl-dfinish
5257 @opindex fdump-rtl-regclass
5258 @opindex fdump-rtl-subregs_of_mode_init
5259 @opindex fdump-rtl-subregs_of_mode_finish
5260 @opindex fdump-rtl-dfinit
5261 @opindex fdump-rtl-dfinish
5262 These dumps are defined but always produce empty files.
5264 @item -fdump-rtl-all
5265 @opindex fdump-rtl-all
5266 Produce all the dumps listed above.
5270 Annotate the assembler output with miscellaneous debugging information.
5274 Dump all macro definitions, at the end of preprocessing, in addition to
5279 Produce a core dump whenever an error occurs.
5283 Print statistics on memory usage, at the end of the run, to
5288 Annotate the assembler output with a comment indicating which
5289 pattern and alternative was used. The length of each instruction is
5294 Dump the RTL in the assembler output as a comment before each instruction.
5295 Also turns on @option{-dp} annotation.
5299 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
5300 dump a representation of the control flow graph suitable for viewing with VCG
5301 to @file{@var{file}.@var{pass}.vcg}.
5305 Just generate RTL for a function instead of compiling it. Usually used
5306 with @option{-fdump-rtl-expand}.
5310 @opindex fdump-noaddr
5311 When doing debugging dumps, suppress address output. This makes it more
5312 feasible to use diff on debugging dumps for compiler invocations with
5313 different compiler binaries and/or different
5314 text / bss / data / heap / stack / dso start locations.
5316 @item -fdump-unnumbered
5317 @opindex fdump-unnumbered
5318 When doing debugging dumps, suppress instruction numbers and address output.
5319 This makes it more feasible to use diff on debugging dumps for compiler
5320 invocations with different options, in particular with and without
5323 @item -fdump-unnumbered-links
5324 @opindex fdump-unnumbered-links
5325 When doing debugging dumps (see @option{-d} option above), suppress
5326 instruction numbers for the links to the previous and next instructions
5329 @item -fdump-translation-unit @r{(C++ only)}
5330 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
5331 @opindex fdump-translation-unit
5332 Dump a representation of the tree structure for the entire translation
5333 unit to a file. The file name is made by appending @file{.tu} to the
5334 source file name, and the file is created in the same directory as the
5335 output file. If the @samp{-@var{options}} form is used, @var{options}
5336 controls the details of the dump as described for the
5337 @option{-fdump-tree} options.
5339 @item -fdump-class-hierarchy @r{(C++ only)}
5340 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
5341 @opindex fdump-class-hierarchy
5342 Dump a representation of each class's hierarchy and virtual function
5343 table layout to a file. The file name is made by appending
5344 @file{.class} to the source file name, and the file is created in the
5345 same directory as the output file. If the @samp{-@var{options}} form
5346 is used, @var{options} controls the details of the dump as described
5347 for the @option{-fdump-tree} options.
5349 @item -fdump-ipa-@var{switch}
5351 Control the dumping at various stages of inter-procedural analysis
5352 language tree to a file. The file name is generated by appending a
5353 switch specific suffix to the source file name, and the file is created
5354 in the same directory as the output file. The following dumps are
5359 Enables all inter-procedural analysis dumps.
5362 Dumps information about call-graph optimization, unused function removal,
5363 and inlining decisions.
5366 Dump after function inlining.
5370 @item -fdump-statistics-@var{option}
5371 @opindex fdump-statistics
5372 Enable and control dumping of pass statistics in a separate file. The
5373 file name is generated by appending a suffix ending in
5374 @samp{.statistics} to the source file name, and the file is created in
5375 the same directory as the output file. If the @samp{-@var{option}}
5376 form is used, @samp{-stats} will cause counters to be summed over the
5377 whole compilation unit while @samp{-details} will dump every event as
5378 the passes generate them. The default with no option is to sum
5379 counters for each function compiled.
5381 @item -fdump-tree-@var{switch}
5382 @itemx -fdump-tree-@var{switch}-@var{options}
5384 Control the dumping at various stages of processing the intermediate
5385 language tree to a file. The file name is generated by appending a
5386 switch specific suffix to the source file name, and the file is
5387 created in the same directory as the output file. If the
5388 @samp{-@var{options}} form is used, @var{options} is a list of
5389 @samp{-} separated options that control the details of the dump. Not
5390 all options are applicable to all dumps, those which are not
5391 meaningful will be ignored. The following options are available
5395 Print the address of each node. Usually this is not meaningful as it
5396 changes according to the environment and source file. Its primary use
5397 is for tying up a dump file with a debug environment.
5399 If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
5400 in the dump instead of @code{DECL_NAME}. Its primary use is ease of
5401 use working backward from mangled names in the assembly file.
5403 Inhibit dumping of members of a scope or body of a function merely
5404 because that scope has been reached. Only dump such items when they
5405 are directly reachable by some other path. When dumping pretty-printed
5406 trees, this option inhibits dumping the bodies of control structures.
5408 Print a raw representation of the tree. By default, trees are
5409 pretty-printed into a C-like representation.
5411 Enable more detailed dumps (not honored by every dump option).
5413 Enable dumping various statistics about the pass (not honored by every dump
5416 Enable showing basic block boundaries (disabled in raw dumps).
5418 Enable showing virtual operands for every statement.
5420 Enable showing line numbers for statements.
5422 Enable showing the unique ID (@code{DECL_UID}) for each variable.
5424 Enable showing the tree dump for each statement.
5426 Enable showing the EH region number holding each statement.
5428 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
5429 and @option{lineno}.
5432 The following tree dumps are possible:
5436 @opindex fdump-tree-original
5437 Dump before any tree based optimization, to @file{@var{file}.original}.
5440 @opindex fdump-tree-optimized
5441 Dump after all tree based optimization, to @file{@var{file}.optimized}.
5444 @opindex fdump-tree-gimple
5445 Dump each function before and after the gimplification pass to a file. The
5446 file name is made by appending @file{.gimple} to the source file name.
5449 @opindex fdump-tree-cfg
5450 Dump the control flow graph of each function to a file. The file name is
5451 made by appending @file{.cfg} to the source file name.
5454 @opindex fdump-tree-vcg
5455 Dump the control flow graph of each function to a file in VCG format. The
5456 file name is made by appending @file{.vcg} to the source file name. Note
5457 that if the file contains more than one function, the generated file cannot
5458 be used directly by VCG@. You will need to cut and paste each function's
5459 graph into its own separate file first.
5462 @opindex fdump-tree-ch
5463 Dump each function after copying loop headers. The file name is made by
5464 appending @file{.ch} to the source file name.
5467 @opindex fdump-tree-ssa
5468 Dump SSA related information to a file. The file name is made by appending
5469 @file{.ssa} to the source file name.
5472 @opindex fdump-tree-alias
5473 Dump aliasing information for each function. The file name is made by
5474 appending @file{.alias} to the source file name.
5477 @opindex fdump-tree-ccp
5478 Dump each function after CCP@. The file name is made by appending
5479 @file{.ccp} to the source file name.
5482 @opindex fdump-tree-storeccp
5483 Dump each function after STORE-CCP@. The file name is made by appending
5484 @file{.storeccp} to the source file name.
5487 @opindex fdump-tree-pre
5488 Dump trees after partial redundancy elimination. The file name is made
5489 by appending @file{.pre} to the source file name.
5492 @opindex fdump-tree-fre
5493 Dump trees after full redundancy elimination. The file name is made
5494 by appending @file{.fre} to the source file name.
5497 @opindex fdump-tree-copyprop
5498 Dump trees after copy propagation. The file name is made
5499 by appending @file{.copyprop} to the source file name.
5501 @item store_copyprop
5502 @opindex fdump-tree-store_copyprop
5503 Dump trees after store copy-propagation. The file name is made
5504 by appending @file{.store_copyprop} to the source file name.
5507 @opindex fdump-tree-dce
5508 Dump each function after dead code elimination. The file name is made by
5509 appending @file{.dce} to the source file name.
5512 @opindex fdump-tree-mudflap
5513 Dump each function after adding mudflap instrumentation. The file name is
5514 made by appending @file{.mudflap} to the source file name.
5517 @opindex fdump-tree-sra
5518 Dump each function after performing scalar replacement of aggregates. The
5519 file name is made by appending @file{.sra} to the source file name.
5522 @opindex fdump-tree-sink
5523 Dump each function after performing code sinking. The file name is made
5524 by appending @file{.sink} to the source file name.
5527 @opindex fdump-tree-dom
5528 Dump each function after applying dominator tree optimizations. The file
5529 name is made by appending @file{.dom} to the source file name.
5532 @opindex fdump-tree-dse
5533 Dump each function after applying dead store elimination. The file
5534 name is made by appending @file{.dse} to the source file name.
5537 @opindex fdump-tree-phiopt
5538 Dump each function after optimizing PHI nodes into straightline code. The file
5539 name is made by appending @file{.phiopt} to the source file name.
5542 @opindex fdump-tree-forwprop
5543 Dump each function after forward propagating single use variables. The file
5544 name is made by appending @file{.forwprop} to the source file name.
5547 @opindex fdump-tree-copyrename
5548 Dump each function after applying the copy rename optimization. The file
5549 name is made by appending @file{.copyrename} to the source file name.
5552 @opindex fdump-tree-nrv
5553 Dump each function after applying the named return value optimization on
5554 generic trees. The file name is made by appending @file{.nrv} to the source
5558 @opindex fdump-tree-vect
5559 Dump each function after applying vectorization of loops. The file name is
5560 made by appending @file{.vect} to the source file name.
5563 @opindex fdump-tree-slp
5564 Dump each function after applying vectorization of basic blocks. The file name
5565 is made by appending @file{.slp} to the source file name.
5568 @opindex fdump-tree-vrp
5569 Dump each function after Value Range Propagation (VRP). The file name
5570 is made by appending @file{.vrp} to the source file name.
5573 @opindex fdump-tree-all
5574 Enable all the available tree dumps with the flags provided in this option.
5577 @item -ftree-vectorizer-verbose=@var{n}
5578 @opindex ftree-vectorizer-verbose
5579 This option controls the amount of debugging output the vectorizer prints.
5580 This information is written to standard error, unless
5581 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
5582 in which case it is output to the usual dump listing file, @file{.vect}.
5583 For @var{n}=0 no diagnostic information is reported.
5584 If @var{n}=1 the vectorizer reports each loop that got vectorized,
5585 and the total number of loops that got vectorized.
5586 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
5587 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
5588 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
5589 level that @option{-fdump-tree-vect-stats} uses.
5590 Higher verbosity levels mean either more information dumped for each
5591 reported loop, or same amount of information reported for more loops:
5592 if @var{n}=3, vectorizer cost model information is reported.
5593 If @var{n}=4, alignment related information is added to the reports.
5594 If @var{n}=5, data-references related information (e.g.@: memory dependences,
5595 memory access-patterns) is added to the reports.
5596 If @var{n}=6, the vectorizer reports also non-vectorized inner-most loops
5597 that did not pass the first analysis phase (i.e., may not be countable, or
5598 may have complicated control-flow).
5599 If @var{n}=7, the vectorizer reports also non-vectorized nested loops.
5600 If @var{n}=8, SLP related information is added to the reports.
5601 For @var{n}=9, all the information the vectorizer generates during its
5602 analysis and transformation is reported. This is the same verbosity level
5603 that @option{-fdump-tree-vect-details} uses.
5605 @item -frandom-seed=@var{string}
5606 @opindex frandom-seed
5607 This option provides a seed that GCC uses when it would otherwise use
5608 random numbers. It is used to generate certain symbol names
5609 that have to be different in every compiled file. It is also used to
5610 place unique stamps in coverage data files and the object files that
5611 produce them. You can use the @option{-frandom-seed} option to produce
5612 reproducibly identical object files.
5614 The @var{string} should be different for every file you compile.
5616 @item -fsched-verbose=@var{n}
5617 @opindex fsched-verbose
5618 On targets that use instruction scheduling, this option controls the
5619 amount of debugging output the scheduler prints. This information is
5620 written to standard error, unless @option{-fdump-rtl-sched1} or
5621 @option{-fdump-rtl-sched2} is specified, in which case it is output
5622 to the usual dump listing file, @file{.sched1} or @file{.sched2}
5623 respectively. However for @var{n} greater than nine, the output is
5624 always printed to standard error.
5626 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5627 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5628 For @var{n} greater than one, it also output basic block probabilities,
5629 detailed ready list information and unit/insn info. For @var{n} greater
5630 than two, it includes RTL at abort point, control-flow and regions info.
5631 And for @var{n} over four, @option{-fsched-verbose} also includes
5635 @itemx -save-temps=cwd
5637 Store the usual ``temporary'' intermediate files permanently; place them
5638 in the current directory and name them based on the source file. Thus,
5639 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5640 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5641 preprocessed @file{foo.i} output file even though the compiler now
5642 normally uses an integrated preprocessor.
5644 When used in combination with the @option{-x} command line option,
5645 @option{-save-temps} is sensible enough to avoid over writing an
5646 input source file with the same extension as an intermediate file.
5647 The corresponding intermediate file may be obtained by renaming the
5648 source file before using @option{-save-temps}.
5650 If you invoke GCC in parallel, compiling several different source
5651 files that share a common base name in different subdirectories or the
5652 same source file compiled for multiple output destinations, it is
5653 likely that the different parallel compilers will interfere with each
5654 other, and overwrite the temporary files. For instance:
5657 gcc -save-temps -o outdir1/foo.o indir1/foo.c&
5658 gcc -save-temps -o outdir2/foo.o indir2/foo.c&
5661 may result in @file{foo.i} and @file{foo.o} being written to
5662 simultaneously by both compilers.
5664 @item -save-temps=obj
5665 @opindex save-temps=obj
5666 Store the usual ``temporary'' intermediate files permanently. If the
5667 @option{-o} option is used, the temporary files are based on the
5668 object file. If the @option{-o} option is not used, the
5669 @option{-save-temps=obj} switch behaves like @option{-save-temps}.
5674 gcc -save-temps=obj -c foo.c
5675 gcc -save-temps=obj -c bar.c -o dir/xbar.o
5676 gcc -save-temps=obj foobar.c -o dir2/yfoobar
5679 would create @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
5680 @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
5681 @file{dir2/yfoobar.o}.
5683 @item -time@r{[}=@var{file}@r{]}
5685 Report the CPU time taken by each subprocess in the compilation
5686 sequence. For C source files, this is the compiler proper and assembler
5687 (plus the linker if linking is done).
5689 Without the specification of an output file, the output looks like this:
5696 The first number on each line is the ``user time'', that is time spent
5697 executing the program itself. The second number is ``system time'',
5698 time spent executing operating system routines on behalf of the program.
5699 Both numbers are in seconds.
5701 With the specification of an output file, the output is appended to the
5702 named file, and it looks like this:
5705 0.12 0.01 cc1 @var{options}
5706 0.00 0.01 as @var{options}
5709 The ``user time'' and the ``system time'' are moved before the program
5710 name, and the options passed to the program are displayed, so that one
5711 can later tell what file was being compiled, and with which options.
5713 @item -fvar-tracking
5714 @opindex fvar-tracking
5715 Run variable tracking pass. It computes where variables are stored at each
5716 position in code. Better debugging information is then generated
5717 (if the debugging information format supports this information).
5719 It is enabled by default when compiling with optimization (@option{-Os},
5720 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5721 the debug info format supports it.
5723 @item -fvar-tracking-assignments
5724 @opindex fvar-tracking-assignments
5725 @opindex fno-var-tracking-assignments
5726 Annotate assignments to user variables early in the compilation and
5727 attempt to carry the annotations over throughout the compilation all the
5728 way to the end, in an attempt to improve debug information while
5729 optimizing. Use of @option{-gdwarf-4} is recommended along with it.
5731 It can be enabled even if var-tracking is disabled, in which case
5732 annotations will be created and maintained, but discarded at the end.
5734 @item -fvar-tracking-assignments-toggle
5735 @opindex fvar-tracking-assignments-toggle
5736 @opindex fno-var-tracking-assignments-toggle
5737 Toggle @option{-fvar-tracking-assignments}, in the same way that
5738 @option{-gtoggle} toggles @option{-g}.
5740 @item -print-file-name=@var{library}
5741 @opindex print-file-name
5742 Print the full absolute name of the library file @var{library} that
5743 would be used when linking---and don't do anything else. With this
5744 option, GCC does not compile or link anything; it just prints the
5747 @item -print-multi-directory
5748 @opindex print-multi-directory
5749 Print the directory name corresponding to the multilib selected by any
5750 other switches present in the command line. This directory is supposed
5751 to exist in @env{GCC_EXEC_PREFIX}.
5753 @item -print-multi-lib
5754 @opindex print-multi-lib
5755 Print the mapping from multilib directory names to compiler switches
5756 that enable them. The directory name is separated from the switches by
5757 @samp{;}, and each switch starts with an @samp{@@} instead of the
5758 @samp{-}, without spaces between multiple switches. This is supposed to
5759 ease shell-processing.
5761 @item -print-multi-os-directory
5762 @opindex print-multi-os-directory
5763 Print the path to OS libraries for the selected
5764 multilib, relative to some @file{lib} subdirectory. If OS libraries are
5765 present in the @file{lib} subdirectory and no multilibs are used, this is
5766 usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
5767 sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
5768 @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
5769 subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
5771 @item -print-prog-name=@var{program}
5772 @opindex print-prog-name
5773 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5775 @item -print-libgcc-file-name
5776 @opindex print-libgcc-file-name
5777 Same as @option{-print-file-name=libgcc.a}.
5779 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5780 but you do want to link with @file{libgcc.a}. You can do
5783 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5786 @item -print-search-dirs
5787 @opindex print-search-dirs
5788 Print the name of the configured installation directory and a list of
5789 program and library directories @command{gcc} will search---and don't do anything else.
5791 This is useful when @command{gcc} prints the error message
5792 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5793 To resolve this you either need to put @file{cpp0} and the other compiler
5794 components where @command{gcc} expects to find them, or you can set the environment
5795 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5796 Don't forget the trailing @samp{/}.
5797 @xref{Environment Variables}.
5799 @item -print-sysroot
5800 @opindex print-sysroot
5801 Print the target sysroot directory that will be used during
5802 compilation. This is the target sysroot specified either at configure
5803 time or using the @option{--sysroot} option, possibly with an extra
5804 suffix that depends on compilation options. If no target sysroot is
5805 specified, the option prints nothing.
5807 @item -print-sysroot-headers-suffix
5808 @opindex print-sysroot-headers-suffix
5809 Print the suffix added to the target sysroot when searching for
5810 headers, or give an error if the compiler is not configured with such
5811 a suffix---and don't do anything else.
5814 @opindex dumpmachine
5815 Print the compiler's target machine (for example,
5816 @samp{i686-pc-linux-gnu})---and don't do anything else.
5819 @opindex dumpversion
5820 Print the compiler version (for example, @samp{3.0})---and don't do
5825 Print the compiler's built-in specs---and don't do anything else. (This
5826 is used when GCC itself is being built.) @xref{Spec Files}.
5828 @item -feliminate-unused-debug-types
5829 @opindex feliminate-unused-debug-types
5830 Normally, when producing DWARF2 output, GCC will emit debugging
5831 information for all types declared in a compilation
5832 unit, regardless of whether or not they are actually used
5833 in that compilation unit. Sometimes this is useful, such as
5834 if, in the debugger, you want to cast a value to a type that is
5835 not actually used in your program (but is declared). More often,
5836 however, this results in a significant amount of wasted space.
5837 With this option, GCC will avoid producing debug symbol output
5838 for types that are nowhere used in the source file being compiled.
5841 @node Optimize Options
5842 @section Options That Control Optimization
5843 @cindex optimize options
5844 @cindex options, optimization
5846 These options control various sorts of optimizations.
5848 Without any optimization option, the compiler's goal is to reduce the
5849 cost of compilation and to make debugging produce the expected
5850 results. Statements are independent: if you stop the program with a
5851 breakpoint between statements, you can then assign a new value to any
5852 variable or change the program counter to any other statement in the
5853 function and get exactly the results you would expect from the source
5856 Turning on optimization flags makes the compiler attempt to improve
5857 the performance and/or code size at the expense of compilation time
5858 and possibly the ability to debug the program.
5860 The compiler performs optimization based on the knowledge it has of the
5861 program. Compiling multiple files at once to a single output file mode allows
5862 the compiler to use information gained from all of the files when compiling
5865 Not all optimizations are controlled directly by a flag. Only
5866 optimizations that have a flag are listed in this section.
5868 Most optimizations are only enabled if an @option{-O} level is set on
5869 the command line. Otherwise they are disabled, even if individual
5870 optimization flags are specified.
5872 Depending on the target and how GCC was configured, a slightly different
5873 set of optimizations may be enabled at each @option{-O} level than
5874 those listed here. You can invoke GCC with @samp{-Q --help=optimizers}
5875 to find out the exact set of optimizations that are enabled at each level.
5876 @xref{Overall Options}, for examples.
5883 Optimize. Optimizing compilation takes somewhat more time, and a lot
5884 more memory for a large function.
5886 With @option{-O}, the compiler tries to reduce code size and execution
5887 time, without performing any optimizations that take a great deal of
5890 @option{-O} turns on the following optimization flags:
5894 -fcprop-registers @gol
5897 -fdelayed-branch @gol
5899 -fguess-branch-probability @gol
5900 -fif-conversion2 @gol
5901 -fif-conversion @gol
5902 -fipa-pure-const @gol
5904 -fipa-reference @gol
5906 -fsplit-wide-types @gol
5908 -ftree-builtin-call-dce @gol
5911 -ftree-copyrename @gol
5913 -ftree-dominator-opts @gol
5915 -ftree-forwprop @gol
5923 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5924 where doing so does not interfere with debugging.
5928 Optimize even more. GCC performs nearly all supported optimizations
5929 that do not involve a space-speed tradeoff.
5930 As compared to @option{-O}, this option increases both compilation time
5931 and the performance of the generated code.
5933 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5934 also turns on the following optimization flags:
5935 @gccoptlist{-fthread-jumps @gol
5936 -falign-functions -falign-jumps @gol
5937 -falign-loops -falign-labels @gol
5940 -fcse-follow-jumps -fcse-skip-blocks @gol
5941 -fdelete-null-pointer-checks @gol
5943 -fexpensive-optimizations @gol
5944 -fgcse -fgcse-lm @gol
5945 -finline-small-functions @gol
5946 -findirect-inlining @gol
5948 -foptimize-sibling-calls @gol
5949 -fpartial-inlining @gol
5952 -freorder-blocks -freorder-functions @gol
5953 -frerun-cse-after-loop @gol
5954 -fsched-interblock -fsched-spec @gol
5955 -fschedule-insns -fschedule-insns2 @gol
5956 -fstrict-aliasing -fstrict-overflow @gol
5957 -ftree-switch-conversion @gol
5961 Please note the warning under @option{-fgcse} about
5962 invoking @option{-O2} on programs that use computed gotos.
5966 Optimize yet more. @option{-O3} turns on all optimizations specified
5967 by @option{-O2} and also turns on the @option{-finline-functions},
5968 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5969 @option{-fgcse-after-reload}, @option{-ftree-vectorize} and
5970 @option{-fipa-cp-clone} options.
5974 Reduce compilation time and make debugging produce the expected
5975 results. This is the default.
5979 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5980 do not typically increase code size. It also performs further
5981 optimizations designed to reduce code size.
5983 @option{-Os} disables the following optimization flags:
5984 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5985 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5986 -fprefetch-loop-arrays -ftree-vect-loop-version}
5990 Disregard strict standards compliance. @option{-Ofast} enables all
5991 @option{-O3} optimizations. It also enables optimizations that are not
5992 valid for all standard compliant programs.
5993 It turns on @option{-ffast-math}.
5995 If you use multiple @option{-O} options, with or without level numbers,
5996 the last such option is the one that is effective.
5999 Options of the form @option{-f@var{flag}} specify machine-independent
6000 flags. Most flags have both positive and negative forms; the negative
6001 form of @option{-ffoo} would be @option{-fno-foo}. In the table
6002 below, only one of the forms is listed---the one you typically will
6003 use. You can figure out the other form by either removing @samp{no-}
6006 The following options control specific optimizations. They are either
6007 activated by @option{-O} options or are related to ones that are. You
6008 can use the following flags in the rare cases when ``fine-tuning'' of
6009 optimizations to be performed is desired.
6012 @item -fno-default-inline
6013 @opindex fno-default-inline
6014 Do not make member functions inline by default merely because they are
6015 defined inside the class scope (C++ only). Otherwise, when you specify
6016 @w{@option{-O}}, member functions defined inside class scope are compiled
6017 inline by default; i.e., you don't need to add @samp{inline} in front of
6018 the member function name.
6020 @item -fno-defer-pop
6021 @opindex fno-defer-pop
6022 Always pop the arguments to each function call as soon as that function
6023 returns. For machines which must pop arguments after a function call,
6024 the compiler normally lets arguments accumulate on the stack for several
6025 function calls and pops them all at once.
6027 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6029 @item -fforward-propagate
6030 @opindex fforward-propagate
6031 Perform a forward propagation pass on RTL@. The pass tries to combine two
6032 instructions and checks if the result can be simplified. If loop unrolling
6033 is active, two passes are performed and the second is scheduled after
6036 This option is enabled by default at optimization levels @option{-O},
6037 @option{-O2}, @option{-O3}, @option{-Os}.
6039 @item -ffp-contract=@var{style}
6040 @opindex ffp-contract
6041 @option{-ffp-contract=off} disables floating-point expression contraction.
6042 @option{-ffp-contract=fast} enables floating-point expression contraction
6043 such as forming of fused multiply-add operations if the target has
6044 native support for them.
6045 @option{-ffp-contract=on} enables floating-point expression contraction
6046 if allowed by the language standard. This is currently not implemented
6047 and treated equal to @option{-ffp-contract=off}.
6049 The default is @option{-ffp-contract=fast}.
6051 @item -fomit-frame-pointer
6052 @opindex fomit-frame-pointer
6053 Don't keep the frame pointer in a register for functions that
6054 don't need one. This avoids the instructions to save, set up and
6055 restore frame pointers; it also makes an extra register available
6056 in many functions. @strong{It also makes debugging impossible on
6059 On some machines, such as the VAX, this flag has no effect, because
6060 the standard calling sequence automatically handles the frame pointer
6061 and nothing is saved by pretending it doesn't exist. The
6062 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
6063 whether a target machine supports this flag. @xref{Registers,,Register
6064 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
6066 Starting with GCC version 4.6, the default setting (when not optimizing for
6067 size) for 32-bit Linux x86 and 32-bit Darwin x86 targets has been changed to
6068 @option{-fomit-frame-pointer}. The default can be reverted to
6069 @option{-fno-omit-frame-pointer} by configuring GCC with the
6070 @option{--enable-frame-pointer} configure option.
6072 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6074 @item -foptimize-sibling-calls
6075 @opindex foptimize-sibling-calls
6076 Optimize sibling and tail recursive calls.
6078 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6082 Don't pay attention to the @code{inline} keyword. Normally this option
6083 is used to keep the compiler from expanding any functions inline.
6084 Note that if you are not optimizing, no functions can be expanded inline.
6086 @item -finline-small-functions
6087 @opindex finline-small-functions
6088 Integrate functions into their callers when their body is smaller than expected
6089 function call code (so overall size of program gets smaller). The compiler
6090 heuristically decides which functions are simple enough to be worth integrating
6093 Enabled at level @option{-O2}.
6095 @item -findirect-inlining
6096 @opindex findirect-inlining
6097 Inline also indirect calls that are discovered to be known at compile
6098 time thanks to previous inlining. This option has any effect only
6099 when inlining itself is turned on by the @option{-finline-functions}
6100 or @option{-finline-small-functions} options.
6102 Enabled at level @option{-O2}.
6104 @item -finline-functions
6105 @opindex finline-functions
6106 Integrate all simple functions into their callers. The compiler
6107 heuristically decides which functions are simple enough to be worth
6108 integrating in this way.
6110 If all calls to a given function are integrated, and the function is
6111 declared @code{static}, then the function is normally not output as
6112 assembler code in its own right.
6114 Enabled at level @option{-O3}.
6116 @item -finline-functions-called-once
6117 @opindex finline-functions-called-once
6118 Consider all @code{static} functions called once for inlining into their
6119 caller even if they are not marked @code{inline}. If a call to a given
6120 function is integrated, then the function is not output as assembler code
6123 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
6125 @item -fearly-inlining
6126 @opindex fearly-inlining
6127 Inline functions marked by @code{always_inline} and functions whose body seems
6128 smaller than the function call overhead early before doing
6129 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
6130 makes profiling significantly cheaper and usually inlining faster on programs
6131 having large chains of nested wrapper functions.
6137 Perform interprocedural scalar replacement of aggregates, removal of
6138 unused parameters and replacement of parameters passed by reference
6139 by parameters passed by value.
6141 Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
6143 @item -finline-limit=@var{n}
6144 @opindex finline-limit
6145 By default, GCC limits the size of functions that can be inlined. This flag
6146 allows coarse control of this limit. @var{n} is the size of functions that
6147 can be inlined in number of pseudo instructions.
6149 Inlining is actually controlled by a number of parameters, which may be
6150 specified individually by using @option{--param @var{name}=@var{value}}.
6151 The @option{-finline-limit=@var{n}} option sets some of these parameters
6155 @item max-inline-insns-single
6156 is set to @var{n}/2.
6157 @item max-inline-insns-auto
6158 is set to @var{n}/2.
6161 See below for a documentation of the individual
6162 parameters controlling inlining and for the defaults of these parameters.
6164 @emph{Note:} there may be no value to @option{-finline-limit} that results
6165 in default behavior.
6167 @emph{Note:} pseudo instruction represents, in this particular context, an
6168 abstract measurement of function's size. In no way does it represent a count
6169 of assembly instructions and as such its exact meaning might change from one
6170 release to an another.
6172 @item -fno-keep-inline-dllexport
6173 @opindex -fno-keep-inline-dllexport
6174 This is a more fine-grained version of @option{-fkeep-inline-functions},
6175 which applies only to functions that are declared using the @code{dllexport}
6176 attribute or declspec (@xref{Function Attributes,,Declaring Attributes of
6179 @item -fkeep-inline-functions
6180 @opindex fkeep-inline-functions
6181 In C, emit @code{static} functions that are declared @code{inline}
6182 into the object file, even if the function has been inlined into all
6183 of its callers. This switch does not affect functions using the
6184 @code{extern inline} extension in GNU C90@. In C++, emit any and all
6185 inline functions into the object file.
6187 @item -fkeep-static-consts
6188 @opindex fkeep-static-consts
6189 Emit variables declared @code{static const} when optimization isn't turned
6190 on, even if the variables aren't referenced.
6192 GCC enables this option by default. If you want to force the compiler to
6193 check if the variable was referenced, regardless of whether or not
6194 optimization is turned on, use the @option{-fno-keep-static-consts} option.
6196 @item -fmerge-constants
6197 @opindex fmerge-constants
6198 Attempt to merge identical constants (string constants and floating point
6199 constants) across compilation units.
6201 This option is the default for optimized compilation if the assembler and
6202 linker support it. Use @option{-fno-merge-constants} to inhibit this
6205 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6207 @item -fmerge-all-constants
6208 @opindex fmerge-all-constants
6209 Attempt to merge identical constants and identical variables.
6211 This option implies @option{-fmerge-constants}. In addition to
6212 @option{-fmerge-constants} this considers e.g.@: even constant initialized
6213 arrays or initialized constant variables with integral or floating point
6214 types. Languages like C or C++ require each variable, including multiple
6215 instances of the same variable in recursive calls, to have distinct locations,
6216 so using this option will result in non-conforming
6219 @item -fmodulo-sched
6220 @opindex fmodulo-sched
6221 Perform swing modulo scheduling immediately before the first scheduling
6222 pass. This pass looks at innermost loops and reorders their
6223 instructions by overlapping different iterations.
6225 @item -fmodulo-sched-allow-regmoves
6226 @opindex fmodulo-sched-allow-regmoves
6227 Perform more aggressive SMS based modulo scheduling with register moves
6228 allowed. By setting this flag certain anti-dependences edges will be
6229 deleted which will trigger the generation of reg-moves based on the
6230 life-range analysis. This option is effective only with
6231 @option{-fmodulo-sched} enabled.
6233 @item -fno-branch-count-reg
6234 @opindex fno-branch-count-reg
6235 Do not use ``decrement and branch'' instructions on a count register,
6236 but instead generate a sequence of instructions that decrement a
6237 register, compare it against zero, then branch based upon the result.
6238 This option is only meaningful on architectures that support such
6239 instructions, which include x86, PowerPC, IA-64 and S/390.
6241 The default is @option{-fbranch-count-reg}.
6243 @item -fno-function-cse
6244 @opindex fno-function-cse
6245 Do not put function addresses in registers; make each instruction that
6246 calls a constant function contain the function's address explicitly.
6248 This option results in less efficient code, but some strange hacks
6249 that alter the assembler output may be confused by the optimizations
6250 performed when this option is not used.
6252 The default is @option{-ffunction-cse}
6254 @item -fno-zero-initialized-in-bss
6255 @opindex fno-zero-initialized-in-bss
6256 If the target supports a BSS section, GCC by default puts variables that
6257 are initialized to zero into BSS@. This can save space in the resulting
6260 This option turns off this behavior because some programs explicitly
6261 rely on variables going to the data section. E.g., so that the
6262 resulting executable can find the beginning of that section and/or make
6263 assumptions based on that.
6265 The default is @option{-fzero-initialized-in-bss}.
6267 @item -fmudflap -fmudflapth -fmudflapir
6271 @cindex bounds checking
6273 For front-ends that support it (C and C++), instrument all risky
6274 pointer/array dereferencing operations, some standard library
6275 string/heap functions, and some other associated constructs with
6276 range/validity tests. Modules so instrumented should be immune to
6277 buffer overflows, invalid heap use, and some other classes of C/C++
6278 programming errors. The instrumentation relies on a separate runtime
6279 library (@file{libmudflap}), which will be linked into a program if
6280 @option{-fmudflap} is given at link time. Run-time behavior of the
6281 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
6282 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
6285 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
6286 link if your program is multi-threaded. Use @option{-fmudflapir}, in
6287 addition to @option{-fmudflap} or @option{-fmudflapth}, if
6288 instrumentation should ignore pointer reads. This produces less
6289 instrumentation (and therefore faster execution) and still provides
6290 some protection against outright memory corrupting writes, but allows
6291 erroneously read data to propagate within a program.
6293 @item -fthread-jumps
6294 @opindex fthread-jumps
6295 Perform optimizations where we check to see if a jump branches to a
6296 location where another comparison subsumed by the first is found. If
6297 so, the first branch is redirected to either the destination of the
6298 second branch or a point immediately following it, depending on whether
6299 the condition is known to be true or false.
6301 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6303 @item -fsplit-wide-types
6304 @opindex fsplit-wide-types
6305 When using a type that occupies multiple registers, such as @code{long
6306 long} on a 32-bit system, split the registers apart and allocate them
6307 independently. This normally generates better code for those types,
6308 but may make debugging more difficult.
6310 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
6313 @item -fcse-follow-jumps
6314 @opindex fcse-follow-jumps
6315 In common subexpression elimination (CSE), scan through jump instructions
6316 when the target of the jump is not reached by any other path. For
6317 example, when CSE encounters an @code{if} statement with an
6318 @code{else} clause, CSE will follow the jump when the condition
6321 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6323 @item -fcse-skip-blocks
6324 @opindex fcse-skip-blocks
6325 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
6326 follow jumps which conditionally skip over blocks. When CSE
6327 encounters a simple @code{if} statement with no else clause,
6328 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
6329 body of the @code{if}.
6331 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6333 @item -frerun-cse-after-loop
6334 @opindex frerun-cse-after-loop
6335 Re-run common subexpression elimination after loop optimizations has been
6338 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6342 Perform a global common subexpression elimination pass.
6343 This pass also performs global constant and copy propagation.
6345 @emph{Note:} When compiling a program using computed gotos, a GCC
6346 extension, you may get better runtime performance if you disable
6347 the global common subexpression elimination pass by adding
6348 @option{-fno-gcse} to the command line.
6350 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6354 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
6355 attempt to move loads which are only killed by stores into themselves. This
6356 allows a loop containing a load/store sequence to be changed to a load outside
6357 the loop, and a copy/store within the loop.
6359 Enabled by default when gcse is enabled.
6363 When @option{-fgcse-sm} is enabled, a store motion pass is run after
6364 global common subexpression elimination. This pass will attempt to move
6365 stores out of loops. When used in conjunction with @option{-fgcse-lm},
6366 loops containing a load/store sequence can be changed to a load before
6367 the loop and a store after the loop.
6369 Not enabled at any optimization level.
6373 When @option{-fgcse-las} is enabled, the global common subexpression
6374 elimination pass eliminates redundant loads that come after stores to the
6375 same memory location (both partial and full redundancies).
6377 Not enabled at any optimization level.
6379 @item -fgcse-after-reload
6380 @opindex fgcse-after-reload
6381 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
6382 pass is performed after reload. The purpose of this pass is to cleanup
6385 @item -funsafe-loop-optimizations
6386 @opindex funsafe-loop-optimizations
6387 If given, the loop optimizer will assume that loop indices do not
6388 overflow, and that the loops with nontrivial exit condition are not
6389 infinite. This enables a wider range of loop optimizations even if
6390 the loop optimizer itself cannot prove that these assumptions are valid.
6391 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
6392 if it finds this kind of loop.
6394 @item -fcrossjumping
6395 @opindex fcrossjumping
6396 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
6397 resulting code may or may not perform better than without cross-jumping.
6399 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6401 @item -fauto-inc-dec
6402 @opindex fauto-inc-dec
6403 Combine increments or decrements of addresses with memory accesses.
6404 This pass is always skipped on architectures that do not have
6405 instructions to support this. Enabled by default at @option{-O} and
6406 higher on architectures that support this.
6410 Perform dead code elimination (DCE) on RTL@.
6411 Enabled by default at @option{-O} and higher.
6415 Perform dead store elimination (DSE) on RTL@.
6416 Enabled by default at @option{-O} and higher.
6418 @item -fif-conversion
6419 @opindex fif-conversion
6420 Attempt to transform conditional jumps into branch-less equivalents. This
6421 include use of conditional moves, min, max, set flags and abs instructions, and
6422 some tricks doable by standard arithmetics. The use of conditional execution
6423 on chips where it is available is controlled by @code{if-conversion2}.
6425 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6427 @item -fif-conversion2
6428 @opindex fif-conversion2
6429 Use conditional execution (where available) to transform conditional jumps into
6430 branch-less equivalents.
6432 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6434 @item -fdelete-null-pointer-checks
6435 @opindex fdelete-null-pointer-checks
6436 Assume that programs cannot safely dereference null pointers, and that
6437 no code or data element resides there. This enables simple constant
6438 folding optimizations at all optimization levels. In addition, other
6439 optimization passes in GCC use this flag to control global dataflow
6440 analyses that eliminate useless checks for null pointers; these assume
6441 that if a pointer is checked after it has already been dereferenced,
6444 Note however that in some environments this assumption is not true.
6445 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
6446 for programs which depend on that behavior.
6448 Some targets, especially embedded ones, disable this option at all levels.
6449 Otherwise it is enabled at all levels: @option{-O0}, @option{-O1},
6450 @option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information
6451 are enabled independently at different optimization levels.
6453 @item -fdevirtualize
6454 @opindex fdevirtualize
6455 Attempt to convert calls to virtual functions to direct calls. This
6456 is done both within a procedure and interprocedurally as part of
6457 indirect inlining (@code{-findirect-inlining}) and interprocedural constant
6458 propagation (@option{-fipa-cp}).
6459 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6461 @item -fexpensive-optimizations
6462 @opindex fexpensive-optimizations
6463 Perform a number of minor optimizations that are relatively expensive.
6465 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6467 @item -foptimize-register-move
6469 @opindex foptimize-register-move
6471 Attempt to reassign register numbers in move instructions and as
6472 operands of other simple instructions in order to maximize the amount of
6473 register tying. This is especially helpful on machines with two-operand
6476 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
6479 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6481 @item -fira-algorithm=@var{algorithm}
6482 Use specified coloring algorithm for the integrated register
6483 allocator. The @var{algorithm} argument should be @code{priority} or
6484 @code{CB}. The first algorithm specifies Chow's priority coloring,
6485 the second one specifies Chaitin-Briggs coloring. The second
6486 algorithm can be unimplemented for some architectures. If it is
6487 implemented, it is the default because Chaitin-Briggs coloring as a
6488 rule generates a better code.
6490 @item -fira-region=@var{region}
6491 Use specified regions for the integrated register allocator. The
6492 @var{region} argument should be one of @code{all}, @code{mixed}, or
6493 @code{one}. The first value means using all loops as register
6494 allocation regions, the second value which is the default means using
6495 all loops except for loops with small register pressure as the
6496 regions, and third one means using all function as a single region.
6497 The first value can give best result for machines with small size and
6498 irregular register set, the third one results in faster and generates
6499 decent code and the smallest size code, and the default value usually
6500 give the best results in most cases and for most architectures.
6502 @item -fira-loop-pressure
6503 @opindex fira-loop-pressure
6504 Use IRA to evaluate register pressure in loops for decision to move
6505 loop invariants. Usage of this option usually results in generation
6506 of faster and smaller code on machines with big register files (>= 32
6507 registers) but it can slow compiler down.
6509 This option is enabled at level @option{-O3} for some targets.
6511 @item -fno-ira-share-save-slots
6512 @opindex fno-ira-share-save-slots
6513 Switch off sharing stack slots used for saving call used hard
6514 registers living through a call. Each hard register will get a
6515 separate stack slot and as a result function stack frame will be
6518 @item -fno-ira-share-spill-slots
6519 @opindex fno-ira-share-spill-slots
6520 Switch off sharing stack slots allocated for pseudo-registers. Each
6521 pseudo-register which did not get a hard register will get a separate
6522 stack slot and as a result function stack frame will be bigger.
6524 @item -fira-verbose=@var{n}
6525 @opindex fira-verbose
6526 Set up how verbose dump file for the integrated register allocator
6527 will be. Default value is 5. If the value is greater or equal to 10,
6528 the dump file will be stderr as if the value were @var{n} minus 10.
6530 @item -fdelayed-branch
6531 @opindex fdelayed-branch
6532 If supported for the target machine, attempt to reorder instructions
6533 to exploit instruction slots available after delayed branch
6536 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6538 @item -fschedule-insns
6539 @opindex fschedule-insns
6540 If supported for the target machine, attempt to reorder instructions to
6541 eliminate execution stalls due to required data being unavailable. This
6542 helps machines that have slow floating point or memory load instructions
6543 by allowing other instructions to be issued until the result of the load
6544 or floating point instruction is required.
6546 Enabled at levels @option{-O2}, @option{-O3}.
6548 @item -fschedule-insns2
6549 @opindex fschedule-insns2
6550 Similar to @option{-fschedule-insns}, but requests an additional pass of
6551 instruction scheduling after register allocation has been done. This is
6552 especially useful on machines with a relatively small number of
6553 registers and where memory load instructions take more than one cycle.
6555 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6557 @item -fno-sched-interblock
6558 @opindex fno-sched-interblock
6559 Don't schedule instructions across basic blocks. This is normally
6560 enabled by default when scheduling before register allocation, i.e.@:
6561 with @option{-fschedule-insns} or at @option{-O2} or higher.
6563 @item -fno-sched-spec
6564 @opindex fno-sched-spec
6565 Don't allow speculative motion of non-load instructions. This is normally
6566 enabled by default when scheduling before register allocation, i.e.@:
6567 with @option{-fschedule-insns} or at @option{-O2} or higher.
6569 @item -fsched-pressure
6570 @opindex fsched-pressure
6571 Enable register pressure sensitive insn scheduling before the register
6572 allocation. This only makes sense when scheduling before register
6573 allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
6574 @option{-O2} or higher. Usage of this option can improve the
6575 generated code and decrease its size by preventing register pressure
6576 increase above the number of available hard registers and as a
6577 consequence register spills in the register allocation.
6579 @item -fsched-spec-load
6580 @opindex fsched-spec-load
6581 Allow speculative motion of some load instructions. This only makes
6582 sense when scheduling before register allocation, i.e.@: with
6583 @option{-fschedule-insns} or at @option{-O2} or higher.
6585 @item -fsched-spec-load-dangerous
6586 @opindex fsched-spec-load-dangerous
6587 Allow speculative motion of more load instructions. This only makes
6588 sense when scheduling before register allocation, i.e.@: with
6589 @option{-fschedule-insns} or at @option{-O2} or higher.
6591 @item -fsched-stalled-insns
6592 @itemx -fsched-stalled-insns=@var{n}
6593 @opindex fsched-stalled-insns
6594 Define how many insns (if any) can be moved prematurely from the queue
6595 of stalled insns into the ready list, during the second scheduling pass.
6596 @option{-fno-sched-stalled-insns} means that no insns will be moved
6597 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
6598 on how many queued insns can be moved prematurely.
6599 @option{-fsched-stalled-insns} without a value is equivalent to
6600 @option{-fsched-stalled-insns=1}.
6602 @item -fsched-stalled-insns-dep
6603 @itemx -fsched-stalled-insns-dep=@var{n}
6604 @opindex fsched-stalled-insns-dep
6605 Define how many insn groups (cycles) will be examined for a dependency
6606 on a stalled insn that is candidate for premature removal from the queue
6607 of stalled insns. This has an effect only during the second scheduling pass,
6608 and only if @option{-fsched-stalled-insns} is used.
6609 @option{-fno-sched-stalled-insns-dep} is equivalent to
6610 @option{-fsched-stalled-insns-dep=0}.
6611 @option{-fsched-stalled-insns-dep} without a value is equivalent to
6612 @option{-fsched-stalled-insns-dep=1}.
6614 @item -fsched2-use-superblocks
6615 @opindex fsched2-use-superblocks
6616 When scheduling after register allocation, do use superblock scheduling
6617 algorithm. Superblock scheduling allows motion across basic block boundaries
6618 resulting on faster schedules. This option is experimental, as not all machine
6619 descriptions used by GCC model the CPU closely enough to avoid unreliable
6620 results from the algorithm.
6622 This only makes sense when scheduling after register allocation, i.e.@: with
6623 @option{-fschedule-insns2} or at @option{-O2} or higher.
6625 @item -fsched-group-heuristic
6626 @opindex fsched-group-heuristic
6627 Enable the group heuristic in the scheduler. This heuristic favors
6628 the instruction that belongs to a schedule group. This is enabled
6629 by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6630 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6632 @item -fsched-critical-path-heuristic
6633 @opindex fsched-critical-path-heuristic
6634 Enable the critical-path heuristic in the scheduler. This heuristic favors
6635 instructions on the critical path. This is enabled by default when
6636 scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6637 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6639 @item -fsched-spec-insn-heuristic
6640 @opindex fsched-spec-insn-heuristic
6641 Enable the speculative instruction heuristic in the scheduler. This
6642 heuristic favors speculative instructions with greater dependency weakness.
6643 This is enabled by default when scheduling is enabled, i.e.@:
6644 with @option{-fschedule-insns} or @option{-fschedule-insns2}
6645 or at @option{-O2} or higher.
6647 @item -fsched-rank-heuristic
6648 @opindex fsched-rank-heuristic
6649 Enable the rank heuristic in the scheduler. This heuristic favors
6650 the instruction belonging to a basic block with greater size or frequency.
6651 This is enabled by default when scheduling is enabled, i.e.@:
6652 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6653 at @option{-O2} or higher.
6655 @item -fsched-last-insn-heuristic
6656 @opindex fsched-last-insn-heuristic
6657 Enable the last-instruction heuristic in the scheduler. This heuristic
6658 favors the instruction that is less dependent on the last instruction
6659 scheduled. This is enabled by default when scheduling is enabled,
6660 i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6661 at @option{-O2} or higher.
6663 @item -fsched-dep-count-heuristic
6664 @opindex fsched-dep-count-heuristic
6665 Enable the dependent-count heuristic in the scheduler. This heuristic
6666 favors the instruction that has more instructions depending on it.
6667 This is enabled by default when scheduling is enabled, i.e.@:
6668 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6669 at @option{-O2} or higher.
6671 @item -freschedule-modulo-scheduled-loops
6672 @opindex freschedule-modulo-scheduled-loops
6673 The modulo scheduling comes before the traditional scheduling, if a loop
6674 was modulo scheduled we may want to prevent the later scheduling passes
6675 from changing its schedule, we use this option to control that.
6677 @item -fselective-scheduling
6678 @opindex fselective-scheduling
6679 Schedule instructions using selective scheduling algorithm. Selective
6680 scheduling runs instead of the first scheduler pass.
6682 @item -fselective-scheduling2
6683 @opindex fselective-scheduling2
6684 Schedule instructions using selective scheduling algorithm. Selective
6685 scheduling runs instead of the second scheduler pass.
6687 @item -fsel-sched-pipelining
6688 @opindex fsel-sched-pipelining
6689 Enable software pipelining of innermost loops during selective scheduling.
6690 This option has no effect until one of @option{-fselective-scheduling} or
6691 @option{-fselective-scheduling2} is turned on.
6693 @item -fsel-sched-pipelining-outer-loops
6694 @opindex fsel-sched-pipelining-outer-loops
6695 When pipelining loops during selective scheduling, also pipeline outer loops.
6696 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
6698 @item -fcaller-saves
6699 @opindex fcaller-saves
6700 Enable values to be allocated in registers that will be clobbered by
6701 function calls, by emitting extra instructions to save and restore the
6702 registers around such calls. Such allocation is done only when it
6703 seems to result in better code than would otherwise be produced.
6705 This option is always enabled by default on certain machines, usually
6706 those which have no call-preserved registers to use instead.
6708 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6710 @item -fcombine-stack-adjustments
6711 @opindex fcombine-stack-adjustments
6712 Tracks stack adjustments (pushes and pops) and stack memory references
6713 and then tries to find ways to combine them.
6715 Enabled by default at @option{-O1} and higher.
6717 @item -fconserve-stack
6718 @opindex fconserve-stack
6719 Attempt to minimize stack usage. The compiler will attempt to use less
6720 stack space, even if that makes the program slower. This option
6721 implies setting the @option{large-stack-frame} parameter to 100
6722 and the @option{large-stack-frame-growth} parameter to 400.
6724 @item -ftree-reassoc
6725 @opindex ftree-reassoc
6726 Perform reassociation on trees. This flag is enabled by default
6727 at @option{-O} and higher.
6731 Perform partial redundancy elimination (PRE) on trees. This flag is
6732 enabled by default at @option{-O2} and @option{-O3}.
6734 @item -ftree-forwprop
6735 @opindex ftree-forwprop
6736 Perform forward propagation on trees. This flag is enabled by default
6737 at @option{-O} and higher.
6741 Perform full redundancy elimination (FRE) on trees. The difference
6742 between FRE and PRE is that FRE only considers expressions
6743 that are computed on all paths leading to the redundant computation.
6744 This analysis is faster than PRE, though it exposes fewer redundancies.
6745 This flag is enabled by default at @option{-O} and higher.
6747 @item -ftree-phiprop
6748 @opindex ftree-phiprop
6749 Perform hoisting of loads from conditional pointers on trees. This
6750 pass is enabled by default at @option{-O} and higher.
6752 @item -ftree-copy-prop
6753 @opindex ftree-copy-prop
6754 Perform copy propagation on trees. This pass eliminates unnecessary
6755 copy operations. This flag is enabled by default at @option{-O} and
6758 @item -fipa-pure-const
6759 @opindex fipa-pure-const
6760 Discover which functions are pure or constant.
6761 Enabled by default at @option{-O} and higher.
6763 @item -fipa-reference
6764 @opindex fipa-reference
6765 Discover which static variables do not escape cannot escape the
6767 Enabled by default at @option{-O} and higher.
6771 Perform interprocedural pointer analysis and interprocedural modification
6772 and reference analysis. This option can cause excessive memory and
6773 compile-time usage on large compilation units. It is not enabled by
6774 default at any optimization level.
6777 @opindex fipa-profile
6778 Perform interprocedural profile propagation. The functions called only from
6779 cold functions are marked as cold. Also functions executed once (such as
6780 @code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
6781 functions and loop less parts of functions executed once are then optimized for
6783 Enabled by default at @option{-O} and higher.
6787 Perform interprocedural constant propagation.
6788 This optimization analyzes the program to determine when values passed
6789 to functions are constants and then optimizes accordingly.
6790 This optimization can substantially increase performance
6791 if the application has constants passed to functions.
6792 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
6794 @item -fipa-cp-clone
6795 @opindex fipa-cp-clone
6796 Perform function cloning to make interprocedural constant propagation stronger.
6797 When enabled, interprocedural constant propagation will perform function cloning
6798 when externally visible function can be called with constant arguments.
6799 Because this optimization can create multiple copies of functions,
6800 it may significantly increase code size
6801 (see @option{--param ipcp-unit-growth=@var{value}}).
