@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
-@c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+@c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
@c Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@c man begin COPYRIGHT
Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
-1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
@table @emph
@item Overall Options
@xref{Overall Options,,Options Controlling the Kind of Output}.
-@gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
+@gccoptlist{-c -S -E -o @var{file} -combine -no-canonical-prefixes @gol
+-pipe -pass-exit-codes @gol
-x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
--version -wrapper@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg}}
-fno-nonansi-builtins -fno-operator-names @gol
-fno-optional-diags -fpermissive @gol
-fno-pretty-templates @gol
--frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
+-frepo -fno-rtti -fstats -ftemplate-depth=@var{n} @gol
-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
-fno-default-inline -fvisibility-inlines-hidden @gol
-fvisibility-ms-compat @gol
--Wabi -Wctor-dtor-privacy @gol
+-Wabi -Wconversion-null -Wctor-dtor-privacy @gol
-Wnon-virtual-dtor -Wreorder @gol
-Weffc++ -Wstrict-null-sentinel @gol
-Wno-non-template-friend -Wold-style-cast @gol
-Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
-Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
--Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
+-Wunknown-pragmas -Wno-pragmas @gol
-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
--Wunused-label -Wunused-parameter -Wunused-value -Wunused-variable @gol
+-Wunused-label -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable @gol
-Wvariadic-macros -Wvla @gol
-Wvolatile-register-var -Wwrite-strings}
-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
-feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
-feliminate-unused-debug-symbols -femit-class-debug-always @gol
+-fenable-icf-debug @gol
-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
-ftest-coverage -ftime-report -fvar-tracking @gol
+-fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol
-g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
--ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
+-ggdb -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
+-gvms -gxcoff -gxcoff+ @gol
-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
-fdebug-prefix-map=@var{old}=@var{new} @gol
-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
--print-multi-directory -print-multi-lib @gol
+-print-multi-directory -print-multi-lib -print-multi-os-directory @gol
-print-prog-name=@var{program} -print-search-dirs -Q @gol
-print-sysroot -print-sysroot-headers-suffix @gol
-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
-fdata-sections -fdce -fdce @gol
-fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
--fearly-inlining -fexpensive-optimizations -ffast-math @gol
+-fearly-inlining -fipa-sra -fexpensive-optimizations -ffast-math @gol
-ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
-fforward-propagate -ffunction-sections @gol
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
-fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
-finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
--finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
+-finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
-fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
-fipa-type-escape -fira-algorithm=@var{algorithm} @gol
--fira-region=@var{region} -fira-coalesce -fno-ira-share-save-slots @gol
+-fira-region=@var{region} -fira-coalesce @gol
+-fira-loop-pressure -fno-ira-share-save-slots @gol
-fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
-fivopts -fkeep-inline-functions -fkeep-static-consts @gol
--floop-block -floop-interchange -floop-strip-mine @gol
--fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
+-floop-block -floop-interchange -floop-strip-mine -fgraphite-identity @gol
+-floop-parallelize-all -flto -flto-compression-level -flto-report -fltrans @gol
+-fltrans-output-list -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
-fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
-fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
-fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
-freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
-freorder-blocks-and-partition -freorder-functions @gol
-frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
--frounding-math -fsched2-use-superblocks @gol
--fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
+-frounding-math -fsched2-use-superblocks -fsched-pressure @gol
+-fsched-spec-load -fsched-spec-load-dangerous @gol
-fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
--fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
+-fsched-group-heuristic -fsched-critical-path-heuristic @gol
+-fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
+-fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
+-fschedule-insns -fschedule-insns2 -fsection-anchors @gol
-fselective-scheduling -fselective-scheduling2 @gol
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
-fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
-funit-at-a-time -funroll-all-loops -funroll-loops @gol
-funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
-fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
--fwhole-program @gol
+-fwhole-program -fwhopr -fwpa -fuse-linker-plugin @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os}
@xref{Link Options,,Options for Linking}.
@gccoptlist{@var{object-file-name} -l@var{library} @gol
-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
--s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
+-s -static -static-libgcc -static-libstdc++ -shared @gol
+-shared-libgcc -symbolic @gol
-T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
-u @var{symbol}}
-msched-prolog -mno-sched-prolog @gol
-mlittle-endian -mbig-endian -mwords-little-endian @gol
-mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
+-mfp16-format=@var{name}
-mthumb-interwork -mno-thumb-interwork @gol
-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
-mstructure-size-boundary=@var{n} @gol
-mfix-cortex-m3-ldrd}
@emph{AVR Options}
-@gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
+@gccoptlist{-mmcu=@var{mcu} -mno-interrupts @gol
-mcall-prologues -mtiny-stack -mint8}
@emph{Blackfin Options}
-mmemory-latency=@var{time}}
@emph{DEC Alpha/VMS Options}
-@gccoptlist{-mvms-return-codes}
+@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
@emph{FR30 Options}
@gccoptlist{-msmall-model -mno-lsim}
-mincoming-stack-boundary=@var{num}
-mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip @gol
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
--maes -mpclmul @gol
--msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
+-maes -mpclmul -mfused-madd @gol
+-msse4a -m3dnow -mpopcnt -mabm -mfma4 -mxop -mlwp @gol
-mthreads -mno-align-stringops -minline-all-stringops @gol
-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
-mcmodel=@var{code-model} -mabi=@var{name} @gol
-m32 -m64 -mlarge-data-threshold=@var{num} @gol
--mfused-madd -mno-fused-madd -msse2avx}
+-msse2avx}
@emph{IA-64 Options}
@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
+@emph{IA-64/VMS Options}
+@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
+
+@emph{LM32 Options}
+@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
+-msign-extend-enabled -muser-enabled}
+
@emph{M32R/D Options}
@gccoptlist{-m32r2 -m32rx -m32r @gol
-mdebug @gol
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
+@emph{MeP Options}
+@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
+-mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
+-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
+-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
+-mtiny=@var{n}}
+
@emph{MIPS Options}
@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
-mflush-func=@var{func} -mno-flush-func @gol
-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
-mfp-exceptions -mno-fp-exceptions @gol
--mvr4130-align -mno-vr4130-align}
+-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
+-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address}
@emph{MMIX Options}
@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
-maltivec -mno-altivec @gol
-mpowerpc-gpopt -mno-powerpc-gpopt @gol
-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
--mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
+-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
+-mfprnd -mno-fprnd @gol
-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
-mnew-mnemonics -mold-mnemonics @gol
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
-mstrict-align -mno-strict-align -mrelocatable @gol
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
--mdynamic-no-pic -maltivec -mswdiv @gol
+-mdynamic-no-pic -maltivec -mswdiv @gol
-mprioritize-restricted-insns=@var{priority} @gol
-msched-costly-dep=@var{dependence_type} @gol
-minsert-sched-nops=@var{scheme} @gol
-msim -mmvme -mads -myellowknife -memb -msdata @gol
-msdata=@var{opt} -mvxworks -G @var{num} -pthread}
+@emph{RX Options}
+@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
+-mcpu= -patch=@gol
+-mbig-endian-data -mlittle-endian-data @gol
+-msmall-data @gol
+-msim -mno-sim@gol
+-mas100-syntax -mno-as100-syntax@gol
+-mrelax@gol
+-mmax-constant-size=@gol
+-mint-register=@gol
+-msave-acc-in-interrupts}
+
@emph{S/390 and zSeries Options}
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
-mscore5 -mscore5u -mscore7 -mscore7d}
@emph{SH Options}
-@gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
+@gccoptlist{-m1 -m2 -m2e @gol
+-m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
+-m3 -m3e @gol
-m4-nofpu -m4-single-only -m4-single -m4 @gol
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
-m5-64media -m5-64media-nofpu @gol
-m5-32media -m5-32media-nofpu @gol
-m5-compact -m5-compact-nofpu @gol
-mb -ml -mdalign -mrelax @gol
--mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
+-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
-mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
-mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
-msafe-dma -munsafe-dma @gol
-mbranch-hints @gol
-msmall-mem -mlarge-mem -mstdmain @gol
--mfixed-range=@var{register-range}}
+-mfixed-range=@var{register-range} @gol
+-mea32 -mea64 @gol
+-maddress-space-conversion -mno-address-space-conversion @gol
+-mcache-size=@var{cache-size} @gol
+-matomic-updates -mno-atomic-updates}
@emph{System V Options}
@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
@emph{i386 and x86-64 Windows Options}
@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll
--mnop-fun-dllimport -mthread -municode -mwin32 -mwindows}
+-mnop-fun-dllimport -mthread -municode -mwin32 -mwindows
+-fno-set-stack-executable}
@emph{Xstormy16 Options}
@gccoptlist{-msim}
option.
@item @var{language}
-This will display the options supported for @var{language}, where
-@var{language} is the name of one of the languages supported in this
+This will display the options supported for @var{language}, where
+@var{language} is the name of one of the languages supported in this
version of GCC.
@item @samp{common}
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
@end smallexample
+@item -no-canonical-prefixes
+@opindex no-canonical-prefixes
+Do not expand any symbolic links, resolve references to @samp{/../}
+or @samp{/./}, or make the path absolute when generating a relative
+prefix.
+
@item --version
@opindex version
Display the version number and copyrights of the invoked GCC@.
@opindex std
Determine the language standard. @xref{Standards,,Language Standards
Supported by GCC}, for details of these standard versions. This option
-is currently only supported when compiling C or C++.
+is currently only supported when compiling C or C++.
The compiler can accept several base standards, such as @samp{c89} or
@samp{c++98}, and GNU dialects of those standards, such as
The default is version 2.
+Version 3 corrects an error in mangling a constant address as a
+template argument.
+
+Version 4 implements a standard mangling for vector types.
+
+See also @option{-Wabi}.
+
@item -fno-access-control
@opindex fno-access-control
Turn off all access checking. This switch is mainly useful for working
This option is no longer useful on most targets, now that support has
been added for putting variables into BSS without making them common.
+@item -fno-deduce-init-list
+@opindex fno-deduce-init-list
+Disable deduction of a template type parameter as
+std::initializer_list from a brace-enclosed initializer list, i.e.
+
+@smallexample
+template <class T> auto forward(T t) -> decltype (realfn (t))
+@{
+ return realfn (t);
+@}
+
+void f()
+@{
+ forward(@{1,2@}); // call forward<std::initializer_list<int>>
+@}
+@end smallexample
+
+This option is present because this deduction is an extension to the
+current specification in the C++0x working draft, and there was
+some concern about potential overload resolution problems.
