1 @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,
2 @c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
8 @chapter Target Description Macros and Functions
9 @cindex machine description macros
10 @cindex target description macros
11 @cindex macros, target description
12 @cindex @file{tm.h} macros
14 In addition to the file @file{@var{machine}.md}, a machine description
15 includes a C header file conventionally given the name
16 @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
17 The header file defines numerous macros that convey the information
18 about the target machine that does not fit into the scheme of the
19 @file{.md} file. The file @file{tm.h} should be a link to
20 @file{@var{machine}.h}. The header file @file{config.h} includes
21 @file{tm.h} and most compiler source files include @file{config.h}. The
22 source file defines a variable @code{targetm}, which is a structure
23 containing pointers to functions and data relating to the target
24 machine. @file{@var{machine}.c} should also contain their definitions,
25 if they are not defined elsewhere in GCC, and other functions called
26 through the macros defined in the @file{.h} file.
29 * Target Structure:: The @code{targetm} variable.
30 * Driver:: Controlling how the driver runs the compilation passes.
31 * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
32 * Per-Function Data:: Defining data structures for per-function information.
33 * Storage Layout:: Defining sizes and alignments of data.
34 * Type Layout:: Defining sizes and properties of basic user data types.
35 * Registers:: Naming and describing the hardware registers.
36 * Register Classes:: Defining the classes of hardware registers.
37 * Old Constraints:: The old way to define machine-specific constraints.
38 * Stack and Calling:: Defining which way the stack grows and by how much.
39 * Varargs:: Defining the varargs macros.
40 * Trampolines:: Code set up at run time to enter a nested function.
41 * Library Calls:: Controlling how library routines are implicitly called.
42 * Addressing Modes:: Defining addressing modes valid for memory operands.
43 * Anchored Addresses:: Defining how @option{-fsection-anchors} should work.
44 * Condition Code:: Defining how insns update the condition code.
45 * Costs:: Defining relative costs of different operations.
46 * Scheduling:: Adjusting the behavior of the instruction scheduler.
47 * Sections:: Dividing storage into text, data, and other sections.
48 * PIC:: Macros for position independent code.
49 * Assembler Format:: Defining how to write insns and pseudo-ops to output.
50 * Debugging Info:: Defining the format of debugging output.
51 * Floating Point:: Handling floating point for cross-compilers.
52 * Mode Switching:: Insertion of mode-switching instructions.
53 * Target Attributes:: Defining target-specific uses of @code{__attribute__}.
54 * Emulated TLS:: Emulated TLS support.
55 * MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
56 * PCH Target:: Validity checking for precompiled headers.
57 * C++ ABI:: Controlling C++ ABI changes.
58 * Named Address Spaces:: Adding support for named address spaces
59 * Misc:: Everything else.
62 @node Target Structure
63 @section The Global @code{targetm} Variable
65 @cindex target functions
67 @deftypevar {struct gcc_target} targetm
68 The target @file{.c} file must define the global @code{targetm} variable
69 which contains pointers to functions and data relating to the target
70 machine. The variable is declared in @file{target.h};
71 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
72 used to initialize the variable, and macros for the default initializers
73 for elements of the structure. The @file{.c} file should override those
74 macros for which the default definition is inappropriate. For example:
77 #include "target-def.h"
79 /* @r{Initialize the GCC target structure.} */
81 #undef TARGET_COMP_TYPE_ATTRIBUTES
82 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
84 struct gcc_target targetm = TARGET_INITIALIZER;
88 Where a macro should be defined in the @file{.c} file in this manner to
89 form part of the @code{targetm} structure, it is documented below as a
90 ``Target Hook'' with a prototype. Many macros will change in future
91 from being defined in the @file{.h} file to being part of the
92 @code{targetm} structure.
95 @section Controlling the Compilation Driver, @file{gcc}
97 @cindex controlling the compilation driver
99 @c prevent bad page break with this line
100 You can control the compilation driver.
102 @defmac SWITCH_TAKES_ARG (@var{char})
103 A C expression which determines whether the option @option{-@var{char}}
104 takes arguments. The value should be the number of arguments that
105 option takes--zero, for many options.
107 By default, this macro is defined as
108 @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options
109 properly. You need not define @code{SWITCH_TAKES_ARG} unless you
110 wish to add additional options which take arguments. Any redefinition
111 should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for
115 @defmac WORD_SWITCH_TAKES_ARG (@var{name})
116 A C expression which determines whether the option @option{-@var{name}}
117 takes arguments. The value should be the number of arguments that
118 option takes--zero, for many options. This macro rather than
119 @code{SWITCH_TAKES_ARG} is used for multi-character option names.
121 By default, this macro is defined as
122 @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options
123 properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you
124 wish to add additional options which take arguments. Any redefinition
125 should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for
129 @defmac SWITCH_CURTAILS_COMPILATION (@var{char})
130 A C expression which determines whether the option @option{-@var{char}}
131 stops compilation before the generation of an executable. The value is
132 boolean, nonzero if the option does stop an executable from being
133 generated, zero otherwise.
135 By default, this macro is defined as
136 @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard
137 options properly. You need not define
138 @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional
139 options which affect the generation of an executable. Any redefinition
140 should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check
141 for additional options.
144 @defmac SWITCHES_NEED_SPACES
145 A string-valued C expression which enumerates the options for which
146 the linker needs a space between the option and its argument.
148 If this macro is not defined, the default value is @code{""}.
151 @defmac TARGET_OPTION_TRANSLATE_TABLE
152 If defined, a list of pairs of strings, the first of which is a
153 potential command line target to the @file{gcc} driver program, and the
154 second of which is a space-separated (tabs and other whitespace are not
155 supported) list of options with which to replace the first option. The
156 target defining this list is responsible for assuring that the results
157 are valid. Replacement options may not be the @code{--opt} style, they
158 must be the @code{-opt} style. It is the intention of this macro to
159 provide a mechanism for substitution that affects the multilibs chosen,
160 such as one option that enables many options, some of which select
161 multilibs. Example nonsensical definition, where @option{-malt-abi},
162 @option{-EB}, and @option{-mspoo} cause different multilibs to be chosen:
165 #define TARGET_OPTION_TRANSLATE_TABLE \
166 @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \
167 @{ "-compat", "-EB -malign=4 -mspoo" @}
171 @defmac DRIVER_SELF_SPECS
172 A list of specs for the driver itself. It should be a suitable
173 initializer for an array of strings, with no surrounding braces.
175 The driver applies these specs to its own command line between loading
176 default @file{specs} files (but not command-line specified ones) and
177 choosing the multilib directory or running any subcommands. It
178 applies them in the order given, so each spec can depend on the
179 options added by earlier ones. It is also possible to remove options
180 using @samp{%<@var{option}} in the usual way.
182 This macro can be useful when a port has several interdependent target
183 options. It provides a way of standardizing the command line so
184 that the other specs are easier to write.
186 Do not define this macro if it does not need to do anything.
189 @defmac OPTION_DEFAULT_SPECS
190 A list of specs used to support configure-time default options (i.e.@:
191 @option{--with} options) in the driver. It should be a suitable initializer
192 for an array of structures, each containing two strings, without the
193 outermost pair of surrounding braces.
195 The first item in the pair is the name of the default. This must match
196 the code in @file{config.gcc} for the target. The second item is a spec
197 to apply if a default with this name was specified. The string
198 @samp{%(VALUE)} in the spec will be replaced by the value of the default
199 everywhere it occurs.
201 The driver will apply these specs to its own command line between loading
202 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
203 the same mechanism as @code{DRIVER_SELF_SPECS}.
205 Do not define this macro if it does not need to do anything.
209 A C string constant that tells the GCC driver program options to
210 pass to CPP@. It can also specify how to translate options you
211 give to GCC into options for GCC to pass to the CPP@.
213 Do not define this macro if it does not need to do anything.
216 @defmac CPLUSPLUS_CPP_SPEC
217 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
218 than C@. If you do not define this macro, then the value of
219 @code{CPP_SPEC} (if any) will be used instead.
223 A C string constant that tells the GCC driver program options to
224 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
226 It can also specify how to translate options you give to GCC into options
227 for GCC to pass to front ends.
229 Do not define this macro if it does not need to do anything.
233 A C string constant that tells the GCC driver program options to
234 pass to @code{cc1plus}. It can also specify how to translate options you
235 give to GCC into options for GCC to pass to the @code{cc1plus}.
237 Do not define this macro if it does not need to do anything.
238 Note that everything defined in CC1_SPEC is already passed to
239 @code{cc1plus} so there is no need to duplicate the contents of
240 CC1_SPEC in CC1PLUS_SPEC@.
244 A C string constant that tells the GCC driver program options to
245 pass to the assembler. It can also specify how to translate options
246 you give to GCC into options for GCC to pass to the assembler.
247 See the file @file{sun3.h} for an example of this.
249 Do not define this macro if it does not need to do anything.
252 @defmac ASM_FINAL_SPEC
253 A C string constant that tells the GCC driver program how to
254 run any programs which cleanup after the normal assembler.
255 Normally, this is not needed. See the file @file{mips.h} for
258 Do not define this macro if it does not need to do anything.
261 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
262 Define this macro, with no value, if the driver should give the assembler
263 an argument consisting of a single dash, @option{-}, to instruct it to
264 read from its standard input (which will be a pipe connected to the
265 output of the compiler proper). This argument is given after any
266 @option{-o} option specifying the name of the output file.
268 If you do not define this macro, the assembler is assumed to read its
269 standard input if given no non-option arguments. If your assembler
270 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
271 see @file{mips.h} for instance.
275 A C string constant that tells the GCC driver program options to
276 pass to the linker. It can also specify how to translate options you
277 give to GCC into options for GCC to pass to the linker.
279 Do not define this macro if it does not need to do anything.
283 Another C string constant used much like @code{LINK_SPEC}. The difference
284 between the two is that @code{LIB_SPEC} is used at the end of the
285 command given to the linker.
287 If this macro is not defined, a default is provided that
288 loads the standard C library from the usual place. See @file{gcc.c}.
292 Another C string constant that tells the GCC driver program
293 how and when to place a reference to @file{libgcc.a} into the
294 linker command line. This constant is placed both before and after
295 the value of @code{LIB_SPEC}.
297 If this macro is not defined, the GCC driver provides a default that
298 passes the string @option{-lgcc} to the linker.
301 @defmac REAL_LIBGCC_SPEC
302 By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
303 @code{LIBGCC_SPEC} is not directly used by the driver program but is
304 instead modified to refer to different versions of @file{libgcc.a}
305 depending on the values of the command line flags @option{-static},
306 @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
307 targets where these modifications are inappropriate, define
308 @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
309 driver how to place a reference to @file{libgcc} on the link command
310 line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
313 @defmac USE_LD_AS_NEEDED
314 A macro that controls the modifications to @code{LIBGCC_SPEC}
315 mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
316 generated that uses --as-needed and the shared libgcc in place of the
317 static exception handler library, when linking without any of
318 @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
322 If defined, this C string constant is added to @code{LINK_SPEC}.
323 When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
324 the modifications to @code{LIBGCC_SPEC} mentioned in
325 @code{REAL_LIBGCC_SPEC}.
328 @defmac STARTFILE_SPEC
329 Another C string constant used much like @code{LINK_SPEC}. The
330 difference between the two is that @code{STARTFILE_SPEC} is used at
331 the very beginning of the command given to the linker.
333 If this macro is not defined, a default is provided that loads the
334 standard C startup file from the usual place. See @file{gcc.c}.
338 Another C string constant used much like @code{LINK_SPEC}. The
339 difference between the two is that @code{ENDFILE_SPEC} is used at
340 the very end of the command given to the linker.
342 Do not define this macro if it does not need to do anything.
345 @defmac THREAD_MODEL_SPEC
346 GCC @code{-v} will print the thread model GCC was configured to use.
347 However, this doesn't work on platforms that are multilibbed on thread
348 models, such as AIX 4.3. On such platforms, define
349 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
350 blanks that names one of the recognized thread models. @code{%*}, the
351 default value of this macro, will expand to the value of
352 @code{thread_file} set in @file{config.gcc}.
355 @defmac SYSROOT_SUFFIX_SPEC
356 Define this macro to add a suffix to the target sysroot when GCC is
357 configured with a sysroot. This will cause GCC to search for usr/lib,
358 et al, within sysroot+suffix.
361 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
362 Define this macro to add a headers_suffix to the target sysroot when
363 GCC is configured with a sysroot. This will cause GCC to pass the
364 updated sysroot+headers_suffix to CPP, causing it to search for
365 usr/include, et al, within sysroot+headers_suffix.
369 Define this macro to provide additional specifications to put in the
370 @file{specs} file that can be used in various specifications like
373 The definition should be an initializer for an array of structures,
374 containing a string constant, that defines the specification name, and a
375 string constant that provides the specification.
377 Do not define this macro if it does not need to do anything.
379 @code{EXTRA_SPECS} is useful when an architecture contains several
380 related targets, which have various @code{@dots{}_SPECS} which are similar
381 to each other, and the maintainer would like one central place to keep
384 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
385 define either @code{_CALL_SYSV} when the System V calling sequence is
386 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
389 The @file{config/rs6000/rs6000.h} target file defines:
392 #define EXTRA_SPECS \
393 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
395 #define CPP_SYS_DEFAULT ""
398 The @file{config/rs6000/sysv.h} target file defines:
402 "%@{posix: -D_POSIX_SOURCE @} \
403 %@{mcall-sysv: -D_CALL_SYSV @} \
404 %@{!mcall-sysv: %(cpp_sysv_default) @} \
405 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
407 #undef CPP_SYSV_DEFAULT
408 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
411 while the @file{config/rs6000/eabiaix.h} target file defines
412 @code{CPP_SYSV_DEFAULT} as:
415 #undef CPP_SYSV_DEFAULT
416 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
420 @defmac LINK_LIBGCC_SPECIAL_1
421 Define this macro if the driver program should find the library
422 @file{libgcc.a}. If you do not define this macro, the driver program will pass
423 the argument @option{-lgcc} to tell the linker to do the search.
426 @defmac LINK_GCC_C_SEQUENCE_SPEC
427 The sequence in which libgcc and libc are specified to the linker.
428 By default this is @code{%G %L %G}.
431 @defmac LINK_COMMAND_SPEC
432 A C string constant giving the complete command line need to execute the
433 linker. When you do this, you will need to update your port each time a
434 change is made to the link command line within @file{gcc.c}. Therefore,
435 define this macro only if you need to completely redefine the command
436 line for invoking the linker and there is no other way to accomplish
437 the effect you need. Overriding this macro may be avoidable by overriding
438 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
441 @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
442 A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
443 directories from linking commands. Do not give it a nonzero value if
444 removing duplicate search directories changes the linker's semantics.
447 @defmac MULTILIB_DEFAULTS
448 Define this macro as a C expression for the initializer of an array of
449 string to tell the driver program which options are defaults for this
450 target and thus do not need to be handled specially when using
451 @code{MULTILIB_OPTIONS}.
453 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
454 the target makefile fragment or if none of the options listed in
455 @code{MULTILIB_OPTIONS} are set by default.
456 @xref{Target Fragment}.
459 @defmac RELATIVE_PREFIX_NOT_LINKDIR
460 Define this macro to tell @command{gcc} that it should only translate
461 a @option{-B} prefix into a @option{-L} linker option if the prefix
462 indicates an absolute file name.
465 @defmac MD_EXEC_PREFIX
466 If defined, this macro is an additional prefix to try after
467 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
468 when the compiler is built as a cross
469 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
470 to the list of directories used to find the assembler in @file{configure.in}.
473 @defmac STANDARD_STARTFILE_PREFIX
474 Define this macro as a C string constant if you wish to override the
475 standard choice of @code{libdir} as the default prefix to
476 try when searching for startup files such as @file{crt0.o}.
477 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
478 is built as a cross compiler.
481 @defmac STANDARD_STARTFILE_PREFIX_1
482 Define this macro as a C string constant if you wish to override the
483 standard choice of @code{/lib} as a prefix to try after the default prefix
484 when searching for startup files such as @file{crt0.o}.
485 @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
486 is built as a cross compiler.
489 @defmac STANDARD_STARTFILE_PREFIX_2
490 Define this macro as a C string constant if you wish to override the
491 standard choice of @code{/lib} as yet another prefix to try after the
492 default prefix when searching for startup files such as @file{crt0.o}.
493 @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
494 is built as a cross compiler.
497 @defmac MD_STARTFILE_PREFIX
498 If defined, this macro supplies an additional prefix to try after the
499 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
500 compiler is built as a cross compiler.
503 @defmac MD_STARTFILE_PREFIX_1
504 If defined, this macro supplies yet another prefix to try after the
505 standard prefixes. It is not searched when the compiler is built as a
509 @defmac INIT_ENVIRONMENT
510 Define this macro as a C string constant if you wish to set environment
511 variables for programs called by the driver, such as the assembler and
512 loader. The driver passes the value of this macro to @code{putenv} to
513 initialize the necessary environment variables.
516 @defmac LOCAL_INCLUDE_DIR
517 Define this macro as a C string constant if you wish to override the
518 standard choice of @file{/usr/local/include} as the default prefix to
519 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
520 comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
522 Cross compilers do not search either @file{/usr/local/include} or its
526 @defmac MODIFY_TARGET_NAME
527 Define this macro if you wish to define command-line switches that
528 modify the default target name.
530 For each switch, you can include a string to be appended to the first
531 part of the configuration name or a string to be deleted from the
532 configuration name, if present. The definition should be an initializer
533 for an array of structures. Each array element should have three
534 elements: the switch name (a string constant, including the initial
535 dash), one of the enumeration codes @code{ADD} or @code{DELETE} to
536 indicate whether the string should be inserted or deleted, and the string
537 to be inserted or deleted (a string constant).
539 For example, on a machine where @samp{64} at the end of the
540 configuration name denotes a 64-bit target and you want the @option{-32}
541 and @option{-64} switches to select between 32- and 64-bit targets, you would
545 #define MODIFY_TARGET_NAME \
546 @{ @{ "-32", DELETE, "64"@}, \
547 @{"-64", ADD, "64"@}@}
551 @defmac SYSTEM_INCLUDE_DIR
552 Define this macro as a C string constant if you wish to specify a
553 system-specific directory to search for header files before the standard
554 directory. @code{SYSTEM_INCLUDE_DIR} comes before
555 @code{STANDARD_INCLUDE_DIR} in the search order.
557 Cross compilers do not use this macro and do not search the directory
561 @defmac STANDARD_INCLUDE_DIR
562 Define this macro as a C string constant if you wish to override the
563 standard choice of @file{/usr/include} as the default prefix to
564 try when searching for header files.
566 Cross compilers ignore this macro and do not search either
567 @file{/usr/include} or its replacement.
570 @defmac STANDARD_INCLUDE_COMPONENT
571 The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
572 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
573 If you do not define this macro, no component is used.
576 @defmac INCLUDE_DEFAULTS
577 Define this macro if you wish to override the entire default search path
578 for include files. For a native compiler, the default search path
579 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
580 @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
581 @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
582 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
583 and specify private search areas for GCC@. The directory
584 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
586 The definition should be an initializer for an array of structures.
587 Each array element should have four elements: the directory name (a
588 string constant), the component name (also a string constant), a flag
589 for C++-only directories,
590 and a flag showing that the includes in the directory don't need to be
591 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
592 the array with a null element.
594 The component name denotes what GNU package the include file is part of,
595 if any, in all uppercase letters. For example, it might be @samp{GCC}
596 or @samp{BINUTILS}. If the package is part of a vendor-supplied
597 operating system, code the component name as @samp{0}.
599 For example, here is the definition used for VAX/VMS:
602 #define INCLUDE_DEFAULTS \
604 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
605 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
606 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
613 Here is the order of prefixes tried for exec files:
617 Any prefixes specified by the user with @option{-B}.
620 The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX}
621 is not set and the compiler has not been installed in the configure-time
622 @var{prefix}, the location in which the compiler has actually been installed.
625 The directories specified by the environment variable @code{COMPILER_PATH}.
628 The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed
629 in the configured-time @var{prefix}.
632 The location @file{/usr/libexec/gcc/}, but only if this is a native compiler.
635 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
638 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
642 Here is the order of prefixes tried for startfiles:
646 Any prefixes specified by the user with @option{-B}.
649 The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined
650 value based on the installed toolchain location.
653 The directories specified by the environment variable @code{LIBRARY_PATH}
654 (or port-specific name; native only, cross compilers do not use this).
657 The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed
658 in the configured @var{prefix} or this is a native compiler.
661 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
664 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
668 The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a
669 native compiler, or we have a target system root.
672 The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a
673 native compiler, or we have a target system root.
676 The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications.
677 If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and
678 the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix.
681 The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native
682 compiler, or we have a target system root. The default for this macro is
686 The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native
687 compiler, or we have a target system root. The default for this macro is
691 @node Run-time Target
692 @section Run-time Target Specification
693 @cindex run-time target specification
694 @cindex predefined macros
695 @cindex target specifications
697 @c prevent bad page break with this line
698 Here are run-time target specifications.
700 @defmac TARGET_CPU_CPP_BUILTINS ()
701 This function-like macro expands to a block of code that defines
702 built-in preprocessor macros and assertions for the target CPU, using
703 the functions @code{builtin_define}, @code{builtin_define_std} and
704 @code{builtin_assert}. When the front end
705 calls this macro it provides a trailing semicolon, and since it has
706 finished command line option processing your code can use those
709 @code{builtin_assert} takes a string in the form you pass to the
710 command-line option @option{-A}, such as @code{cpu=mips}, and creates
711 the assertion. @code{builtin_define} takes a string in the form
712 accepted by option @option{-D} and unconditionally defines the macro.
714 @code{builtin_define_std} takes a string representing the name of an
715 object-like macro. If it doesn't lie in the user's namespace,
716 @code{builtin_define_std} defines it unconditionally. Otherwise, it
717 defines a version with two leading underscores, and another version
718 with two leading and trailing underscores, and defines the original
719 only if an ISO standard was not requested on the command line. For
720 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
721 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
722 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
723 defines only @code{_ABI64}.
725 You can also test for the C dialect being compiled. The variable
726 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
727 or @code{clk_objective_c}. Note that if we are preprocessing
728 assembler, this variable will be @code{clk_c} but the function-like
729 macro @code{preprocessing_asm_p()} will return true, so you might want
730 to check for that first. If you need to check for strict ANSI, the
731 variable @code{flag_iso} can be used. The function-like macro
732 @code{preprocessing_trad_p()} can be used to check for traditional
736 @defmac TARGET_OS_CPP_BUILTINS ()
737 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
738 and is used for the target operating system instead.
741 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
742 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
743 and is used for the target object format. @file{elfos.h} uses this
744 macro to define @code{__ELF__}, so you probably do not need to define
748 @deftypevar {extern int} target_flags
749 This variable is declared in @file{options.h}, which is included before
750 any target-specific headers.
753 @deftypevr {Target Hook} int TARGET_DEFAULT_TARGET_FLAGS
754 This variable specifies the initial value of @code{target_flags}.
755 Its default setting is 0.
758 @cindex optional hardware or system features
759 @cindex features, optional, in system conventions
761 @deftypefn {Target Hook} bool TARGET_HANDLE_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value})
762 This hook is called whenever the user specifies one of the
763 target-specific options described by the @file{.opt} definition files
764 (@pxref{Options}). It has the opportunity to do some option-specific
765 processing and should return true if the option is valid. The default
766 definition does nothing but return true.
768 @var{code} specifies the @code{OPT_@var{name}} enumeration value
769 associated with the selected option; @var{name} is just a rendering of
770 the option name in which non-alphanumeric characters are replaced by
771 underscores. @var{arg} specifies the string argument and is null if
772 no argument was given. If the option is flagged as a @code{UInteger}
773 (@pxref{Option properties}), @var{value} is the numeric value of the
774 argument. Otherwise @var{value} is 1 if the positive form of the
775 option was used and 0 if the ``no-'' form was.
778 @deftypefn {Target Hook} bool TARGET_HANDLE_C_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value})
779 This target hook is called whenever the user specifies one of the
780 target-specific C language family options described by the @file{.opt}
781 definition files(@pxref{Options}). It has the opportunity to do some
782 option-specific processing and should return true if the option is
783 valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The
784 default definition does nothing but return false.
786 In general, you should use @code{TARGET_HANDLE_OPTION} to handle
787 options. However, if processing an option requires routines that are
788 only available in the C (and related language) front ends, then you
789 should use @code{TARGET_HANDLE_C_OPTION} instead.
792 @defmac TARGET_VERSION
793 This macro is a C statement to print on @code{stderr} a string
794 describing the particular machine description choice. Every machine
795 description should define @code{TARGET_VERSION}. For example:
799 #define TARGET_VERSION \
800 fprintf (stderr, " (68k, Motorola syntax)");
802 #define TARGET_VERSION \
803 fprintf (stderr, " (68k, MIT syntax)");
808 @defmac OVERRIDE_OPTIONS
809 Sometimes certain combinations of command options do not make sense on
810 a particular target machine. You can define a macro
811 @code{OVERRIDE_OPTIONS} to take account of this. This macro, if
812 defined, is executed once just after all the command options have been
815 Don't use this macro to turn on various extra optimizations for
816 @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for.
818 If you need to do something whenever the optimization level is
819 changed via the optimize attribute or pragma, see
820 @code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}
823 @deftypefn {Target Hook} void TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE (void)
824 This target function is similar to the macro @code{OVERRIDE_OPTIONS}
825 but is called when the optimize level is changed via an attribute or
826 pragma or when it is reset at the end of the code affected by the
827 attribute or pragma. It is not called at the beginning of compilation
828 when @code{OVERRIDE_OPTIONS} is called so if you want to perform these
829 actions then, you should have @code{OVERRIDE_OPTIONS} call
830 @code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}.
833 @defmac C_COMMON_OVERRIDE_OPTIONS
834 This is similar to @code{OVERRIDE_OPTIONS} but is only used in the C
835 language frontends (C, Objective-C, C++, Objective-C++) and so can be
836 used to alter option flag variables which only exist in those
840 @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size})
841 Some machines may desire to change what optimizations are performed for
842 various optimization levels. This macro, if defined, is executed once
843 just after the optimization level is determined and before the remainder
844 of the command options have been parsed. Values set in this macro are
845 used as the default values for the other command line options.
847 @var{level} is the optimization level specified; 2 if @option{-O2} is
848 specified, 1 if @option{-O} is specified, and 0 if neither is specified.
850 @var{size} is nonzero if @option{-Os} is specified and zero otherwise.
852 This macro is run once at program startup and when the optimization
853 options are changed via @code{#pragma GCC optimize} or by using the
854 @code{optimize} attribute.
856 @strong{Do not examine @code{write_symbols} in
857 this macro!} The debugging options are not supposed to alter the
861 @deftypefn {Target Hook} void TARGET_HELP (void)
862 This hook is called in response to the user invoking
863 @option{--target-help} on the command line. It gives the target a
864 chance to display extra information on the target specific command
865 line options found in its @file{.opt} file.
868 @defmac CAN_DEBUG_WITHOUT_FP
869 Define this macro if debugging can be performed even without a frame
870 pointer. If this macro is defined, GCC will turn on the
871 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
874 @node Per-Function Data
875 @section Defining data structures for per-function information.
876 @cindex per-function data
877 @cindex data structures
879 If the target needs to store information on a per-function basis, GCC
880 provides a macro and a couple of variables to allow this. Note, just
881 using statics to store the information is a bad idea, since GCC supports
882 nested functions, so you can be halfway through encoding one function
883 when another one comes along.
885 GCC defines a data structure called @code{struct function} which
886 contains all of the data specific to an individual function. This
887 structure contains a field called @code{machine} whose type is
888 @code{struct machine_function *}, which can be used by targets to point
889 to their own specific data.
891 If a target needs per-function specific data it should define the type
892 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
893 This macro should be used to initialize the function pointer
894 @code{init_machine_status}. This pointer is explained below.
896 One typical use of per-function, target specific data is to create an
897 RTX to hold the register containing the function's return address. This
898 RTX can then be used to implement the @code{__builtin_return_address}
899 function, for level 0.
901 Note---earlier implementations of GCC used a single data area to hold
902 all of the per-function information. Thus when processing of a nested
903 function began the old per-function data had to be pushed onto a
904 stack, and when the processing was finished, it had to be popped off the
905 stack. GCC used to provide function pointers called
906 @code{save_machine_status} and @code{restore_machine_status} to handle
907 the saving and restoring of the target specific information. Since the
908 single data area approach is no longer used, these pointers are no
911 @defmac INIT_EXPANDERS
912 Macro called to initialize any target specific information. This macro
913 is called once per function, before generation of any RTL has begun.
914 The intention of this macro is to allow the initialization of the
915 function pointer @code{init_machine_status}.
918 @deftypevar {void (*)(struct function *)} init_machine_status
919 If this function pointer is non-@code{NULL} it will be called once per
920 function, before function compilation starts, in order to allow the
921 target to perform any target specific initialization of the
922 @code{struct function} structure. It is intended that this would be
923 used to initialize the @code{machine} of that structure.
925 @code{struct machine_function} structures are expected to be freed by GC@.
926 Generally, any memory that they reference must be allocated by using
927 GC allocation, including the structure itself.
931 @section Storage Layout
932 @cindex storage layout
934 Note that the definitions of the macros in this table which are sizes or
935 alignments measured in bits do not need to be constant. They can be C
936 expressions that refer to static variables, such as the @code{target_flags}.
937 @xref{Run-time Target}.
939 @defmac BITS_BIG_ENDIAN
940 Define this macro to have the value 1 if the most significant bit in a
941 byte has the lowest number; otherwise define it to have the value zero.
942 This means that bit-field instructions count from the most significant
943 bit. If the machine has no bit-field instructions, then this must still
944 be defined, but it doesn't matter which value it is defined to. This
945 macro need not be a constant.
947 This macro does not affect the way structure fields are packed into
948 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
951 @defmac BYTES_BIG_ENDIAN
952 Define this macro to have the value 1 if the most significant byte in a
953 word has the lowest number. This macro need not be a constant.
956 @defmac WORDS_BIG_ENDIAN
957 Define this macro to have the value 1 if, in a multiword object, the
958 most significant word has the lowest number. This applies to both
959 memory locations and registers; GCC fundamentally assumes that the
960 order of words in memory is the same as the order in registers. This
961 macro need not be a constant.
964 @defmac LIBGCC2_WORDS_BIG_ENDIAN
965 Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a
966 constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
967 used only when compiling @file{libgcc2.c}. Typically the value will be set
968 based on preprocessor defines.
971 @defmac FLOAT_WORDS_BIG_ENDIAN
972 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
973 @code{TFmode} floating point numbers are stored in memory with the word
974 containing the sign bit at the lowest address; otherwise define it to
975 have the value 0. This macro need not be a constant.
977 You need not define this macro if the ordering is the same as for
981 @defmac BITS_PER_UNIT
982 Define this macro to be the number of bits in an addressable storage
983 unit (byte). If you do not define this macro the default is 8.
986 @defmac BITS_PER_WORD
987 Number of bits in a word. If you do not define this macro, the default
988 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
991 @defmac MAX_BITS_PER_WORD
992 Maximum number of bits in a word. If this is undefined, the default is
993 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
994 largest value that @code{BITS_PER_WORD} can have at run-time.
997 @defmac UNITS_PER_WORD
998 Number of storage units in a word; normally the size of a general-purpose
999 register, a power of two from 1 or 8.
1002 @defmac MIN_UNITS_PER_WORD
1003 Minimum number of units in a word. If this is undefined, the default is
1004 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
1005 smallest value that @code{UNITS_PER_WORD} can have at run-time.
1008 @defmac UNITS_PER_SIMD_WORD (@var{mode})
1009 Number of units in the vectors that the vectorizer can produce for
1010 scalar mode @var{mode}. The default is equal to @code{UNITS_PER_WORD},
1011 because the vectorizer can do some transformations even in absence of
1012 specialized @acronym{SIMD} hardware.
1015 @defmac POINTER_SIZE
1016 Width of a pointer, in bits. You must specify a value no wider than the
1017 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
1018 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
1019 a value the default is @code{BITS_PER_WORD}.
1022 @defmac POINTERS_EXTEND_UNSIGNED
1023 A C expression that determines how pointers should be extended from
1024 @code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is
1025 greater than zero if pointers should be zero-extended, zero if they
1026 should be sign-extended, and negative if some other sort of conversion
1027 is needed. In the last case, the extension is done by the target's
1028 @code{ptr_extend} instruction.
1030 You need not define this macro if the @code{ptr_mode}, @code{Pmode}
1031 and @code{word_mode} are all the same width.
1034 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
1035 A macro to update @var{m} and @var{unsignedp} when an object whose type
1036 is @var{type} and which has the specified mode and signedness is to be
1037 stored in a register. This macro is only called when @var{type} is a
1040 On most RISC machines, which only have operations that operate on a full
1041 register, define this macro to set @var{m} to @code{word_mode} if
1042 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
1043 cases, only integer modes should be widened because wider-precision
1044 floating-point operations are usually more expensive than their narrower
1047 For most machines, the macro definition does not change @var{unsignedp}.
1048 However, some machines, have instructions that preferentially handle
1049 either signed or unsigned quantities of certain modes. For example, on
1050 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
1051 sign-extend the result to 64 bits. On such machines, set
1052 @var{unsignedp} according to which kind of extension is more efficient.
1054 Do not define this macro if it would never modify @var{m}.
1057 @deftypefn {Target Hook} {enum machine_mode} TARGET_PROMOTE_FUNCTION_MODE (const_tree @var{type}, enum machine_mode @var{mode}, int *@var{punsignedp}, const_tree @var{funtype}, int @var{for_return})
1058 Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or
1059 function return values. The target hook should return the new mode
1060 and possibly change @code{*@var{punsignedp}} if the promotion should
1061 change signedness. This function is called only for scalar @emph{or
1064 @var{for_return} allows to distinguish the promotion of arguments and
1065 return values. If it is @code{1}, a return value is being promoted and
1066 @code{TARGET_FUNCTION_VALUE} must perform the same promotions done here.
1067 If it is @code{2}, the returned mode should be that of the register in
1068 which an incoming parameter is copied, or the outgoing result is computed;
1069 then the hook should return the same mode as @code{promote_mode}, though
1070 the signedness may be different.
1072 The default is to not promote arguments and return values. You can
1073 also define the hook to @code{default_promote_function_mode_always_promote}
1074 if you would like to apply the same rules given by @code{PROMOTE_MODE}.
1077 @defmac PARM_BOUNDARY
1078 Normal alignment required for function parameters on the stack, in
1079 bits. All stack parameters receive at least this much alignment
1080 regardless of data type. On most machines, this is the same as the
1084 @defmac STACK_BOUNDARY
1085 Define this macro to the minimum alignment enforced by hardware for the
1086 stack pointer on this machine. The definition is a C expression for the
1087 desired alignment (measured in bits). This value is used as a default
1088 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
1089 this should be the same as @code{PARM_BOUNDARY}.
1092 @defmac PREFERRED_STACK_BOUNDARY
1093 Define this macro if you wish to preserve a certain alignment for the
1094 stack pointer, greater than what the hardware enforces. The definition
1095 is a C expression for the desired alignment (measured in bits). This
1096 macro must evaluate to a value equal to or larger than
1097 @code{STACK_BOUNDARY}.
1100 @defmac INCOMING_STACK_BOUNDARY
1101 Define this macro if the incoming stack boundary may be different
1102 from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate
1103 to a value equal to or larger than @code{STACK_BOUNDARY}.
1106 @defmac FUNCTION_BOUNDARY
1107 Alignment required for a function entry point, in bits.
1110 @defmac BIGGEST_ALIGNMENT
1111 Biggest alignment that any data type can require on this machine, in
1112 bits. Note that this is not the biggest alignment that is supported,
1113 just the biggest alignment that, when violated, may cause a fault.
1116 @defmac MALLOC_ABI_ALIGNMENT
1117 Alignment, in bits, a C conformant malloc implementation has to
1118 provide. If not defined, the default value is @code{BITS_PER_WORD}.
1121 @defmac ATTRIBUTE_ALIGNED_VALUE
1122 Alignment used by the @code{__attribute__ ((aligned))} construct. If
1123 not defined, the default value is @code{BIGGEST_ALIGNMENT}.
1126 @defmac MINIMUM_ATOMIC_ALIGNMENT
1127 If defined, the smallest alignment, in bits, that can be given to an
1128 object that can be referenced in one operation, without disturbing any
1129 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1130 on machines that don't have byte or half-word store operations.
1133 @defmac BIGGEST_FIELD_ALIGNMENT
1134 Biggest alignment that any structure or union field can require on this
1135 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1136 structure and union fields only, unless the field alignment has been set
1137 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1140 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1141 An expression for the alignment of a structure field @var{field} if the
1142 alignment computed in the usual way (including applying of
1143 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1144 alignment) is @var{computed}. It overrides alignment only if the
1145 field alignment has not been set by the
1146 @code{__attribute__ ((aligned (@var{n})))} construct.
1149 @defmac MAX_STACK_ALIGNMENT
1150 Biggest stack alignment guaranteed by the backend. Use this macro
1151 to specify the maximum alignment of a variable on stack.
1153 If not defined, the default value is @code{STACK_BOUNDARY}.
1155 @c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
1156 @c But the fix for PR 32893 indicates that we can only guarantee
1157 @c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
1158 @c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
1161 @defmac MAX_OFILE_ALIGNMENT
1162 Biggest alignment supported by the object file format of this machine.
1163 Use this macro to limit the alignment which can be specified using the
1164 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1165 the default value is @code{BIGGEST_ALIGNMENT}.
1167 On systems that use ELF, the default (in @file{config/elfos.h}) is
1168 the largest supported 32-bit ELF section alignment representable on
1169 a 32-bit host e.g. @samp{(((unsigned HOST_WIDEST_INT) 1 << 28) * 8)}.
1170 On 32-bit ELF the largest supported section alignment in bits is
1171 @samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
1174 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1175 If defined, a C expression to compute the alignment for a variable in
1176 the static store. @var{type} is the data type, and @var{basic-align} is
1177 the alignment that the object would ordinarily have. The value of this
1178 macro is used instead of that alignment to align the object.
1180 If this macro is not defined, then @var{basic-align} is used.
1183 One use of this macro is to increase alignment of medium-size data to
1184 make it all fit in fewer cache lines. Another is to cause character
1185 arrays to be word-aligned so that @code{strcpy} calls that copy
1186 constants to character arrays can be done inline.
1189 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1190 If defined, a C expression to compute the alignment given to a constant
1191 that is being placed in memory. @var{constant} is the constant and
1192 @var{basic-align} is the alignment that the object would ordinarily
1193 have. The value of this macro is used instead of that alignment to
1196 If this macro is not defined, then @var{basic-align} is used.
1198 The typical use of this macro is to increase alignment for string
1199 constants to be word aligned so that @code{strcpy} calls that copy
1200 constants can be done inline.
1203 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1204 If defined, a C expression to compute the alignment for a variable in
1205 the local store. @var{type} is the data type, and @var{basic-align} is
1206 the alignment that the object would ordinarily have. The value of this
1207 macro is used instead of that alignment to align the object.
1209 If this macro is not defined, then @var{basic-align} is used.
1211 One use of this macro is to increase alignment of medium-size data to
1212 make it all fit in fewer cache lines.
1215 @defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
1216 If defined, a C expression to compute the alignment for stack slot.
1217 @var{type} is the data type, @var{mode} is the widest mode available,
1218 and @var{basic-align} is the alignment that the slot would ordinarily
1219 have. The value of this macro is used instead of that alignment to
1222 If this macro is not defined, then @var{basic-align} is used when
1223 @var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will
1226 This macro is to set alignment of stack slot to the maximum alignment
1227 of all possible modes which the slot may have.