6802 This flag is enabled by default at @option{-O3}.
6804 @item -fipa-matrix-reorg
6805 @opindex fipa-matrix-reorg
6806 Perform matrix flattening and transposing.
6807 Matrix flattening tries to replace an @math{m}-dimensional matrix
6808 with its equivalent @math{n}-dimensional matrix, where @math{n < m}.
6809 This reduces the level of indirection needed for accessing the elements
6810 of the matrix. The second optimization is matrix transposing that
6811 attempts to change the order of the matrix's dimensions in order to
6812 improve cache locality.
6813 Both optimizations need the @option{-fwhole-program} flag.
6814 Transposing is enabled only if profiling information is available.
6818 Perform forward store motion on trees. This flag is
6819 enabled by default at @option{-O} and higher.
6821 @item -ftree-bit-ccp
6822 @opindex ftree-bit-ccp
6823 Perform sparse conditional bit constant propagation on trees and propagate
6824 pointer alignment information.
6825 This pass only operates on local scalar variables and is enabled by default
6826 at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
6830 Perform sparse conditional constant propagation (CCP) on trees. This
6831 pass only operates on local scalar variables and is enabled by default
6832 at @option{-O} and higher.
6834 @item -ftree-switch-conversion
6835 Perform conversion of simple initializations in a switch to
6836 initializations from a scalar array. This flag is enabled by default
6837 at @option{-O2} and higher.
6841 Perform dead code elimination (DCE) on trees. This flag is enabled by
6842 default at @option{-O} and higher.
6844 @item -ftree-builtin-call-dce
6845 @opindex ftree-builtin-call-dce
6846 Perform conditional dead code elimination (DCE) for calls to builtin functions
6847 that may set @code{errno} but are otherwise side-effect free. This flag is
6848 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6851 @item -ftree-dominator-opts
6852 @opindex ftree-dominator-opts
6853 Perform a variety of simple scalar cleanups (constant/copy
6854 propagation, redundancy elimination, range propagation and expression
6855 simplification) based on a dominator tree traversal. This also
6856 performs jump threading (to reduce jumps to jumps). This flag is
6857 enabled by default at @option{-O} and higher.
6861 Perform dead store elimination (DSE) on trees. A dead store is a store into
6862 a memory location which will later be overwritten by another store without
6863 any intervening loads. In this case the earlier store can be deleted. This
6864 flag is enabled by default at @option{-O} and higher.
6868 Perform loop header copying on trees. This is beneficial since it increases
6869 effectiveness of code motion optimizations. It also saves one jump. This flag
6870 is enabled by default at @option{-O} and higher. It is not enabled
6871 for @option{-Os}, since it usually increases code size.
6873 @item -ftree-loop-optimize
6874 @opindex ftree-loop-optimize
6875 Perform loop optimizations on trees. This flag is enabled by default
6876 at @option{-O} and higher.
6878 @item -ftree-loop-linear
6879 @opindex ftree-loop-linear
6880 Perform loop interchange transformations on tree. Same as
6881 @option{-floop-interchange}. To use this code transformation, GCC has
6882 to be configured with @option{--with-ppl} and @option{--with-cloog} to
6883 enable the Graphite loop transformation infrastructure.
6885 @item -floop-interchange
6886 @opindex floop-interchange
6887 Perform loop interchange transformations on loops. Interchanging two
6888 nested loops switches the inner and outer loops. For example, given a
6893 A(J, I) = A(J, I) * C
6897 loop interchange will transform the loop as if the user had written:
6901 A(J, I) = A(J, I) * C
6905 which can be beneficial when @code{N} is larger than the caches,
6906 because in Fortran, the elements of an array are stored in memory
6907 contiguously by column, and the original loop iterates over rows,
6908 potentially creating at each access a cache miss. This optimization
6909 applies to all the languages supported by GCC and is not limited to
6910 Fortran. To use this code transformation, GCC has to be configured
6911 with @option{--with-ppl} and @option{--with-cloog} to enable the
6912 Graphite loop transformation infrastructure.
6914 @item -floop-strip-mine
6915 @opindex floop-strip-mine
6916 Perform loop strip mining transformations on loops. Strip mining
6917 splits a loop into two nested loops. The outer loop has strides
6918 equal to the strip size and the inner loop has strides of the
6919 original loop within a strip. The strip length can be changed
6920 using the @option{loop-block-tile-size} parameter. For example,
6927 loop strip mining will transform the loop as if the user had written:
6930 DO I = II, min (II + 50, N)
6935 This optimization applies to all the languages supported by GCC and is
6936 not limited to Fortran. To use this code transformation, GCC has to
6937 be configured with @option{--with-ppl} and @option{--with-cloog} to
6938 enable the Graphite loop transformation infrastructure.
6941 @opindex floop-block
6942 Perform loop blocking transformations on loops. Blocking strip mines
6943 each loop in the loop nest such that the memory accesses of the
6944 element loops fit inside caches. The strip length can be changed
6945 using the @option{loop-block-tile-size} parameter. For example, given
6950 A(J, I) = B(I) + C(J)
6954 loop blocking will transform the loop as if the user had written:
6958 DO I = II, min (II + 50, N)
6959 DO J = JJ, min (JJ + 50, M)
6960 A(J, I) = B(I) + C(J)
6966 which can be beneficial when @code{M} is larger than the caches,
6967 because the innermost loop will iterate over a smaller amount of data
6968 that can be kept in the caches. This optimization applies to all the
6969 languages supported by GCC and is not limited to Fortran. To use this
6970 code transformation, GCC has to be configured with @option{--with-ppl}
6971 and @option{--with-cloog} to enable the Graphite loop transformation
6974 @item -fgraphite-identity
6975 @opindex fgraphite-identity
6976 Enable the identity transformation for graphite. For every SCoP we generate
6977 the polyhedral representation and transform it back to gimple. Using
6978 @option{-fgraphite-identity} we can check the costs or benefits of the
6979 GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
6980 are also performed by the code generator CLooG, like index splitting and
6981 dead code elimination in loops.
6983 @item -floop-flatten
6984 @opindex floop-flatten
6985 Removes the loop nesting structure: transforms the loop nest into a
6986 single loop. This transformation can be useful to vectorize all the
6987 levels of the loop nest.
6989 @item -floop-parallelize-all
6990 @opindex floop-parallelize-all
6991 Use the Graphite data dependence analysis to identify loops that can
6992 be parallelized. Parallelize all the loops that can be analyzed to
6993 not contain loop carried dependences without checking that it is
6994 profitable to parallelize the loops.
6996 @item -fcheck-data-deps
6997 @opindex fcheck-data-deps
6998 Compare the results of several data dependence analyzers. This option
6999 is used for debugging the data dependence analyzers.
7001 @item -ftree-loop-if-convert
7002 Attempt to transform conditional jumps in the innermost loops to
7003 branch-less equivalents. The intent is to remove control-flow from
7004 the innermost loops in order to improve the ability of the
7005 vectorization pass to handle these loops. This is enabled by default
7006 if vectorization is enabled.
7008 @item -ftree-loop-if-convert-stores
7009 Attempt to also if-convert conditional jumps containing memory writes.
7010 This transformation can be unsafe for multi-threaded programs as it
7011 transforms conditional memory writes into unconditional memory writes.
7014 for (i = 0; i < N; i++)
7018 would be transformed to
7020 for (i = 0; i < N; i++)
7021 A[i] = cond ? expr : A[i];
7023 potentially producing data races.
7025 @item -ftree-loop-distribution
7026 Perform loop distribution. This flag can improve cache performance on
7027 big loop bodies and allow further loop optimizations, like
7028 parallelization or vectorization, to take place. For example, the loop
7045 @item -ftree-loop-distribute-patterns
7046 Perform loop distribution of patterns that can be code generated with
7047 calls to a library. This flag is enabled by default at @option{-O3}.
7049 This pass distributes the initialization loops and generates a call to
7050 memset zero. For example, the loop
7066 and the initialization loop is transformed into a call to memset zero.
7068 @item -ftree-loop-im
7069 @opindex ftree-loop-im
7070 Perform loop invariant motion on trees. This pass moves only invariants that
7071 would be hard to handle at RTL level (function calls, operations that expand to
7072 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
7073 operands of conditions that are invariant out of the loop, so that we can use
7074 just trivial invariantness analysis in loop unswitching. The pass also includes
7077 @item -ftree-loop-ivcanon
7078 @opindex ftree-loop-ivcanon
7079 Create a canonical counter for number of iterations in the loop for that
7080 determining number of iterations requires complicated analysis. Later
7081 optimizations then may determine the number easily. Useful especially
7082 in connection with unrolling.
7086 Perform induction variable optimizations (strength reduction, induction
7087 variable merging and induction variable elimination) on trees.
7089 @item -ftree-parallelize-loops=n
7090 @opindex ftree-parallelize-loops
7091 Parallelize loops, i.e., split their iteration space to run in n threads.
7092 This is only possible for loops whose iterations are independent
7093 and can be arbitrarily reordered. The optimization is only
7094 profitable on multiprocessor machines, for loops that are CPU-intensive,
7095 rather than constrained e.g.@: by memory bandwidth. This option
7096 implies @option{-pthread}, and thus is only supported on targets
7097 that have support for @option{-pthread}.
7101 Perform function-local points-to analysis on trees. This flag is
7102 enabled by default at @option{-O} and higher.
7106 Perform scalar replacement of aggregates. This pass replaces structure
7107 references with scalars to prevent committing structures to memory too
7108 early. This flag is enabled by default at @option{-O} and higher.
7110 @item -ftree-copyrename
7111 @opindex ftree-copyrename
7112 Perform copy renaming on trees. This pass attempts to rename compiler
7113 temporaries to other variables at copy locations, usually resulting in
7114 variable names which more closely resemble the original variables. This flag
7115 is enabled by default at @option{-O} and higher.
7119 Perform temporary expression replacement during the SSA->normal phase. Single
7120 use/single def temporaries are replaced at their use location with their
7121 defining expression. This results in non-GIMPLE code, but gives the expanders
7122 much more complex trees to work on resulting in better RTL generation. This is
7123 enabled by default at @option{-O} and higher.
7125 @item -ftree-vectorize
7126 @opindex ftree-vectorize
7127 Perform loop vectorization on trees. This flag is enabled by default at
7130 @item -ftree-slp-vectorize
7131 @opindex ftree-slp-vectorize
7132 Perform basic block vectorization on trees. This flag is enabled by default at
7133 @option{-O3} and when @option{-ftree-vectorize} is enabled.
7135 @item -ftree-vect-loop-version
7136 @opindex ftree-vect-loop-version
7137 Perform loop versioning when doing loop vectorization on trees. When a loop
7138 appears to be vectorizable except that data alignment or data dependence cannot
7139 be determined at compile time then vectorized and non-vectorized versions of
7140 the loop are generated along with runtime checks for alignment or dependence
7141 to control which version is executed. This option is enabled by default
7142 except at level @option{-Os} where it is disabled.
7144 @item -fvect-cost-model
7145 @opindex fvect-cost-model
7146 Enable cost model for vectorization.
7150 Perform Value Range Propagation on trees. This is similar to the
7151 constant propagation pass, but instead of values, ranges of values are
7152 propagated. This allows the optimizers to remove unnecessary range
7153 checks like array bound checks and null pointer checks. This is
7154 enabled by default at @option{-O2} and higher. Null pointer check
7155 elimination is only done if @option{-fdelete-null-pointer-checks} is
7160 Perform tail duplication to enlarge superblock size. This transformation
7161 simplifies the control flow of the function allowing other optimizations to do
7164 @item -funroll-loops
7165 @opindex funroll-loops
7166 Unroll loops whose number of iterations can be determined at compile
7167 time or upon entry to the loop. @option{-funroll-loops} implies
7168 @option{-frerun-cse-after-loop}. This option makes code larger,
7169 and may or may not make it run faster.
7171 @item -funroll-all-loops
7172 @opindex funroll-all-loops
7173 Unroll all loops, even if their number of iterations is uncertain when
7174 the loop is entered. This usually makes programs run more slowly.
7175 @option{-funroll-all-loops} implies the same options as
7176 @option{-funroll-loops},
7178 @item -fsplit-ivs-in-unroller
7179 @opindex fsplit-ivs-in-unroller
7180 Enables expressing of values of induction variables in later iterations
7181 of the unrolled loop using the value in the first iteration. This breaks
7182 long dependency chains, thus improving efficiency of the scheduling passes.
7184 Combination of @option{-fweb} and CSE is often sufficient to obtain the
7185 same effect. However in cases the loop body is more complicated than
7186 a single basic block, this is not reliable. It also does not work at all
7187 on some of the architectures due to restrictions in the CSE pass.
7189 This optimization is enabled by default.
7191 @item -fvariable-expansion-in-unroller
7192 @opindex fvariable-expansion-in-unroller
7193 With this option, the compiler will create multiple copies of some
7194 local variables when unrolling a loop which can result in superior code.
7196 @item -fpartial-inlining
7197 @opindex fpartial-inlining
7198 Inline parts of functions. This option has any effect only
7199 when inlining itself is turned on by the @option{-finline-functions}
7200 or @option{-finline-small-functions} options.
7202 Enabled at level @option{-O2}.
7204 @item -fpredictive-commoning
7205 @opindex fpredictive-commoning
7206 Perform predictive commoning optimization, i.e., reusing computations
7207 (especially memory loads and stores) performed in previous
7208 iterations of loops.
7210 This option is enabled at level @option{-O3}.
7212 @item -fprefetch-loop-arrays
7213 @opindex fprefetch-loop-arrays
7214 If supported by the target machine, generate instructions to prefetch
7215 memory to improve the performance of loops that access large arrays.
7217 This option may generate better or worse code; results are highly
7218 dependent on the structure of loops within the source code.
7220 Disabled at level @option{-Os}.
7223 @itemx -fno-peephole2
7224 @opindex fno-peephole
7225 @opindex fno-peephole2
7226 Disable any machine-specific peephole optimizations. The difference
7227 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
7228 are implemented in the compiler; some targets use one, some use the
7229 other, a few use both.
7231 @option{-fpeephole} is enabled by default.
7232 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7234 @item -fno-guess-branch-probability
7235 @opindex fno-guess-branch-probability
7236 Do not guess branch probabilities using heuristics.
7238 GCC will use heuristics to guess branch probabilities if they are
7239 not provided by profiling feedback (@option{-fprofile-arcs}). These
7240 heuristics are based on the control flow graph. If some branch probabilities
7241 are specified by @samp{__builtin_expect}, then the heuristics will be
7242 used to guess branch probabilities for the rest of the control flow graph,
7243 taking the @samp{__builtin_expect} info into account. The interactions
7244 between the heuristics and @samp{__builtin_expect} can be complex, and in
7245 some cases, it may be useful to disable the heuristics so that the effects
7246 of @samp{__builtin_expect} are easier to understand.
7248 The default is @option{-fguess-branch-probability} at levels
7249 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7251 @item -freorder-blocks
7252 @opindex freorder-blocks
7253 Reorder basic blocks in the compiled function in order to reduce number of
7254 taken branches and improve code locality.
7256 Enabled at levels @option{-O2}, @option{-O3}.
7258 @item -freorder-blocks-and-partition
7259 @opindex freorder-blocks-and-partition
7260 In addition to reordering basic blocks in the compiled function, in order
7261 to reduce number of taken branches, partitions hot and cold basic blocks
7262 into separate sections of the assembly and .o files, to improve
7263 paging and cache locality performance.
7265 This optimization is automatically turned off in the presence of
7266 exception handling, for linkonce sections, for functions with a user-defined
7267 section attribute and on any architecture that does not support named
7270 @item -freorder-functions
7271 @opindex freorder-functions
7272 Reorder functions in the object file in order to
7273 improve code locality. This is implemented by using special
7274 subsections @code{.text.hot} for most frequently executed functions and
7275 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
7276 the linker so object file format must support named sections and linker must
7277 place them in a reasonable way.
7279 Also profile feedback must be available in to make this option effective. See
7280 @option{-fprofile-arcs} for details.
7282 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7284 @item -fstrict-aliasing
7285 @opindex fstrict-aliasing
7286 Allow the compiler to assume the strictest aliasing rules applicable to
7287 the language being compiled. For C (and C++), this activates
7288 optimizations based on the type of expressions. In particular, an
7289 object of one type is assumed never to reside at the same address as an
7290 object of a different type, unless the types are almost the same. For
7291 example, an @code{unsigned int} can alias an @code{int}, but not a
7292 @code{void*} or a @code{double}. A character type may alias any other
7295 @anchor{Type-punning}Pay special attention to code like this:
7308 The practice of reading from a different union member than the one most
7309 recently written to (called ``type-punning'') is common. Even with
7310 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
7311 is accessed through the union type. So, the code above will work as
7312 expected. @xref{Structures unions enumerations and bit-fields
7313 implementation}. However, this code might not:
7324 Similarly, access by taking the address, casting the resulting pointer
7325 and dereferencing the result has undefined behavior, even if the cast
7326 uses a union type, e.g.:
7330 return ((union a_union *) &d)->i;
7334 The @option{-fstrict-aliasing} option is enabled at levels
7335 @option{-O2}, @option{-O3}, @option{-Os}.
7337 @item -fstrict-overflow
7338 @opindex fstrict-overflow
7339 Allow the compiler to assume strict signed overflow rules, depending
7340 on the language being compiled. For C (and C++) this means that
7341 overflow when doing arithmetic with signed numbers is undefined, which
7342 means that the compiler may assume that it will not happen. This
7343 permits various optimizations. For example, the compiler will assume
7344 that an expression like @code{i + 10 > i} will always be true for
7345 signed @code{i}. This assumption is only valid if signed overflow is
7346 undefined, as the expression is false if @code{i + 10} overflows when
7347 using twos complement arithmetic. When this option is in effect any
7348 attempt to determine whether an operation on signed numbers will
7349 overflow must be written carefully to not actually involve overflow.
7351 This option also allows the compiler to assume strict pointer
7352 semantics: given a pointer to an object, if adding an offset to that
7353 pointer does not produce a pointer to the same object, the addition is
7354 undefined. This permits the compiler to conclude that @code{p + u >
7355 p} is always true for a pointer @code{p} and unsigned integer
7356 @code{u}. This assumption is only valid because pointer wraparound is
7357 undefined, as the expression is false if @code{p + u} overflows using
7358 twos complement arithmetic.
7360 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
7361 that integer signed overflow is fully defined: it wraps. When
7362 @option{-fwrapv} is used, there is no difference between
7363 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
7364 integers. With @option{-fwrapv} certain types of overflow are
7365 permitted. For example, if the compiler gets an overflow when doing
7366 arithmetic on constants, the overflowed value can still be used with
7367 @option{-fwrapv}, but not otherwise.
7369 The @option{-fstrict-overflow} option is enabled at levels
7370 @option{-O2}, @option{-O3}, @option{-Os}.
7372 @item -falign-functions
7373 @itemx -falign-functions=@var{n}
7374 @opindex falign-functions
7375 Align the start of functions to the next power-of-two greater than
7376 @var{n}, skipping up to @var{n} bytes. For instance,
7377 @option{-falign-functions=32} aligns functions to the next 32-byte
7378 boundary, but @option{-falign-functions=24} would align to the next
7379 32-byte boundary only if this can be done by skipping 23 bytes or less.
7381 @option{-fno-align-functions} and @option{-falign-functions=1} are
7382 equivalent and mean that functions will not be aligned.
7384 Some assemblers only support this flag when @var{n} is a power of two;
7385 in that case, it is rounded up.
7387 If @var{n} is not specified or is zero, use a machine-dependent default.
7389 Enabled at levels @option{-O2}, @option{-O3}.
7391 @item -falign-labels
7392 @itemx -falign-labels=@var{n}
7393 @opindex falign-labels
7394 Align all branch targets to a power-of-two boundary, skipping up to
7395 @var{n} bytes like @option{-falign-functions}. This option can easily
7396 make code slower, because it must insert dummy operations for when the
7397 branch target is reached in the usual flow of the code.
7399 @option{-fno-align-labels} and @option{-falign-labels=1} are
7400 equivalent and mean that labels will not be aligned.
7402 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
7403 are greater than this value, then their values are used instead.
7405 If @var{n} is not specified or is zero, use a machine-dependent default
7406 which is very likely to be @samp{1}, meaning no alignment.
7408 Enabled at levels @option{-O2}, @option{-O3}.
7411 @itemx -falign-loops=@var{n}
7412 @opindex falign-loops
7413 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
7414 like @option{-falign-functions}. The hope is that the loop will be
7415 executed many times, which will make up for any execution of the dummy
7418 @option{-fno-align-loops} and @option{-falign-loops=1} are
7419 equivalent and mean that loops will not be aligned.
7421 If @var{n} is not specified or is zero, use a machine-dependent default.
7423 Enabled at levels @option{-O2}, @option{-O3}.
7426 @itemx -falign-jumps=@var{n}
7427 @opindex falign-jumps
7428 Align branch targets to a power-of-two boundary, for branch targets
7429 where the targets can only be reached by jumping, skipping up to @var{n}
7430 bytes like @option{-falign-functions}. In this case, no dummy operations
7433 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
7434 equivalent and mean that loops will not be aligned.
7436 If @var{n} is not specified or is zero, use a machine-dependent default.
7438 Enabled at levels @option{-O2}, @option{-O3}.
7440 @item -funit-at-a-time
7441 @opindex funit-at-a-time
7442 This option is left for compatibility reasons. @option{-funit-at-a-time}
7443 has no effect, while @option{-fno-unit-at-a-time} implies
7444 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
7448 @item -fno-toplevel-reorder
7449 @opindex fno-toplevel-reorder
7450 Do not reorder top-level functions, variables, and @code{asm}
7451 statements. Output them in the same order that they appear in the
7452 input file. When this option is used, unreferenced static variables
7453 will not be removed. This option is intended to support existing code
7454 which relies on a particular ordering. For new code, it is better to
7457 Enabled at level @option{-O0}. When disabled explicitly, it also imply
7458 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
7463 Constructs webs as commonly used for register allocation purposes and assign
7464 each web individual pseudo register. This allows the register allocation pass
7465 to operate on pseudos directly, but also strengthens several other optimization
7466 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
7467 however, make debugging impossible, since variables will no longer stay in a
7470 Enabled by default with @option{-funroll-loops}.
7472 @item -fwhole-program
7473 @opindex fwhole-program
7474 Assume that the current compilation unit represents the whole program being
7475 compiled. All public functions and variables with the exception of @code{main}
7476 and those merged by attribute @code{externally_visible} become static functions
7477 and in effect are optimized more aggressively by interprocedural optimizers. If @command{gold} is used as the linker plugin, @code{externally_visible} attributes are automatically added to functions (not variable yet due to a current @command{gold} issue) that are accessed outside of LTO objects according to resolution file produced by @command{gold}. For other linkers that cannot generate resolution file, explicit @code{externally_visible} attributes are still necessary.
7478 While this option is equivalent to proper use of the @code{static} keyword for
7479 programs consisting of a single file, in combination with option
7480 @option{-flto} this flag can be used to
7481 compile many smaller scale programs since the functions and variables become
7482 local for the whole combined compilation unit, not for the single source file
7485 This option implies @option{-fwhole-file} for Fortran programs.
7487 @item -flto[=@var{n}]
7489 This option runs the standard link-time optimizer. When invoked
7490 with source code, it generates GIMPLE (one of GCC's internal
7491 representations) and writes it to special ELF sections in the object
7492 file. When the object files are linked together, all the function
7493 bodies are read from these ELF sections and instantiated as if they
7494 had been part of the same translation unit.
7496 To use the link-timer optimizer, @option{-flto} needs to be specified at
7497 compile time and during the final link. For example,
7500 gcc -c -O2 -flto foo.c
7501 gcc -c -O2 -flto bar.c
7502 gcc -o myprog -flto -O2 foo.o bar.o
7505 The first two invocations to GCC will save a bytecode representation
7506 of GIMPLE into special ELF sections inside @file{foo.o} and
7507 @file{bar.o}. The final invocation will read the GIMPLE bytecode from
7508 @file{foo.o} and @file{bar.o}, merge the two files into a single
7509 internal image, and compile the result as usual. Since both
7510 @file{foo.o} and @file{bar.o} are merged into a single image, this
7511 causes all the inter-procedural analyses and optimizations in GCC to
7512 work across the two files as if they were a single one. This means,
7513 for example, that the inliner will be able to inline functions in
7514 @file{bar.o} into functions in @file{foo.o} and vice-versa.
7516 Another (simpler) way to enable link-time optimization is,
7519 gcc -o myprog -flto -O2 foo.c bar.c
7522 The above will generate bytecode for @file{foo.c} and @file{bar.c},
7523 merge them together into a single GIMPLE representation and optimize
7524 them as usual to produce @file{myprog}.
7526 The only important thing to keep in mind is that to enable link-time
7527 optimizations the @option{-flto} flag needs to be passed to both the
7528 compile and the link commands.
7530 To make whole program optimization effective, it is necessary to make
7531 certain whole program assumptions. The compiler needs to know
7532 what functions and variables can be accessed by libraries and runtime
7533 outside of the link time optimized unit. When supported by the linker,
7534 the linker plugin (see @option{-fuse-linker-plugin}) passes to the
7535 compiler information about used and externally visible symbols. When
7536 the linker plugin is not available, @option{-fwhole-program} should be
7537 used to allow the compiler to make these assumptions, which will lead
7538 to more aggressive optimization decisions.
7540 Note that when a file is compiled with @option{-flto}, the generated
7541 object file will be larger than a regular object file because it will
7542 contain GIMPLE bytecodes and the usual final code. This means that
7543 object files with LTO information can be linked as a normal object
7544 file. So, in the previous example, if the final link is done with
7547 gcc -o myprog foo.o bar.o
7550 The only difference will be that no inter-procedural optimizations
7551 will be applied to produce @file{myprog}. The two object files
7552 @file{foo.o} and @file{bar.o} will be simply sent to the regular
7555 Additionally, the optimization flags used to compile individual files
7556 are not necessarily related to those used at link-time. For instance,
7559 gcc -c -O0 -flto foo.c
7560 gcc -c -O0 -flto bar.c
7561 gcc -o myprog -flto -O3 foo.o bar.o
7564 This will produce individual object files with unoptimized assembler
7565 code, but the resulting binary @file{myprog} will be optimized at
7566 @option{-O3}. Now, if the final binary is generated without
7567 @option{-flto}, then @file{myprog} will not be optimized.
7569 When producing the final binary with @option{-flto}, GCC will only
7570 apply link-time optimizations to those files that contain bytecode.
7571 Therefore, you can mix and match object files and libraries with
7572 GIMPLE bytecodes and final object code. GCC will automatically select
7573 which files to optimize in LTO mode and which files to link without
7576 There are some code generation flags that GCC will preserve when
7577 generating bytecodes, as they need to be used during the final link
7578 stage. Currently, the following options are saved into the GIMPLE
7579 bytecode files: @option{-fPIC}, @option{-fcommon} and all the
7580 @option{-m} target flags.
7582 At link time, these options are read-in and reapplied. Note that the
7583 current implementation makes no attempt at recognizing conflicting
7584 values for these options. If two or more files have a conflicting
7585 value (e.g., one file is compiled with @option{-fPIC} and another
7586 isn't), the compiler will simply use the last value read from the
7587 bytecode files. It is recommended, then, that all the files
7588 participating in the same link be compiled with the same options.
7590 Another feature of LTO is that it is possible to apply interprocedural
7591 optimizations on files written in different languages. This requires
7592 some support in the language front end. Currently, the C, C++ and
7593 Fortran front ends are capable of emitting GIMPLE bytecodes, so
7594 something like this should work
7599 gfortran -c -flto baz.f90
7600 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
7603 Notice that the final link is done with @command{g++} to get the C++
7604 runtime libraries and @option{-lgfortran} is added to get the Fortran
7605 runtime libraries. In general, when mixing languages in LTO mode, you
7606 should use the same link command used when mixing languages in a
7607 regular (non-LTO) compilation. This means that if your build process
7608 was mixing languages before, all you need to add is @option{-flto} to
7609 all the compile and link commands.
7611 If LTO encounters objects with C linkage declared with incompatible
7612 types in separate translation units to be linked together (undefined
7613 behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
7614 issued. The behavior is still undefined at runtime.
7616 If object files containing GIMPLE bytecode are stored in a library archive, say
7617 @file{libfoo.a}, it is possible to extract and use them in an LTO link if you
7618 are using a linker with linker plugin support. To enable this feature, use
7619 the flag @option{-fuse-linker-plugin} at link-time:
7622 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
7625 With the linker plugin enabled, the linker will extract the needed
7626 GIMPLE files from @file{libfoo.a} and pass them on to the running GCC
7627 to make them part of the aggregated GIMPLE image to be optimized.
7629 If you are not using a linker with linker plugin support and/or do not
7630 enable linker plugin then the objects inside @file{libfoo.a}
7631 will be extracted and linked as usual, but they will not participate
7632 in the LTO optimization process.
7634 Link time optimizations do not require the presence of the whole program to
7635 operate. If the program does not require any symbols to be exported, it is
7636 possible to combine @option{-flto} and with @option{-fwhole-program} to allow
7637 the interprocedural optimizers to use more aggressive assumptions which may
7638 lead to improved optimization opportunities.
7639 Use of @option{-fwhole-program} is not needed when linker plugin is
7640 active (see @option{-fuse-linker-plugin}).
7642 Regarding portability: the current implementation of LTO makes no
7643 attempt at generating bytecode that can be ported between different
7644 types of hosts. The bytecode files are versioned and there is a
7645 strict version check, so bytecode files generated in one version of
7646 GCC will not work with an older/newer version of GCC.
7648 Link time optimization does not play well with generating debugging
7649 information. Combining @option{-flto} with
7650 @option{-g} is currently experimental and expected to produce wrong
7653 If you specify the optional @var{n}, the optimization and code
7654 generation done at link time is executed in parallel using @var{n}
7655 parallel jobs by utilizing an installed @command{make} program. The
7656 environment variable @env{MAKE} may be used to override the program
7657 used. The default value for @var{n} is 1.
7659 You can also specify @option{-flto=jobserver} to use GNU make's
7660 job server mode to determine the number of parallel jobs. This
7661 is useful when the Makefile calling GCC is already executing in parallel.
7662 The parent Makefile will need a @samp{+} prepended to the command recipe
7663 for this to work. This will likely only work if @env{MAKE} is
7666 This option is disabled by default.
7668 @item -flto-partition=@var{alg}
7669 @opindex flto-partition
7670 Specify the partitioning algorithm used by the link time optimizer.
7671 The value is either @code{1to1} to specify a partitioning mirroring
7672 the original source files or @code{balanced} to specify partitioning
7673 into equally sized chunks (whenever possible). Specifying @code{none}
7674 as an algorithm disables partitioning and streaming completely. The
7675 default value is @code{balanced}.
7677 @item -flto-compression-level=@var{n}
7678 This option specifies the level of compression used for intermediate
7679 language written to LTO object files, and is only meaningful in
7680 conjunction with LTO mode (@option{-flto}). Valid
7681 values are 0 (no compression) to 9 (maximum compression). Values
7682 outside this range are clamped to either 0 or 9. If the option is not
7683 given, a default balanced compression setting is used.
7686 Prints a report with internal details on the workings of the link-time
7687 optimizer. The contents of this report vary from version to version,
7688 it is meant to be useful to GCC developers when processing object
7689 files in LTO mode (via @option{-flto}).
7691 Disabled by default.
7693 @item -fuse-linker-plugin
7694 Enables the use of linker plugin during link time optimization. This option
7695 relies on the linker plugin support in linker that is available in gold
7696 or in GNU ld 2.21 or newer.
7698 This option enables the extraction of object files with GIMPLE bytecode out of
7699 library archives. This improves the quality of optimization by exposing more
7700 code the the link time optimizer. This information specify what symbols
7701 can be accessed externally (by non-LTO object or during dynamic linking).
7702 Resulting code quality improvements on binaries (and shared libraries that do
7703 use hidden visibility) is similar to @code{-fwhole-program}. See
7704 @option{-flto} for a description on the effect of this flag and how to use it.
7706 Enabled by default when LTO support in GCC is enabled and GCC was compiled
7707 with a linker supporting plugins (GNU ld 2.21 or newer or gold).
7709 @item -fcompare-elim
7710 @opindex fcompare-elim
7711 After register allocation and post-register allocation instruction splitting,
7712 identify arithmetic instructions that compute processor flags similar to a
7713 comparison operation based on that arithmetic. If possible, eliminate the
7714 explicit comparison operation.
7716 This pass only applies to certain targets that cannot explicitly represent
7717 the comparison operation before register allocation is complete.
7719 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7721 @item -fcprop-registers
7722 @opindex fcprop-registers
7723 After register allocation and post-register allocation instruction splitting,
7724 we perform a copy-propagation pass to try to reduce scheduling dependencies
7725 and occasionally eliminate the copy.
7727 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7729 @item -fprofile-correction
7730 @opindex fprofile-correction
7731 Profiles collected using an instrumented binary for multi-threaded programs may
7732 be inconsistent due to missed counter updates. When this option is specified,
7733 GCC will use heuristics to correct or smooth out such inconsistencies. By
7734 default, GCC will emit an error message when an inconsistent profile is detected.
7736 @item -fprofile-dir=@var{path}
7737 @opindex fprofile-dir
7739 Set the directory to search for the profile data files in to @var{path}.
7740 This option affects only the profile data generated by
7741 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
7742 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
7743 and its related options.
7744 By default, GCC will use the current directory as @var{path}, thus the
7745 profile data file will appear in the same directory as the object file.
7747 @item -fprofile-generate
7748 @itemx -fprofile-generate=@var{path}
7749 @opindex fprofile-generate
7751 Enable options usually used for instrumenting application to produce
7752 profile useful for later recompilation with profile feedback based
7753 optimization. You must use @option{-fprofile-generate} both when
7754 compiling and when linking your program.
7756 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
7758 If @var{path} is specified, GCC will look at the @var{path} to find
7759 the profile feedback data files. See @option{-fprofile-dir}.
7762 @itemx -fprofile-use=@var{path}
7763 @opindex fprofile-use
7764 Enable profile feedback directed optimizations, and optimizations
7765 generally profitable only with profile feedback available.
7767 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
7768 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
7770 By default, GCC emits an error message if the feedback profiles do not
7771 match the source code. This error can be turned into a warning by using
7772 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
7775 If @var{path} is specified, GCC will look at the @var{path} to find
7776 the profile feedback data files. See @option{-fprofile-dir}.
7779 The following options control compiler behavior regarding floating
7780 point arithmetic. These options trade off between speed and
7781 correctness. All must be specifically enabled.
7785 @opindex ffloat-store
7786 Do not store floating point variables in registers, and inhibit other
7787 options that might change whether a floating point value is taken from a
7790 @cindex floating point precision
7791 This option prevents undesirable excess precision on machines such as
7792 the 68000 where the floating registers (of the 68881) keep more
7793 precision than a @code{double} is supposed to have. Similarly for the
7794 x86 architecture. For most programs, the excess precision does only
7795 good, but a few programs rely on the precise definition of IEEE floating
7796 point. Use @option{-ffloat-store} for such programs, after modifying
7797 them to store all pertinent intermediate computations into variables.
7799 @item -fexcess-precision=@var{style}
7800 @opindex fexcess-precision
7801 This option allows further control over excess precision on machines
7802 where floating-point registers have more precision than the IEEE
7803 @code{float} and @code{double} types and the processor does not
7804 support operations rounding to those types. By default,
7805 @option{-fexcess-precision=fast} is in effect; this means that
7806 operations are carried out in the precision of the registers and that
7807 it is unpredictable when rounding to the types specified in the source
7808 code takes place. When compiling C, if
7809 @option{-fexcess-precision=standard} is specified then excess
7810 precision will follow the rules specified in ISO C99; in particular,
7811 both casts and assignments cause values to be rounded to their
7812 semantic types (whereas @option{-ffloat-store} only affects
7813 assignments). This option is enabled by default for C if a strict
7814 conformance option such as @option{-std=c99} is used.
7817 @option{-fexcess-precision=standard} is not implemented for languages
7818 other than C, and has no effect if
7819 @option{-funsafe-math-optimizations} or @option{-ffast-math} is
7820 specified. On the x86, it also has no effect if @option{-mfpmath=sse}
7821 or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
7822 semantics apply without excess precision, and in the latter, rounding
7827 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
7828 @option{-ffinite-math-only}, @option{-fno-rounding-math},
7829 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
7831 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
7833 This option is not turned on by any @option{-O} option besides
7834 @option{-Ofast} since it can result in incorrect output for programs
7835 which depend on an exact implementation of IEEE or ISO rules/specifications
7836 for math functions. It may, however, yield faster code for programs
7837 that do not require the guarantees of these specifications.
7839 @item -fno-math-errno
7840 @opindex fno-math-errno
7841 Do not set ERRNO after calling math functions that are executed
7842 with a single instruction, e.g., sqrt. A program that relies on
7843 IEEE exceptions for math error handling may want to use this flag
7844 for speed while maintaining IEEE arithmetic compatibility.
7846 This option is not turned on by any @option{-O} option since
7847 it can result in incorrect output for programs which depend on
7848 an exact implementation of IEEE or ISO rules/specifications for
7849 math functions. It may, however, yield faster code for programs
7850 that do not require the guarantees of these specifications.
7852 The default is @option{-fmath-errno}.
7854 On Darwin systems, the math library never sets @code{errno}. There is
7855 therefore no reason for the compiler to consider the possibility that
7856 it might, and @option{-fno-math-errno} is the default.
7858 @item -funsafe-math-optimizations
7859 @opindex funsafe-math-optimizations
7861 Allow optimizations for floating-point arithmetic that (a) assume
7862 that arguments and results are valid and (b) may violate IEEE or
7863 ANSI standards. When used at link-time, it may include libraries
7864 or startup files that change the default FPU control word or other
7865 similar optimizations.
7867 This option is not turned on by any @option{-O} option since
7868 it can result in incorrect output for programs which depend on
7869 an exact implementation of IEEE or ISO rules/specifications for
7870 math functions. It may, however, yield faster code for programs
7871 that do not require the guarantees of these specifications.
7872 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
7873 @option{-fassociative-math} and @option{-freciprocal-math}.
7875 The default is @option{-fno-unsafe-math-optimizations}.
7877 @item -fassociative-math
7878 @opindex fassociative-math
7880 Allow re-association of operands in series of floating-point operations.
7881 This violates the ISO C and C++ language standard by possibly changing
7882 computation result. NOTE: re-ordering may change the sign of zero as
7883 well as ignore NaNs and inhibit or create underflow or overflow (and
7884 thus cannot be used on a code which relies on rounding behavior like
7885 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
7886 and thus may not be used when ordered comparisons are required.
7887 This option requires that both @option{-fno-signed-zeros} and
7888 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
7889 much sense with @option{-frounding-math}. For Fortran the option
7890 is automatically enabled when both @option{-fno-signed-zeros} and
7891 @option{-fno-trapping-math} are in effect.
7893 The default is @option{-fno-associative-math}.
7895 @item -freciprocal-math
7896 @opindex freciprocal-math
7898 Allow the reciprocal of a value to be used instead of dividing by
7899 the value if this enables optimizations. For example @code{x / y}
7900 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
7901 is subject to common subexpression elimination. Note that this loses
7902 precision and increases the number of flops operating on the value.
7904 The default is @option{-fno-reciprocal-math}.
7906 @item -ffinite-math-only
7907 @opindex ffinite-math-only
7908 Allow optimizations for floating-point arithmetic that assume
7909 that arguments and results are not NaNs or +-Infs.
7911 This option is not turned on by any @option{-O} option since
7912 it can result in incorrect output for programs which depend on
7913 an exact implementation of IEEE or ISO rules/specifications for
7914 math functions. It may, however, yield faster code for programs
7915 that do not require the guarantees of these specifications.
7917 The default is @option{-fno-finite-math-only}.
7919 @item -fno-signed-zeros
7920 @opindex fno-signed-zeros
7921 Allow optimizations for floating point arithmetic that ignore the
7922 signedness of zero. IEEE arithmetic specifies the behavior of
7923 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
7924 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
7925 This option implies that the sign of a zero result isn't significant.
7927 The default is @option{-fsigned-zeros}.
7929 @item -fno-trapping-math
7930 @opindex fno-trapping-math
7931 Compile code assuming that floating-point operations cannot generate
7932 user-visible traps. These traps include division by zero, overflow,
7933 underflow, inexact result and invalid operation. This option requires
7934 that @option{-fno-signaling-nans} be in effect. Setting this option may
7935 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
7937 This option should never be turned on by any @option{-O} option since
7938 it can result in incorrect output for programs which depend on
7939 an exact implementation of IEEE or ISO rules/specifications for
7942 The default is @option{-ftrapping-math}.
7944 @item -frounding-math
7945 @opindex frounding-math
7946 Disable transformations and optimizations that assume default floating
7947 point rounding behavior. This is round-to-zero for all floating point
7948 to integer conversions, and round-to-nearest for all other arithmetic
7949 truncations. This option should be specified for programs that change
7950 the FP rounding mode dynamically, or that may be executed with a
7951 non-default rounding mode. This option disables constant folding of
7952 floating point expressions at compile-time (which may be affected by
7953 rounding mode) and arithmetic transformations that are unsafe in the
7954 presence of sign-dependent rounding modes.
7956 The default is @option{-fno-rounding-math}.
7958 This option is experimental and does not currently guarantee to
7959 disable all GCC optimizations that are affected by rounding mode.
7960 Future versions of GCC may provide finer control of this setting
7961 using C99's @code{FENV_ACCESS} pragma. This command line option
7962 will be used to specify the default state for @code{FENV_ACCESS}.
7964 @item -fsignaling-nans
7965 @opindex fsignaling-nans
7966 Compile code assuming that IEEE signaling NaNs may generate user-visible
7967 traps during floating-point operations. Setting this option disables
7968 optimizations that may change the number of exceptions visible with
7969 signaling NaNs. This option implies @option{-ftrapping-math}.
7971 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
7974 The default is @option{-fno-signaling-nans}.
7976 This option is experimental and does not currently guarantee to
7977 disable all GCC optimizations that affect signaling NaN behavior.
7979 @item -fsingle-precision-constant
7980 @opindex fsingle-precision-constant
7981 Treat floating point constant as single precision constant instead of
7982 implicitly converting it to double precision constant.
7984 @item -fcx-limited-range
7985 @opindex fcx-limited-range
7986 When enabled, this option states that a range reduction step is not
7987 needed when performing complex division. Also, there is no checking
7988 whether the result of a complex multiplication or division is @code{NaN
7989 + I*NaN}, with an attempt to rescue the situation in that case. The
7990 default is @option{-fno-cx-limited-range}, but is enabled by
7991 @option{-ffast-math}.
7993 This option controls the default setting of the ISO C99
7994 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
7997 @item -fcx-fortran-rules
7998 @opindex fcx-fortran-rules
7999 Complex multiplication and division follow Fortran rules. Range
8000 reduction is done as part of complex division, but there is no checking
8001 whether the result of a complex multiplication or division is @code{NaN
8002 + I*NaN}, with an attempt to rescue the situation in that case.
8004 The default is @option{-fno-cx-fortran-rules}.
8008 The following options control optimizations that may improve
8009 performance, but are not enabled by any @option{-O} options. This
8010 section includes experimental options that may produce broken code.
8013 @item -fbranch-probabilities
8014 @opindex fbranch-probabilities
8015 After running a program compiled with @option{-fprofile-arcs}
8016 (@pxref{Debugging Options,, Options for Debugging Your Program or
8017 @command{gcc}}), you can compile it a second time using
8018 @option{-fbranch-probabilities}, to improve optimizations based on
8019 the number of times each branch was taken. When the program
8020 compiled with @option{-fprofile-arcs} exits it saves arc execution
8021 counts to a file called @file{@var{sourcename}.gcda} for each source
8022 file. The information in this data file is very dependent on the
8023 structure of the generated code, so you must use the same source code
8024 and the same optimization options for both compilations.
8026 With @option{-fbranch-probabilities}, GCC puts a
8027 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
8028 These can be used to improve optimization. Currently, they are only
8029 used in one place: in @file{reorg.c}, instead of guessing which path a
8030 branch is most likely to take, the @samp{REG_BR_PROB} values are used to
8031 exactly determine which path is taken more often.
8033 @item -fprofile-values
8034 @opindex fprofile-values
8035 If combined with @option{-fprofile-arcs}, it adds code so that some
8036 data about values of expressions in the program is gathered.
8038 With @option{-fbranch-probabilities}, it reads back the data gathered
8039 from profiling values of expressions for usage in optimizations.
8041 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
8045 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
8046 a code to gather information about values of expressions.
8048 With @option{-fbranch-probabilities}, it reads back the data gathered
8049 and actually performs the optimizations based on them.
8050 Currently the optimizations include specialization of division operation
8051 using the knowledge about the value of the denominator.
8053 @item -frename-registers
8054 @opindex frename-registers
8055 Attempt to avoid false dependencies in scheduled code by making use
8056 of registers left over after register allocation. This optimization
8057 will most benefit processors with lots of registers. Depending on the
8058 debug information format adopted by the target, however, it can
8059 make debugging impossible, since variables will no longer stay in
8060 a ``home register''.
8062 Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
8066 Perform tail duplication to enlarge superblock size. This transformation
8067 simplifies the control flow of the function allowing other optimizations to do
8070 Enabled with @option{-fprofile-use}.
8072 @item -funroll-loops
8073 @opindex funroll-loops
8074 Unroll loops whose number of iterations can be determined at compile time or
8075 upon entry to the loop. @option{-funroll-loops} implies
8076 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
8077 It also turns on complete loop peeling (i.e.@: complete removal of loops with
8078 small constant number of iterations). This option makes code larger, and may
8079 or may not make it run faster.
8081 Enabled with @option{-fprofile-use}.
8083 @item -funroll-all-loops
8084 @opindex funroll-all-loops
8085 Unroll all loops, even if their number of iterations is uncertain when
8086 the loop is entered. This usually makes programs run more slowly.
8087 @option{-funroll-all-loops} implies the same options as
8088 @option{-funroll-loops}.
8091 @opindex fpeel-loops
8092 Peels the loops for that there is enough information that they do not
8093 roll much (from profile feedback). It also turns on complete loop peeling
8094 (i.e.@: complete removal of loops with small constant number of iterations).
8096 Enabled with @option{-fprofile-use}.
8098 @item -fmove-loop-invariants
8099 @opindex fmove-loop-invariants
8100 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
8101 at level @option{-O1}
8103 @item -funswitch-loops
8104 @opindex funswitch-loops
8105 Move branches with loop invariant conditions out of the loop, with duplicates
8106 of the loop on both branches (modified according to result of the condition).
8108 @item -ffunction-sections
8109 @itemx -fdata-sections
8110 @opindex ffunction-sections
8111 @opindex fdata-sections
8112 Place each function or data item into its own section in the output
8113 file if the target supports arbitrary sections. The name of the
8114 function or the name of the data item determines the section's name
8117 Use these options on systems where the linker can perform optimizations
8118 to improve locality of reference in the instruction space. Most systems
8119 using the ELF object format and SPARC processors running Solaris 2 have
8120 linkers with such optimizations. AIX may have these optimizations in
8123 Only use these options when there are significant benefits from doing
8124 so. When you specify these options, the assembler and linker will
8125 create larger object and executable files and will also be slower.
8126 You will not be able to use @code{gprof} on all systems if you
8127 specify this option and you may have problems with debugging if
8128 you specify both this option and @option{-g}.
8130 @item -fbranch-target-load-optimize
8131 @opindex fbranch-target-load-optimize
8132 Perform branch target register load optimization before prologue / epilogue
8134 The use of target registers can typically be exposed only during reload,
8135 thus hoisting loads out of loops and doing inter-block scheduling needs
8136 a separate optimization pass.
8138 @item -fbranch-target-load-optimize2
8139 @opindex fbranch-target-load-optimize2
8140 Perform branch target register load optimization after prologue / epilogue
8143 @item -fbtr-bb-exclusive
8144 @opindex fbtr-bb-exclusive
8145 When performing branch target register load optimization, don't reuse
8146 branch target registers in within any basic block.
8148 @item -fstack-protector
8149 @opindex fstack-protector
8150 Emit extra code to check for buffer overflows, such as stack smashing
8151 attacks. This is done by adding a guard variable to functions with
8152 vulnerable objects. This includes functions that call alloca, and
8153 functions with buffers larger than 8 bytes. The guards are initialized
8154 when a function is entered and then checked when the function exits.
8155 If a guard check fails, an error message is printed and the program exits.
8157 @item -fstack-protector-all
8158 @opindex fstack-protector-all
8159 Like @option{-fstack-protector} except that all functions are protected.
8161 @item -fsection-anchors
8162 @opindex fsection-anchors
8163 Try to reduce the number of symbolic address calculations by using
8164 shared ``anchor'' symbols to address nearby objects. This transformation
8165 can help to reduce the number of GOT entries and GOT accesses on some
8168 For example, the implementation of the following function @code{foo}:
8172 int foo (void) @{ return a + b + c; @}
8175 would usually calculate the addresses of all three variables, but if you
8176 compile it with @option{-fsection-anchors}, it will access the variables
8177 from a common anchor point instead. The effect is similar to the
8178 following pseudocode (which isn't valid C):
8183 register int *xr = &x;
8184 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
8188 Not all targets support this option.
8190 @item --param @var{name}=@var{value}
8192 In some places, GCC uses various constants to control the amount of
8193 optimization that is done. For example, GCC will not inline functions
8194 that contain more that a certain number of instructions. You can
8195 control some of these constants on the command-line using the
8196 @option{--param} option.
8198 The names of specific parameters, and the meaning of the values, are
8199 tied to the internals of the compiler, and are subject to change
8200 without notice in future releases.
8202 In each case, the @var{value} is an integer. The allowable choices for
8203 @var{name} are given in the following table:
8206 @item predictable-branch-outcome
8207 When branch is predicted to be taken with probability lower than this threshold
8208 (in percent), then it is considered well predictable. The default is 10.
8210 @item max-crossjump-edges
8211 The maximum number of incoming edges to consider for crossjumping.
8212 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
8213 the number of edges incoming to each block. Increasing values mean
8214 more aggressive optimization, making the compile time increase with
8215 probably small improvement in executable size.
8217 @item min-crossjump-insns
8218 The minimum number of instructions which must be matched at the end
8219 of two blocks before crossjumping will be performed on them. This
8220 value is ignored in the case where all instructions in the block being
8221 crossjumped from are matched. The default value is 5.
8223 @item max-grow-copy-bb-insns
8224 The maximum code size expansion factor when copying basic blocks
8225 instead of jumping. The expansion is relative to a jump instruction.
8226 The default value is 8.
8228 @item max-goto-duplication-insns
8229 The maximum number of instructions to duplicate to a block that jumps
8230 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
8231 passes, GCC factors computed gotos early in the compilation process,
8232 and unfactors them as late as possible. Only computed jumps at the
8233 end of a basic blocks with no more than max-goto-duplication-insns are
8234 unfactored. The default value is 8.
8236 @item max-delay-slot-insn-search
8237 The maximum number of instructions to consider when looking for an
8238 instruction to fill a delay slot. If more than this arbitrary number of
8239 instructions is searched, the time savings from filling the delay slot
8240 will be minimal so stop searching. Increasing values mean more
8241 aggressive optimization, making the compile time increase with probably
8242 small improvement in executable run time.
8244 @item max-delay-slot-live-search
8245 When trying to fill delay slots, the maximum number of instructions to
8246 consider when searching for a block with valid live register
8247 information. Increasing this arbitrarily chosen value means more
8248 aggressive optimization, increasing the compile time. This parameter
8249 should be removed when the delay slot code is rewritten to maintain the
8252 @item max-gcse-memory
8253 The approximate maximum amount of memory that will be allocated in
8254 order to perform the global common subexpression elimination
8255 optimization. If more memory than specified is required, the
8256 optimization will not be done.
8258 @item max-gcse-insertion-ratio
8259 If the ratio of expression insertions to deletions is larger than this value
8260 for any expression, then RTL PRE will insert or remove the expression and thus
8261 leave partially redundant computations in the instruction stream. The default value is 20.
8263 @item max-pending-list-length
8264 The maximum number of pending dependencies scheduling will allow
8265 before flushing the current state and starting over. Large functions
8266 with few branches or calls can create excessively large lists which
8267 needlessly consume memory and resources.
8269 @item max-inline-insns-single
8270 Several parameters control the tree inliner used in gcc.
8271 This number sets the maximum number of instructions (counted in GCC's
8272 internal representation) in a single function that the tree inliner
8273 will consider for inlining. This only affects functions declared
8274 inline and methods implemented in a class declaration (C++).