+
@item -ffriend-injection
@opindex ffriend-injection
Inject friend functions into the enclosing namespace, so that they are
Emit statistics about front-end processing at the end of the compilation.
This information is generally only useful to the G++ development team.
-@item -ftemplate-depth-@var{n}
+@item -ftemplate-depth=@var{n}
@opindex ftemplate-depth
Set the maximum instantiation depth for template classes to @var{n}.
A limit on the template instantiation depth is needed to detect
endless recursions during template class instantiation. ANSI/ISO C++
-conforming programs must not rely on a maximum depth greater than 17.
+conforming programs must not rely on a maximum depth greater than 17
+(changed to 1024 in C++0x).
@item -fno-threadsafe-statics
@opindex fno-threadsafe-statics
concerned about the fact that code generated by G++ may not be binary
compatible with code generated by other compilers.
-The known incompatibilities at this point include:
+The known incompatibilities in @option{-fabi-version=2} (the default) include:
+
+@itemize @bullet
+
+@item
+A template with a non-type template parameter of reference type is
+mangled incorrectly:
+@smallexample
+extern int N;
+template <int &> struct S @{@};
+void n (S<N>) @{2@}
+@end smallexample
+
+This is fixed in @option{-fabi-version=3}.
+
+@item
+SIMD vector types declared using @code{__attribute ((vector_size))} are
+mangled in a non-standard way that does not allow for overloading of
+functions taking vectors of different sizes.
+
+The mangling is changed in @option{-fabi-version=4}.
+@end itemize
+
+The known incompatibilities in @option{-fabi-version=1} include:
@itemize @bullet
A pointer is compared against integer zero with @samp{<}, @samp{<=},
@samp{>}, or @samp{>=}.
-@item
+@item
(C++ only) An enumerator and a non-enumerator both appear in a
conditional expression.
-@item
+@item
(C++ only) Ambiguous virtual bases.
-@item
+@item
(C++ only) Subscripting an array which has been declared @samp{register}.
-@item
+@item
(C++ only) Taking the address of a variable which has been declared
@samp{register}.
-@item
+@item
(C++ only) A base class is not initialized in a derived class' copy
constructor.
@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
can be disabled with the @option{-Wno-nonnull} option.
-@item -Wjump-misses-init @r{(C, Objective-C only)}
-@opindex Wjump-misses-init
-@opindex Wno-jump-misses-init
-Warn if a @code{goto} statement or a @code{switch} statement jumps
-forward across the initialization of a variable, or jumps backward to a
-label after the variable has been initialized. This only warns about
-variables which are initialized when they are declared. This warning is
-only supported for C and Objective C; in C++ this sort of branch is an
-error in any case.
-
-@option{-Wjump-misses-init} is included in @option{-Wall} and
-@option{-Wc++-compat}. It can be disabled with the
-@option{-Wno-jump-misses-init} option.
-
@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
@opindex Winit-self
@opindex Wno-init-self
To suppress this warning use the @samp{unused} attribute
(@pxref{Variable Attributes}).
+@item -Wno-unused-result
+@opindex Wunused-result
+@opindex Wno-unused-result
+Do not warn if a caller of a function marked with attribute
+@code{warn_unused_result} (@pxref{Variable Attributes}) does not use
+its return value. The default is @option{-Wunused-result}.
+
@item -Wunused-variable
@opindex Wunused-variable
@opindex Wno-unused-variable
Level 1: Most aggressive, quick, least accurate.
Possibly useful when higher levels
-do not warn but -fstrict-aliasing still breaks the code, as it has very few
+do not warn but -fstrict-aliasing still breaks the code, as it has very few
false negatives. However, it has many false positives.
-Warns for all pointer conversions between possibly incompatible types,
+Warns for all pointer conversions between possibly incompatible types,
even if never dereferenced. Runs in the frontend only.
Level 2: Aggressive, quick, not too precise.
Unlike level 1, it only warns when an address is taken. Warns about
incomplete types. Runs in the frontend only.
-Level 3 (default for @option{-Wstrict-aliasing}):
-Should have very few false positives and few false
+Level 3 (default for @option{-Wstrict-aliasing}):
+Should have very few false positives and few false
negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
Takes care of the common punn+dereference pattern in the frontend:
@code{*(int*)&some_float}.
-If optimization is enabled, it also runs in the backend, where it deals
+If optimization is enabled, it also runs in the backend, where it deals
with multiple statement cases using flow-sensitive points-to information.
Only warns when the converted pointer is dereferenced.
Does not warn about incomplete types.
conversions between signed and unsigned integers can be disabled by
using @option{-Wno-sign-conversion}.
-For C++, also warn for conversions between @code{NULL} and non-pointer
-types; confusing overload resolution for user-defined conversions; and
-conversions that will never use a type conversion operator:
-conversions to @code{void}, the same type, a base class or a reference
-to them. Warnings about conversions between signed and unsigned
-integers are disabled by default in C++ unless
+For C++, also warn for confusing overload resolution for user-defined
+conversions; and conversions that will never use a type conversion
+operator: conversions to @code{void}, the same type, a base class or a
+reference to them. Warnings about conversions between signed and
+unsigned integers are disabled by default in C++ unless
@option{-Wsign-conversion} is explicitly enabled.
+@item -Wno-conversion-null @r{(C++)}
+@opindex Wconversion-null
+@opindex Wno-conversion-null
+Do not warn for conversions between @code{NULL} and non-pointer
+types. @option{-Wconversion-null} is enabled by default.
+
@item -Wempty-body
@opindex Wempty-body
@opindex Wno-empty-body
this warning is enabled by default. In C this warning is enabled by
@option{-Wall}.
+@item -Wjump-misses-init @r{(C, Objective-C only)}
+@opindex Wjump-misses-init
+@opindex Wno-jump-misses-init
+Warn if a @code{goto} statement or a @code{switch} statement jumps
+forward across the initialization of a variable, or jumps backward to a
+label after the variable has been initialized. This only warns about
+variables which are initialized when they are declared. This warning is
+only supported for C and Objective C; in C++ this sort of branch is an
+error in any case.
+
+@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
+can be disabled with the @option{-Wno-jump-misses-init} option.
+
@item -Wsign-compare
@opindex Wsign-compare
@opindex Wno-sign-compare
@opindex Wno-nested-externs
Warn if an @code{extern} declaration is encountered within a function.
-@item -Wunreachable-code
-@opindex Wunreachable-code
-@opindex Wno-unreachable-code
-Warn if the compiler detects that code will never be executed.
-
-This option is intended to warn when the compiler detects that at
-least a whole line of source code will never be executed, because
-some condition is never satisfied or because it is after a
-procedure that never returns.
-
-It is possible for this option to produce a warning even though there
-are circumstances under which part of the affected line can be executed,
-so care should be taken when removing apparently-unreachable code.
-
-For instance, when a function is inlined, a warning may mean that the
-line is unreachable in only one inlined copy of the function.
-
-This option is not made part of @option{-Wall} because in a debugging
-version of a program there is often substantial code which checks
-correct functioning of the program and is, hopefully, unreachable
-because the program does work. Another common use of unreachable
-code is to provide behavior which is selectable at compile-time.
-
@item -Winline
@opindex Winline
@opindex Wno-inline
This option is implied by @option{-pedantic}, and can be disabled with
@option{-Wno-overlength-strings}.
-@item -Wunsuffixed-float-constants
+@item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
@opindex Wunsuffixed-float-constants
GCC will issue a warning for any floating constant that does not have
@opindex gdwarf-@var{version}
Produce debugging information in DWARF format (if that is
supported). This is the format used by DBX on IRIX 6. The value
-of @var{version} may be either 2 or 3; the default version is 2.
+of @var{version} may be either 2, 3 or 4; the default version is 2.
Note that with DWARF version 2 some ports require, and will always
use, some non-conflicting DWARF 3 extensions in the unwind tables.
+Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
+for maximum benefit.
+
+@item -gstrict-dwarf
+@opindex gstrict-dwarf
+Disallow using extensions of later DWARF standard version than selected
+with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
+DWARF extensions from later standard versions is allowed.
+
+@item -gno-strict-dwarf
+@opindex gno-strict-dwarf
+Allow using extensions of later DWARF standard version than selected with
+@option{-gdwarf-@var{version}}.
+
@item -gvms
@opindex gvms
Produce debugging information in VMS debug format (if that is
many times it is given. This is mainly intended to be used with
@option{-fcompare-debug}.
-@item -fdump-final-insns=@var{file}
-@opindex fdump-final-insns=
-Dump the final internal representation (RTL) to @var{file}.
+@item -fdump-final-insns@r{[}=@var{file}@r{]}
+@opindex fdump-final-insns
+Dump the final internal representation (RTL) to @var{file}. If the
+optional argument is omitted (or if @var{file} is @code{.}), the name
+of the dump file will be determined by appending @code{.gkd} to the
+compilation output file name.
@item -fcompare-debug@r{[}=@var{opts}@r{]}
@opindex fcompare-debug
This option works only with DWARF 2.
+@item -fenable-icf-debug
+@opindex fenable-icf-debug
+Generate additional debug information to support identical code folding (ICF).
+This option only works with DWARF version 2 or higher.
+
@item -fno-merge-debug-strings
@opindex fmerge-debug-strings
@opindex fno-merge-debug-strings
@item -fdbg-cnt=@var{counter-value-list}
@opindex fdbg-cnt
-Set the internal debug counter upperbound. @var{counter-value-list}
+Set the internal debug counter upperbound. @var{counter-value-list}
is a comma-separated list of @var{name}:@var{value} pairs
which sets the upperbound of each debug counter @var{name} to @var{value}.
All debug counters have the initial upperbound of @var{UINT_MAX},
@opindex fdump-rtl-ce3
@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
@option{-fdump-rtl-ce3} enable dumping after the three
-if conversion passes.
+if conversion passes.
@itemx -fdump-rtl-cprop_hardreg
@opindex fdump-rtl-cprop_hardreg
@item -fdump-rtl-seqabstr
@opindex fdump-rtl-seqabstr
-Dump after common sequence discovery.
+Dump after common sequence discovery.
@item -fdump-rtl-shorten
@opindex fdump-rtl-shorten
Print the address of each node. Usually this is not meaningful as it
changes according to the environment and source file. Its primary use
is for tying up a dump file with a debug environment.