1230 @defmac LOCAL_DECL_ALIGNMENT (@var{decl})
1231 If defined, a C expression to compute the alignment for a local
1232 variable @var{decl}.
1234 If this macro is not defined, then
1235 @code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
1238 One use of this macro is to increase alignment of medium-size data to
1239 make it all fit in fewer cache lines.
1242 @defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
1243 If defined, a C expression to compute the minimum required alignment
1244 for dynamic stack realignment purposes for @var{exp} (a type or decl),
1245 @var{mode}, assuming normal alignment @var{align}.
1247 If this macro is not defined, then @var{align} will be used.
1250 @defmac EMPTY_FIELD_BOUNDARY
1251 Alignment in bits to be given to a structure bit-field that follows an
1252 empty field such as @code{int : 0;}.
1254 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1257 @defmac STRUCTURE_SIZE_BOUNDARY
1258 Number of bits which any structure or union's size must be a multiple of.
1259 Each structure or union's size is rounded up to a multiple of this.
1261 If you do not define this macro, the default is the same as
1262 @code{BITS_PER_UNIT}.
1265 @defmac STRICT_ALIGNMENT
1266 Define this macro to be the value 1 if instructions will fail to work
1267 if given data not on the nominal alignment. If instructions will merely
1268 go slower in that case, define this macro as 0.
1271 @defmac PCC_BITFIELD_TYPE_MATTERS
1272 Define this if you wish to imitate the way many other C compilers handle
1273 alignment of bit-fields and the structures that contain them.
1275 The behavior is that the type written for a named bit-field (@code{int},
1276 @code{short}, or other integer type) imposes an alignment for the entire
1277 structure, as if the structure really did contain an ordinary field of
1278 that type. In addition, the bit-field is placed within the structure so
1279 that it would fit within such a field, not crossing a boundary for it.
1281 Thus, on most machines, a named bit-field whose type is written as
1282 @code{int} would not cross a four-byte boundary, and would force
1283 four-byte alignment for the whole structure. (The alignment used may
1284 not be four bytes; it is controlled by the other alignment parameters.)
1286 An unnamed bit-field will not affect the alignment of the containing
1289 If the macro is defined, its definition should be a C expression;
1290 a nonzero value for the expression enables this behavior.
1292 Note that if this macro is not defined, or its value is zero, some
1293 bit-fields may cross more than one alignment boundary. The compiler can
1294 support such references if there are @samp{insv}, @samp{extv}, and
1295 @samp{extzv} insns that can directly reference memory.
1297 The other known way of making bit-fields work is to define
1298 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1299 Then every structure can be accessed with fullwords.
1301 Unless the machine has bit-field instructions or you define
1302 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1303 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1305 If your aim is to make GCC use the same conventions for laying out
1306 bit-fields as are used by another compiler, here is how to investigate
1307 what the other compiler does. Compile and run this program:
1326 printf ("Size of foo1 is %d\n",
1327 sizeof (struct foo1));
1328 printf ("Size of foo2 is %d\n",
1329 sizeof (struct foo2));
1334 If this prints 2 and 5, then the compiler's behavior is what you would
1335 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1338 @defmac BITFIELD_NBYTES_LIMITED
1339 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1340 to aligning a bit-field within the structure.
1343 @deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELD (void)
1344 When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
1345 whether unnamed bitfields affect the alignment of the containing
1346 structure. The hook should return true if the structure should inherit
1347 the alignment requirements of an unnamed bitfield's type.
1350 @deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELD (void)
1351 This target hook should return @code{true} if accesses to volatile bitfields
1352 should use the narrowest mode possible. It should return @code{false} if
1353 these accesses should use the bitfield container type.
1355 The default is @code{!TARGET_STRICT_ALIGN}.
1358 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1359 Return 1 if a structure or array containing @var{field} should be accessed using
1362 If @var{field} is the only field in the structure, @var{mode} is its
1363 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1364 case where structures of one field would require the structure's mode to
1365 retain the field's mode.
1367 Normally, this is not needed.
1370 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1371 Define this macro as an expression for the alignment of a type (given
1372 by @var{type} as a tree node) if the alignment computed in the usual
1373 way is @var{computed} and the alignment explicitly specified was
1376 The default is to use @var{specified} if it is larger; otherwise, use
1377 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1380 @defmac MAX_FIXED_MODE_SIZE
1381 An integer expression for the size in bits of the largest integer
1382 machine mode that should actually be used. All integer machine modes of
1383 this size or smaller can be used for structures and unions with the
1384 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1385 (DImode)} is assumed.
1388 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1389 If defined, an expression of type @code{enum machine_mode} that
1390 specifies the mode of the save area operand of a
1391 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1392 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1393 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1394 having its mode specified.
1396 You need not define this macro if it always returns @code{Pmode}. You
1397 would most commonly define this macro if the
1398 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1402 @defmac STACK_SIZE_MODE
1403 If defined, an expression of type @code{enum machine_mode} that
1404 specifies the mode of the size increment operand of an
1405 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1407 You need not define this macro if it always returns @code{word_mode}.
1408 You would most commonly define this macro if the @code{allocate_stack}
1409 pattern needs to support both a 32- and a 64-bit mode.
1412 @deftypefn {Target Hook} {enum machine_mode} TARGET_LIBGCC_CMP_RETURN_MODE (void)
1413 This target hook should return the mode to be used for the return value
1414 of compare instructions expanded to libgcc calls. If not defined
1415 @code{word_mode} is returned which is the right choice for a majority of
1419 @deftypefn {Target Hook} {enum machine_mode} TARGET_LIBGCC_SHIFT_COUNT_MODE (void)
1420 This target hook should return the mode to be used for the shift count operand
1421 of shift instructions expanded to libgcc calls. If not defined
1422 @code{word_mode} is returned which is the right choice for a majority of
1426 @deftypefn {Target Hook} {enum machine_mode} TARGET_UNWIND_WORD_MODE (void)
1427 Return machine mode to be used for @code{_Unwind_Word} type.
1428 The default is to use @code{word_mode}.
1431 @defmac ROUND_TOWARDS_ZERO
1432 If defined, this macro should be true if the prevailing rounding
1433 mode is towards zero.
1435 Defining this macro only affects the way @file{libgcc.a} emulates
1436 floating-point arithmetic.
1438 Not defining this macro is equivalent to returning zero.
1441 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1442 This macro should return true if floats with @var{size}
1443 bits do not have a NaN or infinity representation, but use the largest
1444 exponent for normal numbers instead.
1446 Defining this macro only affects the way @file{libgcc.a} emulates
1447 floating-point arithmetic.
1449 The default definition of this macro returns false for all sizes.
1452 @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (const_tree @var{record_type})
1453 This target hook returns @code{true} if bit-fields in the given
1454 @var{record_type} are to be laid out following the rules of Microsoft
1455 Visual C/C++, namely: (i) a bit-field won't share the same storage
1456 unit with the previous bit-field if their underlying types have
1457 different sizes, and the bit-field will be aligned to the highest
1458 alignment of the underlying types of itself and of the previous
1459 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1460 the whole enclosing structure, even if it is unnamed; except that
1461 (iii) a zero-sized bit-field will be disregarded unless it follows
1462 another bit-field of nonzero size. If this hook returns @code{true},
1463 other macros that control bit-field layout are ignored.
1465 When a bit-field is inserted into a packed record, the whole size
1466 of the underlying type is used by one or more same-size adjacent
1467 bit-fields (that is, if its long:3, 32 bits is used in the record,
1468 and any additional adjacent long bit-fields are packed into the same
1469 chunk of 32 bits. However, if the size changes, a new field of that
1470 size is allocated). In an unpacked record, this is the same as using
1471 alignment, but not equivalent when packing.
1473 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1474 the latter will take precedence. If @samp{__attribute__((packed))} is
1475 used on a single field when MS bit-fields are in use, it will take
1476 precedence for that field, but the alignment of the rest of the structure
1477 may affect its placement.
1480 @deftypefn {Target Hook} bool TARGET_DECIMAL_FLOAT_SUPPORTED_P (void)
1481 Returns true if the target supports decimal floating point.
1484 @deftypefn {Target Hook} bool TARGET_FIXED_POINT_SUPPORTED_P (void)
1485 Returns true if the target supports fixed-point arithmetic.
1488 @deftypefn {Target Hook} void TARGET_EXPAND_TO_RTL_HOOK (void)
1489 This hook is called just before expansion into rtl, allowing the target
1490 to perform additional initializations or analysis before the expansion.
1491 For example, the rs6000 port uses it to allocate a scratch stack slot
1492 for use in copying SDmode values between memory and floating point
1493 registers whenever the function being expanded has any SDmode
1497 @deftypefn {Target Hook} void TARGET_INSTANTIATE_DECLS (void)
1498 This hook allows the backend to perform additional instantiations on rtl
1499 that are not actually in any insns yet, but will be later.
1502 @deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (const_tree @var{type})
1503 If your target defines any fundamental types, or any types your target
1504 uses should be mangled differently from the default, define this hook
1505 to return the appropriate encoding for these types as part of a C++
1506 mangled name. The @var{type} argument is the tree structure representing
1507 the type to be mangled. The hook may be applied to trees which are
1508 not target-specific fundamental types; it should return @code{NULL}
1509 for all such types, as well as arguments it does not recognize. If the
1510 return value is not @code{NULL}, it must point to a statically-allocated
1513 Target-specific fundamental types might be new fundamental types or
1514 qualified versions of ordinary fundamental types. Encode new
1515 fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
1516 is the name used for the type in source code, and @var{n} is the
1517 length of @var{name} in decimal. Encode qualified versions of
1518 ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
1519 @var{name} is the name used for the type qualifier in source code,
1520 @var{n} is the length of @var{name} as above, and @var{code} is the
1521 code used to represent the unqualified version of this type. (See
1522 @code{write_builtin_type} in @file{cp/mangle.c} for the list of
1523 codes.) In both cases the spaces are for clarity; do not include any
1524 spaces in your string.
1526 This hook is applied to types prior to typedef resolution. If the mangled
1527 name for a particular type depends only on that type's main variant, you
1528 can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT}
1531 The default version of this hook always returns @code{NULL}, which is
1532 appropriate for a target that does not define any new fundamental
1537 @section Layout of Source Language Data Types
1539 These macros define the sizes and other characteristics of the standard
1540 basic data types used in programs being compiled. Unlike the macros in
1541 the previous section, these apply to specific features of C and related
1542 languages, rather than to fundamental aspects of storage layout.
1544 @defmac INT_TYPE_SIZE
1545 A C expression for the size in bits of the type @code{int} on the
1546 target machine. If you don't define this, the default is one word.
1549 @defmac SHORT_TYPE_SIZE
1550 A C expression for the size in bits of the type @code{short} on the
1551 target machine. If you don't define this, the default is half a word.
1552 (If this would be less than one storage unit, it is rounded up to one
1556 @defmac LONG_TYPE_SIZE
1557 A C expression for the size in bits of the type @code{long} on the
1558 target machine. If you don't define this, the default is one word.
1561 @defmac ADA_LONG_TYPE_SIZE
1562 On some machines, the size used for the Ada equivalent of the type
1563 @code{long} by a native Ada compiler differs from that used by C@. In
1564 that situation, define this macro to be a C expression to be used for
1565 the size of that type. If you don't define this, the default is the
1566 value of @code{LONG_TYPE_SIZE}.
1569 @defmac LONG_LONG_TYPE_SIZE
1570 A C expression for the size in bits of the type @code{long long} on the
1571 target machine. If you don't define this, the default is two
1572 words. If you want to support GNU Ada on your machine, the value of this
1573 macro must be at least 64.
1576 @defmac CHAR_TYPE_SIZE
1577 A C expression for the size in bits of the type @code{char} on the
1578 target machine. If you don't define this, the default is
1579 @code{BITS_PER_UNIT}.
1582 @defmac BOOL_TYPE_SIZE
1583 A C expression for the size in bits of the C++ type @code{bool} and
1584 C99 type @code{_Bool} on the target machine. If you don't define
1585 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1588 @defmac FLOAT_TYPE_SIZE
1589 A C expression for the size in bits of the type @code{float} on the
1590 target machine. If you don't define this, the default is one word.
1593 @defmac DOUBLE_TYPE_SIZE
1594 A C expression for the size in bits of the type @code{double} on the
1595 target machine. If you don't define this, the default is two
1599 @defmac LONG_DOUBLE_TYPE_SIZE
1600 A C expression for the size in bits of the type @code{long double} on
1601 the target machine. If you don't define this, the default is two
1605 @defmac SHORT_FRACT_TYPE_SIZE
1606 A C expression for the size in bits of the type @code{short _Fract} on
1607 the target machine. If you don't define this, the default is
1608 @code{BITS_PER_UNIT}.
1611 @defmac FRACT_TYPE_SIZE
1612 A C expression for the size in bits of the type @code{_Fract} on
1613 the target machine. If you don't define this, the default is
1614 @code{BITS_PER_UNIT * 2}.
1617 @defmac LONG_FRACT_TYPE_SIZE
1618 A C expression for the size in bits of the type @code{long _Fract} on
1619 the target machine. If you don't define this, the default is
1620 @code{BITS_PER_UNIT * 4}.
1623 @defmac LONG_LONG_FRACT_TYPE_SIZE
1624 A C expression for the size in bits of the type @code{long long _Fract} on
1625 the target machine. If you don't define this, the default is
1626 @code{BITS_PER_UNIT * 8}.
1629 @defmac SHORT_ACCUM_TYPE_SIZE
1630 A C expression for the size in bits of the type @code{short _Accum} on
1631 the target machine. If you don't define this, the default is
1632 @code{BITS_PER_UNIT * 2}.
1635 @defmac ACCUM_TYPE_SIZE
1636 A C expression for the size in bits of the type @code{_Accum} on
1637 the target machine. If you don't define this, the default is
1638 @code{BITS_PER_UNIT * 4}.
1641 @defmac LONG_ACCUM_TYPE_SIZE
1642 A C expression for the size in bits of the type @code{long _Accum} on
1643 the target machine. If you don't define this, the default is
1644 @code{BITS_PER_UNIT * 8}.
1647 @defmac LONG_LONG_ACCUM_TYPE_SIZE
1648 A C expression for the size in bits of the type @code{long long _Accum} on
1649 the target machine. If you don't define this, the default is
1650 @code{BITS_PER_UNIT * 16}.
1653 @defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE
1654 Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or
1655 if you want routines in @file{libgcc2.a} for a size other than
1656 @code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the
1657 default is @code{LONG_DOUBLE_TYPE_SIZE}.
1660 @defmac LIBGCC2_HAS_DF_MODE
1661 Define this macro if neither @code{LIBGCC2_DOUBLE_TYPE_SIZE} nor
1662 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is
1663 @code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a}
1664 anyway. If you don't define this and either @code{LIBGCC2_DOUBLE_TYPE_SIZE}
1665 or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1,
1669 @defmac LIBGCC2_HAS_XF_MODE
1670 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1671 @code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a}
1672 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1673 is 80 then the default is 1, otherwise it is 0.
1676 @defmac LIBGCC2_HAS_TF_MODE
1677 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1678 @code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a}
1679 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1680 is 128 then the default is 1, otherwise it is 0.
1687 Define these macros to be the size in bits of the mantissa of
1688 @code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values,
1689 if the defaults in @file{libgcc2.h} are inappropriate. By default,
1690 @code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG}
1691 for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or
1692 @code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether
1693 @code{LIBGCC2_DOUBLE_TYPE_SIZE} or
1694 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64.
1697 @defmac TARGET_FLT_EVAL_METHOD
1698 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1699 assuming, if applicable, that the floating-point control word is in its
1700 default state. If you do not define this macro the value of
1701 @code{FLT_EVAL_METHOD} will be zero.
1704 @defmac WIDEST_HARDWARE_FP_SIZE
1705 A C expression for the size in bits of the widest floating-point format
1706 supported by the hardware. If you define this macro, you must specify a
1707 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1708 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1712 @defmac DEFAULT_SIGNED_CHAR
1713 An expression whose value is 1 or 0, according to whether the type
1714 @code{char} should be signed or unsigned by default. The user can
1715 always override this default with the options @option{-fsigned-char}
1716 and @option{-funsigned-char}.
1719 @deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void)
1720 This target hook should return true if the compiler should give an
1721 @code{enum} type only as many bytes as it takes to represent the range
1722 of possible values of that type. It should return false if all
1723 @code{enum} types should be allocated like @code{int}.
1725 The default is to return false.
1729 A C expression for a string describing the name of the data type to use
1730 for size values. The typedef name @code{size_t} is defined using the
1731 contents of the string.
1733 The string can contain more than one keyword. If so, separate them with
1734 spaces, and write first any length keyword, then @code{unsigned} if
1735 appropriate, and finally @code{int}. The string must exactly match one
1736 of the data type names defined in the function
1737 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1738 omit @code{int} or change the order---that would cause the compiler to
1741 If you don't define this macro, the default is @code{"long unsigned
1745 @defmac PTRDIFF_TYPE
1746 A C expression for a string describing the name of the data type to use
1747 for the result of subtracting two pointers. The typedef name
1748 @code{ptrdiff_t} is defined using the contents of the string. See
1749 @code{SIZE_TYPE} above for more information.
1751 If you don't define this macro, the default is @code{"long int"}.
1755 A C expression for a string describing the name of the data type to use
1756 for wide characters. The typedef name @code{wchar_t} is defined using
1757 the contents of the string. See @code{SIZE_TYPE} above for more
1760 If you don't define this macro, the default is @code{"int"}.
1763 @defmac WCHAR_TYPE_SIZE
1764 A C expression for the size in bits of the data type for wide
1765 characters. This is used in @code{cpp}, which cannot make use of
1770 A C expression for a string describing the name of the data type to
1771 use for wide characters passed to @code{printf} and returned from
1772 @code{getwc}. The typedef name @code{wint_t} is defined using the
1773 contents of the string. See @code{SIZE_TYPE} above for more
1776 If you don't define this macro, the default is @code{"unsigned int"}.
1780 A C expression for a string describing the name of the data type that
1781 can represent any value of any standard or extended signed integer type.
1782 The typedef name @code{intmax_t} is defined using the contents of the
1783 string. See @code{SIZE_TYPE} above for more information.
1785 If you don't define this macro, the default is the first of
1786 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1787 much precision as @code{long long int}.
1790 @defmac UINTMAX_TYPE
1791 A C expression for a string describing the name of the data type that
1792 can represent any value of any standard or extended unsigned integer
1793 type. The typedef name @code{uintmax_t} is defined using the contents
1794 of the string. See @code{SIZE_TYPE} above for more information.
1796 If you don't define this macro, the default is the first of
1797 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1798 unsigned int"} that has as much precision as @code{long long unsigned
1802 @defmac SIG_ATOMIC_TYPE
1808 @defmacx UINT16_TYPE
1809 @defmacx UINT32_TYPE
1810 @defmacx UINT64_TYPE
1811 @defmacx INT_LEAST8_TYPE
1812 @defmacx INT_LEAST16_TYPE
1813 @defmacx INT_LEAST32_TYPE
1814 @defmacx INT_LEAST64_TYPE
1815 @defmacx UINT_LEAST8_TYPE
1816 @defmacx UINT_LEAST16_TYPE
1817 @defmacx UINT_LEAST32_TYPE
1818 @defmacx UINT_LEAST64_TYPE
1819 @defmacx INT_FAST8_TYPE
1820 @defmacx INT_FAST16_TYPE
1821 @defmacx INT_FAST32_TYPE
1822 @defmacx INT_FAST64_TYPE
1823 @defmacx UINT_FAST8_TYPE
1824 @defmacx UINT_FAST16_TYPE
1825 @defmacx UINT_FAST32_TYPE
1826 @defmacx UINT_FAST64_TYPE
1827 @defmacx INTPTR_TYPE
1828 @defmacx UINTPTR_TYPE
1829 C expressions for the standard types @code{sig_atomic_t},
1830 @code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
1831 @code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
1832 @code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
1833 @code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
1834 @code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
1835 @code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
1836 @code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
1837 @code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See
1838 @code{SIZE_TYPE} above for more information.
1840 If any of these macros evaluates to a null pointer, the corresponding
1841 type is not supported; if GCC is configured to provide
1842 @code{<stdint.h>} in such a case, the header provided may not conform
1843 to C99, depending on the type in question. The defaults for all of
1844 these macros are null pointers.
1847 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1848 The C++ compiler represents a pointer-to-member-function with a struct
1855 ptrdiff_t vtable_index;
1862 The C++ compiler must use one bit to indicate whether the function that
1863 will be called through a pointer-to-member-function is virtual.
1864 Normally, we assume that the low-order bit of a function pointer must
1865 always be zero. Then, by ensuring that the vtable_index is odd, we can
1866 distinguish which variant of the union is in use. But, on some
1867 platforms function pointers can be odd, and so this doesn't work. In
1868 that case, we use the low-order bit of the @code{delta} field, and shift
1869 the remainder of the @code{delta} field to the left.
1871 GCC will automatically make the right selection about where to store
1872 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1873 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1874 set such that functions always start at even addresses, but the lowest
1875 bit of pointers to functions indicate whether the function at that
1876 address is in ARM or Thumb mode. If this is the case of your
1877 architecture, you should define this macro to
1878 @code{ptrmemfunc_vbit_in_delta}.
1880 In general, you should not have to define this macro. On architectures
1881 in which function addresses are always even, according to
1882 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1883 @code{ptrmemfunc_vbit_in_pfn}.
1886 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1887 Normally, the C++ compiler uses function pointers in vtables. This
1888 macro allows the target to change to use ``function descriptors''
1889 instead. Function descriptors are found on targets for whom a
1890 function pointer is actually a small data structure. Normally the
1891 data structure consists of the actual code address plus a data
1892 pointer to which the function's data is relative.
1894 If vtables are used, the value of this macro should be the number
1895 of words that the function descriptor occupies.
1898 @defmac TARGET_VTABLE_ENTRY_ALIGN
1899 By default, the vtable entries are void pointers, the so the alignment
1900 is the same as pointer alignment. The value of this macro specifies
1901 the alignment of the vtable entry in bits. It should be defined only
1902 when special alignment is necessary. */
1905 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1906 There are a few non-descriptor entries in the vtable at offsets below
1907 zero. If these entries must be padded (say, to preserve the alignment
1908 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1909 of words in each data entry.
1913 @section Register Usage
1914 @cindex register usage
1916 This section explains how to describe what registers the target machine
1917 has, and how (in general) they can be used.
1919 The description of which registers a specific instruction can use is
1920 done with register classes; see @ref{Register Classes}. For information
1921 on using registers to access a stack frame, see @ref{Frame Registers}.
1922 For passing values in registers, see @ref{Register Arguments}.
1923 For returning values in registers, see @ref{Scalar Return}.
1926 * Register Basics:: Number and kinds of registers.
1927 * Allocation Order:: Order in which registers are allocated.
1928 * Values in Registers:: What kinds of values each reg can hold.
1929 * Leaf Functions:: Renumbering registers for leaf functions.
1930 * Stack Registers:: Handling a register stack such as 80387.
1933 @node Register Basics
1934 @subsection Basic Characteristics of Registers
1936 @c prevent bad page break with this line
1937 Registers have various characteristics.
1939 @defmac FIRST_PSEUDO_REGISTER
1940 Number of hardware registers known to the compiler. They receive
1941 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1942 pseudo register's number really is assigned the number
1943 @code{FIRST_PSEUDO_REGISTER}.
1946 @defmac FIXED_REGISTERS
1947 @cindex fixed register
1948 An initializer that says which registers are used for fixed purposes
1949 all throughout the compiled code and are therefore not available for
1950 general allocation. These would include the stack pointer, the frame
1951 pointer (except on machines where that can be used as a general
1952 register when no frame pointer is needed), the program counter on
1953 machines where that is considered one of the addressable registers,
1954 and any other numbered register with a standard use.
1956 This information is expressed as a sequence of numbers, separated by
1957 commas and surrounded by braces. The @var{n}th number is 1 if
1958 register @var{n} is fixed, 0 otherwise.
1960 The table initialized from this macro, and the table initialized by
1961 the following one, may be overridden at run time either automatically,
1962 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1963 the user with the command options @option{-ffixed-@var{reg}},
1964 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1967 @defmac CALL_USED_REGISTERS
1968 @cindex call-used register
1969 @cindex call-clobbered register
1970 @cindex call-saved register
1971 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1972 clobbered (in general) by function calls as well as for fixed
1973 registers. This macro therefore identifies the registers that are not
1974 available for general allocation of values that must live across
1977 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1978 automatically saves it on function entry and restores it on function
1979 exit, if the register is used within the function.
1982 @defmac CALL_REALLY_USED_REGISTERS
1983 @cindex call-used register
1984 @cindex call-clobbered register
1985 @cindex call-saved register
1986 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1987 that the entire set of @code{FIXED_REGISTERS} be included.
1988 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1989 This macro is optional. If not specified, it defaults to the value
1990 of @code{CALL_USED_REGISTERS}.
1993 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1994 @cindex call-used register
1995 @cindex call-clobbered register
1996 @cindex call-saved register
1997 A C expression that is nonzero if it is not permissible to store a
1998 value of mode @var{mode} in hard register number @var{regno} across a
1999 call without some part of it being clobbered. For most machines this
2000 macro need not be defined. It is only required for machines that do not
2001 preserve the entire contents of a register across a call.
2005 @findex call_used_regs
2008 @findex reg_class_contents
2009 @defmac CONDITIONAL_REGISTER_USAGE
2010 Zero or more C statements that may conditionally modify five variables
2011 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
2012 @code{reg_names}, and @code{reg_class_contents}, to take into account
2013 any dependence of these register sets on target flags. The first three
2014 of these are of type @code{char []} (interpreted as Boolean vectors).
2015 @code{global_regs} is a @code{const char *[]}, and
2016 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
2017 called, @code{fixed_regs}, @code{call_used_regs},
2018 @code{reg_class_contents}, and @code{reg_names} have been initialized
2019 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
2020 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
2021 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
2022 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
2023 command options have been applied.
2025 You need not define this macro if it has no work to do.
2027 @cindex disabling certain registers
2028 @cindex controlling register usage
2029 If the usage of an entire class of registers depends on the target
2030 flags, you may indicate this to GCC by using this macro to modify
2031 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
2032 registers in the classes which should not be used by GCC@. Also define
2033 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
2034 to return @code{NO_REGS} if it
2035 is called with a letter for a class that shouldn't be used.
2037 (However, if this class is not included in @code{GENERAL_REGS} and all
2038 of the insn patterns whose constraints permit this class are
2039 controlled by target switches, then GCC will automatically avoid using
2040 these registers when the target switches are opposed to them.)
2043 @defmac INCOMING_REGNO (@var{out})
2044 Define this macro if the target machine has register windows. This C
2045 expression returns the register number as seen by the called function
2046 corresponding to the register number @var{out} as seen by the calling
2047 function. Return @var{out} if register number @var{out} is not an
2051 @defmac OUTGOING_REGNO (@var{in})
2052 Define this macro if the target machine has register windows. This C
2053 expression returns the register number as seen by the calling function
2054 corresponding to the register number @var{in} as seen by the called
2055 function. Return @var{in} if register number @var{in} is not an inbound
2059 @defmac LOCAL_REGNO (@var{regno})
2060 Define this macro if the target machine has register windows. This C
2061 expression returns true if the register is call-saved but is in the
2062 register window. Unlike most call-saved registers, such registers
2063 need not be explicitly restored on function exit or during non-local
2068 If the program counter has a register number, define this as that
2069 register number. Otherwise, do not define it.
2072 @node Allocation Order
2073 @subsection Order of Allocation of Registers
2074 @cindex order of register allocation
2075 @cindex register allocation order
2077 @c prevent bad page break with this line
2078 Registers are allocated in order.
2080 @defmac REG_ALLOC_ORDER
2081 If defined, an initializer for a vector of integers, containing the
2082 numbers of hard registers in the order in which GCC should prefer
2083 to use them (from most preferred to least).
2085 If this macro is not defined, registers are used lowest numbered first
2086 (all else being equal).
2088 One use of this macro is on machines where the highest numbered
2089 registers must always be saved and the save-multiple-registers
2090 instruction supports only sequences of consecutive registers. On such
2091 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
2092 the highest numbered allocable register first.
2095 @defmac ADJUST_REG_ALLOC_ORDER
2096 A C statement (sans semicolon) to choose the order in which to allocate
2097 hard registers for pseudo-registers local to a basic block.
2099 Store the desired register order in the array @code{reg_alloc_order}.
2100 Element 0 should be the register to allocate first; element 1, the next
2101 register; and so on.
2103 The macro body should not assume anything about the contents of
2104 @code{reg_alloc_order} before execution of the macro.
2106 On most machines, it is not necessary to define this macro.
2109 @defmac HONOR_REG_ALLOC_ORDER
2110 Normally, IRA tries to estimate the costs for saving a register in the
2111 prologue and restoring it in the epilogue. This discourages it from
2112 using call-saved registers. If a machine wants to ensure that IRA
2113 allocates registers in the order given by REG_ALLOC_ORDER even if some
2114 call-saved registers appear earlier than call-used ones, this macro
2118 @defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
2119 In some case register allocation order is not enough for the
2120 Integrated Register Allocator (@acronym{IRA}) to generate a good code.
2121 If this macro is defined, it should return a floating point value
2122 based on @var{regno}. The cost of using @var{regno} for a pseudo will
2123 be increased by approximately the pseudo's usage frequency times the
2124 value returned by this macro. Not defining this macro is equivalent
2125 to having it always return @code{0.0}.
2127 On most machines, it is not necessary to define this macro.
2130 @node Values in Registers
2131 @subsection How Values Fit in Registers
2133 This section discusses the macros that describe which kinds of values
2134 (specifically, which machine modes) each register can hold, and how many
2135 consecutive registers are needed for a given mode.
2137 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
2138 A C expression for the number of consecutive hard registers, starting
2139 at register number @var{regno}, required to hold a value of mode
2140 @var{mode}. This macro must never return zero, even if a register
2141 cannot hold the requested mode - indicate that with HARD_REGNO_MODE_OK
2142 and/or CANNOT_CHANGE_MODE_CLASS instead.
2144 On a machine where all registers are exactly one word, a suitable
2145 definition of this macro is
2148 #define HARD_REGNO_NREGS(REGNO, MODE) \
2149 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
2154 @defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
2155 A C expression that is nonzero if a value of mode @var{mode}, stored
2156 in memory, ends with padding that causes it to take up more space than
2157 in registers starting at register number @var{regno} (as determined by
2158 multiplying GCC's notion of the size of the register when containing
2159 this mode by the number of registers returned by
2160 @code{HARD_REGNO_NREGS}). By default this is zero.
2162 For example, if a floating-point value is stored in three 32-bit
2163 registers but takes up 128 bits in memory, then this would be
2166 This macros only needs to be defined if there are cases where
2167 @code{subreg_get_info}
2168 would otherwise wrongly determine that a @code{subreg} can be
2169 represented by an offset to the register number, when in fact such a
2170 @code{subreg} would contain some of the padding not stored in
2171 registers and so not be representable.
2174 @defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
2175 For values of @var{regno} and @var{mode} for which
2176 @code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
2177 returning the greater number of registers required to hold the value
2178 including any padding. In the example above, the value would be four.
2181 @defmac REGMODE_NATURAL_SIZE (@var{mode})
2182 Define this macro if the natural size of registers that hold values
2183 of mode @var{mode} is not the word size. It is a C expression that
2184 should give the natural size in bytes for the specified mode. It is
2185 used by the register allocator to try to optimize its results. This
2186 happens for example on SPARC 64-bit where the natural size of
2187 floating-point registers is still 32-bit.
2190 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
2191 A C expression that is nonzero if it is permissible to store a value
2192 of mode @var{mode} in hard register number @var{regno} (or in several
2193 registers starting with that one). For a machine where all registers
2194 are equivalent, a suitable definition is
2197 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
2200 You need not include code to check for the numbers of fixed registers,
2201 because the allocation mechanism considers them to be always occupied.
2203 @cindex register pairs
2204 On some machines, double-precision values must be kept in even/odd
2205 register pairs. You can implement that by defining this macro to reject
2206 odd register numbers for such modes.
2208 The minimum requirement for a mode to be OK in a register is that the
2209 @samp{mov@var{mode}} instruction pattern support moves between the
2210 register and other hard register in the same class and that moving a
2211 value into the register and back out not alter it.
2213 Since the same instruction used to move @code{word_mode} will work for
2214 all narrower integer modes, it is not necessary on any machine for
2215 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
2216 you define patterns @samp{movhi}, etc., to take advantage of this. This
2217 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
2218 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
2221 Many machines have special registers for floating point arithmetic.
2222 Often people assume that floating point machine modes are allowed only
2223 in floating point registers. This is not true. Any registers that
2224 can hold integers can safely @emph{hold} a floating point machine
2225 mode, whether or not floating arithmetic can be done on it in those
2226 registers. Integer move instructions can be used to move the values.
2228 On some machines, though, the converse is true: fixed-point machine
2229 modes may not go in floating registers. This is true if the floating
2230 registers normalize any value stored in them, because storing a
2231 non-floating value there would garble it. In this case,
2232 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2233 floating registers. But if the floating registers do not automatically
2234 normalize, if you can store any bit pattern in one and retrieve it
2235 unchanged without a trap, then any machine mode may go in a floating
2236 register, so you can define this macro to say so.
2238 The primary significance of special floating registers is rather that
2239 they are the registers acceptable in floating point arithmetic
2240 instructions. However, this is of no concern to
2241 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2242 constraints for those instructions.
2244 On some machines, the floating registers are especially slow to access,
2245 so that it is better to store a value in a stack frame than in such a
2246 register if floating point arithmetic is not being done. As long as the
2247 floating registers are not in class @code{GENERAL_REGS}, they will not
2248 be used unless some pattern's constraint asks for one.
2251 @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
2252 A C expression that is nonzero if it is OK to rename a hard register
2253 @var{from} to another hard register @var{to}.
2255 One common use of this macro is to prevent renaming of a register to
2256 another register that is not saved by a prologue in an interrupt
2259 The default is always nonzero.
2262 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2263 A C expression that is nonzero if a value of mode
2264 @var{mode1} is accessible in mode @var{mode2} without copying.
2266 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2267 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2268 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2269 should be nonzero. If they differ for any @var{r}, you should define
2270 this macro to return zero unless some other mechanism ensures the
2271 accessibility of the value in a narrower mode.
2273 You should define this macro to return nonzero in as many cases as
2274 possible since doing so will allow GCC to perform better register
2278 @deftypefn {Target Hook} bool TARGET_HARD_REGNO_SCRATCH_OK (unsigned int @var{regno})
2279 This target hook should return @code{true} if it is OK to use a hard register
2280 @var{regno} as scratch reg in peephole2.
2282 One common use of this macro is to prevent using of a register that
2283 is not saved by a prologue in an interrupt handler.
2285 The default version of this hook always returns @code{true}.
2288 @defmac AVOID_CCMODE_COPIES
2289 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2290 registers. You should only define this macro if support for copying to/from
2291 @code{CCmode} is incomplete.
2294 @node Leaf Functions
2295 @subsection Handling Leaf Functions
2297 @cindex leaf functions
2298 @cindex functions, leaf
2299 On some machines, a leaf function (i.e., one which makes no calls) can run
2300 more efficiently if it does not make its own register window. Often this
2301 means it is required to receive its arguments in the registers where they
2302 are passed by the caller, instead of the registers where they would
2305 The special treatment for leaf functions generally applies only when
2306 other conditions are met; for example, often they may use only those
2307 registers for its own variables and temporaries. We use the term ``leaf
2308 function'' to mean a function that is suitable for this special
2309 handling, so that functions with no calls are not necessarily ``leaf
2312 GCC assigns register numbers before it knows whether the function is
2313 suitable for leaf function treatment. So it needs to renumber the
2314 registers in order to output a leaf function. The following macros
2317 @defmac LEAF_REGISTERS
2318 Name of a char vector, indexed by hard register number, which
2319 contains 1 for a register that is allowable in a candidate for leaf
2322 If leaf function treatment involves renumbering the registers, then the
2323 registers marked here should be the ones before renumbering---those that
2324 GCC would ordinarily allocate. The registers which will actually be
2325 used in the assembler code, after renumbering, should not be marked with 1
2328 Define this macro only if the target machine offers a way to optimize
2329 the treatment of leaf functions.
2332 @defmac LEAF_REG_REMAP (@var{regno})
2333 A C expression whose value is the register number to which @var{regno}
2334 should be renumbered, when a function is treated as a leaf function.
2336 If @var{regno} is a register number which should not appear in a leaf
2337 function before renumbering, then the expression should yield @minus{}1, which
2338 will cause the compiler to abort.
2340 Define this macro only if the target machine offers a way to optimize the
2341 treatment of leaf functions, and registers need to be renumbered to do
2345 @findex current_function_is_leaf
2346 @findex current_function_uses_only_leaf_regs
2347 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2348 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2349 specially. They can test the C variable @code{current_function_is_leaf}
2350 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2351 set prior to local register allocation and is valid for the remaining
2352 compiler passes. They can also test the C variable
2353 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2354 functions which only use leaf registers.
2355 @code{current_function_uses_only_leaf_regs} is valid after all passes
2356 that modify the instructions have been run and is only useful if
2357 @code{LEAF_REGISTERS} is defined.
2358 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2359 @c of the next paragraph?! --mew 2feb93
2361 @node Stack Registers
2362 @subsection Registers That Form a Stack
2364 There are special features to handle computers where some of the
2365 ``registers'' form a stack. Stack registers are normally written by
2366 pushing onto the stack, and are numbered relative to the top of the
2369 Currently, GCC can only handle one group of stack-like registers, and
2370 they must be consecutively numbered. Furthermore, the existing
2371 support for stack-like registers is specific to the 80387 floating
2372 point coprocessor. If you have a new architecture that uses
2373 stack-like registers, you will need to do substantial work on
2374 @file{reg-stack.c} and write your machine description to cooperate
2375 with it, as well as defining these macros.
2378 Define this if the machine has any stack-like registers.
2381 @defmac STACK_REG_COVER_CLASS
2382 This is a cover class containing the stack registers. Define this if
2383 the machine has any stack-like registers.
2386 @defmac FIRST_STACK_REG
2387 The number of the first stack-like register. This one is the top
2391 @defmac LAST_STACK_REG
2392 The number of the last stack-like register. This one is the bottom of
2396 @node Register Classes
2397 @section Register Classes
2398 @cindex register class definitions
2399 @cindex class definitions, register
2401 On many machines, the numbered registers are not all equivalent.
2402 For example, certain registers may not be allowed for indexed addressing;
2403 certain registers may not be allowed in some instructions. These machine
2404 restrictions are described to the compiler using @dfn{register classes}.
2406 You define a number of register classes, giving each one a name and saying
2407 which of the registers belong to it. Then you can specify register classes
2408 that are allowed as operands to particular instruction patterns.
2412 In general, each register will belong to several classes. In fact, one
2413 class must be named @code{ALL_REGS} and contain all the registers. Another
2414 class must be named @code{NO_REGS} and contain no registers. Often the
2415 union of two classes will be another class; however, this is not required.
2417 @findex GENERAL_REGS
2418 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2419 terribly special about the name, but the operand constraint letters
2420 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2421 the same as @code{ALL_REGS}, just define it as a macro which expands
2424 Order the classes so that if class @var{x} is contained in class @var{y}
2425 then @var{x} has a lower class number than @var{y}.
2427 The way classes other than @code{GENERAL_REGS} are specified in operand
2428 constraints is through machine-dependent operand constraint letters.
2429 You can define such letters to correspond to various classes, then use
2430 them in operand constraints.