8275 The default value is 400.
8277 @item max-inline-insns-auto
8278 When you use @option{-finline-functions} (included in @option{-O3}),
8279 a lot of functions that would otherwise not be considered for inlining
8280 by the compiler will be investigated. To those functions, a different
8281 (more restrictive) limit compared to functions declared inline can
8283 The default value is 40.
8285 @item large-function-insns
8286 The limit specifying really large functions. For functions larger than this
8287 limit after inlining, inlining is constrained by
8288 @option{--param large-function-growth}. This parameter is useful primarily
8289 to avoid extreme compilation time caused by non-linear algorithms used by the
8291 The default value is 2700.
8293 @item large-function-growth
8294 Specifies maximal growth of large function caused by inlining in percents.
8295 The default value is 100 which limits large function growth to 2.0 times
8298 @item large-unit-insns
8299 The limit specifying large translation unit. Growth caused by inlining of
8300 units larger than this limit is limited by @option{--param inline-unit-growth}.
8301 For small units this might be too tight (consider unit consisting of function A
8302 that is inline and B that just calls A three time. If B is small relative to
8303 A, the growth of unit is 300\% and yet such inlining is very sane. For very
8304 large units consisting of small inlineable functions however the overall unit
8305 growth limit is needed to avoid exponential explosion of code size. Thus for
8306 smaller units, the size is increased to @option{--param large-unit-insns}
8307 before applying @option{--param inline-unit-growth}. The default is 10000
8309 @item inline-unit-growth
8310 Specifies maximal overall growth of the compilation unit caused by inlining.
8311 The default value is 30 which limits unit growth to 1.3 times the original
8314 @item ipcp-unit-growth
8315 Specifies maximal overall growth of the compilation unit caused by
8316 interprocedural constant propagation. The default value is 10 which limits
8317 unit growth to 1.1 times the original size.
8319 @item large-stack-frame
8320 The limit specifying large stack frames. While inlining the algorithm is trying
8321 to not grow past this limit too much. Default value is 256 bytes.
8323 @item large-stack-frame-growth
8324 Specifies maximal growth of large stack frames caused by inlining in percents.
8325 The default value is 1000 which limits large stack frame growth to 11 times
8328 @item max-inline-insns-recursive
8329 @itemx max-inline-insns-recursive-auto
8330 Specifies maximum number of instructions out-of-line copy of self recursive inline
8331 function can grow into by performing recursive inlining.
8333 For functions declared inline @option{--param max-inline-insns-recursive} is
8334 taken into account. For function not declared inline, recursive inlining
8335 happens only when @option{-finline-functions} (included in @option{-O3}) is
8336 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
8337 default value is 450.
8339 @item max-inline-recursive-depth
8340 @itemx max-inline-recursive-depth-auto
8341 Specifies maximum recursion depth used by the recursive inlining.
8343 For functions declared inline @option{--param max-inline-recursive-depth} is
8344 taken into account. For function not declared inline, recursive inlining
8345 happens only when @option{-finline-functions} (included in @option{-O3}) is
8346 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
8349 @item min-inline-recursive-probability
8350 Recursive inlining is profitable only for function having deep recursion
8351 in average and can hurt for function having little recursion depth by
8352 increasing the prologue size or complexity of function body to other
8355 When profile feedback is available (see @option{-fprofile-generate}) the actual
8356 recursion depth can be guessed from probability that function will recurse via
8357 given call expression. This parameter limits inlining only to call expression
8358 whose probability exceeds given threshold (in percents). The default value is
8361 @item early-inlining-insns
8362 Specify growth that early inliner can make. In effect it increases amount of
8363 inlining for code having large abstraction penalty. The default value is 10.
8365 @item max-early-inliner-iterations
8366 @itemx max-early-inliner-iterations
8367 Limit of iterations of early inliner. This basically bounds number of nested
8368 indirect calls early inliner can resolve. Deeper chains are still handled by
8371 @item comdat-sharing-probability
8372 @itemx comdat-sharing-probability
8373 Probability (in percent) that C++ inline function with comdat visibility
8374 will be shared across multiple compilation units. The default value is 20.
8376 @item min-vect-loop-bound
8377 The minimum number of iterations under which a loop will not get vectorized
8378 when @option{-ftree-vectorize} is used. The number of iterations after
8379 vectorization needs to be greater than the value specified by this option
8380 to allow vectorization. The default value is 0.
8382 @item gcse-cost-distance-ratio
8383 Scaling factor in calculation of maximum distance an expression
8384 can be moved by GCSE optimizations. This is currently supported only in the
8385 code hoisting pass. The bigger the ratio, the more aggressive code hoisting
8386 will be with simple expressions, i.e., the expressions which have cost
8387 less than @option{gcse-unrestricted-cost}. Specifying 0 will disable
8388 hoisting of simple expressions. The default value is 10.
8390 @item gcse-unrestricted-cost
8391 Cost, roughly measured as the cost of a single typical machine
8392 instruction, at which GCSE optimizations will not constrain
8393 the distance an expression can travel. This is currently
8394 supported only in the code hoisting pass. The lesser the cost,
8395 the more aggressive code hoisting will be. Specifying 0 will
8396 allow all expressions to travel unrestricted distances.
8397 The default value is 3.
8399 @item max-hoist-depth
8400 The depth of search in the dominator tree for expressions to hoist.
8401 This is used to avoid quadratic behavior in hoisting algorithm.
8402 The value of 0 will avoid limiting the search, but may slow down compilation
8403 of huge functions. The default value is 30.
8405 @item max-unrolled-insns
8406 The maximum number of instructions that a loop should have if that loop
8407 is unrolled, and if the loop is unrolled, it determines how many times
8408 the loop code is unrolled.
8410 @item max-average-unrolled-insns
8411 The maximum number of instructions biased by probabilities of their execution
8412 that a loop should have if that loop is unrolled, and if the loop is unrolled,
8413 it determines how many times the loop code is unrolled.
8415 @item max-unroll-times
8416 The maximum number of unrollings of a single loop.
8418 @item max-peeled-insns
8419 The maximum number of instructions that a loop should have if that loop
8420 is peeled, and if the loop is peeled, it determines how many times
8421 the loop code is peeled.
8423 @item max-peel-times
8424 The maximum number of peelings of a single loop.
8426 @item max-completely-peeled-insns
8427 The maximum number of insns of a completely peeled loop.
8429 @item max-completely-peel-times
8430 The maximum number of iterations of a loop to be suitable for complete peeling.
8432 @item max-completely-peel-loop-nest-depth
8433 The maximum depth of a loop nest suitable for complete peeling.
8435 @item max-unswitch-insns
8436 The maximum number of insns of an unswitched loop.
8438 @item max-unswitch-level
8439 The maximum number of branches unswitched in a single loop.
8442 The minimum cost of an expensive expression in the loop invariant motion.
8444 @item iv-consider-all-candidates-bound
8445 Bound on number of candidates for induction variables below that
8446 all candidates are considered for each use in induction variable
8447 optimizations. Only the most relevant candidates are considered
8448 if there are more candidates, to avoid quadratic time complexity.
8450 @item iv-max-considered-uses
8451 The induction variable optimizations give up on loops that contain more
8452 induction variable uses.
8454 @item iv-always-prune-cand-set-bound
8455 If number of candidates in the set is smaller than this value,
8456 we always try to remove unnecessary ivs from the set during its
8457 optimization when a new iv is added to the set.
8459 @item scev-max-expr-size
8460 Bound on size of expressions used in the scalar evolutions analyzer.
8461 Large expressions slow the analyzer.
8463 @item scev-max-expr-complexity
8464 Bound on the complexity of the expressions in the scalar evolutions analyzer.
8465 Complex expressions slow the analyzer.
8467 @item omega-max-vars
8468 The maximum number of variables in an Omega constraint system.
8469 The default value is 128.
8471 @item omega-max-geqs
8472 The maximum number of inequalities in an Omega constraint system.
8473 The default value is 256.
8476 The maximum number of equalities in an Omega constraint system.
8477 The default value is 128.
8479 @item omega-max-wild-cards
8480 The maximum number of wildcard variables that the Omega solver will
8481 be able to insert. The default value is 18.
8483 @item omega-hash-table-size
8484 The size of the hash table in the Omega solver. The default value is
8487 @item omega-max-keys
8488 The maximal number of keys used by the Omega solver. The default
8491 @item omega-eliminate-redundant-constraints
8492 When set to 1, use expensive methods to eliminate all redundant
8493 constraints. The default value is 0.
8495 @item vect-max-version-for-alignment-checks
8496 The maximum number of runtime checks that can be performed when
8497 doing loop versioning for alignment in the vectorizer. See option
8498 ftree-vect-loop-version for more information.
8500 @item vect-max-version-for-alias-checks
8501 The maximum number of runtime checks that can be performed when
8502 doing loop versioning for alias in the vectorizer. See option
8503 ftree-vect-loop-version for more information.
8505 @item max-iterations-to-track
8507 The maximum number of iterations of a loop the brute force algorithm
8508 for analysis of # of iterations of the loop tries to evaluate.
8510 @item hot-bb-count-fraction
8511 Select fraction of the maximal count of repetitions of basic block in program
8512 given basic block needs to have to be considered hot.
8514 @item hot-bb-frequency-fraction
8515 Select fraction of the entry block frequency of executions of basic block in
8516 function given basic block needs to have to be considered hot.
8518 @item max-predicted-iterations
8519 The maximum number of loop iterations we predict statically. This is useful
8520 in cases where function contain single loop with known bound and other loop
8521 with unknown. We predict the known number of iterations correctly, while
8522 the unknown number of iterations average to roughly 10. This means that the
8523 loop without bounds would appear artificially cold relative to the other one.
8525 @item align-threshold
8527 Select fraction of the maximal frequency of executions of basic block in
8528 function given basic block will get aligned.
8530 @item align-loop-iterations
8532 A loop expected to iterate at lest the selected number of iterations will get
8535 @item tracer-dynamic-coverage
8536 @itemx tracer-dynamic-coverage-feedback
8538 This value is used to limit superblock formation once the given percentage of
8539 executed instructions is covered. This limits unnecessary code size
8542 The @option{tracer-dynamic-coverage-feedback} is used only when profile
8543 feedback is available. The real profiles (as opposed to statically estimated
8544 ones) are much less balanced allowing the threshold to be larger value.
8546 @item tracer-max-code-growth
8547 Stop tail duplication once code growth has reached given percentage. This is
8548 rather hokey argument, as most of the duplicates will be eliminated later in
8549 cross jumping, so it may be set to much higher values than is the desired code
8552 @item tracer-min-branch-ratio
8554 Stop reverse growth when the reverse probability of best edge is less than this
8555 threshold (in percent).
8557 @item tracer-min-branch-ratio
8558 @itemx tracer-min-branch-ratio-feedback
8560 Stop forward growth if the best edge do have probability lower than this
8563 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
8564 compilation for profile feedback and one for compilation without. The value
8565 for compilation with profile feedback needs to be more conservative (higher) in
8566 order to make tracer effective.
8568 @item max-cse-path-length
8570 Maximum number of basic blocks on path that cse considers. The default is 10.
8573 The maximum instructions CSE process before flushing. The default is 1000.
8575 @item ggc-min-expand
8577 GCC uses a garbage collector to manage its own memory allocation. This
8578 parameter specifies the minimum percentage by which the garbage
8579 collector's heap should be allowed to expand between collections.
8580 Tuning this may improve compilation speed; it has no effect on code
8583 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
8584 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
8585 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
8586 GCC is not able to calculate RAM on a particular platform, the lower
8587 bound of 30% is used. Setting this parameter and
8588 @option{ggc-min-heapsize} to zero causes a full collection to occur at
8589 every opportunity. This is extremely slow, but can be useful for
8592 @item ggc-min-heapsize
8594 Minimum size of the garbage collector's heap before it begins bothering
8595 to collect garbage. The first collection occurs after the heap expands
8596 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
8597 tuning this may improve compilation speed, and has no effect on code
8600 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
8601 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
8602 with a lower bound of 4096 (four megabytes) and an upper bound of
8603 131072 (128 megabytes). If GCC is not able to calculate RAM on a
8604 particular platform, the lower bound is used. Setting this parameter
8605 very large effectively disables garbage collection. Setting this
8606 parameter and @option{ggc-min-expand} to zero causes a full collection
8607 to occur at every opportunity.
8609 @item max-reload-search-insns
8610 The maximum number of instruction reload should look backward for equivalent
8611 register. Increasing values mean more aggressive optimization, making the
8612 compile time increase with probably slightly better performance. The default
8615 @item max-cselib-memory-locations
8616 The maximum number of memory locations cselib should take into account.
8617 Increasing values mean more aggressive optimization, making the compile time
8618 increase with probably slightly better performance. The default value is 500.
8620 @item reorder-blocks-duplicate
8621 @itemx reorder-blocks-duplicate-feedback
8623 Used by basic block reordering pass to decide whether to use unconditional
8624 branch or duplicate the code on its destination. Code is duplicated when its
8625 estimated size is smaller than this value multiplied by the estimated size of
8626 unconditional jump in the hot spots of the program.
8628 The @option{reorder-block-duplicate-feedback} is used only when profile
8629 feedback is available and may be set to higher values than
8630 @option{reorder-block-duplicate} since information about the hot spots is more
8633 @item max-sched-ready-insns
8634 The maximum number of instructions ready to be issued the scheduler should
8635 consider at any given time during the first scheduling pass. Increasing
8636 values mean more thorough searches, making the compilation time increase
8637 with probably little benefit. The default value is 100.
8639 @item max-sched-region-blocks
8640 The maximum number of blocks in a region to be considered for
8641 interblock scheduling. The default value is 10.
8643 @item max-pipeline-region-blocks
8644 The maximum number of blocks in a region to be considered for
8645 pipelining in the selective scheduler. The default value is 15.
8647 @item max-sched-region-insns
8648 The maximum number of insns in a region to be considered for
8649 interblock scheduling. The default value is 100.
8651 @item max-pipeline-region-insns
8652 The maximum number of insns in a region to be considered for
8653 pipelining in the selective scheduler. The default value is 200.
8656 The minimum probability (in percents) of reaching a source block
8657 for interblock speculative scheduling. The default value is 40.
8659 @item max-sched-extend-regions-iters
8660 The maximum number of iterations through CFG to extend regions.
8661 0 - disable region extension,
8662 N - do at most N iterations.
8663 The default value is 0.
8665 @item max-sched-insn-conflict-delay
8666 The maximum conflict delay for an insn to be considered for speculative motion.
8667 The default value is 3.
8669 @item sched-spec-prob-cutoff
8670 The minimal probability of speculation success (in percents), so that
8671 speculative insn will be scheduled.
8672 The default value is 40.
8674 @item sched-mem-true-dep-cost
8675 Minimal distance (in CPU cycles) between store and load targeting same
8676 memory locations. The default value is 1.
8678 @item selsched-max-lookahead
8679 The maximum size of the lookahead window of selective scheduling. It is a
8680 depth of search for available instructions.
8681 The default value is 50.
8683 @item selsched-max-sched-times
8684 The maximum number of times that an instruction will be scheduled during
8685 selective scheduling. This is the limit on the number of iterations
8686 through which the instruction may be pipelined. The default value is 2.
8688 @item selsched-max-insns-to-rename
8689 The maximum number of best instructions in the ready list that are considered
8690 for renaming in the selective scheduler. The default value is 2.
8692 @item max-last-value-rtl
8693 The maximum size measured as number of RTLs that can be recorded in an expression
8694 in combiner for a pseudo register as last known value of that register. The default
8697 @item integer-share-limit
8698 Small integer constants can use a shared data structure, reducing the
8699 compiler's memory usage and increasing its speed. This sets the maximum
8700 value of a shared integer constant. The default value is 256.
8702 @item min-virtual-mappings
8703 Specifies the minimum number of virtual mappings in the incremental
8704 SSA updater that should be registered to trigger the virtual mappings
8705 heuristic defined by virtual-mappings-ratio. The default value is
8708 @item virtual-mappings-ratio
8709 If the number of virtual mappings is virtual-mappings-ratio bigger
8710 than the number of virtual symbols to be updated, then the incremental
8711 SSA updater switches to a full update for those symbols. The default
8714 @item ssp-buffer-size
8715 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
8716 protection when @option{-fstack-protection} is used.
8718 @item max-jump-thread-duplication-stmts
8719 Maximum number of statements allowed in a block that needs to be
8720 duplicated when threading jumps.
8722 @item max-fields-for-field-sensitive
8723 Maximum number of fields in a structure we will treat in
8724 a field sensitive manner during pointer analysis. The default is zero
8725 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
8727 @item prefetch-latency
8728 Estimate on average number of instructions that are executed before
8729 prefetch finishes. The distance we prefetch ahead is proportional
8730 to this constant. Increasing this number may also lead to less
8731 streams being prefetched (see @option{simultaneous-prefetches}).
8733 @item simultaneous-prefetches
8734 Maximum number of prefetches that can run at the same time.
8736 @item l1-cache-line-size
8737 The size of cache line in L1 cache, in bytes.
8740 The size of L1 cache, in kilobytes.
8743 The size of L2 cache, in kilobytes.
8745 @item min-insn-to-prefetch-ratio
8746 The minimum ratio between the number of instructions and the
8747 number of prefetches to enable prefetching in a loop.
8749 @item prefetch-min-insn-to-mem-ratio
8750 The minimum ratio between the number of instructions and the
8751 number of memory references to enable prefetching in a loop.
8753 @item use-canonical-types
8754 Whether the compiler should use the ``canonical'' type system. By
8755 default, this should always be 1, which uses a more efficient internal
8756 mechanism for comparing types in C++ and Objective-C++. However, if
8757 bugs in the canonical type system are causing compilation failures,
8758 set this value to 0 to disable canonical types.
8760 @item switch-conversion-max-branch-ratio
8761 Switch initialization conversion will refuse to create arrays that are
8762 bigger than @option{switch-conversion-max-branch-ratio} times the number of
8763 branches in the switch.
8765 @item max-partial-antic-length
8766 Maximum length of the partial antic set computed during the tree
8767 partial redundancy elimination optimization (@option{-ftree-pre}) when
8768 optimizing at @option{-O3} and above. For some sorts of source code
8769 the enhanced partial redundancy elimination optimization can run away,
8770 consuming all of the memory available on the host machine. This
8771 parameter sets a limit on the length of the sets that are computed,
8772 which prevents the runaway behavior. Setting a value of 0 for
8773 this parameter will allow an unlimited set length.
8775 @item sccvn-max-scc-size
8776 Maximum size of a strongly connected component (SCC) during SCCVN
8777 processing. If this limit is hit, SCCVN processing for the whole
8778 function will not be done and optimizations depending on it will
8779 be disabled. The default maximum SCC size is 10000.
8781 @item ira-max-loops-num
8782 IRA uses a regional register allocation by default. If a function
8783 contains loops more than number given by the parameter, only at most
8784 given number of the most frequently executed loops will form regions
8785 for the regional register allocation. The default value of the
8788 @item ira-max-conflict-table-size
8789 Although IRA uses a sophisticated algorithm of compression conflict
8790 table, the table can be still big for huge functions. If the conflict
8791 table for a function could be more than size in MB given by the
8792 parameter, the conflict table is not built and faster, simpler, and
8793 lower quality register allocation algorithm will be used. The
8794 algorithm do not use pseudo-register conflicts. The default value of
8795 the parameter is 2000.
8797 @item ira-loop-reserved-regs
8798 IRA can be used to evaluate more accurate register pressure in loops
8799 for decision to move loop invariants (see @option{-O3}). The number
8800 of available registers reserved for some other purposes is described
8801 by this parameter. The default value of the parameter is 2 which is
8802 minimal number of registers needed for execution of typical
8803 instruction. This value is the best found from numerous experiments.
8805 @item loop-invariant-max-bbs-in-loop
8806 Loop invariant motion can be very expensive, both in compile time and
8807 in amount of needed compile time memory, with very large loops. Loops
8808 with more basic blocks than this parameter won't have loop invariant
8809 motion optimization performed on them. The default value of the
8810 parameter is 1000 for -O1 and 10000 for -O2 and above.
8812 @item max-vartrack-size
8813 Sets a maximum number of hash table slots to use during variable
8814 tracking dataflow analysis of any function. If this limit is exceeded
8815 with variable tracking at assignments enabled, analysis for that
8816 function is retried without it, after removing all debug insns from
8817 the function. If the limit is exceeded even without debug insns, var
8818 tracking analysis is completely disabled for the function. Setting
8819 the parameter to zero makes it unlimited.
8821 @item min-nondebug-insn-uid
8822 Use uids starting at this parameter for nondebug insns. The range below
8823 the parameter is reserved exclusively for debug insns created by
8824 @option{-fvar-tracking-assignments}, but debug insns may get
8825 (non-overlapping) uids above it if the reserved range is exhausted.
8827 @item ipa-sra-ptr-growth-factor
8828 IPA-SRA will replace a pointer to an aggregate with one or more new
8829 parameters only when their cumulative size is less or equal to
8830 @option{ipa-sra-ptr-growth-factor} times the size of the original
8833 @item graphite-max-nb-scop-params
8834 To avoid exponential effects in the Graphite loop transforms, the
8835 number of parameters in a Static Control Part (SCoP) is bounded. The
8836 default value is 10 parameters. A variable whose value is unknown at
8837 compile time and defined outside a SCoP is a parameter of the SCoP.
8839 @item graphite-max-bbs-per-function
8840 To avoid exponential effects in the detection of SCoPs, the size of
8841 the functions analyzed by Graphite is bounded. The default value is
8844 @item loop-block-tile-size
8845 Loop blocking or strip mining transforms, enabled with
8846 @option{-floop-block} or @option{-floop-strip-mine}, strip mine each
8847 loop in the loop nest by a given number of iterations. The strip
8848 length can be changed using the @option{loop-block-tile-size}
8849 parameter. The default value is 51 iterations.
8851 @item devirt-type-list-size
8852 IPA-CP attempts to track all possible types passed to a function's
8853 parameter in order to perform devirtualization.
8854 @option{devirt-type-list-size} is the maximum number of types it
8855 stores per a single formal parameter of a function.
8857 @item lto-partitions
8858 Specify desired number of partitions produced during WHOPR compilation.
8859 The number of partitions should exceed the number of CPUs used for compilation.
8860 The default value is 32.
8862 @item lto-minpartition
8863 Size of minimal partition for WHOPR (in estimated instructions).
8864 This prevents expenses of splitting very small programs into too many
8867 @item cxx-max-namespaces-for-diagnostic-help
8868 The maximum number of namespaces to consult for suggestions when C++
8869 name lookup fails for an identifier. The default is 1000.
8874 @node Preprocessor Options
8875 @section Options Controlling the Preprocessor
8876 @cindex preprocessor options
8877 @cindex options, preprocessor
8879 These options control the C preprocessor, which is run on each C source
8880 file before actual compilation.
8882 If you use the @option{-E} option, nothing is done except preprocessing.
8883 Some of these options make sense only together with @option{-E} because
8884 they cause the preprocessor output to be unsuitable for actual
8888 @item -Wp,@var{option}
8890 You can use @option{-Wp,@var{option}} to bypass the compiler driver
8891 and pass @var{option} directly through to the preprocessor. If
8892 @var{option} contains commas, it is split into multiple options at the
8893 commas. However, many options are modified, translated or interpreted
8894 by the compiler driver before being passed to the preprocessor, and
8895 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
8896 interface is undocumented and subject to change, so whenever possible
8897 you should avoid using @option{-Wp} and let the driver handle the
8900 @item -Xpreprocessor @var{option}
8901 @opindex Xpreprocessor
8902 Pass @var{option} as an option to the preprocessor. You can use this to
8903 supply system-specific preprocessor options which GCC does not know how to
8906 If you want to pass an option that takes an argument, you must use
8907 @option{-Xpreprocessor} twice, once for the option and once for the argument.
8910 @include cppopts.texi
8912 @node Assembler Options
8913 @section Passing Options to the Assembler
8915 @c prevent bad page break with this line
8916 You can pass options to the assembler.
8919 @item -Wa,@var{option}
8921 Pass @var{option} as an option to the assembler. If @var{option}
8922 contains commas, it is split into multiple options at the commas.
8924 @item -Xassembler @var{option}
8926 Pass @var{option} as an option to the assembler. You can use this to
8927 supply system-specific assembler options which GCC does not know how to
8930 If you want to pass an option that takes an argument, you must use
8931 @option{-Xassembler} twice, once for the option and once for the argument.
8936 @section Options for Linking
8937 @cindex link options
8938 @cindex options, linking
8940 These options come into play when the compiler links object files into
8941 an executable output file. They are meaningless if the compiler is
8942 not doing a link step.
8946 @item @var{object-file-name}
8947 A file name that does not end in a special recognized suffix is
8948 considered to name an object file or library. (Object files are
8949 distinguished from libraries by the linker according to the file
8950 contents.) If linking is done, these object files are used as input
8959 If any of these options is used, then the linker is not run, and
8960 object file names should not be used as arguments. @xref{Overall
8964 @item -l@var{library}
8965 @itemx -l @var{library}
8967 Search the library named @var{library} when linking. (The second
8968 alternative with the library as a separate argument is only for
8969 POSIX compliance and is not recommended.)
8971 It makes a difference where in the command you write this option; the
8972 linker searches and processes libraries and object files in the order they
8973 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
8974 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
8975 to functions in @samp{z}, those functions may not be loaded.
8977 The linker searches a standard list of directories for the library,
8978 which is actually a file named @file{lib@var{library}.a}. The linker
8979 then uses this file as if it had been specified precisely by name.
8981 The directories searched include several standard system directories
8982 plus any that you specify with @option{-L}.
8984 Normally the files found this way are library files---archive files
8985 whose members are object files. The linker handles an archive file by
8986 scanning through it for members which define symbols that have so far
8987 been referenced but not defined. But if the file that is found is an
8988 ordinary object file, it is linked in the usual fashion. The only
8989 difference between using an @option{-l} option and specifying a file name
8990 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
8991 and searches several directories.
8995 You need this special case of the @option{-l} option in order to
8996 link an Objective-C or Objective-C++ program.
8999 @opindex nostartfiles
9000 Do not use the standard system startup files when linking.
9001 The standard system libraries are used normally, unless @option{-nostdlib}
9002 or @option{-nodefaultlibs} is used.
9004 @item -nodefaultlibs
9005 @opindex nodefaultlibs
9006 Do not use the standard system libraries when linking.
9007 Only the libraries you specify will be passed to the linker, options
9008 specifying linkage of the system libraries, such as @code{-static-libgcc}
9009 or @code{-shared-libgcc}, will be ignored.
9010 The standard startup files are used normally, unless @option{-nostartfiles}
9011 is used. The compiler may generate calls to @code{memcmp},
9012 @code{memset}, @code{memcpy} and @code{memmove}.
9013 These entries are usually resolved by entries in
9014 libc. These entry points should be supplied through some other
9015 mechanism when this option is specified.
9019 Do not use the standard system startup files or libraries when linking.
9020 No startup files and only the libraries you specify will be passed to
9021 the linker, options specifying linkage of the system libraries, such as
9022 @code{-static-libgcc} or @code{-shared-libgcc}, will be ignored.
9023 The compiler may generate calls to @code{memcmp}, @code{memset},
9024 @code{memcpy} and @code{memmove}.
9025 These entries are usually resolved by entries in
9026 libc. These entry points should be supplied through some other
9027 mechanism when this option is specified.
9029 @cindex @option{-lgcc}, use with @option{-nostdlib}
9030 @cindex @option{-nostdlib} and unresolved references
9031 @cindex unresolved references and @option{-nostdlib}
9032 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
9033 @cindex @option{-nodefaultlibs} and unresolved references
9034 @cindex unresolved references and @option{-nodefaultlibs}
9035 One of the standard libraries bypassed by @option{-nostdlib} and
9036 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
9037 that GCC uses to overcome shortcomings of particular machines, or special
9038 needs for some languages.
9039 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
9040 Collection (GCC) Internals},
9041 for more discussion of @file{libgcc.a}.)
9042 In most cases, you need @file{libgcc.a} even when you want to avoid
9043 other standard libraries. In other words, when you specify @option{-nostdlib}
9044 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
9045 This ensures that you have no unresolved references to internal GCC
9046 library subroutines. (For example, @samp{__main}, used to ensure C++
9047 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
9048 GNU Compiler Collection (GCC) Internals}.)
9052 Produce a position independent executable on targets which support it.
9053 For predictable results, you must also specify the same set of options
9054 that were used to generate code (@option{-fpie}, @option{-fPIE},
9055 or model suboptions) when you specify this option.
9059 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
9060 that support it. This instructs the linker to add all symbols, not
9061 only used ones, to the dynamic symbol table. This option is needed
9062 for some uses of @code{dlopen} or to allow obtaining backtraces
9063 from within a program.
9067 Remove all symbol table and relocation information from the executable.
9071 On systems that support dynamic linking, this prevents linking with the shared
9072 libraries. On other systems, this option has no effect.
9076 Produce a shared object which can then be linked with other objects to
9077 form an executable. Not all systems support this option. For predictable
9078 results, you must also specify the same set of options that were used to
9079 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
9080 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
9081 needs to build supplementary stub code for constructors to work. On
9082 multi-libbed systems, @samp{gcc -shared} must select the correct support
9083 libraries to link against. Failing to supply the correct flags may lead
9084 to subtle defects. Supplying them in cases where they are not necessary
9087 @item -shared-libgcc
9088 @itemx -static-libgcc
9089 @opindex shared-libgcc
9090 @opindex static-libgcc
9091 On systems that provide @file{libgcc} as a shared library, these options
9092 force the use of either the shared or static version respectively.
9093 If no shared version of @file{libgcc} was built when the compiler was
9094 configured, these options have no effect.
9096 There are several situations in which an application should use the
9097 shared @file{libgcc} instead of the static version. The most common
9098 of these is when the application wishes to throw and catch exceptions
9099 across different shared libraries. In that case, each of the libraries
9100 as well as the application itself should use the shared @file{libgcc}.
9102 Therefore, the G++ and GCJ drivers automatically add
9103 @option{-shared-libgcc} whenever you build a shared library or a main
9104 executable, because C++ and Java programs typically use exceptions, so
9105 this is the right thing to do.
9107 If, instead, you use the GCC driver to create shared libraries, you may
9108 find that they will not always be linked with the shared @file{libgcc}.
9109 If GCC finds, at its configuration time, that you have a non-GNU linker
9110 or a GNU linker that does not support option @option{--eh-frame-hdr},
9111 it will link the shared version of @file{libgcc} into shared libraries
9112 by default. Otherwise, it will take advantage of the linker and optimize
9113 away the linking with the shared version of @file{libgcc}, linking with
9114 the static version of libgcc by default. This allows exceptions to
9115 propagate through such shared libraries, without incurring relocation
9116 costs at library load time.
9118 However, if a library or main executable is supposed to throw or catch
9119 exceptions, you must link it using the G++ or GCJ driver, as appropriate
9120 for the languages used in the program, or using the option
9121 @option{-shared-libgcc}, such that it is linked with the shared
9124 @item -static-libstdc++
9125 When the @command{g++} program is used to link a C++ program, it will
9126 normally automatically link against @option{libstdc++}. If
9127 @file{libstdc++} is available as a shared library, and the
9128 @option{-static} option is not used, then this will link against the
9129 shared version of @file{libstdc++}. That is normally fine. However, it
9130 is sometimes useful to freeze the version of @file{libstdc++} used by
9131 the program without going all the way to a fully static link. The
9132 @option{-static-libstdc++} option directs the @command{g++} driver to
9133 link @file{libstdc++} statically, without necessarily linking other
9134 libraries statically.
9138 Bind references to global symbols when building a shared object. Warn
9139 about any unresolved references (unless overridden by the link editor
9140 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
9143 @item -T @var{script}
9145 @cindex linker script
9146 Use @var{script} as the linker script. This option is supported by most
9147 systems using the GNU linker. On some targets, such as bare-board
9148 targets without an operating system, the @option{-T} option may be required
9149 when linking to avoid references to undefined symbols.
9151 @item -Xlinker @var{option}
9153 Pass @var{option} as an option to the linker. You can use this to
9154 supply system-specific linker options which GCC does not know how to
9157 If you want to pass an option that takes a separate argument, you must use
9158 @option{-Xlinker} twice, once for the option and once for the argument.
9159 For example, to pass @option{-assert definitions}, you must write
9160 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
9161 @option{-Xlinker "-assert definitions"}, because this passes the entire
9162 string as a single argument, which is not what the linker expects.
9164 When using the GNU linker, it is usually more convenient to pass
9165 arguments to linker options using the @option{@var{option}=@var{value}}
9166 syntax than as separate arguments. For example, you can specify
9167 @samp{-Xlinker -Map=output.map} rather than
9168 @samp{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
9169 this syntax for command-line options.
9171 @item -Wl,@var{option}
9173 Pass @var{option} as an option to the linker. If @var{option} contains
9174 commas, it is split into multiple options at the commas. You can use this
9175 syntax to pass an argument to the option.
9176 For example, @samp{-Wl,-Map,output.map} passes @samp{-Map output.map} to the
9177 linker. When using the GNU linker, you can also get the same effect with
9178 @samp{-Wl,-Map=output.map}.
9180 @item -u @var{symbol}
9182 Pretend the symbol @var{symbol} is undefined, to force linking of
9183 library modules to define it. You can use @option{-u} multiple times with
9184 different symbols to force loading of additional library modules.
9187 @node Directory Options
9188 @section Options for Directory Search
9189 @cindex directory options
9190 @cindex options, directory search
9193 These options specify directories to search for header files, for
9194 libraries and for parts of the compiler:
9199 Add the directory @var{dir} to the head of the list of directories to be
9200 searched for header files. This can be used to override a system header
9201 file, substituting your own version, since these directories are
9202 searched before the system header file directories. However, you should
9203 not use this option to add directories that contain vendor-supplied
9204 system header files (use @option{-isystem} for that). If you use more than
9205 one @option{-I} option, the directories are scanned in left-to-right
9206 order; the standard system directories come after.
9208 If a standard system include directory, or a directory specified with
9209 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
9210 option will be ignored. The directory will still be searched but as a
9211 system directory at its normal position in the system include chain.
9212 This is to ensure that GCC's procedure to fix buggy system headers and
9213 the ordering for the include_next directive are not inadvertently changed.
9214 If you really need to change the search order for system directories,
9215 use the @option{-nostdinc} and/or @option{-isystem} options.
9217 @item -iplugindir=@var{dir}
9218 Set the directory to search for plugins which are passed
9219 by @option{-fplugin=@var{name}} instead of
9220 @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
9221 to be used by the user, but only passed by the driver.
9223 @item -iquote@var{dir}
9225 Add the directory @var{dir} to the head of the list of directories to
9226 be searched for header files only for the case of @samp{#include
9227 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
9228 otherwise just like @option{-I}.
9232 Add directory @var{dir} to the list of directories to be searched
9235 @item -B@var{prefix}
9237 This option specifies where to find the executables, libraries,
9238 include files, and data files of the compiler itself.
9240 The compiler driver program runs one or more of the subprograms
9241 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
9242 @var{prefix} as a prefix for each program it tries to run, both with and
9243 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
9245 For each subprogram to be run, the compiler driver first tries the
9246 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
9247 was not specified, the driver tries two standard prefixes, which are
9248 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
9249 those results in a file name that is found, the unmodified program
9250 name is searched for using the directories specified in your
9251 @env{PATH} environment variable.
9253 The compiler will check to see if the path provided by the @option{-B}
9254 refers to a directory, and if necessary it will add a directory
9255 separator character at the end of the path.
9257 @option{-B} prefixes that effectively specify directory names also apply
9258 to libraries in the linker, because the compiler translates these
9259 options into @option{-L} options for the linker. They also apply to
9260 includes files in the preprocessor, because the compiler translates these
9261 options into @option{-isystem} options for the preprocessor. In this case,
9262 the compiler appends @samp{include} to the prefix.
9264 The run-time support file @file{libgcc.a} can also be searched for using
9265 the @option{-B} prefix, if needed. If it is not found there, the two
9266 standard prefixes above are tried, and that is all. The file is left
9267 out of the link if it is not found by those means.
9269 Another way to specify a prefix much like the @option{-B} prefix is to use
9270 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
9273 As a special kludge, if the path provided by @option{-B} is
9274 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
9275 9, then it will be replaced by @file{[dir/]include}. This is to help
9276 with boot-strapping the compiler.
9278 @item -specs=@var{file}
9280 Process @var{file} after the compiler reads in the standard @file{specs}
9281 file, in order to override the defaults that the @file{gcc} driver
9282 program uses when determining what switches to pass to @file{cc1},
9283 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
9284 @option{-specs=@var{file}} can be specified on the command line, and they
9285 are processed in order, from left to right.
9287 @item --sysroot=@var{dir}
9289 Use @var{dir} as the logical root directory for headers and libraries.
9290 For example, if the compiler would normally search for headers in
9291 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
9292 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
9294 If you use both this option and the @option{-isysroot} option, then
9295 the @option{--sysroot} option will apply to libraries, but the
9296 @option{-isysroot} option will apply to header files.
9298 The GNU linker (beginning with version 2.16) has the necessary support
9299 for this option. If your linker does not support this option, the
9300 header file aspect of @option{--sysroot} will still work, but the
9301 library aspect will not.
9305 This option has been deprecated. Please use @option{-iquote} instead for
9306 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
9307 Any directories you specify with @option{-I} options before the @option{-I-}
9308 option are searched only for the case of @samp{#include "@var{file}"};
9309 they are not searched for @samp{#include <@var{file}>}.
9311 If additional directories are specified with @option{-I} options after
9312 the @option{-I-}, these directories are searched for all @samp{#include}
9313 directives. (Ordinarily @emph{all} @option{-I} directories are used
9316 In addition, the @option{-I-} option inhibits the use of the current
9317 directory (where the current input file came from) as the first search
9318 directory for @samp{#include "@var{file}"}. There is no way to
9319 override this effect of @option{-I-}. With @option{-I.} you can specify
9320 searching the directory which was current when the compiler was
9321 invoked. That is not exactly the same as what the preprocessor does
9322 by default, but it is often satisfactory.
9324 @option{-I-} does not inhibit the use of the standard system directories
9325 for header files. Thus, @option{-I-} and @option{-nostdinc} are
9332 @section Specifying subprocesses and the switches to pass to them
9335 @command{gcc} is a driver program. It performs its job by invoking a
9336 sequence of other programs to do the work of compiling, assembling and
9337 linking. GCC interprets its command-line parameters and uses these to
9338 deduce which programs it should invoke, and which command-line options
9339 it ought to place on their command lines. This behavior is controlled
9340 by @dfn{spec strings}. In most cases there is one spec string for each
9341 program that GCC can invoke, but a few programs have multiple spec
9342 strings to control their behavior. The spec strings built into GCC can
9343 be overridden by using the @option{-specs=} command-line switch to specify
9346 @dfn{Spec files} are plaintext files that are used to construct spec
9347 strings. They consist of a sequence of directives separated by blank
9348 lines. The type of directive is determined by the first non-whitespace
9349 character on the line and it can be one of the following:
9352 @item %@var{command}
9353 Issues a @var{command} to the spec file processor. The commands that can
9357 @item %include <@var{file}>
9358 @cindex @code{%include}
9359 Search for @var{file} and insert its text at the current point in the
9362 @item %include_noerr <@var{file}>
9363 @cindex @code{%include_noerr}
9364 Just like @samp{%include}, but do not generate an error message if the include
9365 file cannot be found.
9367 @item %rename @var{old_name} @var{new_name}
9368 @cindex @code{%rename}
9369 Rename the spec string @var{old_name} to @var{new_name}.
9373 @item *[@var{spec_name}]:
9374 This tells the compiler to create, override or delete the named spec
9375 string. All lines after this directive up to the next directive or
9376 blank line are considered to be the text for the spec string. If this
9377 results in an empty string then the spec will be deleted. (Or, if the
9378 spec did not exist, then nothing will happened.) Otherwise, if the spec
9379 does not currently exist a new spec will be created. If the spec does
9380 exist then its contents will be overridden by the text of this
9381 directive, unless the first character of that text is the @samp{+}
9382 character, in which case the text will be appended to the spec.
9384 @item [@var{suffix}]:
9385 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
9386 and up to the next directive or blank line are considered to make up the
9387 spec string for the indicated suffix. When the compiler encounters an
9388 input file with the named suffix, it will processes the spec string in
9389 order to work out how to compile that file. For example:
9396 This says that any input file whose name ends in @samp{.ZZ} should be
9397 passed to the program @samp{z-compile}, which should be invoked with the
9398 command-line switch @option{-input} and with the result of performing the
9399 @samp{%i} substitution. (See below.)
9401 As an alternative to providing a spec string, the text that follows a
9402 suffix directive can be one of the following:
9405 @item @@@var{language}
9406 This says that the suffix is an alias for a known @var{language}. This is
9407 similar to using the @option{-x} command-line switch to GCC to specify a
9408 language explicitly. For example:
9415 Says that .ZZ files are, in fact, C++ source files.
9418 This causes an error messages saying:
9421 @var{name} compiler not installed on this system.
9425 GCC already has an extensive list of suffixes built into it.
9426 This directive will add an entry to the end of the list of suffixes, but
9427 since the list is searched from the end backwards, it is effectively
9428 possible to override earlier entries using this technique.
9432 GCC has the following spec strings built into it. Spec files can
9433 override these strings or create their own. Note that individual
9434 targets can also add their own spec strings to this list.
9437 asm Options to pass to the assembler
9438 asm_final Options to pass to the assembler post-processor
9439 cpp Options to pass to the C preprocessor
9440 cc1 Options to pass to the C compiler
9441 cc1plus Options to pass to the C++ compiler
9442 endfile Object files to include at the end of the link
9443 link Options to pass to the linker
9444 lib Libraries to include on the command line to the linker
9445 libgcc Decides which GCC support library to pass to the linker
9446 linker Sets the name of the linker
9447 predefines Defines to be passed to the C preprocessor
9448 signed_char Defines to pass to CPP to say whether @code{char} is signed
9450 startfile Object files to include at the start of the link
9453 Here is a small example of a spec file:
9459 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
9462 This example renames the spec called @samp{lib} to @samp{old_lib} and
9463 then overrides the previous definition of @samp{lib} with a new one.
9464 The new definition adds in some extra command-line options before
9465 including the text of the old definition.
9467 @dfn{Spec strings} are a list of command-line options to be passed to their
9468 corresponding program. In addition, the spec strings can contain
9469 @samp{%}-prefixed sequences to substitute variable text or to
9470 conditionally insert text into the command line. Using these constructs
9471 it is possible to generate quite complex command lines.
9473 Here is a table of all defined @samp{%}-sequences for spec
9474 strings. Note that spaces are not generated automatically around the
9475 results of expanding these sequences. Therefore you can concatenate them
9476 together or combine them with constant text in a single argument.
9480 Substitute one @samp{%} into the program name or argument.
9483 Substitute the name of the input file being processed.
9486 Substitute the basename of the input file being processed.
9487 This is the substring up to (and not including) the last period
9488 and not including the directory.
9491 This is the same as @samp{%b}, but include the file suffix (text after
9495 Marks the argument containing or following the @samp{%d} as a
9496 temporary file name, so that that file will be deleted if GCC exits
9497 successfully. Unlike @samp{%g}, this contributes no text to the
9500 @item %g@var{suffix}
9501 Substitute a file name that has suffix @var{suffix} and is chosen
9502 once per compilation, and mark the argument in the same way as
9503 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
9504 name is now chosen in a way that is hard to predict even when previously
9505 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
9506 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
9507 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
9508 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
9509 was simply substituted with a file name chosen once per compilation,
9510 without regard to any appended suffix (which was therefore treated
9511 just like ordinary text), making such attacks more likely to succeed.
9513 @item %u@var{suffix}
9514 Like @samp{%g}, but generates a new temporary file name even if
9515 @samp{%u@var{suffix}} was already seen.
9517 @item %U@var{suffix}
9518 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
9519 new one if there is no such last file name. In the absence of any
9520 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
9521 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
9522 would involve the generation of two distinct file names, one
9523 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
9524 simply substituted with a file name chosen for the previous @samp{%u},
9525 without regard to any appended suffix.
9527 @item %j@var{suffix}
9528 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
9529 writable, and if save-temps is off; otherwise, substitute the name
9530 of a temporary file, just like @samp{%u}. This temporary file is not
9531 meant for communication between processes, but rather as a junk
9534 @item %|@var{suffix}
9535 @itemx %m@var{suffix}
9536 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
9537 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
9538 all. These are the two most common ways to instruct a program that it
9539 should read from standard input or write to standard output. If you
9540 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
9541 construct: see for example @file{f/lang-specs.h}.
9543 @item %.@var{SUFFIX}
9544 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
9545 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
9546 terminated by the next space or %.
9549 Marks the argument containing or following the @samp{%w} as the
9550 designated output file of this compilation. This puts the argument
9551 into the sequence of arguments that @samp{%o} will substitute later.
9554 Substitutes the names of all the output files, with spaces
9555 automatically placed around them. You should write spaces
9556 around the @samp{%o} as well or the results are undefined.
9557 @samp{%o} is for use in the specs for running the linker.
9558 Input files whose names have no recognized suffix are not compiled
9559 at all, but they are included among the output files, so they will
9563 Substitutes the suffix for object files. Note that this is
9564 handled specially when it immediately follows @samp{%g, %u, or %U},
9565 because of the need for those to form complete file names. The
9566 handling is such that @samp{%O} is treated exactly as if it had already
9567 been substituted, except that @samp{%g, %u, and %U} do not currently
9568 support additional @var{suffix} characters following @samp{%O} as they would
9569 following, for example, @samp{.o}.
9572 Substitutes the standard macro predefinitions for the
9573 current target machine. Use this when running @code{cpp}.
9576 Like @samp{%p}, but puts @samp{__} before and after the name of each
9577 predefined macro, except for macros that start with @samp{__} or with
9578 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
9582 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
9583 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
9584 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
9585 and @option{-imultilib} as necessary.
9588 Current argument is the name of a library or startup file of some sort.
9589 Search for that file in a standard list of directories and substitute
9590 the full name found. The current working directory is included in the
9591 list of directories scanned.
9594 Current argument is the name of a linker script. Search for that file
9595 in the current list of directories to scan for libraries. If the file
9596 is located insert a @option{--script} option into the command line
9597 followed by the full path name found. If the file is not found then
9598 generate an error message. Note: the current working directory is not
9602 Print @var{str} as an error message. @var{str} is terminated by a newline.
9603 Use this when inconsistent options are detected.
9606 Substitute the contents of spec string @var{name} at this point.
9609 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
9611 @item %x@{@var{option}@}
9612 Accumulate an option for @samp{%X}.
9615 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
9619 Output the accumulated assembler options specified by @option{-Wa}.
9622 Output the accumulated preprocessor options specified by @option{-Wp}.
9625 Process the @code{asm} spec. This is used to compute the
9626 switches to be passed to the assembler.
9629 Process the @code{asm_final} spec. This is a spec string for
9630 passing switches to an assembler post-processor, if such a program is
9634 Process the @code{link} spec. This is the spec for computing the
9635 command line passed to the linker. Typically it will make use of the
9636 @samp{%L %G %S %D and %E} sequences.
9639 Dump out a @option{-L} option for each directory that GCC believes might
9640 contain startup files. If the target supports multilibs then the
9641 current multilib directory will be prepended to each of these paths.
9644 Process the @code{lib} spec. This is a spec string for deciding which
9645 libraries should be included on the command line to the linker.
9648 Process the @code{libgcc} spec. This is a spec string for deciding
9649 which GCC support library should be included on the command line to the linker.
9652 Process the @code{startfile} spec. This is a spec for deciding which
9653 object files should be the first ones passed to the linker. Typically
9654 this might be a file named @file{crt0.o}.
9657 Process the @code{endfile} spec. This is a spec string that specifies
9658 the last object files that will be passed to the linker.
9661 Process the @code{cpp} spec. This is used to construct the arguments
9662 to be passed to the C preprocessor.
9665 Process the @code{cc1} spec. This is used to construct the options to be
9666 passed to the actual C compiler (@samp{cc1}).
9669 Process the @code{cc1plus} spec. This is used to construct the options to be
9670 passed to the actual C++ compiler (@samp{cc1plus}).
9673 Substitute the variable part of a matched option. See below.
9674 Note that each comma in the substituted string is replaced by
9678 Remove all occurrences of @code{-S} from the command line. Note---this
9679 command is position dependent. @samp{%} commands in the spec string
9680 before this one will see @code{-S}, @samp{%} commands in the spec string
9681 after this one will not.
9683 @item %:@var{function}(@var{args})
9684 Call the named function @var{function}, passing it @var{args}.
9685 @var{args} is first processed as a nested spec string, then split
9686 into an argument vector in the usual fashion. The function returns
9687 a string which is processed as if it had appeared literally as part
9688 of the current spec.
9690 The following built-in spec functions are provided:
9694 The @code{getenv} spec function takes two arguments: an environment
9695 variable name and a string. If the environment variable is not
9696 defined, a fatal error is issued. Otherwise, the return value is the
9697 value of the environment variable concatenated with the string. For
9698 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
9701 %:getenv(TOPDIR /include)
9704 expands to @file{/path/to/top/include}.
9706 @item @code{if-exists}
9707 The @code{if-exists} spec function takes one argument, an absolute
9708 pathname to a file. If the file exists, @code{if-exists} returns the
9709 pathname. Here is a small example of its usage:
9713 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
9716 @item @code{if-exists-else}
9717 The @code{if-exists-else} spec function is similar to the @code{if-exists}
9718 spec function, except that it takes two arguments. The first argument is
9719 an absolute pathname to a file. If the file exists, @code{if-exists-else}
9720 returns the pathname. If it does not exist, it returns the second argument.
9721 This way, @code{if-exists-else} can be used to select one file or another,
9722 based on the existence of the first. Here is a small example of its usage:
9726 crt0%O%s %:if-exists(crti%O%s) \
9727 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
9730 @item @code{replace-outfile}
9731 The @code{replace-outfile} spec function takes two arguments. It looks for the
9732 first argument in the outfiles array and replaces it with the second argument. Here
9733 is a small example of its usage:
9736 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
9739 @item @code{remove-outfile}
9740 The @code{remove-outfile} spec function takes one argument. It looks for the
9741 first argument in the outfiles array and removes it. Here is a small example
9745 %:remove-outfile(-lm)
9748 @item @code{pass-through-libs}
9749 The @code{pass-through-libs} spec function takes any number of arguments. It
9750 finds any @option{-l} options and any non-options ending in ".a" (which it
9751 assumes are the names of linker input library archive files) and returns a
9752 result containing all the found arguments each prepended by
9753 @option{-plugin-opt=-pass-through=} and joined by spaces. This list is
9754 intended to be passed to the LTO linker plugin.
9757 %:pass-through-libs(%G %L %G)
9760 @item @code{print-asm-header}
9761 The @code{print-asm-header} function takes no arguments and simply
9762 prints a banner like:
9768 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
9771 It is used to separate compiler options from assembler options
9772 in the @option{--target-help} output.
9776 Substitutes the @code{-S} switch, if that switch was given to GCC@.
9777 If that switch was not specified, this substitutes nothing. Note that
9778 the leading dash is omitted when specifying this option, and it is
9779 automatically inserted if the substitution is performed. Thus the spec
9780 string @samp{%@{foo@}} would match the command-line option @option{-foo}
9781 and would output the command line option @option{-foo}.
9783 @item %W@{@code{S}@}
9784 Like %@{@code{S}@} but mark last argument supplied within as a file to be
9787 @item %@{@code{S}*@}
9788 Substitutes all the switches specified to GCC whose names start
9789 with @code{-S}, but which also take an argument. This is used for
9790 switches like @option{-o}, @option{-D}, @option{-I}, etc.
9791 GCC considers @option{-o foo} as being
9792 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
9793 text, including the space. Thus two arguments would be generated.
9795 @item %@{@code{S}*&@code{T}*@}
9796 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
9797 (the order of @code{S} and @code{T} in the spec is not significant).
9798 There can be any number of ampersand-separated variables; for each the
9799 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
9801 @item %@{@code{S}:@code{X}@}
9802 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
9804 @item %@{!@code{S}:@code{X}@}
9805 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
9807 @item %@{@code{S}*:@code{X}@}
9808 Substitutes @code{X} if one or more switches whose names start with
9809 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
9810 once, no matter how many such switches appeared. However, if @code{%*}
9811 appears somewhere in @code{X}, then @code{X} will be substituted once
9812 for each matching switch, with the @code{%*} replaced by the part of
9813 that switch that matched the @code{*}.
9815 @item %@{.@code{S}:@code{X}@}
9816 Substitutes @code{X}, if processing a file with suffix @code{S}.
9818 @item %@{!.@code{S}:@code{X}@}
9819 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
9821 @item %@{,@code{S}:@code{X}@}
9822 Substitutes @code{X}, if processing a file for language @code{S}.
9824 @item %@{!,@code{S}:@code{X}@}
9825 Substitutes @code{X}, if not processing a file for language @code{S}.
9827 @item %@{@code{S}|@code{P}:@code{X}@}
9828 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
9829 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
9830 @code{*} sequences as well, although they have a stronger binding than
9831 the @samp{|}. If @code{%*} appears in @code{X}, all of the
9832 alternatives must be starred, and only the first matching alternative
9835 For example, a spec string like this:
9838 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
9841 will output the following command-line options from the following input
9842 command-line options:
9847 -d fred.c -foo -baz -boggle
9848 -d jim.d -bar -baz -boggle
9851 @item %@{S:X; T:Y; :D@}
9853 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
9854 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
9855 be as many clauses as you need. This may be combined with @code{.},
9856 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
9861 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
9862 construct may contain other nested @samp{%} constructs or spaces, or
9863 even newlines. They are processed as usual, as described above.