+@item asmname
+If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
+in the dump instead of @code{DECL_NAME}. Its primary use is ease of
+use working backward from mangled names in the assembly file.
@item slim
Inhibit dumping of members of a scope or body of a function merely
because that scope has been reached. Only dump such items when they
Enable showing the unique ID (@code{DECL_UID}) for each variable.
@item verbose
Enable showing the tree dump for each statement.
+@item eh
+Enable showing the EH region number holding each statement.
@item all
Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
and @option{lineno}.
Dump each function after applying vectorization of loops. The file name is
made by appending @file{.vect} to the source file name.
+@item slp
+@opindex fdump-tree-slp
+Dump each function after applying vectorization of basic blocks. The file name
+is made by appending @file{.slp} to the source file name.
+
@item vrp
@opindex fdump-tree-vrp
Dump each function after Value Range Propagation (VRP). The file name
level that @option{-fdump-tree-vect-stats} uses.
Higher verbosity levels mean either more information dumped for each
reported loop, or same amount of information reported for more loops:
-If @var{n}=3, alignment related information is added to the reports.
-If @var{n}=4, data-references related information (e.g.@: memory dependences,
+if @var{n}=3, vectorizer cost model information is reported.
+If @var{n}=4, alignment related information is added to the reports.
+If @var{n}=5, data-references related information (e.g.@: memory dependences,
memory access-patterns) is added to the reports.
-If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
+If @var{n}=6, the vectorizer reports also non-vectorized inner-most loops
that did not pass the first analysis phase (i.e., may not be countable, or
may have complicated control-flow).
-If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
-For @var{n}=7, all the information the vectorizer generates during its
+If @var{n}=7, the vectorizer reports also non-vectorized nested loops.
+If @var{n}=8, SLP related information is added to the reports.
+For @var{n}=9, all the information the vectorizer generates during its
analysis and transformation is reported. This is the same verbosity level
that @option{-fdump-tree-vect-details} uses.
amount of debugging output the scheduler prints. This information is
written to standard error, unless @option{-fdump-rtl-sched1} or
@option{-fdump-rtl-sched2} is specified, in which case it is output
-to the usual dump listing file, @file{.sched} or @file{.sched2}
+to the usual dump listing file, @file{.sched1} or @file{.sched2}
respectively. However for @var{n} greater than nine, the output is
always printed to standard error.
@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
the debug info format supports it.
+@item -fvar-tracking-assignments
+@opindex fvar-tracking-assignments
+@opindex fno-var-tracking-assignments
+Annotate assignments to user variables early in the compilation and
+attempt to carry the annotations over throughout the compilation all the
+way to the end, in an attempt to improve debug information while
+optimizing. Use of @option{-gdwarf-4} is recommended along with it.
+
+It can be enabled even if var-tracking is disabled, in which case
+annotations will be created and maintained, but discarded at the end.
+
+@item -fvar-tracking-assignments-toggle
+@opindex fvar-tracking-assignments-toggle
+@opindex fno-var-tracking-assignments-toggle
+Toggle @option{-fvar-tracking-assignments}, in the same way that
+@option{-gtoggle} toggles @option{-g}.
+
@item -print-file-name=@var{library}
@opindex print-file-name
Print the full absolute name of the library file @var{library} that
@samp{-}, without spaces between multiple switches. This is supposed to
ease shell-processing.
+@item -print-multi-os-directory
+@opindex print-multi-os-directory
+Print the path to OS libraries for the selected
+multilib, relative to some @file{lib} subdirectory. If OS libraries are
+present in the @file{lib} subdirectory and no multilibs are used, this is
+usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
+sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
+@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
+subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
+
@item -print-prog-name=@var{program}
@opindex print-prog-name
Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
Not all optimizations are controlled directly by a flag. Only
optimizations that have a flag are listed in this section.
-Depending on the target and how GCC was configured, a slightly different
-set of optimizations may be enabled at each @option{-O} level than
-those listed here. You can invoke GCC with @samp{-Q --help=optimizers}
+Most optimizations are only enabled if an @option{-O} level is set on
+the command line. Otherwise they are disabled, even if individual
+optimization flags are specified.
+
+Depending on the target and how GCC was configured, a slightly different
+set of optimizations may be enabled at each @option{-O} level than
+those listed here. You can invoke GCC with @samp{-Q --help=optimizers}
to find out the exact set of optimizations that are enabled at each level.
@xref{Overall Options}, for examples.
-fguess-branch-probability @gol
-fif-conversion2 @gol
-fif-conversion @gol
--finline-small-functions @gol
-fipa-pure-const @gol
-fipa-reference @gol
-fmerge-constants
-fdelete-null-pointer-checks @gol
-fexpensive-optimizations @gol
-fgcse -fgcse-lm @gol
+-finline-small-functions @gol
-findirect-inlining @gol
+-fipa-sra @gol
-foptimize-sibling-calls @gol
-fpeephole2 @gol
-fregmove @gol
Enabled by default.
+@item -fipa-sra
+@opindex fipa-sra
+Perform interprocedural scalar replacement of aggregates, removal of
+unused parameters and replacement of parameters passed by reference
+by parameters passed by value.
+
+Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
+
@item -finline-limit=@var{n}
@opindex finline-limit
By default, GCC limits the size of functions that can be inlined. This flag
Do optimistic register coalescing. This option might be profitable for
architectures with big regular register files.
+@item -fira-loop-pressure
+@opindex fira-loop-pressure
+Use IRA to evaluate register pressure in loops for decision to move
+loop invariants. Usage of this option usually results in generation
+of faster and smaller code on machines with big register files (>= 32
+registers) but it can slow compiler down.
+
+This option is enabled at level @option{-O3} for some targets.
+
@item -fno-ira-share-save-slots
@opindex fno-ira-share-save-slots
Switch off sharing stack slots used for saving call used hard
by allowing other instructions to be issued until the result of the load
or floating point instruction is required.
-Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
+Enabled at levels @option{-O2}, @option{-O3}.
@item -fschedule-insns2
@opindex fschedule-insns2
enabled by default when scheduling before register allocation, i.e.@:
with @option{-fschedule-insns} or at @option{-O2} or higher.
+@item -fsched-pressure
+@opindex fsched-pressure
+Enable register pressure sensitive insn scheduling before the register
+allocation. This only makes sense when scheduling before register
+allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
+@option{-O2} or higher. Usage of this option can improve the
+generated code and decrease its size by preventing register pressure
+increase above the number of available hard registers and as a
+consequence register spills in the register allocation.
+
@item -fsched-spec-load
@opindex fsched-spec-load
Allow speculative motion of some load instructions. This only makes
This only makes sense when scheduling after register allocation, i.e.@: with
@option{-fschedule-insns2} or at @option{-O2} or higher.
-@item -fsched2-use-traces
-@opindex fsched2-use-traces
-Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
-allocation and additionally perform code duplication in order to increase the
-size of superblocks using tracer pass. See @option{-ftracer} for details on
-trace formation.
-
-This mode should produce faster but significantly longer programs. Also
-without @option{-fbranch-probabilities} the traces constructed may not
-match the reality and hurt the performance. This only makes
-sense when scheduling after register allocation, i.e.@: with
-@option{-fschedule-insns2} or at @option{-O2} or higher.
-
-@item -fsee
-@opindex fsee
-Eliminate redundant sign extension instructions and move the non-redundant
-ones to optimal placement using lazy code motion (LCM).
+@item -fsched-group-heuristic
+@opindex fsched-group-heuristic
+Enable the group heuristic in the scheduler. This heuristic favors
+the instruction that belongs to a schedule group. This is enabled
+by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
+or @option{-fschedule-insns2} or at @option{-O2} or higher.
+
+@item -fsched-critical-path-heuristic
+@opindex fsched-critical-path-heuristic
+Enable the critical-path heuristic in the scheduler. This heuristic favors
+instructions on the critical path. This is enabled by default when
+scheduling is enabled, i.e.@: with @option{-fschedule-insns}
+or @option{-fschedule-insns2} or at @option{-O2} or higher.
+
+@item -fsched-spec-insn-heuristic
+@opindex fsched-spec-insn-heuristic
+Enable the speculative instruction heuristic in the scheduler. This
+heuristic favors speculative instructions with greater dependency weakness.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2}
+or at @option{-O2} or higher.
+
+@item -fsched-rank-heuristic
+@opindex fsched-rank-heuristic
+Enable the rank heuristic in the scheduler. This heuristic favors
+the instruction belonging to a basic block with greater size or frequency.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
+
+@item -fsched-last-insn-heuristic
+@opindex fsched-last-insn-heuristic
+Enable the last-instruction heuristic in the scheduler. This heuristic
+favors the instruction that is less dependent on the last instruction
+scheduled. This is enabled by default when scheduling is enabled,
+i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
+
+@item -fsched-dep-count-heuristic
+@opindex fsched-dep-count-heuristic
+Enable the dependent-count heuristic in the scheduler. This heuristic
+favors the instruction that has more instructions depending on it.
+This is enabled by default when scheduling is enabled, i.e.@:
+with @option{-fschedule-insns} or @option{-fschedule-insns2} or
+at @option{-O2} or higher.
@item -freschedule-modulo-scheduled-loops
@opindex freschedule-modulo-scheduled-loops
@item -fsel-sched-pipelining
@opindex fsel-sched-pipelining
-Enable software pipelining of innermost loops during selective scheduling.
-This option has no effect until one of @option{-fselective-scheduling} or
+Enable software pipelining of innermost loops during selective scheduling.
+This option has no effect until one of @option{-fselective-scheduling} or
@option{-fselective-scheduling2} is turned on.
@item -fsel-sched-pipelining-outer-loops
@item -fipa-struct-reorg
@opindex fipa-struct-reorg
-Perform structure reorganization optimization, that change C-like structures
-layout in order to better utilize spatial locality. This transformation is
-affective for programs containing arrays of structures. Available in two
+Perform structure reorganization optimization, that change C-like structures
+layout in order to better utilize spatial locality. This transformation is
+affective for programs containing arrays of structures. Available in two
compilation modes: profile-based (enabled with @option{-fprofile-generate})
or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
to provide the safety of this transformation. It works only in whole program
@opindex fipa-cp
Perform interprocedural constant propagation.
This optimization analyzes the program to determine when values passed
-to functions are constants and then optimizes accordingly.