2432 You should define a class for the union of two classes whenever some
2433 instruction allows both classes. For example, if an instruction allows
2434 either a floating point (coprocessor) register or a general register for a
2435 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2436 which includes both of them. Otherwise you will get suboptimal code.
2438 You must also specify certain redundant information about the register
2439 classes: for each class, which classes contain it and which ones are
2440 contained in it; for each pair of classes, the largest class contained
2443 When a value occupying several consecutive registers is expected in a
2444 certain class, all the registers used must belong to that class.
2445 Therefore, register classes cannot be used to enforce a requirement for
2446 a register pair to start with an even-numbered register. The way to
2447 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2449 Register classes used for input-operands of bitwise-and or shift
2450 instructions have a special requirement: each such class must have, for
2451 each fixed-point machine mode, a subclass whose registers can transfer that
2452 mode to or from memory. For example, on some machines, the operations for
2453 single-byte values (@code{QImode}) are limited to certain registers. When
2454 this is so, each register class that is used in a bitwise-and or shift
2455 instruction must have a subclass consisting of registers from which
2456 single-byte values can be loaded or stored. This is so that
2457 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2459 @deftp {Data type} {enum reg_class}
2460 An enumerated type that must be defined with all the register class names
2461 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
2462 must be the last register class, followed by one more enumerated value,
2463 @code{LIM_REG_CLASSES}, which is not a register class but rather
2464 tells how many classes there are.
2466 Each register class has a number, which is the value of casting
2467 the class name to type @code{int}. The number serves as an index
2468 in many of the tables described below.
2471 @defmac N_REG_CLASSES
2472 The number of distinct register classes, defined as follows:
2475 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2479 @defmac REG_CLASS_NAMES
2480 An initializer containing the names of the register classes as C string
2481 constants. These names are used in writing some of the debugging dumps.
2484 @defmac REG_CLASS_CONTENTS
2485 An initializer containing the contents of the register classes, as integers
2486 which are bit masks. The @var{n}th integer specifies the contents of class
2487 @var{n}. The way the integer @var{mask} is interpreted is that
2488 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2490 When the machine has more than 32 registers, an integer does not suffice.
2491 Then the integers are replaced by sub-initializers, braced groupings containing
2492 several integers. Each sub-initializer must be suitable as an initializer
2493 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2494 In this situation, the first integer in each sub-initializer corresponds to
2495 registers 0 through 31, the second integer to registers 32 through 63, and
2499 @defmac REGNO_REG_CLASS (@var{regno})
2500 A C expression whose value is a register class containing hard register
2501 @var{regno}. In general there is more than one such class; choose a class
2502 which is @dfn{minimal}, meaning that no smaller class also contains the
2506 @defmac BASE_REG_CLASS
2507 A macro whose definition is the name of the class to which a valid
2508 base register must belong. A base register is one used in an address
2509 which is the register value plus a displacement.
2512 @defmac MODE_BASE_REG_CLASS (@var{mode})
2513 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2514 the selection of a base register in a mode dependent manner. If
2515 @var{mode} is VOIDmode then it should return the same value as
2516 @code{BASE_REG_CLASS}.
2519 @defmac MODE_BASE_REG_REG_CLASS (@var{mode})
2520 A C expression whose value is the register class to which a valid
2521 base register must belong in order to be used in a base plus index
2522 register address. You should define this macro if base plus index
2523 addresses have different requirements than other base register uses.
2526 @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code})
2527 A C expression whose value is the register class to which a valid
2528 base register must belong. @var{outer_code} and @var{index_code} define the
2529 context in which the base register occurs. @var{outer_code} is the code of
2530 the immediately enclosing expression (@code{MEM} for the top level of an
2531 address, @code{ADDRESS} for something that occurs in an
2532 @code{address_operand}). @var{index_code} is the code of the corresponding
2533 index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
2536 @defmac INDEX_REG_CLASS
2537 A macro whose definition is the name of the class to which a valid
2538 index register must belong. An index register is one used in an
2539 address where its value is either multiplied by a scale factor or
2540 added to another register (as well as added to a displacement).
2543 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2544 A C expression which is nonzero if register number @var{num} is
2545 suitable for use as a base register in operand addresses.
2546 Like @code{TARGET_LEGITIMATE_ADDRESS_P}, this macro should also
2547 define a strict and a non-strict variant. Both variants behave
2548 the same for hard register; for pseudos, the strict variant will
2549 pass only those that have been allocated to a valid hard registers,
2550 while the non-strict variant will pass all pseudos.
2552 @findex REG_OK_STRICT
2553 Compiler source files that want to use the strict variant of this and
2554 other macros define the macro @code{REG_OK_STRICT}. You should use an
2555 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant in
2556 that case and the non-strict variant otherwise.
2559 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2560 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2561 that expression may examine the mode of the memory reference in
2562 @var{mode}. You should define this macro if the mode of the memory
2563 reference affects whether a register may be used as a base register. If
2564 you define this macro, the compiler will use it instead of
2565 @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for
2566 addresses that appear outside a @code{MEM}, i.e., as an
2567 @code{address_operand}.
2569 This macro also has strict and non-strict variants.
2572 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
2573 A C expression which is nonzero if register number @var{num} is suitable for
2574 use as a base register in base plus index operand addresses, accessing
2575 memory in mode @var{mode}. It may be either a suitable hard register or a
2576 pseudo register that has been allocated such a hard register. You should
2577 define this macro if base plus index addresses have different requirements
2578 than other base register uses.
2580 Use of this macro is deprecated; please use the more general
2581 @code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
2583 This macro also has strict and non-strict variants.
2586 @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code})
2587 A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except
2588 that that expression may examine the context in which the register
2589 appears in the memory reference. @var{outer_code} is the code of the
2590 immediately enclosing expression (@code{MEM} if at the top level of the
2591 address, @code{ADDRESS} for something that occurs in an
2592 @code{address_operand}). @var{index_code} is the code of the
2593 corresponding index expression if @var{outer_code} is @code{PLUS};
2594 @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses
2595 that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
2597 This macro also has strict and non-strict variants.
2600 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2601 A C expression which is nonzero if register number @var{num} is
2602 suitable for use as an index register in operand addresses. It may be
2603 either a suitable hard register or a pseudo register that has been
2604 allocated such a hard register.
2606 The difference between an index register and a base register is that
2607 the index register may be scaled. If an address involves the sum of
2608 two registers, neither one of them scaled, then either one may be
2609 labeled the ``base'' and the other the ``index''; but whichever
2610 labeling is used must fit the machine's constraints of which registers
2611 may serve in each capacity. The compiler will try both labelings,
2612 looking for one that is valid, and will reload one or both registers
2613 only if neither labeling works.
2615 This macro also has strict and non-strict variants.
2618 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2619 A C expression that places additional restrictions on the register class
2620 to use when it is necessary to copy value @var{x} into a register in class
2621 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2622 another, smaller class. On many machines, the following definition is
2626 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2629 Sometimes returning a more restrictive class makes better code. For
2630 example, on the 68000, when @var{x} is an integer constant that is in range
2631 for a @samp{moveq} instruction, the value of this macro is always
2632 @code{DATA_REGS} as long as @var{class} includes the data registers.
2633 Requiring a data register guarantees that a @samp{moveq} will be used.
2635 One case where @code{PREFERRED_RELOAD_CLASS} must not return
2636 @var{class} is if @var{x} is a legitimate constant which cannot be
2637 loaded into some register class. By returning @code{NO_REGS} you can
2638 force @var{x} into a memory location. For example, rs6000 can load
2639 immediate values into general-purpose registers, but does not have an
2640 instruction for loading an immediate value into a floating-point
2641 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2642 @var{x} is a floating-point constant. If the constant can't be loaded
2643 into any kind of register, code generation will be better if
2644 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2645 of using @code{PREFERRED_RELOAD_CLASS}.
2647 If an insn has pseudos in it after register allocation, reload will go
2648 through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
2649 to find the best one. Returning @code{NO_REGS}, in this case, makes
2650 reload add a @code{!} in front of the constraint: the x86 back-end uses
2651 this feature to discourage usage of 387 registers when math is done in
2652 the SSE registers (and vice versa).
2655 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2656 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2657 input reloads. If you don't define this macro, the default is to use
2658 @var{class}, unchanged.
2660 You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
2661 reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}.
2664 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2665 A C expression that places additional restrictions on the register class
2666 to use when it is necessary to be able to hold a value of mode
2667 @var{mode} in a reload register for which class @var{class} would
2670 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2671 there are certain modes that simply can't go in certain reload classes.
2673 The value is a register class; perhaps @var{class}, or perhaps another,
2676 Don't define this macro unless the target machine has limitations which
2677 require the macro to do something nontrivial.
2680 @deftypefn {Target Hook} {enum reg_class} TARGET_SECONDARY_RELOAD (bool @var{in_p}, rtx @var{x}, enum reg_class @var{reload_class}, enum machine_mode @var{reload_mode}, secondary_reload_info *@var{sri})
2681 Many machines have some registers that cannot be copied directly to or
2682 from memory or even from other types of registers. An example is the
2683 @samp{MQ} register, which on most machines, can only be copied to or
2684 from general registers, but not memory. Below, we shall be using the
2685 term 'intermediate register' when a move operation cannot be performed
2686 directly, but has to be done by copying the source into the intermediate
2687 register first, and then copying the intermediate register to the
2688 destination. An intermediate register always has the same mode as
2689 source and destination. Since it holds the actual value being copied,
2690 reload might apply optimizations to re-use an intermediate register
2691 and eliding the copy from the source when it can determine that the
2692 intermediate register still holds the required value.
2694 Another kind of secondary reload is required on some machines which
2695 allow copying all registers to and from memory, but require a scratch
2696 register for stores to some memory locations (e.g., those with symbolic
2697 address on the RT, and those with certain symbolic address on the SPARC
2698 when compiling PIC)@. Scratch registers need not have the same mode
2699 as the value being copied, and usually hold a different value than
2700 that being copied. Special patterns in the md file are needed to
2701 describe how the copy is performed with the help of the scratch register;
2702 these patterns also describe the number, register class(es) and mode(s)
2703 of the scratch register(s).
2705 In some cases, both an intermediate and a scratch register are required.
2707 For input reloads, this target hook is called with nonzero @var{in_p},
2708 and @var{x} is an rtx that needs to be copied to a register of class
2709 @var{reload_class} in @var{reload_mode}. For output reloads, this target
2710 hook is called with zero @var{in_p}, and a register of class @var{reload_class}
2711 needs to be copied to rtx @var{x} in @var{reload_mode}.
2713 If copying a register of @var{reload_class} from/to @var{x} requires
2714 an intermediate register, the hook @code{secondary_reload} should
2715 return the register class required for this intermediate register.
2716 If no intermediate register is required, it should return NO_REGS.
2717 If more than one intermediate register is required, describe the one
2718 that is closest in the copy chain to the reload register.
2720 If scratch registers are needed, you also have to describe how to
2721 perform the copy from/to the reload register to/from this
2722 closest intermediate register. Or if no intermediate register is
2723 required, but still a scratch register is needed, describe the
2724 copy from/to the reload register to/from the reload operand @var{x}.
2726 You do this by setting @code{sri->icode} to the instruction code of a pattern
2727 in the md file which performs the move. Operands 0 and 1 are the output
2728 and input of this copy, respectively. Operands from operand 2 onward are
2729 for scratch operands. These scratch operands must have a mode, and a
2730 single-register-class
2731 @c [later: or memory]
2734 When an intermediate register is used, the @code{secondary_reload}
2735 hook will be called again to determine how to copy the intermediate
2736 register to/from the reload operand @var{x}, so your hook must also
2737 have code to handle the register class of the intermediate operand.
2739 @c [For later: maybe we'll allow multi-alternative reload patterns -
2740 @c the port maintainer could name a mov<mode> pattern that has clobbers -
2741 @c and match the constraints of input and output to determine the required
2742 @c alternative. A restriction would be that constraints used to match
2743 @c against reloads registers would have to be written as register class
2744 @c constraints, or we need a new target macro / hook that tells us if an
2745 @c arbitrary constraint can match an unknown register of a given class.
2746 @c Such a macro / hook would also be useful in other places.]
2749 @var{x} might be a pseudo-register or a @code{subreg} of a
2750 pseudo-register, which could either be in a hard register or in memory.
2751 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2752 in memory and the hard register number if it is in a register.
2754 Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are
2755 currently not supported. For the time being, you will have to continue
2756 to use @code{SECONDARY_MEMORY_NEEDED} for that purpose.
2758 @code{copy_cost} also uses this target hook to find out how values are
2759 copied. If you want it to include some extra cost for the need to allocate
2760 (a) scratch register(s), set @code{sri->extra_cost} to the additional cost.
2761 Or if two dependent moves are supposed to have a lower cost than the sum
2762 of the individual moves due to expected fortuitous scheduling and/or special
2763 forwarding logic, you can set @code{sri->extra_cost} to a negative amount.
2766 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2767 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2768 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2769 These macros are obsolete, new ports should use the target hook
2770 @code{TARGET_SECONDARY_RELOAD} instead.
2772 These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
2773 target hook. Older ports still define these macros to indicate to the
2774 reload phase that it may
2775 need to allocate at least one register for a reload in addition to the
2776 register to contain the data. Specifically, if copying @var{x} to a
2777 register @var{class} in @var{mode} requires an intermediate register,
2778 you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2779 largest register class all of whose registers can be used as
2780 intermediate registers or scratch registers.
2782 If copying a register @var{class} in @var{mode} to @var{x} requires an
2783 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2784 was supposed to be defined be defined to return the largest register
2785 class required. If the
2786 requirements for input and output reloads were the same, the macro
2787 @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
2790 The values returned by these macros are often @code{GENERAL_REGS}.
2791 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2792 can be directly copied to or from a register of @var{class} in
2793 @var{mode} without requiring a scratch register. Do not define this
2794 macro if it would always return @code{NO_REGS}.
2796 If a scratch register is required (either with or without an
2797 intermediate register), you were supposed to define patterns for
2798 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2799 (@pxref{Standard Names}. These patterns, which were normally
2800 implemented with a @code{define_expand}, should be similar to the
2801 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2804 These patterns need constraints for the reload register and scratch
2806 contain a single register class. If the original reload register (whose
2807 class is @var{class}) can meet the constraint given in the pattern, the
2808 value returned by these macros is used for the class of the scratch
2809 register. Otherwise, two additional reload registers are required.
2810 Their classes are obtained from the constraints in the insn pattern.
2812 @var{x} might be a pseudo-register or a @code{subreg} of a
2813 pseudo-register, which could either be in a hard register or in memory.
2814 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2815 in memory and the hard register number if it is in a register.
2817 These macros should not be used in the case where a particular class of
2818 registers can only be copied to memory and not to another class of
2819 registers. In that case, secondary reload registers are not needed and
2820 would not be helpful. Instead, a stack location must be used to perform
2821 the copy and the @code{mov@var{m}} pattern should use memory as an
2822 intermediate storage. This case often occurs between floating-point and
2826 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2827 Certain machines have the property that some registers cannot be copied
2828 to some other registers without using memory. Define this macro on
2829 those machines to be a C expression that is nonzero if objects of mode
2830 @var{m} in registers of @var{class1} can only be copied to registers of
2831 class @var{class2} by storing a register of @var{class1} into memory
2832 and loading that memory location into a register of @var{class2}.
2834 Do not define this macro if its value would always be zero.
2837 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2838 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2839 allocates a stack slot for a memory location needed for register copies.
2840 If this macro is defined, the compiler instead uses the memory location
2841 defined by this macro.
2843 Do not define this macro if you do not define
2844 @code{SECONDARY_MEMORY_NEEDED}.
2847 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2848 When the compiler needs a secondary memory location to copy between two
2849 registers of mode @var{mode}, it normally allocates sufficient memory to
2850 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2851 load operations in a mode that many bits wide and whose class is the
2852 same as that of @var{mode}.
2854 This is right thing to do on most machines because it ensures that all
2855 bits of the register are copied and prevents accesses to the registers
2856 in a narrower mode, which some machines prohibit for floating-point
2859 However, this default behavior is not correct on some machines, such as
2860 the DEC Alpha, that store short integers in floating-point registers
2861 differently than in integer registers. On those machines, the default
2862 widening will not work correctly and you must define this macro to
2863 suppress that widening in some cases. See the file @file{alpha.h} for
2866 Do not define this macro if you do not define
2867 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2868 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2871 @defmac CLASS_LIKELY_SPILLED_P (@var{class})
2872 A C expression whose value is nonzero if pseudos that have been assigned
2873 to registers of class @var{class} would likely be spilled because
2874 registers of @var{class} are needed for spill registers.
2876 The default value of this macro returns 1 if @var{class} has exactly one
2877 register and zero otherwise. On most machines, this default should be
2878 used. Only define this macro to some other expression if pseudos
2879 allocated by @file{local-alloc.c} end up in memory because their hard
2880 registers were needed for spill registers. If this macro returns nonzero
2881 for those classes, those pseudos will only be allocated by
2882 @file{global.c}, which knows how to reallocate the pseudo to another
2883 register. If there would not be another register available for
2884 reallocation, you should not change the definition of this macro since
2885 the only effect of such a definition would be to slow down register
2889 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2890 A C expression for the maximum number of consecutive registers
2891 of class @var{class} needed to hold a value of mode @var{mode}.
2893 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2894 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2895 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2896 @var{mode})} for all @var{regno} values in the class @var{class}.
2898 This macro helps control the handling of multiple-word values
2902 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2903 If defined, a C expression that returns nonzero for a @var{class} for which
2904 a change from mode @var{from} to mode @var{to} is invalid.
2906 For the example, loading 32-bit integer or floating-point objects into
2907 floating-point registers on the Alpha extends them to 64 bits.
2908 Therefore loading a 64-bit object and then storing it as a 32-bit object
2909 does not store the low-order 32 bits, as would be the case for a normal
2910 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2914 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2915 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2916 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2920 @deftypefn {Target Hook} {const enum reg_class *} TARGET_IRA_COVER_CLASSES (void)
2921 Return an array of cover classes for the Integrated Register Allocator
2922 (@acronym{IRA}). Cover classes are a set of non-intersecting register
2923 classes covering all hard registers used for register allocation
2924 purposes. If a move between two registers in the same cover class is
2925 possible, it should be cheaper than a load or store of the registers.
2926 The array is terminated by a @code{LIM_REG_CLASSES} element.
2928 The order of cover classes in the array is important. If two classes
2929 have the same cost of usage for a pseudo, the class occurred first in
2930 the array is chosen for the pseudo.
2932 This hook is called once at compiler startup, after the command-line
2933 options have been processed. It is then re-examined by every call to
2934 @code{target_reinit}.
2936 The default implementation returns @code{IRA_COVER_CLASSES}, if defined,
2937 otherwise there is no default implementation. You must define either this
2938 macro or @code{IRA_COVER_CLASSES} in order to use the integrated register
2939 allocator with Chaitin-Briggs coloring. If the macro is not defined,
2940 the only available coloring algorithm is Chow's priority coloring.
2943 @defmac IRA_COVER_CLASSES
2944 See the documentation for @code{TARGET_IRA_COVER_CLASSES}.
2947 @node Old Constraints
2948 @section Obsolete Macros for Defining Constraints
2949 @cindex defining constraints, obsolete method
2950 @cindex constraints, defining, obsolete method
2952 Machine-specific constraints can be defined with these macros instead
2953 of the machine description constructs described in @ref{Define
2954 Constraints}. This mechanism is obsolete. New ports should not use
2955 it; old ports should convert to the new mechanism.
2957 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2958 For the constraint at the start of @var{str}, which starts with the letter
2959 @var{c}, return the length. This allows you to have register class /
2960 constant / extra constraints that are longer than a single letter;
2961 you don't need to define this macro if you can do with single-letter
2962 constraints only. The definition of this macro should use
2963 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2964 to handle specially.
2965 There are some sanity checks in genoutput.c that check the constraint lengths
2966 for the md file, so you can also use this macro to help you while you are
2967 transitioning from a byzantine single-letter-constraint scheme: when you
2968 return a negative length for a constraint you want to re-use, genoutput
2969 will complain about every instance where it is used in the md file.
2972 @defmac REG_CLASS_FROM_LETTER (@var{char})
2973 A C expression which defines the machine-dependent operand constraint
2974 letters for register classes. If @var{char} is such a letter, the
2975 value should be the register class corresponding to it. Otherwise,
2976 the value should be @code{NO_REGS}. The register letter @samp{r},
2977 corresponding to class @code{GENERAL_REGS}, will not be passed
2978 to this macro; you do not need to handle it.
2981 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2982 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2983 passed in @var{str}, so that you can use suffixes to distinguish between
2987 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2988 A C expression that defines the machine-dependent operand constraint
2989 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2990 particular ranges of integer values. If @var{c} is one of those
2991 letters, the expression should check that @var{value}, an integer, is in
2992 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2993 not one of those letters, the value should be 0 regardless of
2997 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2998 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2999 string passed in @var{str}, so that you can use suffixes to distinguish
3000 between different variants.
3003 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
3004 A C expression that defines the machine-dependent operand constraint
3005 letters that specify particular ranges of @code{const_double} values
3006 (@samp{G} or @samp{H}).
3008 If @var{c} is one of those letters, the expression should check that
3009 @var{value}, an RTX of code @code{const_double}, is in the appropriate
3010 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
3011 letters, the value should be 0 regardless of @var{value}.
3013 @code{const_double} is used for all floating-point constants and for
3014 @code{DImode} fixed-point constants. A given letter can accept either
3015 or both kinds of values. It can use @code{GET_MODE} to distinguish
3016 between these kinds.
3019 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
3020 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
3021 string passed in @var{str}, so that you can use suffixes to distinguish
3022 between different variants.
3025 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
3026 A C expression that defines the optional machine-dependent constraint
3027 letters that can be used to segregate specific types of operands, usually
3028 memory references, for the target machine. Any letter that is not
3029 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
3030 @code{REG_CLASS_FROM_CONSTRAINT}
3031 may be used. Normally this macro will not be defined.
3033 If it is required for a particular target machine, it should return 1
3034 if @var{value} corresponds to the operand type represented by the
3035 constraint letter @var{c}. If @var{c} is not defined as an extra
3036 constraint, the value returned should be 0 regardless of @var{value}.
3038 For example, on the ROMP, load instructions cannot have their output
3039 in r0 if the memory reference contains a symbolic address. Constraint
3040 letter @samp{Q} is defined as representing a memory address that does
3041 @emph{not} contain a symbolic address. An alternative is specified with
3042 a @samp{Q} constraint on the input and @samp{r} on the output. The next
3043 alternative specifies @samp{m} on the input and a register class that
3044 does not include r0 on the output.
3047 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
3048 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
3049 in @var{str}, so that you can use suffixes to distinguish between different
3053 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
3054 A C expression that defines the optional machine-dependent constraint
3055 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
3056 be treated like memory constraints by the reload pass.
3058 It should return 1 if the operand type represented by the constraint
3059 at the start of @var{str}, the first letter of which is the letter @var{c},
3060 comprises a subset of all memory references including
3061 all those whose address is simply a base register. This allows the reload
3062 pass to reload an operand, if it does not directly correspond to the operand
3063 type of @var{c}, by copying its address into a base register.
3065 For example, on the S/390, some instructions do not accept arbitrary
3066 memory references, but only those that do not make use of an index
3067 register. The constraint letter @samp{Q} is defined via
3068 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
3069 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
3070 a @samp{Q} constraint can handle any memory operand, because the
3071 reload pass knows it can be reloaded by copying the memory address
3072 into a base register if required. This is analogous to the way
3073 an @samp{o} constraint can handle any memory operand.
3076 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
3077 A C expression that defines the optional machine-dependent constraint
3078 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
3079 @code{EXTRA_CONSTRAINT_STR}, that should
3080 be treated like address constraints by the reload pass.
3082 It should return 1 if the operand type represented by the constraint
3083 at the start of @var{str}, which starts with the letter @var{c}, comprises
3084 a subset of all memory addresses including
3085 all those that consist of just a base register. This allows the reload
3086 pass to reload an operand, if it does not directly correspond to the operand
3087 type of @var{str}, by copying it into a base register.
3089 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
3090 be used with the @code{address_operand} predicate. It is treated
3091 analogously to the @samp{p} constraint.
3094 @node Stack and Calling
3095 @section Stack Layout and Calling Conventions
3096 @cindex calling conventions
3098 @c prevent bad page break with this line
3099 This describes the stack layout and calling conventions.
3103 * Exception Handling::
3108 * Register Arguments::
3110 * Aggregate Return::
3115 * Stack Smashing Protection::
3119 @subsection Basic Stack Layout
3120 @cindex stack frame layout
3121 @cindex frame layout
3123 @c prevent bad page break with this line
3124 Here is the basic stack layout.
3126 @defmac STACK_GROWS_DOWNWARD
3127 Define this macro if pushing a word onto the stack moves the stack
3128 pointer to a smaller address.
3130 When we say, ``define this macro if @dots{}'', it means that the
3131 compiler checks this macro only with @code{#ifdef} so the precise
3132 definition used does not matter.
3135 @defmac STACK_PUSH_CODE
3136 This macro defines the operation used when something is pushed
3137 on the stack. In RTL, a push operation will be
3138 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
3140 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
3141 and @code{POST_INC}. Which of these is correct depends on
3142 the stack direction and on whether the stack pointer points
3143 to the last item on the stack or whether it points to the
3144 space for the next item on the stack.
3146 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
3147 defined, which is almost always right, and @code{PRE_INC} otherwise,
3148 which is often wrong.
3151 @defmac FRAME_GROWS_DOWNWARD
3152 Define this macro to nonzero value if the addresses of local variable slots
3153 are at negative offsets from the frame pointer.
3156 @defmac ARGS_GROW_DOWNWARD
3157 Define this macro if successive arguments to a function occupy decreasing
3158 addresses on the stack.
3161 @defmac STARTING_FRAME_OFFSET
3162 Offset from the frame pointer to the first local variable slot to be allocated.
3164 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
3165 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
3166 Otherwise, it is found by adding the length of the first slot to the
3167 value @code{STARTING_FRAME_OFFSET}.
3168 @c i'm not sure if the above is still correct.. had to change it to get
3169 @c rid of an overfull. --mew 2feb93
3172 @defmac STACK_ALIGNMENT_NEEDED
3173 Define to zero to disable final alignment of the stack during reload.
3174 The nonzero default for this macro is suitable for most ports.
3176 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
3177 is a register save block following the local block that doesn't require
3178 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
3179 stack alignment and do it in the backend.
3182 @defmac STACK_POINTER_OFFSET
3183 Offset from the stack pointer register to the first location at which
3184 outgoing arguments are placed. If not specified, the default value of
3185 zero is used. This is the proper value for most machines.
3187 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3188 the first location at which outgoing arguments are placed.
3191 @defmac FIRST_PARM_OFFSET (@var{fundecl})
3192 Offset from the argument pointer register to the first argument's
3193 address. On some machines it may depend on the data type of the
3196 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3197 the first argument's address.
3200 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
3201 Offset from the stack pointer register to an item dynamically allocated
3202 on the stack, e.g., by @code{alloca}.
3204 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
3205 length of the outgoing arguments. The default is correct for most
3206 machines. See @file{function.c} for details.
3209 @defmac INITIAL_FRAME_ADDRESS_RTX
3210 A C expression whose value is RTL representing the address of the initial
3211 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
3212 @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable
3213 default value will be used. Define this macro in order to make frame pointer
3214 elimination work in the presence of @code{__builtin_frame_address (count)} and
3215 @code{__builtin_return_address (count)} for @code{count} not equal to zero.
3218 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
3219 A C expression whose value is RTL representing the address in a stack
3220 frame where the pointer to the caller's frame is stored. Assume that
3221 @var{frameaddr} is an RTL expression for the address of the stack frame
3224 If you don't define this macro, the default is to return the value
3225 of @var{frameaddr}---that is, the stack frame address is also the
3226 address of the stack word that points to the previous frame.
3229 @defmac SETUP_FRAME_ADDRESSES
3230 If defined, a C expression that produces the machine-specific code to
3231 setup the stack so that arbitrary frames can be accessed. For example,
3232 on the SPARC, we must flush all of the register windows to the stack
3233 before we can access arbitrary stack frames. You will seldom need to
3237 @deftypefn {Target Hook} rtx TARGET_BUILTIN_SETJMP_FRAME_VALUE (void)
3238 This target hook should return an rtx that is used to store
3239 the address of the current frame into the built in @code{setjmp} buffer.
3240 The default value, @code{virtual_stack_vars_rtx}, is correct for most
3241 machines. One reason you may need to define this target hook is if
3242 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
3245 @defmac FRAME_ADDR_RTX (@var{frameaddr})
3246 A C expression whose value is RTL representing the value of the frame
3247 address for the current frame. @var{frameaddr} is the frame pointer
3248 of the current frame. This is used for __builtin_frame_address.
3249 You need only define this macro if the frame address is not the same
3250 as the frame pointer. Most machines do not need to define it.
3253 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
3254 A C expression whose value is RTL representing the value of the return
3255 address for the frame @var{count} steps up from the current frame, after
3256 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
3257 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
3258 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
3260 The value of the expression must always be the correct address when
3261 @var{count} is zero, but may be @code{NULL_RTX} if there is no way to
3262 determine the return address of other frames.
3265 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
3266 Define this if the return address of a particular stack frame is accessed
3267 from the frame pointer of the previous stack frame.
3270 @defmac INCOMING_RETURN_ADDR_RTX
3271 A C expression whose value is RTL representing the location of the
3272 incoming return address at the beginning of any function, before the
3273 prologue. This RTL is either a @code{REG}, indicating that the return
3274 value is saved in @samp{REG}, or a @code{MEM} representing a location in
3277 You only need to define this macro if you want to support call frame
3278 debugging information like that provided by DWARF 2.
3280 If this RTL is a @code{REG}, you should also define
3281 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
3284 @defmac DWARF_ALT_FRAME_RETURN_COLUMN
3285 A C expression whose value is an integer giving a DWARF 2 column
3286 number that may be used as an alternative return column. The column
3287 must not correspond to any gcc hard register (that is, it must not
3288 be in the range of @code{DWARF_FRAME_REGNUM}).
3290 This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
3291 general register, but an alternative column needs to be used for signal
3292 frames. Some targets have also used different frame return columns
3296 @defmac DWARF_ZERO_REG
3297 A C expression whose value is an integer giving a DWARF 2 register
3298 number that is considered to always have the value zero. This should
3299 only be defined if the target has an architected zero register, and
3300 someone decided it was a good idea to use that register number to
3301 terminate the stack backtrace. New ports should avoid this.
3304 @deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index})
3305 This target hook allows the backend to emit frame-related insns that
3306 contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
3307 info engine will invoke it on insns of the form
3309 (set (reg) (unspec [@dots{}] UNSPEC_INDEX))
3313 (set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)).
3315 to let the backend emit the call frame instructions. @var{label} is
3316 the CFI label attached to the insn, @var{pattern} is the pattern of
3317 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
3320 @defmac INCOMING_FRAME_SP_OFFSET
3321 A C expression whose value is an integer giving the offset, in bytes,
3322 from the value of the stack pointer register to the top of the stack
3323 frame at the beginning of any function, before the prologue. The top of
3324 the frame is defined to be the value of the stack pointer in the
3325 previous frame, just before the call instruction.
3327 You only need to define this macro if you want to support call frame
3328 debugging information like that provided by DWARF 2.
3331 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
3332 A C expression whose value is an integer giving the offset, in bytes,
3333 from the argument pointer to the canonical frame address (cfa). The
3334 final value should coincide with that calculated by
3335 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
3336 during virtual register instantiation.
3338 The default value for this macro is
3339 @code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size},
3340 which is correct for most machines; in general, the arguments are found
3341 immediately before the stack frame. Note that this is not the case on
3342 some targets that save registers into the caller's frame, such as SPARC
3343 and rs6000, and so such targets need to define this macro.
3345 You only need to define this macro if the default is incorrect, and you
3346 want to support call frame debugging information like that provided by
3350 @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
3351 If defined, a C expression whose value is an integer giving the offset
3352 in bytes from the frame pointer to the canonical frame address (cfa).
3353 The final value should coincide with that calculated by
3354 @code{INCOMING_FRAME_SP_OFFSET}.
3356 Normally the CFA is calculated as an offset from the argument pointer,
3357 via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
3358 variable due to the ABI, this may not be possible. If this macro is
3359 defined, it implies that the virtual register instantiation should be
3360 based on the frame pointer instead of the argument pointer. Only one
3361 of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
3365 @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
3366 If defined, a C expression whose value is an integer giving the offset
3367 in bytes from the canonical frame address (cfa) to the frame base used
3368 in DWARF 2 debug information. The default is zero. A different value
3369 may reduce the size of debug information on some ports.
3372 @node Exception Handling
3373 @subsection Exception Handling Support
3374 @cindex exception handling
3376 @defmac EH_RETURN_DATA_REGNO (@var{N})
3377 A C expression whose value is the @var{N}th register number used for
3378 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
3379 @var{N} registers are usable.
3381 The exception handling library routines communicate with the exception
3382 handlers via a set of agreed upon registers. Ideally these registers
3383 should be call-clobbered; it is possible to use call-saved registers,
3384 but may negatively impact code size. The target must support at least
3385 2 data registers, but should define 4 if there are enough free registers.
3387 You must define this macro if you want to support call frame exception
3388 handling like that provided by DWARF 2.
3391 @defmac EH_RETURN_STACKADJ_RTX
3392 A C expression whose value is RTL representing a location in which
3393 to store a stack adjustment to be applied before function return.
3394 This is used to unwind the stack to an exception handler's call frame.
3395 It will be assigned zero on code paths that return normally.
3397 Typically this is a call-clobbered hard register that is otherwise
3398 untouched by the epilogue, but could also be a stack slot.
3400 Do not define this macro if the stack pointer is saved and restored
3401 by the regular prolog and epilog code in the call frame itself; in
3402 this case, the exception handling library routines will update the
3403 stack location to be restored in place. Otherwise, you must define
3404 this macro if you want to support call frame exception handling like
3405 that provided by DWARF 2.
3408 @defmac EH_RETURN_HANDLER_RTX
3409 A C expression whose value is RTL representing a location in which
3410 to store the address of an exception handler to which we should
3411 return. It will not be assigned on code paths that return normally.
3413 Typically this is the location in the call frame at which the normal
3414 return address is stored. For targets that return by popping an
3415 address off the stack, this might be a memory address just below
3416 the @emph{target} call frame rather than inside the current call
3417 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
3418 been assigned, so it may be used to calculate the location of the
3421 Some targets have more complex requirements than storing to an
3422 address calculable during initial code generation. In that case
3423 the @code{eh_return} instruction pattern should be used instead.
3425 If you want to support call frame exception handling, you must
3426 define either this macro or the @code{eh_return} instruction pattern.
3429 @defmac RETURN_ADDR_OFFSET
3430 If defined, an integer-valued C expression for which rtl will be generated
3431 to add it to the exception handler address before it is searched in the
3432 exception handling tables, and to subtract it again from the address before
3433 using it to return to the exception handler.
3436 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3437 This macro chooses the encoding of pointers embedded in the exception
3438 handling sections. If at all possible, this should be defined such
3439 that the exception handling section will not require dynamic relocations,
3440 and so may be read-only.
3442 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3443 @var{global} is true if the symbol may be affected by dynamic relocations.
3444 The macro should return a combination of the @code{DW_EH_PE_*} defines
3445 as found in @file{dwarf2.h}.
3447 If this macro is not defined, pointers will not be encoded but
3448 represented directly.
3451 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3452 This macro allows the target to emit whatever special magic is required
3453 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3454 Generic code takes care of pc-relative and indirect encodings; this must
3455 be defined if the target uses text-relative or data-relative encodings.
3457 This is a C statement that branches to @var{done} if the format was
3458 handled. @var{encoding} is the format chosen, @var{size} is the number
3459 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3463 @defmac MD_UNWIND_SUPPORT
3464 A string specifying a file to be #include'd in unwind-dw2.c. The file
3465 so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}.
3468 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
3469 This macro allows the target to add CPU and operating system specific
3470 code to the call-frame unwinder for use when there is no unwind data
3471 available. The most common reason to implement this macro is to unwind
3472 through signal frames.
3474 This macro is called from @code{uw_frame_state_for} in
3475 @file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
3476 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3477 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3478 for the address of the code being executed and @code{context->cfa} for
3479 the stack pointer value. If the frame can be decoded, the register
3480 save addresses should be updated in @var{fs} and the macro should
3481 evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded,
3482 the macro should evaluate to @code{_URC_END_OF_STACK}.
3484 For proper signal handling in Java this macro is accompanied by
3485 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3488 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
3489 This macro allows the target to add operating system specific code to the
3490 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
3491 usually used for signal or interrupt frames.
3493 This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}.
3494 @var{context} is an @code{_Unwind_Context};
3495 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
3496 for the abi and context in the @code{.unwabi} directive. If the
3497 @code{.unwabi} directive can be handled, the register save addresses should
3498 be updated in @var{fs}.
3501 @defmac TARGET_USES_WEAK_UNWIND_INFO
3502 A C expression that evaluates to true if the target requires unwind
3503 info to be given comdat linkage. Define it to be @code{1} if comdat
3504 linkage is necessary. The default is @code{0}.
3507 @node Stack Checking
3508 @subsection Specifying How Stack Checking is Done
3510 GCC will check that stack references are within the boundaries of the
3511 stack, if the option @option{-fstack-check} is specified, in one of
3516 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3517 will assume that you have arranged for full stack checking to be done
3518 at appropriate places in the configuration files. GCC will not do
3519 other special processing.
3522 If @code{STACK_CHECK_BUILTIN} is zero and the value of the
3523 @code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
3524 that you have arranged for static stack checking (checking of the
3525 static stack frame of functions) to be done at appropriate places
3526 in the configuration files. GCC will only emit code to do dynamic
3527 stack checking (checking on dynamic stack allocations) using the third
3531 If neither of the above are true, GCC will generate code to periodically
3532 ``probe'' the stack pointer using the values of the macros defined below.
3535 If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
3536 GCC will change its allocation strategy for large objects if the option
3537 @option{-fstack-check} is specified: they will always be allocated
3538 dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
3540 @defmac STACK_CHECK_BUILTIN
3541 A nonzero value if stack checking is done by the configuration files in a
3542 machine-dependent manner. You should define this macro if stack checking
3543 is required by the ABI of your machine or if you would like to do stack
3544 checking in some more efficient way than the generic approach. The default
3545 value of this macro is zero.
3548 @defmac STACK_CHECK_STATIC_BUILTIN
3549 A nonzero value if static stack checking is done by the configuration files
3550 in a machine-dependent manner. You should define this macro if you would
3551 like to do static stack checking in some more efficient way than the generic
3552 approach. The default value of this macro is zero.
3555 @defmac STACK_CHECK_PROBE_INTERVAL_EXP
3556 An integer specifying the interval at which GCC must generate stack probe
3557 instructions, defined as 2 raised to this integer. You will normally
3558 define this macro so that the interval be no larger than the size of
3559 the ``guard pages'' at the end of a stack area. The default value
3560 of 12 (4096-byte interval) is suitable for most systems.
3563 @defmac STACK_CHECK_MOVING_SP
3564 An integer which is nonzero if GCC should move the stack pointer page by page
3565 when doing probes. This can be necessary on systems where the stack pointer
3566 contains the bottom address of the memory area accessible to the executing
3567 thread at any point in time. In this situation an alternate signal stack
3568 is required in order to be able to recover from a stack overflow. The
3569 default value of this macro is zero.