9864 Trailing white space in @code{X} is ignored. White space may also
9865 appear anywhere on the left side of the colon in these constructs,
9866 except between @code{.} or @code{*} and the corresponding word.
9868 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
9869 handled specifically in these constructs. If another value of
9870 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
9871 @option{-W} switch is found later in the command line, the earlier
9872 switch value is ignored, except with @{@code{S}*@} where @code{S} is
9873 just one letter, which passes all matching options.
9875 The character @samp{|} at the beginning of the predicate text is used to
9876 indicate that a command should be piped to the following command, but
9877 only if @option{-pipe} is specified.
9879 It is built into GCC which switches take arguments and which do not.
9880 (You might think it would be useful to generalize this to allow each
9881 compiler's spec to say which switches take arguments. But this cannot
9882 be done in a consistent fashion. GCC cannot even decide which input
9883 files have been specified without knowing which switches take arguments,
9884 and it must know which input files to compile in order to tell which
9887 GCC also knows implicitly that arguments starting in @option{-l} are to be
9888 treated as compiler output files, and passed to the linker in their
9889 proper position among the other output files.
9891 @c man begin OPTIONS
9893 @node Target Options
9894 @section Specifying Target Machine and Compiler Version
9895 @cindex target options
9896 @cindex cross compiling
9897 @cindex specifying machine version
9898 @cindex specifying compiler version and target machine
9899 @cindex compiler version, specifying
9900 @cindex target machine, specifying
9902 The usual way to run GCC is to run the executable called @command{gcc}, or
9903 @command{@var{machine}-gcc} when cross-compiling, or
9904 @command{@var{machine}-gcc-@var{version}} to run a version other than the
9905 one that was installed last.
9907 @node Submodel Options
9908 @section Hardware Models and Configurations
9909 @cindex submodel options
9910 @cindex specifying hardware config
9911 @cindex hardware models and configurations, specifying
9912 @cindex machine dependent options
9914 Each target machine types can have its own
9915 special options, starting with @samp{-m}, to choose among various
9916 hardware models or configurations---for example, 68010 vs 68020,
9917 floating coprocessor or none. A single installed version of the
9918 compiler can compile for any model or configuration, according to the
9921 Some configurations of the compiler also support additional special
9922 options, usually for compatibility with other compilers on the same
9925 @c This list is ordered alphanumerically by subsection name.
9926 @c It should be the same order and spelling as these options are listed
9927 @c in Machine Dependent Options
9932 * Blackfin Options::
9935 * DEC Alpha Options::
9936 * DEC Alpha/VMS Options::
9939 * GNU/Linux Options::
9942 * i386 and x86-64 Options::
9943 * i386 and x86-64 Windows Options::
9945 * IA-64/VMS Options::
9952 * MicroBlaze Options::
9957 * picoChip Options::
9959 * RS/6000 and PowerPC Options::
9961 * S/390 and zSeries Options::
9964 * Solaris 2 Options::
9967 * System V Options::
9972 * Xstormy16 Options::
9978 @subsection ARM Options
9981 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
9985 @item -mabi=@var{name}
9987 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
9988 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
9991 @opindex mapcs-frame
9992 Generate a stack frame that is compliant with the ARM Procedure Call
9993 Standard for all functions, even if this is not strictly necessary for
9994 correct execution of the code. Specifying @option{-fomit-frame-pointer}
9995 with this option will cause the stack frames not to be generated for
9996 leaf functions. The default is @option{-mno-apcs-frame}.
10000 This is a synonym for @option{-mapcs-frame}.
10003 @c not currently implemented
10004 @item -mapcs-stack-check
10005 @opindex mapcs-stack-check
10006 Generate code to check the amount of stack space available upon entry to
10007 every function (that actually uses some stack space). If there is
10008 insufficient space available then either the function
10009 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
10010 called, depending upon the amount of stack space required. The run time
10011 system is required to provide these functions. The default is
10012 @option{-mno-apcs-stack-check}, since this produces smaller code.
10014 @c not currently implemented
10016 @opindex mapcs-float
10017 Pass floating point arguments using the float point registers. This is
10018 one of the variants of the APCS@. This option is recommended if the
10019 target hardware has a floating point unit or if a lot of floating point
10020 arithmetic is going to be performed by the code. The default is
10021 @option{-mno-apcs-float}, since integer only code is slightly increased in
10022 size if @option{-mapcs-float} is used.
10024 @c not currently implemented
10025 @item -mapcs-reentrant
10026 @opindex mapcs-reentrant
10027 Generate reentrant, position independent code. The default is
10028 @option{-mno-apcs-reentrant}.
10031 @item -mthumb-interwork
10032 @opindex mthumb-interwork
10033 Generate code which supports calling between the ARM and Thumb
10034 instruction sets. Without this option the two instruction sets cannot
10035 be reliably used inside one program. The default is
10036 @option{-mno-thumb-interwork}, since slightly larger code is generated
10037 when @option{-mthumb-interwork} is specified.
10039 @item -mno-sched-prolog
10040 @opindex mno-sched-prolog
10041 Prevent the reordering of instructions in the function prolog, or the
10042 merging of those instruction with the instructions in the function's
10043 body. This means that all functions will start with a recognizable set
10044 of instructions (or in fact one of a choice from a small set of
10045 different function prologues), and this information can be used to
10046 locate the start if functions inside an executable piece of code. The
10047 default is @option{-msched-prolog}.
10049 @item -mfloat-abi=@var{name}
10050 @opindex mfloat-abi
10051 Specifies which floating-point ABI to use. Permissible values
10052 are: @samp{soft}, @samp{softfp} and @samp{hard}.
10054 Specifying @samp{soft} causes GCC to generate output containing
10055 library calls for floating-point operations.
10056 @samp{softfp} allows the generation of code using hardware floating-point
10057 instructions, but still uses the soft-float calling conventions.
10058 @samp{hard} allows generation of floating-point instructions
10059 and uses FPU-specific calling conventions.
10061 The default depends on the specific target configuration. Note that
10062 the hard-float and soft-float ABIs are not link-compatible; you must
10063 compile your entire program with the same ABI, and link with a
10064 compatible set of libraries.
10067 @opindex mhard-float
10068 Equivalent to @option{-mfloat-abi=hard}.
10071 @opindex msoft-float
10072 Equivalent to @option{-mfloat-abi=soft}.
10074 @item -mlittle-endian
10075 @opindex mlittle-endian
10076 Generate code for a processor running in little-endian mode. This is
10077 the default for all standard configurations.
10080 @opindex mbig-endian
10081 Generate code for a processor running in big-endian mode; the default is
10082 to compile code for a little-endian processor.
10084 @item -mwords-little-endian
10085 @opindex mwords-little-endian
10086 This option only applies when generating code for big-endian processors.
10087 Generate code for a little-endian word order but a big-endian byte
10088 order. That is, a byte order of the form @samp{32107654}. Note: this
10089 option should only be used if you require compatibility with code for
10090 big-endian ARM processors generated by versions of the compiler prior to
10093 @item -mcpu=@var{name}
10095 This specifies the name of the target ARM processor. GCC uses this name
10096 to determine what kind of instructions it can emit when generating
10097 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
10098 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
10099 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
10100 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
10101 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
10103 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
10104 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
10105 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
10106 @samp{strongarm1110},
10107 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
10108 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
10109 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
10110 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
10111 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
10112 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
10113 @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
10114 @samp{cortex-a5}, @samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a15},
10115 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m4}, @samp{cortex-m3},
10118 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
10120 @item -mtune=@var{name}
10122 This option is very similar to the @option{-mcpu=} option, except that
10123 instead of specifying the actual target processor type, and hence
10124 restricting which instructions can be used, it specifies that GCC should
10125 tune the performance of the code as if the target were of the type
10126 specified in this option, but still choosing the instructions that it
10127 will generate based on the CPU specified by a @option{-mcpu=} option.
10128 For some ARM implementations better performance can be obtained by using
10131 @item -march=@var{name}
10133 This specifies the name of the target ARM architecture. GCC uses this
10134 name to determine what kind of instructions it can emit when generating
10135 assembly code. This option can be used in conjunction with or instead
10136 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
10137 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
10138 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
10139 @samp{armv6}, @samp{armv6j},
10140 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
10141 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
10142 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
10144 @item -mfpu=@var{name}
10145 @itemx -mfpe=@var{number}
10146 @itemx -mfp=@var{number}
10150 This specifies what floating point hardware (or hardware emulation) is
10151 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
10152 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-fp16},
10153 @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, @samp{vfpv3xd-fp16},
10154 @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, @samp{vfpv4-d16},
10155 @samp{fpv4-sp-d16} and @samp{neon-vfpv4}.
10156 @option{-mfp} and @option{-mfpe} are synonyms for
10157 @option{-mfpu}=@samp{fpe}@var{number}, for compatibility with older versions
10160 If @option{-msoft-float} is specified this specifies the format of
10161 floating point values.
10163 If the selected floating-point hardware includes the NEON extension
10164 (e.g. @option{-mfpu}=@samp{neon}), note that floating-point
10165 operations will not be used by GCC's auto-vectorization pass unless
10166 @option{-funsafe-math-optimizations} is also specified. This is
10167 because NEON hardware does not fully implement the IEEE 754 standard for
10168 floating-point arithmetic (in particular denormal values are treated as
10169 zero), so the use of NEON instructions may lead to a loss of precision.
10171 @item -mfp16-format=@var{name}
10172 @opindex mfp16-format
10173 Specify the format of the @code{__fp16} half-precision floating-point type.
10174 Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
10175 the default is @samp{none}, in which case the @code{__fp16} type is not
10176 defined. @xref{Half-Precision}, for more information.
10178 @item -mstructure-size-boundary=@var{n}
10179 @opindex mstructure-size-boundary
10180 The size of all structures and unions will be rounded up to a multiple
10181 of the number of bits set by this option. Permissible values are 8, 32
10182 and 64. The default value varies for different toolchains. For the COFF
10183 targeted toolchain the default value is 8. A value of 64 is only allowed
10184 if the underlying ABI supports it.
10186 Specifying the larger number can produce faster, more efficient code, but
10187 can also increase the size of the program. Different values are potentially
10188 incompatible. Code compiled with one value cannot necessarily expect to
10189 work with code or libraries compiled with another value, if they exchange
10190 information using structures or unions.
10192 @item -mabort-on-noreturn
10193 @opindex mabort-on-noreturn
10194 Generate a call to the function @code{abort} at the end of a
10195 @code{noreturn} function. It will be executed if the function tries to
10199 @itemx -mno-long-calls
10200 @opindex mlong-calls
10201 @opindex mno-long-calls
10202 Tells the compiler to perform function calls by first loading the
10203 address of the function into a register and then performing a subroutine
10204 call on this register. This switch is needed if the target function
10205 will lie outside of the 64 megabyte addressing range of the offset based
10206 version of subroutine call instruction.
10208 Even if this switch is enabled, not all function calls will be turned
10209 into long calls. The heuristic is that static functions, functions
10210 which have the @samp{short-call} attribute, functions that are inside
10211 the scope of a @samp{#pragma no_long_calls} directive and functions whose
10212 definitions have already been compiled within the current compilation
10213 unit, will not be turned into long calls. The exception to this rule is
10214 that weak function definitions, functions with the @samp{long-call}
10215 attribute or the @samp{section} attribute, and functions that are within
10216 the scope of a @samp{#pragma long_calls} directive, will always be
10217 turned into long calls.
10219 This feature is not enabled by default. Specifying
10220 @option{-mno-long-calls} will restore the default behavior, as will
10221 placing the function calls within the scope of a @samp{#pragma
10222 long_calls_off} directive. Note these switches have no effect on how
10223 the compiler generates code to handle function calls via function
10226 @item -msingle-pic-base
10227 @opindex msingle-pic-base
10228 Treat the register used for PIC addressing as read-only, rather than
10229 loading it in the prologue for each function. The run-time system is
10230 responsible for initializing this register with an appropriate value
10231 before execution begins.
10233 @item -mpic-register=@var{reg}
10234 @opindex mpic-register
10235 Specify the register to be used for PIC addressing. The default is R10
10236 unless stack-checking is enabled, when R9 is used.
10238 @item -mcirrus-fix-invalid-insns
10239 @opindex mcirrus-fix-invalid-insns
10240 @opindex mno-cirrus-fix-invalid-insns
10241 Insert NOPs into the instruction stream to in order to work around
10242 problems with invalid Maverick instruction combinations. This option
10243 is only valid if the @option{-mcpu=ep9312} option has been used to
10244 enable generation of instructions for the Cirrus Maverick floating
10245 point co-processor. This option is not enabled by default, since the
10246 problem is only present in older Maverick implementations. The default
10247 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
10250 @item -mpoke-function-name
10251 @opindex mpoke-function-name
10252 Write the name of each function into the text section, directly
10253 preceding the function prologue. The generated code is similar to this:
10257 .ascii "arm_poke_function_name", 0
10260 .word 0xff000000 + (t1 - t0)
10261 arm_poke_function_name
10263 stmfd sp!, @{fp, ip, lr, pc@}
10267 When performing a stack backtrace, code can inspect the value of
10268 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
10269 location @code{pc - 12} and the top 8 bits are set, then we know that
10270 there is a function name embedded immediately preceding this location
10271 and has length @code{((pc[-3]) & 0xff000000)}.
10275 Generate code for the Thumb instruction set. The default is to
10276 use the 32-bit ARM instruction set.
10277 This option automatically enables either 16-bit Thumb-1 or
10278 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
10279 and @option{-march=@var{name}} options. This option is not passed to the
10280 assembler. If you want to force assembler files to be interpreted as Thumb code,
10281 either add a @samp{.thumb} directive to the source or pass the @option{-mthumb}
10282 option directly to the assembler by prefixing it with @option{-Wa}.
10285 @opindex mtpcs-frame
10286 Generate a stack frame that is compliant with the Thumb Procedure Call
10287 Standard for all non-leaf functions. (A leaf function is one that does
10288 not call any other functions.) The default is @option{-mno-tpcs-frame}.
10290 @item -mtpcs-leaf-frame
10291 @opindex mtpcs-leaf-frame
10292 Generate a stack frame that is compliant with the Thumb Procedure Call
10293 Standard for all leaf functions. (A leaf function is one that does
10294 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
10296 @item -mcallee-super-interworking
10297 @opindex mcallee-super-interworking
10298 Gives all externally visible functions in the file being compiled an ARM
10299 instruction set header which switches to Thumb mode before executing the
10300 rest of the function. This allows these functions to be called from
10301 non-interworking code. This option is not valid in AAPCS configurations
10302 because interworking is enabled by default.
10304 @item -mcaller-super-interworking
10305 @opindex mcaller-super-interworking
10306 Allows calls via function pointers (including virtual functions) to
10307 execute correctly regardless of whether the target code has been
10308 compiled for interworking or not. There is a small overhead in the cost
10309 of executing a function pointer if this option is enabled. This option
10310 is not valid in AAPCS configurations because interworking is enabled
10313 @item -mtp=@var{name}
10315 Specify the access model for the thread local storage pointer. The valid
10316 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
10317 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
10318 (supported in the arm6k architecture), and @option{auto}, which uses the
10319 best available method for the selected processor. The default setting is
10322 @item -mword-relocations
10323 @opindex mword-relocations
10324 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
10325 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
10326 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
10329 @item -mfix-cortex-m3-ldrd
10330 @opindex mfix-cortex-m3-ldrd
10331 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
10332 with overlapping destination and base registers are used. This option avoids
10333 generating these instructions. This option is enabled by default when
10334 @option{-mcpu=cortex-m3} is specified.
10339 @subsection AVR Options
10340 @cindex AVR Options
10342 These options are defined for AVR implementations:
10345 @item -mmcu=@var{mcu}
10347 Specify ATMEL AVR instruction set or MCU type.
10349 Instruction set avr1 is for the minimal AVR core, not supported by the C
10350 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
10351 attiny11, attiny12, attiny15, attiny28).
10353 Instruction set avr2 (default) is for the classic AVR core with up to
10354 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
10355 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
10356 at90c8534, at90s8535).
10358 Instruction set avr3 is for the classic AVR core with up to 128K program
10359 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
10361 Instruction set avr4 is for the enhanced AVR core with up to 8K program
10362 memory space (MCU types: atmega8, atmega83, atmega85).
10364 Instruction set avr5 is for the enhanced AVR core with up to 128K program
10365 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
10366 atmega64, atmega128, at43usb355, at94k).
10368 @item -mno-interrupts
10369 @opindex mno-interrupts
10370 Generated code is not compatible with hardware interrupts.
10371 Code size will be smaller.
10373 @item -mcall-prologues
10374 @opindex mcall-prologues
10375 Functions prologues/epilogues expanded as call to appropriate
10376 subroutines. Code size will be smaller.
10379 @opindex mtiny-stack
10380 Change only the low 8 bits of the stack pointer.
10384 Assume int to be 8 bit integer. This affects the sizes of all types: A
10385 char will be 1 byte, an int will be 1 byte, a long will be 2 bytes
10386 and long long will be 4 bytes. Please note that this option does not
10387 comply to the C standards, but it will provide you with smaller code
10391 @node Blackfin Options
10392 @subsection Blackfin Options
10393 @cindex Blackfin Options
10396 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
10398 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
10399 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
10400 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
10401 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
10402 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
10403 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
10404 @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
10406 The optional @var{sirevision} specifies the silicon revision of the target
10407 Blackfin processor. Any workarounds available for the targeted silicon revision
10408 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
10409 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
10410 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
10411 hexadecimal digits representing the major and minor numbers in the silicon
10412 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
10413 is not defined. If @var{sirevision} is @samp{any}, the
10414 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
10415 If this optional @var{sirevision} is not used, GCC assumes the latest known
10416 silicon revision of the targeted Blackfin processor.
10418 Support for @samp{bf561} is incomplete. For @samp{bf561},
10419 Only the processor macro is defined.
10420 Without this option, @samp{bf532} is used as the processor by default.
10421 The corresponding predefined processor macros for @var{cpu} is to
10422 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
10423 provided by libgloss to be linked in if @option{-msim} is not given.
10427 Specifies that the program will be run on the simulator. This causes
10428 the simulator BSP provided by libgloss to be linked in. This option
10429 has effect only for @samp{bfin-elf} toolchain.
10430 Certain other options, such as @option{-mid-shared-library} and
10431 @option{-mfdpic}, imply @option{-msim}.
10433 @item -momit-leaf-frame-pointer
10434 @opindex momit-leaf-frame-pointer
10435 Don't keep the frame pointer in a register for leaf functions. This
10436 avoids the instructions to save, set up and restore frame pointers and
10437 makes an extra register available in leaf functions. The option
10438 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10439 which might make debugging harder.
10441 @item -mspecld-anomaly
10442 @opindex mspecld-anomaly
10443 When enabled, the compiler will ensure that the generated code does not
10444 contain speculative loads after jump instructions. If this option is used,
10445 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
10447 @item -mno-specld-anomaly
10448 @opindex mno-specld-anomaly
10449 Don't generate extra code to prevent speculative loads from occurring.
10451 @item -mcsync-anomaly
10452 @opindex mcsync-anomaly
10453 When enabled, the compiler will ensure that the generated code does not
10454 contain CSYNC or SSYNC instructions too soon after conditional branches.
10455 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
10457 @item -mno-csync-anomaly
10458 @opindex mno-csync-anomaly
10459 Don't generate extra code to prevent CSYNC or SSYNC instructions from
10460 occurring too soon after a conditional branch.
10464 When enabled, the compiler is free to take advantage of the knowledge that
10465 the entire program fits into the low 64k of memory.
10468 @opindex mno-low-64k
10469 Assume that the program is arbitrarily large. This is the default.
10471 @item -mstack-check-l1
10472 @opindex mstack-check-l1
10473 Do stack checking using information placed into L1 scratchpad memory by the
10476 @item -mid-shared-library
10477 @opindex mid-shared-library
10478 Generate code that supports shared libraries via the library ID method.
10479 This allows for execute in place and shared libraries in an environment
10480 without virtual memory management. This option implies @option{-fPIC}.
10481 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10483 @item -mno-id-shared-library
10484 @opindex mno-id-shared-library
10485 Generate code that doesn't assume ID based shared libraries are being used.
10486 This is the default.
10488 @item -mleaf-id-shared-library
10489 @opindex mleaf-id-shared-library
10490 Generate code that supports shared libraries via the library ID method,
10491 but assumes that this library or executable won't link against any other
10492 ID shared libraries. That allows the compiler to use faster code for jumps
10495 @item -mno-leaf-id-shared-library
10496 @opindex mno-leaf-id-shared-library
10497 Do not assume that the code being compiled won't link against any ID shared
10498 libraries. Slower code will be generated for jump and call insns.
10500 @item -mshared-library-id=n
10501 @opindex mshared-library-id
10502 Specified the identification number of the ID based shared library being
10503 compiled. Specifying a value of 0 will generate more compact code, specifying
10504 other values will force the allocation of that number to the current
10505 library but is no more space or time efficient than omitting this option.
10509 Generate code that allows the data segment to be located in a different
10510 area of memory from the text segment. This allows for execute in place in
10511 an environment without virtual memory management by eliminating relocations
10512 against the text section.
10514 @item -mno-sep-data
10515 @opindex mno-sep-data
10516 Generate code that assumes that the data segment follows the text segment.
10517 This is the default.
10520 @itemx -mno-long-calls
10521 @opindex mlong-calls
10522 @opindex mno-long-calls
10523 Tells the compiler to perform function calls by first loading the
10524 address of the function into a register and then performing a subroutine
10525 call on this register. This switch is needed if the target function
10526 will lie outside of the 24 bit addressing range of the offset based
10527 version of subroutine call instruction.
10529 This feature is not enabled by default. Specifying
10530 @option{-mno-long-calls} will restore the default behavior. Note these
10531 switches have no effect on how the compiler generates code to handle
10532 function calls via function pointers.
10536 Link with the fast floating-point library. This library relaxes some of
10537 the IEEE floating-point standard's rules for checking inputs against
10538 Not-a-Number (NAN), in the interest of performance.
10541 @opindex minline-plt
10542 Enable inlining of PLT entries in function calls to functions that are
10543 not known to bind locally. It has no effect without @option{-mfdpic}.
10546 @opindex mmulticore
10547 Build standalone application for multicore Blackfin processor. Proper
10548 start files and link scripts will be used to support multicore.
10549 This option defines @code{__BFIN_MULTICORE}. It can only be used with
10550 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
10551 @option{-mcorea} or @option{-mcoreb}. If it's used without
10552 @option{-mcorea} or @option{-mcoreb}, single application/dual core
10553 programming model is used. In this model, the main function of Core B
10554 should be named as coreb_main. If it's used with @option{-mcorea} or
10555 @option{-mcoreb}, one application per core programming model is used.
10556 If this option is not used, single core application programming
10561 Build standalone application for Core A of BF561 when using
10562 one application per core programming model. Proper start files
10563 and link scripts will be used to support Core A. This option
10564 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
10568 Build standalone application for Core B of BF561 when using
10569 one application per core programming model. Proper start files
10570 and link scripts will be used to support Core B. This option
10571 defines @code{__BFIN_COREB}. When this option is used, coreb_main
10572 should be used instead of main. It must be used with
10573 @option{-mmulticore}.
10577 Build standalone application for SDRAM. Proper start files and
10578 link scripts will be used to put the application into SDRAM.
10579 Loader should initialize SDRAM before loading the application
10580 into SDRAM. This option defines @code{__BFIN_SDRAM}.
10584 Assume that ICPLBs are enabled at runtime. This has an effect on certain
10585 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
10586 are enabled; for standalone applications the default is off.
10590 @subsection CRIS Options
10591 @cindex CRIS Options
10593 These options are defined specifically for the CRIS ports.
10596 @item -march=@var{architecture-type}
10597 @itemx -mcpu=@var{architecture-type}
10600 Generate code for the specified architecture. The choices for
10601 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10602 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
10603 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10606 @item -mtune=@var{architecture-type}
10608 Tune to @var{architecture-type} everything applicable about the generated
10609 code, except for the ABI and the set of available instructions. The
10610 choices for @var{architecture-type} are the same as for
10611 @option{-march=@var{architecture-type}}.
10613 @item -mmax-stack-frame=@var{n}
10614 @opindex mmax-stack-frame
10615 Warn when the stack frame of a function exceeds @var{n} bytes.
10621 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10622 @option{-march=v3} and @option{-march=v8} respectively.
10624 @item -mmul-bug-workaround
10625 @itemx -mno-mul-bug-workaround
10626 @opindex mmul-bug-workaround
10627 @opindex mno-mul-bug-workaround
10628 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
10629 models where it applies. This option is active by default.
10633 Enable CRIS-specific verbose debug-related information in the assembly
10634 code. This option also has the effect to turn off the @samp{#NO_APP}
10635 formatted-code indicator to the assembler at the beginning of the
10640 Do not use condition-code results from previous instruction; always emit
10641 compare and test instructions before use of condition codes.
10643 @item -mno-side-effects
10644 @opindex mno-side-effects
10645 Do not emit instructions with side-effects in addressing modes other than
10648 @item -mstack-align
10649 @itemx -mno-stack-align
10650 @itemx -mdata-align
10651 @itemx -mno-data-align
10652 @itemx -mconst-align
10653 @itemx -mno-const-align
10654 @opindex mstack-align
10655 @opindex mno-stack-align
10656 @opindex mdata-align
10657 @opindex mno-data-align
10658 @opindex mconst-align
10659 @opindex mno-const-align
10660 These options (no-options) arranges (eliminate arrangements) for the
10661 stack-frame, individual data and constants to be aligned for the maximum
10662 single data access size for the chosen CPU model. The default is to
10663 arrange for 32-bit alignment. ABI details such as structure layout are
10664 not affected by these options.
10672 Similar to the stack- data- and const-align options above, these options
10673 arrange for stack-frame, writable data and constants to all be 32-bit,
10674 16-bit or 8-bit aligned. The default is 32-bit alignment.
10676 @item -mno-prologue-epilogue
10677 @itemx -mprologue-epilogue
10678 @opindex mno-prologue-epilogue
10679 @opindex mprologue-epilogue
10680 With @option{-mno-prologue-epilogue}, the normal function prologue and
10681 epilogue that sets up the stack-frame are omitted and no return
10682 instructions or return sequences are generated in the code. Use this
10683 option only together with visual inspection of the compiled code: no
10684 warnings or errors are generated when call-saved registers must be saved,
10685 or storage for local variable needs to be allocated.
10689 @opindex mno-gotplt
10691 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10692 instruction sequences that load addresses for functions from the PLT part
10693 of the GOT rather than (traditional on other architectures) calls to the
10694 PLT@. The default is @option{-mgotplt}.
10698 Legacy no-op option only recognized with the cris-axis-elf and
10699 cris-axis-linux-gnu targets.
10703 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10707 This option, recognized for the cris-axis-elf arranges
10708 to link with input-output functions from a simulator library. Code,
10709 initialized data and zero-initialized data are allocated consecutively.
10713 Like @option{-sim}, but pass linker options to locate initialized data at
10714 0x40000000 and zero-initialized data at 0x80000000.
10717 @node Darwin Options
10718 @subsection Darwin Options
10719 @cindex Darwin options
10721 These options are defined for all architectures running the Darwin operating
10724 FSF GCC on Darwin does not create ``fat'' object files; it will create
10725 an object file for the single architecture that it was built to
10726 target. Apple's GCC on Darwin does create ``fat'' files if multiple
10727 @option{-arch} options are used; it does so by running the compiler or
10728 linker multiple times and joining the results together with
10731 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
10732 @samp{i686}) is determined by the flags that specify the ISA
10733 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
10734 @option{-force_cpusubtype_ALL} option can be used to override this.
10736 The Darwin tools vary in their behavior when presented with an ISA
10737 mismatch. The assembler, @file{as}, will only permit instructions to
10738 be used that are valid for the subtype of the file it is generating,
10739 so you cannot put 64-bit instructions in a @samp{ppc750} object file.
10740 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
10741 and print an error if asked to create a shared library with a less
10742 restrictive subtype than its input files (for instance, trying to put
10743 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
10744 for executables, @file{ld}, will quietly give the executable the most
10745 restrictive subtype of any of its input files.
10750 Add the framework directory @var{dir} to the head of the list of
10751 directories to be searched for header files. These directories are
10752 interleaved with those specified by @option{-I} options and are
10753 scanned in a left-to-right order.
10755 A framework directory is a directory with frameworks in it. A
10756 framework is a directory with a @samp{"Headers"} and/or
10757 @samp{"PrivateHeaders"} directory contained directly in it that ends
10758 in @samp{".framework"}. The name of a framework is the name of this
10759 directory excluding the @samp{".framework"}. Headers associated with
10760 the framework are found in one of those two directories, with
10761 @samp{"Headers"} being searched first. A subframework is a framework
10762 directory that is in a framework's @samp{"Frameworks"} directory.
10763 Includes of subframework headers can only appear in a header of a
10764 framework that contains the subframework, or in a sibling subframework
10765 header. Two subframeworks are siblings if they occur in the same
10766 framework. A subframework should not have the same name as a
10767 framework, a warning will be issued if this is violated. Currently a
10768 subframework cannot have subframeworks, in the future, the mechanism
10769 may be extended to support this. The standard frameworks can be found
10770 in @samp{"/System/Library/Frameworks"} and
10771 @samp{"/Library/Frameworks"}. An example include looks like
10772 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
10773 the name of the framework and header.h is found in the
10774 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
10776 @item -iframework@var{dir}
10777 @opindex iframework
10778 Like @option{-F} except the directory is a treated as a system
10779 directory. The main difference between this @option{-iframework} and
10780 @option{-F} is that with @option{-iframework} the compiler does not
10781 warn about constructs contained within header files found via
10782 @var{dir}. This option is valid only for the C family of languages.
10786 Emit debugging information for symbols that are used. For STABS
10787 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
10788 This is by default ON@.
10792 Emit debugging information for all symbols and types.
10794 @item -mmacosx-version-min=@var{version}
10795 The earliest version of MacOS X that this executable will run on
10796 is @var{version}. Typical values of @var{version} include @code{10.1},
10797 @code{10.2}, and @code{10.3.9}.
10799 If the compiler was built to use the system's headers by default,
10800 then the default for this option is the system version on which the
10801 compiler is running, otherwise the default is to make choices which
10802 are compatible with as many systems and code bases as possible.
10806 Enable kernel development mode. The @option{-mkernel} option sets
10807 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
10808 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
10809 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
10810 applicable. This mode also sets @option{-mno-altivec},
10811 @option{-msoft-float}, @option{-fno-builtin} and
10812 @option{-mlong-branch} for PowerPC targets.
10814 @item -mone-byte-bool
10815 @opindex mone-byte-bool
10816 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
10817 By default @samp{sizeof(bool)} is @samp{4} when compiling for
10818 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
10819 option has no effect on x86.
10821 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
10822 to generate code that is not binary compatible with code generated
10823 without that switch. Using this switch may require recompiling all
10824 other modules in a program, including system libraries. Use this
10825 switch to conform to a non-default data model.
10827 @item -mfix-and-continue
10828 @itemx -ffix-and-continue
10829 @itemx -findirect-data
10830 @opindex mfix-and-continue
10831 @opindex ffix-and-continue
10832 @opindex findirect-data
10833 Generate code suitable for fast turn around development. Needed to
10834 enable gdb to dynamically load @code{.o} files into already running
10835 programs. @option{-findirect-data} and @option{-ffix-and-continue}
10836 are provided for backwards compatibility.
10840 Loads all members of static archive libraries.
10841 See man ld(1) for more information.
10843 @item -arch_errors_fatal
10844 @opindex arch_errors_fatal
10845 Cause the errors having to do with files that have the wrong architecture
10848 @item -bind_at_load
10849 @opindex bind_at_load
10850 Causes the output file to be marked such that the dynamic linker will
10851 bind all undefined references when the file is loaded or launched.
10855 Produce a Mach-o bundle format file.
10856 See man ld(1) for more information.
10858 @item -bundle_loader @var{executable}
10859 @opindex bundle_loader
10860 This option specifies the @var{executable} that will be loading the build
10861 output file being linked. See man ld(1) for more information.
10864 @opindex dynamiclib
10865 When passed this option, GCC will produce a dynamic library instead of
10866 an executable when linking, using the Darwin @file{libtool} command.
10868 @item -force_cpusubtype_ALL
10869 @opindex force_cpusubtype_ALL
10870 This causes GCC's output file to have the @var{ALL} subtype, instead of
10871 one controlled by the @option{-mcpu} or @option{-march} option.
10873 @item -allowable_client @var{client_name}
10874 @itemx -client_name
10875 @itemx -compatibility_version
10876 @itemx -current_version
10878 @itemx -dependency-file
10880 @itemx -dylinker_install_name
10882 @itemx -exported_symbols_list
10885 @itemx -flat_namespace
10886 @itemx -force_flat_namespace
10887 @itemx -headerpad_max_install_names
10890 @itemx -install_name
10891 @itemx -keep_private_externs
10892 @itemx -multi_module
10893 @itemx -multiply_defined
10894 @itemx -multiply_defined_unused
10897 @itemx -no_dead_strip_inits_and_terms
10898 @itemx -nofixprebinding
10899 @itemx -nomultidefs
10901 @itemx -noseglinkedit
10902 @itemx -pagezero_size
10904 @itemx -prebind_all_twolevel_modules
10905 @itemx -private_bundle
10907 @itemx -read_only_relocs
10909 @itemx -sectobjectsymbols
10913 @itemx -sectobjectsymbols
10916 @itemx -segs_read_only_addr
10918 @itemx -segs_read_write_addr
10919 @itemx -seg_addr_table
10920 @itemx -seg_addr_table_filename
10921 @itemx -seglinkedit
10923 @itemx -segs_read_only_addr
10924 @itemx -segs_read_write_addr
10925 @itemx -single_module
10927 @itemx -sub_library
10929 @itemx -sub_umbrella
10930 @itemx -twolevel_namespace
10933 @itemx -unexported_symbols_list
10934 @itemx -weak_reference_mismatches
10935 @itemx -whatsloaded
10936 @opindex allowable_client
10937 @opindex client_name
10938 @opindex compatibility_version
10939 @opindex current_version
10940 @opindex dead_strip
10941 @opindex dependency-file
10942 @opindex dylib_file
10943 @opindex dylinker_install_name
10945 @opindex exported_symbols_list
10947 @opindex flat_namespace
10948 @opindex force_flat_namespace
10949 @opindex headerpad_max_install_names
10950 @opindex image_base
10952 @opindex install_name
10953 @opindex keep_private_externs
10954 @opindex multi_module
10955 @opindex multiply_defined
10956 @opindex multiply_defined_unused
10957 @opindex noall_load
10958 @opindex no_dead_strip_inits_and_terms
10959 @opindex nofixprebinding
10960 @opindex nomultidefs
10962 @opindex noseglinkedit
10963 @opindex pagezero_size
10965 @opindex prebind_all_twolevel_modules
10966 @opindex private_bundle
10967 @opindex read_only_relocs
10969 @opindex sectobjectsymbols
10972 @opindex sectcreate
10973 @opindex sectobjectsymbols
10976 @opindex segs_read_only_addr
10977 @opindex segs_read_write_addr
10978 @opindex seg_addr_table
10979 @opindex seg_addr_table_filename
10980 @opindex seglinkedit
10982 @opindex segs_read_only_addr
10983 @opindex segs_read_write_addr
10984 @opindex single_module
10986 @opindex sub_library
10987 @opindex sub_umbrella
10988 @opindex twolevel_namespace
10991 @opindex unexported_symbols_list
10992 @opindex weak_reference_mismatches
10993 @opindex whatsloaded
10994 These options are passed to the Darwin linker. The Darwin linker man page
10995 describes them in detail.
10998 @node DEC Alpha Options
10999 @subsection DEC Alpha Options
11001 These @samp{-m} options are defined for the DEC Alpha implementations:
11004 @item -mno-soft-float
11005 @itemx -msoft-float
11006 @opindex mno-soft-float
11007 @opindex msoft-float
11008 Use (do not use) the hardware floating-point instructions for
11009 floating-point operations. When @option{-msoft-float} is specified,
11010 functions in @file{libgcc.a} will be used to perform floating-point
11011 operations. Unless they are replaced by routines that emulate the
11012 floating-point operations, or compiled in such a way as to call such
11013 emulations routines, these routines will issue floating-point
11014 operations. If you are compiling for an Alpha without floating-point
11015 operations, you must ensure that the library is built so as not to call
11018 Note that Alpha implementations without floating-point operations are
11019 required to have floating-point registers.
11022 @itemx -mno-fp-regs
11024 @opindex mno-fp-regs
11025 Generate code that uses (does not use) the floating-point register set.
11026 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
11027 register set is not used, floating point operands are passed in integer
11028 registers as if they were integers and floating-point results are passed
11029 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
11030 so any function with a floating-point argument or return value called by code
11031 compiled with @option{-mno-fp-regs} must also be compiled with that
11034 A typical use of this option is building a kernel that does not use,
11035 and hence need not save and restore, any floating-point registers.
11039 The Alpha architecture implements floating-point hardware optimized for
11040 maximum performance. It is mostly compliant with the IEEE floating
11041 point standard. However, for full compliance, software assistance is
11042 required. This option generates code fully IEEE compliant code
11043 @emph{except} that the @var{inexact-flag} is not maintained (see below).
11044 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
11045 defined during compilation. The resulting code is less efficient but is
11046 able to correctly support denormalized numbers and exceptional IEEE
11047 values such as not-a-number and plus/minus infinity. Other Alpha
11048 compilers call this option @option{-ieee_with_no_inexact}.
11050 @item -mieee-with-inexact
11051 @opindex mieee-with-inexact
11052 This is like @option{-mieee} except the generated code also maintains
11053 the IEEE @var{inexact-flag}. Turning on this option causes the
11054 generated code to implement fully-compliant IEEE math. In addition to
11055 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
11056 macro. On some Alpha implementations the resulting code may execute
11057 significantly slower than the code generated by default. Since there is
11058 very little code that depends on the @var{inexact-flag}, you should
11059 normally not specify this option. Other Alpha compilers call this
11060 option @option{-ieee_with_inexact}.
11062 @item -mfp-trap-mode=@var{trap-mode}
11063 @opindex mfp-trap-mode
11064 This option controls what floating-point related traps are enabled.
11065 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
11066 The trap mode can be set to one of four values:
11070 This is the default (normal) setting. The only traps that are enabled
11071 are the ones that cannot be disabled in software (e.g., division by zero
11075 In addition to the traps enabled by @samp{n}, underflow traps are enabled
11079 Like @samp{u}, but the instructions are marked to be safe for software
11080 completion (see Alpha architecture manual for details).
11083 Like @samp{su}, but inexact traps are enabled as well.
11086 @item -mfp-rounding-mode=@var{rounding-mode}
11087 @opindex mfp-rounding-mode
11088 Selects the IEEE rounding mode. Other Alpha compilers call this option
11089 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
11094 Normal IEEE rounding mode. Floating point numbers are rounded towards
11095 the nearest machine number or towards the even machine number in case
11099 Round towards minus infinity.
11102 Chopped rounding mode. Floating point numbers are rounded towards zero.
11105 Dynamic rounding mode. A field in the floating point control register
11106 (@var{fpcr}, see Alpha architecture reference manual) controls the
11107 rounding mode in effect. The C library initializes this register for
11108 rounding towards plus infinity. Thus, unless your program modifies the
11109 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
11112 @item -mtrap-precision=@var{trap-precision}
11113 @opindex mtrap-precision
11114 In the Alpha architecture, floating point traps are imprecise. This
11115 means without software assistance it is impossible to recover from a
11116 floating trap and program execution normally needs to be terminated.
11117 GCC can generate code that can assist operating system trap handlers
11118 in determining the exact location that caused a floating point trap.
11119 Depending on the requirements of an application, different levels of
11120 precisions can be selected:
11124 Program precision. This option is the default and means a trap handler
11125 can only identify which program caused a floating point exception.
11128 Function precision. The trap handler can determine the function that
11129 caused a floating point exception.
11132 Instruction precision. The trap handler can determine the exact
11133 instruction that caused a floating point exception.
11136 Other Alpha compilers provide the equivalent options called
11137 @option{-scope_safe} and @option{-resumption_safe}.
11139 @item -mieee-conformant
11140 @opindex mieee-conformant
11141 This option marks the generated code as IEEE conformant. You must not
11142 use this option unless you also specify @option{-mtrap-precision=i} and either
11143 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
11144 is to emit the line @samp{.eflag 48} in the function prologue of the
11145 generated assembly file. Under DEC Unix, this has the effect that
11146 IEEE-conformant math library routines will be linked in.
11148 @item -mbuild-constants
11149 @opindex mbuild-constants
11150 Normally GCC examines a 32- or 64-bit integer constant to
11151 see if it can construct it from smaller constants in two or three
11152 instructions. If it cannot, it will output the constant as a literal and
11153 generate code to load it from the data segment at runtime.
11155 Use this option to require GCC to construct @emph{all} integer constants
11156 using code, even if it takes more instructions (the maximum is six).
11158 You would typically use this option to build a shared library dynamic
11159 loader. Itself a shared library, it must relocate itself in memory
11160 before it can find the variables and constants in its own data segment.
11166 Select whether to generate code to be assembled by the vendor-supplied
11167 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
11185 Indicate whether GCC should generate code to use the optional BWX,
11186 CIX, FIX and MAX instruction sets. The default is to use the instruction
11187 sets supported by the CPU type specified via @option{-mcpu=} option or that
11188 of the CPU on which GCC was built if none was specified.
11191 @itemx -mfloat-ieee
11192 @opindex mfloat-vax
11193 @opindex mfloat-ieee
11194 Generate code that uses (does not use) VAX F and G floating point
11195 arithmetic instead of IEEE single and double precision.
11197 @item -mexplicit-relocs
11198 @itemx -mno-explicit-relocs
11199 @opindex mexplicit-relocs
11200 @opindex mno-explicit-relocs
11201 Older Alpha assemblers provided no way to generate symbol relocations
11202 except via assembler macros. Use of these macros does not allow
11203 optimal instruction scheduling. GNU binutils as of version 2.12
11204 supports a new syntax that allows the compiler to explicitly mark
11205 which relocations should apply to which instructions. This option
11206 is mostly useful for debugging, as GCC detects the capabilities of
11207 the assembler when it is built and sets the default accordingly.
11210 @itemx -mlarge-data
11211 @opindex msmall-data
11212 @opindex mlarge-data
11213 When @option{-mexplicit-relocs} is in effect, static data is
11214 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
11215 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
11216 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
11217 16-bit relocations off of the @code{$gp} register. This limits the
11218 size of the small data area to 64KB, but allows the variables to be
11219 directly accessed via a single instruction.
11221 The default is @option{-mlarge-data}. With this option the data area
11222 is limited to just below 2GB@. Programs that require more than 2GB of
11223 data must use @code{malloc} or @code{mmap} to allocate the data in the
11224 heap instead of in the program's data segment.
11226 When generating code for shared libraries, @option{-fpic} implies
11227 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
11230 @itemx -mlarge-text
11231 @opindex msmall-text
11232 @opindex mlarge-text
11233 When @option{-msmall-text} is used, the compiler assumes that the
11234 code of the entire program (or shared library) fits in 4MB, and is
11235 thus reachable with a branch instruction. When @option{-msmall-data}
11236 is used, the compiler can assume that all local symbols share the
11237 same @code{$gp} value, and thus reduce the number of instructions
11238 required for a function call from 4 to 1.
11240 The default is @option{-mlarge-text}.
11242 @item -mcpu=@var{cpu_type}
11244 Set the instruction set and instruction scheduling parameters for
11245 machine type @var{cpu_type}. You can specify either the @samp{EV}
11246 style name or the corresponding chip number. GCC supports scheduling
11247 parameters for the EV4, EV5 and EV6 family of processors and will
11248 choose the default values for the instruction set from the processor
11249 you specify. If you do not specify a processor type, GCC will default
11250 to the processor on which the compiler was built.
11252 Supported values for @var{cpu_type} are
11258 Schedules as an EV4 and has no instruction set extensions.
11262 Schedules as an EV5 and has no instruction set extensions.
11266 Schedules as an EV5 and supports the BWX extension.
11271 Schedules as an EV5 and supports the BWX and MAX extensions.
11275 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
11279 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
11282 Native Linux/GNU toolchains also support the value @samp{native},
11283 which selects the best architecture option for the host processor.
11284 @option{-mcpu=native} has no effect if GCC does not recognize
11287 @item -mtune=@var{cpu_type}
11289 Set only the instruction scheduling parameters for machine type
11290 @var{cpu_type}. The instruction set is not changed.
11292 Native Linux/GNU toolchains also support the value @samp{native},
11293 which selects the best architecture option for the host processor.
11294 @option{-mtune=native} has no effect if GCC does not recognize
11297 @item -mmemory-latency=@var{time}
11298 @opindex mmemory-latency
11299 Sets the latency the scheduler should assume for typical memory
11300 references as seen by the application. This number is highly
11301 dependent on the memory access patterns used by the application
11302 and the size of the external cache on the machine.
11304 Valid options for @var{time} are
11308 A decimal number representing clock cycles.
11314 The compiler contains estimates of the number of clock cycles for
11315 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
11316 (also called Dcache, Scache, and Bcache), as well as to main memory.
11317 Note that L3 is only valid for EV5.
11322 @node DEC Alpha/VMS Options
11323 @subsection DEC Alpha/VMS Options
11325 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
11328 @item -mvms-return-codes
11329 @opindex mvms-return-codes
11330 Return VMS condition codes from main. The default is to return POSIX
11331 style condition (e.g.@: error) codes.
11333 @item -mdebug-main=@var{prefix}
11334 @opindex mdebug-main=@var{prefix}
11335 Flag the first routine whose name starts with @var{prefix} as the main
11336 routine for the debugger.
11340 Default to 64bit memory allocation routines.
11344 @subsection FR30 Options
11345 @cindex FR30 Options
11347 These options are defined specifically for the FR30 port.
11351 @item -msmall-model
11352 @opindex msmall-model
11353 Use the small address space model. This can produce smaller code, but
11354 it does assume that all symbolic values and addresses will fit into a
11359 Assume that run-time support has been provided and so there is no need
11360 to include the simulator library (@file{libsim.a}) on the linker
11366 @subsection FRV Options
11367 @cindex FRV Options
11373 Only use the first 32 general purpose registers.
11378 Use all 64 general purpose registers.
11383 Use only the first 32 floating point registers.
11388 Use all 64 floating point registers
11391 @opindex mhard-float
11393 Use hardware instructions for floating point operations.
11396 @opindex msoft-float
11398 Use library routines for floating point operations.
11403 Dynamically allocate condition code registers.
11408 Do not try to dynamically allocate condition code registers, only
11409 use @code{icc0} and @code{fcc0}.
11414 Change ABI to use double word insns.
11419 Do not use double word instructions.
11424 Use floating point double instructions.
11427 @opindex mno-double
11429 Do not use floating point double instructions.
11434 Use media instructions.
11439 Do not use media instructions.
11444 Use multiply and add/subtract instructions.
11447 @opindex mno-muladd
11449 Do not use multiply and add/subtract instructions.
11454 Select the FDPIC ABI, that uses function descriptors to represent
11455 pointers to functions. Without any PIC/PIE-related options, it
11456 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
11457 assumes GOT entries and small data are within a 12-bit range from the
11458 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
11459 are computed with 32 bits.
11460 With a @samp{bfin-elf} target, this option implies @option{-msim}.
11463 @opindex minline-plt
11465 Enable inlining of PLT entries in function calls to functions that are
11466 not known to bind locally. It has no effect without @option{-mfdpic}.
11467 It's enabled by default if optimizing for speed and compiling for
11468 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
11469 optimization option such as @option{-O3} or above is present in the
11475 Assume a large TLS segment when generating thread-local code.
11480 Do not assume a large TLS segment when generating thread-local code.
11485 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
11486 that is known to be in read-only sections. It's enabled by default,
11487 except for @option{-fpic} or @option{-fpie}: even though it may help
11488 make the global offset table smaller, it trades 1 instruction for 4.
11489 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
11490 one of which may be shared by multiple symbols, and it avoids the need
11491 for a GOT entry for the referenced symbol, so it's more likely to be a
11492 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
11494 @item -multilib-library-pic
11495 @opindex multilib-library-pic
11497 Link with the (library, not FD) pic libraries. It's implied by
11498 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
11499 @option{-fpic} without @option{-mfdpic}. You should never have to use
11503 @opindex mlinked-fp
11505 Follow the EABI requirement of always creating a frame pointer whenever
11506 a stack frame is allocated. This option is enabled by default and can
11507 be disabled with @option{-mno-linked-fp}.
11510 @opindex mlong-calls
11512 Use indirect addressing to call functions outside the current
11513 compilation unit. This allows the functions to be placed anywhere
11514 within the 32-bit address space.
11516 @item -malign-labels
11517 @opindex malign-labels
11519 Try to align labels to an 8-byte boundary by inserting nops into the
11520 previous packet. This option only has an effect when VLIW packing
11521 is enabled. It doesn't create new packets; it merely adds nops to
11524 @item -mlibrary-pic
11525 @opindex mlibrary-pic
11527 Generate position-independent EABI code.
11532 Use only the first four media accumulator registers.
11537 Use all eight media accumulator registers.
11542 Pack VLIW instructions.
11547 Do not pack VLIW instructions.
11550 @opindex mno-eflags
11552 Do not mark ABI switches in e_flags.
11555 @opindex mcond-move
11557 Enable the use of conditional-move instructions (default).
11559 This switch is mainly for debugging the compiler and will likely be removed
11560 in a future version.
11562 @item -mno-cond-move
11563 @opindex mno-cond-move
11565 Disable the use of conditional-move instructions.
11567 This switch is mainly for debugging the compiler and will likely be removed
11568 in a future version.
11573 Enable the use of conditional set instructions (default).
11575 This switch is mainly for debugging the compiler and will likely be removed
11576 in a future version.
11581 Disable the use of conditional set instructions.
11583 This switch is mainly for debugging the compiler and will likely be removed
11584 in a future version.
11587 @opindex mcond-exec
11589 Enable the use of conditional execution (default).
11591 This switch is mainly for debugging the compiler and will likely be removed
11592 in a future version.
11594 @item -mno-cond-exec
11595 @opindex mno-cond-exec
11597 Disable the use of conditional execution.
11599 This switch is mainly for debugging the compiler and will likely be removed
11600 in a future version.
11602 @item -mvliw-branch
11603 @opindex mvliw-branch
11605 Run a pass to pack branches into VLIW instructions (default).
11607 This switch is mainly for debugging the compiler and will likely be removed
11608 in a future version.
11610 @item -mno-vliw-branch
11611 @opindex mno-vliw-branch
11613 Do not run a pass to pack branches into VLIW instructions.
11615 This switch is mainly for debugging the compiler and will likely be removed
11616 in a future version.
11618 @item -mmulti-cond-exec
11619 @opindex mmulti-cond-exec
11621 Enable optimization of @code{&&} and @code{||} in conditional execution
11624 This switch is mainly for debugging the compiler and will likely be removed
11625 in a future version.
11627 @item -mno-multi-cond-exec
11628 @opindex mno-multi-cond-exec
11630 Disable optimization of @code{&&} and @code{||} in conditional execution.
11632 This switch is mainly for debugging the compiler and will likely be removed
11633 in a future version.
11635 @item -mnested-cond-exec
11636 @opindex mnested-cond-exec
11638 Enable nested conditional execution optimizations (default).
11640 This switch is mainly for debugging the compiler and will likely be removed
11641 in a future version.
11643 @item -mno-nested-cond-exec
11644 @opindex mno-nested-cond-exec
11646 Disable nested conditional execution optimizations.
11648 This switch is mainly for debugging the compiler and will likely be removed
11649 in a future version.
11651 @item -moptimize-membar
11652 @opindex moptimize-membar
11654 This switch removes redundant @code{membar} instructions from the
11655 compiler generated code. It is enabled by default.
11657 @item -mno-optimize-membar
11658 @opindex mno-optimize-membar
11660 This switch disables the automatic removal of redundant @code{membar}
11661 instructions from the generated code.