+to functions are constants and then optimizes accordingly.
This optimization can substantially increase performance
if the application has constants passed to functions.
This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
of the matrix. The second optimization is matrix transposing that
attempts to change the order of the matrix's dimensions in order to
improve cache locality.
-Both optimizations need the @option{-fwhole-program} flag.
+Both optimizations need the @option{-fwhole-program} flag.
Transposing is enabled only if profiling information is available.
-
@item -ftree-sink
@opindex ftree-sink
Perform forward store motion on trees. This flag is
@item -ftree-builtin-call-dce
@opindex ftree-builtin-call-dce
-Perform conditional dead code elimination (DCE) for calls to builtin functions
-that may set @code{errno} but are otherwise side-effect free. This flag is
-enabled by default at @option{-O2} and higher if @option{-Os} is not also
+Perform conditional dead code elimination (DCE) for calls to builtin functions
+that may set @code{errno} but are otherwise side-effect free. This flag is
+enabled by default at @option{-O2} and higher if @option{-Os} is not also
specified.
@item -ftree-dominator-opts
@item -floop-strip-mine
Perform loop strip mining transformations on loops. Strip mining
-splits a loop into two nested loops. The outer loop has strides
-equal to the strip size and the inner loop has strides of the
+splits a loop into two nested loops. The outer loop has strides
+equal to the strip size and the inner loop has strides of the
original loop within a strip. For example, given a loop like:
@smallexample
DO I = 1, N
and @option{--with-cloog} to enable the Graphite loop transformation
infrastructure.
+@item -fgraphite-identity
+@opindex fgraphite-identity
+Enable the identity transformation for graphite. For every SCoP we generate
+the polyhedral representation and transform it back to gimple. Using
+@option{-fgraphite-identity} we can check the costs or benefits of the
+GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
+are also performed by the code generator CLooG, like index splitting and
+dead code elimination in loops.
+
+@item -floop-parallelize-all
+Use the Graphite data dependence analysis to identify loops that can
+be parallelized. Parallelize all the loops that can be analyzed to
+not contain loop carried dependences without checking that it is
+profitable to parallelize the loops.
+
@item -fcheck-data-deps
@opindex fcheck-data-deps
Compare the results of several data dependence analyzers. This option
Perform loop vectorization on trees. This flag is enabled by default at
@option{-O3}.
+@item -ftree-slp-vectorize
+@opindex ftree-slp-vectorize
+Perform basic block vectorization on trees. This flag is enabled by default at
+@option{-O3} and when @option{-ftree-vectorize} is enabled.
+
@item -ftree-vect-loop-version
@opindex ftree-vect-loop-version
Perform loop versioning when doing loop vectorization on trees. When a loop
@item -fstrict-aliasing
@opindex fstrict-aliasing
-Allows the compiler to assume the strictest aliasing rules applicable to
+Allow the compiler to assume the strictest aliasing rules applicable to
the language being compiled. For C (and C++), this activates
optimizations based on the type of expressions. In particular, an
object of one type is assumed never to reside at the same address as an
@};
int f() @{
- a_union t;
+ union a_union t;
t.d = 3.0;
return t.i;
@}
implementation}. However, this code might not:
@smallexample
int f() @{
- a_union t;
+ union a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
and in effect are optimized more aggressively by interprocedural optimizers.
While this option is equivalent to proper use of the @code{static} keyword for
programs consisting of a single file, in combination with option
-@option{--combine} this flag can be used to compile many smaller scale C
-programs since the functions and variables become local for the whole combined
-compilation unit, not for the single source file itself.
+@option{-combine}, @option{-flto} or @option{-fwhopr} this flag can be used to
+compile many smaller scale programs since the functions and variables become
+local for the whole combined compilation unit, not for the single source file
+itself.
This option implies @option{-fwhole-file} for Fortran programs.
+@item -flto
+@opindex flto
+This option runs the standard link-time optimizer. When invoked
+with source code, it generates GIMPLE (one of GCC's internal
+representations) and writes it to special ELF sections in the object
+file. When the object files are linked together, all the function
+bodies are read from these ELF sections and instantiated as if they
+had been part of the same translation unit.
+
+To use the link-timer optimizer, @option{-flto} needs to be specified at
+compile time and during the final link. For example,
+
+@smallexample
+gcc -c -O2 -flto foo.c
+gcc -c -O2 -flto bar.c
+gcc -o myprog -flto -O2 foo.o bar.o
+@end smallexample
+
+The first two invocations to GCC will save a bytecode representation
+of GIMPLE into special ELF sections inside @file{foo.o} and
+@file{bar.o}. The final invocation will read the GIMPLE bytecode from
+@file{foo.o} and @file{bar.o}, merge the two files into a single
+internal image, and compile the result as usual. Since both
+@file{foo.o} and @file{bar.o} are merged into a single image, this
+causes all the inter-procedural analyses and optimizations in GCC to
+work across the two files as if they were a single one. This means,
+for example, that the inliner will be able to inline functions in
+@file{bar.o} into functions in @file{foo.o} and vice-versa.
+
+Another (simpler) way to enable link-time optimization is,
+
+@smallexample
+gcc -o myprog -flto -O2 foo.c bar.c
+@end smallexample
+
+The above will generate bytecode for @file{foo.c} and @file{bar.c},
+merge them together into a single GIMPLE representation and optimize
+them as usual to produce @file{myprog}.
+
+The only important thing to keep in mind is that to enable link-time
+optimizations the @option{-flto} flag needs to be passed to both the
+compile and the link commands.
+
+Note that when a file is compiled with @option{-flto}, the generated
+object file will be larger than a regular object file because it will
+contain GIMPLE bytecodes and the usual final code. This means that
+object files with LTO information can be linked as a normal object
+file. So, in the previous example, if the final link is done with
+
+@smallexample
+gcc -o myprog foo.o bar.o
+@end smallexample
+
+The only difference will be that no inter-procedural optimizations
+will be applied to produce @file{myprog}. The two object files
+@file{foo.o} and @file{bar.o} will be simply sent to the regular
+linker.
+
+Additionally, the optimization flags used to compile individual files
+are not necessarily related to those used at link-time. For instance,
+
+@smallexample
+gcc -c -O0 -flto foo.c
+gcc -c -O0 -flto bar.c
+gcc -o myprog -flto -O3 foo.o bar.o
+@end smallexample
+
+This will produce individual object files with unoptimized assembler
+code, but the resulting binary @file{myprog} will be optimized at
+@option{-O3}. Now, if the final binary is generated without
+@option{-flto}, then @file{myprog} will not be optimized.
+
+When producing the final binary with @option{-flto}, GCC will only
+apply link-time optimizations to those files that contain bytecode.
+Therefore, you can mix and match object files and libraries with
+GIMPLE bytecodes and final object code. GCC will automatically select
+which files to optimize in LTO mode and which files to link without
+further processing.
+
+There are some code generation flags that GCC will preserve when
+generating bytecodes, as they need to be used during the final link
+stage. Currently, the following options are saved into the GIMPLE
+bytecode files: @option{-fPIC}, @option{-fcommon} and all the
+@option{-m} target flags.
+
+At link time, these options are read-in and reapplied. Note that the
+current implementation makes no attempt at recognizing conflicting
+values for these options. If two or more files have a conflicting
+value (e.g., one file is compiled with @option{-fPIC} and another
+isn't), the compiler will simply use the last value read from the
+bytecode files. It is recommended, then, that all the files
+participating in the same link be compiled with the same options.
+
+Another feature of LTO is that it is possible to apply interprocedural
+optimizations on files written in different languages. This requires
+some support in the language front end. Currently, the C, C++ and
+Fortran front ends are capable of emitting GIMPLE bytecodes, so
+something like this should work
+
+@smallexample
+gcc -c -flto foo.c
+g++ -c -flto bar.cc
+gfortran -c -flto baz.f90
+g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
+@end smallexample
+
+Notice that the final link is done with @command{g++} to get the C++
+runtime libraries and @option{-lgfortran} is added to get the Fortran
+runtime libraries. In general, when mixing languages in LTO mode, you
+should use the same link command used when mixing languages in a
+regular (non-LTO) compilation. This means that if your build process
+was mixing languages before, all you need to add is @option{-flto} to
+all the compile and link commands.
+
+If object files containing GIMPLE bytecode are stored in a library
+archive, say @file{libfoo.a}, it is possible to extract and use them
+in an LTO link if you are using @command{gold} as the linker (which,
+in turn requires GCC to be configured with @option{--enable-gold}).
+To enable this feature, use the flag @option{-fuse-linker-plugin} at
+link-time:
+
+@smallexample
+gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
+@end smallexample
+
+With the linker plugin enabled, @command{gold} will extract the needed
+GIMPLE files from @file{libfoo.a} and pass them on to the running GCC
+to make them part of the aggregated GIMPLE image to be optimized.
+
+If you are not using @command{gold} and/or do not specify
+@option{-fuse-linker-plugin} then the objects inside @file{libfoo.a}
+will be extracted and linked as usual, but they will not participate
+in the LTO optimization process.
+
+Link time optimizations do not require the presence of the whole
+program to operate. If the program does not require any symbols to
+be exported, it is possible to combine @option{-flto} and
+@option{-fwhopr} with @option{-fwhole-program} to allow the
+interprocedural optimizers to use more aggressive assumptions which
+may lead to improved optimization opportunities.
+
+Regarding portability: the current implementation of LTO makes no
+attempt at generating bytecode that can be ported between different
+types of hosts. The bytecode files are versioned and there is a
+strict version check, so bytecode files generated in one version of
+GCC will not work with an older/newer version of GCC.
+
+Link time optimization does not play well with generating debugging
+information. Combining @option{-flto} or @option{-fwhopr} with
+@option{-g} is experimental.
+
+This option is disabled by default.
+
+@item -fwhopr
+@opindex fwhopr
+This option is identical in functionality to @option{-flto} but it
+differs in how the final link stage is executed. Instead of loading
+all the function bodies in memory, the callgraph is analyzed and
+optimization decisions are made (whole program analysis or WPA). Once
+optimization decisions are made, the callgraph is partitioned and the
+different sections are compiled separately (local transformations or
+LTRANS)@. This process allows optimizations on very large programs
+that otherwise would not fit in memory. This option enables
+@option{-fwpa} and @option{-fltrans} automatically.
+
+Disabled by default.
+
+This option is experimental.