3572 @defmac STACK_CHECK_PROTECT
3573 The number of bytes of stack needed to recover from a stack overflow, for
3574 languages where such a recovery is supported. The default value of 75 words
3575 with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and
3576 8192 bytes with other exception handling mechanisms should be adequate for
3580 The following macros are relevant only if neither STACK_CHECK_BUILTIN
3581 nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
3582 in the opposite case.
3584 @defmac STACK_CHECK_MAX_FRAME_SIZE
3585 The maximum size of a stack frame, in bytes. GCC will generate probe
3586 instructions in non-leaf functions to ensure at least this many bytes of
3587 stack are available. If a stack frame is larger than this size, stack
3588 checking will not be reliable and GCC will issue a warning. The
3589 default is chosen so that GCC only generates one instruction on most
3590 systems. You should normally not change the default value of this macro.
3593 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3594 GCC uses this value to generate the above warning message. It
3595 represents the amount of fixed frame used by a function, not including
3596 space for any callee-saved registers, temporaries and user variables.
3597 You need only specify an upper bound for this amount and will normally
3598 use the default of four words.
3601 @defmac STACK_CHECK_MAX_VAR_SIZE
3602 The maximum size, in bytes, of an object that GCC will place in the
3603 fixed area of the stack frame when the user specifies
3604 @option{-fstack-check}.
3605 GCC computed the default from the values of the above macros and you will
3606 normally not need to override that default.
3610 @node Frame Registers
3611 @subsection Registers That Address the Stack Frame
3613 @c prevent bad page break with this line
3614 This discusses registers that address the stack frame.
3616 @defmac STACK_POINTER_REGNUM
3617 The register number of the stack pointer register, which must also be a
3618 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3619 the hardware determines which register this is.
3622 @defmac FRAME_POINTER_REGNUM
3623 The register number of the frame pointer register, which is used to
3624 access automatic variables in the stack frame. On some machines, the
3625 hardware determines which register this is. On other machines, you can
3626 choose any register you wish for this purpose.
3629 @defmac HARD_FRAME_POINTER_REGNUM
3630 On some machines the offset between the frame pointer and starting
3631 offset of the automatic variables is not known until after register
3632 allocation has been done (for example, because the saved registers are
3633 between these two locations). On those machines, define
3634 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3635 be used internally until the offset is known, and define
3636 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3637 used for the frame pointer.
3639 You should define this macro only in the very rare circumstances when it
3640 is not possible to calculate the offset between the frame pointer and
3641 the automatic variables until after register allocation has been
3642 completed. When this macro is defined, you must also indicate in your
3643 definition of @code{ELIMINABLE_REGS} how to eliminate
3644 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3645 or @code{STACK_POINTER_REGNUM}.
3647 Do not define this macro if it would be the same as
3648 @code{FRAME_POINTER_REGNUM}.
3651 @defmac ARG_POINTER_REGNUM
3652 The register number of the arg pointer register, which is used to access
3653 the function's argument list. On some machines, this is the same as the
3654 frame pointer register. On some machines, the hardware determines which
3655 register this is. On other machines, you can choose any register you
3656 wish for this purpose. If this is not the same register as the frame
3657 pointer register, then you must mark it as a fixed register according to
3658 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3659 (@pxref{Elimination}).
3662 @defmac RETURN_ADDRESS_POINTER_REGNUM
3663 The register number of the return address pointer register, which is used to
3664 access the current function's return address from the stack. On some
3665 machines, the return address is not at a fixed offset from the frame
3666 pointer or stack pointer or argument pointer. This register can be defined
3667 to point to the return address on the stack, and then be converted by
3668 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3670 Do not define this macro unless there is no other way to get the return
3671 address from the stack.
3674 @defmac STATIC_CHAIN_REGNUM
3675 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3676 Register numbers used for passing a function's static chain pointer. If
3677 register windows are used, the register number as seen by the called
3678 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3679 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3680 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3683 The static chain register need not be a fixed register.
3685 If the static chain is passed in memory, these macros should not be
3686 defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used.
3689 @deftypefn {Target Hook} rtx TARGET_STATIC_CHAIN (const_tree @var{fndecl}, bool @var{incoming_p})
3690 This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for
3691 targets that may use different static chain locations for different
3692 nested functions. This may be required if the target has function
3693 attributes that affect the calling conventions of the function and
3694 those calling conventions use different static chain locations.
3696 The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al.
3698 If the static chain is passed in memory, this hook should be used to
3699 provide rtx giving @code{mem} expressions that denote where they are stored.
3700 Often the @code{mem} expression as seen by the caller will be at an offset
3701 from the stack pointer and the @code{mem} expression as seen by the callee
3702 will be at an offset from the frame pointer.
3703 @findex stack_pointer_rtx
3704 @findex frame_pointer_rtx
3705 @findex arg_pointer_rtx
3706 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3707 @code{arg_pointer_rtx} will have been initialized and should be used
3708 to refer to those items.
3711 @defmac DWARF_FRAME_REGISTERS
3712 This macro specifies the maximum number of hard registers that can be
3713 saved in a call frame. This is used to size data structures used in
3714 DWARF2 exception handling.
3716 Prior to GCC 3.0, this macro was needed in order to establish a stable
3717 exception handling ABI in the face of adding new hard registers for ISA
3718 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3719 in the number of hard registers. Nevertheless, this macro can still be
3720 used to reduce the runtime memory requirements of the exception handling
3721 routines, which can be substantial if the ISA contains a lot of
3722 registers that are not call-saved.
3724 If this macro is not defined, it defaults to
3725 @code{FIRST_PSEUDO_REGISTER}.
3728 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3730 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3731 for backward compatibility in pre GCC 3.0 compiled code.
3733 If this macro is not defined, it defaults to
3734 @code{DWARF_FRAME_REGISTERS}.
3737 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3739 Define this macro if the target's representation for dwarf registers
3740 is different than the internal representation for unwind column.
3741 Given a dwarf register, this macro should return the internal unwind
3742 column number to use instead.
3744 See the PowerPC's SPE target for an example.
3747 @defmac DWARF_FRAME_REGNUM (@var{regno})
3749 Define this macro if the target's representation for dwarf registers
3750 used in .eh_frame or .debug_frame is different from that used in other
3751 debug info sections. Given a GCC hard register number, this macro
3752 should return the .eh_frame register number. The default is
3753 @code{DBX_REGISTER_NUMBER (@var{regno})}.
3757 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
3759 Define this macro to map register numbers held in the call frame info
3760 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
3761 should be output in .debug_frame (@code{@var{for_eh}} is zero) and
3762 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to
3763 return @code{@var{regno}}.
3768 @subsection Eliminating Frame Pointer and Arg Pointer
3770 @c prevent bad page break with this line
3771 This is about eliminating the frame pointer and arg pointer.
3773 @deftypefn {Target Hook} bool TARGET_FRAME_POINTER_REQUIRED (void)
3774 This target hook should return @code{true} if a function must have and use
3775 a frame pointer. This target hook is called in the reload pass. If its return
3776 value is @code{true} the function will have a frame pointer.
3778 This target hook can in principle examine the current function and decide
3779 according to the facts, but on most machines the constant @code{false} or the
3780 constant @code{true} suffices. Use @code{false} when the machine allows code
3781 to be generated with no frame pointer, and doing so saves some time or space.
3782 Use @code{true} when there is no possible advantage to avoiding a frame
3785 In certain cases, the compiler does not know how to produce valid code
3786 without a frame pointer. The compiler recognizes those cases and
3787 automatically gives the function a frame pointer regardless of what
3788 @code{TARGET_FRAME_POINTER_REQUIRED} returns. You don't need to worry about
3791 In a function that does not require a frame pointer, the frame pointer
3792 register can be allocated for ordinary usage, unless you mark it as a
3793 fixed register. See @code{FIXED_REGISTERS} for more information.
3795 Default return value is @code{false}.
3798 @findex get_frame_size
3799 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3800 A C statement to store in the variable @var{depth-var} the difference
3801 between the frame pointer and the stack pointer values immediately after
3802 the function prologue. The value would be computed from information
3803 such as the result of @code{get_frame_size ()} and the tables of
3804 registers @code{regs_ever_live} and @code{call_used_regs}.
3806 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3807 need not be defined. Otherwise, it must be defined even if
3808 @code{TARGET_FRAME_POINTER_REQUIRED} always returns true; in that
3809 case, you may set @var{depth-var} to anything.
3812 @defmac ELIMINABLE_REGS
3813 If defined, this macro specifies a table of register pairs used to
3814 eliminate unneeded registers that point into the stack frame. If it is not
3815 defined, the only elimination attempted by the compiler is to replace
3816 references to the frame pointer with references to the stack pointer.
3818 The definition of this macro is a list of structure initializations, each
3819 of which specifies an original and replacement register.
3821 On some machines, the position of the argument pointer is not known until
3822 the compilation is completed. In such a case, a separate hard register
3823 must be used for the argument pointer. This register can be eliminated by
3824 replacing it with either the frame pointer or the argument pointer,
3825 depending on whether or not the frame pointer has been eliminated.
3827 In this case, you might specify:
3829 #define ELIMINABLE_REGS \
3830 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3831 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3832 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3835 Note that the elimination of the argument pointer with the stack pointer is
3836 specified first since that is the preferred elimination.
3839 @deftypefn {Target Hook} bool TARGET_CAN_ELIMINATE (const int @var{from_reg}, const int @var{to_reg})
3840 This target hook should returns @code{true} if the compiler is allowed to
3841 try to replace register number @var{from_reg} with register number
3842 @var{to_reg}. This target hook need only be defined if @code{ELIMINABLE_REGS}
3843 is defined, and will usually be @code{true}, since most of the cases
3844 preventing register elimination are things that the compiler already
3847 Default return value is @code{true}.
3850 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3851 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3852 specifies the initial difference between the specified pair of
3853 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3857 @node Stack Arguments
3858 @subsection Passing Function Arguments on the Stack
3859 @cindex arguments on stack
3860 @cindex stack arguments
3862 The macros in this section control how arguments are passed
3863 on the stack. See the following section for other macros that
3864 control passing certain arguments in registers.
3866 @deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (const_tree @var{fntype})
3867 This target hook returns @code{true} if an argument declared in a
3868 prototype as an integral type smaller than @code{int} should actually be
3869 passed as an @code{int}. In addition to avoiding errors in certain
3870 cases of mismatch, it also makes for better code on certain machines.
3871 The default is to not promote prototypes.
3875 A C expression. If nonzero, push insns will be used to pass
3877 If the target machine does not have a push instruction, set it to zero.
3878 That directs GCC to use an alternate strategy: to
3879 allocate the entire argument block and then store the arguments into
3880 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3883 @defmac PUSH_ARGS_REVERSED
3884 A C expression. If nonzero, function arguments will be evaluated from
3885 last to first, rather than from first to last. If this macro is not
3886 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3887 and args grow in opposite directions, and 0 otherwise.
3890 @defmac PUSH_ROUNDING (@var{npushed})
3891 A C expression that is the number of bytes actually pushed onto the
3892 stack when an instruction attempts to push @var{npushed} bytes.
3894 On some machines, the definition
3897 #define PUSH_ROUNDING(BYTES) (BYTES)
3901 will suffice. But on other machines, instructions that appear
3902 to push one byte actually push two bytes in an attempt to maintain
3903 alignment. Then the definition should be
3906 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3910 @findex current_function_outgoing_args_size
3911 @defmac ACCUMULATE_OUTGOING_ARGS
3912 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3913 will be computed and placed into the variable
3914 @code{current_function_outgoing_args_size}. No space will be pushed
3915 onto the stack for each call; instead, the function prologue should
3916 increase the stack frame size by this amount.
3918 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3922 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3923 Define this macro if functions should assume that stack space has been
3924 allocated for arguments even when their values are passed in
3927 The value of this macro is the size, in bytes, of the area reserved for
3928 arguments passed in registers for the function represented by @var{fndecl},
3929 which can be zero if GCC is calling a library function.
3930 The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
3933 This space can be allocated by the caller, or be a part of the
3934 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3937 @c above is overfull. not sure what to do. --mew 5feb93 did
3938 @c something, not sure if it looks good. --mew 10feb93
3940 @defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
3941 Define this to a nonzero value if it is the responsibility of the
3942 caller to allocate the area reserved for arguments passed in registers
3943 when calling a function of @var{fntype}. @var{fntype} may be NULL
3944 if the function called is a library function.
3946 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3947 whether the space for these arguments counts in the value of
3948 @code{current_function_outgoing_args_size}.
3951 @defmac STACK_PARMS_IN_REG_PARM_AREA
3952 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3953 stack parameters don't skip the area specified by it.
3954 @c i changed this, makes more sens and it should have taken care of the
3955 @c overfull.. not as specific, tho. --mew 5feb93
3957 Normally, when a parameter is not passed in registers, it is placed on the
3958 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3959 suppresses this behavior and causes the parameter to be passed on the
3960 stack in its natural location.
3963 @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size})
3964 A C expression that should indicate the number of bytes of its own
3965 arguments that a function pops on returning, or 0 if the
3966 function pops no arguments and the caller must therefore pop them all
3967 after the function returns.
3969 @var{fundecl} is a C variable whose value is a tree node that describes
3970 the function in question. Normally it is a node of type
3971 @code{FUNCTION_DECL} that describes the declaration of the function.
3972 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3974 @var{funtype} is a C variable whose value is a tree node that
3975 describes the function in question. Normally it is a node of type
3976 @code{FUNCTION_TYPE} that describes the data type of the function.
3977 From this it is possible to obtain the data types of the value and
3978 arguments (if known).
3980 When a call to a library function is being considered, @var{fundecl}
3981 will contain an identifier node for the library function. Thus, if
3982 you need to distinguish among various library functions, you can do so
3983 by their names. Note that ``library function'' in this context means
3984 a function used to perform arithmetic, whose name is known specially
3985 in the compiler and was not mentioned in the C code being compiled.
3987 @var{stack-size} is the number of bytes of arguments passed on the
3988 stack. If a variable number of bytes is passed, it is zero, and
3989 argument popping will always be the responsibility of the calling function.
3991 On the VAX, all functions always pop their arguments, so the definition
3992 of this macro is @var{stack-size}. On the 68000, using the standard
3993 calling convention, no functions pop their arguments, so the value of
3994 the macro is always 0 in this case. But an alternative calling
3995 convention is available in which functions that take a fixed number of
3996 arguments pop them but other functions (such as @code{printf}) pop
3997 nothing (the caller pops all). When this convention is in use,
3998 @var{funtype} is examined to determine whether a function takes a fixed
3999 number of arguments.
4002 @defmac CALL_POPS_ARGS (@var{cum})
4003 A C expression that should indicate the number of bytes a call sequence
4004 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
4005 when compiling a function call.
4007 @var{cum} is the variable in which all arguments to the called function
4008 have been accumulated.
4010 On certain architectures, such as the SH5, a call trampoline is used
4011 that pops certain registers off the stack, depending on the arguments
4012 that have been passed to the function. Since this is a property of the
4013 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
4017 @node Register Arguments
4018 @subsection Passing Arguments in Registers
4019 @cindex arguments in registers
4020 @cindex registers arguments
4022 This section describes the macros which let you control how various
4023 types of arguments are passed in registers or how they are arranged in
4026 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
4027 A C expression that controls whether a function argument is passed
4028 in a register, and which register.
4030 The arguments are @var{cum}, which summarizes all the previous
4031 arguments; @var{mode}, the machine mode of the argument; @var{type},
4032 the data type of the argument as a tree node or 0 if that is not known
4033 (which happens for C support library functions); and @var{named},
4034 which is 1 for an ordinary argument and 0 for nameless arguments that
4035 correspond to @samp{@dots{}} in the called function's prototype.
4036 @var{type} can be an incomplete type if a syntax error has previously
4039 The value of the expression is usually either a @code{reg} RTX for the
4040 hard register in which to pass the argument, or zero to pass the
4041 argument on the stack.
4043 For machines like the VAX and 68000, where normally all arguments are
4044 pushed, zero suffices as a definition.
4046 The value of the expression can also be a @code{parallel} RTX@. This is
4047 used when an argument is passed in multiple locations. The mode of the
4048 @code{parallel} should be the mode of the entire argument. The
4049 @code{parallel} holds any number of @code{expr_list} pairs; each one
4050 describes where part of the argument is passed. In each
4051 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
4052 register in which to pass this part of the argument, and the mode of the
4053 register RTX indicates how large this part of the argument is. The
4054 second operand of the @code{expr_list} is a @code{const_int} which gives
4055 the offset in bytes into the entire argument of where this part starts.
4056 As a special exception the first @code{expr_list} in the @code{parallel}
4057 RTX may have a first operand of zero. This indicates that the entire
4058 argument is also stored on the stack.
4060 The last time this macro is called, it is called with @code{MODE ==
4061 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
4062 pattern as operands 2 and 3 respectively.
4064 @cindex @file{stdarg.h} and register arguments
4065 The usual way to make the ISO library @file{stdarg.h} work on a machine
4066 where some arguments are usually passed in registers, is to cause
4067 nameless arguments to be passed on the stack instead. This is done
4068 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
4070 @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
4071 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
4072 You may use the hook @code{targetm.calls.must_pass_in_stack}
4073 in the definition of this macro to determine if this argument is of a
4074 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
4075 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
4076 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
4077 defined, the argument will be computed in the stack and then loaded into
4081 @deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (enum machine_mode @var{mode}, const_tree @var{type})
4082 This target hook should return @code{true} if we should not pass @var{type}
4083 solely in registers. The file @file{expr.h} defines a
4084 definition that is usually appropriate, refer to @file{expr.h} for additional
4088 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
4089 Define this macro if the target machine has ``register windows'', so
4090 that the register in which a function sees an arguments is not
4091 necessarily the same as the one in which the caller passed the
4094 For such machines, @code{FUNCTION_ARG} computes the register in which
4095 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
4096 be defined in a similar fashion to tell the function being called
4097 where the arguments will arrive.
4099 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
4100 serves both purposes.
4103 @deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
4104 This target hook returns the number of bytes at the beginning of an
4105 argument that must be put in registers. The value must be zero for
4106 arguments that are passed entirely in registers or that are entirely
4107 pushed on the stack.
4109 On some machines, certain arguments must be passed partially in
4110 registers and partially in memory. On these machines, typically the
4111 first few words of arguments are passed in registers, and the rest
4112 on the stack. If a multi-word argument (a @code{double} or a
4113 structure) crosses that boundary, its first few words must be passed
4114 in registers and the rest must be pushed. This macro tells the
4115 compiler when this occurs, and how many bytes should go in registers.
4117 @code{FUNCTION_ARG} for these arguments should return the first
4118 register to be used by the caller for this argument; likewise
4119 @code{FUNCTION_INCOMING_ARG}, for the called function.
4122 @deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
4123 This target hook should return @code{true} if an argument at the
4124 position indicated by @var{cum} should be passed by reference. This
4125 predicate is queried after target independent reasons for being
4126 passed by reference, such as @code{TREE_ADDRESSABLE (type)}.
4128 If the hook returns true, a copy of that argument is made in memory and a
4129 pointer to the argument is passed instead of the argument itself.
4130 The pointer is passed in whatever way is appropriate for passing a pointer
4134 @deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, const_tree @var{type}, bool @var{named})
4135 The function argument described by the parameters to this hook is
4136 known to be passed by reference. The hook should return true if the
4137 function argument should be copied by the callee instead of copied
4140 For any argument for which the hook returns true, if it can be
4141 determined that the argument is not modified, then a copy need
4144 The default version of this hook always returns false.
4147 @defmac CUMULATIVE_ARGS
4148 A C type for declaring a variable that is used as the first argument of
4149 @code{FUNCTION_ARG} and other related values. For some target machines,
4150 the type @code{int} suffices and can hold the number of bytes of
4153 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
4154 arguments that have been passed on the stack. The compiler has other
4155 variables to keep track of that. For target machines on which all
4156 arguments are passed on the stack, there is no need to store anything in
4157 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
4158 should not be empty, so use @code{int}.
4161 @defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
4162 If defined, this macro is called before generating any code for a
4163 function, but after the @var{cfun} descriptor for the function has been
4164 created. The back end may use this macro to update @var{cfun} to
4165 reflect an ABI other than that which would normally be used by default.
4166 If the compiler is generating code for a compiler-generated function,
4167 @var{fndecl} may be @code{NULL}.
4170 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
4171 A C statement (sans semicolon) for initializing the variable
4172 @var{cum} for the state at the beginning of the argument list. The
4173 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
4174 is the tree node for the data type of the function which will receive
4175 the args, or 0 if the args are to a compiler support library function.
4176 For direct calls that are not libcalls, @var{fndecl} contain the
4177 declaration node of the function. @var{fndecl} is also set when
4178 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
4179 being compiled. @var{n_named_args} is set to the number of named
4180 arguments, including a structure return address if it is passed as a
4181 parameter, when making a call. When processing incoming arguments,
4182 @var{n_named_args} is set to @minus{}1.
4184 When processing a call to a compiler support library function,
4185 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
4186 contains the name of the function, as a string. @var{libname} is 0 when
4187 an ordinary C function call is being processed. Thus, each time this
4188 macro is called, either @var{libname} or @var{fntype} is nonzero, but
4189 never both of them at once.
4192 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
4193 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
4194 it gets a @code{MODE} argument instead of @var{fntype}, that would be
4195 @code{NULL}. @var{indirect} would always be zero, too. If this macro
4196 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
4197 0)} is used instead.
4200 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
4201 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
4202 finding the arguments for the function being compiled. If this macro is
4203 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
4205 The value passed for @var{libname} is always 0, since library routines
4206 with special calling conventions are never compiled with GCC@. The
4207 argument @var{libname} exists for symmetry with
4208 @code{INIT_CUMULATIVE_ARGS}.
4209 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
4210 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
4213 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
4214 A C statement (sans semicolon) to update the summarizer variable
4215 @var{cum} to advance past an argument in the argument list. The
4216 values @var{mode}, @var{type} and @var{named} describe that argument.
4217 Once this is done, the variable @var{cum} is suitable for analyzing
4218 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
4220 This macro need not do anything if the argument in question was passed
4221 on the stack. The compiler knows how to track the amount of stack space
4222 used for arguments without any special help.
4225 @defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type})
4226 If defined, a C expression that is the number of bytes to add to the
4227 offset of the argument passed in memory. This is needed for the SPU,
4228 which passes @code{char} and @code{short} arguments in the preferred
4229 slot that is in the middle of the quad word instead of starting at the
4233 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
4234 If defined, a C expression which determines whether, and in which direction,
4235 to pad out an argument with extra space. The value should be of type
4236 @code{enum direction}: either @code{upward} to pad above the argument,
4237 @code{downward} to pad below, or @code{none} to inhibit padding.
4239 The @emph{amount} of padding is always just enough to reach the next
4240 multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control
4243 This macro has a default definition which is right for most systems.
4244 For little-endian machines, the default is to pad upward. For
4245 big-endian machines, the default is to pad downward for an argument of
4246 constant size shorter than an @code{int}, and upward otherwise.
4249 @defmac PAD_VARARGS_DOWN
4250 If defined, a C expression which determines whether the default
4251 implementation of va_arg will attempt to pad down before reading the
4252 next argument, if that argument is smaller than its aligned space as
4253 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
4254 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
4257 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
4258 Specify padding for the last element of a block move between registers and
4259 memory. @var{first} is nonzero if this is the only element. Defining this
4260 macro allows better control of register function parameters on big-endian
4261 machines, without using @code{PARALLEL} rtl. In particular,
4262 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
4263 registers, as there is no longer a "wrong" part of a register; For example,
4264 a three byte aggregate may be passed in the high part of a register if so
4268 @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type})
4269 If defined, a C expression that gives the alignment boundary, in bits,
4270 of an argument with the specified mode and type. If it is not defined,
4271 @code{PARM_BOUNDARY} is used for all arguments.
4274 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
4275 A C expression that is nonzero if @var{regno} is the number of a hard
4276 register in which function arguments are sometimes passed. This does
4277 @emph{not} include implicit arguments such as the static chain and
4278 the structure-value address. On many machines, no registers can be
4279 used for this purpose since all function arguments are pushed on the
4283 @deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (const_tree @var{type})
4284 This hook should return true if parameter of type @var{type} are passed
4285 as two scalar parameters. By default, GCC will attempt to pack complex
4286 arguments into the target's word size. Some ABIs require complex arguments
4287 to be split and treated as their individual components. For example, on
4288 AIX64, complex floats should be passed in a pair of floating point
4289 registers, even though a complex float would fit in one 64-bit floating
4292 The default value of this hook is @code{NULL}, which is treated as always
4296 @deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void)
4297 This hook returns a type node for @code{va_list} for the target.
4298 The default version of the hook returns @code{void*}.
4301 @deftypefn {Target Hook} int TARGET_ENUM_VA_LIST_P (int @var{idx}, const char ** @var{pname}, tree @var{ptype})
4302 This target hook is used in function @code{c_common_nodes_and_builtins}
4303 to iterate through the target specific builtin types for va_list. The
4304 variable @var{idx} is used as iterator. @var{pname} has to be a pointer
4305 to a @code{const char *} and @var{ptype} a pointer to a @code{tree} typed
4307 The arguments @var{pname} and @var{ptype} are used to store the result of
4308 this macro and are set to the name of the va_list builtin type and its
4310 If the return value of this macro is zero, then there is no more element.
4311 Otherwise the @var{IDX} should be increased for the next call of this
4312 macro to iterate through all types.
4315 @deftypefn {Target Hook} tree TARGET_FN_ABI_VA_LIST (tree @var{fndecl})
4316 This hook returns the va_list type of the calling convention specified by
4318 The default version of this hook returns @code{va_list_type_node}.
4321 @deftypefn {Target Hook} tree TARGET_CANONICAL_VA_LIST_TYPE (tree @var{type})
4322 This hook returns the va_list type of the calling convention specified by the
4323 type of @var{type}. If @var{type} is not a valid va_list type, it returns
4327 @deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, gimple_seq *@var{pre_p}, gimple_seq *@var{post_p})
4328 This hook performs target-specific gimplification of
4329 @code{VA_ARG_EXPR}. The first two parameters correspond to the
4330 arguments to @code{va_arg}; the latter two are as in
4331 @code{gimplify.c:gimplify_expr}.
4334 @deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (enum machine_mode @var{mode})
4335 Define this to return nonzero if the port can handle pointers
4336 with machine mode @var{mode}. The default version of this
4337 hook returns true for both @code{ptr_mode} and @code{Pmode}.
4340 @deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
4341 Define this to return nonzero if the port is prepared to handle
4342 insns involving scalar mode @var{mode}. For a scalar mode to be
4343 considered supported, all the basic arithmetic and comparisons
4346 The default version of this hook returns true for any mode
4347 required to handle the basic C types (as defined by the port).
4348 Included here are the double-word arithmetic supported by the
4349 code in @file{optabs.c}.
4352 @deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
4353 Define this to return nonzero if the port is prepared to handle
4354 insns involving vector mode @var{mode}. At the very least, it
4355 must have move patterns for this mode.
4358 @deftypefn {Target Hook} bool TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P (enum machine_mode @var{mode})
4359 Define this to return nonzero for machine modes for which the port has
4360 small register classes. If this target hook returns nonzero for a given
4361 @var{mode}, the compiler will try to minimize the lifetime of registers
4362 in @var{mode}. The hook may be called with @code{VOIDmode} as argument.
4363 In this case, the hook is expected to return nonzero if it returns nonzero
4366 On some machines, it is risky to let hard registers live across arbitrary
4367 insns. Typically, these machines have instructions that require values
4368 to be in specific registers (like an accumulator), and reload will fail
4369 if the required hard register is used for another purpose across such an
4372 Passes before reload do not know which hard registers will be used
4373 in an instruction, but the machine modes of the registers set or used in
4374 the instruction are already known. And for some machines, register
4375 classes are small for, say, integer registers but not for floating point
4376 registers. For example, the AMD x86-64 architecture requires specific
4377 registers for the legacy x86 integer instructions, but there are many
4378 SSE registers for floating point operations. On such targets, a good
4379 strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P}
4380 machine modes but zero for the SSE register classes.
4382 The default version of this hook retuns false for any mode. It is always
4383 safe to redefine this hook to return with a nonzero value. But if you
4384 unnecessarily define it, you will reduce the amount of optimizations
4385 that can be performed in some cases. If you do not define this hook
4386 to return a nonzero value when it is required, the compiler will run out
4387 of spill registers and print a fatal error message.
4391 @subsection How Scalar Function Values Are Returned
4392 @cindex return values in registers
4393 @cindex values, returned by functions
4394 @cindex scalars, returned as values
4396 This section discusses the macros that control returning scalars as
4397 values---values that can fit in registers.
4399 @deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (const_tree @var{ret_type}, const_tree @var{fn_decl_or_type}, bool @var{outgoing})
4401 Define this to return an RTX representing the place where a function
4402 returns or receives a value of data type @var{ret_type}, a tree node
4403 representing a data type. @var{fn_decl_or_type} is a tree node
4404 representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a
4405 function being called. If @var{outgoing} is false, the hook should
4406 compute the register in which the caller will see the return value.
4407 Otherwise, the hook should return an RTX representing the place where
4408 a function returns a value.
4410 On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant.
4411 (Actually, on most machines, scalar values are returned in the same
4412 place regardless of mode.) The value of the expression is usually a
4413 @code{reg} RTX for the hard register where the return value is stored.
4414 The value can also be a @code{parallel} RTX, if the return value is in
4415 multiple places. See @code{FUNCTION_ARG} for an explanation of the
4416 @code{parallel} form. Note that the callee will populate every
4417 location specified in the @code{parallel}, but if the first element of
4418 the @code{parallel} contains the whole return value, callers will use
4419 that element as the canonical location and ignore the others. The m68k
4420 port uses this type of @code{parallel} to return pointers in both
4421 @samp{%a0} (the canonical location) and @samp{%d0}.
4423 If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply
4424 the same promotion rules specified in @code{PROMOTE_MODE} if
4425 @var{valtype} is a scalar type.
4427 If the precise function being called is known, @var{func} is a tree
4428 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
4429 pointer. This makes it possible to use a different value-returning
4430 convention for specific functions when all their calls are
4433 Some target machines have ``register windows'' so that the register in
4434 which a function returns its value is not the same as the one in which
4435 the caller sees the value. For such machines, you should return
4436 different RTX depending on @var{outgoing}.
4438 @code{TARGET_FUNCTION_VALUE} is not used for return values with
4439 aggregate data types, because these are returned in another way. See
4440 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
4443 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
4444 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
4445 a new target instead.
4448 @defmac LIBCALL_VALUE (@var{mode})
4449 A C expression to create an RTX representing the place where a library
4450 function returns a value of mode @var{mode}.
4452 Note that ``library function'' in this context means a compiler
4453 support routine, used to perform arithmetic, whose name is known
4454 specially by the compiler and was not mentioned in the C code being
4458 @deftypefn {Target Hook} rtx TARGET_LIBCALL_VALUE (enum machine_mode
4459 @var{mode}, const_rtx @var{fun})
4460 Define this hook if the back-end needs to know the name of the libcall
4461 function in order to determine where the result should be returned.
4463 The mode of the result is given by @var{mode} and the name of the called
4464 library function is given by @var{fun}. The hook should return an RTX
4465 representing the place where the library function result will be returned.
4467 If this hook is not defined, then LIBCALL_VALUE will be used.
4470 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
4471 A C expression that is nonzero if @var{regno} is the number of a hard
4472 register in which the values of called function may come back.
4474 A register whose use for returning values is limited to serving as the
4475 second of a pair (for a value of type @code{double}, say) need not be
4476 recognized by this macro. So for most machines, this definition
4480 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
4483 If the machine has register windows, so that the caller and the called
4484 function use different registers for the return value, this macro
4485 should recognize only the caller's register numbers.
4487 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P}
4488 for a new target instead.
4491 @deftypefn {Target Hook} bool TARGET_FUNCTION_VALUE_REGNO_P (const unsigned int @var{regno})
4492 A target hook that return @code{true} if @var{regno} is the number of a hard
4493 register in which the values of called function may come back.
4495 A register whose use for returning values is limited to serving as the
4496 second of a pair (for a value of type @code{double}, say) need not be
4497 recognized by this target hook.
4499 If the machine has register windows, so that the caller and the called
4500 function use different registers for the return value, this target hook
4501 should recognize only the caller's register numbers.
4503 If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used.
4506 @defmac APPLY_RESULT_SIZE
4507 Define this macro if @samp{untyped_call} and @samp{untyped_return}
4508 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
4509 saving and restoring an arbitrary return value.
4512 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (const_tree @var{type})
4513 This hook should return true if values of type @var{type} are returned
4514 at the most significant end of a register (in other words, if they are
4515 padded at the least significant end). You can assume that @var{type}
4516 is returned in a register; the caller is required to check this.
4518 Note that the register provided by @code{TARGET_FUNCTION_VALUE} must
4519 be able to hold the complete return value. For example, if a 1-, 2-
4520 or 3-byte structure is returned at the most significant end of a
4521 4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an
4525 @node Aggregate Return
4526 @subsection How Large Values Are Returned
4527 @cindex aggregates as return values
4528 @cindex large return values
4529 @cindex returning aggregate values
4530 @cindex structure value address
4532 When a function value's mode is @code{BLKmode} (and in some other
4533 cases), the value is not returned according to
4534 @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the
4535 caller passes the address of a block of memory in which the value
4536 should be stored. This address is called the @dfn{structure value
4539 This section describes how to control returning structure values in
4542 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (const_tree @var{type}, const_tree @var{fntype})
4543 This target hook should return a nonzero value to say to return the
4544 function value in memory, just as large structures are always returned.
4545 Here @var{type} will be the data type of the value, and @var{fntype}
4546 will be the type of the function doing the returning, or @code{NULL} for
4549 Note that values of mode @code{BLKmode} must be explicitly handled
4550 by this function. Also, the option @option{-fpcc-struct-return}
4551 takes effect regardless of this macro. On most systems, it is
4552 possible to leave the hook undefined; this causes a default
4553 definition to be used, whose value is the constant 1 for @code{BLKmode}
4554 values, and 0 otherwise.
4556 Do not use this hook to indicate that structures and unions should always
4557 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
4561 @defmac DEFAULT_PCC_STRUCT_RETURN
4562 Define this macro to be 1 if all structure and union return values must be
4563 in memory. Since this results in slower code, this should be defined
4564 only if needed for compatibility with other compilers or with an ABI@.
4565 If you define this macro to be 0, then the conventions used for structure
4566 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
4569 If not defined, this defaults to the value 1.
4572 @deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming})
4573 This target hook should return the location of the structure value
4574 address (normally a @code{mem} or @code{reg}), or 0 if the address is
4575 passed as an ``invisible'' first argument. Note that @var{fndecl} may
4576 be @code{NULL}, for libcalls. You do not need to define this target
4577 hook if the address is always passed as an ``invisible'' first
4580 On some architectures the place where the structure value address
4581 is found by the called function is not the same place that the
4582 caller put it. This can be due to register windows, or it could
4583 be because the function prologue moves it to a different place.
4584 @var{incoming} is @code{1} or @code{2} when the location is needed in
4585 the context of the called function, and @code{0} in the context of
4588 If @var{incoming} is nonzero and the address is to be found on the
4589 stack, return a @code{mem} which refers to the frame pointer. If
4590 @var{incoming} is @code{2}, the result is being used to fetch the
4591 structure value address at the beginning of a function. If you need
4592 to emit adjusting code, you should do it at this point.
4595 @defmac PCC_STATIC_STRUCT_RETURN
4596 Define this macro if the usual system convention on the target machine
4597 for returning structures and unions is for the called function to return
4598 the address of a static variable containing the value.
4600 Do not define this if the usual system convention is for the caller to
4601 pass an address to the subroutine.
4603 This macro has effect in @option{-fpcc-struct-return} mode, but it does
4604 nothing when you use @option{-freg-struct-return} mode.
4608 @subsection Caller-Saves Register Allocation
4610 If you enable it, GCC can save registers around function calls. This
4611 makes it possible to use call-clobbered registers to hold variables that
4612 must live across calls.
4614 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
4615 A C expression to determine whether it is worthwhile to consider placing
4616 a pseudo-register in a call-clobbered hard register and saving and
4617 restoring it around each function call. The expression should be 1 when
4618 this is worth doing, and 0 otherwise.
4620 If you don't define this macro, a default is used which is good on most
4621 machines: @code{4 * @var{calls} < @var{refs}}.
4624 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
4625 A C expression specifying which mode is required for saving @var{nregs}
4626 of a pseudo-register in call-clobbered hard register @var{regno}. If
4627 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4628 returned. For most machines this macro need not be defined since GCC
4629 will select the smallest suitable mode.
4632 @node Function Entry
4633 @subsection Function Entry and Exit
4634 @cindex function entry and exit
4638 This section describes the macros that output function entry
4639 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4641 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4642 If defined, a function that outputs the assembler code for entry to a
4643 function. The prologue is responsible for setting up the stack frame,
4644 initializing the frame pointer register, saving registers that must be
4645 saved, and allocating @var{size} additional bytes of storage for the
4646 local variables. @var{size} is an integer. @var{file} is a stdio
4647 stream to which the assembler code should be output.
4649 The label for the beginning of the function need not be output by this
4650 macro. That has already been done when the macro is run.
4652 @findex regs_ever_live
4653 To determine which registers to save, the macro can refer to the array
4654 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4655 @var{r} is used anywhere within the function. This implies the function
4656 prologue should save register @var{r}, provided it is not one of the
4657 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4658 @code{regs_ever_live}.)
4660 On machines that have ``register windows'', the function entry code does
4661 not save on the stack the registers that are in the windows, even if
4662 they are supposed to be preserved by function calls; instead it takes
4663 appropriate steps to ``push'' the register stack, if any non-call-used
4664 registers are used in the function.
4666 @findex frame_pointer_needed
4667 On machines where functions may or may not have frame-pointers, the
4668 function entry code must vary accordingly; it must set up the frame
4669 pointer if one is wanted, and not otherwise. To determine whether a
4670 frame pointer is in wanted, the macro can refer to the variable
4671 @code{frame_pointer_needed}. The variable's value will be 1 at run
4672 time in a function that needs a frame pointer. @xref{Elimination}.
4674 The function entry code is responsible for allocating any stack space
4675 required for the function. This stack space consists of the regions
4676 listed below. In most cases, these regions are allocated in the
4677 order listed, with the last listed region closest to the top of the
4678 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4679 the highest address if it is not defined). You can use a different order
4680 for a machine if doing so is more convenient or required for
4681 compatibility reasons. Except in cases where required by standard
4682 or by a debugger, there is no reason why the stack layout used by GCC
4683 need agree with that used by other compilers for a machine.
4686 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
4687 If defined, a function that outputs assembler code at the end of a
4688 prologue. This should be used when the function prologue is being
4689 emitted as RTL, and you have some extra assembler that needs to be
4690 emitted. @xref{prologue instruction pattern}.
4693 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
4694 If defined, a function that outputs assembler code at the start of an
4695 epilogue. This should be used when the function epilogue is being
4696 emitted as RTL, and you have some extra assembler that needs to be
4697 emitted. @xref{epilogue instruction pattern}.
4700 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4701 If defined, a function that outputs the assembler code for exit from a
4702 function. The epilogue is responsible for restoring the saved
4703 registers and stack pointer to their values when the function was
4704 called, and returning control to the caller. This macro takes the
4705 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4706 registers to restore are determined from @code{regs_ever_live} and
4707 @code{CALL_USED_REGISTERS} in the same way.
4709 On some machines, there is a single instruction that does all the work
4710 of returning from the function. On these machines, give that
4711 instruction the name @samp{return} and do not define the macro
4712 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4714 Do not define a pattern named @samp{return} if you want the
4715 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4716 switches to control whether return instructions or epilogues are used,
4717 define a @samp{return} pattern with a validity condition that tests the
4718 target switches appropriately. If the @samp{return} pattern's validity
4719 condition is false, epilogues will be used.