11663 @item -mtomcat-stats
11664 @opindex mtomcat-stats
11666 Cause gas to print out tomcat statistics.
11668 @item -mcpu=@var{cpu}
11671 Select the processor type for which to generate code. Possible values are
11672 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
11673 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
11677 @node GNU/Linux Options
11678 @subsection GNU/Linux Options
11680 These @samp{-m} options are defined for GNU/Linux targets:
11685 Use the GNU C library. This is the default except
11686 on @samp{*-*-linux-*uclibc*} and @samp{*-*-linux-*android*} targets.
11690 Use uClibc C library. This is the default on
11691 @samp{*-*-linux-*uclibc*} targets.
11695 Use Bionic C library. This is the default on
11696 @samp{*-*-linux-*android*} targets.
11700 Compile code compatible with Android platform. This is the default on
11701 @samp{*-*-linux-*android*} targets.
11703 When compiling, this option enables @option{-mbionic}, @option{-fPIC},
11704 @option{-fno-exceptions} and @option{-fno-rtti} by default. When linking,
11705 this option makes the GCC driver pass Android-specific options to the linker.
11706 Finally, this option causes the preprocessor macro @code{__ANDROID__}
11709 @item -tno-android-cc
11710 @opindex tno-android-cc
11711 Disable compilation effects of @option{-mandroid}, i.e., do not enable
11712 @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and
11713 @option{-fno-rtti} by default.
11715 @item -tno-android-ld
11716 @opindex tno-android-ld
11717 Disable linking effects of @option{-mandroid}, i.e., pass standard Linux
11718 linking options to the linker.
11722 @node H8/300 Options
11723 @subsection H8/300 Options
11725 These @samp{-m} options are defined for the H8/300 implementations:
11730 Shorten some address references at link time, when possible; uses the
11731 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
11732 ld, Using ld}, for a fuller description.
11736 Generate code for the H8/300H@.
11740 Generate code for the H8S@.
11744 Generate code for the H8S and H8/300H in the normal mode. This switch
11745 must be used either with @option{-mh} or @option{-ms}.
11749 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
11753 Make @code{int} data 32 bits by default.
11756 @opindex malign-300
11757 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
11758 The default for the H8/300H and H8S is to align longs and floats on 4
11760 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
11761 This option has no effect on the H8/300.
11765 @subsection HPPA Options
11766 @cindex HPPA Options
11768 These @samp{-m} options are defined for the HPPA family of computers:
11771 @item -march=@var{architecture-type}
11773 Generate code for the specified architecture. The choices for
11774 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
11775 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
11776 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
11777 architecture option for your machine. Code compiled for lower numbered
11778 architectures will run on higher numbered architectures, but not the
11781 @item -mpa-risc-1-0
11782 @itemx -mpa-risc-1-1
11783 @itemx -mpa-risc-2-0
11784 @opindex mpa-risc-1-0
11785 @opindex mpa-risc-1-1
11786 @opindex mpa-risc-2-0
11787 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
11790 @opindex mbig-switch
11791 Generate code suitable for big switch tables. Use this option only if
11792 the assembler/linker complain about out of range branches within a switch
11795 @item -mjump-in-delay
11796 @opindex mjump-in-delay
11797 Fill delay slots of function calls with unconditional jump instructions
11798 by modifying the return pointer for the function call to be the target
11799 of the conditional jump.
11801 @item -mdisable-fpregs
11802 @opindex mdisable-fpregs
11803 Prevent floating point registers from being used in any manner. This is
11804 necessary for compiling kernels which perform lazy context switching of
11805 floating point registers. If you use this option and attempt to perform
11806 floating point operations, the compiler will abort.
11808 @item -mdisable-indexing
11809 @opindex mdisable-indexing
11810 Prevent the compiler from using indexing address modes. This avoids some
11811 rather obscure problems when compiling MIG generated code under MACH@.
11813 @item -mno-space-regs
11814 @opindex mno-space-regs
11815 Generate code that assumes the target has no space registers. This allows
11816 GCC to generate faster indirect calls and use unscaled index address modes.
11818 Such code is suitable for level 0 PA systems and kernels.
11820 @item -mfast-indirect-calls
11821 @opindex mfast-indirect-calls
11822 Generate code that assumes calls never cross space boundaries. This
11823 allows GCC to emit code which performs faster indirect calls.
11825 This option will not work in the presence of shared libraries or nested
11828 @item -mfixed-range=@var{register-range}
11829 @opindex mfixed-range
11830 Generate code treating the given register range as fixed registers.
11831 A fixed register is one that the register allocator can not use. This is
11832 useful when compiling kernel code. A register range is specified as
11833 two registers separated by a dash. Multiple register ranges can be
11834 specified separated by a comma.
11836 @item -mlong-load-store
11837 @opindex mlong-load-store
11838 Generate 3-instruction load and store sequences as sometimes required by
11839 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
11842 @item -mportable-runtime
11843 @opindex mportable-runtime
11844 Use the portable calling conventions proposed by HP for ELF systems.
11848 Enable the use of assembler directives only GAS understands.
11850 @item -mschedule=@var{cpu-type}
11852 Schedule code according to the constraints for the machine type
11853 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
11854 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
11855 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
11856 proper scheduling option for your machine. The default scheduling is
11860 @opindex mlinker-opt
11861 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
11862 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
11863 linkers in which they give bogus error messages when linking some programs.
11866 @opindex msoft-float
11867 Generate output containing library calls for floating point.
11868 @strong{Warning:} the requisite libraries are not available for all HPPA
11869 targets. Normally the facilities of the machine's usual C compiler are
11870 used, but this cannot be done directly in cross-compilation. You must make
11871 your own arrangements to provide suitable library functions for
11874 @option{-msoft-float} changes the calling convention in the output file;
11875 therefore, it is only useful if you compile @emph{all} of a program with
11876 this option. In particular, you need to compile @file{libgcc.a}, the
11877 library that comes with GCC, with @option{-msoft-float} in order for
11882 Generate the predefine, @code{_SIO}, for server IO@. The default is
11883 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
11884 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
11885 options are available under HP-UX and HI-UX@.
11889 Use GNU ld specific options. This passes @option{-shared} to ld when
11890 building a shared library. It is the default when GCC is configured,
11891 explicitly or implicitly, with the GNU linker. This option does not
11892 have any affect on which ld is called, it only changes what parameters
11893 are passed to that ld. The ld that is called is determined by the
11894 @option{--with-ld} configure option, GCC's program search path, and
11895 finally by the user's @env{PATH}. The linker used by GCC can be printed
11896 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
11897 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11901 Use HP ld specific options. This passes @option{-b} to ld when building
11902 a shared library and passes @option{+Accept TypeMismatch} to ld on all
11903 links. It is the default when GCC is configured, explicitly or
11904 implicitly, with the HP linker. This option does not have any affect on
11905 which ld is called, it only changes what parameters are passed to that
11906 ld. The ld that is called is determined by the @option{--with-ld}
11907 configure option, GCC's program search path, and finally by the user's
11908 @env{PATH}. The linker used by GCC can be printed using @samp{which
11909 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
11910 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11913 @opindex mno-long-calls
11914 Generate code that uses long call sequences. This ensures that a call
11915 is always able to reach linker generated stubs. The default is to generate
11916 long calls only when the distance from the call site to the beginning
11917 of the function or translation unit, as the case may be, exceeds a
11918 predefined limit set by the branch type being used. The limits for
11919 normal calls are 7,600,000 and 240,000 bytes, respectively for the
11920 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
11923 Distances are measured from the beginning of functions when using the
11924 @option{-ffunction-sections} option, or when using the @option{-mgas}
11925 and @option{-mno-portable-runtime} options together under HP-UX with
11928 It is normally not desirable to use this option as it will degrade
11929 performance. However, it may be useful in large applications,
11930 particularly when partial linking is used to build the application.
11932 The types of long calls used depends on the capabilities of the
11933 assembler and linker, and the type of code being generated. The
11934 impact on systems that support long absolute calls, and long pic
11935 symbol-difference or pc-relative calls should be relatively small.
11936 However, an indirect call is used on 32-bit ELF systems in pic code
11937 and it is quite long.
11939 @item -munix=@var{unix-std}
11941 Generate compiler predefines and select a startfile for the specified
11942 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
11943 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
11944 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
11945 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
11946 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
11949 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
11950 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
11951 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
11952 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
11953 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
11954 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
11956 It is @emph{important} to note that this option changes the interfaces
11957 for various library routines. It also affects the operational behavior
11958 of the C library. Thus, @emph{extreme} care is needed in using this
11961 Library code that is intended to operate with more than one UNIX
11962 standard must test, set and restore the variable @var{__xpg4_extended_mask}
11963 as appropriate. Most GNU software doesn't provide this capability.
11967 Suppress the generation of link options to search libdld.sl when the
11968 @option{-static} option is specified on HP-UX 10 and later.
11972 The HP-UX implementation of setlocale in libc has a dependency on
11973 libdld.sl. There isn't an archive version of libdld.sl. Thus,
11974 when the @option{-static} option is specified, special link options
11975 are needed to resolve this dependency.
11977 On HP-UX 10 and later, the GCC driver adds the necessary options to
11978 link with libdld.sl when the @option{-static} option is specified.
11979 This causes the resulting binary to be dynamic. On the 64-bit port,
11980 the linkers generate dynamic binaries by default in any case. The
11981 @option{-nolibdld} option can be used to prevent the GCC driver from
11982 adding these link options.
11986 Add support for multithreading with the @dfn{dce thread} library
11987 under HP-UX@. This option sets flags for both the preprocessor and
11991 @node i386 and x86-64 Options
11992 @subsection Intel 386 and AMD x86-64 Options
11993 @cindex i386 Options
11994 @cindex x86-64 Options
11995 @cindex Intel 386 Options
11996 @cindex AMD x86-64 Options
11998 These @samp{-m} options are defined for the i386 and x86-64 family of
12002 @item -mtune=@var{cpu-type}
12004 Tune to @var{cpu-type} everything applicable about the generated code, except
12005 for the ABI and the set of available instructions. The choices for
12006 @var{cpu-type} are:
12009 Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors.
12010 If you know the CPU on which your code will run, then you should use
12011 the corresponding @option{-mtune} option instead of
12012 @option{-mtune=generic}. But, if you do not know exactly what CPU users
12013 of your application will have, then you should use this option.
12015 As new processors are deployed in the marketplace, the behavior of this
12016 option will change. Therefore, if you upgrade to a newer version of
12017 GCC, the code generated option will change to reflect the processors
12018 that were most common when that version of GCC was released.
12020 There is no @option{-march=generic} option because @option{-march}
12021 indicates the instruction set the compiler can use, and there is no
12022 generic instruction set applicable to all processors. In contrast,
12023 @option{-mtune} indicates the processor (or, in this case, collection of
12024 processors) for which the code is optimized.
12026 This selects the CPU to tune for at compilation time by determining
12027 the processor type of the compiling machine. Using @option{-mtune=native}
12028 will produce code optimized for the local machine under the constraints
12029 of the selected instruction set. Using @option{-march=native} will
12030 enable all instruction subsets supported by the local machine (hence
12031 the result might not run on different machines).
12033 Original Intel's i386 CPU@.
12035 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
12036 @item i586, pentium
12037 Intel Pentium CPU with no MMX support.
12039 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
12041 Intel PentiumPro CPU@.
12043 Same as @code{generic}, but when used as @code{march} option, PentiumPro
12044 instruction set will be used, so the code will run on all i686 family chips.
12046 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
12047 @item pentium3, pentium3m
12048 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
12051 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
12052 support. Used by Centrino notebooks.
12053 @item pentium4, pentium4m
12054 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
12056 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
12059 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
12060 SSE2 and SSE3 instruction set support.
12062 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
12063 instruction set support.
12065 Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1
12066 and SSE4.2 instruction set support.
12068 Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
12069 SSE4.1, SSE4.2, AVX, AES and PCLMUL instruction set support.
12071 Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
12072 instruction set support.
12074 AMD K6 CPU with MMX instruction set support.
12076 Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support.
12077 @item athlon, athlon-tbird
12078 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions
12080 @item athlon-4, athlon-xp, athlon-mp
12081 Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE
12082 instruction set support.
12083 @item k8, opteron, athlon64, athlon-fx
12084 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
12085 MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit instruction set extensions.)
12086 @item k8-sse3, opteron-sse3, athlon64-sse3
12087 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
12088 @item amdfam10, barcelona
12089 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
12090 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit
12091 instruction set extensions.)
12093 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
12096 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@:
12097 instruction set support.
12099 Via C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is
12100 implemented for this chip.)
12102 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
12103 implemented for this chip.)
12105 Embedded AMD CPU with MMX and 3DNow!@: instruction set support.
12108 While picking a specific @var{cpu-type} will schedule things appropriately
12109 for that particular chip, the compiler will not generate any code that
12110 does not run on the i386 without the @option{-march=@var{cpu-type}} option
12113 @item -march=@var{cpu-type}
12115 Generate instructions for the machine type @var{cpu-type}. The choices
12116 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
12117 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
12119 @item -mcpu=@var{cpu-type}
12121 A deprecated synonym for @option{-mtune}.
12123 @item -mfpmath=@var{unit}
12125 Generate floating point arithmetics for selected unit @var{unit}. The choices
12126 for @var{unit} are:
12130 Use the standard 387 floating point coprocessor present majority of chips and
12131 emulated otherwise. Code compiled with this option will run almost everywhere.
12132 The temporary results are computed in 80bit precision instead of precision
12133 specified by the type resulting in slightly different results compared to most
12134 of other chips. See @option{-ffloat-store} for more detailed description.
12136 This is the default choice for i386 compiler.
12139 Use scalar floating point instructions present in the SSE instruction set.
12140 This instruction set is supported by Pentium3 and newer chips, in the AMD line
12141 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
12142 instruction set supports only single precision arithmetics, thus the double and
12143 extended precision arithmetics is still done using 387. Later version, present
12144 only in Pentium4 and the future AMD x86-64 chips supports double precision
12147 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
12148 or @option{-msse2} switches to enable SSE extensions and make this option
12149 effective. For the x86-64 compiler, these extensions are enabled by default.
12151 The resulting code should be considerably faster in the majority of cases and avoid
12152 the numerical instability problems of 387 code, but may break some existing
12153 code that expects temporaries to be 80bit.
12155 This is the default choice for the x86-64 compiler.
12160 Attempt to utilize both instruction sets at once. This effectively double the
12161 amount of available registers and on chips with separate execution units for
12162 387 and SSE the execution resources too. Use this option with care, as it is
12163 still experimental, because the GCC register allocator does not model separate
12164 functional units well resulting in instable performance.
12167 @item -masm=@var{dialect}
12168 @opindex masm=@var{dialect}
12169 Output asm instructions using selected @var{dialect}. Supported
12170 choices are @samp{intel} or @samp{att} (the default one). Darwin does
12171 not support @samp{intel}.
12174 @itemx -mno-ieee-fp
12176 @opindex mno-ieee-fp
12177 Control whether or not the compiler uses IEEE floating point
12178 comparisons. These handle correctly the case where the result of a
12179 comparison is unordered.
12182 @opindex msoft-float
12183 Generate output containing library calls for floating point.
12184 @strong{Warning:} the requisite libraries are not part of GCC@.
12185 Normally the facilities of the machine's usual C compiler are used, but
12186 this can't be done directly in cross-compilation. You must make your
12187 own arrangements to provide suitable library functions for
12190 On machines where a function returns floating point results in the 80387
12191 register stack, some floating point opcodes may be emitted even if
12192 @option{-msoft-float} is used.
12194 @item -mno-fp-ret-in-387
12195 @opindex mno-fp-ret-in-387
12196 Do not use the FPU registers for return values of functions.
12198 The usual calling convention has functions return values of types
12199 @code{float} and @code{double} in an FPU register, even if there
12200 is no FPU@. The idea is that the operating system should emulate
12203 The option @option{-mno-fp-ret-in-387} causes such values to be returned
12204 in ordinary CPU registers instead.
12206 @item -mno-fancy-math-387
12207 @opindex mno-fancy-math-387
12208 Some 387 emulators do not support the @code{sin}, @code{cos} and
12209 @code{sqrt} instructions for the 387. Specify this option to avoid
12210 generating those instructions. This option is the default on FreeBSD,
12211 OpenBSD and NetBSD@. This option is overridden when @option{-march}
12212 indicates that the target CPU will always have an FPU and so the
12213 instruction will not need emulation. As of revision 2.6.1, these
12214 instructions are not generated unless you also use the
12215 @option{-funsafe-math-optimizations} switch.
12217 @item -malign-double
12218 @itemx -mno-align-double
12219 @opindex malign-double
12220 @opindex mno-align-double
12221 Control whether GCC aligns @code{double}, @code{long double}, and
12222 @code{long long} variables on a two word boundary or a one word
12223 boundary. Aligning @code{double} variables on a two word boundary will
12224 produce code that runs somewhat faster on a @samp{Pentium} at the
12225 expense of more memory.
12227 On x86-64, @option{-malign-double} is enabled by default.
12229 @strong{Warning:} if you use the @option{-malign-double} switch,
12230 structures containing the above types will be aligned differently than
12231 the published application binary interface specifications for the 386
12232 and will not be binary compatible with structures in code compiled
12233 without that switch.
12235 @item -m96bit-long-double
12236 @itemx -m128bit-long-double
12237 @opindex m96bit-long-double
12238 @opindex m128bit-long-double
12239 These switches control the size of @code{long double} type. The i386
12240 application binary interface specifies the size to be 96 bits,
12241 so @option{-m96bit-long-double} is the default in 32 bit mode.
12243 Modern architectures (Pentium and newer) would prefer @code{long double}
12244 to be aligned to an 8 or 16 byte boundary. In arrays or structures
12245 conforming to the ABI, this would not be possible. So specifying a
12246 @option{-m128bit-long-double} will align @code{long double}
12247 to a 16 byte boundary by padding the @code{long double} with an additional
12250 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
12251 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
12253 Notice that neither of these options enable any extra precision over the x87
12254 standard of 80 bits for a @code{long double}.
12256 @strong{Warning:} if you override the default value for your target ABI, the
12257 structures and arrays containing @code{long double} variables will change
12258 their size as well as function calling convention for function taking
12259 @code{long double} will be modified. Hence they will not be binary
12260 compatible with arrays or structures in code compiled without that switch.
12262 @item -mlarge-data-threshold=@var{number}
12263 @opindex mlarge-data-threshold=@var{number}
12264 When @option{-mcmodel=medium} is specified, the data greater than
12265 @var{threshold} are placed in large data section. This value must be the
12266 same across all object linked into the binary and defaults to 65535.
12270 Use a different function-calling convention, in which functions that
12271 take a fixed number of arguments return with the @code{ret} @var{num}
12272 instruction, which pops their arguments while returning. This saves one
12273 instruction in the caller since there is no need to pop the arguments
12276 You can specify that an individual function is called with this calling
12277 sequence with the function attribute @samp{stdcall}. You can also
12278 override the @option{-mrtd} option by using the function attribute
12279 @samp{cdecl}. @xref{Function Attributes}.
12281 @strong{Warning:} this calling convention is incompatible with the one
12282 normally used on Unix, so you cannot use it if you need to call
12283 libraries compiled with the Unix compiler.
12285 Also, you must provide function prototypes for all functions that
12286 take variable numbers of arguments (including @code{printf});
12287 otherwise incorrect code will be generated for calls to those
12290 In addition, seriously incorrect code will result if you call a
12291 function with too many arguments. (Normally, extra arguments are
12292 harmlessly ignored.)
12294 @item -mregparm=@var{num}
12296 Control how many registers are used to pass integer arguments. By
12297 default, no registers are used to pass arguments, and at most 3
12298 registers can be used. You can control this behavior for a specific
12299 function by using the function attribute @samp{regparm}.
12300 @xref{Function Attributes}.
12302 @strong{Warning:} if you use this switch, and
12303 @var{num} is nonzero, then you must build all modules with the same
12304 value, including any libraries. This includes the system libraries and
12308 @opindex msseregparm
12309 Use SSE register passing conventions for float and double arguments
12310 and return values. You can control this behavior for a specific
12311 function by using the function attribute @samp{sseregparm}.
12312 @xref{Function Attributes}.
12314 @strong{Warning:} if you use this switch then you must build all
12315 modules with the same value, including any libraries. This includes
12316 the system libraries and startup modules.
12318 @item -mvect8-ret-in-mem
12319 @opindex mvect8-ret-in-mem
12320 Return 8-byte vectors in memory instead of MMX registers. This is the
12321 default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun
12322 Studio compilers until version 12. Later compiler versions (starting
12323 with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which
12324 is the default on Solaris@tie{}10 and later. @emph{Only} use this option if
12325 you need to remain compatible with existing code produced by those
12326 previous compiler versions or older versions of GCC.
12335 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
12336 is specified, the significands of results of floating-point operations are
12337 rounded to 24 bits (single precision); @option{-mpc64} rounds the
12338 significands of results of floating-point operations to 53 bits (double
12339 precision) and @option{-mpc80} rounds the significands of results of
12340 floating-point operations to 64 bits (extended double precision), which is
12341 the default. When this option is used, floating-point operations in higher
12342 precisions are not available to the programmer without setting the FPU
12343 control word explicitly.
12345 Setting the rounding of floating-point operations to less than the default
12346 80 bits can speed some programs by 2% or more. Note that some mathematical
12347 libraries assume that extended precision (80 bit) floating-point operations
12348 are enabled by default; routines in such libraries could suffer significant
12349 loss of accuracy, typically through so-called "catastrophic cancellation",
12350 when this option is used to set the precision to less than extended precision.
12352 @item -mstackrealign
12353 @opindex mstackrealign
12354 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
12355 option will generate an alternate prologue and epilogue that realigns the
12356 runtime stack if necessary. This supports mixing legacy codes that keep
12357 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
12358 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
12359 applicable to individual functions.
12361 @item -mpreferred-stack-boundary=@var{num}
12362 @opindex mpreferred-stack-boundary
12363 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
12364 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
12365 the default is 4 (16 bytes or 128 bits).
12367 @item -mincoming-stack-boundary=@var{num}
12368 @opindex mincoming-stack-boundary
12369 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
12370 boundary. If @option{-mincoming-stack-boundary} is not specified,
12371 the one specified by @option{-mpreferred-stack-boundary} will be used.
12373 On Pentium and PentiumPro, @code{double} and @code{long double} values
12374 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
12375 suffer significant run time performance penalties. On Pentium III, the
12376 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
12377 properly if it is not 16 byte aligned.
12379 To ensure proper alignment of this values on the stack, the stack boundary
12380 must be as aligned as that required by any value stored on the stack.
12381 Further, every function must be generated such that it keeps the stack
12382 aligned. Thus calling a function compiled with a higher preferred
12383 stack boundary from a function compiled with a lower preferred stack
12384 boundary will most likely misalign the stack. It is recommended that
12385 libraries that use callbacks always use the default setting.
12387 This extra alignment does consume extra stack space, and generally
12388 increases code size. Code that is sensitive to stack space usage, such
12389 as embedded systems and operating system kernels, may want to reduce the
12390 preferred alignment to @option{-mpreferred-stack-boundary=2}.
12417 @itemx -mno-fsgsbase
12447 These switches enable or disable the use of instructions in the MMX,
12448 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, FSGSBASE, RDRND,
12449 F16C, SSE4A, FMA4, XOP, LWP, ABM, BMI, or 3DNow!@: extended instruction sets.
12450 These extensions are also available as built-in functions: see
12451 @ref{X86 Built-in Functions}, for details of the functions enabled and
12452 disabled by these switches.
12454 To have SSE/SSE2 instructions generated automatically from floating-point
12455 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
12457 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
12458 generates new AVX instructions or AVX equivalence for all SSEx instructions
12461 These options will enable GCC to use these extended instructions in
12462 generated code, even without @option{-mfpmath=sse}. Applications which
12463 perform runtime CPU detection must compile separate files for each
12464 supported architecture, using the appropriate flags. In particular,
12465 the file containing the CPU detection code should be compiled without
12469 @itemx -mno-fused-madd
12470 @opindex mfused-madd
12471 @opindex mno-fused-madd
12472 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
12473 instructions. The default is to use these instructions.
12477 This option instructs GCC to emit a @code{cld} instruction in the prologue
12478 of functions that use string instructions. String instructions depend on
12479 the DF flag to select between autoincrement or autodecrement mode. While the
12480 ABI specifies the DF flag to be cleared on function entry, some operating
12481 systems violate this specification by not clearing the DF flag in their
12482 exception dispatchers. The exception handler can be invoked with the DF flag
12483 set which leads to wrong direction mode, when string instructions are used.
12484 This option can be enabled by default on 32-bit x86 targets by configuring
12485 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
12486 instructions can be suppressed with the @option{-mno-cld} compiler option
12490 @opindex mvzeroupper
12491 This option instructs GCC to emit a @code{vzeroupper} instruction
12492 before a transfer of control flow out of the function to minimize
12493 AVX to SSE transition penalty as well as remove unnecessary zeroupper
12498 This option will enable GCC to use CMPXCHG16B instruction in generated code.
12499 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
12500 data types. This is useful for high resolution counters that could be updated
12501 by multiple processors (or cores). This instruction is generated as part of
12502 atomic built-in functions: see @ref{Atomic Builtins} for details.
12506 This option will enable GCC to use SAHF instruction in generated 64-bit code.
12507 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
12508 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
12509 SAHF are load and store instructions, respectively, for certain status flags.
12510 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
12511 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
12515 This option will enable GCC to use movbe instruction to implement
12516 @code{__builtin_bswap32} and @code{__builtin_bswap64}.
12520 This option will enable built-in functions, @code{__builtin_ia32_crc32qi},
12521 @code{__builtin_ia32_crc32hi}. @code{__builtin_ia32_crc32si} and
12522 @code{__builtin_ia32_crc32di} to generate the crc32 machine instruction.
12526 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
12527 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson step
12528 to increase precision instead of DIVSS and SQRTSS (and their vectorized
12529 variants) for single precision floating point arguments. These instructions
12530 are generated only when @option{-funsafe-math-optimizations} is enabled
12531 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
12532 Note that while the throughput of the sequence is higher than the throughput
12533 of the non-reciprocal instruction, the precision of the sequence can be
12534 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
12536 Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or RSQRTPS)
12537 already with @option{-ffast-math} (or the above option combination), and
12538 doesn't need @option{-mrecip}.
12540 @item -mveclibabi=@var{type}
12541 @opindex mveclibabi
12542 Specifies the ABI type to use for vectorizing intrinsics using an
12543 external library. Supported types are @code{svml} for the Intel short
12544 vector math library and @code{acml} for the AMD math core library style
12545 of interfacing. GCC will currently emit calls to @code{vmldExp2},
12546 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
12547 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
12548 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
12549 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
12550 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
12551 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
12552 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
12553 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
12554 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
12555 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
12556 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
12557 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
12558 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
12559 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
12560 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
12561 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
12562 compatible library will have to be specified at link time.
12564 @item -mabi=@var{name}
12566 Generate code for the specified calling convention. Permissible values
12567 are: @samp{sysv} for the ABI used on GNU/Linux and other systems and
12568 @samp{ms} for the Microsoft ABI. The default is to use the Microsoft
12569 ABI when targeting Windows. On all other systems, the default is the
12570 SYSV ABI. You can control this behavior for a specific function by
12571 using the function attribute @samp{ms_abi}/@samp{sysv_abi}.
12572 @xref{Function Attributes}.
12575 @itemx -mno-push-args
12576 @opindex mpush-args
12577 @opindex mno-push-args
12578 Use PUSH operations to store outgoing parameters. This method is shorter
12579 and usually equally fast as method using SUB/MOV operations and is enabled
12580 by default. In some cases disabling it may improve performance because of
12581 improved scheduling and reduced dependencies.
12583 @item -maccumulate-outgoing-args
12584 @opindex maccumulate-outgoing-args
12585 If enabled, the maximum amount of space required for outgoing arguments will be
12586 computed in the function prologue. This is faster on most modern CPUs
12587 because of reduced dependencies, improved scheduling and reduced stack usage
12588 when preferred stack boundary is not equal to 2. The drawback is a notable
12589 increase in code size. This switch implies @option{-mno-push-args}.
12593 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
12594 on thread-safe exception handling must compile and link all code with the
12595 @option{-mthreads} option. When compiling, @option{-mthreads} defines
12596 @option{-D_MT}; when linking, it links in a special thread helper library
12597 @option{-lmingwthrd} which cleans up per thread exception handling data.
12599 @item -mno-align-stringops
12600 @opindex mno-align-stringops
12601 Do not align destination of inlined string operations. This switch reduces
12602 code size and improves performance in case the destination is already aligned,
12603 but GCC doesn't know about it.
12605 @item -minline-all-stringops
12606 @opindex minline-all-stringops
12607 By default GCC inlines string operations only when destination is known to be
12608 aligned at least to 4 byte boundary. This enables more inlining, increase code
12609 size, but may improve performance of code that depends on fast memcpy, strlen
12610 and memset for short lengths.
12612 @item -minline-stringops-dynamically
12613 @opindex minline-stringops-dynamically
12614 For string operation of unknown size, inline runtime checks so for small
12615 blocks inline code is used, while for large blocks library call is used.
12617 @item -mstringop-strategy=@var{alg}
12618 @opindex mstringop-strategy=@var{alg}
12619 Overwrite internal decision heuristic about particular algorithm to inline
12620 string operation with. The allowed values are @code{rep_byte},
12621 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
12622 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
12623 expanding inline loop, @code{libcall} for always expanding library call.
12625 @item -momit-leaf-frame-pointer
12626 @opindex momit-leaf-frame-pointer
12627 Don't keep the frame pointer in a register for leaf functions. This
12628 avoids the instructions to save, set up and restore frame pointers and
12629 makes an extra register available in leaf functions. The option
12630 @option{-fomit-frame-pointer} removes the frame pointer for all functions
12631 which might make debugging harder.
12633 @item -mtls-direct-seg-refs
12634 @itemx -mno-tls-direct-seg-refs
12635 @opindex mtls-direct-seg-refs
12636 Controls whether TLS variables may be accessed with offsets from the
12637 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
12638 or whether the thread base pointer must be added. Whether or not this
12639 is legal depends on the operating system, and whether it maps the
12640 segment to cover the entire TLS area.
12642 For systems that use GNU libc, the default is on.
12645 @itemx -mno-sse2avx
12647 Specify that the assembler should encode SSE instructions with VEX
12648 prefix. The option @option{-mavx} turns this on by default.
12653 If profiling is active @option{-pg} put the profiling
12654 counter call before prologue.
12655 Note: On x86 architectures the attribute @code{ms_hook_prologue}
12656 isn't possible at the moment for @option{-mfentry} and @option{-pg}.
12659 @itemx -mno-8bit-idiv
12661 On some processors, like Intel Atom, 8bit unsigned integer divide is
12662 much faster than 32bit/64bit integer divide. This option will generate a
12663 runt-time check. If both dividend and divisor are within range of 0
12664 to 255, 8bit unsigned integer divide will be used instead of
12665 32bit/64bit integer divide.
12669 These @samp{-m} switches are supported in addition to the above
12670 on AMD x86-64 processors in 64-bit environments.
12677 Generate code for a 32-bit or 64-bit environment.
12678 The 32-bit environment sets int, long and pointer to 32 bits and
12679 generates code that runs on any i386 system.
12680 The 64-bit environment sets int to 32 bits and long and pointer
12681 to 64 bits and generates code for AMD's x86-64 architecture. For
12682 darwin only the -m64 option turns off the @option{-fno-pic} and
12683 @option{-mdynamic-no-pic} options.
12685 @item -mno-red-zone
12686 @opindex mno-red-zone
12687 Do not use a so called red zone for x86-64 code. The red zone is mandated
12688 by the x86-64 ABI, it is a 128-byte area beyond the location of the
12689 stack pointer that will not be modified by signal or interrupt handlers
12690 and therefore can be used for temporary data without adjusting the stack
12691 pointer. The flag @option{-mno-red-zone} disables this red zone.
12693 @item -mcmodel=small
12694 @opindex mcmodel=small
12695 Generate code for the small code model: the program and its symbols must
12696 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
12697 Programs can be statically or dynamically linked. This is the default
12700 @item -mcmodel=kernel
12701 @opindex mcmodel=kernel
12702 Generate code for the kernel code model. The kernel runs in the
12703 negative 2 GB of the address space.
12704 This model has to be used for Linux kernel code.
12706 @item -mcmodel=medium
12707 @opindex mcmodel=medium
12708 Generate code for the medium model: The program is linked in the lower 2
12709 GB of the address space. Small symbols are also placed there. Symbols
12710 with sizes larger than @option{-mlarge-data-threshold} are put into
12711 large data or bss sections and can be located above 2GB. Programs can
12712 be statically or dynamically linked.
12714 @item -mcmodel=large
12715 @opindex mcmodel=large
12716 Generate code for the large model: This model makes no assumptions
12717 about addresses and sizes of sections.
12720 @node i386 and x86-64 Windows Options
12721 @subsection i386 and x86-64 Windows Options
12722 @cindex i386 and x86-64 Windows Options
12724 These additional options are available for Windows targets:
12729 This option is available for Cygwin and MinGW targets. It
12730 specifies that a console application is to be generated, by
12731 instructing the linker to set the PE header subsystem type
12732 required for console applications.
12733 This is the default behavior for Cygwin and MinGW targets.
12737 This option is available for Cygwin and MinGW targets. It
12738 specifies that a DLL - a dynamic link library - is to be
12739 generated, enabling the selection of the required runtime
12740 startup object and entry point.
12742 @item -mnop-fun-dllimport
12743 @opindex mnop-fun-dllimport
12744 This option is available for Cygwin and MinGW targets. It
12745 specifies that the dllimport attribute should be ignored.
12749 This option is available for MinGW targets. It specifies
12750 that MinGW-specific thread support is to be used.
12754 This option is available for mingw-w64 targets. It specifies
12755 that the UNICODE macro is getting pre-defined and that the
12756 unicode capable runtime startup code is chosen.
12760 This option is available for Cygwin and MinGW targets. It
12761 specifies that the typical Windows pre-defined macros are to
12762 be set in the pre-processor, but does not influence the choice
12763 of runtime library/startup code.
12767 This option is available for Cygwin and MinGW targets. It
12768 specifies that a GUI application is to be generated by
12769 instructing the linker to set the PE header subsystem type
12772 @item -fno-set-stack-executable
12773 @opindex fno-set-stack-executable
12774 This option is available for MinGW targets. It specifies that
12775 the executable flag for stack used by nested functions isn't
12776 set. This is necessary for binaries running in kernel mode of
12777 Windows, as there the user32 API, which is used to set executable
12778 privileges, isn't available.
12780 @item -mpe-aligned-commons
12781 @opindex mpe-aligned-commons
12782 This option is available for Cygwin and MinGW targets. It
12783 specifies that the GNU extension to the PE file format that
12784 permits the correct alignment of COMMON variables should be
12785 used when generating code. It will be enabled by default if
12786 GCC detects that the target assembler found during configuration
12787 supports the feature.
12790 See also under @ref{i386 and x86-64 Options} for standard options.
12792 @node IA-64 Options
12793 @subsection IA-64 Options
12794 @cindex IA-64 Options
12796 These are the @samp{-m} options defined for the Intel IA-64 architecture.
12800 @opindex mbig-endian
12801 Generate code for a big endian target. This is the default for HP-UX@.
12803 @item -mlittle-endian
12804 @opindex mlittle-endian
12805 Generate code for a little endian target. This is the default for AIX5
12811 @opindex mno-gnu-as
12812 Generate (or don't) code for the GNU assembler. This is the default.
12813 @c Also, this is the default if the configure option @option{--with-gnu-as}
12819 @opindex mno-gnu-ld
12820 Generate (or don't) code for the GNU linker. This is the default.
12821 @c Also, this is the default if the configure option @option{--with-gnu-ld}
12826 Generate code that does not use a global pointer register. The result
12827 is not position independent code, and violates the IA-64 ABI@.
12829 @item -mvolatile-asm-stop
12830 @itemx -mno-volatile-asm-stop
12831 @opindex mvolatile-asm-stop
12832 @opindex mno-volatile-asm-stop
12833 Generate (or don't) a stop bit immediately before and after volatile asm
12836 @item -mregister-names
12837 @itemx -mno-register-names
12838 @opindex mregister-names
12839 @opindex mno-register-names
12840 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
12841 the stacked registers. This may make assembler output more readable.
12847 Disable (or enable) optimizations that use the small data section. This may
12848 be useful for working around optimizer bugs.
12850 @item -mconstant-gp
12851 @opindex mconstant-gp
12852 Generate code that uses a single constant global pointer value. This is
12853 useful when compiling kernel code.
12857 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
12858 This is useful when compiling firmware code.
12860 @item -minline-float-divide-min-latency
12861 @opindex minline-float-divide-min-latency
12862 Generate code for inline divides of floating point values
12863 using the minimum latency algorithm.
12865 @item -minline-float-divide-max-throughput
12866 @opindex minline-float-divide-max-throughput
12867 Generate code for inline divides of floating point values
12868 using the maximum throughput algorithm.
12870 @item -mno-inline-float-divide
12871 @opindex mno-inline-float-divide
12872 Do not generate inline code for divides of floating point values.
12874 @item -minline-int-divide-min-latency
12875 @opindex minline-int-divide-min-latency
12876 Generate code for inline divides of integer values
12877 using the minimum latency algorithm.
12879 @item -minline-int-divide-max-throughput
12880 @opindex minline-int-divide-max-throughput
12881 Generate code for inline divides of integer values
12882 using the maximum throughput algorithm.
12884 @item -mno-inline-int-divide
12885 @opindex mno-inline-int-divide
12886 Do not generate inline code for divides of integer values.
12888 @item -minline-sqrt-min-latency
12889 @opindex minline-sqrt-min-latency
12890 Generate code for inline square roots
12891 using the minimum latency algorithm.
12893 @item -minline-sqrt-max-throughput
12894 @opindex minline-sqrt-max-throughput
12895 Generate code for inline square roots
12896 using the maximum throughput algorithm.
12898 @item -mno-inline-sqrt
12899 @opindex mno-inline-sqrt
12900 Do not generate inline code for sqrt.
12903 @itemx -mno-fused-madd
12904 @opindex mfused-madd
12905 @opindex mno-fused-madd
12906 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
12907 instructions. The default is to use these instructions.
12909 @item -mno-dwarf2-asm
12910 @itemx -mdwarf2-asm
12911 @opindex mno-dwarf2-asm
12912 @opindex mdwarf2-asm
12913 Don't (or do) generate assembler code for the DWARF2 line number debugging
12914 info. This may be useful when not using the GNU assembler.
12916 @item -mearly-stop-bits
12917 @itemx -mno-early-stop-bits
12918 @opindex mearly-stop-bits
12919 @opindex mno-early-stop-bits
12920 Allow stop bits to be placed earlier than immediately preceding the
12921 instruction that triggered the stop bit. This can improve instruction
12922 scheduling, but does not always do so.
12924 @item -mfixed-range=@var{register-range}
12925 @opindex mfixed-range
12926 Generate code treating the given register range as fixed registers.
12927 A fixed register is one that the register allocator can not use. This is
12928 useful when compiling kernel code. A register range is specified as
12929 two registers separated by a dash. Multiple register ranges can be
12930 specified separated by a comma.
12932 @item -mtls-size=@var{tls-size}
12934 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
12937 @item -mtune=@var{cpu-type}
12939 Tune the instruction scheduling for a particular CPU, Valid values are
12940 itanium, itanium1, merced, itanium2, and mckinley.
12946 Generate code for a 32-bit or 64-bit environment.
12947 The 32-bit environment sets int, long and pointer to 32 bits.
12948 The 64-bit environment sets int to 32 bits and long and pointer
12949 to 64 bits. These are HP-UX specific flags.
12951 @item -mno-sched-br-data-spec
12952 @itemx -msched-br-data-spec
12953 @opindex mno-sched-br-data-spec
12954 @opindex msched-br-data-spec
12955 (Dis/En)able data speculative scheduling before reload.
12956 This will result in generation of the ld.a instructions and
12957 the corresponding check instructions (ld.c / chk.a).
12958 The default is 'disable'.
12960 @item -msched-ar-data-spec
12961 @itemx -mno-sched-ar-data-spec
12962 @opindex msched-ar-data-spec
12963 @opindex mno-sched-ar-data-spec
12964 (En/Dis)able data speculative scheduling after reload.
12965 This will result in generation of the ld.a instructions and
12966 the corresponding check instructions (ld.c / chk.a).
12967 The default is 'enable'.
12969 @item -mno-sched-control-spec
12970 @itemx -msched-control-spec
12971 @opindex mno-sched-control-spec
12972 @opindex msched-control-spec
12973 (Dis/En)able control speculative scheduling. This feature is
12974 available only during region scheduling (i.e.@: before reload).
12975 This will result in generation of the ld.s instructions and
12976 the corresponding check instructions chk.s .
12977 The default is 'disable'.
12979 @item -msched-br-in-data-spec
12980 @itemx -mno-sched-br-in-data-spec
12981 @opindex msched-br-in-data-spec
12982 @opindex mno-sched-br-in-data-spec
12983 (En/Dis)able speculative scheduling of the instructions that
12984 are dependent on the data speculative loads before reload.
12985 This is effective only with @option{-msched-br-data-spec} enabled.
12986 The default is 'enable'.
12988 @item -msched-ar-in-data-spec
12989 @itemx -mno-sched-ar-in-data-spec
12990 @opindex msched-ar-in-data-spec
12991 @opindex mno-sched-ar-in-data-spec
12992 (En/Dis)able speculative scheduling of the instructions that
12993 are dependent on the data speculative loads after reload.
12994 This is effective only with @option{-msched-ar-data-spec} enabled.
12995 The default is 'enable'.
12997 @item -msched-in-control-spec
12998 @itemx -mno-sched-in-control-spec
12999 @opindex msched-in-control-spec
13000 @opindex mno-sched-in-control-spec
13001 (En/Dis)able speculative scheduling of the instructions that
13002 are dependent on the control speculative loads.
13003 This is effective only with @option{-msched-control-spec} enabled.
13004 The default is 'enable'.
13006 @item -mno-sched-prefer-non-data-spec-insns
13007 @itemx -msched-prefer-non-data-spec-insns
13008 @opindex mno-sched-prefer-non-data-spec-insns
13009 @opindex msched-prefer-non-data-spec-insns
13010 If enabled, data speculative instructions will be chosen for schedule
13011 only if there are no other choices at the moment. This will make
13012 the use of the data speculation much more conservative.
13013 The default is 'disable'.
13015 @item -mno-sched-prefer-non-control-spec-insns
13016 @itemx -msched-prefer-non-control-spec-insns
13017 @opindex mno-sched-prefer-non-control-spec-insns
13018 @opindex msched-prefer-non-control-spec-insns
13019 If enabled, control speculative instructions will be chosen for schedule
13020 only if there are no other choices at the moment. This will make
13021 the use of the control speculation much more conservative.
13022 The default is 'disable'.
13024 @item -mno-sched-count-spec-in-critical-path
13025 @itemx -msched-count-spec-in-critical-path
13026 @opindex mno-sched-count-spec-in-critical-path
13027 @opindex msched-count-spec-in-critical-path
13028 If enabled, speculative dependencies will be considered during
13029 computation of the instructions priorities. This will make the use of the
13030 speculation a bit more conservative.
13031 The default is 'disable'.
13033 @item -msched-spec-ldc
13034 @opindex msched-spec-ldc
13035 Use a simple data speculation check. This option is on by default.
13037 @item -msched-control-spec-ldc
13038 @opindex msched-spec-ldc
13039 Use a simple check for control speculation. This option is on by default.
13041 @item -msched-stop-bits-after-every-cycle
13042 @opindex msched-stop-bits-after-every-cycle
13043 Place a stop bit after every cycle when scheduling. This option is on
13046 @item -msched-fp-mem-deps-zero-cost
13047 @opindex msched-fp-mem-deps-zero-cost
13048 Assume that floating-point stores and loads are not likely to cause a conflict
13049 when placed into the same instruction group. This option is disabled by
13052 @item -msel-sched-dont-check-control-spec
13053 @opindex msel-sched-dont-check-control-spec
13054 Generate checks for control speculation in selective scheduling.
13055 This flag is disabled by default.
13057 @item -msched-max-memory-insns=@var{max-insns}
13058 @opindex msched-max-memory-insns
13059 Limit on the number of memory insns per instruction group, giving lower
13060 priority to subsequent memory insns attempting to schedule in the same
13061 instruction group. Frequently useful to prevent cache bank conflicts.
13062 The default value is 1.
13064 @item -msched-max-memory-insns-hard-limit
13065 @opindex msched-max-memory-insns-hard-limit
13066 Disallow more than `msched-max-memory-insns' in instruction group.
13067 Otherwise, limit is `soft' meaning that we would prefer non-memory operations
13068 when limit is reached but may still schedule memory operations.
13072 @node IA-64/VMS Options
13073 @subsection IA-64/VMS Options
13075 These @samp{-m} options are defined for the IA-64/VMS implementations:
13078 @item -mvms-return-codes
13079 @opindex mvms-return-codes
13080 Return VMS condition codes from main. The default is to return POSIX
13081 style condition (e.g.@ error) codes.
13083 @item -mdebug-main=@var{prefix}
13084 @opindex mdebug-main=@var{prefix}
13085 Flag the first routine whose name starts with @var{prefix} as the main
13086 routine for the debugger.
13090 Default to 64bit memory allocation routines.
13094 @subsection LM32 Options
13095 @cindex LM32 options
13097 These @option{-m} options are defined for the Lattice Mico32 architecture:
13100 @item -mbarrel-shift-enabled
13101 @opindex mbarrel-shift-enabled
13102 Enable barrel-shift instructions.
13104 @item -mdivide-enabled
13105 @opindex mdivide-enabled
13106 Enable divide and modulus instructions.
13108 @item -mmultiply-enabled
13109 @opindex multiply-enabled
13110 Enable multiply instructions.
13112 @item -msign-extend-enabled
13113 @opindex msign-extend-enabled
13114 Enable sign extend instructions.
13116 @item -muser-enabled
13117 @opindex muser-enabled
13118 Enable user-defined instructions.
13123 @subsection M32C Options
13124 @cindex M32C options
13127 @item -mcpu=@var{name}
13129 Select the CPU for which code is generated. @var{name} may be one of
13130 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
13131 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
13132 the M32C/80 series.
13136 Specifies that the program will be run on the simulator. This causes
13137 an alternate runtime library to be linked in which supports, for
13138 example, file I/O@. You must not use this option when generating
13139 programs that will run on real hardware; you must provide your own
13140 runtime library for whatever I/O functions are needed.
13142 @item -memregs=@var{number}
13144 Specifies the number of memory-based pseudo-registers GCC will use
13145 during code generation. These pseudo-registers will be used like real
13146 registers, so there is a tradeoff between GCC's ability to fit the
13147 code into available registers, and the performance penalty of using
13148 memory instead of registers. Note that all modules in a program must
13149 be compiled with the same value for this option. Because of that, you
13150 must not use this option with the default runtime libraries gcc
13155 @node M32R/D Options
13156 @subsection M32R/D Options
13157 @cindex M32R/D options
13159 These @option{-m} options are defined for Renesas M32R/D architectures:
13164 Generate code for the M32R/2@.
13168 Generate code for the M32R/X@.
13172 Generate code for the M32R@. This is the default.
13174 @item -mmodel=small
13175 @opindex mmodel=small
13176 Assume all objects live in the lower 16MB of memory (so that their addresses
13177 can be loaded with the @code{ld24} instruction), and assume all subroutines
13178 are reachable with the @code{bl} instruction.
13179 This is the default.
13181 The addressability of a particular object can be set with the
13182 @code{model} attribute.
13184 @item -mmodel=medium
13185 @opindex mmodel=medium
13186 Assume objects may be anywhere in the 32-bit address space (the compiler
13187 will generate @code{seth/add3} instructions to load their addresses), and
13188 assume all subroutines are reachable with the @code{bl} instruction.
13190 @item -mmodel=large
13191 @opindex mmodel=large
13192 Assume objects may be anywhere in the 32-bit address space (the compiler
13193 will generate @code{seth/add3} instructions to load their addresses), and
13194 assume subroutines may not be reachable with the @code{bl} instruction
13195 (the compiler will generate the much slower @code{seth/add3/jl}
13196 instruction sequence).
13199 @opindex msdata=none
13200 Disable use of the small data area. Variables will be put into
13201 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
13202 @code{section} attribute has been specified).
13203 This is the default.
13205 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
13206 Objects may be explicitly put in the small data area with the
13207 @code{section} attribute using one of these sections.
13209 @item -msdata=sdata
13210 @opindex msdata=sdata
13211 Put small global and static data in the small data area, but do not
13212 generate special code to reference them.
13215 @opindex msdata=use
13216 Put small global and static data in the small data area, and generate
13217 special instructions to reference them.
13221 @cindex smaller data references
13222 Put global and static objects less than or equal to @var{num} bytes
13223 into the small data or bss sections instead of the normal data or bss
13224 sections. The default value of @var{num} is 8.
13225 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
13226 for this option to have any effect.
13228 All modules should be compiled with the same @option{-G @var{num}} value.
13229 Compiling with different values of @var{num} may or may not work; if it
13230 doesn't the linker will give an error message---incorrect code will not be
13235 Makes the M32R specific code in the compiler display some statistics
13236 that might help in debugging programs.
13238 @item -malign-loops
13239 @opindex malign-loops
13240 Align all loops to a 32-byte boundary.
13242 @item -mno-align-loops
13243 @opindex mno-align-loops
13244 Do not enforce a 32-byte alignment for loops. This is the default.
13246 @item -missue-rate=@var{number}
13247 @opindex missue-rate=@var{number}
13248 Issue @var{number} instructions per cycle. @var{number} can only be 1
13251 @item -mbranch-cost=@var{number}
13252 @opindex mbranch-cost=@var{number}
13253 @var{number} can only be 1 or 2. If it is 1 then branches will be
13254 preferred over conditional code, if it is 2, then the opposite will
13257 @item -mflush-trap=@var{number}
13258 @opindex mflush-trap=@var{number}
13259 Specifies the trap number to use to flush the cache. The default is
13260 12. Valid numbers are between 0 and 15 inclusive.
13262 @item -mno-flush-trap
13263 @opindex mno-flush-trap
13264 Specifies that the cache cannot be flushed by using a trap.
13266 @item -mflush-func=@var{name}
13267 @opindex mflush-func=@var{name}
13268 Specifies the name of the operating system function to call to flush
13269 the cache. The default is @emph{_flush_cache}, but a function call
13270 will only be used if a trap is not available.
13272 @item -mno-flush-func
13273 @opindex mno-flush-func
13274 Indicates that there is no OS function for flushing the cache.
13278 @node M680x0 Options
13279 @subsection M680x0 Options
13280 @cindex M680x0 options
13282 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
13283 The default settings depend on which architecture was selected when
13284 the compiler was configured; the defaults for the most common choices
13288 @item -march=@var{arch}
13290 Generate code for a specific M680x0 or ColdFire instruction set
13291 architecture. Permissible values of @var{arch} for M680x0
13292 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
13293 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
13294 architectures are selected according to Freescale's ISA classification
13295 and the permissible values are: @samp{isaa}, @samp{isaaplus},
13296 @samp{isab} and @samp{isac}.
13298 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
13299 code for a ColdFire target. The @var{arch} in this macro is one of the
13300 @option{-march} arguments given above.
13302 When used together, @option{-march} and @option{-mtune} select code
13303 that runs on a family of similar processors but that is optimized
13304 for a particular microarchitecture.
13306 @item -mcpu=@var{cpu}
13308 Generate code for a specific M680x0 or ColdFire processor.
13309 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
13310 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
13311 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
13312 below, which also classifies the CPUs into families:
13314 @multitable @columnfractions 0.20 0.80
13315 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
13316 @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51cn} @samp{51em} @samp{51qe}
13317 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
13318 @item @samp{5206e} @tab @samp{5206e}
13319 @item @samp{5208} @tab @samp{5207} @samp{5208}
13320 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
13321 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
13322 @item @samp{5216} @tab @samp{5214} @samp{5216}
13323 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
13324 @item @samp{5225} @tab @samp{5224} @samp{5225}
13325 @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
13326 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
13327 @item @samp{5249} @tab @samp{5249}
13328 @item @samp{5250} @tab @samp{5250}
13329 @item @samp{5271} @tab @samp{5270} @samp{5271}
13330 @item @samp{5272} @tab @samp{5272}
13331 @item @samp{5275} @tab @samp{5274} @samp{5275}
13332 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
13333 @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
13334 @item @samp{5307} @tab @samp{5307}
13335 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
13336 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
13337 @item @samp{5407} @tab @samp{5407}
13338 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
13341 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
13342 @var{arch} is compatible with @var{cpu}. Other combinations of
13343 @option{-mcpu} and @option{-march} are rejected.
13345 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
13346 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
13347 where the value of @var{family} is given by the table above.
13349 @item -mtune=@var{tune}
13351 Tune the code for a particular microarchitecture, within the
13352 constraints set by @option{-march} and @option{-mcpu}.