+
+@item -fwpa
+@opindex fwpa
+This is an internal option used by GCC when compiling with
+@option{-fwhopr}. You should never need to use it.
+
+This option runs the link-time optimizer in the whole-program-analysis
+(WPA) mode, which reads in summary information from all inputs and
+performs a whole-program analysis based on summary information only.
+It generates object files for subsequent runs of the link-time
+optimizer where individual object files are optimized using both
+summary information from the WPA mode and the actual function bodies.
+It then drives the LTRANS phase.
+
+Disabled by default.
+
+@item -fltrans
+@opindex fltrans
+This is an internal option used by GCC when compiling with
+@option{-fwhopr}. You should never need to use it.
+
+This option runs the link-time optimizer in the local-transformation (LTRANS)
+mode, which reads in output from a previous run of the LTO in WPA mode.
+In the LTRANS mode, LTO optimizes an object and produces the final assembly.
+
+Disabled by default.
+
+@item -fltrans-output-list=@var{file}
+@opindex fltrans-output-list
+This is an internal option used by GCC when compiling with
+@option{-fwhopr}. You should never need to use it.
+
+This option specifies a file to which the names of LTRANS output files are
+written. This option is only meaningful in conjunction with @option{-fwpa}.
+
+Disabled by default.
+
+@item -flto-compression-level=@var{n}
+This option specifies the level of compression used for intermediate
+language written to LTO object files, and is only meaningful in
+conjunction with LTO mode (@option{-fwhopr}, @option{-flto}). Valid
+values are 0 (no compression) to 9 (maximum compression). Values
+outside this range are clamped to either 0 or 9. If the option is not
+given, a default balanced compression setting is used.
+
+@item -flto-report
+Prints a report with internal details on the workings of the link-time
+optimizer. The contents of this report vary from version to version,
+it is meant to be useful to GCC developers when processing object
+files in LTO mode (via @option{-fwhopr} or @option{-flto}).
+
+Disabled by default.
+
+@item -fuse-linker-plugin
+Enables the extraction of objects with GIMPLE bytecode information
+from library archives. This option relies on features available only
+in @command{gold}, so to use this you must configure GCC with
+@option{--enable-gold}. See @option{-flto} for a description on the
+effect of this flag and how to use it.
+
+Disabled by default.
+
@item -fcprop-registers
@opindex fcprop-registers
After register allocation and post-register allocation instruction splitting,
Set the directory to search the profile data files in to @var{path}.
This option affects only the profile data generated by
@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
-and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
+and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
and its related options.
By default, GCC will use the current directory as @var{path}
thus the profile data file will appear in the same directory as the object file.
and thus may not be used when ordered comparisons are required.
This option requires that both @option{-fno-signed-zeros} and
@option{-fno-trapping-math} be in effect. Moreover, it doesn't make
-much sense with @option{-frounding-math}.
+much sense with @option{-frounding-math}. For Fortran the option
+is automatically enabled when both @option{-fno-signed-zeros} and
+@option{-fno-trapping-math} are in effect.
The default is @option{-fno-associative-math}.
make debugging impossible, since variables will no longer stay in
a ``home register''.
-Enabled by default with @option{-funroll-loops}.
+Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
@item -ftracer
@opindex ftracer
The threshold ratio (as a percentage) between a structure frequency
and the frequency of the hottest structure in the program. This parameter
is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
-We say that if the ratio of a structure frequency, calculated by profiling,
-to the hottest structure frequency in the program is less than this
+We say that if the ratio of a structure frequency, calculated by profiling,
+to the hottest structure frequency in the program is less than this
parameter, then structure reorganization is not applied to this structure.
The default is 10.
-@item predictable-branch-cost-outcome
+@item predictable-branch-outcome
When branch is predicted to be taken with probability lower than this threshold
(in percent), then it is considered well predictable. The default is 10.
by the compiler will be investigated. To those functions, a different
(more restrictive) limit compared to functions declared inline can
be applied.
-The default value is 60.
+The default value is 50.
@item large-function-insns
The limit specifying really large functions. For functions larger than this
@item early-inlining-insns
Specify growth that early inliner can make. In effect it increases amount of
-inlining for code having large abstraction penalty. The default value is 12.
+inlining for code having large abstraction penalty. The default value is 8.
@item max-early-inliner-iterations
@itemx max-early-inliner-iterations
The default value is 50.
@item selsched-max-sched-times
-The maximum number of times that an instruction will be scheduled during
-selective scheduling. This is the limit on the number of iterations
+The maximum number of times that an instruction will be scheduled during
+selective scheduling. This is the limit on the number of iterations
through which the instruction may be pipelined. The default value is 2.
@item selsched-max-insns-to-rename
The size of L2 cache, in kilobytes.
@item min-insn-to-prefetch-ratio
-The minimum ratio between the number of instructions and the
-number of prefetches to enable prefetching in a loop with an
+The minimum ratio between the number of instructions and the
+number of prefetches to enable prefetching in a loop with an
unknown trip count.
@item prefetch-min-insn-to-mem-ratio
-The minimum ratio between the number of instructions and the
+The minimum ratio between the number of instructions and the
number of memory references to enable prefetching in a loop.
@item use-canonical-types
algorithm do not use pseudo-register conflicts. The default value of
the parameter is 2000.
+@item ira-loop-reserved-regs
+IRA can be used to evaluate more accurate register pressure in loops
+for decision to move loop invariants (see @option{-O3}). The number
+of available registers reserved for some other purposes is described
+by this parameter. The default value of the parameter is 2 which is
+minimal number of registers needed for execution of typical
+instruction. This value is the best found from numerous experiments.
+
@item loop-invariant-max-bbs-in-loop
Loop invariant motion can be very expensive, both in compile time and
in amount of needed compile time memory, with very large loops. Loops
motion optimization performed on them. The default value of the
parameter is 1000 for -O1 and 10000 for -O2 and above.
+@item max-vartrack-size
+Sets a maximum number of hash table slots to use during variable
+tracking dataflow analysis of any function. If this limit is exceeded
+with variable tracking at assignments enabled, analysis for that
+function is retried without it, after removing all debug insns from
+the function. If the limit is exceeded even without debug insns, var
+tracking analysis is completely disabled for the function. Setting
+the parameter to zero makes it unlimited.
+
+@item min-nondebug-insn-uid
+Use uids starting at this parameter for nondebug insns. The range below
+the parameter is reserved exclusively for debug insns created by
+@option{-fvar-tracking-assignments}, but debug insns may get
+(non-overlapping) uids above it if the reserved range is exhausted.
+
+@item ipa-sra-ptr-growth-factor
+IPA-SRA will replace a pointer to an aggregate with one or more new
+parameters only when their cumulative size is less or equal to
+@option{ipa-sra-ptr-growth-factor} times the size of the original
+pointer parameter.
+
@end table
@end table
@item -nodefaultlibs
@opindex nodefaultlibs
Do not use the standard system libraries when linking.
-Only the libraries you specify will be passed to the linker.
+Only the libraries you specify will be passed to the linker, options
+specifying linkage of the system libraries, such as @code{-static-libgcc}
+or @code{-shared-libgcc}, will be ignored.
The standard startup files are used normally, unless @option{-nostartfiles}
is used. The compiler may generate calls to @code{memcmp},
@code{memset}, @code{memcpy} and @code{memmove}.
@opindex nostdlib
Do not use the standard system startup files or libraries when linking.
No startup files and only the libraries you specify will be passed to
-the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
+the linker, options specifying linkage of the system libraries, such as
+@code{-static-libgcc} or @code{-shared-libgcc}, will be ignored.
+The compiler may generate calls to @code{memcmp}, @code{memset},
@code{memcpy} and @code{memmove}.
These entries are usually resolved by entries in
libc. These entry points should be supplied through some other
@option{-shared-libgcc}, such that it is linked with the shared
@file{libgcc}.
+@item -static-libstdc++
+When the @command{g++} program is used to link a C++ program, it will
+normally automatically link against @option{libstdc++}. If
+@file{libstdc++} is available as a shared library, and the
+@option{-static} option is not used, then this will link against the
+shared version of @file{libstdc++}. That is normally fine. However, it
+is sometimes useful to freeze the version of @file{libstdc++} used by
+the program without going all the way to a fully static link. The
+@option{-static-libstdc++} option directs the @command{g++} driver to
+link @file{libstdc++} statically, without necessarily linking other
+libraries statically.
+
@item -symbolic
@opindex symbolic
Bind references to global symbols when building a shared object. Warn
@cindex linker script
Use @var{script} as the linker script. This option is supported by most
systems using the GNU linker. On some targets, such as bare-board
-targets without an operating system, the @option{-T} option may be required
+targets without an operating system, the @option{-T} option may be required
when linking to avoid references to undefined symbols.
@item -Xlinker @var{option}
@option{-Xlinker "-assert definitions"}, because this passes the entire
string as a single argument, which is not what the linker expects.
-When using the GNU linker, it is usually more convenient to pass
+When using the GNU linker, it is usually more convenient to pass
arguments to linker options using the @option{@var{option}=@var{value}}
syntax than as separate arguments. For example, you can specify
@samp{-Xlinker -Map=output.map} rather than
@opindex Wl
Pass @var{option} as an option to the linker. If @var{option} contains
commas, it is split into multiple options at the commas. You can use this
-syntax to pass an argument to the option.
+syntax to pass an argument to the option.
For example, @samp{-Wl,-Map,output.map} passes @samp{-Map output.map} to the
linker. When using the GNU linker, you can also get the same effect with
@samp{-Wl,-Map=output.map}.
@item %s
Current argument is the name of a library or startup file of some sort.
Search for that file in a standard list of directories and substitute
-the full name found.
+the full name found. The current working directory is included in the
+list of directories scanned.
+
+@item %T
+Current argument is the name of a linker script. Search for that file
+in the current list of directories to scan for libraries. If the file
+is located insert a @option{--script} option into the command line
+followed by the full path name found. If the file is not found then
+generate an error message. Note: the current working directory is not
+searched.
@item %e@var{str}
Print @var{str} as an error message. @var{str} is terminated by a newline.