4721 On machines where functions may or may not have frame-pointers, the
4722 function exit code must vary accordingly. Sometimes the code for these
4723 two cases is completely different. To determine whether a frame pointer
4724 is wanted, the macro can refer to the variable
4725 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4726 a function that needs a frame pointer.
4728 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4729 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4730 The C variable @code{current_function_is_leaf} is nonzero for such a
4731 function. @xref{Leaf Functions}.
4733 On some machines, some functions pop their arguments on exit while
4734 others leave that for the caller to do. For example, the 68020 when
4735 given @option{-mrtd} pops arguments in functions that take a fixed
4736 number of arguments.
4738 @findex current_function_pops_args
4739 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4740 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4741 needs to know what was decided. The number of bytes of the current
4742 function's arguments that this function should pop is available in
4743 @code{crtl->args.pops_args}. @xref{Scalar Return}.
4748 @findex current_function_pretend_args_size
4749 A region of @code{current_function_pretend_args_size} bytes of
4750 uninitialized space just underneath the first argument arriving on the
4751 stack. (This may not be at the very start of the allocated stack region
4752 if the calling sequence has pushed anything else since pushing the stack
4753 arguments. But usually, on such machines, nothing else has been pushed
4754 yet, because the function prologue itself does all the pushing.) This
4755 region is used on machines where an argument may be passed partly in
4756 registers and partly in memory, and, in some cases to support the
4757 features in @code{<stdarg.h>}.
4760 An area of memory used to save certain registers used by the function.
4761 The size of this area, which may also include space for such things as
4762 the return address and pointers to previous stack frames, is
4763 machine-specific and usually depends on which registers have been used
4764 in the function. Machines with register windows often do not require
4768 A region of at least @var{size} bytes, possibly rounded up to an allocation
4769 boundary, to contain the local variables of the function. On some machines,
4770 this region and the save area may occur in the opposite order, with the
4771 save area closer to the top of the stack.
4774 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4775 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4776 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4777 argument lists of the function. @xref{Stack Arguments}.
4780 @defmac EXIT_IGNORE_STACK
4781 Define this macro as a C expression that is nonzero if the return
4782 instruction or the function epilogue ignores the value of the stack
4783 pointer; in other words, if it is safe to delete an instruction to
4784 adjust the stack pointer before a return from the function. The
4787 Note that this macro's value is relevant only for functions for which
4788 frame pointers are maintained. It is never safe to delete a final
4789 stack adjustment in a function that has no frame pointer, and the
4790 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4793 @defmac EPILOGUE_USES (@var{regno})
4794 Define this macro as a C expression that is nonzero for registers that are
4795 used by the epilogue or the @samp{return} pattern. The stack and frame
4796 pointer registers are already assumed to be used as needed.
4799 @defmac EH_USES (@var{regno})
4800 Define this macro as a C expression that is nonzero for registers that are
4801 used by the exception handling mechanism, and so should be considered live
4802 on entry to an exception edge.
4805 @defmac DELAY_SLOTS_FOR_EPILOGUE
4806 Define this macro if the function epilogue contains delay slots to which
4807 instructions from the rest of the function can be ``moved''. The
4808 definition should be a C expression whose value is an integer
4809 representing the number of delay slots there.
4812 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4813 A C expression that returns 1 if @var{insn} can be placed in delay
4814 slot number @var{n} of the epilogue.
4816 The argument @var{n} is an integer which identifies the delay slot now
4817 being considered (since different slots may have different rules of
4818 eligibility). It is never negative and is always less than the number
4819 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4820 If you reject a particular insn for a given delay slot, in principle, it
4821 may be reconsidered for a subsequent delay slot. Also, other insns may
4822 (at least in principle) be considered for the so far unfilled delay
4825 @findex current_function_epilogue_delay_list
4826 @findex final_scan_insn
4827 The insns accepted to fill the epilogue delay slots are put in an RTL
4828 list made with @code{insn_list} objects, stored in the variable
4829 @code{current_function_epilogue_delay_list}. The insn for the first
4830 delay slot comes first in the list. Your definition of the macro
4831 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4832 outputting the insns in this list, usually by calling
4833 @code{final_scan_insn}.
4835 You need not define this macro if you did not define
4836 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4839 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function})
4840 A function that outputs the assembler code for a thunk
4841 function, used to implement C++ virtual function calls with multiple
4842 inheritance. The thunk acts as a wrapper around a virtual function,
4843 adjusting the implicit object parameter before handing control off to
4846 First, emit code to add the integer @var{delta} to the location that
4847 contains the incoming first argument. Assume that this argument
4848 contains a pointer, and is the one used to pass the @code{this} pointer
4849 in C++. This is the incoming argument @emph{before} the function prologue,
4850 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4851 all other incoming arguments.
4853 Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
4854 made after adding @code{delta}. In particular, if @var{p} is the
4855 adjusted pointer, the following adjustment should be made:
4858 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4861 After the additions, emit code to jump to @var{function}, which is a
4862 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4863 not touch the return address. Hence returning from @var{FUNCTION} will
4864 return to whoever called the current @samp{thunk}.
4866 The effect must be as if @var{function} had been called directly with
4867 the adjusted first argument. This macro is responsible for emitting all
4868 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4869 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4871 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4872 have already been extracted from it.) It might possibly be useful on
4873 some targets, but probably not.
4875 If you do not define this macro, the target-independent code in the C++
4876 front end will generate a less efficient heavyweight thunk that calls
4877 @var{function} instead of jumping to it. The generic approach does
4878 not support varargs.
4881 @deftypefn {Target Hook} bool TARGET_ASM_CAN_OUTPUT_MI_THUNK (const_tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, const_tree @var{function})
4882 A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
4883 to output the assembler code for the thunk function specified by the
4884 arguments it is passed, and false otherwise. In the latter case, the
4885 generic approach will be used by the C++ front end, with the limitations
4890 @subsection Generating Code for Profiling
4891 @cindex profiling, code generation
4893 These macros will help you generate code for profiling.
4895 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4896 A C statement or compound statement to output to @var{file} some
4897 assembler code to call the profiling subroutine @code{mcount}.
4900 The details of how @code{mcount} expects to be called are determined by
4901 your operating system environment, not by GCC@. To figure them out,
4902 compile a small program for profiling using the system's installed C
4903 compiler and look at the assembler code that results.
4905 Older implementations of @code{mcount} expect the address of a counter
4906 variable to be loaded into some register. The name of this variable is
4907 @samp{LP} followed by the number @var{labelno}, so you would generate
4908 the name using @samp{LP%d} in a @code{fprintf}.
4911 @defmac PROFILE_HOOK
4912 A C statement or compound statement to output to @var{file} some assembly
4913 code to call the profiling subroutine @code{mcount} even the target does
4914 not support profiling.
4917 @defmac NO_PROFILE_COUNTERS
4918 Define this macro to be an expression with a nonzero value if the
4919 @code{mcount} subroutine on your system does not need a counter variable
4920 allocated for each function. This is true for almost all modern
4921 implementations. If you define this macro, you must not use the
4922 @var{labelno} argument to @code{FUNCTION_PROFILER}.
4925 @defmac PROFILE_BEFORE_PROLOGUE
4926 Define this macro if the code for function profiling should come before
4927 the function prologue. Normally, the profiling code comes after.
4931 @subsection Permitting tail calls
4934 @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
4935 True if it is ok to do sibling call optimization for the specified
4936 call expression @var{exp}. @var{decl} will be the called function,
4937 or @code{NULL} if this is an indirect call.
4939 It is not uncommon for limitations of calling conventions to prevent
4940 tail calls to functions outside the current unit of translation, or
4941 during PIC compilation. The hook is used to enforce these restrictions,
4942 as the @code{sibcall} md pattern can not fail, or fall over to a
4943 ``normal'' call. The criteria for successful sibling call optimization
4944 may vary greatly between different architectures.
4947 @deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap @var{regs})
4948 Add any hard registers to @var{regs} that are live on entry to the
4949 function. This hook only needs to be defined to provide registers that
4950 cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved
4951 registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM,
4952 TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES,
4953 FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.
4956 @node Stack Smashing Protection
4957 @subsection Stack smashing protection
4958 @cindex stack smashing protection
4960 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void)
4961 This hook returns a @code{DECL} node for the external variable to use
4962 for the stack protection guard. This variable is initialized by the
4963 runtime to some random value and is used to initialize the guard value
4964 that is placed at the top of the local stack frame. The type of this
4965 variable must be @code{ptr_type_node}.
4967 The default version of this hook creates a variable called
4968 @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
4971 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void)
4972 This hook returns a tree expression that alerts the runtime that the
4973 stack protect guard variable has been modified. This expression should
4974 involve a call to a @code{noreturn} function.
4976 The default version of this hook invokes a function called
4977 @samp{__stack_chk_fail}, taking no arguments. This function is
4978 normally defined in @file{libgcc2.c}.
4982 @section Implementing the Varargs Macros
4983 @cindex varargs implementation
4985 GCC comes with an implementation of @code{<varargs.h>} and
4986 @code{<stdarg.h>} that work without change on machines that pass arguments
4987 on the stack. Other machines require their own implementations of
4988 varargs, and the two machine independent header files must have
4989 conditionals to include it.
4991 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4992 the calling convention for @code{va_start}. The traditional
4993 implementation takes just one argument, which is the variable in which
4994 to store the argument pointer. The ISO implementation of
4995 @code{va_start} takes an additional second argument. The user is
4996 supposed to write the last named argument of the function here.
4998 However, @code{va_start} should not use this argument. The way to find
4999 the end of the named arguments is with the built-in functions described
5002 @defmac __builtin_saveregs ()
5003 Use this built-in function to save the argument registers in memory so
5004 that the varargs mechanism can access them. Both ISO and traditional
5005 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
5006 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
5008 On some machines, @code{__builtin_saveregs} is open-coded under the
5009 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
5010 other machines, it calls a routine written in assembler language,
5011 found in @file{libgcc2.c}.
5013 Code generated for the call to @code{__builtin_saveregs} appears at the
5014 beginning of the function, as opposed to where the call to
5015 @code{__builtin_saveregs} is written, regardless of what the code is.
5016 This is because the registers must be saved before the function starts
5017 to use them for its own purposes.
5018 @c i rewrote the first sentence above to fix an overfull hbox. --mew
5022 @defmac __builtin_args_info (@var{category})
5023 Use this built-in function to find the first anonymous arguments in
5026 In general, a machine may have several categories of registers used for
5027 arguments, each for a particular category of data types. (For example,
5028 on some machines, floating-point registers are used for floating-point
5029 arguments while other arguments are passed in the general registers.)
5030 To make non-varargs functions use the proper calling convention, you
5031 have defined the @code{CUMULATIVE_ARGS} data type to record how many
5032 registers in each category have been used so far
5034 @code{__builtin_args_info} accesses the same data structure of type
5035 @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished
5036 with it, with @var{category} specifying which word to access. Thus, the
5037 value indicates the first unused register in a given category.
5039 Normally, you would use @code{__builtin_args_info} in the implementation
5040 of @code{va_start}, accessing each category just once and storing the
5041 value in the @code{va_list} object. This is because @code{va_list} will
5042 have to update the values, and there is no way to alter the
5043 values accessed by @code{__builtin_args_info}.
5046 @defmac __builtin_next_arg (@var{lastarg})
5047 This is the equivalent of @code{__builtin_args_info}, for stack
5048 arguments. It returns the address of the first anonymous stack
5049 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
5050 returns the address of the location above the first anonymous stack
5051 argument. Use it in @code{va_start} to initialize the pointer for
5052 fetching arguments from the stack. Also use it in @code{va_start} to
5053 verify that the second parameter @var{lastarg} is the last named argument
5054 of the current function.
5057 @defmac __builtin_classify_type (@var{object})
5058 Since each machine has its own conventions for which data types are
5059 passed in which kind of register, your implementation of @code{va_arg}
5060 has to embody these conventions. The easiest way to categorize the
5061 specified data type is to use @code{__builtin_classify_type} together
5062 with @code{sizeof} and @code{__alignof__}.
5064 @code{__builtin_classify_type} ignores the value of @var{object},
5065 considering only its data type. It returns an integer describing what
5066 kind of type that is---integer, floating, pointer, structure, and so on.
5068 The file @file{typeclass.h} defines an enumeration that you can use to
5069 interpret the values of @code{__builtin_classify_type}.
5072 These machine description macros help implement varargs:
5074 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void)
5075 If defined, this hook produces the machine-specific code for a call to
5076 @code{__builtin_saveregs}. This code will be moved to the very
5077 beginning of the function, before any parameter access are made. The
5078 return value of this function should be an RTX that contains the value
5079 to use as the return of @code{__builtin_saveregs}.
5082 @deftypefn {Target Hook} void TARGET_SETUP_INCOMING_VARARGS (CUMULATIVE_ARGS *@var{args_so_far}, enum machine_mode @var{mode}, tree @var{type}, int *@var{pretend_args_size}, int @var{second_time})
5083 This target hook offers an alternative to using
5084 @code{__builtin_saveregs} and defining the hook
5085 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
5086 register arguments into the stack so that all the arguments appear to
5087 have been passed consecutively on the stack. Once this is done, you can
5088 use the standard implementation of varargs that works for machines that
5089 pass all their arguments on the stack.
5091 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
5092 structure, containing the values that are obtained after processing the
5093 named arguments. The arguments @var{mode} and @var{type} describe the
5094 last named argument---its machine mode and its data type as a tree node.
5096 The target hook should do two things: first, push onto the stack all the
5097 argument registers @emph{not} used for the named arguments, and second,
5098 store the size of the data thus pushed into the @code{int}-valued
5099 variable pointed to by @var{pretend_args_size}. The value that you
5100 store here will serve as additional offset for setting up the stack
5103 Because you must generate code to push the anonymous arguments at
5104 compile time without knowing their data types,
5105 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
5106 have just a single category of argument register and use it uniformly
5109 If the argument @var{second_time} is nonzero, it means that the
5110 arguments of the function are being analyzed for the second time. This
5111 happens for an inline function, which is not actually compiled until the
5112 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
5113 not generate any instructions in this case.
5116 @deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca})
5117 Define this hook to return @code{true} if the location where a function
5118 argument is passed depends on whether or not it is a named argument.
5120 This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
5121 is set for varargs and stdarg functions. If this hook returns
5122 @code{true}, the @var{named} argument is always true for named
5123 arguments, and false for unnamed arguments. If it returns @code{false},
5124 but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
5125 then all arguments are treated as named. Otherwise, all named arguments
5126 except the last are treated as named.
5128 You need not define this hook if it always returns @code{false}.
5131 @deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED (CUMULATIVE_ARGS *@var{ca})
5132 If you need to conditionally change ABIs so that one works with
5133 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
5134 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
5135 defined, then define this hook to return @code{true} if
5136 @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
5137 Otherwise, you should not define this hook.
5141 @section Trampolines for Nested Functions
5142 @cindex trampolines for nested functions
5143 @cindex nested functions, trampolines for
5145 A @dfn{trampoline} is a small piece of code that is created at run time
5146 when the address of a nested function is taken. It normally resides on
5147 the stack, in the stack frame of the containing function. These macros
5148 tell GCC how to generate code to allocate and initialize a
5151 The instructions in the trampoline must do two things: load a constant
5152 address into the static chain register, and jump to the real address of
5153 the nested function. On CISC machines such as the m68k, this requires
5154 two instructions, a move immediate and a jump. Then the two addresses
5155 exist in the trampoline as word-long immediate operands. On RISC
5156 machines, it is often necessary to load each address into a register in
5157 two parts. Then pieces of each address form separate immediate
5160 The code generated to initialize the trampoline must store the variable
5161 parts---the static chain value and the function address---into the
5162 immediate operands of the instructions. On a CISC machine, this is
5163 simply a matter of copying each address to a memory reference at the
5164 proper offset from the start of the trampoline. On a RISC machine, it
5165 may be necessary to take out pieces of the address and store them
5168 @deftypefn {Target Hook} void TARGET_ASM_TRAMPOLINE_TEMPLATE (FILE *@var{f})
5169 This hook is called by @code{assemble_trampoline_template} to output,
5170 on the stream @var{f}, assembler code for a block of data that contains
5171 the constant parts of a trampoline. This code should not include a
5172 label---the label is taken care of automatically.
5174 If you do not define this hook, it means no template is needed
5175 for the target. Do not define this hook on systems where the block move
5176 code to copy the trampoline into place would be larger than the code
5177 to generate it on the spot.
5180 @defmac TRAMPOLINE_SECTION
5181 Return the section into which the trampoline template is to be placed
5182 (@pxref{Sections}). The default value is @code{readonly_data_section}.
5185 @defmac TRAMPOLINE_SIZE
5186 A C expression for the size in bytes of the trampoline, as an integer.
5189 @defmac TRAMPOLINE_ALIGNMENT
5190 Alignment required for trampolines, in bits.
5192 If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT}
5193 is used for aligning trampolines.
5196 @deftypefn {Target Hook} void TARGET_TRAMPOLINE_INIT (rtx @var{m_tramp}, tree @var{fndecl}, rtx @var{static_chain})
5197 This hook is called to initialize a trampoline.
5198 @var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl}
5199 is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an
5200 RTX for the static chain value that should be passed to the function
5203 If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the
5204 first thing this hook should do is emit a block move into @var{m_tramp}
5205 from the memory block returned by @code{assemble_trampoline_template}.
5206 Note that the block move need only cover the constant parts of the
5207 trampoline. If the target isolates the variable parts of the trampoline
5208 to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied.
5210 If the target requires any other actions, such as flushing caches or
5211 enabling stack execution, these actions should be performed after
5212 initializing the trampoline proper.
5215 @deftypefn {Target Hook} rtx TARGET_TRAMPOLINE_ADJUST_ADDRESS (rtx @var{addr})
5216 This hook should perform any machine-specific adjustment in
5217 the address of the trampoline. Its argument contains the address of the
5218 memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}. In case
5219 the address to be used for a function call should be different from the
5220 address at which the template was stored, the different address should
5221 be returned; otherwise @var{addr} should be returned unchanged.
5222 If this hook is not defined, @var{addr} will be used for function calls.
5225 Implementing trampolines is difficult on many machines because they have
5226 separate instruction and data caches. Writing into a stack location
5227 fails to clear the memory in the instruction cache, so when the program
5228 jumps to that location, it executes the old contents.
5230 Here are two possible solutions. One is to clear the relevant parts of
5231 the instruction cache whenever a trampoline is set up. The other is to
5232 make all trampolines identical, by having them jump to a standard
5233 subroutine. The former technique makes trampoline execution faster; the
5234 latter makes initialization faster.
5236 To clear the instruction cache when a trampoline is initialized, define
5237 the following macro.
5239 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
5240 If defined, expands to a C expression clearing the @emph{instruction
5241 cache} in the specified interval. The definition of this macro would
5242 typically be a series of @code{asm} statements. Both @var{beg} and
5243 @var{end} are both pointer expressions.
5246 The operating system may also require the stack to be made executable
5247 before calling the trampoline. To implement this requirement, define
5248 the following macro.
5250 @defmac ENABLE_EXECUTE_STACK
5251 Define this macro if certain operations must be performed before executing
5252 code located on the stack. The macro should expand to a series of C
5253 file-scope constructs (e.g.@: functions) and provide a unique entry point
5254 named @code{__enable_execute_stack}. The target is responsible for
5255 emitting calls to the entry point in the code, for example from the
5256 @code{TARGET_TRAMPOLINE_INIT} hook.
5259 To use a standard subroutine, define the following macro. In addition,
5260 you must make sure that the instructions in a trampoline fill an entire
5261 cache line with identical instructions, or else ensure that the
5262 beginning of the trampoline code is always aligned at the same point in
5263 its cache line. Look in @file{m68k.h} as a guide.
5265 @defmac TRANSFER_FROM_TRAMPOLINE
5266 Define this macro if trampolines need a special subroutine to do their
5267 work. The macro should expand to a series of @code{asm} statements
5268 which will be compiled with GCC@. They go in a library function named
5269 @code{__transfer_from_trampoline}.
5271 If you need to avoid executing the ordinary prologue code of a compiled
5272 C function when you jump to the subroutine, you can do so by placing a
5273 special label of your own in the assembler code. Use one @code{asm}
5274 statement to generate an assembler label, and another to make the label
5275 global. Then trampolines can use that label to jump directly to your
5276 special assembler code.
5280 @section Implicit Calls to Library Routines
5281 @cindex library subroutine names
5282 @cindex @file{libgcc.a}
5284 @c prevent bad page break with this line
5285 Here is an explanation of implicit calls to library routines.
5287 @defmac DECLARE_LIBRARY_RENAMES
5288 This macro, if defined, should expand to a piece of C code that will get
5289 expanded when compiling functions for libgcc.a. It can be used to
5290 provide alternate names for GCC's internal library functions if there
5291 are ABI-mandated names that the compiler should provide.
5294 @findex set_optab_libfunc
5295 @findex init_one_libfunc
5296 @deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void)
5297 This hook should declare additional library routines or rename
5298 existing ones, using the functions @code{set_optab_libfunc} and
5299 @code{init_one_libfunc} defined in @file{optabs.c}.
5300 @code{init_optabs} calls this macro after initializing all the normal
5303 The default is to do nothing. Most ports don't need to define this hook.
5306 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
5307 This macro should return @code{true} if the library routine that
5308 implements the floating point comparison operator @var{comparison} in
5309 mode @var{mode} will return a boolean, and @var{false} if it will
5312 GCC's own floating point libraries return tristates from the
5313 comparison operators, so the default returns false always. Most ports
5314 don't need to define this macro.
5317 @defmac TARGET_LIB_INT_CMP_BIASED
5318 This macro should evaluate to @code{true} if the integer comparison
5319 functions (like @code{__cmpdi2}) return 0 to indicate that the first
5320 operand is smaller than the second, 1 to indicate that they are equal,
5321 and 2 to indicate that the first operand is greater than the second.
5322 If this macro evaluates to @code{false} the comparison functions return
5323 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
5324 in @file{libgcc.a}, you do not need to define this macro.
5327 @cindex US Software GOFAST, floating point emulation library
5328 @cindex floating point emulation library, US Software GOFAST
5329 @cindex GOFAST, floating point emulation library
5330 @findex gofast_maybe_init_libfuncs
5331 @defmac US_SOFTWARE_GOFAST
5332 Define this macro if your system C library uses the US Software GOFAST
5333 library to provide floating point emulation.
5335 In addition to defining this macro, your architecture must set
5336 @code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or
5337 else call that function from its version of that hook. It is defined
5338 in @file{config/gofast.h}, which must be included by your
5339 architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for
5342 If this macro is defined, the
5343 @code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return
5344 false for @code{SFmode} and @code{DFmode} comparisons.
5347 @cindex @code{EDOM}, implicit usage
5350 The value of @code{EDOM} on the target machine, as a C integer constant
5351 expression. If you don't define this macro, GCC does not attempt to
5352 deposit the value of @code{EDOM} into @code{errno} directly. Look in
5353 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
5356 If you do not define @code{TARGET_EDOM}, then compiled code reports
5357 domain errors by calling the library function and letting it report the
5358 error. If mathematical functions on your system use @code{matherr} when
5359 there is an error, then you should leave @code{TARGET_EDOM} undefined so
5360 that @code{matherr} is used normally.
5363 @cindex @code{errno}, implicit usage
5364 @defmac GEN_ERRNO_RTX
5365 Define this macro as a C expression to create an rtl expression that
5366 refers to the global ``variable'' @code{errno}. (On certain systems,
5367 @code{errno} may not actually be a variable.) If you don't define this
5368 macro, a reasonable default is used.
5371 @cindex C99 math functions, implicit usage
5372 @defmac TARGET_C99_FUNCTIONS
5373 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
5374 @code{sinf} and similarly for other functions defined by C99 standard. The
5375 default is zero because a number of existing systems lack support for these
5376 functions in their runtime so this macro needs to be redefined to one on
5377 systems that do support the C99 runtime.
5380 @cindex sincos math function, implicit usage
5381 @defmac TARGET_HAS_SINCOS
5382 When this macro is nonzero, GCC will implicitly optimize calls to @code{sin}
5383 and @code{cos} with the same argument to a call to @code{sincos}. The
5384 default is zero. The target has to provide the following functions:
5386 void sincos(double x, double *sin, double *cos);
5387 void sincosf(float x, float *sin, float *cos);
5388 void sincosl(long double x, long double *sin, long double *cos);
5392 @defmac NEXT_OBJC_RUNTIME
5393 Define this macro to generate code for Objective-C message sending using
5394 the calling convention of the NeXT system. This calling convention
5395 involves passing the object, the selector and the method arguments all
5396 at once to the method-lookup library function.
5398 The default calling convention passes just the object and the selector
5399 to the lookup function, which returns a pointer to the method.
5402 @node Addressing Modes
5403 @section Addressing Modes
5404 @cindex addressing modes
5406 @c prevent bad page break with this line
5407 This is about addressing modes.
5409 @defmac HAVE_PRE_INCREMENT
5410 @defmacx HAVE_PRE_DECREMENT
5411 @defmacx HAVE_POST_INCREMENT
5412 @defmacx HAVE_POST_DECREMENT
5413 A C expression that is nonzero if the machine supports pre-increment,
5414 pre-decrement, post-increment, or post-decrement addressing respectively.
5417 @defmac HAVE_PRE_MODIFY_DISP
5418 @defmacx HAVE_POST_MODIFY_DISP
5419 A C expression that is nonzero if the machine supports pre- or
5420 post-address side-effect generation involving constants other than
5421 the size of the memory operand.
5424 @defmac HAVE_PRE_MODIFY_REG
5425 @defmacx HAVE_POST_MODIFY_REG
5426 A C expression that is nonzero if the machine supports pre- or
5427 post-address side-effect generation involving a register displacement.
5430 @defmac CONSTANT_ADDRESS_P (@var{x})
5431 A C expression that is 1 if the RTX @var{x} is a constant which
5432 is a valid address. On most machines the default definition of
5433 @code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)}
5434 is acceptable, but a few machines are more restrictive as to which
5435 constant addresses are supported.
5438 @defmac CONSTANT_P (@var{x})
5439 @code{CONSTANT_P}, which is defined by target-independent code,
5440 accepts integer-values expressions whose values are not explicitly
5441 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
5442 expressions and @code{const} arithmetic expressions, in addition to
5443 @code{const_int} and @code{const_double} expressions.
5446 @defmac MAX_REGS_PER_ADDRESS
5447 A number, the maximum number of registers that can appear in a valid
5448 memory address. Note that it is up to you to specify a value equal to
5449 the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
5453 @deftypefn {Target Hook} bool TARGET_LEGITIMATE_ADDRESS_P (enum machine_mode @var{mode}, rtx @var{x}, bool @var{strict})
5454 A function that returns whether @var{x} (an RTX) is a legitimate memory
5455 address on the target machine for a memory operand of mode @var{mode}.
5457 Legitimate addresses are defined in two variants: a strict variant and a
5458 non-strict one. The @var{strict} parameter chooses which variant is
5459 desired by the caller.
5461 The strict variant is used in the reload pass. It must be defined so
5462 that any pseudo-register that has not been allocated a hard register is
5463 considered a memory reference. This is because in contexts where some
5464 kind of register is required, a pseudo-register with no hard register
5465 must be rejected. For non-hard registers, the strict variant should look
5466 up the @code{reg_renumber} array; it should then proceed using the hard
5467 register number in the array, or treat the pseudo as a memory reference
5468 if the array holds @code{-1}.
5470 The non-strict variant is used in other passes. It must be defined to
5471 accept all pseudo-registers in every context where some kind of
5472 register is required.
5474 Normally, constant addresses which are the sum of a @code{symbol_ref}
5475 and an integer are stored inside a @code{const} RTX to mark them as
5476 constant. Therefore, there is no need to recognize such sums
5477 specifically as legitimate addresses. Normally you would simply
5478 recognize any @code{const} as legitimate.
5480 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
5481 sums that are not marked with @code{const}. It assumes that a naked
5482 @code{plus} indicates indexing. If so, then you @emph{must} reject such
5483 naked constant sums as illegitimate addresses, so that none of them will
5484 be given to @code{PRINT_OPERAND_ADDRESS}.
5486 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
5487 On some machines, whether a symbolic address is legitimate depends on
5488 the section that the address refers to. On these machines, define the
5489 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
5490 into the @code{symbol_ref}, and then check for it here. When you see a
5491 @code{const}, you will have to look inside it to find the
5492 @code{symbol_ref} in order to determine the section. @xref{Assembler
5495 @cindex @code{GO_IF_LEGITIMATE_ADDRESS}
5496 Some ports are still using a deprecated legacy substitute for
5497 this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro
5501 #define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
5505 and should @code{goto @var{label}} if the address @var{x} is a valid
5506 address on the target machine for a memory operand of mode @var{mode}.
5507 Whether the strict or non-strict variants are desired is defined by
5508 the @code{REG_OK_STRICT} macro introduced earlier in this section.
5509 Using the hook is usually simpler because it limits the number of
5510 files that are recompiled when changes are made.
5513 @defmac TARGET_MEM_CONSTRAINT
5514 A single character to be used instead of the default @code{'m'}
5515 character for general memory addresses. This defines the constraint
5516 letter which matches the memory addresses accepted by
5517 @code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to
5518 support new address formats in your back end without changing the
5519 semantics of the @code{'m'} constraint. This is necessary in order to
5520 preserve functionality of inline assembly constructs using the
5521 @code{'m'} constraint.
5524 @defmac FIND_BASE_TERM (@var{x})
5525 A C expression to determine the base term of address @var{x},
5526 or to provide a simplified version of @var{x} from which @file{alias.c}
5527 can easily find the base term. This macro is used in only two places:
5528 @code{find_base_value} and @code{find_base_term} in @file{alias.c}.
5530 It is always safe for this macro to not be defined. It exists so
5531 that alias analysis can understand machine-dependent addresses.
5533 The typical use of this macro is to handle addresses containing
5534 a label_ref or symbol_ref within an UNSPEC@.
5537 @deftypefn {Target Hook} rtx TARGET_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, enum machine_mode @var{mode})
5538 This hook is given an invalid memory address @var{x} for an
5539 operand of mode @var{mode} and should try to return a valid memory
5542 @findex break_out_memory_refs
5543 @var{x} will always be the result of a call to @code{break_out_memory_refs},
5544 and @var{oldx} will be the operand that was given to that function to produce
5547 The code of the hook should not alter the substructure of
5548 @var{x}. If it transforms @var{x} into a more legitimate form, it
5549 should return the new @var{x}.
5551 It is not necessary for this hook to come up with a legitimate address.
5552 The compiler has standard ways of doing so in all cases. In fact, it
5553 is safe to omit this hook or make it return @var{x} if it cannot find
5554 a valid way to legitimize the address. But often a machine-dependent
5555 strategy can generate better code.
5558 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
5559 A C compound statement that attempts to replace @var{x}, which is an address
5560 that needs reloading, with a valid memory address for an operand of mode
5561 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
5562 It is not necessary to define this macro, but it might be useful for
5563 performance reasons.
5565 For example, on the i386, it is sometimes possible to use a single
5566 reload register instead of two by reloading a sum of two pseudo
5567 registers into a register. On the other hand, for number of RISC
5568 processors offsets are limited so that often an intermediate address
5569 needs to be generated in order to address a stack slot. By defining
5570 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
5571 generated for adjacent some stack slots can be made identical, and thus
5574 @emph{Note}: This macro should be used with caution. It is necessary
5575 to know something of how reload works in order to effectively use this,
5576 and it is quite easy to produce macros that build in too much knowledge
5577 of reload internals.
5579 @emph{Note}: This macro must be able to reload an address created by a
5580 previous invocation of this macro. If it fails to handle such addresses
5581 then the compiler may generate incorrect code or abort.
5584 The macro definition should use @code{push_reload} to indicate parts that
5585 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
5586 suitable to be passed unaltered to @code{push_reload}.
5588 The code generated by this macro must not alter the substructure of
5589 @var{x}. If it transforms @var{x} into a more legitimate form, it
5590 should assign @var{x} (which will always be a C variable) a new value.
5591 This also applies to parts that you change indirectly by calling
5594 @findex strict_memory_address_p
5595 The macro definition may use @code{strict_memory_address_p} to test if
5596 the address has become legitimate.
5599 If you want to change only a part of @var{x}, one standard way of doing
5600 this is to use @code{copy_rtx}. Note, however, that it unshares only a
5601 single level of rtl. Thus, if the part to be changed is not at the
5602 top level, you'll need to replace first the top level.
5603 It is not necessary for this macro to come up with a legitimate
5604 address; but often a machine-dependent strategy can generate better code.
5607 @deftypefn {Target Hook} bool TARGET_MODE_DEPENDENT_ADDRESS_P (const_rtx @var{addr})
5608 This hook returns @code{true} if memory address @var{addr} can have
5609 different meanings depending on the machine mode of the memory
5610 reference it is used for or if the address is valid for some modes
5613 Autoincrement and autodecrement addresses typically have mode-dependent
5614 effects because the amount of the increment or decrement is the size
5615 of the operand being addressed. Some machines have other mode-dependent
5616 addresses. Many RISC machines have no mode-dependent addresses.
5618 You may assume that @var{addr} is a valid address for the machine.
5620 The default version of this hook returns @code{false}.
5623 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
5624 A C statement or compound statement with a conditional @code{goto
5625 @var{label};} executed if memory address @var{x} (an RTX) can have
5626 different meanings depending on the machine mode of the memory
5627 reference it is used for or if the address is valid for some modes
5630 Autoincrement and autodecrement addresses typically have mode-dependent
5631 effects because the amount of the increment or decrement is the size
5632 of the operand being addressed. Some machines have other mode-dependent
5633 addresses. Many RISC machines have no mode-dependent addresses.
5635 You may assume that @var{addr} is a valid address for the machine.
5637 These are obsolete macros, replaced by the
5638 @code{TARGET_MODE_DEPENDENT_ADDRESS_P} target hook.
5641 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5642 A C expression that is nonzero if @var{x} is a legitimate constant for
5643 an immediate operand on the target machine. You can assume that
5644 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5645 @samp{1} is a suitable definition for this macro on machines where
5646 anything @code{CONSTANT_P} is valid.
5649 @deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x})
5650 This hook is used to undo the possibly obfuscating effects of the
5651 @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
5652 macros. Some backend implementations of these macros wrap symbol
5653 references inside an @code{UNSPEC} rtx to represent PIC or similar
5654 addressing modes. This target hook allows GCC's optimizers to understand
5655 the semantics of these opaque @code{UNSPEC}s by converting them back
5656 into their original form.
5659 @deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (rtx @var{x})
5660 This hook should return true if @var{x} is of a form that cannot (or
5661 should not) be spilled to the constant pool. The default version of
5662 this hook returns false.
5664 The primary reason to define this hook is to prevent reload from
5665 deciding that a non-legitimate constant would be better reloaded
5666 from the constant pool instead of spilling and reloading a register
5667 holding the constant. This restriction is often true of addresses
5668 of TLS symbols for various targets.
5671 @deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (enum machine_mode @var{mode}, const_rtx @var{x})
5672 This hook should return true if pool entries for constant @var{x} can
5673 be placed in an @code{object_block} structure. @var{mode} is the mode
5676 The default version returns false for all constants.
5679 @deftypefn {Target Hook} tree TARGET_BUILTIN_RECIPROCAL (unsigned @var{fn}, bool @var{md_fn}, bool @var{sqrt})
5680 This hook should return the DECL of a function that implements reciprocal of
5681 the builtin function with builtin function code @var{fn}, or
5682 @code{NULL_TREE} if such a function is not available. @var{md_fn} is true
5683 when @var{fn} is a code of a machine-dependent builtin function. When
5684 @var{sqrt} is true, additional optimizations that apply only to the reciprocal
5685 of a square root function are performed, and only reciprocals of @code{sqrt}
5689 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void)
5690 This hook should return the DECL of a function @var{f} that given an
5691 address @var{addr} as an argument returns a mask @var{m} that can be
5692 used to extract from two vectors the relevant data that resides in
5693 @var{addr} in case @var{addr} is not properly aligned.
5695 The autovectorizer, when vectorizing a load operation from an address
5696 @var{addr} that may be unaligned, will generate two vector loads from
5697 the two aligned addresses around @var{addr}. It then generates a
5698 @code{REALIGN_LOAD} operation to extract the relevant data from the
5699 two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
5700 @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
5701 the third argument, @var{OFF}, defines how the data will be extracted
5702 from these two vectors: if @var{OFF} is 0, then the returned vector is
5703 @var{v2}; otherwise, the returned vector is composed from the last
5704 @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
5705 @var{OFF} elements of @var{v2}.
5707 If this hook is defined, the autovectorizer will generate a call
5708 to @var{f} (using the DECL tree that this hook returns) and will
5709 use the return value of @var{f} as the argument @var{OFF} to
5710 @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
5711 should comply with the semantics expected by @code{REALIGN_LOAD}
5713 If this hook is not defined, then @var{addr} will be used as
5714 the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
5715 log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered.
5718 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN (tree @var{x})
5719 This hook should return the DECL of a function @var{f} that implements
5720 widening multiplication of the even elements of two input vectors of type @var{x}.
5722 If this hook is defined, the autovectorizer will use it along with the
5723 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD} target hook when vectorizing
5724 widening multiplication in cases that the order of the results does not have to be
5725 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5726 @code{widen_mult_hi/lo} idioms will be used.
5729 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD (tree @var{x})
5730 This hook should return the DECL of a function @var{f} that implements
5731 widening multiplication of the odd elements of two input vectors of type @var{x}.
5733 If this hook is defined, the autovectorizer will use it along with the
5734 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN} target hook when vectorizing
5735 widening multiplication in cases that the order of the results does not have to be
5736 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5737 @code{widen_mult_hi/lo} idioms will be used.
5740 @deftypefn {Target Hook} int TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST (enum vect_cost_for_stmt @var{type_of_cost})
5741 Returns cost of different scalar or vector statements for vectorization cost model.
5744 @deftypefn {Target Hook} bool TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE (const_tree @var{type}, bool @var{is_packed})
5745 Return true if vector alignment is reachable (by peeling N iterations) for the given type.
5748 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_VEC_PERM (tree @var{type}, tree *@var{mask_element_type})
5749 Target builtin that implements vector permute.
5752 @deftypefn {Target Hook} bool TARGET_VECTORIZE_BUILTIN_VEC_PERM_OK (tree @var{vec_type}, tree @var{mask})
5753 Return true if a vector created for @code{builtin_vec_perm} is valid.
5756 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_CONVERSION (unsigned @var{code}, tree @var{dest_type}, tree @var{src_type})
5757 This hook should return the DECL of a function that implements conversion of the
5758 input vector of type @var{src_type} to type @var{dest_type}.
5759 The value of @var{code} is one of the enumerators in @code{enum tree_code} and
5760 specifies how the conversion is to be applied
5761 (truncation, rounding, etc.).
5763 If this hook is defined, the autovectorizer will use the
5764 @code{TARGET_VECTORIZE_BUILTIN_CONVERSION} target hook when vectorizing
5765 conversion. Otherwise, it will return @code{NULL_TREE}.
5768 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION (tree @var{fndecl}, tree @var{vec_type_out}, tree @var{vec_type_in})
5769 This hook should return the decl of a function that implements the
5770 vectorized variant of the builtin function with builtin function code
5771 @var{code} or @code{NULL_TREE} if such a function is not available.
5772 The value of @var{fndecl} is the builtin function declaration. The
5773 return type of the vectorized function shall be of vector type
5774 @var{vec_type_out} and the argument types should be @var{vec_type_in}.