13353 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
13354 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
13355 and @samp{cpu32}. The ColdFire microarchitectures
13356 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
13358 You can also use @option{-mtune=68020-40} for code that needs
13359 to run relatively well on 68020, 68030 and 68040 targets.
13360 @option{-mtune=68020-60} is similar but includes 68060 targets
13361 as well. These two options select the same tuning decisions as
13362 @option{-m68020-40} and @option{-m68020-60} respectively.
13364 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
13365 when tuning for 680x0 architecture @var{arch}. It also defines
13366 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
13367 option is used. If gcc is tuning for a range of architectures,
13368 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
13369 it defines the macros for every architecture in the range.
13371 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
13372 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
13373 of the arguments given above.
13379 Generate output for a 68000. This is the default
13380 when the compiler is configured for 68000-based systems.
13381 It is equivalent to @option{-march=68000}.
13383 Use this option for microcontrollers with a 68000 or EC000 core,
13384 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
13388 Generate output for a 68010. This is the default
13389 when the compiler is configured for 68010-based systems.
13390 It is equivalent to @option{-march=68010}.
13396 Generate output for a 68020. This is the default
13397 when the compiler is configured for 68020-based systems.
13398 It is equivalent to @option{-march=68020}.
13402 Generate output for a 68030. This is the default when the compiler is
13403 configured for 68030-based systems. It is equivalent to
13404 @option{-march=68030}.
13408 Generate output for a 68040. This is the default when the compiler is
13409 configured for 68040-based systems. It is equivalent to
13410 @option{-march=68040}.
13412 This option inhibits the use of 68881/68882 instructions that have to be
13413 emulated by software on the 68040. Use this option if your 68040 does not
13414 have code to emulate those instructions.
13418 Generate output for a 68060. This is the default when the compiler is
13419 configured for 68060-based systems. It is equivalent to
13420 @option{-march=68060}.
13422 This option inhibits the use of 68020 and 68881/68882 instructions that
13423 have to be emulated by software on the 68060. Use this option if your 68060
13424 does not have code to emulate those instructions.
13428 Generate output for a CPU32. This is the default
13429 when the compiler is configured for CPU32-based systems.
13430 It is equivalent to @option{-march=cpu32}.
13432 Use this option for microcontrollers with a
13433 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
13434 68336, 68340, 68341, 68349 and 68360.
13438 Generate output for a 520X ColdFire CPU@. This is the default
13439 when the compiler is configured for 520X-based systems.
13440 It is equivalent to @option{-mcpu=5206}, and is now deprecated
13441 in favor of that option.
13443 Use this option for microcontroller with a 5200 core, including
13444 the MCF5202, MCF5203, MCF5204 and MCF5206.
13448 Generate output for a 5206e ColdFire CPU@. The option is now
13449 deprecated in favor of the equivalent @option{-mcpu=5206e}.
13453 Generate output for a member of the ColdFire 528X family.
13454 The option is now deprecated in favor of the equivalent
13455 @option{-mcpu=528x}.
13459 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
13460 in favor of the equivalent @option{-mcpu=5307}.
13464 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
13465 in favor of the equivalent @option{-mcpu=5407}.
13469 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
13470 This includes use of hardware floating point instructions.
13471 The option is equivalent to @option{-mcpu=547x}, and is now
13472 deprecated in favor of that option.
13476 Generate output for a 68040, without using any of the new instructions.
13477 This results in code which can run relatively efficiently on either a
13478 68020/68881 or a 68030 or a 68040. The generated code does use the
13479 68881 instructions that are emulated on the 68040.
13481 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
13485 Generate output for a 68060, without using any of the new instructions.
13486 This results in code which can run relatively efficiently on either a
13487 68020/68881 or a 68030 or a 68040. The generated code does use the
13488 68881 instructions that are emulated on the 68060.
13490 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
13494 @opindex mhard-float
13496 Generate floating-point instructions. This is the default for 68020
13497 and above, and for ColdFire devices that have an FPU@. It defines the
13498 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
13499 on ColdFire targets.
13502 @opindex msoft-float
13503 Do not generate floating-point instructions; use library calls instead.
13504 This is the default for 68000, 68010, and 68832 targets. It is also
13505 the default for ColdFire devices that have no FPU.
13511 Generate (do not generate) ColdFire hardware divide and remainder
13512 instructions. If @option{-march} is used without @option{-mcpu},
13513 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
13514 architectures. Otherwise, the default is taken from the target CPU
13515 (either the default CPU, or the one specified by @option{-mcpu}). For
13516 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
13517 @option{-mcpu=5206e}.
13519 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
13523 Consider type @code{int} to be 16 bits wide, like @code{short int}.
13524 Additionally, parameters passed on the stack are also aligned to a
13525 16-bit boundary even on targets whose API mandates promotion to 32-bit.
13529 Do not consider type @code{int} to be 16 bits wide. This is the default.
13532 @itemx -mno-bitfield
13533 @opindex mnobitfield
13534 @opindex mno-bitfield
13535 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
13536 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
13540 Do use the bit-field instructions. The @option{-m68020} option implies
13541 @option{-mbitfield}. This is the default if you use a configuration
13542 designed for a 68020.
13546 Use a different function-calling convention, in which functions
13547 that take a fixed number of arguments return with the @code{rtd}
13548 instruction, which pops their arguments while returning. This
13549 saves one instruction in the caller since there is no need to pop
13550 the arguments there.
13552 This calling convention is incompatible with the one normally
13553 used on Unix, so you cannot use it if you need to call libraries
13554 compiled with the Unix compiler.
13556 Also, you must provide function prototypes for all functions that
13557 take variable numbers of arguments (including @code{printf});
13558 otherwise incorrect code will be generated for calls to those
13561 In addition, seriously incorrect code will result if you call a
13562 function with too many arguments. (Normally, extra arguments are
13563 harmlessly ignored.)
13565 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
13566 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
13570 Do not use the calling conventions selected by @option{-mrtd}.
13571 This is the default.
13574 @itemx -mno-align-int
13575 @opindex malign-int
13576 @opindex mno-align-int
13577 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
13578 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
13579 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
13580 Aligning variables on 32-bit boundaries produces code that runs somewhat
13581 faster on processors with 32-bit busses at the expense of more memory.
13583 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
13584 align structures containing the above types differently than
13585 most published application binary interface specifications for the m68k.
13589 Use the pc-relative addressing mode of the 68000 directly, instead of
13590 using a global offset table. At present, this option implies @option{-fpic},
13591 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
13592 not presently supported with @option{-mpcrel}, though this could be supported for
13593 68020 and higher processors.
13595 @item -mno-strict-align
13596 @itemx -mstrict-align
13597 @opindex mno-strict-align
13598 @opindex mstrict-align
13599 Do not (do) assume that unaligned memory references will be handled by
13603 Generate code that allows the data segment to be located in a different
13604 area of memory from the text segment. This allows for execute in place in
13605 an environment without virtual memory management. This option implies
13608 @item -mno-sep-data
13609 Generate code that assumes that the data segment follows the text segment.
13610 This is the default.
13612 @item -mid-shared-library
13613 Generate code that supports shared libraries via the library ID method.
13614 This allows for execute in place and shared libraries in an environment
13615 without virtual memory management. This option implies @option{-fPIC}.
13617 @item -mno-id-shared-library
13618 Generate code that doesn't assume ID based shared libraries are being used.
13619 This is the default.
13621 @item -mshared-library-id=n
13622 Specified the identification number of the ID based shared library being
13623 compiled. Specifying a value of 0 will generate more compact code, specifying
13624 other values will force the allocation of that number to the current
13625 library but is no more space or time efficient than omitting this option.
13631 When generating position-independent code for ColdFire, generate code
13632 that works if the GOT has more than 8192 entries. This code is
13633 larger and slower than code generated without this option. On M680x0
13634 processors, this option is not needed; @option{-fPIC} suffices.
13636 GCC normally uses a single instruction to load values from the GOT@.
13637 While this is relatively efficient, it only works if the GOT
13638 is smaller than about 64k. Anything larger causes the linker
13639 to report an error such as:
13641 @cindex relocation truncated to fit (ColdFire)
13643 relocation truncated to fit: R_68K_GOT16O foobar
13646 If this happens, you should recompile your code with @option{-mxgot}.
13647 It should then work with very large GOTs. However, code generated with
13648 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
13649 the value of a global symbol.
13651 Note that some linkers, including newer versions of the GNU linker,
13652 can create multiple GOTs and sort GOT entries. If you have such a linker,
13653 you should only need to use @option{-mxgot} when compiling a single
13654 object file that accesses more than 8192 GOT entries. Very few do.
13656 These options have no effect unless GCC is generating
13657 position-independent code.
13661 @node MCore Options
13662 @subsection MCore Options
13663 @cindex MCore options
13665 These are the @samp{-m} options defined for the Motorola M*Core
13671 @itemx -mno-hardlit
13673 @opindex mno-hardlit
13674 Inline constants into the code stream if it can be done in two
13675 instructions or less.
13681 Use the divide instruction. (Enabled by default).
13683 @item -mrelax-immediate
13684 @itemx -mno-relax-immediate
13685 @opindex mrelax-immediate
13686 @opindex mno-relax-immediate
13687 Allow arbitrary sized immediates in bit operations.
13689 @item -mwide-bitfields
13690 @itemx -mno-wide-bitfields
13691 @opindex mwide-bitfields
13692 @opindex mno-wide-bitfields
13693 Always treat bit-fields as int-sized.
13695 @item -m4byte-functions
13696 @itemx -mno-4byte-functions
13697 @opindex m4byte-functions
13698 @opindex mno-4byte-functions
13699 Force all functions to be aligned to a four byte boundary.
13701 @item -mcallgraph-data
13702 @itemx -mno-callgraph-data
13703 @opindex mcallgraph-data
13704 @opindex mno-callgraph-data
13705 Emit callgraph information.
13708 @itemx -mno-slow-bytes
13709 @opindex mslow-bytes
13710 @opindex mno-slow-bytes
13711 Prefer word access when reading byte quantities.
13713 @item -mlittle-endian
13714 @itemx -mbig-endian
13715 @opindex mlittle-endian
13716 @opindex mbig-endian
13717 Generate code for a little endian target.
13723 Generate code for the 210 processor.
13727 Assume that run-time support has been provided and so omit the
13728 simulator library (@file{libsim.a)} from the linker command line.
13730 @item -mstack-increment=@var{size}
13731 @opindex mstack-increment
13732 Set the maximum amount for a single stack increment operation. Large
13733 values can increase the speed of programs which contain functions
13734 that need a large amount of stack space, but they can also trigger a
13735 segmentation fault if the stack is extended too much. The default
13741 @subsection MeP Options
13742 @cindex MeP options
13748 Enables the @code{abs} instruction, which is the absolute difference
13749 between two registers.
13753 Enables all the optional instructions - average, multiply, divide, bit
13754 operations, leading zero, absolute difference, min/max, clip, and
13760 Enables the @code{ave} instruction, which computes the average of two
13763 @item -mbased=@var{n}
13765 Variables of size @var{n} bytes or smaller will be placed in the
13766 @code{.based} section by default. Based variables use the @code{$tp}
13767 register as a base register, and there is a 128 byte limit to the
13768 @code{.based} section.
13772 Enables the bit operation instructions - bit test (@code{btstm}), set
13773 (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
13774 test-and-set (@code{tas}).
13776 @item -mc=@var{name}
13778 Selects which section constant data will be placed in. @var{name} may
13779 be @code{tiny}, @code{near}, or @code{far}.
13783 Enables the @code{clip} instruction. Note that @code{-mclip} is not
13784 useful unless you also provide @code{-mminmax}.
13786 @item -mconfig=@var{name}
13788 Selects one of the build-in core configurations. Each MeP chip has
13789 one or more modules in it; each module has a core CPU and a variety of
13790 coprocessors, optional instructions, and peripherals. The
13791 @code{MeP-Integrator} tool, not part of GCC, provides these
13792 configurations through this option; using this option is the same as
13793 using all the corresponding command line options. The default
13794 configuration is @code{default}.
13798 Enables the coprocessor instructions. By default, this is a 32-bit
13799 coprocessor. Note that the coprocessor is normally enabled via the
13800 @code{-mconfig=} option.
13804 Enables the 32-bit coprocessor's instructions.
13808 Enables the 64-bit coprocessor's instructions.
13812 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
13816 Causes constant variables to be placed in the @code{.near} section.
13820 Enables the @code{div} and @code{divu} instructions.
13824 Generate big-endian code.
13828 Generate little-endian code.
13830 @item -mio-volatile
13831 @opindex mio-volatile
13832 Tells the compiler that any variable marked with the @code{io}
13833 attribute is to be considered volatile.
13837 Causes variables to be assigned to the @code{.far} section by default.
13841 Enables the @code{leadz} (leading zero) instruction.
13845 Causes variables to be assigned to the @code{.near} section by default.
13849 Enables the @code{min} and @code{max} instructions.
13853 Enables the multiplication and multiply-accumulate instructions.
13857 Disables all the optional instructions enabled by @code{-mall-opts}.
13861 Enables the @code{repeat} and @code{erepeat} instructions, used for
13862 low-overhead looping.
13866 Causes all variables to default to the @code{.tiny} section. Note
13867 that there is a 65536 byte limit to this section. Accesses to these
13868 variables use the @code{%gp} base register.
13872 Enables the saturation instructions. Note that the compiler does not
13873 currently generate these itself, but this option is included for
13874 compatibility with other tools, like @code{as}.
13878 Link the SDRAM-based runtime instead of the default ROM-based runtime.
13882 Link the simulator runtime libraries.
13886 Link the simulator runtime libraries, excluding built-in support
13887 for reset and exception vectors and tables.
13891 Causes all functions to default to the @code{.far} section. Without
13892 this option, functions default to the @code{.near} section.
13894 @item -mtiny=@var{n}
13896 Variables that are @var{n} bytes or smaller will be allocated to the
13897 @code{.tiny} section. These variables use the @code{$gp} base
13898 register. The default for this option is 4, but note that there's a
13899 65536 byte limit to the @code{.tiny} section.
13903 @node MicroBlaze Options
13904 @subsection MicroBlaze Options
13905 @cindex MicroBlaze Options
13910 @opindex msoft-float
13911 Use software emulation for floating point (default).
13914 @opindex mhard-float
13915 Use hardware floating point instructions.
13919 Do not optimize block moves, use @code{memcpy}.
13921 @item -mno-clearbss
13922 @opindex mno-clearbss
13923 This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead.
13925 @item -mcpu=@var{cpu-type}
13927 Use features of and schedule code for given CPU.
13928 Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}},
13929 where @var{X} is a major version, @var{YY} is the minor version, and
13930 @var{Z} is compatibility code. Example values are @samp{v3.00.a},
13931 @samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}.
13933 @item -mxl-soft-mul
13934 @opindex mxl-soft-mul
13935 Use software multiply emulation (default).
13937 @item -mxl-soft-div
13938 @opindex mxl-soft-div
13939 Use software emulation for divides (default).
13941 @item -mxl-barrel-shift
13942 @opindex mxl-barrel-shift
13943 Use the hardware barrel shifter.
13945 @item -mxl-pattern-compare
13946 @opindex mxl-pattern-compare
13947 Use pattern compare instructions.
13949 @item -msmall-divides
13950 @opindex msmall-divides
13951 Use table lookup optimization for small signed integer divisions.
13953 @item -mxl-stack-check
13954 @opindex mxl-stack-check
13955 This option is deprecated. Use -fstack-check instead.
13958 @opindex mxl-gp-opt
13959 Use GP relative sdata/sbss sections.
13961 @item -mxl-multiply-high
13962 @opindex mxl-multiply-high
13963 Use multiply high instructions for high part of 32x32 multiply.
13965 @item -mxl-float-convert
13966 @opindex mxl-float-convert
13967 Use hardware floating point conversion instructions.
13969 @item -mxl-float-sqrt
13970 @opindex mxl-float-sqrt
13971 Use hardware floating point square root instruction.
13973 @item -mxl-mode-@var{app-model}
13974 Select application model @var{app-model}. Valid models are
13977 normal executable (default), uses startup code @file{crt0.o}.
13980 for use with Xilinx Microprocessor Debugger (XMD) based
13981 software intrusive debug agent called xmdstub. This uses startup file
13982 @file{crt1.o} and sets the start address of the program to be 0x800.
13985 for applications that are loaded using a bootloader.
13986 This model uses startup file @file{crt2.o} which does not contain a processor
13987 reset vector handler. This is suitable for transferring control on a
13988 processor reset to the bootloader rather than the application.
13991 for applications that do not require any of the
13992 MicroBlaze vectors. This option may be useful for applications running
13993 within a monitoring application. This model uses @file{crt3.o} as a startup file.
13996 Option @option{-xl-mode-@var{app-model}} is a deprecated alias for
13997 @option{-mxl-mode-@var{app-model}}.
14002 @subsection MIPS Options
14003 @cindex MIPS options
14009 Generate big-endian code.
14013 Generate little-endian code. This is the default for @samp{mips*el-*-*}
14016 @item -march=@var{arch}
14018 Generate code that will run on @var{arch}, which can be the name of a
14019 generic MIPS ISA, or the name of a particular processor.
14021 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
14022 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
14023 The processor names are:
14024 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
14025 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
14026 @samp{5kc}, @samp{5kf},
14028 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
14029 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
14030 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
14031 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
14032 @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
14033 @samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a},
14037 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
14038 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
14039 @samp{rm7000}, @samp{rm9000},
14040 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
14043 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
14044 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
14046 The special value @samp{from-abi} selects the
14047 most compatible architecture for the selected ABI (that is,
14048 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
14050 Native Linux/GNU toolchains also support the value @samp{native},
14051 which selects the best architecture option for the host processor.
14052 @option{-march=native} has no effect if GCC does not recognize
14055 In processor names, a final @samp{000} can be abbreviated as @samp{k}
14056 (for example, @samp{-march=r2k}). Prefixes are optional, and
14057 @samp{vr} may be written @samp{r}.
14059 Names of the form @samp{@var{n}f2_1} refer to processors with
14060 FPUs clocked at half the rate of the core, names of the form
14061 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
14062 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
14063 processors with FPUs clocked a ratio of 3:2 with respect to the core.
14064 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
14065 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
14066 accepted as synonyms for @samp{@var{n}f1_1}.
14068 GCC defines two macros based on the value of this option. The first
14069 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
14070 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
14071 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
14072 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
14073 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
14075 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
14076 above. In other words, it will have the full prefix and will not
14077 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
14078 the macro names the resolved architecture (either @samp{"mips1"} or
14079 @samp{"mips3"}). It names the default architecture when no
14080 @option{-march} option is given.
14082 @item -mtune=@var{arch}
14084 Optimize for @var{arch}. Among other things, this option controls
14085 the way instructions are scheduled, and the perceived cost of arithmetic
14086 operations. The list of @var{arch} values is the same as for
14089 When this option is not used, GCC will optimize for the processor
14090 specified by @option{-march}. By using @option{-march} and
14091 @option{-mtune} together, it is possible to generate code that will
14092 run on a family of processors, but optimize the code for one
14093 particular member of that family.
14095 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
14096 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
14097 @samp{-march} ones described above.
14101 Equivalent to @samp{-march=mips1}.
14105 Equivalent to @samp{-march=mips2}.
14109 Equivalent to @samp{-march=mips3}.
14113 Equivalent to @samp{-march=mips4}.
14117 Equivalent to @samp{-march=mips32}.
14121 Equivalent to @samp{-march=mips32r2}.
14125 Equivalent to @samp{-march=mips64}.
14129 Equivalent to @samp{-march=mips64r2}.
14134 @opindex mno-mips16
14135 Generate (do not generate) MIPS16 code. If GCC is targetting a
14136 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
14138 MIPS16 code generation can also be controlled on a per-function basis
14139 by means of @code{mips16} and @code{nomips16} attributes.
14140 @xref{Function Attributes}, for more information.
14142 @item -mflip-mips16
14143 @opindex mflip-mips16
14144 Generate MIPS16 code on alternating functions. This option is provided
14145 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
14146 not intended for ordinary use in compiling user code.
14148 @item -minterlink-mips16
14149 @itemx -mno-interlink-mips16
14150 @opindex minterlink-mips16
14151 @opindex mno-interlink-mips16
14152 Require (do not require) that non-MIPS16 code be link-compatible with
14155 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
14156 it must either use a call or an indirect jump. @option{-minterlink-mips16}
14157 therefore disables direct jumps unless GCC knows that the target of the
14158 jump is not MIPS16.
14170 Generate code for the given ABI@.
14172 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
14173 generates 64-bit code when you select a 64-bit architecture, but you
14174 can use @option{-mgp32} to get 32-bit code instead.
14176 For information about the O64 ABI, see
14177 @uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}.
14179 GCC supports a variant of the o32 ABI in which floating-point registers
14180 are 64 rather than 32 bits wide. You can select this combination with
14181 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
14182 and @samp{mfhc1} instructions and is therefore only supported for
14183 MIPS32R2 processors.
14185 The register assignments for arguments and return values remain the
14186 same, but each scalar value is passed in a single 64-bit register
14187 rather than a pair of 32-bit registers. For example, scalar
14188 floating-point values are returned in @samp{$f0} only, not a
14189 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
14190 remains the same, but all 64 bits are saved.
14193 @itemx -mno-abicalls
14195 @opindex mno-abicalls
14196 Generate (do not generate) code that is suitable for SVR4-style
14197 dynamic objects. @option{-mabicalls} is the default for SVR4-based
14202 Generate (do not generate) code that is fully position-independent,
14203 and that can therefore be linked into shared libraries. This option
14204 only affects @option{-mabicalls}.
14206 All @option{-mabicalls} code has traditionally been position-independent,
14207 regardless of options like @option{-fPIC} and @option{-fpic}. However,
14208 as an extension, the GNU toolchain allows executables to use absolute
14209 accesses for locally-binding symbols. It can also use shorter GP
14210 initialization sequences and generate direct calls to locally-defined
14211 functions. This mode is selected by @option{-mno-shared}.
14213 @option{-mno-shared} depends on binutils 2.16 or higher and generates
14214 objects that can only be linked by the GNU linker. However, the option
14215 does not affect the ABI of the final executable; it only affects the ABI
14216 of relocatable objects. Using @option{-mno-shared} will generally make
14217 executables both smaller and quicker.
14219 @option{-mshared} is the default.
14225 Assume (do not assume) that the static and dynamic linkers
14226 support PLTs and copy relocations. This option only affects
14227 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
14228 has no effect without @samp{-msym32}.
14230 You can make @option{-mplt} the default by configuring
14231 GCC with @option{--with-mips-plt}. The default is
14232 @option{-mno-plt} otherwise.
14238 Lift (do not lift) the usual restrictions on the size of the global
14241 GCC normally uses a single instruction to load values from the GOT@.
14242 While this is relatively efficient, it will only work if the GOT
14243 is smaller than about 64k. Anything larger will cause the linker
14244 to report an error such as:
14246 @cindex relocation truncated to fit (MIPS)
14248 relocation truncated to fit: R_MIPS_GOT16 foobar
14251 If this happens, you should recompile your code with @option{-mxgot}.
14252 It should then work with very large GOTs, although it will also be
14253 less efficient, since it will take three instructions to fetch the
14254 value of a global symbol.
14256 Note that some linkers can create multiple GOTs. If you have such a
14257 linker, you should only need to use @option{-mxgot} when a single object
14258 file accesses more than 64k's worth of GOT entries. Very few do.
14260 These options have no effect unless GCC is generating position
14265 Assume that general-purpose registers are 32 bits wide.
14269 Assume that general-purpose registers are 64 bits wide.
14273 Assume that floating-point registers are 32 bits wide.
14277 Assume that floating-point registers are 64 bits wide.
14280 @opindex mhard-float
14281 Use floating-point coprocessor instructions.
14284 @opindex msoft-float
14285 Do not use floating-point coprocessor instructions. Implement
14286 floating-point calculations using library calls instead.
14288 @item -msingle-float
14289 @opindex msingle-float
14290 Assume that the floating-point coprocessor only supports single-precision
14293 @item -mdouble-float
14294 @opindex mdouble-float
14295 Assume that the floating-point coprocessor supports double-precision
14296 operations. This is the default.
14302 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
14303 implement atomic memory built-in functions. When neither option is
14304 specified, GCC will use the instructions if the target architecture
14307 @option{-mllsc} is useful if the runtime environment can emulate the
14308 instructions and @option{-mno-llsc} can be useful when compiling for
14309 nonstandard ISAs. You can make either option the default by
14310 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
14311 respectively. @option{--with-llsc} is the default for some
14312 configurations; see the installation documentation for details.
14318 Use (do not use) revision 1 of the MIPS DSP ASE@.
14319 @xref{MIPS DSP Built-in Functions}. This option defines the
14320 preprocessor macro @samp{__mips_dsp}. It also defines
14321 @samp{__mips_dsp_rev} to 1.
14327 Use (do not use) revision 2 of the MIPS DSP ASE@.
14328 @xref{MIPS DSP Built-in Functions}. This option defines the
14329 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
14330 It also defines @samp{__mips_dsp_rev} to 2.
14333 @itemx -mno-smartmips
14334 @opindex msmartmips
14335 @opindex mno-smartmips
14336 Use (do not use) the MIPS SmartMIPS ASE.
14338 @item -mpaired-single
14339 @itemx -mno-paired-single
14340 @opindex mpaired-single
14341 @opindex mno-paired-single
14342 Use (do not use) paired-single floating-point instructions.
14343 @xref{MIPS Paired-Single Support}. This option requires
14344 hardware floating-point support to be enabled.
14350 Use (do not use) MIPS Digital Media Extension instructions.
14351 This option can only be used when generating 64-bit code and requires
14352 hardware floating-point support to be enabled.
14357 @opindex mno-mips3d
14358 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
14359 The option @option{-mips3d} implies @option{-mpaired-single}.
14365 Use (do not use) MT Multithreading instructions.
14369 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
14370 an explanation of the default and the way that the pointer size is
14375 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
14377 The default size of @code{int}s, @code{long}s and pointers depends on
14378 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
14379 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
14380 32-bit @code{long}s. Pointers are the same size as @code{long}s,
14381 or the same size as integer registers, whichever is smaller.
14387 Assume (do not assume) that all symbols have 32-bit values, regardless
14388 of the selected ABI@. This option is useful in combination with
14389 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
14390 to generate shorter and faster references to symbolic addresses.
14394 Put definitions of externally-visible data in a small data section
14395 if that data is no bigger than @var{num} bytes. GCC can then access
14396 the data more efficiently; see @option{-mgpopt} for details.
14398 The default @option{-G} option depends on the configuration.
14400 @item -mlocal-sdata
14401 @itemx -mno-local-sdata
14402 @opindex mlocal-sdata
14403 @opindex mno-local-sdata
14404 Extend (do not extend) the @option{-G} behavior to local data too,
14405 such as to static variables in C@. @option{-mlocal-sdata} is the
14406 default for all configurations.
14408 If the linker complains that an application is using too much small data,
14409 you might want to try rebuilding the less performance-critical parts with
14410 @option{-mno-local-sdata}. You might also want to build large
14411 libraries with @option{-mno-local-sdata}, so that the libraries leave
14412 more room for the main program.
14414 @item -mextern-sdata
14415 @itemx -mno-extern-sdata
14416 @opindex mextern-sdata
14417 @opindex mno-extern-sdata
14418 Assume (do not assume) that externally-defined data will be in
14419 a small data section if that data is within the @option{-G} limit.
14420 @option{-mextern-sdata} is the default for all configurations.
14422 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
14423 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
14424 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
14425 is placed in a small data section. If @var{Var} is defined by another
14426 module, you must either compile that module with a high-enough
14427 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
14428 definition. If @var{Var} is common, you must link the application
14429 with a high-enough @option{-G} setting.
14431 The easiest way of satisfying these restrictions is to compile
14432 and link every module with the same @option{-G} option. However,
14433 you may wish to build a library that supports several different
14434 small data limits. You can do this by compiling the library with
14435 the highest supported @option{-G} setting and additionally using
14436 @option{-mno-extern-sdata} to stop the library from making assumptions
14437 about externally-defined data.
14443 Use (do not use) GP-relative accesses for symbols that are known to be
14444 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
14445 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
14448 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
14449 might not hold the value of @code{_gp}. For example, if the code is
14450 part of a library that might be used in a boot monitor, programs that
14451 call boot monitor routines will pass an unknown value in @code{$gp}.
14452 (In such situations, the boot monitor itself would usually be compiled
14453 with @option{-G0}.)
14455 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
14456 @option{-mno-extern-sdata}.
14458 @item -membedded-data
14459 @itemx -mno-embedded-data
14460 @opindex membedded-data
14461 @opindex mno-embedded-data
14462 Allocate variables to the read-only data section first if possible, then
14463 next in the small data section if possible, otherwise in data. This gives
14464 slightly slower code than the default, but reduces the amount of RAM required
14465 when executing, and thus may be preferred for some embedded systems.
14467 @item -muninit-const-in-rodata
14468 @itemx -mno-uninit-const-in-rodata
14469 @opindex muninit-const-in-rodata
14470 @opindex mno-uninit-const-in-rodata
14471 Put uninitialized @code{const} variables in the read-only data section.
14472 This option is only meaningful in conjunction with @option{-membedded-data}.
14474 @item -mcode-readable=@var{setting}
14475 @opindex mcode-readable
14476 Specify whether GCC may generate code that reads from executable sections.
14477 There are three possible settings:
14480 @item -mcode-readable=yes
14481 Instructions may freely access executable sections. This is the
14484 @item -mcode-readable=pcrel
14485 MIPS16 PC-relative load instructions can access executable sections,
14486 but other instructions must not do so. This option is useful on 4KSc
14487 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
14488 It is also useful on processors that can be configured to have a dual
14489 instruction/data SRAM interface and that, like the M4K, automatically
14490 redirect PC-relative loads to the instruction RAM.
14492 @item -mcode-readable=no
14493 Instructions must not access executable sections. This option can be
14494 useful on targets that are configured to have a dual instruction/data
14495 SRAM interface but that (unlike the M4K) do not automatically redirect
14496 PC-relative loads to the instruction RAM.
14499 @item -msplit-addresses
14500 @itemx -mno-split-addresses
14501 @opindex msplit-addresses
14502 @opindex mno-split-addresses
14503 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
14504 relocation operators. This option has been superseded by
14505 @option{-mexplicit-relocs} but is retained for backwards compatibility.
14507 @item -mexplicit-relocs
14508 @itemx -mno-explicit-relocs
14509 @opindex mexplicit-relocs
14510 @opindex mno-explicit-relocs
14511 Use (do not use) assembler relocation operators when dealing with symbolic
14512 addresses. The alternative, selected by @option{-mno-explicit-relocs},
14513 is to use assembler macros instead.
14515 @option{-mexplicit-relocs} is the default if GCC was configured
14516 to use an assembler that supports relocation operators.
14518 @item -mcheck-zero-division
14519 @itemx -mno-check-zero-division
14520 @opindex mcheck-zero-division
14521 @opindex mno-check-zero-division
14522 Trap (do not trap) on integer division by zero.
14524 The default is @option{-mcheck-zero-division}.
14526 @item -mdivide-traps
14527 @itemx -mdivide-breaks
14528 @opindex mdivide-traps
14529 @opindex mdivide-breaks
14530 MIPS systems check for division by zero by generating either a
14531 conditional trap or a break instruction. Using traps results in
14532 smaller code, but is only supported on MIPS II and later. Also, some
14533 versions of the Linux kernel have a bug that prevents trap from
14534 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
14535 allow conditional traps on architectures that support them and
14536 @option{-mdivide-breaks} to force the use of breaks.
14538 The default is usually @option{-mdivide-traps}, but this can be
14539 overridden at configure time using @option{--with-divide=breaks}.
14540 Divide-by-zero checks can be completely disabled using
14541 @option{-mno-check-zero-division}.
14546 @opindex mno-memcpy
14547 Force (do not force) the use of @code{memcpy()} for non-trivial block
14548 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
14549 most constant-sized copies.
14552 @itemx -mno-long-calls
14553 @opindex mlong-calls
14554 @opindex mno-long-calls
14555 Disable (do not disable) use of the @code{jal} instruction. Calling
14556 functions using @code{jal} is more efficient but requires the caller
14557 and callee to be in the same 256 megabyte segment.
14559 This option has no effect on abicalls code. The default is
14560 @option{-mno-long-calls}.
14566 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
14567 instructions, as provided by the R4650 ISA@.
14570 @itemx -mno-fused-madd
14571 @opindex mfused-madd
14572 @opindex mno-fused-madd
14573 Enable (disable) use of the floating point multiply-accumulate
14574 instructions, when they are available. The default is
14575 @option{-mfused-madd}.
14577 When multiply-accumulate instructions are used, the intermediate
14578 product is calculated to infinite precision and is not subject to
14579 the FCSR Flush to Zero bit. This may be undesirable in some
14584 Tell the MIPS assembler to not run its preprocessor over user
14585 assembler files (with a @samp{.s} suffix) when assembling them.
14588 @itemx -mno-fix-r4000
14589 @opindex mfix-r4000
14590 @opindex mno-fix-r4000
14591 Work around certain R4000 CPU errata:
14594 A double-word or a variable shift may give an incorrect result if executed
14595 immediately after starting an integer division.
14597 A double-word or a variable shift may give an incorrect result if executed
14598 while an integer multiplication is in progress.
14600 An integer division may give an incorrect result if started in a delay slot
14601 of a taken branch or a jump.
14605 @itemx -mno-fix-r4400
14606 @opindex mfix-r4400
14607 @opindex mno-fix-r4400
14608 Work around certain R4400 CPU errata:
14611 A double-word or a variable shift may give an incorrect result if executed
14612 immediately after starting an integer division.
14616 @itemx -mno-fix-r10000
14617 @opindex mfix-r10000
14618 @opindex mno-fix-r10000
14619 Work around certain R10000 errata:
14622 @code{ll}/@code{sc} sequences may not behave atomically on revisions
14623 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
14626 This option can only be used if the target architecture supports
14627 branch-likely instructions. @option{-mfix-r10000} is the default when
14628 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
14632 @itemx -mno-fix-vr4120
14633 @opindex mfix-vr4120
14634 Work around certain VR4120 errata:
14637 @code{dmultu} does not always produce the correct result.
14639 @code{div} and @code{ddiv} do not always produce the correct result if one
14640 of the operands is negative.
14642 The workarounds for the division errata rely on special functions in
14643 @file{libgcc.a}. At present, these functions are only provided by
14644 the @code{mips64vr*-elf} configurations.
14646 Other VR4120 errata require a nop to be inserted between certain pairs of
14647 instructions. These errata are handled by the assembler, not by GCC itself.
14650 @opindex mfix-vr4130
14651 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
14652 workarounds are implemented by the assembler rather than by GCC,
14653 although GCC will avoid using @code{mflo} and @code{mfhi} if the
14654 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
14655 instructions are available instead.
14658 @itemx -mno-fix-sb1
14660 Work around certain SB-1 CPU core errata.
14661 (This flag currently works around the SB-1 revision 2
14662 ``F1'' and ``F2'' floating point errata.)
14664 @item -mr10k-cache-barrier=@var{setting}
14665 @opindex mr10k-cache-barrier
14666 Specify whether GCC should insert cache barriers to avoid the
14667 side-effects of speculation on R10K processors.
14669 In common with many processors, the R10K tries to predict the outcome
14670 of a conditional branch and speculatively executes instructions from
14671 the ``taken'' branch. It later aborts these instructions if the
14672 predicted outcome was wrong. However, on the R10K, even aborted
14673 instructions can have side effects.
14675 This problem only affects kernel stores and, depending on the system,
14676 kernel loads. As an example, a speculatively-executed store may load
14677 the target memory into cache and mark the cache line as dirty, even if
14678 the store itself is later aborted. If a DMA operation writes to the
14679 same area of memory before the ``dirty'' line is flushed, the cached
14680 data will overwrite the DMA-ed data. See the R10K processor manual
14681 for a full description, including other potential problems.
14683 One workaround is to insert cache barrier instructions before every memory
14684 access that might be speculatively executed and that might have side
14685 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
14686 controls GCC's implementation of this workaround. It assumes that
14687 aborted accesses to any byte in the following regions will not have
14692 the memory occupied by the current function's stack frame;
14695 the memory occupied by an incoming stack argument;
14698 the memory occupied by an object with a link-time-constant address.
14701 It is the kernel's responsibility to ensure that speculative
14702 accesses to these regions are indeed safe.
14704 If the input program contains a function declaration such as:
14710 then the implementation of @code{foo} must allow @code{j foo} and
14711 @code{jal foo} to be executed speculatively. GCC honors this
14712 restriction for functions it compiles itself. It expects non-GCC
14713 functions (such as hand-written assembly code) to do the same.
14715 The option has three forms:
14718 @item -mr10k-cache-barrier=load-store
14719 Insert a cache barrier before a load or store that might be
14720 speculatively executed and that might have side effects even
14723 @item -mr10k-cache-barrier=store
14724 Insert a cache barrier before a store that might be speculatively
14725 executed and that might have side effects even if aborted.
14727 @item -mr10k-cache-barrier=none
14728 Disable the insertion of cache barriers. This is the default setting.
14731 @item -mflush-func=@var{func}
14732 @itemx -mno-flush-func
14733 @opindex mflush-func
14734 Specifies the function to call to flush the I and D caches, or to not
14735 call any such function. If called, the function must take the same
14736 arguments as the common @code{_flush_func()}, that is, the address of the
14737 memory range for which the cache is being flushed, the size of the
14738 memory range, and the number 3 (to flush both caches). The default
14739 depends on the target GCC was configured for, but commonly is either
14740 @samp{_flush_func} or @samp{__cpu_flush}.
14742 @item mbranch-cost=@var{num}
14743 @opindex mbranch-cost
14744 Set the cost of branches to roughly @var{num} ``simple'' instructions.
14745 This cost is only a heuristic and is not guaranteed to produce
14746 consistent results across releases. A zero cost redundantly selects
14747 the default, which is based on the @option{-mtune} setting.
14749 @item -mbranch-likely
14750 @itemx -mno-branch-likely
14751 @opindex mbranch-likely
14752 @opindex mno-branch-likely
14753 Enable or disable use of Branch Likely instructions, regardless of the
14754 default for the selected architecture. By default, Branch Likely
14755 instructions may be generated if they are supported by the selected
14756 architecture. An exception is for the MIPS32 and MIPS64 architectures
14757 and processors which implement those architectures; for those, Branch
14758 Likely instructions will not be generated by default because the MIPS32
14759 and MIPS64 architectures specifically deprecate their use.
14761 @item -mfp-exceptions
14762 @itemx -mno-fp-exceptions
14763 @opindex mfp-exceptions
14764 Specifies whether FP exceptions are enabled. This affects how we schedule
14765 FP instructions for some processors. The default is that FP exceptions are
14768 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
14769 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
14772 @item -mvr4130-align
14773 @itemx -mno-vr4130-align
14774 @opindex mvr4130-align
14775 The VR4130 pipeline is two-way superscalar, but can only issue two
14776 instructions together if the first one is 8-byte aligned. When this
14777 option is enabled, GCC will align pairs of instructions that it
14778 thinks should execute in parallel.
14780 This option only has an effect when optimizing for the VR4130.
14781 It normally makes code faster, but at the expense of making it bigger.
14782 It is enabled by default at optimization level @option{-O3}.
14787 Enable (disable) generation of @code{synci} instructions on
14788 architectures that support it. The @code{synci} instructions (if
14789 enabled) will be generated when @code{__builtin___clear_cache()} is
14792 This option defaults to @code{-mno-synci}, but the default can be
14793 overridden by configuring with @code{--with-synci}.
14795 When compiling code for single processor systems, it is generally safe
14796 to use @code{synci}. However, on many multi-core (SMP) systems, it
14797 will not invalidate the instruction caches on all cores and may lead
14798 to undefined behavior.
14800 @item -mrelax-pic-calls
14801 @itemx -mno-relax-pic-calls
14802 @opindex mrelax-pic-calls
14803 Try to turn PIC calls that are normally dispatched via register
14804 @code{$25} into direct calls. This is only possible if the linker can
14805 resolve the destination at link-time and if the destination is within
14806 range for a direct call.
14808 @option{-mrelax-pic-calls} is the default if GCC was configured to use
14809 an assembler and a linker that supports the @code{.reloc} assembly
14810 directive and @code{-mexplicit-relocs} is in effect. With
14811 @code{-mno-explicit-relocs}, this optimization can be performed by the
14812 assembler and the linker alone without help from the compiler.
14814 @item -mmcount-ra-address
14815 @itemx -mno-mcount-ra-address
14816 @opindex mmcount-ra-address
14817 @opindex mno-mcount-ra-address
14818 Emit (do not emit) code that allows @code{_mcount} to modify the
14819 calling function's return address. When enabled, this option extends
14820 the usual @code{_mcount} interface with a new @var{ra-address}
14821 parameter, which has type @code{intptr_t *} and is passed in register
14822 @code{$12}. @code{_mcount} can then modify the return address by
14823 doing both of the following:
14826 Returning the new address in register @code{$31}.
14828 Storing the new address in @code{*@var{ra-address}},
14829 if @var{ra-address} is nonnull.
14832 The default is @option{-mno-mcount-ra-address}.
14837 @subsection MMIX Options
14838 @cindex MMIX Options
14840 These options are defined for the MMIX:
14844 @itemx -mno-libfuncs
14846 @opindex mno-libfuncs
14847 Specify that intrinsic library functions are being compiled, passing all
14848 values in registers, no matter the size.
14851 @itemx -mno-epsilon
14853 @opindex mno-epsilon
14854 Generate floating-point comparison instructions that compare with respect
14855 to the @code{rE} epsilon register.
14857 @item -mabi=mmixware
14859 @opindex mabi=mmixware
14861 Generate code that passes function parameters and return values that (in
14862 the called function) are seen as registers @code{$0} and up, as opposed to
14863 the GNU ABI which uses global registers @code{$231} and up.
14865 @item -mzero-extend
14866 @itemx -mno-zero-extend
14867 @opindex mzero-extend
14868 @opindex mno-zero-extend
14869 When reading data from memory in sizes shorter than 64 bits, use (do not
14870 use) zero-extending load instructions by default, rather than
14871 sign-extending ones.
14874 @itemx -mno-knuthdiv
14876 @opindex mno-knuthdiv
14877 Make the result of a division yielding a remainder have the same sign as
14878 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
14879 remainder follows the sign of the dividend. Both methods are
14880 arithmetically valid, the latter being almost exclusively used.
14882 @item -mtoplevel-symbols
14883 @itemx -mno-toplevel-symbols
14884 @opindex mtoplevel-symbols
14885 @opindex mno-toplevel-symbols
14886 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
14887 code can be used with the @code{PREFIX} assembly directive.
14891 Generate an executable in the ELF format, rather than the default
14892 @samp{mmo} format used by the @command{mmix} simulator.
14894 @item -mbranch-predict
14895 @itemx -mno-branch-predict
14896 @opindex mbranch-predict
14897 @opindex mno-branch-predict
14898 Use (do not use) the probable-branch instructions, when static branch
14899 prediction indicates a probable branch.
14901 @item -mbase-addresses
14902 @itemx -mno-base-addresses
14903 @opindex mbase-addresses
14904 @opindex mno-base-addresses
14905 Generate (do not generate) code that uses @emph{base addresses}. Using a
14906 base address automatically generates a request (handled by the assembler
14907 and the linker) for a constant to be set up in a global register. The
14908 register is used for one or more base address requests within the range 0
14909 to 255 from the value held in the register. The generally leads to short
14910 and fast code, but the number of different data items that can be
14911 addressed is limited. This means that a program that uses lots of static
14912 data may require @option{-mno-base-addresses}.
14914 @item -msingle-exit
14915 @itemx -mno-single-exit
14916 @opindex msingle-exit
14917 @opindex mno-single-exit
14918 Force (do not force) generated code to have a single exit point in each
14922 @node MN10300 Options
14923 @subsection MN10300 Options
14924 @cindex MN10300 options
14926 These @option{-m} options are defined for Matsushita MN10300 architectures:
14931 Generate code to avoid bugs in the multiply instructions for the MN10300
14932 processors. This is the default.
14934 @item -mno-mult-bug
14935 @opindex mno-mult-bug
14936 Do not generate code to avoid bugs in the multiply instructions for the
14937 MN10300 processors.
14941 Generate code which uses features specific to the AM33 processor.
14945 Do not generate code which uses features specific to the AM33 processor. This
14950 Generate code which uses features specific to the AM33/2.0 processor.
14954 Generate code which uses features specific to the AM34 processor.
14956 @item -mtune=@var{cpu-type}
14958 Use the timing characteristics of the indicated CPU type when
14959 scheduling instructions. This does not change the targeted processor
14960 type. The CPU type must be one of @samp{mn10300}, @samp{am33},
14961 @samp{am33-2} or @samp{am34}.
14963 @item -mreturn-pointer-on-d0
14964 @opindex mreturn-pointer-on-d0
14965 When generating a function which returns a pointer, return the pointer
14966 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
14967 only in a0, and attempts to call such functions without a prototype
14968 would result in errors. Note that this option is on by default; use
14969 @option{-mno-return-pointer-on-d0} to disable it.
14973 Do not link in the C run-time initialization object file.
14977 Indicate to the linker that it should perform a relaxation optimization pass
14978 to shorten branches, calls and absolute memory addresses. This option only
14979 has an effect when used on the command line for the final link step.
14981 This option makes symbolic debugging impossible.
14985 Allow the compiler to generate @emph{Long Instruction Word}
14986 instructions if the target is the @samp{AM33} or later. This is the
14987 default. This option defines the preprocessor macro @samp{__LIW__}.
14991 Do not allow the compiler to generate @emph{Long Instruction Word}
14992 instructions. This option defines the preprocessor macro
14997 Allow the compiler to generate the @emph{SETLB} and @emph{Lcc}
14998 instructions if the target is the @samp{AM33} or later. This is the
14999 default. This option defines the preprocessor macro @samp{__SETLB__}.
15003 Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc}
15004 instructions. This option defines the preprocessor macro
15005 @samp{__NO_SETLB__}.
15009 @node PDP-11 Options
15010 @subsection PDP-11 Options
15011 @cindex PDP-11 Options
15013 These options are defined for the PDP-11:
15018 Use hardware FPP floating point. This is the default. (FIS floating
15019 point on the PDP-11/40 is not supported.)
15022 @opindex msoft-float
15023 Do not use hardware floating point.
15027 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
15031 Return floating-point results in memory. This is the default.
15035 Generate code for a PDP-11/40.
15039 Generate code for a PDP-11/45. This is the default.
15043 Generate code for a PDP-11/10.
15045 @item -mbcopy-builtin
15046 @opindex mbcopy-builtin
15047 Use inline @code{movmemhi} patterns for copying memory. This is the
15052 Do not use inline @code{movmemhi} patterns for copying memory.
15058 Use 16-bit @code{int}. This is the default.
15064 Use 32-bit @code{int}.
15067 @itemx -mno-float32
15069 @opindex mno-float32
15070 Use 64-bit @code{float}. This is the default.
15073 @itemx -mno-float64
15075 @opindex mno-float64
15076 Use 32-bit @code{float}.
15080 Use @code{abshi2} pattern. This is the default.
15084 Do not use @code{abshi2} pattern.
15086 @item -mbranch-expensive
15087 @opindex mbranch-expensive
15088 Pretend that branches are expensive. This is for experimenting with
15089 code generation only.
15091 @item -mbranch-cheap
15092 @opindex mbranch-cheap
15093 Do not pretend that branches are expensive. This is the default.
15097 Use Unix assembler syntax. This is the default when configured for
15098 @samp{pdp11-*-bsd}.
15102 Use DEC assembler syntax. This is the default when configured for any
15103 PDP-11 target other than @samp{pdp11-*-bsd}.
15106 @node picoChip Options
15107 @subsection picoChip Options
15108 @cindex picoChip options
15110 These @samp{-m} options are defined for picoChip implementations:
15114 @item -mae=@var{ae_type}
15116 Set the instruction set, register set, and instruction scheduling
15117 parameters for array element type @var{ae_type}. Supported values
15118 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
15120 @option{-mae=ANY} selects a completely generic AE type. Code
15121 generated with this option will run on any of the other AE types. The
15122 code will not be as efficient as it would be if compiled for a specific
15123 AE type, and some types of operation (e.g., multiplication) will not
15124 work properly on all types of AE.
15126 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
15127 for compiled code, and is the default.
15129 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
15130 option may suffer from poor performance of byte (char) manipulation,
15131 since the DSP AE does not provide hardware support for byte load/stores.
15133 @item -msymbol-as-address
15134 Enable the compiler to directly use a symbol name as an address in a
15135 load/store instruction, without first loading it into a
15136 register. Typically, the use of this option will generate larger
15137 programs, which run faster than when the option isn't used. However, the
15138 results vary from program to program, so it is left as a user option,
15139 rather than being permanently enabled.
15141 @item -mno-inefficient-warnings
15142 Disables warnings about the generation of inefficient code. These
15143 warnings can be generated, for example, when compiling code which
15144 performs byte-level memory operations on the MAC AE type. The MAC AE has
15145 no hardware support for byte-level memory operations, so all byte
15146 load/stores must be synthesized from word load/store operations. This is
15147 inefficient and a warning will be generated indicating to the programmer
15148 that they should rewrite the code to avoid byte operations, or to target
15149 an AE type which has the necessary hardware support. This option enables
15150 the warning to be turned off.
15154 @node PowerPC Options
15155 @subsection PowerPC Options
15156 @cindex PowerPC options
15158 These are listed under @xref{RS/6000 and PowerPC Options}.
15160 @node RS/6000 and PowerPC Options
15161 @subsection IBM RS/6000 and PowerPC Options
15162 @cindex RS/6000 and PowerPC Options
15163 @cindex IBM RS/6000 and PowerPC Options
15165 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
15172 @itemx -mno-powerpc
15173 @itemx -mpowerpc-gpopt
15174 @itemx -mno-powerpc-gpopt
15175 @itemx -mpowerpc-gfxopt
15176 @itemx -mno-powerpc-gfxopt
15179 @itemx -mno-powerpc64
15183 @itemx -mno-popcntb
15185 @itemx -mno-popcntd
15194 @itemx -mno-hard-dfp
15198 @opindex mno-power2
15200 @opindex mno-powerpc
15201 @opindex mpowerpc-gpopt
15202 @opindex mno-powerpc-gpopt
15203 @opindex mpowerpc-gfxopt
15204 @opindex mno-powerpc-gfxopt
15205 @opindex mpowerpc64
15206 @opindex mno-powerpc64
15210 @opindex mno-popcntb
15212 @opindex mno-popcntd
15218 @opindex mno-mfpgpr
15220 @opindex mno-hard-dfp
15221 GCC supports two related instruction set architectures for the
15222 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
15223 instructions supported by the @samp{rios} chip set used in the original
15224 RS/6000 systems and the @dfn{PowerPC} instruction set is the
15225 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
15226 the IBM 4xx, 6xx, and follow-on microprocessors.
15228 Neither architecture is a subset of the other. However there is a
15229 large common subset of instructions supported by both. An MQ
15230 register is included in processors supporting the POWER architecture.
15232 You use these options to specify which instructions are available on the
15233 processor you are using. The default value of these options is
15234 determined when configuring GCC@. Specifying the
15235 @option{-mcpu=@var{cpu_type}} overrides the specification of these
15236 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
15237 rather than the options listed above.
15239 The @option{-mpower} option allows GCC to generate instructions that
15240 are found only in the POWER architecture and to use the MQ register.
15241 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
15242 to generate instructions that are present in the POWER2 architecture but
15243 not the original POWER architecture.
15245 The @option{-mpowerpc} option allows GCC to generate instructions that
15246 are found only in the 32-bit subset of the PowerPC architecture.
15247 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
15248 GCC to use the optional PowerPC architecture instructions in the
15249 General Purpose group, including floating-point square root. Specifying
15250 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
15251 use the optional PowerPC architecture instructions in the Graphics
15252 group, including floating-point select.
15254 The @option{-mmfcrf} option allows GCC to generate the move from
15255 condition register field instruction implemented on the POWER4
15256 processor and other processors that support the PowerPC V2.01
15258 The @option{-mpopcntb} option allows GCC to generate the popcount and
15259 double precision FP reciprocal estimate instruction implemented on the
15260 POWER5 processor and other processors that support the PowerPC V2.02
15262 The @option{-mpopcntd} option allows GCC to generate the popcount
15263 instruction implemented on the POWER7 processor and other processors
15264 that support the PowerPC V2.06 architecture.
15265 The @option{-mfprnd} option allows GCC to generate the FP round to
15266 integer instructions implemented on the POWER5+ processor and other
15267 processors that support the PowerPC V2.03 architecture.
15268 The @option{-mcmpb} option allows GCC to generate the compare bytes
15269 instruction implemented on the POWER6 processor and other processors
15270 that support the PowerPC V2.05 architecture.