* i386 and x86-64 Options::
* i386 and x86-64 Windows Options::
* IA-64 Options::
+* IA-64/VMS Options::
+* LM32 Options::
* M32C Options::
* M32R/D Options::
* M680x0 Options::
* M68hc1x Options::
* MCore Options::
+* MeP Options::
* MIPS Options::
* MMIX Options::
* MN10300 Options::
* picoChip Options::
* PowerPC Options::
* RS/6000 and PowerPC Options::
+* RX Options::
* S/390 and zSeries Options::
* Score Options::
* SH Options::
Specifies which floating-point ABI to use. Permissible values
are: @samp{soft}, @samp{softfp} and @samp{hard}.
-Specifying @samp{soft} causes GCC to generate output containing
+Specifying @samp{soft} causes GCC to generate output containing
library calls for floating-point operations.
-@samp{softfp} allows the generation of code using hardware floating-point
-instructions, but still uses the soft-float calling conventions.
-@samp{hard} allows generation of floating-point instructions
+@samp{softfp} allows the generation of code using hardware floating-point
+instructions, but still uses the soft-float calling conventions.
+@samp{hard} allows generation of floating-point instructions
and uses FPU-specific calling conventions.
-Using @option{-mfloat-abi=hard} with VFP coprocessors is not supported.
-Use @option{-mfloat-abi=softfp} with the appropriate @option{-mfpu} option
-to allow the compiler to generate code that makes use of the hardware
-floating-point capabilities for these CPUs.
-
The default depends on the specific target configuration. Note that
the hard-float and soft-float ABIs are not link-compatible; you must
compile your entire program with the same ABI, and link with a
@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
-@samp{cortex-a8}, @samp{cortex-a9},
+@samp{cortex-a5}, @samp{cortex-a8}, @samp{cortex-a9},
@samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
@samp{cortex-m1},
+@samp{cortex-m0},
@samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
@item -mtune=@var{name}
@opindex mfp
This specifies what floating point hardware (or hardware emulation) is
available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
-@samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
-@samp{neon}. @option{-mfp} and @option{-mfpe}
-are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
-with older versions of GCC@.
+@samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-fp16},
+@samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, @samp{vfpv3xd-fp16},
+@samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, @samp{vfpv4-d16},
+@samp{fpv4-sp-d16} and @samp{neon-vfpv4}.
+@option{-mfp} and @option{-mfpe} are synonyms for
+@option{-mfpu}=@samp{fpe}@var{number}, for compatibility with older versions
+of GCC@.
If @option{-msoft-float} is specified this specifies the format of
floating point values.
+@item -mfp16-format=@var{name}
+@opindex mfp16-format
+Specify the format of the @code{__fp16} half-precision floating-point type.
+Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
+the default is @samp{none}, in which case the @code{__fp16} type is not
+defined. @xref{Half-Precision}, for more information.
+
@item -mstructure-size-boundary=@var{n}
@opindex mstructure-size-boundary
The size of all structures and unions will be rounded up to a multiple
use the 32-bit ARM instruction set.
This option automatically enables either 16-bit Thumb-1 or
mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
-and @option{-march=@var{name}} options. This option is not passed to the
+and @option{-march=@var{name}} options. This option is not passed to the
assembler. If you want to force assembler files to be interpreted as Thumb code,
-either add a @samp{.thumb} directive to the source or pass the @option{-mthumb}
+either add a @samp{.thumb} directive to the source or pass the @option{-mthumb}
option directly to the assembler by prefixing it with @option{-Wa}.
@item -mtpcs-frame
Gives all externally visible functions in the file being compiled an ARM
instruction set header which switches to Thumb mode before executing the
rest of the function. This allows these functions to be called from
-non-interworking code.
+non-interworking code. This option is not valid in AAPCS configurations
+because interworking is enabled by default.
@item -mcaller-super-interworking
@opindex mcaller-super-interworking
Allows calls via function pointers (including virtual functions) to
execute correctly regardless of whether the target code has been
compiled for interworking or not. There is a small overhead in the cost
-of executing a function pointer if this option is enabled.
+of executing a function pointer if this option is enabled. This option
+is not valid in AAPCS configurations because interworking is enabled
+by default.
@item -mtp=@var{name}
@opindex mtp
memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
atmega64, atmega128, at43usb355, at94k).
-@item -msize
-@opindex msize
-Output instruction sizes to the asm file.
-
-@item -minit-stack=@var{N}
-@opindex minit-stack
-Specify the initial stack address, which may be a symbol or numeric value,
-@samp{__stack} is the default.
-
@item -mno-interrupts
@opindex mno-interrupts
Generated code is not compatible with hardware interrupts.
@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
+@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
@samp{bf561}.
The optional @var{sirevision} specifies the silicon revision of the target
Blackfin processor. Any workarounds available for the targeted silicon revision
and link scripts will be used to support Core B. This option
defines @code{__BFIN_COREB}. When this option is used, coreb_main
should be used instead of main. It must be used with
-@option{-mmulticore}.
+@option{-mmulticore}.
@item -msdram
@opindex msdram
@opindex mvms-return-codes
Return VMS condition codes from main. The default is to return POSIX
style condition (e.g.@: error) codes.
+
+@item -mdebug-main=@var{prefix}
+@opindex mdebug-main=@var{prefix}
+Flag the first routine whose name starts with @var{prefix} as the main
+routine for the debugger.
+
+@item -mmalloc64
+@opindex mmalloc64
+Default to 64bit memory allocation routines.
@end table
@node FR30 Options
libraries assume that extended precision (80 bit) floating-point operations
are enabled by default; routines in such libraries could suffer significant
loss of accuracy, typically through so-called "catastrophic cancellation",
-when this option is used to set the precision to less than extended precision.
+when this option is used to set the precision to less than extended precision.
@item -mstackrealign
@opindex mstackrealign
@itemx -mno-pclmul
@itemx -msse4a
@itemx -mno-sse4a
-@itemx -msse5
-@itemx -mno-sse5
+@itemx -mfma4
+@itemx -mno-fma4
+@itemx -mxop
+@itemx -mno-xop
+@itemx -mlwp
+@itemx -mno-lwp
@itemx -m3dnow
@itemx -mno-3dnow
@itemx -mpopcnt
@opindex m3dnow
@opindex mno-3dnow
These switches enable or disable the use of instructions in the MMX,
-SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, SSE5, ABM or
-3DNow!@: extended instruction sets.
+SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, FMA4, XOP,
+LWP, ABM or 3DNow!@: extended instruction sets.
These extensions are also available as built-in functions: see
@ref{X86 Built-in Functions}, for details of the functions enabled and
disabled by these switches.
the file containing the CPU detection code should be compiled without
these options.
+@item -mfused-madd
+@itemx -mno-fused-madd
+@opindex mfused-madd
+@opindex mno-fused-madd
+Do (don't) generate code that uses the fused multiply/add or multiply/subtract
+instructions. The default is to use these instructions.
+
@item -mcld
@opindex mcld
This option instructs GCC to emit a @code{cld} instruction in the prologue
of the non-reciprocal instruction, the precision of the sequence can be
decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
+Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or RSQRTPS)
+already with @option{-ffast-math} (or the above option combination), and
+doesn't need @option{-mrecip}.
+
@item -mveclibabi=@var{type}
@opindex mveclibabi
Specifies the ABI type to use for vectorizing intrinsics using an
For systems that use GNU libc, the default is on.
-@item -mfused-madd
-@itemx -mno-fused-madd
-@opindex mfused-madd
-Enable automatic generation of fused floating point multiply-add instructions
-if the ISA supports such instructions. The -mfused-madd option is on by
-default. The fused multiply-add instructions have a different
-rounding behavior compared to executing a multiply followed by an add.
-
@item -msse2avx
@itemx -mno-sse2avx
@opindex msse2avx
@opindex mfused-madd
@opindex mno-fused-madd
Do (don't) generate code that uses the fused multiply/add or multiply/subtract
-instructions. The default is to use these instructions.
+instructions. The default is to use these instructions.
@item -mno-dwarf2-asm
@itemx -mdwarf2-asm
@end table
+@node IA-64/VMS Options
+@subsection IA-64/VMS Options
+
+These @samp{-m} options are defined for the IA-64/VMS implementations:
+
+@table @gcctabopt
+@item -mvms-return-codes
+@opindex mvms-return-codes
+Return VMS condition codes from main. The default is to return POSIX
+style condition (e.g.@ error) codes.
+
+@item -mdebug-main=@var{prefix}
+@opindex mdebug-main=@var{prefix}
+Flag the first routine whose name starts with @var{prefix} as the main
+routine for the debugger.
+
+@item -mmalloc64
+@opindex mmalloc64
+Default to 64bit memory allocation routines.
+@end table
+
+@node LM32 Options
+@subsection LM32 Options
+@cindex LM32 options
+
+These @option{-m} options are defined for the Lattice Mico32 architecture:
+
+@table @gcctabopt
+@item -mbarrel-shift-enabled
+@opindex mbarrel-shift-enabled
+Enable barrel-shift instructions.
+
+@item -mdivide-enabled
+@opindex mdivide-enabled
+Enable divide and modulus instructions.
+
+@item -mmultiply-enabled
+@opindex multiply-enabled
+Enable multiply instructions.
+
+@item -msign-extend-enabled
+@opindex msign-extend-enabled
+Enable sign extend instructions.
+
+@item -muser-enabled
+@opindex muser-enabled
+Enable user-defined instructions.
+
+@end table
+
@node M32C Options
@subsection M32C Options
@cindex M32C options
@end table
+@node MeP Options
+@subsection MeP Options
+@cindex MeP options
+
+@table @gcctabopt
+
+@item -mabsdiff
+@opindex mabsdiff
+Enables the @code{abs} instruction, which is the absolute difference
+between two registers.
+
+@item -mall-opts
+@opindex mall-opts
+Enables all the optional instructions - average, multiply, divide, bit
+operations, leading zero, absolute difference, min/max, clip, and
+saturation.
+
+
+@item -maverage
+@opindex maverage
+Enables the @code{ave} instruction, which computes the average of two
+registers.
+
+@item -mbased=@var{n}
+@opindex mbased=
+Variables of size @var{n} bytes or smaller will be placed in the
+@code{.based} section by default. Based variables use the @code{$tp}
+register as a base register, and there is a 128 byte limit to the
+@code{.based} section.
+
+@item -mbitops
+@opindex mbitops
+Enables the bit operation instructions - bit test (@code{btstm}), set
+(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
+test-and-set (@code{tas}).
+
+@item -mc=@var{name}
+@opindex mc=
+Selects which section constant data will be placed in. @var{name} may
+be @code{tiny}, @code{near}, or @code{far}.