5777 @deftypefn {Target Hook} bool TARGET_SUPPORT_VECTOR_MISALIGNMENT (enum machine_mode @var{mode}, const_tree @var{type}, int @var{misalignment}, bool @var{is_packed})
5778 This hook should return true if the target supports misaligned vector
5779 store/load of a specific factor denoted in the @var{misalignment}
5780 parameter. The vector store/load should be of machine mode @var{mode} and
5781 the elements in the vectors should be of type @var{type}. @var{is_packed}
5782 parameter is true if the memory access is defined in a packed struct.
5785 @node Anchored Addresses
5786 @section Anchored Addresses
5787 @cindex anchored addresses
5788 @cindex @option{-fsection-anchors}
5790 GCC usually addresses every static object as a separate entity.
5791 For example, if we have:
5795 int foo (void) @{ return a + b + c; @}
5798 the code for @code{foo} will usually calculate three separate symbolic
5799 addresses: those of @code{a}, @code{b} and @code{c}. On some targets,
5800 it would be better to calculate just one symbolic address and access
5801 the three variables relative to it. The equivalent pseudocode would
5807 register int *xr = &x;
5808 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
5812 (which isn't valid C). We refer to shared addresses like @code{x} as
5813 ``section anchors''. Their use is controlled by @option{-fsection-anchors}.
5815 The hooks below describe the target properties that GCC needs to know
5816 in order to make effective use of section anchors. It won't use
5817 section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
5818 or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
5820 @deftypevr {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET
5821 The minimum offset that should be applied to a section anchor.
5822 On most targets, it should be the smallest offset that can be
5823 applied to a base register while still giving a legitimate address
5824 for every mode. The default value is 0.
5827 @deftypevr {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET
5828 Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive)
5829 offset that should be applied to section anchors. The default
5833 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x})
5834 Write the assembly code to define section anchor @var{x}, which is a
5835 @code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true.
5836 The hook is called with the assembly output position set to the beginning
5837 of @code{SYMBOL_REF_BLOCK (@var{x})}.
5839 If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses
5840 it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}.
5841 If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition
5842 is @code{NULL}, which disables the use of section anchors altogether.
5845 @deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (const_rtx @var{x})
5846 Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF}
5847 @var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and
5848 @samp{!SYMBOL_REF_ANCHOR_P (@var{x})}.
5850 The default version is correct for most targets, but you might need to
5851 intercept this hook to handle things like target-specific attributes
5852 or target-specific sections.
5855 @node Condition Code
5856 @section Condition Code Status
5857 @cindex condition code status
5859 The macros in this section can be split in two families, according to the
5860 two ways of representing condition codes in GCC.
5862 The first representation is the so called @code{(cc0)} representation
5863 (@pxref{Jump Patterns}), where all instructions can have an implicit
5864 clobber of the condition codes. The second is the condition code
5865 register representation, which provides better schedulability for
5866 architectures that do have a condition code register, but on which
5867 most instructions do not affect it. The latter category includes
5870 The implicit clobbering poses a strong restriction on the placement of
5871 the definition and use of the condition code, which need to be in adjacent
5872 insns for machines using @code{(cc0)}. This can prevent important
5873 optimizations on some machines. For example, on the IBM RS/6000, there
5874 is a delay for taken branches unless the condition code register is set
5875 three instructions earlier than the conditional branch. The instruction
5876 scheduler cannot perform this optimization if it is not permitted to
5877 separate the definition and use of the condition code register.
5879 For this reason, it is possible and suggested to use a register to
5880 represent the condition code for new ports. If there is a specific
5881 condition code register in the machine, use a hard register. If the
5882 condition code or comparison result can be placed in any general register,
5883 or if there are multiple condition registers, use a pseudo register.
5884 Registers used to store the condition code value will usually have a mode
5885 that is in class @code{MODE_CC}.
5887 Alternatively, you can use @code{BImode} if the comparison operator is
5888 specified already in the compare instruction. In this case, you are not
5889 interested in most macros in this section.
5892 * CC0 Condition Codes:: Old style representation of condition codes.
5893 * MODE_CC Condition Codes:: Modern representation of condition codes.
5894 * Cond. Exec. Macros:: Macros to control conditional execution.
5897 @node CC0 Condition Codes
5898 @subsection Representation of condition codes using @code{(cc0)}
5902 The file @file{conditions.h} defines a variable @code{cc_status} to
5903 describe how the condition code was computed (in case the interpretation of
5904 the condition code depends on the instruction that it was set by). This
5905 variable contains the RTL expressions on which the condition code is
5906 currently based, and several standard flags.
5908 Sometimes additional machine-specific flags must be defined in the machine
5909 description header file. It can also add additional machine-specific
5910 information by defining @code{CC_STATUS_MDEP}.
5912 @defmac CC_STATUS_MDEP
5913 C code for a data type which is used for declaring the @code{mdep}
5914 component of @code{cc_status}. It defaults to @code{int}.
5916 This macro is not used on machines that do not use @code{cc0}.
5919 @defmac CC_STATUS_MDEP_INIT
5920 A C expression to initialize the @code{mdep} field to ``empty''.
5921 The default definition does nothing, since most machines don't use
5922 the field anyway. If you want to use the field, you should probably
5923 define this macro to initialize it.
5925 This macro is not used on machines that do not use @code{cc0}.
5928 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5929 A C compound statement to set the components of @code{cc_status}
5930 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5931 this macro's responsibility to recognize insns that set the condition
5932 code as a byproduct of other activity as well as those that explicitly
5935 This macro is not used on machines that do not use @code{cc0}.
5937 If there are insns that do not set the condition code but do alter
5938 other machine registers, this macro must check to see whether they
5939 invalidate the expressions that the condition code is recorded as
5940 reflecting. For example, on the 68000, insns that store in address
5941 registers do not set the condition code, which means that usually
5942 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5943 insns. But suppose that the previous insn set the condition code
5944 based on location @samp{a4@@(102)} and the current insn stores a new
5945 value in @samp{a4}. Although the condition code is not changed by
5946 this, it will no longer be true that it reflects the contents of
5947 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5948 @code{cc_status} in this case to say that nothing is known about the
5949 condition code value.
5951 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5952 with the results of peephole optimization: insns whose patterns are
5953 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5954 constants which are just the operands. The RTL structure of these
5955 insns is not sufficient to indicate what the insns actually do. What
5956 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5957 @code{CC_STATUS_INIT}.
5959 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5960 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5961 @samp{cc}. This avoids having detailed information about patterns in
5962 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5965 @node MODE_CC Condition Codes
5966 @subsection Representation of condition codes using registers
5970 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5971 On many machines, the condition code may be produced by other instructions
5972 than compares, for example the branch can use directly the condition
5973 code set by a subtract instruction. However, on some machines
5974 when the condition code is set this way some bits (such as the overflow
5975 bit) are not set in the same way as a test instruction, so that a different
5976 branch instruction must be used for some conditional branches. When
5977 this happens, use the machine mode of the condition code register to
5978 record different formats of the condition code register. Modes can
5979 also be used to record which compare instruction (e.g. a signed or an
5980 unsigned comparison) produced the condition codes.
5982 If other modes than @code{CCmode} are required, add them to
5983 @file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
5984 a mode given an operand of a compare. This is needed because the modes
5985 have to be chosen not only during RTL generation but also, for example,
5986 by instruction combination. The result of @code{SELECT_CC_MODE} should
5987 be consistent with the mode used in the patterns; for example to support
5988 the case of the add on the SPARC discussed above, we have the pattern
5992 [(set (reg:CC_NOOV 0)
5994 (plus:SI (match_operand:SI 0 "register_operand" "%r")
5995 (match_operand:SI 1 "arith_operand" "rI"))
6002 together with a @code{SELECT_CC_MODE} that returns @code{CC_NOOVmode}
6003 for comparisons whose argument is a @code{plus}:
6006 #define SELECT_CC_MODE(OP,X,Y) \
6007 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
6008 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
6009 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
6010 || GET_CODE (X) == NEG) \
6011 ? CC_NOOVmode : CCmode))
6014 Another reason to use modes is to retain information on which operands
6015 were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
6018 You should define this macro if and only if you define extra CC modes
6019 in @file{@var{machine}-modes.def}.
6022 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
6023 On some machines not all possible comparisons are defined, but you can
6024 convert an invalid comparison into a valid one. For example, the Alpha
6025 does not have a @code{GT} comparison, but you can use an @code{LT}
6026 comparison instead and swap the order of the operands.
6028 On such machines, define this macro to be a C statement to do any
6029 required conversions. @var{code} is the initial comparison code
6030 and @var{op0} and @var{op1} are the left and right operands of the
6031 comparison, respectively. You should modify @var{code}, @var{op0}, and
6032 @var{op1} as required.
6034 GCC will not assume that the comparison resulting from this macro is
6035 valid but will see if the resulting insn matches a pattern in the
6038 You need not define this macro if it would never change the comparison
6042 @defmac REVERSIBLE_CC_MODE (@var{mode})
6043 A C expression whose value is one if it is always safe to reverse a
6044 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
6045 can ever return @var{mode} for a floating-point inequality comparison,
6046 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
6048 You need not define this macro if it would always returns zero or if the
6049 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
6050 For example, here is the definition used on the SPARC, where floating-point
6051 inequality comparisons are always given @code{CCFPEmode}:
6054 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
6058 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
6059 A C expression whose value is reversed condition code of the @var{code} for
6060 comparison done in CC_MODE @var{mode}. The macro is used only in case
6061 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
6062 machine has some non-standard way how to reverse certain conditionals. For
6063 instance in case all floating point conditions are non-trapping, compiler may
6064 freely convert unordered compares to ordered one. Then definition may look
6068 #define REVERSE_CONDITION(CODE, MODE) \
6069 ((MODE) != CCFPmode ? reverse_condition (CODE) \
6070 : reverse_condition_maybe_unordered (CODE))
6074 @deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *@var{p1}, unsigned int *@var{p2})
6075 On targets which do not use @code{(cc0)}, and which use a hard
6076 register rather than a pseudo-register to hold condition codes, the
6077 regular CSE passes are often not able to identify cases in which the
6078 hard register is set to a common value. Use this hook to enable a
6079 small pass which optimizes such cases. This hook should return true
6080 to enable this pass, and it should set the integers to which its
6081 arguments point to the hard register numbers used for condition codes.
6082 When there is only one such register, as is true on most systems, the
6083 integer pointed to by @var{p2} should be set to
6084 @code{INVALID_REGNUM}.
6086 The default version of this hook returns false.
6089 @deftypefn {Target Hook} {enum machine_mode} TARGET_CC_MODES_COMPATIBLE (enum machine_mode @var{m1}, enum machine_mode @var{m2})
6090 On targets which use multiple condition code modes in class
6091 @code{MODE_CC}, it is sometimes the case that a comparison can be
6092 validly done in more than one mode. On such a system, define this
6093 target hook to take two mode arguments and to return a mode in which
6094 both comparisons may be validly done. If there is no such mode,
6095 return @code{VOIDmode}.
6097 The default version of this hook checks whether the modes are the
6098 same. If they are, it returns that mode. If they are different, it
6099 returns @code{VOIDmode}.
6102 @node Cond. Exec. Macros
6103 @subsection Macros to control conditional execution
6104 @findex conditional execution
6107 There is one macro that may need to be defined for targets
6108 supporting conditional execution, independent of how they
6109 represent conditional branches.
6111 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2})
6112 A C expression that returns true if the conditional execution predicate
6113 @var{op1}, a comparison operation, is the inverse of @var{op2} and vice
6114 versa. Define this to return 0 if the target has conditional execution
6115 predicates that cannot be reversed safely. There is no need to validate
6116 that the arguments of op1 and op2 are the same, this is done separately.
6117 If no expansion is specified, this macro is defined as follows:
6120 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
6121 (GET_CODE ((x)) == reversed_comparison_code ((y), NULL))
6126 @section Describing Relative Costs of Operations
6127 @cindex costs of instructions
6128 @cindex relative costs
6129 @cindex speed of instructions
6131 These macros let you describe the relative speed of various operations
6132 on the target machine.
6134 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
6135 A C expression for the cost of moving data of mode @var{mode} from a
6136 register in class @var{from} to one in class @var{to}. The classes are
6137 expressed using the enumeration values such as @code{GENERAL_REGS}. A
6138 value of 2 is the default; other values are interpreted relative to
6141 It is not required that the cost always equal 2 when @var{from} is the
6142 same as @var{to}; on some machines it is expensive to move between
6143 registers if they are not general registers.
6145 If reload sees an insn consisting of a single @code{set} between two
6146 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
6147 classes returns a value of 2, reload does not check to ensure that the
6148 constraints of the insn are met. Setting a cost of other than 2 will
6149 allow reload to verify that the constraints are met. You should do this
6150 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
6153 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
6154 A C expression for the cost of moving data of mode @var{mode} between a
6155 register of class @var{class} and memory; @var{in} is zero if the value
6156 is to be written to memory, nonzero if it is to be read in. This cost
6157 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
6158 registers and memory is more expensive than between two registers, you
6159 should define this macro to express the relative cost.
6161 If you do not define this macro, GCC uses a default cost of 4 plus
6162 the cost of copying via a secondary reload register, if one is
6163 needed. If your machine requires a secondary reload register to copy
6164 between memory and a register of @var{class} but the reload mechanism is
6165 more complex than copying via an intermediate, define this macro to
6166 reflect the actual cost of the move.
6168 GCC defines the function @code{memory_move_secondary_cost} if
6169 secondary reloads are needed. It computes the costs due to copying via
6170 a secondary register. If your machine copies from memory using a
6171 secondary register in the conventional way but the default base value of
6172 4 is not correct for your machine, define this macro to add some other
6173 value to the result of that function. The arguments to that function
6174 are the same as to this macro.
6176 These macros are obsolete, new ports should use the target hook
6177 @code{TARGET_MEMORY_MOVE_COST} instead.
6180 @deftypefn {Target Hook} int TARGET_MEMORY_MOVE_COST (enum machine_mode @var{mode}, enum reg_class @var{regclass}, bool @var{in})
6181 This target hook should return the cost of moving data of mode @var{mode}
6182 between a register of class @var{class} and memory; @var{in} is @code{false}
6183 if the value is to be written to memory, @code{true} if it is to be read in.
6184 This cost is relative to those in @code{REGISTER_MOVE_COST}. If moving
6185 between registers and memory is more expensive than between two registers,
6186 you should add this target hook to express the relative cost.
6188 If you do not add this target hook, GCC uses a default cost of 4 plus
6189 the cost of copying via a secondary reload register, if one is
6190 needed. If your machine requires a secondary reload register to copy
6191 between memory and a register of @var{class} but the reload mechanism is
6192 more complex than copying via an intermediate, use this target hook to
6193 reflect the actual cost of the move.
6195 GCC defines the function @code{memory_move_secondary_cost} if
6196 secondary reloads are needed. It computes the costs due to copying via
6197 a secondary register. If your machine copies from memory using a
6198 secondary register in the conventional way but the default base value of
6199 4 is not correct for your machine, use this target hook to add some other
6200 value to the result of that function. The arguments to that function
6201 are the same as to this target hook.
6204 @defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
6205 A C expression for the cost of a branch instruction. A value of 1 is the
6206 default; other values are interpreted relative to that. Parameter @var{speed_p}
6207 is true when the branch in question should be optimized for speed. When
6208 it is false, @code{BRANCH_COST} should be returning value optimal for code size
6209 rather then performance considerations. @var{predictable_p} is true for well
6210 predictable branches. On many architectures the @code{BRANCH_COST} can be
6214 Here are additional macros which do not specify precise relative costs,
6215 but only that certain actions are more expensive than GCC would
6218 @defmac SLOW_BYTE_ACCESS
6219 Define this macro as a C expression which is nonzero if accessing less
6220 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
6221 faster than accessing a word of memory, i.e., if such access
6222 require more than one instruction or if there is no difference in cost
6223 between byte and (aligned) word loads.
6225 When this macro is not defined, the compiler will access a field by
6226 finding the smallest containing object; when it is defined, a fullword
6227 load will be used if alignment permits. Unless bytes accesses are
6228 faster than word accesses, using word accesses is preferable since it
6229 may eliminate subsequent memory access if subsequent accesses occur to
6230 other fields in the same word of the structure, but to different bytes.
6233 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
6234 Define this macro to be the value 1 if memory accesses described by the
6235 @var{mode} and @var{alignment} parameters have a cost many times greater
6236 than aligned accesses, for example if they are emulated in a trap
6239 When this macro is nonzero, the compiler will act as if
6240 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
6241 moves. This can cause significantly more instructions to be produced.
6242 Therefore, do not set this macro nonzero if unaligned accesses only add a
6243 cycle or two to the time for a memory access.
6245 If the value of this macro is always zero, it need not be defined. If
6246 this macro is defined, it should produce a nonzero value when
6247 @code{STRICT_ALIGNMENT} is nonzero.
6250 @defmac MOVE_RATIO (@var{speed})
6251 The threshold of number of scalar memory-to-memory move insns, @emph{below}
6252 which a sequence of insns should be generated instead of a
6253 string move insn or a library call. Increasing the value will always
6254 make code faster, but eventually incurs high cost in increased code size.
6256 Note that on machines where the corresponding move insn is a
6257 @code{define_expand} that emits a sequence of insns, this macro counts
6258 the number of such sequences.
6260 The parameter @var{speed} is true if the code is currently being
6261 optimized for speed rather than size.
6263 If you don't define this, a reasonable default is used.
6266 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
6267 A C expression used to determine whether @code{move_by_pieces} will be used to
6268 copy a chunk of memory, or whether some other block move mechanism
6269 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6270 than @code{MOVE_RATIO}.
6273 @defmac MOVE_MAX_PIECES
6274 A C expression used by @code{move_by_pieces} to determine the largest unit
6275 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
6278 @defmac CLEAR_RATIO (@var{speed})
6279 The threshold of number of scalar move insns, @emph{below} which a sequence
6280 of insns should be generated to clear memory instead of a string clear insn
6281 or a library call. Increasing the value will always make code faster, but
6282 eventually incurs high cost in increased code size.
6284 The parameter @var{speed} is true if the code is currently being
6285 optimized for speed rather than size.
6287 If you don't define this, a reasonable default is used.
6290 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
6291 A C expression used to determine whether @code{clear_by_pieces} will be used
6292 to clear a chunk of memory, or whether some other block clear mechanism
6293 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6294 than @code{CLEAR_RATIO}.
6297 @defmac SET_RATIO (@var{speed})
6298 The threshold of number of scalar move insns, @emph{below} which a sequence
6299 of insns should be generated to set memory to a constant value, instead of
6300 a block set insn or a library call.
6301 Increasing the value will always make code faster, but
6302 eventually incurs high cost in increased code size.
6304 The parameter @var{speed} is true if the code is currently being
6305 optimized for speed rather than size.
6307 If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
6310 @defmac SET_BY_PIECES_P (@var{size}, @var{alignment})
6311 A C expression used to determine whether @code{store_by_pieces} will be
6312 used to set a chunk of memory to a constant value, or whether some
6313 other mechanism will be used. Used by @code{__builtin_memset} when
6314 storing values other than constant zero.
6315 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6316 than @code{SET_RATIO}.
6319 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
6320 A C expression used to determine whether @code{store_by_pieces} will be
6321 used to set a chunk of memory to a constant string value, or whether some
6322 other mechanism will be used. Used by @code{__builtin_strcpy} when
6323 called with a constant source string.
6324 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6325 than @code{MOVE_RATIO}.
6328 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
6329 A C expression used to determine whether a load postincrement is a good
6330 thing to use for a given mode. Defaults to the value of
6331 @code{HAVE_POST_INCREMENT}.
6334 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
6335 A C expression used to determine whether a load postdecrement is a good
6336 thing to use for a given mode. Defaults to the value of
6337 @code{HAVE_POST_DECREMENT}.
6340 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
6341 A C expression used to determine whether a load preincrement is a good
6342 thing to use for a given mode. Defaults to the value of
6343 @code{HAVE_PRE_INCREMENT}.
6346 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
6347 A C expression used to determine whether a load predecrement is a good
6348 thing to use for a given mode. Defaults to the value of
6349 @code{HAVE_PRE_DECREMENT}.
6352 @defmac USE_STORE_POST_INCREMENT (@var{mode})
6353 A C expression used to determine whether a store postincrement is a good
6354 thing to use for a given mode. Defaults to the value of
6355 @code{HAVE_POST_INCREMENT}.
6358 @defmac USE_STORE_POST_DECREMENT (@var{mode})
6359 A C expression used to determine whether a store postdecrement is a good
6360 thing to use for a given mode. Defaults to the value of
6361 @code{HAVE_POST_DECREMENT}.
6364 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
6365 This macro is used to determine whether a store preincrement is a good
6366 thing to use for a given mode. Defaults to the value of
6367 @code{HAVE_PRE_INCREMENT}.
6370 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
6371 This macro is used to determine whether a store predecrement is a good
6372 thing to use for a given mode. Defaults to the value of
6373 @code{HAVE_PRE_DECREMENT}.
6376 @defmac NO_FUNCTION_CSE
6377 Define this macro if it is as good or better to call a constant
6378 function address than to call an address kept in a register.
6381 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
6382 Define this macro if a non-short-circuit operation produced by
6383 @samp{fold_range_test ()} is optimal. This macro defaults to true if
6384 @code{BRANCH_COST} is greater than or equal to the value 2.
6387 @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total}, bool @var{speed})
6388 This target hook describes the relative costs of RTL expressions.
6390 The cost may depend on the precise form of the expression, which is
6391 available for examination in @var{x}, and the rtx code of the expression
6392 in which it is contained, found in @var{outer_code}. @var{code} is the
6393 expression code---redundant, since it can be obtained with
6394 @code{GET_CODE (@var{x})}.
6396 In implementing this hook, you can use the construct
6397 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
6400 On entry to the hook, @code{*@var{total}} contains a default estimate
6401 for the cost of the expression. The hook should modify this value as
6402 necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
6403 for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
6404 operations, and @code{COSTS_N_INSNS (1)} for all other operations.
6406 When optimizing for code size, i.e.@: when @code{speed} is
6407 false, this target hook should be used to estimate the relative
6408 size cost of an expression, again relative to @code{COSTS_N_INSNS}.
6410 The hook returns true when all subexpressions of @var{x} have been
6411 processed, and false when @code{rtx_cost} should recurse.
6414 @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address}, bool @var{speed})
6415 This hook computes the cost of an addressing mode that contains
6416 @var{address}. If not defined, the cost is computed from
6417 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
6419 For most CISC machines, the default cost is a good approximation of the
6420 true cost of the addressing mode. However, on RISC machines, all
6421 instructions normally have the same length and execution time. Hence
6422 all addresses will have equal costs.
6424 In cases where more than one form of an address is known, the form with
6425 the lowest cost will be used. If multiple forms have the same, lowest,
6426 cost, the one that is the most complex will be used.
6428 For example, suppose an address that is equal to the sum of a register
6429 and a constant is used twice in the same basic block. When this macro
6430 is not defined, the address will be computed in a register and memory
6431 references will be indirect through that register. On machines where
6432 the cost of the addressing mode containing the sum is no higher than
6433 that of a simple indirect reference, this will produce an additional
6434 instruction and possibly require an additional register. Proper
6435 specification of this macro eliminates this overhead for such machines.
6437 This hook is never called with an invalid address.
6439 On machines where an address involving more than one register is as
6440 cheap as an address computation involving only one register, defining
6441 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
6442 be live over a region of code where only one would have been if
6443 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
6444 should be considered in the definition of this macro. Equivalent costs
6445 should probably only be given to addresses with different numbers of
6446 registers on machines with lots of registers.
6450 @section Adjusting the Instruction Scheduler
6452 The instruction scheduler may need a fair amount of machine-specific
6453 adjustment in order to produce good code. GCC provides several target
6454 hooks for this purpose. It is usually enough to define just a few of
6455 them: try the first ones in this list first.
6457 @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
6458 This hook returns the maximum number of instructions that can ever
6459 issue at the same time on the target machine. The default is one.
6460 Although the insn scheduler can define itself the possibility of issue
6461 an insn on the same cycle, the value can serve as an additional
6462 constraint to issue insns on the same simulated processor cycle (see
6463 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
6464 This value must be constant over the entire compilation. If you need
6465 it to vary depending on what the instructions are, you must use
6466 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
6469 @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
6470 This hook is executed by the scheduler after it has scheduled an insn
6471 from the ready list. It should return the number of insns which can
6472 still be issued in the current cycle. The default is
6473 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
6474 @code{USE}, which normally are not counted against the issue rate.
6475 You should define this hook if some insns take more machine resources
6476 than others, so that fewer insns can follow them in the same cycle.
6477 @var{file} is either a null pointer, or a stdio stream to write any
6478 debug output to. @var{verbose} is the verbose level provided by
6479 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
6483 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
6484 This function corrects the value of @var{cost} based on the
6485 relationship between @var{insn} and @var{dep_insn} through the
6486 dependence @var{link}. It should return the new value. The default
6487 is to make no adjustment to @var{cost}. This can be used for example
6488 to specify to the scheduler using the traditional pipeline description
6489 that an output- or anti-dependence does not incur the same cost as a
6490 data-dependence. If the scheduler using the automaton based pipeline
6491 description, the cost of anti-dependence is zero and the cost of
6492 output-dependence is maximum of one and the difference of latency
6493 times of the first and the second insns. If these values are not
6494 acceptable, you could use the hook to modify them too. See also
6495 @pxref{Processor pipeline description}.
6498 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
6499 This hook adjusts the integer scheduling priority @var{priority} of
6500 @var{insn}. It should return the new priority. Increase the priority to
6501 execute @var{insn} earlier, reduce the priority to execute @var{insn}
6502 later. Do not define this hook if you do not need to adjust the
6503 scheduling priorities of insns.
6506 @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
6507 This hook is executed by the scheduler after it has scheduled the ready
6508 list, to allow the machine description to reorder it (for example to
6509 combine two small instructions together on @samp{VLIW} machines).
6510 @var{file} is either a null pointer, or a stdio stream to write any
6511 debug output to. @var{verbose} is the verbose level provided by
6512 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
6513 list of instructions that are ready to be scheduled. @var{n_readyp} is
6514 a pointer to the number of elements in the ready list. The scheduler
6515 reads the ready list in reverse order, starting with
6516 @var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0]. @var{clock}
6517 is the timer tick of the scheduler. You may modify the ready list and
6518 the number of ready insns. The return value is the number of insns that
6519 can issue this cycle; normally this is just @code{issue_rate}. See also
6520 @samp{TARGET_SCHED_REORDER2}.
6523 @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
6524 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
6525 function is called whenever the scheduler starts a new cycle. This one
6526 is called once per iteration over a cycle, immediately after
6527 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
6528 return the number of insns to be scheduled in the same cycle. Defining
6529 this hook can be useful if there are frequent situations where
6530 scheduling one insn causes other insns to become ready in the same
6531 cycle. These other insns can then be taken into account properly.
6534 @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail})
6535 This hook is called after evaluation forward dependencies of insns in
6536 chain given by two parameter values (@var{head} and @var{tail}
6537 correspondingly) but before insns scheduling of the insn chain. For
6538 example, it can be used for better insn classification if it requires
6539 analysis of dependencies. This hook can use backward and forward
6540 dependencies of the insn scheduler because they are already
6544 @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
6545 This hook is executed by the scheduler at the beginning of each block of
6546 instructions that are to be scheduled. @var{file} is either a null
6547 pointer, or a stdio stream to write any debug output to. @var{verbose}
6548 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6549 @var{max_ready} is the maximum number of insns in the current scheduling
6550 region that can be live at the same time. This can be used to allocate
6551 scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
6554 @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
6555 This hook is executed by the scheduler at the end of each block of
6556 instructions that are to be scheduled. It can be used to perform
6557 cleanup of any actions done by the other scheduling hooks. @var{file}
6558 is either a null pointer, or a stdio stream to write any debug output
6559 to. @var{verbose} is the verbose level provided by
6560 @option{-fsched-verbose-@var{n}}.
6563 @deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid})
6564 This hook is executed by the scheduler after function level initializations.
6565 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6566 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6567 @var{old_max_uid} is the maximum insn uid when scheduling begins.
6570 @deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose})
6571 This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
6572 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6573 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6576 @deftypefn {Target Hook} rtx TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
6577 The hook returns an RTL insn. The automaton state used in the
6578 pipeline hazard recognizer is changed as if the insn were scheduled
6579 when the new simulated processor cycle starts. Usage of the hook may
6580 simplify the automaton pipeline description for some @acronym{VLIW}
6581 processors. If the hook is defined, it is used only for the automaton
6582 based pipeline description. The default is not to change the state
6583 when the new simulated processor cycle starts.
6586 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
6587 The hook can be used to initialize data used by the previous hook.
6590 @deftypefn {Target Hook} rtx TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
6591 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6592 to changed the state as if the insn were scheduled when the new
6593 simulated processor cycle finishes.
6596 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
6597 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
6598 used to initialize data used by the previous hook.
6601 @deftypefn {Target Hook} void TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE (void)
6602 The hook to notify target that the current simulated cycle is about to finish.
6603 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6604 to change the state in more complicated situations - e.g., when advancing
6605 state on a single insn is not enough.
6608 @deftypefn {Target Hook} void TARGET_SCHED_DFA_POST_ADVANCE_CYCLE (void)
6609 The hook to notify target that new simulated cycle has just started.
6610 The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used
6611 to change the state in more complicated situations - e.g., when advancing
6612 state on a single insn is not enough.
6615 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
6616 This hook controls better choosing an insn from the ready insn queue
6617 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
6618 chooses the first insn from the queue. If the hook returns a positive
6619 value, an additional scheduler code tries all permutations of
6620 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
6621 subsequent ready insns to choose an insn whose issue will result in
6622 maximal number of issued insns on the same cycle. For the
6623 @acronym{VLIW} processor, the code could actually solve the problem of
6624 packing simple insns into the @acronym{VLIW} insn. Of course, if the
6625 rules of @acronym{VLIW} packing are described in the automaton.
6627 This code also could be used for superscalar @acronym{RISC}
6628 processors. Let us consider a superscalar @acronym{RISC} processor
6629 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
6630 @var{B}, some insns can be executed only in pipelines @var{B} or
6631 @var{C}, and one insn can be executed in pipeline @var{B}. The
6632 processor may issue the 1st insn into @var{A} and the 2nd one into
6633 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
6634 until the next cycle. If the scheduler issues the 3rd insn the first,
6635 the processor could issue all 3 insns per cycle.
6637 Actually this code demonstrates advantages of the automaton based
6638 pipeline hazard recognizer. We try quickly and easy many insn
6639 schedules to choose the best one.
6641 The default is no multipass scheduling.
6644 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx @var{insn})
6646 This hook controls what insns from the ready insn queue will be
6647 considered for the multipass insn scheduling. If the hook returns
6648 zero for @var{insn}, the insn will be not chosen to
6651 The default is that any ready insns can be chosen to be issued.
6654 @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *@var{dump}, int @var{verbose}, rtx @var{insn}, int @var{last_clock}, int @var{clock}, int *@var{sort_p})
6656 This hook is called by the insn scheduler before issuing @var{insn}
6657 on cycle @var{clock}. If the hook returns nonzero,
6658 @var{insn} is not issued on this processor cycle. Instead,
6659 the processor cycle is advanced. If *@var{sort_p}
6660 is zero, the insn ready queue is not sorted on the new cycle
6661 start as usually. @var{dump} and @var{verbose} specify the file and
6662 verbosity level to use for debugging output.
6663 @var{last_clock} and @var{clock} are, respectively, the
6664 processor cycle on which the previous insn has been issued,
6665 and the current processor cycle.
6668 @deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (struct _dep *@var{_dep}, int @var{cost}, int @var{distance})
6669 This hook is used to define which dependences are considered costly by
6670 the target, so costly that it is not advisable to schedule the insns that
6671 are involved in the dependence too close to one another. The parameters
6672 to this hook are as follows: The first parameter @var{_dep} is the dependence
6673 being evaluated. The second parameter @var{cost} is the cost of the
6674 dependence as estimated by the scheduler, and the third
6675 parameter @var{distance} is the distance in cycles between the two insns.
6676 The hook returns @code{true} if considering the distance between the two
6677 insns the dependence between them is considered costly by the target,
6678 and @code{false} otherwise.
6680 Defining this hook can be useful in multiple-issue out-of-order machines,
6681 where (a) it's practically hopeless to predict the actual data/resource
6682 delays, however: (b) there's a better chance to predict the actual grouping
6683 that will be formed, and (c) correctly emulating the grouping can be very
6684 important. In such targets one may want to allow issuing dependent insns
6685 closer to one another---i.e., closer than the dependence distance; however,
6686 not in cases of ``costly dependences'', which this hooks allows to define.
6689 @deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void)
6690 This hook is called by the insn scheduler after emitting a new instruction to
6691 the instruction stream. The hook notifies a target backend to extend its
6692 per instruction data structures.
6695 @deftypefn {Target Hook} {void *} TARGET_SCHED_ALLOC_SCHED_CONTEXT (void)
6696 Return a pointer to a store large enough to hold target scheduling context.
6699 @deftypefn {Target Hook} void TARGET_SCHED_INIT_SCHED_CONTEXT (void *@var{tc}, bool @var{clean_p})
6700 Initialize store pointed to by @var{tc} to hold target scheduling context.
6701 It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
6702 beginning of the block. Otherwise, copy the current context into @var{tc}.
6705 @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_CONTEXT (void *@var{tc})
6706 Copy target scheduling context pointed to by @var{tc} to the current context.
6709 @deftypefn {Target Hook} void TARGET_SCHED_CLEAR_SCHED_CONTEXT (void *@var{tc})
6710 Deallocate internal data in target scheduling context pointed to by @var{tc}.
6713 @deftypefn {Target Hook} void TARGET_SCHED_FREE_SCHED_CONTEXT (void *@var{tc})
6714 Deallocate a store for target scheduling context pointed to by @var{tc}.
6717 @deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx @var{insn}, int @var{request}, rtx *@var{new_pat})
6718 This hook is called by the insn scheduler when @var{insn} has only
6719 speculative dependencies and therefore can be scheduled speculatively.
6720 The hook is used to check if the pattern of @var{insn} has a speculative
6721 version and, in case of successful check, to generate that speculative
6722 pattern. The hook should return 1, if the instruction has a speculative form,
6723 or @minus{}1, if it doesn't. @var{request} describes the type of requested
6724 speculation. If the return value equals 1 then @var{new_pat} is assigned
6725 the generated speculative pattern.
6728 @deftypefn {Target Hook} bool TARGET_SCHED_NEEDS_BLOCK_P (int @var{dep_status})
6729 This hook is called by the insn scheduler during generation of recovery code
6730 for @var{insn}. It should return @code{true}, if the corresponding check
6731 instruction should branch to recovery code, or @code{false} otherwise.
6734 @deftypefn {Target Hook} rtx TARGET_SCHED_GEN_SPEC_CHECK (rtx @var{insn}, rtx @var{label}, int @var{mutate_p})
6735 This hook is called by the insn scheduler to generate a pattern for recovery
6736 check instruction. If @var{mutate_p} is zero, then @var{insn} is a
6737 speculative instruction for which the check should be generated.
6738 @var{label} is either a label of a basic block, where recovery code should
6739 be emitted, or a null pointer, when requested check doesn't branch to
6740 recovery code (a simple check). If @var{mutate_p} is nonzero, then
6741 a pattern for a branchy check corresponding to a simple check denoted by
6742 @var{insn} should be generated. In this case @var{label} can't be null.
6745 @deftypefn {Target Hook} bool TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC (const_rtx @var{insn})
6746 This hook is used as a workaround for
6747 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being
6748 called on the first instruction of the ready list. The hook is used to
6749 discard speculative instructions that stand first in the ready list from
6750 being scheduled on the current cycle. If the hook returns @code{false},
6751 @var{insn} will not be chosen to be issued.
6752 For non-speculative instructions,
6753 the hook should always return @code{true}. For example, in the ia64 backend
6754 the hook is used to cancel data speculative insns when the ALAT table
6758 @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (struct spec_info_def *@var{spec_info})
6759 This hook is used by the insn scheduler to find out what features should be
6761 The structure *@var{spec_info} should be filled in by the target.
6762 The structure describes speculation types that can be used in the scheduler.
6765 @deftypefn {Target Hook} int TARGET_SCHED_SMS_RES_MII (struct ddg *@var{g})
6766 This hook is called by the swing modulo scheduler to calculate a
6767 resource-based lower bound which is based on the resources available in
6768 the machine and the resources required by each instruction. The target
6769 backend can use @var{g} to calculate such bound. A very simple lower
6770 bound will be used in case this hook is not implemented: the total number
6771 of instructions divided by the issue rate.
6775 @section Dividing the Output into Sections (Texts, Data, @dots{})
6776 @c the above section title is WAY too long. maybe cut the part between
6777 @c the (...)? --mew 10feb93
6779 An object file is divided into sections containing different types of
6780 data. In the most common case, there are three sections: the @dfn{text
6781 section}, which holds instructions and read-only data; the @dfn{data
6782 section}, which holds initialized writable data; and the @dfn{bss
6783 section}, which holds uninitialized data. Some systems have other kinds
6786 @file{varasm.c} provides several well-known sections, such as
6787 @code{text_section}, @code{data_section} and @code{bss_section}.
6788 The normal way of controlling a @code{@var{foo}_section} variable
6789 is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
6790 as described below. The macros are only read once, when @file{varasm.c}
6791 initializes itself, so their values must be run-time constants.
6792 They may however depend on command-line flags.
6794 @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
6795 use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
6796 to be string literals.
6798 Some assemblers require a different string to be written every time a
6799 section is selected. If your assembler falls into this category, you
6800 should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
6801 @code{get_unnamed_section} to set up the sections.
6803 You must always create a @code{text_section}, either by defining
6804 @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
6805 in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of
6806 @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not
6807 create a distinct @code{readonly_data_section}, the default is to
6808 reuse @code{text_section}.
6810 All the other @file{varasm.c} sections are optional, and are null
6811 if the target does not provide them.
6813 @defmac TEXT_SECTION_ASM_OP
6814 A C expression whose value is a string, including spacing, containing the
6815 assembler operation that should precede instructions and read-only data.
6816 Normally @code{"\t.text"} is right.
6819 @defmac HOT_TEXT_SECTION_NAME
6820 If defined, a C string constant for the name of the section containing most
6821 frequently executed functions of the program. If not defined, GCC will provide
6822 a default definition if the target supports named sections.
6825 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
6826 If defined, a C string constant for the name of the section containing unlikely
6827 executed functions in the program.
6830 @defmac DATA_SECTION_ASM_OP
6831 A C expression whose value is a string, including spacing, containing the
6832 assembler operation to identify the following data as writable initialized
6833 data. Normally @code{"\t.data"} is right.
6836 @defmac SDATA_SECTION_ASM_OP
6837 If defined, a C expression whose value is a string, including spacing,
6838 containing the assembler operation to identify the following data as
6839 initialized, writable small data.
6842 @defmac READONLY_DATA_SECTION_ASM_OP
6843 A C expression whose value is a string, including spacing, containing the
6844 assembler operation to identify the following data as read-only initialized
6848 @defmac BSS_SECTION_ASM_OP
6849 If defined, a C expression whose value is a string, including spacing,
6850 containing the assembler operation to identify the following data as
6851 uninitialized global data. If not defined, and neither
6852 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
6853 uninitialized global data will be output in the data section if
6854 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
6858 @defmac SBSS_SECTION_ASM_OP
6859 If defined, a C expression whose value is a string, including spacing,
6860 containing the assembler operation to identify the following data as
6861 uninitialized, writable small data.