15271 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
15272 general purpose register instructions implemented on the POWER6X
15273 processor and other processors that support the extended PowerPC V2.05
15275 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
15276 point instructions implemented on some POWER processors.
15278 The @option{-mpowerpc64} option allows GCC to generate the additional
15279 64-bit instructions that are found in the full PowerPC64 architecture
15280 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
15281 @option{-mno-powerpc64}.
15283 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
15284 will use only the instructions in the common subset of both
15285 architectures plus some special AIX common-mode calls, and will not use
15286 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
15287 permits GCC to use any instruction from either architecture and to
15288 allow use of the MQ register; specify this for the Motorola MPC601.
15290 @item -mnew-mnemonics
15291 @itemx -mold-mnemonics
15292 @opindex mnew-mnemonics
15293 @opindex mold-mnemonics
15294 Select which mnemonics to use in the generated assembler code. With
15295 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
15296 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
15297 assembler mnemonics defined for the POWER architecture. Instructions
15298 defined in only one architecture have only one mnemonic; GCC uses that
15299 mnemonic irrespective of which of these options is specified.
15301 GCC defaults to the mnemonics appropriate for the architecture in
15302 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
15303 value of these option. Unless you are building a cross-compiler, you
15304 should normally not specify either @option{-mnew-mnemonics} or
15305 @option{-mold-mnemonics}, but should instead accept the default.
15307 @item -mcpu=@var{cpu_type}
15309 Set architecture type, register usage, choice of mnemonics, and
15310 instruction scheduling parameters for machine type @var{cpu_type}.
15311 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
15312 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
15313 @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
15314 @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
15315 @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
15316 @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
15317 @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{ec603e}, @samp{G3},
15318 @samp{G4}, @samp{G5}, @samp{titan}, @samp{power}, @samp{power2}, @samp{power3},
15319 @samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x},
15320 @samp{power7}, @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
15321 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
15323 @option{-mcpu=common} selects a completely generic processor. Code
15324 generated under this option will run on any POWER or PowerPC processor.
15325 GCC will use only the instructions in the common subset of both
15326 architectures, and will not use the MQ register. GCC assumes a generic
15327 processor model for scheduling purposes.
15329 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
15330 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
15331 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
15332 types, with an appropriate, generic processor model assumed for
15333 scheduling purposes.
15335 The other options specify a specific processor. Code generated under
15336 those options will run best on that processor, and may not run at all on
15339 The @option{-mcpu} options automatically enable or disable the
15342 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
15343 -mnew-mnemonics -mpopcntb -mpopcntd -mpower -mpower2 -mpowerpc64 @gol
15344 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
15345 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx}
15347 The particular options set for any particular CPU will vary between
15348 compiler versions, depending on what setting seems to produce optimal
15349 code for that CPU; it doesn't necessarily reflect the actual hardware's
15350 capabilities. If you wish to set an individual option to a particular
15351 value, you may specify it after the @option{-mcpu} option, like
15352 @samp{-mcpu=970 -mno-altivec}.
15354 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
15355 not enabled or disabled by the @option{-mcpu} option at present because
15356 AIX does not have full support for these options. You may still
15357 enable or disable them individually if you're sure it'll work in your
15360 @item -mtune=@var{cpu_type}
15362 Set the instruction scheduling parameters for machine type
15363 @var{cpu_type}, but do not set the architecture type, register usage, or
15364 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
15365 values for @var{cpu_type} are used for @option{-mtune} as for
15366 @option{-mcpu}. If both are specified, the code generated will use the
15367 architecture, registers, and mnemonics set by @option{-mcpu}, but the
15368 scheduling parameters set by @option{-mtune}.
15370 @item -mcmodel=small
15371 @opindex mcmodel=small
15372 Generate PowerPC64 code for the small model: The TOC is limited to
15375 @item -mcmodel=medium
15376 @opindex mcmodel=medium
15377 Generate PowerPC64 code for the medium model: The TOC and other static
15378 data may be up to a total of 4G in size.
15380 @item -mcmodel=large
15381 @opindex mcmodel=large
15382 Generate PowerPC64 code for the large model: The TOC may be up to 4G
15383 in size. Other data and code is only limited by the 64-bit address
15387 @itemx -mno-altivec
15389 @opindex mno-altivec
15390 Generate code that uses (does not use) AltiVec instructions, and also
15391 enable the use of built-in functions that allow more direct access to
15392 the AltiVec instruction set. You may also need to set
15393 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
15399 @opindex mno-vrsave
15400 Generate VRSAVE instructions when generating AltiVec code.
15402 @item -mgen-cell-microcode
15403 @opindex mgen-cell-microcode
15404 Generate Cell microcode instructions
15406 @item -mwarn-cell-microcode
15407 @opindex mwarn-cell-microcode
15408 Warning when a Cell microcode instruction is going to emitted. An example
15409 of a Cell microcode instruction is a variable shift.
15412 @opindex msecure-plt
15413 Generate code that allows ld and ld.so to build executables and shared
15414 libraries with non-exec .plt and .got sections. This is a PowerPC
15415 32-bit SYSV ABI option.
15419 Generate code that uses a BSS .plt section that ld.so fills in, and
15420 requires .plt and .got sections that are both writable and executable.
15421 This is a PowerPC 32-bit SYSV ABI option.
15427 This switch enables or disables the generation of ISEL instructions.
15429 @item -misel=@var{yes/no}
15430 This switch has been deprecated. Use @option{-misel} and
15431 @option{-mno-isel} instead.
15437 This switch enables or disables the generation of SPE simd
15443 @opindex mno-paired
15444 This switch enables or disables the generation of PAIRED simd
15447 @item -mspe=@var{yes/no}
15448 This option has been deprecated. Use @option{-mspe} and
15449 @option{-mno-spe} instead.
15455 Generate code that uses (does not use) vector/scalar (VSX)
15456 instructions, and also enable the use of built-in functions that allow
15457 more direct access to the VSX instruction set.
15459 @item -mfloat-gprs=@var{yes/single/double/no}
15460 @itemx -mfloat-gprs
15461 @opindex mfloat-gprs
15462 This switch enables or disables the generation of floating point
15463 operations on the general purpose registers for architectures that
15466 The argument @var{yes} or @var{single} enables the use of
15467 single-precision floating point operations.
15469 The argument @var{double} enables the use of single and
15470 double-precision floating point operations.
15472 The argument @var{no} disables floating point operations on the
15473 general purpose registers.
15475 This option is currently only available on the MPC854x.
15481 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
15482 targets (including GNU/Linux). The 32-bit environment sets int, long
15483 and pointer to 32 bits and generates code that runs on any PowerPC
15484 variant. The 64-bit environment sets int to 32 bits and long and
15485 pointer to 64 bits, and generates code for PowerPC64, as for
15486 @option{-mpowerpc64}.
15489 @itemx -mno-fp-in-toc
15490 @itemx -mno-sum-in-toc
15491 @itemx -mminimal-toc
15493 @opindex mno-fp-in-toc
15494 @opindex mno-sum-in-toc
15495 @opindex mminimal-toc
15496 Modify generation of the TOC (Table Of Contents), which is created for
15497 every executable file. The @option{-mfull-toc} option is selected by
15498 default. In that case, GCC will allocate at least one TOC entry for
15499 each unique non-automatic variable reference in your program. GCC
15500 will also place floating-point constants in the TOC@. However, only
15501 16,384 entries are available in the TOC@.
15503 If you receive a linker error message that saying you have overflowed
15504 the available TOC space, you can reduce the amount of TOC space used
15505 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
15506 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
15507 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
15508 generate code to calculate the sum of an address and a constant at
15509 run-time instead of putting that sum into the TOC@. You may specify one
15510 or both of these options. Each causes GCC to produce very slightly
15511 slower and larger code at the expense of conserving TOC space.
15513 If you still run out of space in the TOC even when you specify both of
15514 these options, specify @option{-mminimal-toc} instead. This option causes
15515 GCC to make only one TOC entry for every file. When you specify this
15516 option, GCC will produce code that is slower and larger but which
15517 uses extremely little TOC space. You may wish to use this option
15518 only on files that contain less frequently executed code.
15524 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
15525 @code{long} type, and the infrastructure needed to support them.
15526 Specifying @option{-maix64} implies @option{-mpowerpc64} and
15527 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
15528 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
15531 @itemx -mno-xl-compat
15532 @opindex mxl-compat
15533 @opindex mno-xl-compat
15534 Produce code that conforms more closely to IBM XL compiler semantics
15535 when using AIX-compatible ABI@. Pass floating-point arguments to
15536 prototyped functions beyond the register save area (RSA) on the stack
15537 in addition to argument FPRs. Do not assume that most significant
15538 double in 128-bit long double value is properly rounded when comparing
15539 values and converting to double. Use XL symbol names for long double
15542 The AIX calling convention was extended but not initially documented to
15543 handle an obscure K&R C case of calling a function that takes the
15544 address of its arguments with fewer arguments than declared. IBM XL
15545 compilers access floating point arguments which do not fit in the
15546 RSA from the stack when a subroutine is compiled without
15547 optimization. Because always storing floating-point arguments on the
15548 stack is inefficient and rarely needed, this option is not enabled by
15549 default and only is necessary when calling subroutines compiled by IBM
15550 XL compilers without optimization.
15554 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
15555 application written to use message passing with special startup code to
15556 enable the application to run. The system must have PE installed in the
15557 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
15558 must be overridden with the @option{-specs=} option to specify the
15559 appropriate directory location. The Parallel Environment does not
15560 support threads, so the @option{-mpe} option and the @option{-pthread}
15561 option are incompatible.
15563 @item -malign-natural
15564 @itemx -malign-power
15565 @opindex malign-natural
15566 @opindex malign-power
15567 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
15568 @option{-malign-natural} overrides the ABI-defined alignment of larger
15569 types, such as floating-point doubles, on their natural size-based boundary.
15570 The option @option{-malign-power} instructs GCC to follow the ABI-specified
15571 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
15573 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
15577 @itemx -mhard-float
15578 @opindex msoft-float
15579 @opindex mhard-float
15580 Generate code that does not use (uses) the floating-point register set.
15581 Software floating point emulation is provided if you use the
15582 @option{-msoft-float} option, and pass the option to GCC when linking.
15584 @item -msingle-float
15585 @itemx -mdouble-float
15586 @opindex msingle-float
15587 @opindex mdouble-float
15588 Generate code for single or double-precision floating point operations.
15589 @option{-mdouble-float} implies @option{-msingle-float}.
15592 @opindex msimple-fpu
15593 Do not generate sqrt and div instructions for hardware floating point unit.
15597 Specify type of floating point unit. Valid values are @var{sp_lite}
15598 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
15599 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
15600 and @var{dp_full} (equivalent to -mdouble-float).
15603 @opindex mxilinx-fpu
15604 Perform optimizations for floating point unit on Xilinx PPC 405/440.
15607 @itemx -mno-multiple
15609 @opindex mno-multiple
15610 Generate code that uses (does not use) the load multiple word
15611 instructions and the store multiple word instructions. These
15612 instructions are generated by default on POWER systems, and not
15613 generated on PowerPC systems. Do not use @option{-mmultiple} on little
15614 endian PowerPC systems, since those instructions do not work when the
15615 processor is in little endian mode. The exceptions are PPC740 and
15616 PPC750 which permit the instructions usage in little endian mode.
15621 @opindex mno-string
15622 Generate code that uses (does not use) the load string instructions
15623 and the store string word instructions to save multiple registers and
15624 do small block moves. These instructions are generated by default on
15625 POWER systems, and not generated on PowerPC systems. Do not use
15626 @option{-mstring} on little endian PowerPC systems, since those
15627 instructions do not work when the processor is in little endian mode.
15628 The exceptions are PPC740 and PPC750 which permit the instructions
15629 usage in little endian mode.
15634 @opindex mno-update
15635 Generate code that uses (does not use) the load or store instructions
15636 that update the base register to the address of the calculated memory
15637 location. These instructions are generated by default. If you use
15638 @option{-mno-update}, there is a small window between the time that the
15639 stack pointer is updated and the address of the previous frame is
15640 stored, which means code that walks the stack frame across interrupts or
15641 signals may get corrupted data.
15643 @item -mavoid-indexed-addresses
15644 @itemx -mno-avoid-indexed-addresses
15645 @opindex mavoid-indexed-addresses
15646 @opindex mno-avoid-indexed-addresses
15647 Generate code that tries to avoid (not avoid) the use of indexed load
15648 or store instructions. These instructions can incur a performance
15649 penalty on Power6 processors in certain situations, such as when
15650 stepping through large arrays that cross a 16M boundary. This option
15651 is enabled by default when targetting Power6 and disabled otherwise.
15654 @itemx -mno-fused-madd
15655 @opindex mfused-madd
15656 @opindex mno-fused-madd
15657 Generate code that uses (does not use) the floating point multiply and
15658 accumulate instructions. These instructions are generated by default
15659 if hardware floating point is used. The machine dependent
15660 @option{-mfused-madd} option is now mapped to the machine independent
15661 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
15662 mapped to @option{-ffp-contract=off}.
15668 Generate code that uses (does not use) the half-word multiply and
15669 multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
15670 These instructions are generated by default when targetting those
15677 Generate code that uses (does not use) the string-search @samp{dlmzb}
15678 instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
15679 generated by default when targetting those processors.
15681 @item -mno-bit-align
15683 @opindex mno-bit-align
15684 @opindex mbit-align
15685 On System V.4 and embedded PowerPC systems do not (do) force structures
15686 and unions that contain bit-fields to be aligned to the base type of the
15689 For example, by default a structure containing nothing but 8
15690 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
15691 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
15692 the structure would be aligned to a 1 byte boundary and be one byte in
15695 @item -mno-strict-align
15696 @itemx -mstrict-align
15697 @opindex mno-strict-align
15698 @opindex mstrict-align
15699 On System V.4 and embedded PowerPC systems do not (do) assume that
15700 unaligned memory references will be handled by the system.
15702 @item -mrelocatable
15703 @itemx -mno-relocatable
15704 @opindex mrelocatable
15705 @opindex mno-relocatable
15706 Generate code that allows (does not allow) a static executable to be
15707 relocated to a different address at runtime. A simple embedded
15708 PowerPC system loader should relocate the entire contents of
15709 @code{.got2} and 4-byte locations listed in the @code{.fixup} section,
15710 a table of 32-bit addresses generated by this option. For this to
15711 work, all objects linked together must be compiled with
15712 @option{-mrelocatable} or @option{-mrelocatable-lib}.
15713 @option{-mrelocatable} code aligns the stack to an 8 byte boundary.
15715 @item -mrelocatable-lib
15716 @itemx -mno-relocatable-lib
15717 @opindex mrelocatable-lib
15718 @opindex mno-relocatable-lib
15719 Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a
15720 @code{.fixup} section to allow static executables to be relocated at
15721 runtime, but @option{-mrelocatable-lib} does not use the smaller stack
15722 alignment of @option{-mrelocatable}. Objects compiled with
15723 @option{-mrelocatable-lib} may be linked with objects compiled with
15724 any combination of the @option{-mrelocatable} options.
15730 On System V.4 and embedded PowerPC systems do not (do) assume that
15731 register 2 contains a pointer to a global area pointing to the addresses
15732 used in the program.
15735 @itemx -mlittle-endian
15737 @opindex mlittle-endian
15738 On System V.4 and embedded PowerPC systems compile code for the
15739 processor in little endian mode. The @option{-mlittle-endian} option is
15740 the same as @option{-mlittle}.
15743 @itemx -mbig-endian
15745 @opindex mbig-endian
15746 On System V.4 and embedded PowerPC systems compile code for the
15747 processor in big endian mode. The @option{-mbig-endian} option is
15748 the same as @option{-mbig}.
15750 @item -mdynamic-no-pic
15751 @opindex mdynamic-no-pic
15752 On Darwin and Mac OS X systems, compile code so that it is not
15753 relocatable, but that its external references are relocatable. The
15754 resulting code is suitable for applications, but not shared
15757 @item -msingle-pic-base
15758 @opindex msingle-pic-base
15759 Treat the register used for PIC addressing as read-only, rather than
15760 loading it in the prologue for each function. The run-time system is
15761 responsible for initializing this register with an appropriate value
15762 before execution begins.
15764 @item -mprioritize-restricted-insns=@var{priority}
15765 @opindex mprioritize-restricted-insns
15766 This option controls the priority that is assigned to
15767 dispatch-slot restricted instructions during the second scheduling
15768 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
15769 @var{no/highest/second-highest} priority to dispatch slot restricted
15772 @item -msched-costly-dep=@var{dependence_type}
15773 @opindex msched-costly-dep
15774 This option controls which dependences are considered costly
15775 by the target during instruction scheduling. The argument
15776 @var{dependence_type} takes one of the following values:
15777 @var{no}: no dependence is costly,
15778 @var{all}: all dependences are costly,
15779 @var{true_store_to_load}: a true dependence from store to load is costly,
15780 @var{store_to_load}: any dependence from store to load is costly,
15781 @var{number}: any dependence which latency >= @var{number} is costly.
15783 @item -minsert-sched-nops=@var{scheme}
15784 @opindex minsert-sched-nops
15785 This option controls which nop insertion scheme will be used during
15786 the second scheduling pass. The argument @var{scheme} takes one of the
15788 @var{no}: Don't insert nops.
15789 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
15790 according to the scheduler's grouping.
15791 @var{regroup_exact}: Insert nops to force costly dependent insns into
15792 separate groups. Insert exactly as many nops as needed to force an insn
15793 to a new group, according to the estimated processor grouping.
15794 @var{number}: Insert nops to force costly dependent insns into
15795 separate groups. Insert @var{number} nops to force an insn to a new group.
15798 @opindex mcall-sysv
15799 On System V.4 and embedded PowerPC systems compile code using calling
15800 conventions that adheres to the March 1995 draft of the System V
15801 Application Binary Interface, PowerPC processor supplement. This is the
15802 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
15804 @item -mcall-sysv-eabi
15806 @opindex mcall-sysv-eabi
15807 @opindex mcall-eabi
15808 Specify both @option{-mcall-sysv} and @option{-meabi} options.
15810 @item -mcall-sysv-noeabi
15811 @opindex mcall-sysv-noeabi
15812 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
15814 @item -mcall-aixdesc
15816 On System V.4 and embedded PowerPC systems compile code for the AIX
15820 @opindex mcall-linux
15821 On System V.4 and embedded PowerPC systems compile code for the
15822 Linux-based GNU system.
15824 @item -mcall-freebsd
15825 @opindex mcall-freebsd
15826 On System V.4 and embedded PowerPC systems compile code for the
15827 FreeBSD operating system.
15829 @item -mcall-netbsd
15830 @opindex mcall-netbsd
15831 On System V.4 and embedded PowerPC systems compile code for the
15832 NetBSD operating system.
15834 @item -mcall-openbsd
15835 @opindex mcall-netbsd
15836 On System V.4 and embedded PowerPC systems compile code for the
15837 OpenBSD operating system.
15839 @item -maix-struct-return
15840 @opindex maix-struct-return
15841 Return all structures in memory (as specified by the AIX ABI)@.
15843 @item -msvr4-struct-return
15844 @opindex msvr4-struct-return
15845 Return structures smaller than 8 bytes in registers (as specified by the
15848 @item -mabi=@var{abi-type}
15850 Extend the current ABI with a particular extension, or remove such extension.
15851 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
15852 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
15856 Extend the current ABI with SPE ABI extensions. This does not change
15857 the default ABI, instead it adds the SPE ABI extensions to the current
15861 @opindex mabi=no-spe
15862 Disable Booke SPE ABI extensions for the current ABI@.
15864 @item -mabi=ibmlongdouble
15865 @opindex mabi=ibmlongdouble
15866 Change the current ABI to use IBM extended precision long double.
15867 This is a PowerPC 32-bit SYSV ABI option.
15869 @item -mabi=ieeelongdouble
15870 @opindex mabi=ieeelongdouble
15871 Change the current ABI to use IEEE extended precision long double.
15872 This is a PowerPC 32-bit Linux ABI option.
15875 @itemx -mno-prototype
15876 @opindex mprototype
15877 @opindex mno-prototype
15878 On System V.4 and embedded PowerPC systems assume that all calls to
15879 variable argument functions are properly prototyped. Otherwise, the
15880 compiler must insert an instruction before every non prototyped call to
15881 set or clear bit 6 of the condition code register (@var{CR}) to
15882 indicate whether floating point values were passed in the floating point
15883 registers in case the function takes a variable arguments. With
15884 @option{-mprototype}, only calls to prototyped variable argument functions
15885 will set or clear the bit.
15889 On embedded PowerPC systems, assume that the startup module is called
15890 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
15891 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
15896 On embedded PowerPC systems, assume that the startup module is called
15897 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
15902 On embedded PowerPC systems, assume that the startup module is called
15903 @file{crt0.o} and the standard C libraries are @file{libads.a} and
15906 @item -myellowknife
15907 @opindex myellowknife
15908 On embedded PowerPC systems, assume that the startup module is called
15909 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
15914 On System V.4 and embedded PowerPC systems, specify that you are
15915 compiling for a VxWorks system.
15919 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
15920 header to indicate that @samp{eabi} extended relocations are used.
15926 On System V.4 and embedded PowerPC systems do (do not) adhere to the
15927 Embedded Applications Binary Interface (eabi) which is a set of
15928 modifications to the System V.4 specifications. Selecting @option{-meabi}
15929 means that the stack is aligned to an 8 byte boundary, a function
15930 @code{__eabi} is called to from @code{main} to set up the eabi
15931 environment, and the @option{-msdata} option can use both @code{r2} and
15932 @code{r13} to point to two separate small data areas. Selecting
15933 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
15934 do not call an initialization function from @code{main}, and the
15935 @option{-msdata} option will only use @code{r13} to point to a single
15936 small data area. The @option{-meabi} option is on by default if you
15937 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
15940 @opindex msdata=eabi
15941 On System V.4 and embedded PowerPC systems, put small initialized
15942 @code{const} global and static data in the @samp{.sdata2} section, which
15943 is pointed to by register @code{r2}. Put small initialized
15944 non-@code{const} global and static data in the @samp{.sdata} section,
15945 which is pointed to by register @code{r13}. Put small uninitialized
15946 global and static data in the @samp{.sbss} section, which is adjacent to
15947 the @samp{.sdata} section. The @option{-msdata=eabi} option is
15948 incompatible with the @option{-mrelocatable} option. The
15949 @option{-msdata=eabi} option also sets the @option{-memb} option.
15952 @opindex msdata=sysv
15953 On System V.4 and embedded PowerPC systems, put small global and static
15954 data in the @samp{.sdata} section, which is pointed to by register
15955 @code{r13}. Put small uninitialized global and static data in the
15956 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
15957 The @option{-msdata=sysv} option is incompatible with the
15958 @option{-mrelocatable} option.
15960 @item -msdata=default
15962 @opindex msdata=default
15964 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
15965 compile code the same as @option{-msdata=eabi}, otherwise compile code the
15966 same as @option{-msdata=sysv}.
15969 @opindex msdata=data
15970 On System V.4 and embedded PowerPC systems, put small global
15971 data in the @samp{.sdata} section. Put small uninitialized global
15972 data in the @samp{.sbss} section. Do not use register @code{r13}
15973 to address small data however. This is the default behavior unless
15974 other @option{-msdata} options are used.
15978 @opindex msdata=none
15980 On embedded PowerPC systems, put all initialized global and static data
15981 in the @samp{.data} section, and all uninitialized data in the
15982 @samp{.bss} section.
15984 @item -mblock-move-inline-limit=@var{num}
15985 @opindex mblock-move-inline-limit
15986 Inline all block moves (such as calls to @code{memcpy} or structure
15987 copies) less than or equal to @var{num} bytes. The minimum value for
15988 @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit
15989 targets. The default value is target-specific.
15993 @cindex smaller data references (PowerPC)
15994 @cindex .sdata/.sdata2 references (PowerPC)
15995 On embedded PowerPC systems, put global and static items less than or
15996 equal to @var{num} bytes into the small data or bss sections instead of
15997 the normal data or bss section. By default, @var{num} is 8. The
15998 @option{-G @var{num}} switch is also passed to the linker.
15999 All modules should be compiled with the same @option{-G @var{num}} value.
16002 @itemx -mno-regnames
16004 @opindex mno-regnames
16005 On System V.4 and embedded PowerPC systems do (do not) emit register
16006 names in the assembly language output using symbolic forms.
16009 @itemx -mno-longcall
16011 @opindex mno-longcall
16012 By default assume that all calls are far away so that a longer more
16013 expensive calling sequence is required. This is required for calls
16014 further than 32 megabytes (33,554,432 bytes) from the current location.
16015 A short call will be generated if the compiler knows
16016 the call cannot be that far away. This setting can be overridden by
16017 the @code{shortcall} function attribute, or by @code{#pragma
16020 Some linkers are capable of detecting out-of-range calls and generating
16021 glue code on the fly. On these systems, long calls are unnecessary and
16022 generate slower code. As of this writing, the AIX linker can do this,
16023 as can the GNU linker for PowerPC/64. It is planned to add this feature
16024 to the GNU linker for 32-bit PowerPC systems as well.
16026 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
16027 callee, L42'', plus a ``branch island'' (glue code). The two target
16028 addresses represent the callee and the ``branch island''. The
16029 Darwin/PPC linker will prefer the first address and generate a ``bl
16030 callee'' if the PPC ``bl'' instruction will reach the callee directly;
16031 otherwise, the linker will generate ``bl L42'' to call the ``branch
16032 island''. The ``branch island'' is appended to the body of the
16033 calling function; it computes the full 32-bit address of the callee
16036 On Mach-O (Darwin) systems, this option directs the compiler emit to
16037 the glue for every direct call, and the Darwin linker decides whether
16038 to use or discard it.
16040 In the future, we may cause GCC to ignore all longcall specifications
16041 when the linker is known to generate glue.
16043 @item -mtls-markers
16044 @itemx -mno-tls-markers
16045 @opindex mtls-markers
16046 @opindex mno-tls-markers
16047 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
16048 specifying the function argument. The relocation allows ld to
16049 reliably associate function call with argument setup instructions for
16050 TLS optimization, which in turn allows gcc to better schedule the
16055 Adds support for multithreading with the @dfn{pthreads} library.
16056 This option sets flags for both the preprocessor and linker.
16061 This option will enable GCC to use the reciprocal estimate and
16062 reciprocal square root estimate instructions with additional
16063 Newton-Raphson steps to increase precision instead of doing a divide or
16064 square root and divide for floating point arguments. You should use
16065 the @option{-ffast-math} option when using @option{-mrecip} (or at
16066 least @option{-funsafe-math-optimizations},
16067 @option{-finite-math-only}, @option{-freciprocal-math} and
16068 @option{-fno-trapping-math}). Note that while the throughput of the
16069 sequence is generally higher than the throughput of the non-reciprocal
16070 instruction, the precision of the sequence can be decreased by up to 2
16071 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square
16074 @item -mrecip=@var{opt}
16075 @opindex mrecip=opt
16076 This option allows to control which reciprocal estimate instructions
16077 may be used. @var{opt} is a comma separated list of options, that may
16078 be preceded by a @code{!} to invert the option:
16079 @code{all}: enable all estimate instructions,
16080 @code{default}: enable the default instructions, equivalent to @option{-mrecip},
16081 @code{none}: disable all estimate instructions, equivalent to @option{-mno-recip};
16082 @code{div}: enable the reciprocal approximation instructions for both single and double precision;
16083 @code{divf}: enable the single precision reciprocal approximation instructions;
16084 @code{divd}: enable the double precision reciprocal approximation instructions;
16085 @code{rsqrt}: enable the reciprocal square root approximation instructions for both single and double precision;
16086 @code{rsqrtf}: enable the single precision reciprocal square root approximation instructions;
16087 @code{rsqrtd}: enable the double precision reciprocal square root approximation instructions;
16089 So for example, @option{-mrecip=all,!rsqrtd} would enable the
16090 all of the reciprocal estimate instructions, except for the
16091 @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions
16092 which handle the double precision reciprocal square root calculations.
16094 @item -mrecip-precision
16095 @itemx -mno-recip-precision
16096 @opindex mrecip-precision
16097 Assume (do not assume) that the reciprocal estimate instructions
16098 provide higher precision estimates than is mandated by the powerpc
16099 ABI. Selecting @option{-mcpu=power6} or @option{-mcpu=power7}
16100 automatically selects @option{-mrecip-precision}. The double
16101 precision square root estimate instructions are not generated by
16102 default on low precision machines, since they do not provide an
16103 estimate that converges after three steps.
16105 @item -mveclibabi=@var{type}
16106 @opindex mveclibabi
16107 Specifies the ABI type to use for vectorizing intrinsics using an
16108 external library. The only type supported at present is @code{mass},
16109 which specifies to use IBM's Mathematical Acceleration Subsystem
16110 (MASS) libraries for vectorizing intrinsics using external libraries.
16111 GCC will currently emit calls to @code{acosd2}, @code{acosf4},
16112 @code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4},
16113 @code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4},
16114 @code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4},
16115 @code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4},
16116 @code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4},
16117 @code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4},
16118 @code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4},
16119 @code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4},
16120 @code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4},
16121 @code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4},
16122 @code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2},
16123 @code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2},
16124 @code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code
16125 for power7. Both @option{-ftree-vectorize} and
16126 @option{-funsafe-math-optimizations} have to be enabled. The MASS
16127 libraries will have to be specified at link time.
16132 Generate (do not generate) the @code{friz} instruction when the
16133 @option{-funsafe-math-optimizations} option is used to optimize
16134 rounding a floating point value to 64-bit integer and back to floating
16135 point. The @code{friz} instruction does not return the same value if
16136 the floating point number is too large to fit in an integer.
16140 @subsection RX Options
16143 These command line options are defined for RX targets:
16146 @item -m64bit-doubles
16147 @itemx -m32bit-doubles
16148 @opindex m64bit-doubles
16149 @opindex m32bit-doubles
16150 Make the @code{double} data type be 64-bits (@option{-m64bit-doubles})
16151 or 32-bits (@option{-m32bit-doubles}) in size. The default is
16152 @option{-m32bit-doubles}. @emph{Note} RX floating point hardware only
16153 works on 32-bit values, which is why the default is
16154 @option{-m32bit-doubles}.
16160 Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX
16161 floating point hardware. The default is enabled for the @var{RX600}
16162 series and disabled for the @var{RX200} series.
16164 Floating point instructions will only be generated for 32-bit floating
16165 point values however, so if the @option{-m64bit-doubles} option is in
16166 use then the FPU hardware will not be used for doubles.
16168 @emph{Note} If the @option{-fpu} option is enabled then
16169 @option{-funsafe-math-optimizations} is also enabled automatically.
16170 This is because the RX FPU instructions are themselves unsafe.
16172 @item -mcpu=@var{name}
16174 Selects the type of RX CPU to be targeted. Currently three types are
16175 supported, the generic @var{RX600} and @var{RX200} series hardware and
16176 the specific @var{RX610} CPU. The default is @var{RX600}.
16178 The only difference between @var{RX600} and @var{RX610} is that the
16179 @var{RX610} does not support the @code{MVTIPL} instruction.
16181 The @var{RX200} series does not have a hardware floating point unit
16182 and so @option{-nofpu} is enabled by default when this type is
16185 @item -mbig-endian-data
16186 @itemx -mlittle-endian-data
16187 @opindex mbig-endian-data
16188 @opindex mlittle-endian-data
16189 Store data (but not code) in the big-endian format. The default is
16190 @option{-mlittle-endian-data}, i.e.@: to store data in the little endian
16193 @item -msmall-data-limit=@var{N}
16194 @opindex msmall-data-limit
16195 Specifies the maximum size in bytes of global and static variables
16196 which can be placed into the small data area. Using the small data
16197 area can lead to smaller and faster code, but the size of area is
16198 limited and it is up to the programmer to ensure that the area does
16199 not overflow. Also when the small data area is used one of the RX's
16200 registers (@code{r13}) is reserved for use pointing to this area, so
16201 it is no longer available for use by the compiler. This could result
16202 in slower and/or larger code if variables which once could have been
16203 held in @code{r13} are now pushed onto the stack.
16205 Note, common variables (variables which have not been initialised) and
16206 constants are not placed into the small data area as they are assigned
16207 to other sections in the output executable.
16209 The default value is zero, which disables this feature. Note, this
16210 feature is not enabled by default with higher optimization levels
16211 (@option{-O2} etc) because of the potentially detrimental effects of
16212 reserving register @code{r13}. It is up to the programmer to
16213 experiment and discover whether this feature is of benefit to their
16220 Use the simulator runtime. The default is to use the libgloss board
16223 @item -mas100-syntax
16224 @itemx -mno-as100-syntax
16225 @opindex mas100-syntax
16226 @opindex mno-as100-syntax
16227 When generating assembler output use a syntax that is compatible with
16228 Renesas's AS100 assembler. This syntax can also be handled by the GAS
16229 assembler but it has some restrictions so generating it is not the
16232 @item -mmax-constant-size=@var{N}
16233 @opindex mmax-constant-size
16234 Specifies the maximum size, in bytes, of a constant that can be used as
16235 an operand in a RX instruction. Although the RX instruction set does
16236 allow constants of up to 4 bytes in length to be used in instructions,
16237 a longer value equates to a longer instruction. Thus in some
16238 circumstances it can be beneficial to restrict the size of constants
16239 that are used in instructions. Constants that are too big are instead
16240 placed into a constant pool and referenced via register indirection.
16242 The value @var{N} can be between 0 and 4. A value of 0 (the default)
16243 or 4 means that constants of any size are allowed.
16247 Enable linker relaxation. Linker relaxation is a process whereby the
16248 linker will attempt to reduce the size of a program by finding shorter
16249 versions of various instructions. Disabled by default.
16251 @item -mint-register=@var{N}
16252 @opindex mint-register
16253 Specify the number of registers to reserve for fast interrupt handler
16254 functions. The value @var{N} can be between 0 and 4. A value of 1
16255 means that register @code{r13} will be reserved for the exclusive use
16256 of fast interrupt handlers. A value of 2 reserves @code{r13} and
16257 @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
16258 @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
16259 A value of 0, the default, does not reserve any registers.
16261 @item -msave-acc-in-interrupts
16262 @opindex msave-acc-in-interrupts
16263 Specifies that interrupt handler functions should preserve the
16264 accumulator register. This is only necessary if normal code might use
16265 the accumulator register, for example because it performs 64-bit
16266 multiplications. The default is to ignore the accumulator as this
16267 makes the interrupt handlers faster.
16271 @emph{Note:} The generic GCC command line @option{-ffixed-@var{reg}}
16272 has special significance to the RX port when used with the
16273 @code{interrupt} function attribute. This attribute indicates a
16274 function intended to process fast interrupts. GCC will will ensure
16275 that it only uses the registers @code{r10}, @code{r11}, @code{r12}
16276 and/or @code{r13} and only provided that the normal use of the
16277 corresponding registers have been restricted via the
16278 @option{-ffixed-@var{reg}} or @option{-mint-register} command line
16281 @node S/390 and zSeries Options
16282 @subsection S/390 and zSeries Options
16283 @cindex S/390 and zSeries Options
16285 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
16289 @itemx -msoft-float
16290 @opindex mhard-float
16291 @opindex msoft-float
16292 Use (do not use) the hardware floating-point instructions and registers
16293 for floating-point operations. When @option{-msoft-float} is specified,
16294 functions in @file{libgcc.a} will be used to perform floating-point
16295 operations. When @option{-mhard-float} is specified, the compiler
16296 generates IEEE floating-point instructions. This is the default.
16299 @itemx -mno-hard-dfp
16301 @opindex mno-hard-dfp
16302 Use (do not use) the hardware decimal-floating-point instructions for
16303 decimal-floating-point operations. When @option{-mno-hard-dfp} is
16304 specified, functions in @file{libgcc.a} will be used to perform
16305 decimal-floating-point operations. When @option{-mhard-dfp} is
16306 specified, the compiler generates decimal-floating-point hardware
16307 instructions. This is the default for @option{-march=z9-ec} or higher.
16309 @item -mlong-double-64
16310 @itemx -mlong-double-128
16311 @opindex mlong-double-64
16312 @opindex mlong-double-128
16313 These switches control the size of @code{long double} type. A size
16314 of 64bit makes the @code{long double} type equivalent to the @code{double}
16315 type. This is the default.
16318 @itemx -mno-backchain
16319 @opindex mbackchain
16320 @opindex mno-backchain
16321 Store (do not store) the address of the caller's frame as backchain pointer
16322 into the callee's stack frame.
16323 A backchain may be needed to allow debugging using tools that do not understand
16324 DWARF-2 call frame information.
16325 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
16326 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
16327 the backchain is placed into the topmost word of the 96/160 byte register
16330 In general, code compiled with @option{-mbackchain} is call-compatible with
16331 code compiled with @option{-mmo-backchain}; however, use of the backchain
16332 for debugging purposes usually requires that the whole binary is built with
16333 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
16334 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
16335 to build a linux kernel use @option{-msoft-float}.
16337 The default is to not maintain the backchain.
16339 @item -mpacked-stack
16340 @itemx -mno-packed-stack
16341 @opindex mpacked-stack
16342 @opindex mno-packed-stack
16343 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
16344 specified, the compiler uses the all fields of the 96/160 byte register save
16345 area only for their default purpose; unused fields still take up stack space.
16346 When @option{-mpacked-stack} is specified, register save slots are densely
16347 packed at the top of the register save area; unused space is reused for other
16348 purposes, allowing for more efficient use of the available stack space.
16349 However, when @option{-mbackchain} is also in effect, the topmost word of
16350 the save area is always used to store the backchain, and the return address
16351 register is always saved two words below the backchain.
16353 As long as the stack frame backchain is not used, code generated with
16354 @option{-mpacked-stack} is call-compatible with code generated with
16355 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
16356 S/390 or zSeries generated code that uses the stack frame backchain at run
16357 time, not just for debugging purposes. Such code is not call-compatible
16358 with code compiled with @option{-mpacked-stack}. Also, note that the
16359 combination of @option{-mbackchain},
16360 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
16361 to build a linux kernel use @option{-msoft-float}.
16363 The default is to not use the packed stack layout.
16366 @itemx -mno-small-exec
16367 @opindex msmall-exec
16368 @opindex mno-small-exec
16369 Generate (or do not generate) code using the @code{bras} instruction
16370 to do subroutine calls.
16371 This only works reliably if the total executable size does not
16372 exceed 64k. The default is to use the @code{basr} instruction instead,
16373 which does not have this limitation.
16379 When @option{-m31} is specified, generate code compliant to the
16380 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
16381 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
16382 particular to generate 64-bit instructions. For the @samp{s390}
16383 targets, the default is @option{-m31}, while the @samp{s390x}
16384 targets default to @option{-m64}.
16390 When @option{-mzarch} is specified, generate code using the
16391 instructions available on z/Architecture.
16392 When @option{-mesa} is specified, generate code using the
16393 instructions available on ESA/390. Note that @option{-mesa} is
16394 not possible with @option{-m64}.
16395 When generating code compliant to the GNU/Linux for S/390 ABI,
16396 the default is @option{-mesa}. When generating code compliant
16397 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
16403 Generate (or do not generate) code using the @code{mvcle} instruction
16404 to perform block moves. When @option{-mno-mvcle} is specified,
16405 use a @code{mvc} loop instead. This is the default unless optimizing for
16412 Print (or do not print) additional debug information when compiling.
16413 The default is to not print debug information.
16415 @item -march=@var{cpu-type}
16417 Generate code that will run on @var{cpu-type}, which is the name of a system
16418 representing a certain processor type. Possible values for
16419 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
16420 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
16421 When generating code using the instructions available on z/Architecture,
16422 the default is @option{-march=z900}. Otherwise, the default is
16423 @option{-march=g5}.
16425 @item -mtune=@var{cpu-type}
16427 Tune to @var{cpu-type} everything applicable about the generated code,
16428 except for the ABI and the set of available instructions.
16429 The list of @var{cpu-type} values is the same as for @option{-march}.
16430 The default is the value used for @option{-march}.
16433 @itemx -mno-tpf-trace
16434 @opindex mtpf-trace
16435 @opindex mno-tpf-trace
16436 Generate code that adds (does not add) in TPF OS specific branches to trace
16437 routines in the operating system. This option is off by default, even
16438 when compiling for the TPF OS@.
16441 @itemx -mno-fused-madd
16442 @opindex mfused-madd
16443 @opindex mno-fused-madd
16444 Generate code that uses (does not use) the floating point multiply and
16445 accumulate instructions. These instructions are generated by default if
16446 hardware floating point is used.
16448 @item -mwarn-framesize=@var{framesize}
16449 @opindex mwarn-framesize
16450 Emit a warning if the current function exceeds the given frame size. Because
16451 this is a compile time check it doesn't need to be a real problem when the program
16452 runs. It is intended to identify functions which most probably cause
16453 a stack overflow. It is useful to be used in an environment with limited stack
16454 size e.g.@: the linux kernel.
16456 @item -mwarn-dynamicstack
16457 @opindex mwarn-dynamicstack
16458 Emit a warning if the function calls alloca or uses dynamically
16459 sized arrays. This is generally a bad idea with a limited stack size.
16461 @item -mstack-guard=@var{stack-guard}
16462 @itemx -mstack-size=@var{stack-size}
16463 @opindex mstack-guard
16464 @opindex mstack-size
16465 If these options are provided the s390 back end emits additional instructions in
16466 the function prologue which trigger a trap if the stack size is @var{stack-guard}
16467 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
16468 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
16469 the frame size of the compiled function is chosen.
16470 These options are intended to be used to help debugging stack overflow problems.
16471 The additionally emitted code causes only little overhead and hence can also be
16472 used in production like systems without greater performance degradation. The given
16473 values have to be exact powers of 2 and @var{stack-size} has to be greater than
16474 @var{stack-guard} without exceeding 64k.
16475 In order to be efficient the extra code makes the assumption that the stack starts
16476 at an address aligned to the value given by @var{stack-size}.
16477 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
16480 @node Score Options
16481 @subsection Score Options
16482 @cindex Score Options
16484 These options are defined for Score implementations:
16489 Compile code for big endian mode. This is the default.
16493 Compile code for little endian mode.
16497 Disable generate bcnz instruction.
16501 Enable generate unaligned load and store instruction.
16505 Enable the use of multiply-accumulate instructions. Disabled by default.
16509 Specify the SCORE5 as the target architecture.
16513 Specify the SCORE5U of the target architecture.
16517 Specify the SCORE7 as the target architecture. This is the default.
16521 Specify the SCORE7D as the target architecture.
16525 @subsection SH Options
16527 These @samp{-m} options are defined for the SH implementations:
16532 Generate code for the SH1.
16536 Generate code for the SH2.
16539 Generate code for the SH2e.
16543 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
16544 that the floating-point unit is not used.
16546 @item -m2a-single-only
16547 @opindex m2a-single-only
16548 Generate code for the SH2a-FPU, in such a way that no double-precision
16549 floating point operations are used.
16552 @opindex m2a-single
16553 Generate code for the SH2a-FPU assuming the floating-point unit is in
16554 single-precision mode by default.
16558 Generate code for the SH2a-FPU assuming the floating-point unit is in
16559 double-precision mode by default.
16563 Generate code for the SH3.
16567 Generate code for the SH3e.
16571 Generate code for the SH4 without a floating-point unit.
16573 @item -m4-single-only
16574 @opindex m4-single-only
16575 Generate code for the SH4 with a floating-point unit that only
16576 supports single-precision arithmetic.
16580 Generate code for the SH4 assuming the floating-point unit is in
16581 single-precision mode by default.
16585 Generate code for the SH4.
16589 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
16590 floating-point unit is not used.
16592 @item -m4a-single-only
16593 @opindex m4a-single-only
16594 Generate code for the SH4a, in such a way that no double-precision
16595 floating point operations are used.
16598 @opindex m4a-single
16599 Generate code for the SH4a assuming the floating-point unit is in
16600 single-precision mode by default.
16604 Generate code for the SH4a.
16608 Same as @option{-m4a-nofpu}, except that it implicitly passes
16609 @option{-dsp} to the assembler. GCC doesn't generate any DSP
16610 instructions at the moment.
16614 Compile code for the processor in big endian mode.
16618 Compile code for the processor in little endian mode.
16622 Align doubles at 64-bit boundaries. Note that this changes the calling
16623 conventions, and thus some functions from the standard C library will
16624 not work unless you recompile it first with @option{-mdalign}.
16628 Shorten some address references at link time, when possible; uses the
16629 linker option @option{-relax}.
16633 Use 32-bit offsets in @code{switch} tables. The default is to use
16638 Enable the use of bit manipulation instructions on SH2A.
16642 Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
16643 alignment constraints.
16647 Comply with the calling conventions defined by Renesas.
16651 Comply with the calling conventions defined by Renesas.
16655 Comply with the calling conventions defined for GCC before the Renesas
16656 conventions were available. This option is the default for all
16657 targets of the SH toolchain.
16660 @opindex mnomacsave
16661 Mark the @code{MAC} register as call-clobbered, even if
16662 @option{-mhitachi} is given.
16666 Increase IEEE-compliance of floating-point code.
16667 At the moment, this is equivalent to @option{-fno-finite-math-only}.
16668 When generating 16 bit SH opcodes, getting IEEE-conforming results for
16669 comparisons of NANs / infinities incurs extra overhead in every
16670 floating point comparison, therefore the default is set to
16671 @option{-ffinite-math-only}.
16673 @item -minline-ic_invalidate
16674 @opindex minline-ic_invalidate
16675 Inline code to invalidate instruction cache entries after setting up
16676 nested function trampolines.
16677 This option has no effect if -musermode is in effect and the selected
16678 code generation option (e.g. -m4) does not allow the use of the icbi
16680 If the selected code generation option does not allow the use of the icbi
16681 instruction, and -musermode is not in effect, the inlined code will
16682 manipulate the instruction cache address array directly with an associative
16683 write. This not only requires privileged mode, but it will also
16684 fail if the cache line had been mapped via the TLB and has become unmapped.
16688 Dump instruction size and location in the assembly code.
16691 @opindex mpadstruct
16692 This option is deprecated. It pads structures to multiple of 4 bytes,
16693 which is incompatible with the SH ABI@.
16697 Optimize for space instead of speed. Implied by @option{-Os}.
16700 @opindex mprefergot
16701 When generating position-independent code, emit function calls using
16702 the Global Offset Table instead of the Procedure Linkage Table.
16706 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
16707 if the inlined code would not work in user mode.
16708 This is the default when the target is @code{sh-*-linux*}.
16710 @item -multcost=@var{number}
16711 @opindex multcost=@var{number}
16712 Set the cost to assume for a multiply insn.
16714 @item -mdiv=@var{strategy}
16715 @opindex mdiv=@var{strategy}
16716 Set the division strategy to use for SHmedia code. @var{strategy} must be
16717 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
16718 inv:call2, inv:fp .
16719 "fp" performs the operation in floating point. This has a very high latency,
16720 but needs only a few instructions, so it might be a good choice if
16721 your code has enough easily exploitable ILP to allow the compiler to
16722 schedule the floating point instructions together with other instructions.
16723 Division by zero causes a floating point exception.
16724 "inv" uses integer operations to calculate the inverse of the divisor,
16725 and then multiplies the dividend with the inverse. This strategy allows
16726 cse and hoisting of the inverse calculation. Division by zero calculates
16727 an unspecified result, but does not trap.
16728 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
16729 have been found, or if the entire operation has been hoisted to the same
16730 place, the last stages of the inverse calculation are intertwined with the
16731 final multiply to reduce the overall latency, at the expense of using a few
16732 more instructions, and thus offering fewer scheduling opportunities with
16734 "call" calls a library function that usually implements the inv:minlat
16736 This gives high code density for m5-*media-nofpu compilations.
16737 "call2" uses a different entry point of the same library function, where it
16738 assumes that a pointer to a lookup table has already been set up, which
16739 exposes the pointer load to cse / code hoisting optimizations.
16740 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
16741 code generation, but if the code stays unoptimized, revert to the "call",
16742 "call2", or "fp" strategies, respectively. Note that the
16743 potentially-trapping side effect of division by zero is carried by a
16744 separate instruction, so it is possible that all the integer instructions
16745 are hoisted out, but the marker for the side effect stays where it is.
16746 A recombination to fp operations or a call is not possible in that case.
16747 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
16748 that the inverse calculation was nor separated from the multiply, they speed
16749 up division where the dividend fits into 20 bits (plus sign where applicable),
16750 by inserting a test to skip a number of operations in this case; this test
16751 slows down the case of larger dividends. inv20u assumes the case of a such
16752 a small dividend to be unlikely, and inv20l assumes it to be likely.
16754 @item -maccumulate-outgoing-args
16755 @opindex maccumulate-outgoing-args
16756 Reserve space once for outgoing arguments in the function prologue rather
16757 than around each call. Generally beneficial for performance and size. Also
16758 needed for unwinding to avoid changing the stack frame around conditional code.
16760 @item -mdivsi3_libfunc=@var{name}
16761 @opindex mdivsi3_libfunc=@var{name}
16762 Set the name of the library function used for 32 bit signed division to
16763 @var{name}. This only affect the name used in the call and inv:call
16764 division strategies, and the compiler will still expect the same
16765 sets of input/output/clobbered registers as if this option was not present.
16767 @item -mfixed-range=@var{register-range}
16768 @opindex mfixed-range
16769 Generate code treating the given register range as fixed registers.
16770 A fixed register is one that the register allocator can not use. This is
16771 useful when compiling kernel code. A register range is specified as
16772 two registers separated by a dash. Multiple register ranges can be
16773 specified separated by a comma.
16775 @item -madjust-unroll
16776 @opindex madjust-unroll
16777 Throttle unrolling to avoid thrashing target registers.
16778 This option only has an effect if the gcc code base supports the
16779 TARGET_ADJUST_UNROLL_MAX target hook.
16781 @item -mindexed-addressing
16782 @opindex mindexed-addressing
16783 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
16784 This is only safe if the hardware and/or OS implement 32 bit wrap-around
16785 semantics for the indexed addressing mode. The architecture allows the
16786 implementation of processors with 64 bit MMU, which the OS could use to
16787 get 32 bit addressing, but since no current hardware implementation supports
16788 this or any other way to make the indexed addressing mode safe to use in
16789 the 32 bit ABI, the default is -mno-indexed-addressing.
16791 @item -mgettrcost=@var{number}
16792 @opindex mgettrcost=@var{number}
16793 Set the cost assumed for the gettr instruction to @var{number}.
16794 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
16798 Assume pt* instructions won't trap. This will generally generate better
16799 scheduled code, but is unsafe on current hardware. The current architecture
16800 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
16801 This has the unintentional effect of making it unsafe to schedule ptabs /
16802 ptrel before a branch, or hoist it out of a loop. For example,
16803 __do_global_ctors, a part of libgcc that runs constructors at program
16804 startup, calls functions in a list which is delimited by @minus{}1. With the
16805 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
16806 That means that all the constructors will be run a bit quicker, but when
16807 the loop comes to the end of the list, the program crashes because ptabs
16808 loads @minus{}1 into a target register. Since this option is unsafe for any
16809 hardware implementing the current architecture specification, the default
16810 is -mno-pt-fixed. Unless the user specifies a specific cost with
16811 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
16812 this deters register allocation using target registers for storing
16815 @item -minvalid-symbols
16816 @opindex minvalid-symbols
16817 Assume symbols might be invalid. Ordinary function symbols generated by
16818 the compiler will always be valid to load with movi/shori/ptabs or
16819 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
16820 to generate symbols that will cause ptabs / ptrel to trap.
16821 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
16822 It will then prevent cross-basic-block cse, hoisting and most scheduling
16823 of symbol loads. The default is @option{-mno-invalid-symbols}.
16826 @node Solaris 2 Options
16827 @subsection Solaris 2 Options
16828 @cindex Solaris 2 options
16830 These @samp{-m} options are supported on Solaris 2:
16833 @item -mimpure-text
16834 @opindex mimpure-text
16835 @option{-mimpure-text}, used in addition to @option{-shared}, tells
16836 the compiler to not pass @option{-z text} to the linker when linking a
16837 shared object. Using this option, you can link position-dependent
16838 code into a shared object.
16840 @option{-mimpure-text} suppresses the ``relocations remain against
16841 allocatable but non-writable sections'' linker error message.
16842 However, the necessary relocations will trigger copy-on-write, and the
16843 shared object is not actually shared across processes. Instead of
16844 using @option{-mimpure-text}, you should compile all source code with
16845 @option{-fpic} or @option{-fPIC}.
16849 These switches are supported in addition to the above on Solaris 2:
16854 Add support for multithreading using the POSIX threads library. This
16855 option sets flags for both the preprocessor and linker. This option does
16856 not affect the thread safety of object code produced by the compiler or
16857 that of libraries supplied with it.