+
+@item -mclip
+@opindex mclip
+Enables the @code{clip} instruction. Note that @code{-mclip} is not
+useful unless you also provide @code{-mminmax}.
+
+@item -mconfig=@var{name}
+@opindex mconfig=
+Selects one of the build-in core configurations. Each MeP chip has
+one or more modules in it; each module has a core CPU and a variety of
+coprocessors, optional instructions, and peripherals. The
+@code{MeP-Integrator} tool, not part of GCC, provides these
+configurations through this option; using this option is the same as
+using all the corresponding command line options. The default
+configuration is @code{default}.
+
+@item -mcop
+@opindex mcop
+Enables the coprocessor instructions. By default, this is a 32-bit
+coprocessor. Note that the coprocessor is normally enabled via the
+@code{-mconfig=} option.
+
+@item -mcop32
+@opindex mcop32
+Enables the 32-bit coprocessor's instructions.
+
+@item -mcop64
+@opindex mcop64
+Enables the 64-bit coprocessor's instructions.
+
+@item -mivc2
+@opindex mivc2
+Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
+
+@item -mdc
+@opindex mdc
+Causes constant variables to be placed in the @code{.near} section.
+
+@item -mdiv
+@opindex mdiv
+Enables the @code{div} and @code{divu} instructions.
+
+@item -meb
+@opindex meb
+Generate big-endian code.
+
+@item -mel
+@opindex mel
+Generate little-endian code.
+
+@item -mio-volatile
+@opindex mio-volatile
+Tells the compiler that any variable marked with the @code{io}
+attribute is to be considered volatile.
+
+@item -ml
+@opindex ml
+Causes variables to be assigned to the @code{.far} section by default.
+
+@item -mleadz
+@opindex mleadz
+Enables the @code{leadz} (leading zero) instruction.
+
+@item -mm
+@opindex mm
+Causes variables to be assigned to the @code{.near} section by default.
+
+@item -mminmax
+@opindex mminmax
+Enables the @code{min} and @code{max} instructions.
+
+@item -mmult
+@opindex mmult
+Enables the multiplication and multiply-accumulate instructions.
+
+@item -mno-opts
+@opindex mno-opts
+Disables all the optional instructions enabled by @code{-mall-opts}.
+
+@item -mrepeat
+@opindex mrepeat
+Enables the @code{repeat} and @code{erepeat} instructions, used for
+low-overhead looping.
+
+@item -ms
+@opindex ms
+Causes all variables to default to the @code{.tiny} section. Note
+that there is a 65536 byte limit to this section. Accesses to these
+variables use the @code{%gp} base register.
+
+@item -msatur
+@opindex msatur
+Enables the saturation instructions. Note that the compiler does not
+currently generate these itself, but this option is included for
+compatibility with other tools, like @code{as}.
+
+@item -msdram
+@opindex msdram
+Link the SDRAM-based runtime instead of the default ROM-based runtime.
+
+@item -msim
+@opindex msim
+Link the simulator runtime libraries.
+
+@item -msimnovec
+@opindex msimnovec
+Link the simulator runtime libraries, excluding built-in support
+for reset and exception vectors and tables.
+
+@item -mtf
+@opindex mtf
+Causes all functions to default to the @code{.far} section. Without
+this option, functions default to the @code{.near} section.
+
+@item -mtiny=@var{n}
+@opindex mtiny=
+Variables that are @var{n} bytes or smaller will be allocated to the
+@code{.tiny} section. These variables use the @code{$gp} base
+register. The default for this option is 4, but note that there's a
+65536 byte limit to the @code{.tiny} section.
+
+@end table
+
@node MIPS Options
@subsection MIPS Options
@cindex MIPS options
@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
+@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
@samp{loongson2e}, @samp{loongson2f},
@samp{m4k},
@samp{octeon},
MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
MIPS16 code generation can also be controlled on a per-function basis
-by means of @code{mips16} and @code{nomips16} attributes.
+by means of @code{mips16} and @code{nomips16} attributes.
@xref{Function Attributes}, for more information.
@item -mflip-mips16
This option only has an effect when optimizing for the VR4130.
It normally makes code faster, but at the expense of making it bigger.
It is enabled by default at optimization level @option{-O3}.
+
+@item -msynci
+@itemx -mno-synci
+@opindex msynci
+Enable (disable) generation of @code{synci} instructions on
+architectures that support it. The @code{synci} instructions (if
+enabled) will be generated when @code{__builtin___clear_cache()} is
+compiled.
+
+This option defaults to @code{-mno-synci}, but the default can be
+overridden by configuring with @code{--with-synci}.
+
+When compiling code for single processor systems, it is generally safe
+to use @code{synci}. However, on many multi-core (SMP) systems, it
+will not invalidate the instruction caches on all cores and may lead
+to undefined behavior.
+
+@item -mrelax-pic-calls
+@itemx -mno-relax-pic-calls
+@opindex mrelax-pic-calls
+Try to turn PIC calls that are normally dispatched via register
+@code{$25} into direct calls. This is only possible if the linker can
+resolve the destination at link-time and if the destination is within
+range for a direct call.
+
+@option{-mrelax-pic-calls} is the default if GCC was configured to use
+an assembler and a linker that supports the @code{.reloc} assembly
+directive and @code{-mexplicit-relocs} is in effect. With
+@code{-mno-explicit-relocs}, this optimization can be performed by the
+assembler and the linker alone without help from the compiler.
+
+@item -mmcount-ra-address
+@itemx -mno-mcount-ra-address
+@opindex mmcount-ra-address
+@opindex mno-mcount-ra-address
+Emit (do not emit) code that allows @code{_mcount} to modify the
+calling function's return address. When enabled, this option extends
+the usual @code{_mcount} interface with a new @var{ra-address}
+parameter, which has type @code{intptr_t *} and is passed in register
+@code{$12}. @code{_mcount} can then modify the return address by
+doing both of the following:
+@itemize
+@item
+Returning the new address in register @code{$31}.
+@item
+Storing the new address in @code{*@var{ra-address}},
+if @var{ra-address} is nonnull.
+@end itemize
+
+The default is @option{-mno-mcount-ra-address}.
+
@end table
@node MMIX Options
@itemx -mno-mfcrf
@itemx -mpopcntb
@itemx -mno-popcntb
+@itemx -mpopcntd
+@itemx -mno-popcntd
@itemx -mfprnd
@itemx -mno-fprnd
@itemx -mcmpb
@opindex mno-mfcrf
@opindex mpopcntb
@opindex mno-popcntb
+@opindex mpopcntd
+@opindex mno-popcntd
@opindex mfprnd
@opindex mno-fprnd
@opindex mcmpb
double precision FP reciprocal estimate instruction implemented on the
POWER5 processor and other processors that support the PowerPC V2.02
architecture.
+The @option{-mpopcntd} option allows GCC to generate the popcount
+instruction implemented on the POWER7 processor and other processors
+that support the PowerPC V2.06 architecture.
The @option{-mfprnd} option allows GCC to generate the FP round to
integer instructions implemented on the POWER5+ processor and other
processors that support the PowerPC V2.03 architecture.
instruction scheduling parameters for machine type @var{cpu_type}.
Supported values for @var{cpu_type} are @samp{401}, @samp{403},
@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
-@samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
-@samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
-@samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
-@samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
-@samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
-@samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
-@samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
-@samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
+@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
+@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
+@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
+@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
+@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{ec603e}, @samp{G3},
+@samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
+@samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x},
+@samp{power7}, @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
@samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
@option{-mcpu=common} selects a completely generic processor. Code
following options:
@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
--mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
+-mnew-mnemonics -mpopcntb -mpopcntd -mpower -mpower2 -mpowerpc64 @gol
-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
--msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr}
+-msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx}
The particular options set for any particular CPU will vary between
compiler versions, depending on what setting seems to produce optimal
This option has been deprecated. Use @option{-mspe} and
@option{-mno-spe} instead.
+@item -mvsx
+@itemx -mno-vsx
+@opindex mvsx
+@opindex mno-vsx
+Generate code that uses (does not use) vector/scalar (VSX)
+instructions, and also enable the use of built-in functions that allow
+more direct access to the VSX instruction set.
+
@item -mfloat-gprs=@var{yes/single/double/no}
@itemx -mfloat-gprs
@opindex mfloat-gprs
@itemx -mdouble-float
@opindex msingle-float
@opindex mdouble-float
-Generate code for single or double-precision floating point operations.
-@option{-mdouble-float} implies @option{-msingle-float}.
+Generate code for single or double-precision floating point operations.
+@option{-mdouble-float} implies @option{-msingle-float}.
@item -msimple-fpu
@opindex msimple-fpu
@item -mfpu
@opindex mfpu
-Specify type of floating point unit. Valid values are @var{sp_lite}
+Specify type of floating point unit. Valid values are @var{sp_lite}
(equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
and @var{dp_full} (equivalent to -mdouble-float).
signals may get corrupted data.
@item -mavoid-indexed-addresses
-@item -mno-avoid-indexed-addresses
+@itemx -mno-avoid-indexed-addresses
@opindex mavoid-indexed-addresses
@opindex mno-avoid-indexed-addresses
Generate code that tries to avoid (not avoid) the use of indexed load
@opindex mmulhw
@opindex mno-mulhw
Generate code that uses (does not use) the half-word multiply and
-multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
+multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
These instructions are generated by default when targetting those
processors.
@opindex mdlmzb
@opindex mno-dlmzb
Generate code that uses (does not use) the string-search @samp{dlmzb}
-instruction on the IBM 405, 440 and 464 processors. This instruction is
+instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
generated by default when targetting those processors.
@item -mno-bit-align
@end table
+@node RX Options
+@subsection RX Options
+@cindex RX Options
+
+These command line options are defined for RX targets:
+
+@table @gcctabopt
+@item -m64bit-doubles
+@itemx -m32bit-doubles
+@opindex m64bit-doubles
+@opindex m32bit-doubles
+Make the @code{double} data type be 64-bits (@option{-m64bit-doubles})
+or 32-bits (@option{-m32bit-doubles}) in size. The default is
+@option{-m32bit-doubles}. @emph{Note} RX floating point hardware only
+works on 32-bit values, which is why the default is
+@option{-m32bit-doubles}.