6864 @defmac TLS_COMMON_ASM_OP
6865 If defined, a C expression whose value is a string containing the
6866 assembler operation to identify the following data as thread-local
6867 common data. The default is @code{".tls_common"}.
6870 @defmac TLS_SECTION_ASM_FLAG
6871 If defined, a C expression whose value is a character constant
6872 containing the flag used to mark a section as a TLS section. The
6873 default is @code{'T'}.
6876 @defmac INIT_SECTION_ASM_OP
6877 If defined, a C expression whose value is a string, including spacing,
6878 containing the assembler operation to identify the following data as
6879 initialization code. If not defined, GCC will assume such a section does
6880 not exist. This section has no corresponding @code{init_section}
6881 variable; it is used entirely in runtime code.
6884 @defmac FINI_SECTION_ASM_OP
6885 If defined, a C expression whose value is a string, including spacing,
6886 containing the assembler operation to identify the following data as
6887 finalization code. If not defined, GCC will assume such a section does
6888 not exist. This section has no corresponding @code{fini_section}
6889 variable; it is used entirely in runtime code.
6892 @defmac INIT_ARRAY_SECTION_ASM_OP
6893 If defined, a C expression whose value is a string, including spacing,
6894 containing the assembler operation to identify the following data as
6895 part of the @code{.init_array} (or equivalent) section. If not
6896 defined, GCC will assume such a section does not exist. Do not define
6897 both this macro and @code{INIT_SECTION_ASM_OP}.
6900 @defmac FINI_ARRAY_SECTION_ASM_OP
6901 If defined, a C expression whose value is a string, including spacing,
6902 containing the assembler operation to identify the following data as
6903 part of the @code{.fini_array} (or equivalent) section. If not
6904 defined, GCC will assume such a section does not exist. Do not define
6905 both this macro and @code{FINI_SECTION_ASM_OP}.
6908 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
6909 If defined, an ASM statement that switches to a different section
6910 via @var{section_op}, calls @var{function}, and switches back to
6911 the text section. This is used in @file{crtstuff.c} if
6912 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
6913 to initialization and finalization functions from the init and fini
6914 sections. By default, this macro uses a simple function call. Some
6915 ports need hand-crafted assembly code to avoid dependencies on
6916 registers initialized in the function prologue or to ensure that
6917 constant pools don't end up too far way in the text section.
6920 @defmac TARGET_LIBGCC_SDATA_SECTION
6921 If defined, a string which names the section into which small
6922 variables defined in crtstuff and libgcc should go. This is useful
6923 when the target has options for optimizing access to small data, and
6924 you want the crtstuff and libgcc routines to be conservative in what
6925 they expect of your application yet liberal in what your application
6926 expects. For example, for targets with a @code{.sdata} section (like
6927 MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
6928 require small data support from your application, but use this macro
6929 to put small data into @code{.sdata} so that your application can
6930 access these variables whether it uses small data or not.
6933 @defmac FORCE_CODE_SECTION_ALIGN
6934 If defined, an ASM statement that aligns a code section to some
6935 arbitrary boundary. This is used to force all fragments of the
6936 @code{.init} and @code{.fini} sections to have to same alignment
6937 and thus prevent the linker from having to add any padding.
6940 @defmac JUMP_TABLES_IN_TEXT_SECTION
6941 Define this macro to be an expression with a nonzero value if jump
6942 tables (for @code{tablejump} insns) should be output in the text
6943 section, along with the assembler instructions. Otherwise, the
6944 readonly data section is used.
6946 This macro is irrelevant if there is no separate readonly data section.
6949 @deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void)
6950 Define this hook if you need to do something special to set up the
6951 @file{varasm.c} sections, or if your target has some special sections
6952 of its own that you need to create.
6954 GCC calls this hook after processing the command line, but before writing
6955 any assembly code, and before calling any of the section-returning hooks
6959 @deftypefn {Target Hook} int TARGET_ASM_RELOC_RW_MASK (void)
6960 Return a mask describing how relocations should be treated when
6961 selecting sections. Bit 1 should be set if global relocations
6962 should be placed in a read-write section; bit 0 should be set if
6963 local relocations should be placed in a read-write section.
6965 The default version of this function returns 3 when @option{-fpic}
6966 is in effect, and 0 otherwise. The hook is typically redefined
6967 when the target cannot support (some kinds of) dynamic relocations
6968 in read-only sections even in executables.
6971 @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
6972 Return the section into which @var{exp} should be placed. You can
6973 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
6974 some sort. @var{reloc} indicates whether the initial value of @var{exp}
6975 requires link-time relocations. Bit 0 is set when variable contains
6976 local relocations only, while bit 1 is set for global relocations.
6977 @var{align} is the constant alignment in bits.
6979 The default version of this function takes care of putting read-only
6980 variables in @code{readonly_data_section}.
6982 See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
6985 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS
6986 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
6987 for @code{FUNCTION_DECL}s as well as for variables and constants.
6989 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
6990 function has been determined to be likely to be called, and nonzero if
6991 it is unlikely to be called.
6994 @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
6995 Build up a unique section name, expressed as a @code{STRING_CST} node,
6996 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
6997 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
6998 the initial value of @var{exp} requires link-time relocations.
7000 The default version of this function appends the symbol name to the
7001 ELF section name that would normally be used for the symbol. For
7002 example, the function @code{foo} would be placed in @code{.text.foo}.
7003 Whatever the actual target object format, this is often good enough.
7006 @deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl})
7007 Return the readonly data section associated with
7008 @samp{DECL_SECTION_NAME (@var{decl})}.
7009 The default version of this function selects @code{.gnu.linkonce.r.name} if
7010 the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name}
7011 if function is in @code{.text.name}, and the normal readonly-data section
7015 @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
7016 Return the section into which a constant @var{x}, of mode @var{mode},
7017 should be placed. You can assume that @var{x} is some kind of
7018 constant in RTL@. The argument @var{mode} is redundant except in the
7019 case of a @code{const_int} rtx. @var{align} is the constant alignment
7022 The default version of this function takes care of putting symbolic
7023 constants in @code{flag_pic} mode in @code{data_section} and everything
7024 else in @code{readonly_data_section}.
7027 @deftypefn {Target Hook} tree TARGET_MANGLE_DECL_ASSEMBLER_NAME (tree @var{decl}, tree @var{id})
7028 Define this hook if you need to postprocess the assembler name generated
7029 by target-independent code. The @var{id} provided to this hook will be
7030 the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C,
7031 or the mangled name of the @var{decl} in C++). The return value of the
7032 hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on
7033 your target system. The default implementation of this hook just
7034 returns the @var{id} provided.
7037 @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
7038 Define this hook if references to a symbol or a constant must be
7039 treated differently depending on something about the variable or
7040 function named by the symbol (such as what section it is in).
7042 The hook is executed immediately after rtl has been created for
7043 @var{decl}, which may be a variable or function declaration or
7044 an entry in the constant pool. In either case, @var{rtl} is the
7045 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
7046 in this hook; that field may not have been initialized yet.
7048 In the case of a constant, it is safe to assume that the rtl is
7049 a @code{mem} whose address is a @code{symbol_ref}. Most decls
7050 will also have this form, but that is not guaranteed. Global
7051 register variables, for instance, will have a @code{reg} for their
7052 rtl. (Normally the right thing to do with such unusual rtl is
7055 The @var{new_decl_p} argument will be true if this is the first time
7056 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
7057 be false for subsequent invocations, which will happen for duplicate
7058 declarations. Whether or not anything must be done for the duplicate
7059 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
7060 @var{new_decl_p} is always true when the hook is called for a constant.
7062 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
7063 The usual thing for this hook to do is to record flags in the
7064 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
7065 Historically, the name string was modified if it was necessary to
7066 encode more than one bit of information, but this practice is now
7067 discouraged; use @code{SYMBOL_REF_FLAGS}.
7069 The default definition of this hook, @code{default_encode_section_info}
7070 in @file{varasm.c}, sets a number of commonly-useful bits in
7071 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
7072 before overriding it.
7075 @deftypefn {Target Hook} {const char *} TARGET_STRIP_NAME_ENCODING (const char *@var{name})
7076 Decode @var{name} and return the real name part, sans
7077 the characters that @code{TARGET_ENCODE_SECTION_INFO}
7081 @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (const_tree @var{exp})
7082 Returns true if @var{exp} should be placed into a ``small data'' section.
7083 The default version of this hook always returns false.
7086 @deftypevr {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
7087 Contains the value true if the target places read-only
7088 ``small data'' into a separate section. The default value is false.
7091 @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (const_tree @var{exp})
7092 Returns true if @var{exp} names an object for which name resolution
7093 rules must resolve to the current ``module'' (dynamic shared library
7094 or executable image).
7096 The default version of this hook implements the name resolution rules
7097 for ELF, which has a looser model of global name binding than other
7098 currently supported object file formats.
7101 @deftypevr {Target Hook} bool TARGET_HAVE_TLS
7102 Contains the value true if the target supports thread-local storage.
7103 The default value is false.
7108 @section Position Independent Code
7109 @cindex position independent code
7112 This section describes macros that help implement generation of position
7113 independent code. Simply defining these macros is not enough to
7114 generate valid PIC; you must also add support to the hook
7115 @code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
7116 @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You
7117 must modify the definition of @samp{movsi} to do something appropriate
7118 when the source operand contains a symbolic address. You may also
7119 need to alter the handling of switch statements so that they use
7121 @c i rearranged the order of the macros above to try to force one of
7122 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
7124 @defmac PIC_OFFSET_TABLE_REGNUM
7125 The register number of the register used to address a table of static
7126 data addresses in memory. In some cases this register is defined by a
7127 processor's ``application binary interface'' (ABI)@. When this macro
7128 is defined, RTL is generated for this register once, as with the stack
7129 pointer and frame pointer registers. If this macro is not defined, it
7130 is up to the machine-dependent files to allocate such a register (if
7131 necessary). Note that this register must be fixed when in use (e.g.@:
7132 when @code{flag_pic} is true).
7135 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
7136 Define this macro if the register defined by
7137 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define
7138 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
7141 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
7142 A C expression that is nonzero if @var{x} is a legitimate immediate
7143 operand on the target machine when generating position independent code.
7144 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
7145 check this. You can also assume @var{flag_pic} is true, so you need not
7146 check it either. You need not define this macro if all constants
7147 (including @code{SYMBOL_REF}) can be immediate operands when generating
7148 position independent code.
7151 @node Assembler Format
7152 @section Defining the Output Assembler Language
7154 This section describes macros whose principal purpose is to describe how
7155 to write instructions in assembler language---rather than what the
7159 * File Framework:: Structural information for the assembler file.
7160 * Data Output:: Output of constants (numbers, strings, addresses).
7161 * Uninitialized Data:: Output of uninitialized variables.
7162 * Label Output:: Output and generation of labels.
7163 * Initialization:: General principles of initialization
7164 and termination routines.
7165 * Macros for Initialization::
7166 Specific macros that control the handling of
7167 initialization and termination routines.
7168 * Instruction Output:: Output of actual instructions.
7169 * Dispatch Tables:: Output of jump tables.
7170 * Exception Region Output:: Output of exception region code.
7171 * Alignment Output:: Pseudo ops for alignment and skipping data.
7174 @node File Framework
7175 @subsection The Overall Framework of an Assembler File
7176 @cindex assembler format
7177 @cindex output of assembler code
7179 @c prevent bad page break with this line
7180 This describes the overall framework of an assembly file.
7182 @findex default_file_start
7183 @deftypefn {Target Hook} void TARGET_ASM_FILE_START (void)
7184 Output to @code{asm_out_file} any text which the assembler expects to
7185 find at the beginning of a file. The default behavior is controlled
7186 by two flags, documented below. Unless your target's assembler is
7187 quite unusual, if you override the default, you should call
7188 @code{default_file_start} at some point in your target hook. This
7189 lets other target files rely on these variables.
7192 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
7193 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
7194 printed as the very first line in the assembly file, unless
7195 @option{-fverbose-asm} is in effect. (If that macro has been defined
7196 to the empty string, this variable has no effect.) With the normal
7197 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
7198 assembler that it need not bother stripping comments or extra
7199 whitespace from its input. This allows it to work a bit faster.
7201 The default is false. You should not set it to true unless you have
7202 verified that your port does not generate any extra whitespace or
7203 comments that will cause GAS to issue errors in NO_APP mode.
7206 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
7207 If this flag is true, @code{output_file_directive} will be called
7208 for the primary source file, immediately after printing
7209 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
7210 this to be done. The default is false.
7213 @deftypefn {Target Hook} void TARGET_ASM_FILE_END (void)
7214 Output to @code{asm_out_file} any text which the assembler expects
7215 to find at the end of a file. The default is to output nothing.
7218 @deftypefun void file_end_indicate_exec_stack ()
7219 Some systems use a common convention, the @samp{.note.GNU-stack}
7220 special section, to indicate whether or not an object file relies on
7221 the stack being executable. If your system uses this convention, you
7222 should define @code{TARGET_ASM_FILE_END} to this function. If you
7223 need to do other things in that hook, have your hook function call
7227 @deftypefn {Target Hook} void TARGET_ASM_LTO_START (void)
7228 Output to @code{asm_out_file} any text which the assembler expects
7229 to find at the start of an LTO section. The default is to output
7233 @deftypefn {Target Hook} void TARGET_ASM_LTO_END (void)
7234 Output to @code{asm_out_file} any text which the assembler expects
7235 to find at the end of an LTO section. The default is to output
7239 @deftypefn {Target Hook} void TARGET_ASM_CODE_END (void)
7240 Output to @code{asm_out_file} any text which is needed before emitting
7241 unwind info and debug info at the end of a file. Some targets emit
7242 here PIC setup thunks that cannot be emitted at the end of file,
7243 because they couldn't have unwind info then. The default is to output
7247 @defmac ASM_COMMENT_START
7248 A C string constant describing how to begin a comment in the target
7249 assembler language. The compiler assumes that the comment will end at
7250 the end of the line.
7254 A C string constant for text to be output before each @code{asm}
7255 statement or group of consecutive ones. Normally this is
7256 @code{"#APP"}, which is a comment that has no effect on most
7257 assemblers but tells the GNU assembler that it must check the lines
7258 that follow for all valid assembler constructs.
7262 A C string constant for text to be output after each @code{asm}
7263 statement or group of consecutive ones. Normally this is
7264 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
7265 time-saving assumptions that are valid for ordinary compiler output.
7268 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
7269 A C statement to output COFF information or DWARF debugging information
7270 which indicates that filename @var{name} is the current source file to
7271 the stdio stream @var{stream}.
7273 This macro need not be defined if the standard form of output
7274 for the file format in use is appropriate.
7277 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
7278 A C statement to output the string @var{string} to the stdio stream
7279 @var{stream}. If you do not call the function @code{output_quoted_string}
7280 in your config files, GCC will only call it to output filenames to
7281 the assembler source. So you can use it to canonicalize the format
7282 of the filename using this macro.
7285 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
7286 A C statement to output something to the assembler file to handle a
7287 @samp{#ident} directive containing the text @var{string}. If this
7288 macro is not defined, nothing is output for a @samp{#ident} directive.
7291 @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, tree @var{decl})
7292 Output assembly directives to switch to section @var{name}. The section
7293 should have attributes as specified by @var{flags}, which is a bit mask
7294 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{decl}
7295 is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which
7296 this section is associated.
7299 @deftypevr {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
7300 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
7303 @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
7304 @deftypevr {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
7305 This flag is true if we can create zeroed data by switching to a BSS
7306 section and then using @code{ASM_OUTPUT_SKIP} to allocate the space.
7307 This is true on most ELF targets.
7310 @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
7311 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
7312 based on a variable or function decl, a section name, and whether or not the
7313 declaration's initializer may contain runtime relocations. @var{decl} may be
7314 null, in which case read-write data should be assumed.
7316 The default version of this function handles choosing code vs data,
7317 read-only vs read-write data, and @code{flag_pic}. You should only
7318 need to override this if your target has special flags that might be
7319 set via @code{__attribute__}.
7322 @deftypefn {Target Hook} int TARGET_ASM_RECORD_GCC_SWITCHES (print_switch_type @var{type}, const char *@var{text})
7323 Provides the target with the ability to record the gcc command line
7324 switches that have been passed to the compiler, and options that are
7325 enabled. The @var{type} argument specifies what is being recorded.
7326 It can take the following values:
7329 @item SWITCH_TYPE_PASSED
7330 @var{text} is a command line switch that has been set by the user.
7332 @item SWITCH_TYPE_ENABLED
7333 @var{text} is an option which has been enabled. This might be as a
7334 direct result of a command line switch, or because it is enabled by
7335 default or because it has been enabled as a side effect of a different
7336 command line switch. For example, the @option{-O2} switch enables
7337 various different individual optimization passes.
7339 @item SWITCH_TYPE_DESCRIPTIVE
7340 @var{text} is either NULL or some descriptive text which should be
7341 ignored. If @var{text} is NULL then it is being used to warn the
7342 target hook that either recording is starting or ending. The first
7343 time @var{type} is SWITCH_TYPE_DESCRIPTIVE and @var{text} is NULL, the
7344 warning is for start up and the second time the warning is for
7345 wind down. This feature is to allow the target hook to make any
7346 necessary preparations before it starts to record switches and to
7347 perform any necessary tidying up after it has finished recording
7350 @item SWITCH_TYPE_LINE_START
7351 This option can be ignored by this target hook.
7353 @item SWITCH_TYPE_LINE_END
7354 This option can be ignored by this target hook.
7357 The hook's return value must be zero. Other return values may be
7358 supported in the future.
7360 By default this hook is set to NULL, but an example implementation is
7361 provided for ELF based targets. Called @var{elf_record_gcc_switches},
7362 it records the switches as ASCII text inside a new, string mergeable
7363 section in the assembler output file. The name of the new section is
7364 provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target
7368 @deftypevr {Target Hook} {const char *} TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
7369 This is the name of the section that will be created by the example
7370 ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target
7376 @subsection Output of Data
7379 @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
7380 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
7381 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
7382 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
7383 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
7384 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
7385 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
7386 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
7387 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
7388 These hooks specify assembly directives for creating certain kinds
7389 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
7390 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
7391 aligned two-byte object, and so on. Any of the hooks may be
7392 @code{NULL}, indicating that no suitable directive is available.
7394 The compiler will print these strings at the start of a new line,
7395 followed immediately by the object's initial value. In most cases,
7396 the string should contain a tab, a pseudo-op, and then another tab.
7399 @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
7400 The @code{assemble_integer} function uses this hook to output an
7401 integer object. @var{x} is the object's value, @var{size} is its size
7402 in bytes and @var{aligned_p} indicates whether it is aligned. The
7403 function should return @code{true} if it was able to output the
7404 object. If it returns false, @code{assemble_integer} will try to
7405 split the object into smaller parts.
7407 The default implementation of this hook will use the
7408 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
7409 when the relevant string is @code{NULL}.
7412 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
7413 A C statement to recognize @var{rtx} patterns that
7414 @code{output_addr_const} can't deal with, and output assembly code to
7415 @var{stream} corresponding to the pattern @var{x}. This may be used to
7416 allow machine-dependent @code{UNSPEC}s to appear within constants.
7418 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
7419 @code{goto fail}, so that a standard error message is printed. If it
7420 prints an error message itself, by calling, for example,
7421 @code{output_operand_lossage}, it may just complete normally.
7424 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
7425 A C statement to output to the stdio stream @var{stream} an assembler
7426 instruction to assemble a string constant containing the @var{len}
7427 bytes at @var{ptr}. @var{ptr} will be a C expression of type
7428 @code{char *} and @var{len} a C expression of type @code{int}.
7430 If the assembler has a @code{.ascii} pseudo-op as found in the
7431 Berkeley Unix assembler, do not define the macro
7432 @code{ASM_OUTPUT_ASCII}.
7435 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
7436 A C statement to output word @var{n} of a function descriptor for
7437 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
7438 is defined, and is otherwise unused.
7441 @defmac CONSTANT_POOL_BEFORE_FUNCTION
7442 You may define this macro as a C expression. You should define the
7443 expression to have a nonzero value if GCC should output the constant
7444 pool for a function before the code for the function, or a zero value if
7445 GCC should output the constant pool after the function. If you do
7446 not define this macro, the usual case, GCC will output the constant
7447 pool before the function.
7450 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
7451 A C statement to output assembler commands to define the start of the
7452 constant pool for a function. @var{funname} is a string giving
7453 the name of the function. Should the return type of the function
7454 be required, it can be obtained via @var{fundecl}. @var{size}
7455 is the size, in bytes, of the constant pool that will be written
7456 immediately after this call.
7458 If no constant-pool prefix is required, the usual case, this macro need
7462 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
7463 A C statement (with or without semicolon) to output a constant in the
7464 constant pool, if it needs special treatment. (This macro need not do
7465 anything for RTL expressions that can be output normally.)
7467 The argument @var{file} is the standard I/O stream to output the
7468 assembler code on. @var{x} is the RTL expression for the constant to
7469 output, and @var{mode} is the machine mode (in case @var{x} is a
7470 @samp{const_int}). @var{align} is the required alignment for the value
7471 @var{x}; you should output an assembler directive to force this much
7474 The argument @var{labelno} is a number to use in an internal label for
7475 the address of this pool entry. The definition of this macro is
7476 responsible for outputting the label definition at the proper place.
7477 Here is how to do this:
7480 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
7483 When you output a pool entry specially, you should end with a
7484 @code{goto} to the label @var{jumpto}. This will prevent the same pool
7485 entry from being output a second time in the usual manner.
7487 You need not define this macro if it would do nothing.
7490 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
7491 A C statement to output assembler commands to at the end of the constant
7492 pool for a function. @var{funname} is a string giving the name of the
7493 function. Should the return type of the function be required, you can
7494 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
7495 constant pool that GCC wrote immediately before this call.
7497 If no constant-pool epilogue is required, the usual case, you need not
7501 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
7502 Define this macro as a C expression which is nonzero if @var{C} is
7503 used as a logical line separator by the assembler. @var{STR} points
7504 to the position in the string where @var{C} was found; this can be used if
7505 a line separator uses multiple characters.
7507 If you do not define this macro, the default is that only
7508 the character @samp{;} is treated as a logical line separator.
7511 @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
7512 @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
7513 These target hooks are C string constants, describing the syntax in the
7514 assembler for grouping arithmetic expressions. If not overridden, they
7515 default to normal parentheses, which is correct for most assemblers.
7518 These macros are provided by @file{real.h} for writing the definitions
7519 of @code{ASM_OUTPUT_DOUBLE} and the like:
7521 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
7522 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
7523 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
7524 @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
7525 @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
7526 @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
7527 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
7528 target's floating point representation, and store its bit pattern in
7529 the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and
7530 @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
7531 simple @code{long int}. For the others, it should be an array of
7532 @code{long int}. The number of elements in this array is determined
7533 by the size of the desired target floating point data type: 32 bits of
7534 it go in each @code{long int} array element. Each array element holds
7535 32 bits of the result, even if @code{long int} is wider than 32 bits
7536 on the host machine.
7538 The array element values are designed so that you can print them out
7539 using @code{fprintf} in the order they should appear in the target
7543 @node Uninitialized Data
7544 @subsection Output of Uninitialized Variables
7546 Each of the macros in this section is used to do the whole job of
7547 outputting a single uninitialized variable.
7549 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
7550 A C statement (sans semicolon) to output to the stdio stream
7551 @var{stream} the assembler definition of a common-label named
7552 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7553 is the size rounded up to whatever alignment the caller wants. It is
7554 possible that @var{size} may be zero, for instance if a struct with no
7555 other member than a zero-length array is defined. In this case, the
7556 backend must output a symbol definition that allocates at least one
7557 byte, both so that the address of the resulting object does not compare
7558 equal to any other, and because some object formats cannot even express
7559 the concept of a zero-sized common symbol, as that is how they represent
7560 an ordinary undefined external.
7562 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7563 output the name itself; before and after that, output the additional
7564 assembler syntax for defining the name, and a newline.
7566 This macro controls how the assembler definitions of uninitialized
7567 common global variables are output.
7570 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
7571 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
7572 separate, explicit argument. If you define this macro, it is used in
7573 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
7574 handling the required alignment of the variable. The alignment is specified
7575 as the number of bits.
7578 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7579 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
7580 variable to be output, if there is one, or @code{NULL_TREE} if there
7581 is no corresponding variable. If you define this macro, GCC will use it
7582 in place of both @code{ASM_OUTPUT_COMMON} and
7583 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
7584 the variable's decl in order to chose what to output.
7587 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
7588 A C statement (sans semicolon) to output to the stdio stream
7589 @var{stream} the assembler definition of uninitialized global @var{decl} named
7590 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7591 is the size rounded up to whatever alignment the caller wants.
7593 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
7594 defining this macro. If unable, use the expression
7595 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
7596 before and after that, output the additional assembler syntax for defining
7597 the name, and a newline.
7599 There are two ways of handling global BSS@. One is to define either
7600 this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}.
7601 The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
7602 switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
7603 You do not need to do both.
7605 Some languages do not have @code{common} data, and require a
7606 non-common form of global BSS in order to handle uninitialized globals
7607 efficiently. C++ is one example of this. However, if the target does
7608 not support global BSS, the front end may choose to make globals
7609 common in order to save space in the object file.
7612 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7613 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
7614 separate, explicit argument. If you define this macro, it is used in
7615 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
7616 handling the required alignment of the variable. The alignment is specified
7617 as the number of bits.
7619 Try to use function @code{asm_output_aligned_bss} defined in file
7620 @file{varasm.c} when defining this macro.
7623 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
7624 A C statement (sans semicolon) to output to the stdio stream
7625 @var{stream} the assembler definition of a local-common-label named
7626 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7627 is the size rounded up to whatever alignment the caller wants.
7629 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7630 output the name itself; before and after that, output the additional
7631 assembler syntax for defining the name, and a newline.
7633 This macro controls how the assembler definitions of uninitialized
7634 static variables are output.
7637 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
7638 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
7639 separate, explicit argument. If you define this macro, it is used in
7640 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
7641 handling the required alignment of the variable. The alignment is specified
7642 as the number of bits.
7645 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7646 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
7647 variable to be output, if there is one, or @code{NULL_TREE} if there
7648 is no corresponding variable. If you define this macro, GCC will use it
7649 in place of both @code{ASM_OUTPUT_DECL} and
7650 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
7651 the variable's decl in order to chose what to output.
7655 @subsection Output and Generation of Labels
7657 @c prevent bad page break with this line
7658 This is about outputting labels.
7660 @findex assemble_name
7661 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
7662 A C statement (sans semicolon) to output to the stdio stream
7663 @var{stream} the assembler definition of a label named @var{name}.
7664 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7665 output the name itself; before and after that, output the additional
7666 assembler syntax for defining the name, and a newline. A default
7667 definition of this macro is provided which is correct for most systems.
7670 @findex assemble_name_raw
7671 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
7672 Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
7673 to refer to a compiler-generated label. The default definition uses
7674 @code{assemble_name_raw}, which is like @code{assemble_name} except
7675 that it is more efficient.
7679 A C string containing the appropriate assembler directive to specify the
7680 size of a symbol, without any arguments. On systems that use ELF, the
7681 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
7682 systems, the default is not to define this macro.
7684 Define this macro only if it is correct to use the default definitions
7685 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
7686 for your system. If you need your own custom definitions of those
7687 macros, or if you do not need explicit symbol sizes at all, do not
7691 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
7692 A C statement (sans semicolon) to output to the stdio stream
7693 @var{stream} a directive telling the assembler that the size of the
7694 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
7695 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7699 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
7700 A C statement (sans semicolon) to output to the stdio stream
7701 @var{stream} a directive telling the assembler to calculate the size of
7702 the symbol @var{name} by subtracting its address from the current
7705 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7706 provided. The default assumes that the assembler recognizes a special
7707 @samp{.} symbol as referring to the current address, and can calculate
7708 the difference between this and another symbol. If your assembler does
7709 not recognize @samp{.} or cannot do calculations with it, you will need
7710 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
7714 A C string containing the appropriate assembler directive to specify the
7715 type of a symbol, without any arguments. On systems that use ELF, the
7716 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
7717 systems, the default is not to define this macro.
7719 Define this macro only if it is correct to use the default definition of
7720 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7721 custom definition of this macro, or if you do not need explicit symbol
7722 types at all, do not define this macro.
7725 @defmac TYPE_OPERAND_FMT
7726 A C string which specifies (using @code{printf} syntax) the format of
7727 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
7728 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
7729 the default is not to define this macro.
7731 Define this macro only if it is correct to use the default definition of
7732 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7733 custom definition of this macro, or if you do not need explicit symbol
7734 types at all, do not define this macro.
7737 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
7738 A C statement (sans semicolon) to output to the stdio stream
7739 @var{stream} a directive telling the assembler that the type of the
7740 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
7741 that string is always either @samp{"function"} or @samp{"object"}, but
7742 you should not count on this.
7744 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
7745 definition of this macro is provided.
7748 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
7749 A C statement (sans semicolon) to output to the stdio stream
7750 @var{stream} any text necessary for declaring the name @var{name} of a
7751 function which is being defined. This macro is responsible for
7752 outputting the label definition (perhaps using
7753 @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the
7754 @code{FUNCTION_DECL} tree node representing the function.
7756 If this macro is not defined, then the function name is defined in the
7757 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7759 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
7763 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
7764 A C statement (sans semicolon) to output to the stdio stream
7765 @var{stream} any text necessary for declaring the size of a function
7766 which is being defined. The argument @var{name} is the name of the
7767 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
7768 representing the function.
7770 If this macro is not defined, then the function size is not defined.
7772 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
7776 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
7777 A C statement (sans semicolon) to output to the stdio stream
7778 @var{stream} any text necessary for declaring the name @var{name} of an
7779 initialized variable which is being defined. This macro must output the
7780 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
7781 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
7783 If this macro is not defined, then the variable name is defined in the
7784 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7786 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
7787 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
7790 @deftypefn {Target Hook} void TARGET_ASM_DECLARE_CONSTANT_NAME (FILE * @var{file}, const char * @var{name}, const_tree @var{expr}, HOST_WIDE_INT @var{size})
7791 A target hook to output to the stdio stream @var{file} any text necessary
7792 for declaring the name @var{name} of a constant which is being defined. This
7793 target hook is responsible for outputting the label definition (perhaps using
7794 @code{assemble_label}). The argument @var{exp} is the value of the constant,
7795 and @var{size} is the size of the constant in bytes. The @var{name}
7796 will be an internal label.
7798 The default version of this target hook, define the @var{name} in the
7799 usual manner as a label (by means of @code{assemble_label}).
7801 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook.
7804 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
7805 A C statement (sans semicolon) to output to the stdio stream
7806 @var{stream} any text necessary for claiming a register @var{regno}
7807 for a global variable @var{decl} with name @var{name}.
7809 If you don't define this macro, that is equivalent to defining it to do
7813 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
7814 A C statement (sans semicolon) to finish up declaring a variable name
7815 once the compiler has processed its initializer fully and thus has had a
7816 chance to determine the size of an array when controlled by an
7817 initializer. This is used on systems where it's necessary to declare
7818 something about the size of the object.
7820 If you don't define this macro, that is equivalent to defining it to do
7823 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
7824 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
7827 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
7828 This target hook is a function to output to the stdio stream
7829 @var{stream} some commands that will make the label @var{name} global;
7830 that is, available for reference from other files.
7832 The default implementation relies on a proper definition of
7833 @code{GLOBAL_ASM_OP}.
7836 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_DECL_NAME (FILE *@var{stream}, tree @var{decl})
7837 This target hook is a function to output to the stdio stream
7838 @var{stream} some commands that will make the name associated with @var{decl}
7839 global; that is, available for reference from other files.
7841 The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.
7844 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
7845 A C statement (sans semicolon) to output to the stdio stream
7846 @var{stream} some commands that will make the label @var{name} weak;
7847 that is, available for reference from other files but only used if
7848 no other definition is available. Use the expression
7849 @code{assemble_name (@var{stream}, @var{name})} to output the name
7850 itself; before and after that, output the additional assembler syntax
7851 for making that name weak, and a newline.
7853 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
7854 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
7858 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
7859 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
7860 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
7861 or variable decl. If @var{value} is not @code{NULL}, this C statement
7862 should output to the stdio stream @var{stream} assembler code which
7863 defines (equates) the weak symbol @var{name} to have the value
7864 @var{value}. If @var{value} is @code{NULL}, it should output commands
7865 to make @var{name} weak.
7868 @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
7869 Outputs a directive that enables @var{name} to be used to refer to
7870 symbol @var{value} with weak-symbol semantics. @code{decl} is the
7871 declaration of @code{name}.
7874 @defmac SUPPORTS_WEAK
7875 A C expression which evaluates to true if the target supports weak symbols.
7877 If you don't define this macro, @file{defaults.h} provides a default
7878 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
7879 is defined, the default definition is @samp{1}; otherwise, it is
7880 @samp{0}. Define this macro if you want to control weak symbol support
7881 with a compiler flag such as @option{-melf}.
7884 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
7885 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
7886 public symbol such that extra copies in multiple translation units will
7887 be discarded by the linker. Define this macro if your object file
7888 format provides support for this concept, such as the @samp{COMDAT}
7889 section flags in the Microsoft Windows PE/COFF format, and this support
7890 requires changes to @var{decl}, such as putting it in a separate section.
7893 @defmac SUPPORTS_ONE_ONLY
7894 A C expression which evaluates to true if the target supports one-only
7897 If you don't define this macro, @file{varasm.c} provides a default
7898 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
7899 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
7900 you want to control one-only symbol support with a compiler flag, or if
7901 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
7902 be emitted as one-only.
7905 @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, int @var{visibility})
7906 This target hook is a function to output to @var{asm_out_file} some
7907 commands that will make the symbol(s) associated with @var{decl} have
7908 hidden, protected or internal visibility as specified by @var{visibility}.
7911 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
7912 A C expression that evaluates to true if the target's linker expects
7913 that weak symbols do not appear in a static archive's table of contents.
7914 The default is @code{0}.
7916 Leaving weak symbols out of an archive's table of contents means that,
7917 if a symbol will only have a definition in one translation unit and
7918 will have undefined references from other translation units, that
7919 symbol should not be weak. Defining this macro to be nonzero will
7920 thus have the effect that certain symbols that would normally be weak
7921 (explicit template instantiations, and vtables for polymorphic classes
7922 with noninline key methods) will instead be nonweak.
7924 The C++ ABI requires this macro to be zero. Define this macro for
7925 targets where full C++ ABI compliance is impossible and where linker
7926 restrictions require weak symbols to be left out of a static archive's
7930 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
7931 A C statement (sans semicolon) to output to the stdio stream
7932 @var{stream} any text necessary for declaring the name of an external
7933 symbol named @var{name} which is referenced in this compilation but
7934 not defined. The value of @var{decl} is the tree node for the
7937 This macro need not be defined if it does not need to output anything.
7938 The GNU assembler and most Unix assemblers don't require anything.
7941 @deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref})
7942 This target hook is a function to output to @var{asm_out_file} an assembler
7943 pseudo-op to declare a library function name external. The name of the
7944 library function is given by @var{symref}, which is a @code{symbol_ref}.
7947 @deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (const char *@var{symbol})
7948 This target hook is a function to output to @var{asm_out_file} an assembler
7949 directive to annotate @var{symbol} as used. The Darwin target uses the
7950 .no_dead_code_strip directive.
7953 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
7954 A C statement (sans semicolon) to output to the stdio stream
7955 @var{stream} a reference in assembler syntax to a label named
7956 @var{name}. This should add @samp{_} to the front of the name, if that
7957 is customary on your operating system, as it is in most Berkeley Unix
7958 systems. This macro is used in @code{assemble_name}.
7961 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
7962 A C statement (sans semicolon) to output a reference to
7963 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
7964 will be used to output the name of the symbol. This macro may be used
7965 to modify the way a symbol is referenced depending on information
7966 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
7969 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
7970 A C statement (sans semicolon) to output a reference to @var{buf}, the
7971 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
7972 @code{assemble_name} will be used to output the name of the symbol.
7973 This macro is not used by @code{output_asm_label}, or the @code{%l}
7974 specifier that calls it; the intention is that this macro should be set
7975 when it is necessary to output a label differently when its address is
7979 @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
7980 A function to output to the stdio stream @var{stream} a label whose
7981 name is made from the string @var{prefix} and the number @var{labelno}.
7983 It is absolutely essential that these labels be distinct from the labels
7984 used for user-level functions and variables. Otherwise, certain programs
7985 will have name conflicts with internal labels.
7987 It is desirable to exclude internal labels from the symbol table of the
7988 object file. Most assemblers have a naming convention for labels that
7989 should be excluded; on many systems, the letter @samp{L} at the
7990 beginning of a label has this effect. You should find out what
7991 convention your system uses, and follow it.
7993 The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
7996 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
7997 A C statement to output to the stdio stream @var{stream} a debug info
7998 label whose name is made from the string @var{prefix} and the number
7999 @var{num}. This is useful for VLIW targets, where debug info labels
8000 may need to be treated differently than branch target labels. On some
8001 systems, branch target labels must be at the beginning of instruction
8002 bundles, but debug info labels can occur in the middle of instruction
8005 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
8009 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
8010 A C statement to store into the string @var{string} a label whose name
8011 is made from the string @var{prefix} and the number @var{num}.
8013 This string, when output subsequently by @code{assemble_name}, should
8014 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
8015 with the same @var{prefix} and @var{num}.
8017 If the string begins with @samp{*}, then @code{assemble_name} will
8018 output the rest of the string unchanged. It is often convenient for
8019 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
8020 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
8021 to output the string, and may change it. (Of course,
8022 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
8023 you should know what it does on your machine.)
8026 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
8027 A C expression to assign to @var{outvar} (which is a variable of type
8028 @code{char *}) a newly allocated string made from the string
8029 @var{name} and the number @var{number}, with some suitable punctuation
8030 added. Use @code{alloca} to get space for the string.
8032 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
8033 produce an assembler label for an internal static variable whose name is
8034 @var{name}. Therefore, the string must be such as to result in valid
8035 assembler code. The argument @var{number} is different each time this
8036 macro is executed; it prevents conflicts between similarly-named
8037 internal static variables in different scopes.
8039 Ideally this string should not be a valid C identifier, to prevent any
8040 conflict with the user's own symbols. Most assemblers allow periods
8041 or percent signs in assembler symbols; putting at least one of these
8042 between the name and the number will suffice.
8044 If this macro is not defined, a default definition will be provided
8045 which is correct for most systems.
8048 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
8049 A C statement to output to the stdio stream @var{stream} assembler code
8050 which defines (equates) the symbol @var{name} to have the value @var{value}.
8053 If @code{SET_ASM_OP} is defined, a default definition is provided which is
8054 correct for most systems.
8057 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
8058 A C statement to output to the stdio stream @var{stream} assembler code
8059 which defines (equates) the symbol whose tree node is @var{decl_of_name}
8060 to have the value of the tree node @var{decl_of_value}. This macro will
8061 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
8062 the tree nodes are available.
8065 If @code{SET_ASM_OP} is defined, a default definition is provided which is
8066 correct for most systems.
8069 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
8070 A C statement that evaluates to true if the assembler code which defines
8071 (equates) the symbol whose tree node is @var{decl_of_name} to have the value
8072 of the tree node @var{decl_of_value} should be emitted near the end of the
8073 current compilation unit. The default is to not defer output of defines.
8074 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
8075 @samp{ASM_OUTPUT_DEF_FROM_DECLS}.
8078 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
8079 A C statement to output to the stdio stream @var{stream} assembler code
8080 which defines (equates) the weak symbol @var{name} to have the value
8081 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
8082 an undefined weak symbol.
8084 Define this macro if the target only supports weak aliases; define
8085 @code{ASM_OUTPUT_DEF} instead if possible.