16861 This is a synonym for @option{-pthreads}.
16864 @node SPARC Options
16865 @subsection SPARC Options
16866 @cindex SPARC options
16868 These @samp{-m} options are supported on the SPARC:
16871 @item -mno-app-regs
16873 @opindex mno-app-regs
16875 Specify @option{-mapp-regs} to generate output using the global registers
16876 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
16879 To be fully SVR4 ABI compliant at the cost of some performance loss,
16880 specify @option{-mno-app-regs}. You should compile libraries and system
16881 software with this option.
16884 @itemx -mhard-float
16886 @opindex mhard-float
16887 Generate output containing floating point instructions. This is the
16891 @itemx -msoft-float
16893 @opindex msoft-float
16894 Generate output containing library calls for floating point.
16895 @strong{Warning:} the requisite libraries are not available for all SPARC
16896 targets. Normally the facilities of the machine's usual C compiler are
16897 used, but this cannot be done directly in cross-compilation. You must make
16898 your own arrangements to provide suitable library functions for
16899 cross-compilation. The embedded targets @samp{sparc-*-aout} and
16900 @samp{sparclite-*-*} do provide software floating point support.
16902 @option{-msoft-float} changes the calling convention in the output file;
16903 therefore, it is only useful if you compile @emph{all} of a program with
16904 this option. In particular, you need to compile @file{libgcc.a}, the
16905 library that comes with GCC, with @option{-msoft-float} in order for
16908 @item -mhard-quad-float
16909 @opindex mhard-quad-float
16910 Generate output containing quad-word (long double) floating point
16913 @item -msoft-quad-float
16914 @opindex msoft-quad-float
16915 Generate output containing library calls for quad-word (long double)
16916 floating point instructions. The functions called are those specified
16917 in the SPARC ABI@. This is the default.
16919 As of this writing, there are no SPARC implementations that have hardware
16920 support for the quad-word floating point instructions. They all invoke
16921 a trap handler for one of these instructions, and then the trap handler
16922 emulates the effect of the instruction. Because of the trap handler overhead,
16923 this is much slower than calling the ABI library routines. Thus the
16924 @option{-msoft-quad-float} option is the default.
16926 @item -mno-unaligned-doubles
16927 @itemx -munaligned-doubles
16928 @opindex mno-unaligned-doubles
16929 @opindex munaligned-doubles
16930 Assume that doubles have 8 byte alignment. This is the default.
16932 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
16933 alignment only if they are contained in another type, or if they have an
16934 absolute address. Otherwise, it assumes they have 4 byte alignment.
16935 Specifying this option avoids some rare compatibility problems with code
16936 generated by other compilers. It is not the default because it results
16937 in a performance loss, especially for floating point code.
16939 @item -mno-faster-structs
16940 @itemx -mfaster-structs
16941 @opindex mno-faster-structs
16942 @opindex mfaster-structs
16943 With @option{-mfaster-structs}, the compiler assumes that structures
16944 should have 8 byte alignment. This enables the use of pairs of
16945 @code{ldd} and @code{std} instructions for copies in structure
16946 assignment, in place of twice as many @code{ld} and @code{st} pairs.
16947 However, the use of this changed alignment directly violates the SPARC
16948 ABI@. Thus, it's intended only for use on targets where the developer
16949 acknowledges that their resulting code will not be directly in line with
16950 the rules of the ABI@.
16952 @item -mcpu=@var{cpu_type}
16954 Set the instruction set, register set, and instruction scheduling parameters
16955 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
16956 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc},
16957 @samp{leon}, @samp{sparclite}, @samp{f930}, @samp{f934}, @samp{sparclite86x},
16958 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
16959 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
16961 Default instruction scheduling parameters are used for values that select
16962 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
16963 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
16965 Here is a list of each supported architecture and their supported
16970 v8: supersparc, hypersparc, leon
16971 sparclite: f930, f934, sparclite86x
16973 v9: ultrasparc, ultrasparc3, niagara, niagara2
16976 By default (unless configured otherwise), GCC generates code for the V7
16977 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
16978 additionally optimizes it for the Cypress CY7C602 chip, as used in the
16979 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
16980 SPARCStation 1, 2, IPX etc.
16982 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
16983 architecture. The only difference from V7 code is that the compiler emits
16984 the integer multiply and integer divide instructions which exist in SPARC-V8
16985 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
16986 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
16989 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
16990 the SPARC architecture. This adds the integer multiply, integer divide step
16991 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
16992 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
16993 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
16994 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
16995 MB86934 chip, which is the more recent SPARClite with FPU@.
16997 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
16998 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
16999 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
17000 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
17001 optimizes it for the TEMIC SPARClet chip.
17003 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
17004 architecture. This adds 64-bit integer and floating-point move instructions,
17005 3 additional floating-point condition code registers and conditional move
17006 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
17007 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
17008 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
17009 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
17010 @option{-mcpu=niagara}, the compiler additionally optimizes it for
17011 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
17012 additionally optimizes it for Sun UltraSPARC T2 chips.
17014 @item -mtune=@var{cpu_type}
17016 Set the instruction scheduling parameters for machine type
17017 @var{cpu_type}, but do not set the instruction set or register set that the
17018 option @option{-mcpu=@var{cpu_type}} would.
17020 The same values for @option{-mcpu=@var{cpu_type}} can be used for
17021 @option{-mtune=@var{cpu_type}}, but the only useful values are those
17022 that select a particular CPU implementation. Those are @samp{cypress},
17023 @samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{f930}, @samp{f934},
17024 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, @samp{ultrasparc3},
17025 @samp{niagara}, and @samp{niagara2}.
17030 @opindex mno-v8plus
17031 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
17032 difference from the V8 ABI is that the global and out registers are
17033 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
17034 mode for all SPARC-V9 processors.
17040 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
17041 Visual Instruction Set extensions. The default is @option{-mno-vis}.
17044 These @samp{-m} options are supported in addition to the above
17045 on SPARC-V9 processors in 64-bit environments:
17048 @item -mlittle-endian
17049 @opindex mlittle-endian
17050 Generate code for a processor running in little-endian mode. It is only
17051 available for a few configurations and most notably not on Solaris and Linux.
17057 Generate code for a 32-bit or 64-bit environment.
17058 The 32-bit environment sets int, long and pointer to 32 bits.
17059 The 64-bit environment sets int to 32 bits and long and pointer
17062 @item -mcmodel=medlow
17063 @opindex mcmodel=medlow
17064 Generate code for the Medium/Low code model: 64-bit addresses, programs
17065 must be linked in the low 32 bits of memory. Programs can be statically
17066 or dynamically linked.
17068 @item -mcmodel=medmid
17069 @opindex mcmodel=medmid
17070 Generate code for the Medium/Middle code model: 64-bit addresses, programs
17071 must be linked in the low 44 bits of memory, the text and data segments must
17072 be less than 2GB in size and the data segment must be located within 2GB of
17075 @item -mcmodel=medany
17076 @opindex mcmodel=medany
17077 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
17078 may be linked anywhere in memory, the text and data segments must be less
17079 than 2GB in size and the data segment must be located within 2GB of the
17082 @item -mcmodel=embmedany
17083 @opindex mcmodel=embmedany
17084 Generate code for the Medium/Anywhere code model for embedded systems:
17085 64-bit addresses, the text and data segments must be less than 2GB in
17086 size, both starting anywhere in memory (determined at link time). The
17087 global register %g4 points to the base of the data segment. Programs
17088 are statically linked and PIC is not supported.
17091 @itemx -mno-stack-bias
17092 @opindex mstack-bias
17093 @opindex mno-stack-bias
17094 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
17095 frame pointer if present, are offset by @minus{}2047 which must be added back
17096 when making stack frame references. This is the default in 64-bit mode.
17097 Otherwise, assume no such offset is present.
17101 @subsection SPU Options
17102 @cindex SPU options
17104 These @samp{-m} options are supported on the SPU:
17108 @itemx -merror-reloc
17109 @opindex mwarn-reloc
17110 @opindex merror-reloc
17112 The loader for SPU does not handle dynamic relocations. By default, GCC
17113 will give an error when it generates code that requires a dynamic
17114 relocation. @option{-mno-error-reloc} disables the error,
17115 @option{-mwarn-reloc} will generate a warning instead.
17118 @itemx -munsafe-dma
17120 @opindex munsafe-dma
17122 Instructions which initiate or test completion of DMA must not be
17123 reordered with respect to loads and stores of the memory which is being
17124 accessed. Users typically address this problem using the volatile
17125 keyword, but that can lead to inefficient code in places where the
17126 memory is known to not change. Rather than mark the memory as volatile
17127 we treat the DMA instructions as potentially effecting all memory. With
17128 @option{-munsafe-dma} users must use the volatile keyword to protect
17131 @item -mbranch-hints
17132 @opindex mbranch-hints
17134 By default, GCC will generate a branch hint instruction to avoid
17135 pipeline stalls for always taken or probably taken branches. A hint
17136 will not be generated closer than 8 instructions away from its branch.
17137 There is little reason to disable them, except for debugging purposes,
17138 or to make an object a little bit smaller.
17142 @opindex msmall-mem
17143 @opindex mlarge-mem
17145 By default, GCC generates code assuming that addresses are never larger
17146 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
17147 a full 32 bit address.
17152 By default, GCC links against startup code that assumes the SPU-style
17153 main function interface (which has an unconventional parameter list).
17154 With @option{-mstdmain}, GCC will link your program against startup
17155 code that assumes a C99-style interface to @code{main}, including a
17156 local copy of @code{argv} strings.
17158 @item -mfixed-range=@var{register-range}
17159 @opindex mfixed-range
17160 Generate code treating the given register range as fixed registers.
17161 A fixed register is one that the register allocator can not use. This is
17162 useful when compiling kernel code. A register range is specified as
17163 two registers separated by a dash. Multiple register ranges can be
17164 specified separated by a comma.
17170 Compile code assuming that pointers to the PPU address space accessed
17171 via the @code{__ea} named address space qualifier are either 32 or 64
17172 bits wide. The default is 32 bits. As this is an ABI changing option,
17173 all object code in an executable must be compiled with the same setting.
17175 @item -maddress-space-conversion
17176 @itemx -mno-address-space-conversion
17177 @opindex maddress-space-conversion
17178 @opindex mno-address-space-conversion
17179 Allow/disallow treating the @code{__ea} address space as superset
17180 of the generic address space. This enables explicit type casts
17181 between @code{__ea} and generic pointer as well as implicit
17182 conversions of generic pointers to @code{__ea} pointers. The
17183 default is to allow address space pointer conversions.
17185 @item -mcache-size=@var{cache-size}
17186 @opindex mcache-size
17187 This option controls the version of libgcc that the compiler links to an
17188 executable and selects a software-managed cache for accessing variables
17189 in the @code{__ea} address space with a particular cache size. Possible
17190 options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
17191 and @samp{128}. The default cache size is 64KB.
17193 @item -matomic-updates
17194 @itemx -mno-atomic-updates
17195 @opindex matomic-updates
17196 @opindex mno-atomic-updates
17197 This option controls the version of libgcc that the compiler links to an
17198 executable and selects whether atomic updates to the software-managed
17199 cache of PPU-side variables are used. If you use atomic updates, changes
17200 to a PPU variable from SPU code using the @code{__ea} named address space
17201 qualifier will not interfere with changes to other PPU variables residing
17202 in the same cache line from PPU code. If you do not use atomic updates,
17203 such interference may occur; however, writing back cache lines will be
17204 more efficient. The default behavior is to use atomic updates.
17207 @itemx -mdual-nops=@var{n}
17208 @opindex mdual-nops
17209 By default, GCC will insert nops to increase dual issue when it expects
17210 it to increase performance. @var{n} can be a value from 0 to 10. A
17211 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
17212 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
17214 @item -mhint-max-nops=@var{n}
17215 @opindex mhint-max-nops
17216 Maximum number of nops to insert for a branch hint. A branch hint must
17217 be at least 8 instructions away from the branch it is effecting. GCC
17218 will insert up to @var{n} nops to enforce this, otherwise it will not
17219 generate the branch hint.
17221 @item -mhint-max-distance=@var{n}
17222 @opindex mhint-max-distance
17223 The encoding of the branch hint instruction limits the hint to be within
17224 256 instructions of the branch it is effecting. By default, GCC makes
17225 sure it is within 125.
17228 @opindex msafe-hints
17229 Work around a hardware bug which causes the SPU to stall indefinitely.
17230 By default, GCC will insert the @code{hbrp} instruction to make sure
17231 this stall won't happen.
17235 @node System V Options
17236 @subsection Options for System V
17238 These additional options are available on System V Release 4 for
17239 compatibility with other compilers on those systems:
17244 Create a shared object.
17245 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
17249 Identify the versions of each tool used by the compiler, in a
17250 @code{.ident} assembler directive in the output.
17254 Refrain from adding @code{.ident} directives to the output file (this is
17257 @item -YP,@var{dirs}
17259 Search the directories @var{dirs}, and no others, for libraries
17260 specified with @option{-l}.
17262 @item -Ym,@var{dir}
17264 Look in the directory @var{dir} to find the M4 preprocessor.
17265 The assembler uses this option.
17266 @c This is supposed to go with a -Yd for predefined M4 macro files, but
17267 @c the generic assembler that comes with Solaris takes just -Ym.
17271 @subsection V850 Options
17272 @cindex V850 Options
17274 These @samp{-m} options are defined for V850 implementations:
17278 @itemx -mno-long-calls
17279 @opindex mlong-calls
17280 @opindex mno-long-calls
17281 Treat all calls as being far away (near). If calls are assumed to be
17282 far away, the compiler will always load the functions address up into a
17283 register, and call indirect through the pointer.
17289 Do not optimize (do optimize) basic blocks that use the same index
17290 pointer 4 or more times to copy pointer into the @code{ep} register, and
17291 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
17292 option is on by default if you optimize.
17294 @item -mno-prolog-function
17295 @itemx -mprolog-function
17296 @opindex mno-prolog-function
17297 @opindex mprolog-function
17298 Do not use (do use) external functions to save and restore registers
17299 at the prologue and epilogue of a function. The external functions
17300 are slower, but use less code space if more than one function saves
17301 the same number of registers. The @option{-mprolog-function} option
17302 is on by default if you optimize.
17306 Try to make the code as small as possible. At present, this just turns
17307 on the @option{-mep} and @option{-mprolog-function} options.
17309 @item -mtda=@var{n}
17311 Put static or global variables whose size is @var{n} bytes or less into
17312 the tiny data area that register @code{ep} points to. The tiny data
17313 area can hold up to 256 bytes in total (128 bytes for byte references).
17315 @item -msda=@var{n}
17317 Put static or global variables whose size is @var{n} bytes or less into
17318 the small data area that register @code{gp} points to. The small data
17319 area can hold up to 64 kilobytes.
17321 @item -mzda=@var{n}
17323 Put static or global variables whose size is @var{n} bytes or less into
17324 the first 32 kilobytes of memory.
17328 Specify that the target processor is the V850.
17331 @opindex mbig-switch
17332 Generate code suitable for big switch tables. Use this option only if
17333 the assembler/linker complain about out of range branches within a switch
17338 This option will cause r2 and r5 to be used in the code generated by
17339 the compiler. This setting is the default.
17341 @item -mno-app-regs
17342 @opindex mno-app-regs
17343 This option will cause r2 and r5 to be treated as fixed registers.
17347 Specify that the target processor is the V850E2V3. The preprocessor
17348 constants @samp{__v850e2v3__} will be defined if
17349 this option is used.
17353 Specify that the target processor is the V850E2. The preprocessor
17354 constants @samp{__v850e2__} will be defined if this option is used.
17358 Specify that the target processor is the V850E1. The preprocessor
17359 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
17360 this option is used.
17364 Specify that the target processor is the V850ES. This is an alias for
17365 the @option{-mv850e1} option.
17369 Specify that the target processor is the V850E@. The preprocessor
17370 constant @samp{__v850e__} will be defined if this option is used.
17372 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
17373 nor @option{-mv850e2} nor @option{-mv850e2v3}
17374 are defined then a default target processor will be chosen and the
17375 relevant @samp{__v850*__} preprocessor constant will be defined.
17377 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
17378 defined, regardless of which processor variant is the target.
17380 @item -mdisable-callt
17381 @opindex mdisable-callt
17382 This option will suppress generation of the CALLT instruction for the
17383 v850e, v850e1, v850e2 and v850e2v3 flavors of the v850 architecture. The default is
17384 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
17389 @subsection VAX Options
17390 @cindex VAX options
17392 These @samp{-m} options are defined for the VAX:
17397 Do not output certain jump instructions (@code{aobleq} and so on)
17398 that the Unix assembler for the VAX cannot handle across long
17403 Do output those jump instructions, on the assumption that you
17404 will assemble with the GNU assembler.
17408 Output code for g-format floating point numbers instead of d-format.
17411 @node VxWorks Options
17412 @subsection VxWorks Options
17413 @cindex VxWorks Options
17415 The options in this section are defined for all VxWorks targets.
17416 Options specific to the target hardware are listed with the other
17417 options for that target.
17422 GCC can generate code for both VxWorks kernels and real time processes
17423 (RTPs). This option switches from the former to the latter. It also
17424 defines the preprocessor macro @code{__RTP__}.
17427 @opindex non-static
17428 Link an RTP executable against shared libraries rather than static
17429 libraries. The options @option{-static} and @option{-shared} can
17430 also be used for RTPs (@pxref{Link Options}); @option{-static}
17437 These options are passed down to the linker. They are defined for
17438 compatibility with Diab.
17441 @opindex Xbind-lazy
17442 Enable lazy binding of function calls. This option is equivalent to
17443 @option{-Wl,-z,now} and is defined for compatibility with Diab.
17447 Disable lazy binding of function calls. This option is the default and
17448 is defined for compatibility with Diab.
17451 @node x86-64 Options
17452 @subsection x86-64 Options
17453 @cindex x86-64 options
17455 These are listed under @xref{i386 and x86-64 Options}.
17457 @node Xstormy16 Options
17458 @subsection Xstormy16 Options
17459 @cindex Xstormy16 Options
17461 These options are defined for Xstormy16:
17466 Choose startup files and linker script suitable for the simulator.
17469 @node Xtensa Options
17470 @subsection Xtensa Options
17471 @cindex Xtensa Options
17473 These options are supported for Xtensa targets:
17477 @itemx -mno-const16
17479 @opindex mno-const16
17480 Enable or disable use of @code{CONST16} instructions for loading
17481 constant values. The @code{CONST16} instruction is currently not a
17482 standard option from Tensilica. When enabled, @code{CONST16}
17483 instructions are always used in place of the standard @code{L32R}
17484 instructions. The use of @code{CONST16} is enabled by default only if
17485 the @code{L32R} instruction is not available.
17488 @itemx -mno-fused-madd
17489 @opindex mfused-madd
17490 @opindex mno-fused-madd
17491 Enable or disable use of fused multiply/add and multiply/subtract
17492 instructions in the floating-point option. This has no effect if the
17493 floating-point option is not also enabled. Disabling fused multiply/add
17494 and multiply/subtract instructions forces the compiler to use separate
17495 instructions for the multiply and add/subtract operations. This may be
17496 desirable in some cases where strict IEEE 754-compliant results are
17497 required: the fused multiply add/subtract instructions do not round the
17498 intermediate result, thereby producing results with @emph{more} bits of
17499 precision than specified by the IEEE standard. Disabling fused multiply
17500 add/subtract instructions also ensures that the program output is not
17501 sensitive to the compiler's ability to combine multiply and add/subtract
17504 @item -mserialize-volatile
17505 @itemx -mno-serialize-volatile
17506 @opindex mserialize-volatile
17507 @opindex mno-serialize-volatile
17508 When this option is enabled, GCC inserts @code{MEMW} instructions before
17509 @code{volatile} memory references to guarantee sequential consistency.
17510 The default is @option{-mserialize-volatile}. Use
17511 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
17513 @item -mforce-no-pic
17514 @opindex mforce-no-pic
17515 For targets, like GNU/Linux, where all user-mode Xtensa code must be
17516 position-independent code (PIC), this option disables PIC for compiling
17519 @item -mtext-section-literals
17520 @itemx -mno-text-section-literals
17521 @opindex mtext-section-literals
17522 @opindex mno-text-section-literals
17523 Control the treatment of literal pools. The default is
17524 @option{-mno-text-section-literals}, which places literals in a separate
17525 section in the output file. This allows the literal pool to be placed
17526 in a data RAM/ROM, and it also allows the linker to combine literal
17527 pools from separate object files to remove redundant literals and
17528 improve code size. With @option{-mtext-section-literals}, the literals
17529 are interspersed in the text section in order to keep them as close as
17530 possible to their references. This may be necessary for large assembly
17533 @item -mtarget-align
17534 @itemx -mno-target-align
17535 @opindex mtarget-align
17536 @opindex mno-target-align
17537 When this option is enabled, GCC instructs the assembler to
17538 automatically align instructions to reduce branch penalties at the
17539 expense of some code density. The assembler attempts to widen density
17540 instructions to align branch targets and the instructions following call
17541 instructions. If there are not enough preceding safe density
17542 instructions to align a target, no widening will be performed. The
17543 default is @option{-mtarget-align}. These options do not affect the
17544 treatment of auto-aligned instructions like @code{LOOP}, which the
17545 assembler will always align, either by widening density instructions or
17546 by inserting no-op instructions.
17549 @itemx -mno-longcalls
17550 @opindex mlongcalls
17551 @opindex mno-longcalls
17552 When this option is enabled, GCC instructs the assembler to translate
17553 direct calls to indirect calls unless it can determine that the target
17554 of a direct call is in the range allowed by the call instruction. This
17555 translation typically occurs for calls to functions in other source
17556 files. Specifically, the assembler translates a direct @code{CALL}
17557 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
17558 The default is @option{-mno-longcalls}. This option should be used in
17559 programs where the call target can potentially be out of range. This
17560 option is implemented in the assembler, not the compiler, so the
17561 assembly code generated by GCC will still show direct call
17562 instructions---look at the disassembled object code to see the actual
17563 instructions. Note that the assembler will use an indirect call for
17564 every cross-file call, not just those that really will be out of range.
17567 @node zSeries Options
17568 @subsection zSeries Options
17569 @cindex zSeries options
17571 These are listed under @xref{S/390 and zSeries Options}.
17573 @node Code Gen Options
17574 @section Options for Code Generation Conventions
17575 @cindex code generation conventions
17576 @cindex options, code generation
17577 @cindex run-time options
17579 These machine-independent options control the interface conventions
17580 used in code generation.
17582 Most of them have both positive and negative forms; the negative form
17583 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
17584 one of the forms is listed---the one which is not the default. You
17585 can figure out the other form by either removing @samp{no-} or adding
17589 @item -fbounds-check
17590 @opindex fbounds-check
17591 For front-ends that support it, generate additional code to check that
17592 indices used to access arrays are within the declared range. This is
17593 currently only supported by the Java and Fortran front-ends, where
17594 this option defaults to true and false respectively.
17598 This option generates traps for signed overflow on addition, subtraction,
17599 multiplication operations.
17603 This option instructs the compiler to assume that signed arithmetic
17604 overflow of addition, subtraction and multiplication wraps around
17605 using twos-complement representation. This flag enables some optimizations
17606 and disables others. This option is enabled by default for the Java
17607 front-end, as required by the Java language specification.
17610 @opindex fexceptions
17611 Enable exception handling. Generates extra code needed to propagate
17612 exceptions. For some targets, this implies GCC will generate frame
17613 unwind information for all functions, which can produce significant data
17614 size overhead, although it does not affect execution. If you do not
17615 specify this option, GCC will enable it by default for languages like
17616 C++ which normally require exception handling, and disable it for
17617 languages like C that do not normally require it. However, you may need
17618 to enable this option when compiling C code that needs to interoperate
17619 properly with exception handlers written in C++. You may also wish to
17620 disable this option if you are compiling older C++ programs that don't
17621 use exception handling.
17623 @item -fnon-call-exceptions
17624 @opindex fnon-call-exceptions
17625 Generate code that allows trapping instructions to throw exceptions.
17626 Note that this requires platform-specific runtime support that does
17627 not exist everywhere. Moreover, it only allows @emph{trapping}
17628 instructions to throw exceptions, i.e.@: memory references or floating
17629 point instructions. It does not allow exceptions to be thrown from
17630 arbitrary signal handlers such as @code{SIGALRM}.
17632 @item -funwind-tables
17633 @opindex funwind-tables
17634 Similar to @option{-fexceptions}, except that it will just generate any needed
17635 static data, but will not affect the generated code in any other way.
17636 You will normally not enable this option; instead, a language processor
17637 that needs this handling would enable it on your behalf.
17639 @item -fasynchronous-unwind-tables
17640 @opindex fasynchronous-unwind-tables
17641 Generate unwind table in dwarf2 format, if supported by target machine. The
17642 table is exact at each instruction boundary, so it can be used for stack
17643 unwinding from asynchronous events (such as debugger or garbage collector).
17645 @item -fpcc-struct-return
17646 @opindex fpcc-struct-return
17647 Return ``short'' @code{struct} and @code{union} values in memory like
17648 longer ones, rather than in registers. This convention is less
17649 efficient, but it has the advantage of allowing intercallability between
17650 GCC-compiled files and files compiled with other compilers, particularly
17651 the Portable C Compiler (pcc).
17653 The precise convention for returning structures in memory depends
17654 on the target configuration macros.
17656 Short structures and unions are those whose size and alignment match
17657 that of some integer type.
17659 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
17660 switch is not binary compatible with code compiled with the
17661 @option{-freg-struct-return} switch.
17662 Use it to conform to a non-default application binary interface.
17664 @item -freg-struct-return
17665 @opindex freg-struct-return
17666 Return @code{struct} and @code{union} values in registers when possible.
17667 This is more efficient for small structures than
17668 @option{-fpcc-struct-return}.
17670 If you specify neither @option{-fpcc-struct-return} nor
17671 @option{-freg-struct-return}, GCC defaults to whichever convention is
17672 standard for the target. If there is no standard convention, GCC
17673 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
17674 the principal compiler. In those cases, we can choose the standard, and
17675 we chose the more efficient register return alternative.
17677 @strong{Warning:} code compiled with the @option{-freg-struct-return}
17678 switch is not binary compatible with code compiled with the
17679 @option{-fpcc-struct-return} switch.
17680 Use it to conform to a non-default application binary interface.
17682 @item -fshort-enums
17683 @opindex fshort-enums
17684 Allocate to an @code{enum} type only as many bytes as it needs for the
17685 declared range of possible values. Specifically, the @code{enum} type
17686 will be equivalent to the smallest integer type which has enough room.
17688 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
17689 code that is not binary compatible with code generated without that switch.
17690 Use it to conform to a non-default application binary interface.
17692 @item -fshort-double
17693 @opindex fshort-double
17694 Use the same size for @code{double} as for @code{float}.
17696 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
17697 code that is not binary compatible with code generated without that switch.
17698 Use it to conform to a non-default application binary interface.
17700 @item -fshort-wchar
17701 @opindex fshort-wchar
17702 Override the underlying type for @samp{wchar_t} to be @samp{short
17703 unsigned int} instead of the default for the target. This option is
17704 useful for building programs to run under WINE@.
17706 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
17707 code that is not binary compatible with code generated without that switch.
17708 Use it to conform to a non-default application binary interface.
17711 @opindex fno-common
17712 In C code, controls the placement of uninitialized global variables.
17713 Unix C compilers have traditionally permitted multiple definitions of
17714 such variables in different compilation units by placing the variables
17716 This is the behavior specified by @option{-fcommon}, and is the default
17717 for GCC on most targets.
17718 On the other hand, this behavior is not required by ISO C, and on some
17719 targets may carry a speed or code size penalty on variable references.
17720 The @option{-fno-common} option specifies that the compiler should place
17721 uninitialized global variables in the data section of the object file,
17722 rather than generating them as common blocks.
17723 This has the effect that if the same variable is declared
17724 (without @code{extern}) in two different compilations,
17725 you will get a multiple-definition error when you link them.
17726 In this case, you must compile with @option{-fcommon} instead.
17727 Compiling with @option{-fno-common} is useful on targets for which
17728 it provides better performance, or if you wish to verify that the
17729 program will work on other systems which always treat uninitialized
17730 variable declarations this way.
17734 Ignore the @samp{#ident} directive.
17736 @item -finhibit-size-directive
17737 @opindex finhibit-size-directive
17738 Don't output a @code{.size} assembler directive, or anything else that
17739 would cause trouble if the function is split in the middle, and the
17740 two halves are placed at locations far apart in memory. This option is
17741 used when compiling @file{crtstuff.c}; you should not need to use it
17744 @item -fverbose-asm
17745 @opindex fverbose-asm
17746 Put extra commentary information in the generated assembly code to
17747 make it more readable. This option is generally only of use to those
17748 who actually need to read the generated assembly code (perhaps while
17749 debugging the compiler itself).
17751 @option{-fno-verbose-asm}, the default, causes the
17752 extra information to be omitted and is useful when comparing two assembler
17755 @item -frecord-gcc-switches
17756 @opindex frecord-gcc-switches
17757 This switch causes the command line that was used to invoke the
17758 compiler to be recorded into the object file that is being created.
17759 This switch is only implemented on some targets and the exact format
17760 of the recording is target and binary file format dependent, but it
17761 usually takes the form of a section containing ASCII text. This
17762 switch is related to the @option{-fverbose-asm} switch, but that
17763 switch only records information in the assembler output file as
17764 comments, so it never reaches the object file.
17768 @cindex global offset table
17770 Generate position-independent code (PIC) suitable for use in a shared
17771 library, if supported for the target machine. Such code accesses all
17772 constant addresses through a global offset table (GOT)@. The dynamic
17773 loader resolves the GOT entries when the program starts (the dynamic
17774 loader is not part of GCC; it is part of the operating system). If
17775 the GOT size for the linked executable exceeds a machine-specific
17776 maximum size, you get an error message from the linker indicating that
17777 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
17778 instead. (These maximums are 8k on the SPARC and 32k
17779 on the m68k and RS/6000. The 386 has no such limit.)
17781 Position-independent code requires special support, and therefore works
17782 only on certain machines. For the 386, GCC supports PIC for System V
17783 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
17784 position-independent.
17786 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
17791 If supported for the target machine, emit position-independent code,
17792 suitable for dynamic linking and avoiding any limit on the size of the
17793 global offset table. This option makes a difference on the m68k,
17794 PowerPC and SPARC@.
17796 Position-independent code requires special support, and therefore works
17797 only on certain machines.
17799 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
17806 These options are similar to @option{-fpic} and @option{-fPIC}, but
17807 generated position independent code can be only linked into executables.
17808 Usually these options are used when @option{-pie} GCC option will be
17809 used during linking.
17811 @option{-fpie} and @option{-fPIE} both define the macros
17812 @code{__pie__} and @code{__PIE__}. The macros have the value 1
17813 for @option{-fpie} and 2 for @option{-fPIE}.
17815 @item -fno-jump-tables
17816 @opindex fno-jump-tables
17817 Do not use jump tables for switch statements even where it would be
17818 more efficient than other code generation strategies. This option is
17819 of use in conjunction with @option{-fpic} or @option{-fPIC} for
17820 building code which forms part of a dynamic linker and cannot
17821 reference the address of a jump table. On some targets, jump tables
17822 do not require a GOT and this option is not needed.
17824 @item -ffixed-@var{reg}
17826 Treat the register named @var{reg} as a fixed register; generated code
17827 should never refer to it (except perhaps as a stack pointer, frame
17828 pointer or in some other fixed role).
17830 @var{reg} must be the name of a register. The register names accepted
17831 are machine-specific and are defined in the @code{REGISTER_NAMES}
17832 macro in the machine description macro file.
17834 This flag does not have a negative form, because it specifies a
17837 @item -fcall-used-@var{reg}
17838 @opindex fcall-used
17839 Treat the register named @var{reg} as an allocable register that is
17840 clobbered by function calls. It may be allocated for temporaries or
17841 variables that do not live across a call. Functions compiled this way
17842 will not save and restore the register @var{reg}.
17844 It is an error to used this flag with the frame pointer or stack pointer.
17845 Use of this flag for other registers that have fixed pervasive roles in
17846 the machine's execution model will produce disastrous results.
17848 This flag does not have a negative form, because it specifies a
17851 @item -fcall-saved-@var{reg}
17852 @opindex fcall-saved
17853 Treat the register named @var{reg} as an allocable register saved by
17854 functions. It may be allocated even for temporaries or variables that
17855 live across a call. Functions compiled this way will save and restore
17856 the register @var{reg} if they use it.
17858 It is an error to used this flag with the frame pointer or stack pointer.
17859 Use of this flag for other registers that have fixed pervasive roles in
17860 the machine's execution model will produce disastrous results.
17862 A different sort of disaster will result from the use of this flag for
17863 a register in which function values may be returned.
17865 This flag does not have a negative form, because it specifies a
17868 @item -fpack-struct[=@var{n}]
17869 @opindex fpack-struct
17870 Without a value specified, pack all structure members together without
17871 holes. When a value is specified (which must be a small power of two), pack
17872 structure members according to this value, representing the maximum
17873 alignment (that is, objects with default alignment requirements larger than
17874 this will be output potentially unaligned at the next fitting location.
17876 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
17877 code that is not binary compatible with code generated without that switch.
17878 Additionally, it makes the code suboptimal.
17879 Use it to conform to a non-default application binary interface.
17881 @item -finstrument-functions
17882 @opindex finstrument-functions
17883 Generate instrumentation calls for entry and exit to functions. Just
17884 after function entry and just before function exit, the following
17885 profiling functions will be called with the address of the current
17886 function and its call site. (On some platforms,
17887 @code{__builtin_return_address} does not work beyond the current
17888 function, so the call site information may not be available to the
17889 profiling functions otherwise.)
17892 void __cyg_profile_func_enter (void *this_fn,
17894 void __cyg_profile_func_exit (void *this_fn,
17898 The first argument is the address of the start of the current function,
17899 which may be looked up exactly in the symbol table.
17901 This instrumentation is also done for functions expanded inline in other
17902 functions. The profiling calls will indicate where, conceptually, the
17903 inline function is entered and exited. This means that addressable
17904 versions of such functions must be available. If all your uses of a
17905 function are expanded inline, this may mean an additional expansion of
17906 code size. If you use @samp{extern inline} in your C code, an
17907 addressable version of such functions must be provided. (This is
17908 normally the case anyways, but if you get lucky and the optimizer always
17909 expands the functions inline, you might have gotten away without
17910 providing static copies.)
17912 A function may be given the attribute @code{no_instrument_function}, in
17913 which case this instrumentation will not be done. This can be used, for
17914 example, for the profiling functions listed above, high-priority
17915 interrupt routines, and any functions from which the profiling functions
17916 cannot safely be called (perhaps signal handlers, if the profiling
17917 routines generate output or allocate memory).
17919 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
17920 @opindex finstrument-functions-exclude-file-list
17922 Set the list of functions that are excluded from instrumentation (see
17923 the description of @code{-finstrument-functions}). If the file that
17924 contains a function definition matches with one of @var{file}, then
17925 that function is not instrumented. The match is done on substrings:
17926 if the @var{file} parameter is a substring of the file name, it is
17927 considered to be a match.
17932 -finstrument-functions-exclude-file-list=/bits/stl,include/sys
17936 will exclude any inline function defined in files whose pathnames
17937 contain @code{/bits/stl} or @code{include/sys}.
17939 If, for some reason, you want to include letter @code{','} in one of
17940 @var{sym}, write @code{'\,'}. For example,
17941 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
17942 (note the single quote surrounding the option).
17944 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
17945 @opindex finstrument-functions-exclude-function-list
17947 This is similar to @code{-finstrument-functions-exclude-file-list},
17948 but this option sets the list of function names to be excluded from
17949 instrumentation. The function name to be matched is its user-visible
17950 name, such as @code{vector<int> blah(const vector<int> &)}, not the
17951 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
17952 match is done on substrings: if the @var{sym} parameter is a substring
17953 of the function name, it is considered to be a match. For C99 and C++
17954 extended identifiers, the function name must be given in UTF-8, not
17955 using universal character names.
17957 @item -fstack-check
17958 @opindex fstack-check
17959 Generate code to verify that you do not go beyond the boundary of the
17960 stack. You should specify this flag if you are running in an
17961 environment with multiple threads, but only rarely need to specify it in
17962 a single-threaded environment since stack overflow is automatically
17963 detected on nearly all systems if there is only one stack.
17965 Note that this switch does not actually cause checking to be done; the
17966 operating system or the language runtime must do that. The switch causes
17967 generation of code to ensure that they see the stack being extended.
17969 You can additionally specify a string parameter: @code{no} means no
17970 checking, @code{generic} means force the use of old-style checking,
17971 @code{specific} means use the best checking method and is equivalent
17972 to bare @option{-fstack-check}.
17974 Old-style checking is a generic mechanism that requires no specific
17975 target support in the compiler but comes with the following drawbacks:
17979 Modified allocation strategy for large objects: they will always be
17980 allocated dynamically if their size exceeds a fixed threshold.
17983 Fixed limit on the size of the static frame of functions: when it is
17984 topped by a particular function, stack checking is not reliable and
17985 a warning is issued by the compiler.
17988 Inefficiency: because of both the modified allocation strategy and the
17989 generic implementation, the performances of the code are hampered.
17992 Note that old-style stack checking is also the fallback method for
17993 @code{specific} if no target support has been added in the compiler.
17995 @item -fstack-limit-register=@var{reg}
17996 @itemx -fstack-limit-symbol=@var{sym}
17997 @itemx -fno-stack-limit
17998 @opindex fstack-limit-register
17999 @opindex fstack-limit-symbol
18000 @opindex fno-stack-limit
18001 Generate code to ensure that the stack does not grow beyond a certain value,
18002 either the value of a register or the address of a symbol. If the stack
18003 would grow beyond the value, a signal is raised. For most targets,
18004 the signal is raised before the stack overruns the boundary, so
18005 it is possible to catch the signal without taking special precautions.
18007 For instance, if the stack starts at absolute address @samp{0x80000000}
18008 and grows downwards, you can use the flags
18009 @option{-fstack-limit-symbol=__stack_limit} and
18010 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
18011 of 128KB@. Note that this may only work with the GNU linker.
18013 @item -fsplit-stack
18014 @opindex fsplit-stack
18015 Generate code to automatically split the stack before it overflows.
18016 The resulting program has a discontiguous stack which can only
18017 overflow if the program is unable to allocate any more memory. This
18018 is most useful when running threaded programs, as it is no longer
18019 necessary to calculate a good stack size to use for each thread. This
18020 is currently only implemented for the i386 and x86_64 backends running
18023 When code compiled with @option{-fsplit-stack} calls code compiled
18024 without @option{-fsplit-stack}, there may not be much stack space
18025 available for the latter code to run. If compiling all code,
18026 including library code, with @option{-fsplit-stack} is not an option,
18027 then the linker can fix up these calls so that the code compiled
18028 without @option{-fsplit-stack} always has a large stack. Support for
18029 this is implemented in the gold linker in GNU binutils release 2.21
18032 @item -fleading-underscore
18033 @opindex fleading-underscore
18034 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
18035 change the way C symbols are represented in the object file. One use
18036 is to help link with legacy assembly code.
18038 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
18039 generate code that is not binary compatible with code generated without that
18040 switch. Use it to conform to a non-default application binary interface.
18041 Not all targets provide complete support for this switch.
18043 @item -ftls-model=@var{model}
18044 @opindex ftls-model
18045 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
18046 The @var{model} argument should be one of @code{global-dynamic},
18047 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
18049 The default without @option{-fpic} is @code{initial-exec}; with
18050 @option{-fpic} the default is @code{global-dynamic}.
18052 @item -fvisibility=@var{default|internal|hidden|protected}
18053 @opindex fvisibility
18054 Set the default ELF image symbol visibility to the specified option---all
18055 symbols will be marked with this unless overridden within the code.
18056 Using this feature can very substantially improve linking and
18057 load times of shared object libraries, produce more optimized
18058 code, provide near-perfect API export and prevent symbol clashes.
18059 It is @strong{strongly} recommended that you use this in any shared objects
18062 Despite the nomenclature, @code{default} always means public; i.e.,
18063 available to be linked against from outside the shared object.
18064 @code{protected} and @code{internal} are pretty useless in real-world
18065 usage so the only other commonly used option will be @code{hidden}.
18066 The default if @option{-fvisibility} isn't specified is
18067 @code{default}, i.e., make every
18068 symbol public---this causes the same behavior as previous versions of
18071 A good explanation of the benefits offered by ensuring ELF
18072 symbols have the correct visibility is given by ``How To Write
18073 Shared Libraries'' by Ulrich Drepper (which can be found at
18074 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
18075 solution made possible by this option to marking things hidden when
18076 the default is public is to make the default hidden and mark things
18077 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
18078 and @code{__attribute__ ((visibility("default")))} instead of
18079 @code{__declspec(dllexport)} you get almost identical semantics with
18080 identical syntax. This is a great boon to those working with
18081 cross-platform projects.
18083 For those adding visibility support to existing code, you may find
18084 @samp{#pragma GCC visibility} of use. This works by you enclosing
18085 the declarations you wish to set visibility for with (for example)
18086 @samp{#pragma GCC visibility push(hidden)} and
18087 @samp{#pragma GCC visibility pop}.
18088 Bear in mind that symbol visibility should be viewed @strong{as
18089 part of the API interface contract} and thus all new code should
18090 always specify visibility when it is not the default; i.e., declarations
18091 only for use within the local DSO should @strong{always} be marked explicitly
18092 as hidden as so to avoid PLT indirection overheads---making this
18093 abundantly clear also aids readability and self-documentation of the code.
18094 Note that due to ISO C++ specification requirements, operator new and
18095 operator delete must always be of default visibility.
18097 Be aware that headers from outside your project, in particular system
18098 headers and headers from any other library you use, may not be
18099 expecting to be compiled with visibility other than the default. You
18100 may need to explicitly say @samp{#pragma GCC visibility push(default)}
18101 before including any such headers.
18103 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
18104 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
18105 no modifications. However, this means that calls to @samp{extern}
18106 functions with no explicit visibility will use the PLT, so it is more
18107 effective to use @samp{__attribute ((visibility))} and/or
18108 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
18109 declarations should be treated as hidden.
18111 Note that @samp{-fvisibility} does affect C++ vague linkage
18112 entities. This means that, for instance, an exception class that will
18113 be thrown between DSOs must be explicitly marked with default
18114 visibility so that the @samp{type_info} nodes will be unified between
18117 An overview of these techniques, their benefits and how to use them
18118 is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
18120 @item -fstrict-volatile-bitfields
18121 @opindex fstrict-volatile-bitfields
18122 This option should be used if accesses to volatile bitfields (or other
18123 structure fields, although the compiler usually honors those types
18124 anyway) should use a single access of the width of the
18125 field's type, aligned to a natural alignment if possible. For
18126 example, targets with memory-mapped peripheral registers might require
18127 all such accesses to be 16 bits wide; with this flag the user could
18128 declare all peripheral bitfields as ``unsigned short'' (assuming short
18129 is 16 bits on these targets) to force GCC to use 16 bit accesses
18130 instead of, perhaps, a more efficient 32 bit access.
18132 If this option is disabled, the compiler will use the most efficient
18133 instruction. In the previous example, that might be a 32-bit load
18134 instruction, even though that will access bytes that do not contain
18135 any portion of the bitfield, or memory-mapped registers unrelated to
18136 the one being updated.
18138 If the target requires strict alignment, and honoring the field
18139 type would require violating this alignment, a warning is issued.
18140 If the field has @code{packed} attribute, the access is done without
18141 honoring the field type. If the field doesn't have @code{packed}
18142 attribute, the access is done honoring the field type. In both cases,
18143 GCC assumes that the user knows something about the target hardware
18144 that it is unaware of.
18146 The default value of this option is determined by the application binary
18147 interface for the target processor.
18153 @node Environment Variables
18154 @section Environment Variables Affecting GCC
18155 @cindex environment variables
18157 @c man begin ENVIRONMENT
18158 This section describes several environment variables that affect how GCC
18159 operates. Some of them work by specifying directories or prefixes to use
18160 when searching for various kinds of files. Some are used to specify other
18161 aspects of the compilation environment.
18163 Note that you can also specify places to search using options such as
18164 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
18165 take precedence over places specified using environment variables, which
18166 in turn take precedence over those specified by the configuration of GCC@.
18167 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
18168 GNU Compiler Collection (GCC) Internals}.
18173 @c @itemx LC_COLLATE
18175 @c @itemx LC_MONETARY
18176 @c @itemx LC_NUMERIC
18181 @c @findex LC_COLLATE
18182 @findex LC_MESSAGES
18183 @c @findex LC_MONETARY
18184 @c @findex LC_NUMERIC
18188 These environment variables control the way that GCC uses
18189 localization information that allow GCC to work with different
18190 national conventions. GCC inspects the locale categories
18191 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
18192 so. These locale categories can be set to any value supported by your
18193 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
18194 Kingdom encoded in UTF-8.
18196 The @env{LC_CTYPE} environment variable specifies character
18197 classification. GCC uses it to determine the character boundaries in
18198 a string; this is needed for some multibyte encodings that contain quote
18199 and escape characters that would otherwise be interpreted as a string
18202 The @env{LC_MESSAGES} environment variable specifies the language to
18203 use in diagnostic messages.
18205 If the @env{LC_ALL} environment variable is set, it overrides the value
18206 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
18207 and @env{LC_MESSAGES} default to the value of the @env{LANG}
18208 environment variable. If none of these variables are set, GCC
18209 defaults to traditional C English behavior.
18213 If @env{TMPDIR} is set, it specifies the directory to use for temporary
18214 files. GCC uses temporary files to hold the output of one stage of
18215 compilation which is to be used as input to the next stage: for example,
18216 the output of the preprocessor, which is the input to the compiler
18219 @item GCC_EXEC_PREFIX
18220 @findex GCC_EXEC_PREFIX
18221 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
18222 names of the subprograms executed by the compiler. No slash is added
18223 when this prefix is combined with the name of a subprogram, but you can
18224 specify a prefix that ends with a slash if you wish.
18226 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
18227 an appropriate prefix to use based on the pathname it was invoked with.
18229 If GCC cannot find the subprogram using the specified prefix, it
18230 tries looking in the usual places for the subprogram.
18232 The default value of @env{GCC_EXEC_PREFIX} is
18233 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
18234 the installed compiler. In many cases @var{prefix} is the value
18235 of @code{prefix} when you ran the @file{configure} script.
18237 Other prefixes specified with @option{-B} take precedence over this prefix.
18239 This prefix is also used for finding files such as @file{crt0.o} that are
18242 In addition, the prefix is used in an unusual way in finding the
18243 directories to search for header files. For each of the standard
18244 directories whose name normally begins with @samp{/usr/local/lib/gcc}
18245 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
18246 replacing that beginning with the specified prefix to produce an
18247 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
18248 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
18249 These alternate directories are searched first; the standard directories
18250 come next. If a standard directory begins with the configured
18251 @var{prefix} then the value of @var{prefix} is replaced by
18252 @env{GCC_EXEC_PREFIX} when looking for header files.
18254 @item COMPILER_PATH
18255 @findex COMPILER_PATH
18256 The value of @env{COMPILER_PATH} is a colon-separated list of
18257 directories, much like @env{PATH}. GCC tries the directories thus
18258 specified when searching for subprograms, if it can't find the
18259 subprograms using @env{GCC_EXEC_PREFIX}.
18262 @findex LIBRARY_PATH
18263 The value of @env{LIBRARY_PATH} is a colon-separated list of
18264 directories, much like @env{PATH}. When configured as a native compiler,
18265 GCC tries the directories thus specified when searching for special
18266 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
18267 using GCC also uses these directories when searching for ordinary
18268 libraries for the @option{-l} option (but directories specified with
18269 @option{-L} come first).
18273 @cindex locale definition
18274 This variable is used to pass locale information to the compiler. One way in
18275 which this information is used is to determine the character set to be used
18276 when character literals, string literals and comments are parsed in C and C++.
18277 When the compiler is configured to allow multibyte characters,
18278 the following values for @env{LANG} are recognized:
18282 Recognize JIS characters.
18284 Recognize SJIS characters.
18286 Recognize EUCJP characters.
18289 If @env{LANG} is not defined, or if it has some other value, then the
18290 compiler will use mblen and mbtowc as defined by the default locale to
18291 recognize and translate multibyte characters.
18295 Some additional environments variables affect the behavior of the
18298 @include cppenv.texi
18302 @node Precompiled Headers
18303 @section Using Precompiled Headers
18304 @cindex precompiled headers
18305 @cindex speed of compilation
18307 Often large projects have many header files that are included in every
18308 source file. The time the compiler takes to process these header files
18309 over and over again can account for nearly all of the time required to
18310 build the project. To make builds faster, GCC allows users to
18311 `precompile' a header file; then, if builds can use the precompiled
18312 header file they will be much faster.
18314 To create a precompiled header file, simply compile it as you would any
18315 other file, if necessary using the @option{-x} option to make the driver
18316 treat it as a C or C++ header file. You will probably want to use a
18317 tool like @command{make} to keep the precompiled header up-to-date when
18318 the headers it contains change.
18320 A precompiled header file will be searched for when @code{#include} is
18321 seen in the compilation. As it searches for the included file
18322 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
18323 compiler looks for a precompiled header in each directory just before it
18324 looks for the include file in that directory. The name searched for is
18325 the name specified in the @code{#include} with @samp{.gch} appended. If
18326 the precompiled header file can't be used, it is ignored.
18328 For instance, if you have @code{#include "all.h"}, and you have
18329 @file{all.h.gch} in the same directory as @file{all.h}, then the
18330 precompiled header file will be used if possible, and the original
18331 header will be used otherwise.
18333 Alternatively, you might decide to put the precompiled header file in a
18334 directory and use @option{-I} to ensure that directory is searched
18335 before (or instead of) the directory containing the original header.
18336 Then, if you want to check that the precompiled header file is always
18337 used, you can put a file of the same name as the original header in this
18338 directory containing an @code{#error} command.
18340 This also works with @option{-include}. So yet another way to use
18341 precompiled headers, good for projects not designed with precompiled
18342 header files in mind, is to simply take most of the header files used by
18343 a project, include them from another header file, precompile that header
18344 file, and @option{-include} the precompiled header. If the header files
18345 have guards against multiple inclusion, they will be skipped because
18346 they've already been included (in the precompiled header).
18348 If you need to precompile the same header file for different
18349 languages, targets, or compiler options, you can instead make a
18350 @emph{directory} named like @file{all.h.gch}, and put each precompiled
18351 header in the directory, perhaps using @option{-o}. It doesn't matter
18352 what you call the files in the directory, every precompiled header in
18353 the directory will be considered. The first precompiled header
18354 encountered in the directory that is valid for this compilation will
18355 be used; they're searched in no particular order.
18357 There are many other possibilities, limited only by your imagination,
18358 good sense, and the constraints of your build system.
18360 A precompiled header file can be used only when these conditions apply:
18364 Only one precompiled header can be used in a particular compilation.
18367 A precompiled header can't be used once the first C token is seen. You
18368 can have preprocessor directives before a precompiled header; you can
18369 even include a precompiled header from inside another header, so long as
18370 there are no C tokens before the @code{#include}.
18373 The precompiled header file must be produced for the same language as
18374 the current compilation. You can't use a C precompiled header for a C++
18378 The precompiled header file must have been produced by the same compiler
18379 binary as the current compilation is using.
18382 Any macros defined before the precompiled header is included must
18383 either be defined in the same way as when the precompiled header was
18384 generated, or must not affect the precompiled header, which usually
18385 means that they don't appear in the precompiled header at all.
18387 The @option{-D} option is one way to define a macro before a
18388 precompiled header is included; using a @code{#define} can also do it.
18389 There are also some options that define macros implicitly, like
18390 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
18393 @item If debugging information is output when using the precompiled
18394 header, using @option{-g} or similar, the same kind of debugging information
18395 must have been output when building the precompiled header. However,
18396 a precompiled header built using @option{-g} can be used in a compilation
18397 when no debugging information is being output.
18399 @item The same @option{-m} options must generally be used when building
18400 and using the precompiled header. @xref{Submodel Options},
18401 for any cases where this rule is relaxed.
18403 @item Each of the following options must be the same when building and using
18404 the precompiled header:
18406 @gccoptlist{-fexceptions}
18409 Some other command-line options starting with @option{-f},
18410 @option{-p}, or @option{-O} must be defined in the same way as when
18411 the precompiled header was generated. At present, it's not clear
18412 which options are safe to change and which are not; the safest choice
18413 is to use exactly the same options when generating and using the
18414 precompiled header. The following are known to be safe:
18416 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
18417 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
18418 -fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol
18423 For all of these except the last, the compiler will automatically
18424 ignore the precompiled header if the conditions aren't met. If you
18425 find an option combination that doesn't work and doesn't cause the
18426 precompiled header to be ignored, please consider filing a bug report,
18429 If you do use differing options when generating and using the
18430 precompiled header, the actual behavior will be a mixture of the
18431 behavior for the options. For instance, if you use @option{-g} to
18432 generate the precompiled header but not when using it, you may or may
18433 not get debugging information for routines in the precompiled header.