+
+@item -fpu
+@itemx -nofpu
+@opindex fpu
+@opindex nofpu
+Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX
+floating point hardware. The default is enabled for the @var{RX600}
+series and disabled for the @var{RX200} series.
+
+Floating point instructions will only be generated for 32-bit floating
+point values however, so if the @option{-m64bit-doubles} option is in
+use then the FPU hardware will not be used for doubles.
+
+@emph{Note} If the @option{-fpu} option is enabled then
+@option{-funsafe-math-optimizations} is also enabled automatically.
+This is because the RX FPU instructions are themselves unsafe.
+
+@item -mcpu=@var{name}
+@itemx -patch=@var{name}
+@opindex -mcpu
+@opindex -patch
+Selects the type of RX CPU to be targeted. Currently three types are
+supported, the generic @var{RX600} and @var{RX200} series hardware and
+the specific @var{RX610} cpu. The default is @var{RX600}.
+
+The only difference between @var{RX600} and @var{RX610} is that the
+@var{RX610} does not support the @code{MVTIPL} instruction.
+
+The @var{RX200} series does not have a hardware floating point unit
+and so @option{-nofpu} is enabled by default when this type is
+selected.
+
+@item -mbig-endian-data
+@itemx -mlittle-endian-data
+@opindex mbig-endian-data
+@opindex mlittle-endian-data
+Store data (but not code) in the big-endian format. The default is
+@option{-mlittle-endian-data}, ie to store data in the little endian
+format.
+
+@item -msmall-data-limit=@var{N}
+@opindex msmall-data-limit
+Specifies the maximum size in bytes of global and static variables
+which can be placed into the small data area. Using the small data
+area can lead to smaller and faster code, but the size of area is
+limited and it is up to the programmer to ensure that the area does
+not overflow. Also when the small data area is used one of the RX's
+registers (@code{r13}) is reserved for use pointing to this area, so
+it is no longer available for use by the compiler. This could result
+in slower and/or larger code if variables which once could have been
+held in @code{r13} are now pushed onto the stack.
+
+Note, common variables (variables which have not been initialised) and
+constants are not placed into the small data area as they are assigned
+to other sections in the output executable.
+
+The default value is zero, which disables this feature. Note, this
+feature is not enabled by default with higher optimization levels
+(@option{-O2} etc) because of the potentially detrimental effects of
+reserving register @code{r13}. It is up to the programmer to
+experiment and discover whether this feature is of benefit to their
+program.
+
+@item -msim
+@itemx -mno-sim
+@opindex msim
+@opindex mno-sim
+Use the simulator runtime. The default is to use the libgloss board
+specific runtime.
+
+@item -mas100-syntax
+@itemx -mno-as100-syntax
+@opindex mas100-syntax
+@opindex mno-as100-syntax
+When generating assembler output use a syntax that is compatible with
+Renesas's AS100 assembler. This syntax can also be handled by the GAS
+assembler but it has some restrictions so generating it is not the
+default option.
+
+@item -mmax-constant-size=@var{N}
+@opindex mmax-constant-size
+Specifies the maxium size, in bytes, of a constant that can be used as
+an operand in a RX instruction. Although the RX instruction set does
+allow constants of up to 4 bytes in length to be used in instructions,
+a longer value equates to a longer instruction. Thus in some
+circumstances it can be beneficial to restrict the size of constants
+that are used in instructions. Constants that are too big are instead
+placed into a constant pool and referenced via register indirection.
+
+The value @var{N} can be between 0 and 4. A value of 0 (the default)
+or 4 means that constants of any size are allowed.
+
+@item -mrelax
+@opindex mrelax
+Enable linker relaxation. Linker relaxation is a process whereby the
+linker will attempt to reduce the size of a program by finding shorter
+versions of various instructions. Disabled by default.
+
+@item -mint-register=@var{N}
+@opindex mint-register
+Specify the number of registers to reserve for fast interrupt handler
+functions. The value @var{N} can be between 0 and 4. A value of 1
+means that register @code{r13} will be reserved for ther exclusive use
+of fast interrupt handlers. A value of 2 reserves @code{r13} and
+@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
+@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
+A value of 0, the default, does not reserve any registers.
+
+@item -msave-acc-in-interrupts
+@opindex msave-acc-in-interrupts
+Specifies that interrupt handler functions should preserve the
+accumulator register. This is only necessary if normal code might use
+the accumulator register, for example because it performs 64-bit
+multiplications. The default is to ignore the accumulator as this
+makes the interrupt handlers faster.
+
+@end table
+
+@emph{Note:} The generic GCC command line @option{-ffixed-@var{reg}}
+has special significance to the RX port when used with the
+@code{interrupt} function attribute. This attribute indicates a
+function intended to process fast interrupts. GCC will will ensure
+that it only uses the registers @code{r10}, @code{r11}, @code{r12}
+and/or @code{r13} and only provided that the normal use of the
+corresponding registers have been restricted via the
+@option{-ffixed-@var{reg}} or @option{-mint-register} command line
+options.
+
@node S/390 and zSeries Options
@subsection S/390 and zSeries Options
@cindex S/390 and zSeries Options
@item -mel
@opindex mel
-Compile code for little endian mode.
+Compile code for little endian mode.
@item -mnhwloop
@opindex mnhwloop
@item -mmac
@opindex mmac
-Enable the use of multiply-accumulate instructions. Disabled by default.
+Enable the use of multiply-accumulate instructions. Disabled by default.
@item -mscore5
@opindex mscore5
@item -m2e
Generate code for the SH2e.
+@item -m2a-nofpu
+@opindex m2a-nofpu
+Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
+that the floating-point unit is not used.
+
+@item -m2a-single-only
+@opindex m2a-single-only
+Generate code for the SH2a-FPU, in such a way that no double-precision
+floating point operations are used.
+
+@item -m2a-single
+@opindex m2a-single
+Generate code for the SH2a-FPU assuming the floating-point unit is in
+single-precision mode by default.
+
+@item -m2a
+@opindex m2a
+Generate code for the SH2a-FPU assuming the floating-point unit is in
+double-precision mode by default.
+
@item -m3
@opindex m3
Generate code for the SH3.
@item -mfmovd
@opindex mfmovd
-Enable the use of the instruction @code{fmovd}.
+Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
+alignment constraints.
@item -mhitachi
@opindex mhitachi
two registers separated by a dash. Multiple register ranges can be
specified separated by a comma.
+@item -mea32
+@itemx -mea64
+@opindex mea32
+@opindex mea64
+Compile code assuming that pointers to the PPU address space accessed
+via the @code{__ea} named address space qualifier are either 32 or 64
+bits wide. The default is 32 bits. As this is an ABI changing option,
+all object code in an executable must be compiled with the same setting.
+
+@item -maddress-space-conversion
+@itemx -mno-address-space-conversion
+@opindex maddress-space-conversion
+@opindex mno-address-space-conversion
+Allow/disallow treating the @code{__ea} address space as superset
+of the generic address space. This enables explicit type casts
+between @code{__ea} and generic pointer as well as implicit
+conversions of generic pointers to @code{__ea} pointers. The
+default is to allow address space pointer conversions.
+
+@item -mcache-size=@var{cache-size}
+@opindex mcache-size
+This option controls the version of libgcc that the compiler links to an
+executable and selects a software-managed cache for accessing variables
+in the @code{__ea} address space with a particular cache size. Possible
+options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
+and @samp{128}. The default cache size is 64KB.
+
+@item -matomic-updates
+@itemx -mno-atomic-updates
+@opindex matomic-updates
+@opindex mno-atomic-updates
+This option controls the version of libgcc that the compiler links to an
+executable and selects whether atomic updates to the software-managed
+cache of PPU-side variables are used. If you use atomic updates, changes
+to a PPU variable from SPU code using the @code{__ea} named address space
+qualifier will not interfere with changes to other PPU variables residing
+in the same cache line from PPU code. If you do not use atomic updates,
+such interference may occur; however, writing back cache lines will be
+more efficient. The default behavior is to use atomic updates.
+
@item -mdual-nops
@itemx -mdual-nops=@var{n}
@opindex mdual-nops
@opindex mhint-max-distance
The encoding of the branch hint instruction limits the hint to be within
256 instructions of the branch it is effecting. By default, GCC makes
-sure it is within 125.
+sure it is within 125.
@item -msafe-hints
@opindex msafe-hints
@opindex municode
This option is available for mingw-w64 targets. It specifies
that the UNICODE macro is getting pre-defined and that the
-unicode capable runtime startup code is choosen.
+unicode capable runtime startup code is chosen.
@item -mwin32
@opindex mwin32
instructing the linker to set the PE header subsystem type
appropriately.
+@item -fno-set-stack-executable
+@opindex fno-set-stack-executable
+This option is available for MinGW targets. It specifies that
+the executable flag for stack used by nested functions isn't
+set. This is necessary for binaries running in kernel mode of
+Windows, as there the user32 API, which is used to set executable
+privileges, isn't available.
+
@item -mpe-aligned-commons
@opindex mpe-aligned-commons
This option is available for Cygwin and MinGW targets. It
-specifies that the GNU extension to the PE file format that
+specifies that the GNU extension to the PE file format that
permits the correct alignment of COMMON variables should be
used when generating code. It will be enabled by default if
GCC detects that the target assembler found during configuration
In C code, controls the placement of uninitialized global variables.
Unix C compilers have traditionally permitted multiple definitions of
such variables in different compilation units by placing the variables
-in a common block.
-This is the behavior specified by @option{-fcommon}, and is the default
-for GCC on most targets.
+in a common block.
+This is the behavior specified by @option{-fcommon}, and is the default
+for GCC on most targets.
On the other hand, this behavior is not required by ISO C, and on some
targets may carry a speed or code size penalty on variable references.
-The @option{-fno-common} option specifies that the compiler should place
+The @option{-fno-common} option specifies that the compiler should place
uninitialized global variables in the data section of the object file,
rather than generating them as common blocks.
-This has the effect that if the same variable is declared
+This has the effect that if the same variable is declared
(without @code{extern}) in two different compilations,
you will get a multiple-definition error when you link them.
-In this case, you must compile with @option{-fcommon} instead.
-Compiling with @option{-fno-common} is useful on targets for which
+In this case, you must compile with @option{-fcommon} instead.
+Compiling with @option{-fno-common} is useful on targets for which
it provides better performance, or if you wish to verify that the
program will work on other systems which always treat uninitialized
variable declarations this way.
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