8088 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
8089 Define this macro to override the default assembler names used for
8090 Objective-C methods.
8092 The default name is a unique method number followed by the name of the
8093 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
8094 the category is also included in the assembler name (e.g.@:
8097 These names are safe on most systems, but make debugging difficult since
8098 the method's selector is not present in the name. Therefore, particular
8099 systems define other ways of computing names.
8101 @var{buf} is an expression of type @code{char *} which gives you a
8102 buffer in which to store the name; its length is as long as
8103 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
8104 50 characters extra.
8106 The argument @var{is_inst} specifies whether the method is an instance
8107 method or a class method; @var{class_name} is the name of the class;
8108 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
8109 in a category); and @var{sel_name} is the name of the selector.
8111 On systems where the assembler can handle quoted names, you can use this
8112 macro to provide more human-readable names.
8115 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
8116 A C statement (sans semicolon) to output to the stdio stream
8117 @var{stream} commands to declare that the label @var{name} is an
8118 Objective-C class reference. This is only needed for targets whose
8119 linkers have special support for NeXT-style runtimes.
8122 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
8123 A C statement (sans semicolon) to output to the stdio stream
8124 @var{stream} commands to declare that the label @var{name} is an
8125 unresolved Objective-C class reference. This is only needed for targets
8126 whose linkers have special support for NeXT-style runtimes.
8129 @node Initialization
8130 @subsection How Initialization Functions Are Handled
8131 @cindex initialization routines
8132 @cindex termination routines
8133 @cindex constructors, output of
8134 @cindex destructors, output of
8136 The compiled code for certain languages includes @dfn{constructors}
8137 (also called @dfn{initialization routines})---functions to initialize
8138 data in the program when the program is started. These functions need
8139 to be called before the program is ``started''---that is to say, before
8140 @code{main} is called.
8142 Compiling some languages generates @dfn{destructors} (also called
8143 @dfn{termination routines}) that should be called when the program
8146 To make the initialization and termination functions work, the compiler
8147 must output something in the assembler code to cause those functions to
8148 be called at the appropriate time. When you port the compiler to a new
8149 system, you need to specify how to do this.
8151 There are two major ways that GCC currently supports the execution of
8152 initialization and termination functions. Each way has two variants.
8153 Much of the structure is common to all four variations.
8155 @findex __CTOR_LIST__
8156 @findex __DTOR_LIST__
8157 The linker must build two lists of these functions---a list of
8158 initialization functions, called @code{__CTOR_LIST__}, and a list of
8159 termination functions, called @code{__DTOR_LIST__}.
8161 Each list always begins with an ignored function pointer (which may hold
8162 0, @minus{}1, or a count of the function pointers after it, depending on
8163 the environment). This is followed by a series of zero or more function
8164 pointers to constructors (or destructors), followed by a function
8165 pointer containing zero.
8167 Depending on the operating system and its executable file format, either
8168 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
8169 time and exit time. Constructors are called in reverse order of the
8170 list; destructors in forward order.
8172 The best way to handle static constructors works only for object file
8173 formats which provide arbitrarily-named sections. A section is set
8174 aside for a list of constructors, and another for a list of destructors.
8175 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
8176 object file that defines an initialization function also puts a word in
8177 the constructor section to point to that function. The linker
8178 accumulates all these words into one contiguous @samp{.ctors} section.
8179 Termination functions are handled similarly.
8181 This method will be chosen as the default by @file{target-def.h} if
8182 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
8183 support arbitrary sections, but does support special designated
8184 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
8185 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
8187 When arbitrary sections are available, there are two variants, depending
8188 upon how the code in @file{crtstuff.c} is called. On systems that
8189 support a @dfn{.init} section which is executed at program startup,
8190 parts of @file{crtstuff.c} are compiled into that section. The
8191 program is linked by the @command{gcc} driver like this:
8194 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
8197 The prologue of a function (@code{__init}) appears in the @code{.init}
8198 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
8199 for the function @code{__fini} in the @dfn{.fini} section. Normally these
8200 files are provided by the operating system or by the GNU C library, but
8201 are provided by GCC for a few targets.
8203 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
8204 compiled from @file{crtstuff.c}. They contain, among other things, code
8205 fragments within the @code{.init} and @code{.fini} sections that branch
8206 to routines in the @code{.text} section. The linker will pull all parts
8207 of a section together, which results in a complete @code{__init} function
8208 that invokes the routines we need at startup.
8210 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
8213 If no init section is available, when GCC compiles any function called
8214 @code{main} (or more accurately, any function designated as a program
8215 entry point by the language front end calling @code{expand_main_function}),
8216 it inserts a procedure call to @code{__main} as the first executable code
8217 after the function prologue. The @code{__main} function is defined
8218 in @file{libgcc2.c} and runs the global constructors.
8220 In file formats that don't support arbitrary sections, there are again
8221 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
8222 and an `a.out' format must be used. In this case,
8223 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
8224 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
8225 and with the address of the void function containing the initialization
8226 code as its value. The GNU linker recognizes this as a request to add
8227 the value to a @dfn{set}; the values are accumulated, and are eventually
8228 placed in the executable as a vector in the format described above, with
8229 a leading (ignored) count and a trailing zero element.
8230 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
8231 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
8232 the compilation of @code{main} to call @code{__main} as above, starting
8233 the initialization process.
8235 The last variant uses neither arbitrary sections nor the GNU linker.
8236 This is preferable when you want to do dynamic linking and when using
8237 file formats which the GNU linker does not support, such as `ECOFF'@. In
8238 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
8239 termination functions are recognized simply by their names. This requires
8240 an extra program in the linkage step, called @command{collect2}. This program
8241 pretends to be the linker, for use with GCC; it does its job by running
8242 the ordinary linker, but also arranges to include the vectors of
8243 initialization and termination functions. These functions are called
8244 via @code{__main} as described above. In order to use this method,
8245 @code{use_collect2} must be defined in the target in @file{config.gcc}.
8248 The following section describes the specific macros that control and
8249 customize the handling of initialization and termination functions.
8252 @node Macros for Initialization
8253 @subsection Macros Controlling Initialization Routines
8255 Here are the macros that control how the compiler handles initialization
8256 and termination functions:
8258 @defmac INIT_SECTION_ASM_OP
8259 If defined, a C string constant, including spacing, for the assembler
8260 operation to identify the following data as initialization code. If not
8261 defined, GCC will assume such a section does not exist. When you are
8262 using special sections for initialization and termination functions, this
8263 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
8264 run the initialization functions.
8267 @defmac HAS_INIT_SECTION
8268 If defined, @code{main} will not call @code{__main} as described above.
8269 This macro should be defined for systems that control start-up code
8270 on a symbol-by-symbol basis, such as OSF/1, and should not
8271 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
8274 @defmac LD_INIT_SWITCH
8275 If defined, a C string constant for a switch that tells the linker that
8276 the following symbol is an initialization routine.
8279 @defmac LD_FINI_SWITCH
8280 If defined, a C string constant for a switch that tells the linker that
8281 the following symbol is a finalization routine.
8284 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
8285 If defined, a C statement that will write a function that can be
8286 automatically called when a shared library is loaded. The function
8287 should call @var{func}, which takes no arguments. If not defined, and
8288 the object format requires an explicit initialization function, then a
8289 function called @code{_GLOBAL__DI} will be generated.
8291 This function and the following one are used by collect2 when linking a
8292 shared library that needs constructors or destructors, or has DWARF2
8293 exception tables embedded in the code.
8296 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
8297 If defined, a C statement that will write a function that can be
8298 automatically called when a shared library is unloaded. The function
8299 should call @var{func}, which takes no arguments. If not defined, and
8300 the object format requires an explicit finalization function, then a
8301 function called @code{_GLOBAL__DD} will be generated.
8304 @defmac INVOKE__main
8305 If defined, @code{main} will call @code{__main} despite the presence of
8306 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
8307 where the init section is not actually run automatically, but is still
8308 useful for collecting the lists of constructors and destructors.
8311 @defmac SUPPORTS_INIT_PRIORITY
8312 If nonzero, the C++ @code{init_priority} attribute is supported and the
8313 compiler should emit instructions to control the order of initialization
8314 of objects. If zero, the compiler will issue an error message upon
8315 encountering an @code{init_priority} attribute.
8318 @deftypevr {Target Hook} bool TARGET_HAVE_CTORS_DTORS
8319 This value is true if the target supports some ``native'' method of
8320 collecting constructors and destructors to be run at startup and exit.
8321 It is false if we must use @command{collect2}.
8324 @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
8325 If defined, a function that outputs assembler code to arrange to call
8326 the function referenced by @var{symbol} at initialization time.
8328 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
8329 no arguments and with no return value. If the target supports initialization
8330 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
8331 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
8333 If this macro is not defined by the target, a suitable default will
8334 be chosen if (1) the target supports arbitrary section names, (2) the
8335 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
8339 @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
8340 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
8341 functions rather than initialization functions.
8344 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
8345 generated for the generated object file will have static linkage.
8347 If your system uses @command{collect2} as the means of processing
8348 constructors, then that program normally uses @command{nm} to scan
8349 an object file for constructor functions to be called.
8351 On certain kinds of systems, you can define this macro to make
8352 @command{collect2} work faster (and, in some cases, make it work at all):
8354 @defmac OBJECT_FORMAT_COFF
8355 Define this macro if the system uses COFF (Common Object File Format)
8356 object files, so that @command{collect2} can assume this format and scan
8357 object files directly for dynamic constructor/destructor functions.
8359 This macro is effective only in a native compiler; @command{collect2} as
8360 part of a cross compiler always uses @command{nm} for the target machine.
8363 @defmac REAL_NM_FILE_NAME
8364 Define this macro as a C string constant containing the file name to use
8365 to execute @command{nm}. The default is to search the path normally for
8368 If your system supports shared libraries and has a program to list the
8369 dynamic dependencies of a given library or executable, you can define
8370 these macros to enable support for running initialization and
8371 termination functions in shared libraries:
8375 Define this macro to a C string constant containing the name of the program
8376 which lists dynamic dependencies, like @command{"ldd"} under SunOS 4.
8379 @defmac PARSE_LDD_OUTPUT (@var{ptr})
8380 Define this macro to be C code that extracts filenames from the output
8381 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
8382 of type @code{char *} that points to the beginning of a line of output
8383 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
8384 code must advance @var{ptr} to the beginning of the filename on that
8385 line. Otherwise, it must set @var{ptr} to @code{NULL}.
8388 @defmac SHLIB_SUFFIX
8389 Define this macro to a C string constant containing the default shared
8390 library extension of the target (e.g., @samp{".so"}). @command{collect2}
8391 strips version information after this suffix when generating global
8392 constructor and destructor names. This define is only needed on targets
8393 that use @command{collect2} to process constructors and destructors.
8396 @node Instruction Output
8397 @subsection Output of Assembler Instructions
8399 @c prevent bad page break with this line
8400 This describes assembler instruction output.
8402 @defmac REGISTER_NAMES
8403 A C initializer containing the assembler's names for the machine
8404 registers, each one as a C string constant. This is what translates
8405 register numbers in the compiler into assembler language.
8408 @defmac ADDITIONAL_REGISTER_NAMES
8409 If defined, a C initializer for an array of structures containing a name
8410 and a register number. This macro defines additional names for hard
8411 registers, thus allowing the @code{asm} option in declarations to refer
8412 to registers using alternate names.
8415 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
8416 Define this macro if you are using an unusual assembler that
8417 requires different names for the machine instructions.
8419 The definition is a C statement or statements which output an
8420 assembler instruction opcode to the stdio stream @var{stream}. The
8421 macro-operand @var{ptr} is a variable of type @code{char *} which
8422 points to the opcode name in its ``internal'' form---the form that is
8423 written in the machine description. The definition should output the
8424 opcode name to @var{stream}, performing any translation you desire, and
8425 increment the variable @var{ptr} to point at the end of the opcode
8426 so that it will not be output twice.
8428 In fact, your macro definition may process less than the entire opcode
8429 name, or more than the opcode name; but if you want to process text
8430 that includes @samp{%}-sequences to substitute operands, you must take
8431 care of the substitution yourself. Just be sure to increment
8432 @var{ptr} over whatever text should not be output normally.
8434 @findex recog_data.operand
8435 If you need to look at the operand values, they can be found as the
8436 elements of @code{recog_data.operand}.
8438 If the macro definition does nothing, the instruction is output
8442 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
8443 If defined, a C statement to be executed just prior to the output of
8444 assembler code for @var{insn}, to modify the extracted operands so
8445 they will be output differently.
8447 Here the argument @var{opvec} is the vector containing the operands
8448 extracted from @var{insn}, and @var{noperands} is the number of
8449 elements of the vector which contain meaningful data for this insn.
8450 The contents of this vector are what will be used to convert the insn
8451 template into assembler code, so you can change the assembler output
8452 by changing the contents of the vector.
8454 This macro is useful when various assembler syntaxes share a single
8455 file of instruction patterns; by defining this macro differently, you
8456 can cause a large class of instructions to be output differently (such
8457 as with rearranged operands). Naturally, variations in assembler
8458 syntax affecting individual insn patterns ought to be handled by
8459 writing conditional output routines in those patterns.
8461 If this macro is not defined, it is equivalent to a null statement.
8464 @deftypefn {Target Hook} void TARGET_ASM_FINAL_POSTSCAN_INSN (FILE *@var{file}, rtx @var{insn}, rtx *@var{opvec}, int @var{noperands})
8465 If defined, this target hook is a function which is executed just after the
8466 output of assembler code for @var{insn}, to change the mode of the assembler
8469 Here the argument @var{opvec} is the vector containing the operands
8470 extracted from @var{insn}, and @var{noperands} is the number of
8471 elements of the vector which contain meaningful data for this insn.
8472 The contents of this vector are what was used to convert the insn
8473 template into assembler code, so you can change the assembler mode
8474 by checking the contents of the vector.
8477 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
8478 A C compound statement to output to stdio stream @var{stream} the
8479 assembler syntax for an instruction operand @var{x}. @var{x} is an
8482 @var{code} is a value that can be used to specify one of several ways
8483 of printing the operand. It is used when identical operands must be
8484 printed differently depending on the context. @var{code} comes from
8485 the @samp{%} specification that was used to request printing of the
8486 operand. If the specification was just @samp{%@var{digit}} then
8487 @var{code} is 0; if the specification was @samp{%@var{ltr}
8488 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
8491 If @var{x} is a register, this macro should print the register's name.
8492 The names can be found in an array @code{reg_names} whose type is
8493 @code{char *[]}. @code{reg_names} is initialized from
8494 @code{REGISTER_NAMES}.
8496 When the machine description has a specification @samp{%@var{punct}}
8497 (a @samp{%} followed by a punctuation character), this macro is called
8498 with a null pointer for @var{x} and the punctuation character for
8502 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
8503 A C expression which evaluates to true if @var{code} is a valid
8504 punctuation character for use in the @code{PRINT_OPERAND} macro. If
8505 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
8506 punctuation characters (except for the standard one, @samp{%}) are used
8510 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
8511 A C compound statement to output to stdio stream @var{stream} the
8512 assembler syntax for an instruction operand that is a memory reference
8513 whose address is @var{x}. @var{x} is an RTL expression.
8515 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
8516 On some machines, the syntax for a symbolic address depends on the
8517 section that the address refers to. On these machines, define the hook
8518 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
8519 @code{symbol_ref}, and then check for it here. @xref{Assembler
8523 @findex dbr_sequence_length
8524 @defmac DBR_OUTPUT_SEQEND (@var{file})
8525 A C statement, to be executed after all slot-filler instructions have
8526 been output. If necessary, call @code{dbr_sequence_length} to
8527 determine the number of slots filled in a sequence (zero if not
8528 currently outputting a sequence), to decide how many no-ops to output,
8531 Don't define this macro if it has nothing to do, but it is helpful in
8532 reading assembly output if the extent of the delay sequence is made
8533 explicit (e.g.@: with white space).
8536 @findex final_sequence
8537 Note that output routines for instructions with delay slots must be
8538 prepared to deal with not being output as part of a sequence
8539 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
8540 found.) The variable @code{final_sequence} is null when not
8541 processing a sequence, otherwise it contains the @code{sequence} rtx
8545 @defmac REGISTER_PREFIX
8546 @defmacx LOCAL_LABEL_PREFIX
8547 @defmacx USER_LABEL_PREFIX
8548 @defmacx IMMEDIATE_PREFIX
8549 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
8550 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
8551 @file{final.c}). These are useful when a single @file{md} file must
8552 support multiple assembler formats. In that case, the various @file{tm.h}
8553 files can define these macros differently.
8556 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
8557 If defined this macro should expand to a series of @code{case}
8558 statements which will be parsed inside the @code{switch} statement of
8559 the @code{asm_fprintf} function. This allows targets to define extra
8560 printf formats which may useful when generating their assembler
8561 statements. Note that uppercase letters are reserved for future
8562 generic extensions to asm_fprintf, and so are not available to target
8563 specific code. The output file is given by the parameter @var{file}.
8564 The varargs input pointer is @var{argptr} and the rest of the format
8565 string, starting the character after the one that is being switched
8566 upon, is pointed to by @var{format}.
8569 @defmac ASSEMBLER_DIALECT
8570 If your target supports multiple dialects of assembler language (such as
8571 different opcodes), define this macro as a C expression that gives the
8572 numeric index of the assembler language dialect to use, with zero as the
8575 If this macro is defined, you may use constructs of the form
8577 @samp{@{option0|option1|option2@dots{}@}}
8580 in the output templates of patterns (@pxref{Output Template}) or in the
8581 first argument of @code{asm_fprintf}. This construct outputs
8582 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
8583 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
8584 within these strings retain their usual meaning. If there are fewer
8585 alternatives within the braces than the value of
8586 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
8588 If you do not define this macro, the characters @samp{@{}, @samp{|} and
8589 @samp{@}} do not have any special meaning when used in templates or
8590 operands to @code{asm_fprintf}.
8592 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
8593 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
8594 the variations in assembler language syntax with that mechanism. Define
8595 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
8596 if the syntax variant are larger and involve such things as different
8597 opcodes or operand order.
8600 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
8601 A C expression to output to @var{stream} some assembler code
8602 which will push hard register number @var{regno} onto the stack.
8603 The code need not be optimal, since this macro is used only when
8607 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
8608 A C expression to output to @var{stream} some assembler code
8609 which will pop hard register number @var{regno} off of the stack.
8610 The code need not be optimal, since this macro is used only when
8614 @node Dispatch Tables
8615 @subsection Output of Dispatch Tables
8617 @c prevent bad page break with this line
8618 This concerns dispatch tables.
8620 @cindex dispatch table
8621 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
8622 A C statement to output to the stdio stream @var{stream} an assembler
8623 pseudo-instruction to generate a difference between two labels.
8624 @var{value} and @var{rel} are the numbers of two internal labels. The
8625 definitions of these labels are output using
8626 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
8627 way here. For example,
8630 fprintf (@var{stream}, "\t.word L%d-L%d\n",
8631 @var{value}, @var{rel})
8634 You must provide this macro on machines where the addresses in a
8635 dispatch table are relative to the table's own address. If defined, GCC
8636 will also use this macro on all machines when producing PIC@.
8637 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
8638 mode and flags can be read.
8641 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
8642 This macro should be provided on machines where the addresses
8643 in a dispatch table are absolute.
8645 The definition should be a C statement to output to the stdio stream
8646 @var{stream} an assembler pseudo-instruction to generate a reference to
8647 a label. @var{value} is the number of an internal label whose
8648 definition is output using @code{(*targetm.asm_out.internal_label)}.
8652 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
8656 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
8657 Define this if the label before a jump-table needs to be output
8658 specially. The first three arguments are the same as for
8659 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
8660 jump-table which follows (a @code{jump_insn} containing an
8661 @code{addr_vec} or @code{addr_diff_vec}).
8663 This feature is used on system V to output a @code{swbeg} statement
8666 If this macro is not defined, these labels are output with
8667 @code{(*targetm.asm_out.internal_label)}.
8670 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
8671 Define this if something special must be output at the end of a
8672 jump-table. The definition should be a C statement to be executed
8673 after the assembler code for the table is written. It should write
8674 the appropriate code to stdio stream @var{stream}. The argument
8675 @var{table} is the jump-table insn, and @var{num} is the label-number
8676 of the preceding label.
8678 If this macro is not defined, nothing special is output at the end of
8682 @deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (FILE *@var{stream}, tree @var{decl}, int @var{for_eh}, int @var{empty})
8683 This target hook emits a label at the beginning of each FDE@. It
8684 should be defined on targets where FDEs need special labels, and it
8685 should write the appropriate label, for the FDE associated with the
8686 function declaration @var{decl}, to the stdio stream @var{stream}.
8687 The third argument, @var{for_eh}, is a boolean: true if this is for an
8688 exception table. The fourth argument, @var{empty}, is a boolean:
8689 true if this is a placeholder label for an omitted FDE@.
8691 The default is that FDEs are not given nonlocal labels.
8694 @deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (FILE *@var{stream})
8695 This target hook emits a label at the beginning of the exception table.
8696 It should be defined on targets where it is desirable for the table
8697 to be broken up according to function.
8699 The default is that no label is emitted.
8702 @deftypefn {Target Hook} void TARGET_UNWIND_EMIT (FILE *@var{stream}, rtx @var{insn})
8703 This target hook emits assembly directives required to unwind the
8704 given instruction. This is only used when TARGET_UNWIND_INFO is set.
8707 @node Exception Region Output
8708 @subsection Assembler Commands for Exception Regions
8710 @c prevent bad page break with this line
8712 This describes commands marking the start and the end of an exception
8715 @defmac EH_FRAME_SECTION_NAME
8716 If defined, a C string constant for the name of the section containing
8717 exception handling frame unwind information. If not defined, GCC will
8718 provide a default definition if the target supports named sections.
8719 @file{crtstuff.c} uses this macro to switch to the appropriate section.
8721 You should define this symbol if your target supports DWARF 2 frame
8722 unwind information and the default definition does not work.
8725 @defmac EH_FRAME_IN_DATA_SECTION
8726 If defined, DWARF 2 frame unwind information will be placed in the
8727 data section even though the target supports named sections. This
8728 might be necessary, for instance, if the system linker does garbage
8729 collection and sections cannot be marked as not to be collected.
8731 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
8735 @defmac EH_TABLES_CAN_BE_READ_ONLY
8736 Define this macro to 1 if your target is such that no frame unwind
8737 information encoding used with non-PIC code will ever require a
8738 runtime relocation, but the linker may not support merging read-only
8739 and read-write sections into a single read-write section.
8742 @defmac MASK_RETURN_ADDR
8743 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
8744 that it does not contain any extraneous set bits in it.
8747 @defmac DWARF2_UNWIND_INFO
8748 Define this macro to 0 if your target supports DWARF 2 frame unwind
8749 information, but it does not yet work with exception handling.
8750 Otherwise, if your target supports this information (if it defines
8751 @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP}
8752 or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1.
8754 If @code{TARGET_UNWIND_INFO} is defined, the target specific unwinder
8755 will be used in all cases. Defining this macro will enable the generation
8756 of DWARF 2 frame debugging information.
8758 If @code{TARGET_UNWIND_INFO} is not defined, and this macro is defined to 1,
8759 the DWARF 2 unwinder will be the default exception handling mechanism;
8760 otherwise, the @code{setjmp}/@code{longjmp}-based scheme will be used by
8764 @defmac TARGET_UNWIND_INFO
8765 Define this macro if your target has ABI specified unwind tables. Usually
8766 these will be output by @code{TARGET_UNWIND_EMIT}.
8769 @deftypevr {Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT
8770 This variable should be set to @code{true} if the target ABI requires unwinding
8771 tables even when exceptions are not used.
8774 @defmac MUST_USE_SJLJ_EXCEPTIONS
8775 This macro need only be defined if @code{DWARF2_UNWIND_INFO} is
8776 runtime-variable. In that case, @file{except.h} cannot correctly
8777 determine the corresponding definition of @code{MUST_USE_SJLJ_EXCEPTIONS},
8778 so the target must provide it directly.
8781 @defmac DONT_USE_BUILTIN_SETJMP
8782 Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
8783 should use the @code{setjmp}/@code{longjmp} functions from the C library
8784 instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
8787 @defmac DWARF_CIE_DATA_ALIGNMENT
8788 This macro need only be defined if the target might save registers in the
8789 function prologue at an offset to the stack pointer that is not aligned to
8790 @code{UNITS_PER_WORD}. The definition should be the negative minimum
8791 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
8792 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
8793 the target supports DWARF 2 frame unwind information.
8796 @deftypevr {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
8797 Contains the value true if the target should add a zero word onto the
8798 end of a Dwarf-2 frame info section when used for exception handling.
8799 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
8803 @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
8804 Given a register, this hook should return a parallel of registers to
8805 represent where to find the register pieces. Define this hook if the
8806 register and its mode are represented in Dwarf in non-contiguous
8807 locations, or if the register should be represented in more than one
8808 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
8809 If not defined, the default is to return @code{NULL_RTX}.
8812 @deftypefn {Target Hook} void TARGET_INIT_DWARF_REG_SIZES_EXTRA (tree @var{address})
8813 If some registers are represented in Dwarf-2 unwind information in
8814 multiple pieces, define this hook to fill in information about the
8815 sizes of those pieces in the table used by the unwinder at runtime.
8816 It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after
8817 filling in a single size corresponding to each hard register;
8818 @var{address} is the address of the table.
8821 @deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym})
8822 This hook is used to output a reference from a frame unwinding table to
8823 the type_info object identified by @var{sym}. It should return @code{true}
8824 if the reference was output. Returning @code{false} will cause the
8825 reference to be output using the normal Dwarf2 routines.
8828 @deftypevr {Target Hook} bool TARGET_ARM_EABI_UNWINDER
8829 This flag should be set to @code{true} on targets that use an ARM EABI
8830 based unwinding library, and @code{false} on other targets. This effects
8831 the format of unwinding tables, and how the unwinder in entered after
8832 running a cleanup. The default is @code{false}.
8835 @node Alignment Output
8836 @subsection Assembler Commands for Alignment
8838 @c prevent bad page break with this line
8839 This describes commands for alignment.
8841 @defmac JUMP_ALIGN (@var{label})
8842 The alignment (log base 2) to put in front of @var{label}, which is
8843 a common destination of jumps and has no fallthru incoming edge.
8845 This macro need not be defined if you don't want any special alignment
8846 to be done at such a time. Most machine descriptions do not currently
8849 Unless it's necessary to inspect the @var{label} parameter, it is better
8850 to set the variable @var{align_jumps} in the target's
8851 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8852 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
8855 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
8856 The alignment (log base 2) to put in front of @var{label}, which follows
8859 This macro need not be defined if you don't want any special alignment
8860 to be done at such a time. Most machine descriptions do not currently
8864 @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
8865 The maximum number of bytes to skip when applying
8866 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
8867 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8870 @defmac LOOP_ALIGN (@var{label})
8871 The alignment (log base 2) to put in front of @var{label}, which follows
8872 a @code{NOTE_INSN_LOOP_BEG} note.
8874 This macro need not be defined if you don't want any special alignment
8875 to be done at such a time. Most machine descriptions do not currently
8878 Unless it's necessary to inspect the @var{label} parameter, it is better
8879 to set the variable @code{align_loops} in the target's
8880 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8881 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
8884 @defmac LOOP_ALIGN_MAX_SKIP
8885 The maximum number of bytes to skip when applying @code{LOOP_ALIGN}.
8886 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8889 @defmac LABEL_ALIGN (@var{label})
8890 The alignment (log base 2) to put in front of @var{label}.
8891 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
8892 the maximum of the specified values is used.
8894 Unless it's necessary to inspect the @var{label} parameter, it is better
8895 to set the variable @code{align_labels} in the target's
8896 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8897 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
8900 @defmac LABEL_ALIGN_MAX_SKIP
8901 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}.
8902 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8905 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
8906 A C statement to output to the stdio stream @var{stream} an assembler
8907 instruction to advance the location counter by @var{nbytes} bytes.
8908 Those bytes should be zero when loaded. @var{nbytes} will be a C
8909 expression of type @code{unsigned HOST_WIDE_INT}.
8912 @defmac ASM_NO_SKIP_IN_TEXT
8913 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
8914 text section because it fails to put zeros in the bytes that are skipped.
8915 This is true on many Unix systems, where the pseudo--op to skip bytes
8916 produces no-op instructions rather than zeros when used in the text
8920 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
8921 A C statement to output to the stdio stream @var{stream} an assembler
8922 command to advance the location counter to a multiple of 2 to the
8923 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
8926 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
8927 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
8928 for padding, if necessary.
8931 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
8932 A C statement to output to the stdio stream @var{stream} an assembler
8933 command to advance the location counter to a multiple of 2 to the
8934 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
8935 satisfy the alignment request. @var{power} and @var{max_skip} will be
8936 a C expression of type @code{int}.
8940 @node Debugging Info
8941 @section Controlling Debugging Information Format
8943 @c prevent bad page break with this line
8944 This describes how to specify debugging information.
8947 * All Debuggers:: Macros that affect all debugging formats uniformly.
8948 * DBX Options:: Macros enabling specific options in DBX format.
8949 * DBX Hooks:: Hook macros for varying DBX format.
8950 * File Names and DBX:: Macros controlling output of file names in DBX format.
8951 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
8952 * VMS Debug:: Macros for VMS debug format.
8956 @subsection Macros Affecting All Debugging Formats
8958 @c prevent bad page break with this line
8959 These macros affect all debugging formats.
8961 @defmac DBX_REGISTER_NUMBER (@var{regno})
8962 A C expression that returns the DBX register number for the compiler
8963 register number @var{regno}. In the default macro provided, the value
8964 of this expression will be @var{regno} itself. But sometimes there are
8965 some registers that the compiler knows about and DBX does not, or vice
8966 versa. In such cases, some register may need to have one number in the
8967 compiler and another for DBX@.
8969 If two registers have consecutive numbers inside GCC, and they can be
8970 used as a pair to hold a multiword value, then they @emph{must} have
8971 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
8972 Otherwise, debuggers will be unable to access such a pair, because they
8973 expect register pairs to be consecutive in their own numbering scheme.
8975 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
8976 does not preserve register pairs, then what you must do instead is
8977 redefine the actual register numbering scheme.
8980 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
8981 A C expression that returns the integer offset value for an automatic
8982 variable having address @var{x} (an RTL expression). The default
8983 computation assumes that @var{x} is based on the frame-pointer and
8984 gives the offset from the frame-pointer. This is required for targets
8985 that produce debugging output for DBX or COFF-style debugging output
8986 for SDB and allow the frame-pointer to be eliminated when the
8987 @option{-g} options is used.
8990 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
8991 A C expression that returns the integer offset value for an argument
8992 having address @var{x} (an RTL expression). The nominal offset is
8996 @defmac PREFERRED_DEBUGGING_TYPE
8997 A C expression that returns the type of debugging output GCC should
8998 produce when the user specifies just @option{-g}. Define
8999 this if you have arranged for GCC to support more than one format of
9000 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
9001 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
9002 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
9004 When the user specifies @option{-ggdb}, GCC normally also uses the
9005 value of this macro to select the debugging output format, but with two
9006 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
9007 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
9008 defined, GCC uses @code{DBX_DEBUG}.
9010 The value of this macro only affects the default debugging output; the
9011 user can always get a specific type of output by using @option{-gstabs},
9012 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
9016 @subsection Specific Options for DBX Output
9018 @c prevent bad page break with this line
9019 These are specific options for DBX output.
9021 @defmac DBX_DEBUGGING_INFO
9022 Define this macro if GCC should produce debugging output for DBX
9023 in response to the @option{-g} option.
9026 @defmac XCOFF_DEBUGGING_INFO
9027 Define this macro if GCC should produce XCOFF format debugging output
9028 in response to the @option{-g} option. This is a variant of DBX format.
9031 @defmac DEFAULT_GDB_EXTENSIONS
9032 Define this macro to control whether GCC should by default generate
9033 GDB's extended version of DBX debugging information (assuming DBX-format
9034 debugging information is enabled at all). If you don't define the
9035 macro, the default is 1: always generate the extended information
9036 if there is any occasion to.
9039 @defmac DEBUG_SYMS_TEXT
9040 Define this macro if all @code{.stabs} commands should be output while
9041 in the text section.
9044 @defmac ASM_STABS_OP
9045 A C string constant, including spacing, naming the assembler pseudo op to
9046 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
9047 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
9048 applies only to DBX debugging information format.
9051 @defmac ASM_STABD_OP
9052 A C string constant, including spacing, naming the assembler pseudo op to
9053 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
9054 value is the current location. If you don't define this macro,
9055 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
9059 @defmac ASM_STABN_OP
9060 A C string constant, including spacing, naming the assembler pseudo op to
9061 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
9062 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
9063 macro applies only to DBX debugging information format.
9066 @defmac DBX_NO_XREFS
9067 Define this macro if DBX on your system does not support the construct
9068 @samp{xs@var{tagname}}. On some systems, this construct is used to
9069 describe a forward reference to a structure named @var{tagname}.
9070 On other systems, this construct is not supported at all.
9073 @defmac DBX_CONTIN_LENGTH
9074 A symbol name in DBX-format debugging information is normally
9075 continued (split into two separate @code{.stabs} directives) when it
9076 exceeds a certain length (by default, 80 characters). On some
9077 operating systems, DBX requires this splitting; on others, splitting
9078 must not be done. You can inhibit splitting by defining this macro
9079 with the value zero. You can override the default splitting-length by
9080 defining this macro as an expression for the length you desire.
9083 @defmac DBX_CONTIN_CHAR
9084 Normally continuation is indicated by adding a @samp{\} character to
9085 the end of a @code{.stabs} string when a continuation follows. To use
9086 a different character instead, define this macro as a character
9087 constant for the character you want to use. Do not define this macro
9088 if backslash is correct for your system.
9091 @defmac DBX_STATIC_STAB_DATA_SECTION
9092 Define this macro if it is necessary to go to the data section before
9093 outputting the @samp{.stabs} pseudo-op for a non-global static
9097 @defmac DBX_TYPE_DECL_STABS_CODE
9098 The value to use in the ``code'' field of the @code{.stabs} directive
9099 for a typedef. The default is @code{N_LSYM}.
9102 @defmac DBX_STATIC_CONST_VAR_CODE
9103 The value to use in the ``code'' field of the @code{.stabs} directive
9104 for a static variable located in the text section. DBX format does not
9105 provide any ``right'' way to do this. The default is @code{N_FUN}.
9108 @defmac DBX_REGPARM_STABS_CODE
9109 The value to use in the ``code'' field of the @code{.stabs} directive
9110 for a parameter passed in registers. DBX format does not provide any
9111 ``right'' way to do this. The default is @code{N_RSYM}.
9114 @defmac DBX_REGPARM_STABS_LETTER
9115 The letter to use in DBX symbol data to identify a symbol as a parameter
9116 passed in registers. DBX format does not customarily provide any way to
9117 do this. The default is @code{'P'}.
9120 @defmac DBX_FUNCTION_FIRST
9121 Define this macro if the DBX information for a function and its
9122 arguments should precede the assembler code for the function. Normally,
9123 in DBX format, the debugging information entirely follows the assembler
9127 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
9128 Define this macro, with value 1, if the value of a symbol describing
9129 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
9130 relative to the start of the enclosing function. Normally, GCC uses
9131 an absolute address.
9134 @defmac DBX_LINES_FUNCTION_RELATIVE
9135 Define this macro, with value 1, if the value of a symbol indicating
9136 the current line number (@code{N_SLINE}) should be relative to the
9137 start of the enclosing function. Normally, GCC uses an absolute address.
9140 @defmac DBX_USE_BINCL
9141 Define this macro if GCC should generate @code{N_BINCL} and
9142 @code{N_EINCL} stabs for included header files, as on Sun systems. This
9143 macro also directs GCC to output a type number as a pair of a file
9144 number and a type number within the file. Normally, GCC does not
9145 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
9146 number for a type number.
9150 @subsection Open-Ended Hooks for DBX Format
9152 @c prevent bad page break with this line
9153 These are hooks for DBX format.
9155 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
9156 Define this macro to say how to output to @var{stream} the debugging
9157 information for the start of a scope level for variable names. The
9158 argument @var{name} is the name of an assembler symbol (for use with
9159 @code{assemble_name}) whose value is the address where the scope begins.
9162 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
9163 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
9166 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
9167 Define this macro if the target machine requires special handling to
9168 output an @code{N_FUN} entry for the function @var{decl}.
9171 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
9172 A C statement to output DBX debugging information before code for line
9173 number @var{line} of the current source file to the stdio stream
9174 @var{stream}. @var{counter} is the number of time the macro was
9175 invoked, including the current invocation; it is intended to generate
9176 unique labels in the assembly output.
9178 This macro should not be defined if the default output is correct, or
9179 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
9182 @defmac NO_DBX_FUNCTION_END
9183 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
9184 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
9185 On those machines, define this macro to turn this feature off without
9186 disturbing the rest of the gdb extensions.
9189 @defmac NO_DBX_BNSYM_ENSYM
9190 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
9191 extension construct. On those machines, define this macro to turn this
9192 feature off without disturbing the rest of the gdb extensions.
9195 @node File Names and DBX
9196 @subsection File Names in DBX Format
9198 @c prevent bad page break with this line
9199 This describes file names in DBX format.
9201 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
9202 A C statement to output DBX debugging information to the stdio stream
9203 @var{stream}, which indicates that file @var{name} is the main source
9204 file---the file specified as the input file for compilation.
9205 This macro is called only once, at the beginning of compilation.
9207 This macro need not be defined if the standard form of output
9208 for DBX debugging information is appropriate.
9210 It may be necessary to refer to a label equal to the beginning of the
9211 text section. You can use @samp{assemble_name (stream, ltext_label_name)}
9212 to do so. If you do this, you must also set the variable
9213 @var{used_ltext_label_name} to @code{true}.
9216 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY
9217 Define this macro, with value 1, if GCC should not emit an indication
9218 of the current directory for compilation and current source language at
9219 the beginning of the file.
9222 @defmac NO_DBX_GCC_MARKER
9223 Define this macro, with value 1, if GCC should not emit an indication
9224 that this object file was compiled by GCC@. The default is to emit
9225 an @code{N_OPT} stab at the beginning of every source file, with
9226 @samp{gcc2_compiled.} for the string and value 0.
9229 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
9230 A C statement to output DBX debugging information at the end of
9231 compilation of the main source file @var{name}. Output should be
9232 written to the stdio stream @var{stream}.
9234 If you don't define this macro, nothing special is output at the end
9235 of compilation, which is correct for most machines.
9238 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
9239 Define this macro @emph{instead of} defining
9240 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
9241 the end of compilation is an @code{N_SO} stab with an empty string,
9242 whose value is the highest absolute text address in the file.
9247 @subsection Macros for SDB and DWARF Output
9249 @c prevent bad page break with this line
9250 Here are macros for SDB and DWARF output.
9252 @defmac SDB_DEBUGGING_INFO
9253 Define this macro if GCC should produce COFF-style debugging output
9254 for SDB in response to the @option{-g} option.
9257 @defmac DWARF2_DEBUGGING_INFO
9258 Define this macro if GCC should produce dwarf version 2 format
9259 debugging output in response to the @option{-g} option.
9261 @deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (const_tree @var{function})
9262 Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
9263 be emitted for each function. Instead of an integer return the enum
9264 value for the @code{DW_CC_} tag.
9267 To support optional call frame debugging information, you must also
9268 define @code{INCOMING_RETURN_ADDR_RTX} and either set
9269 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
9270 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
9271 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
9274 @defmac DWARF2_FRAME_INFO
9275 Define this macro to a nonzero value if GCC should always output
9276 Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO}
9277 (@pxref{Exception Region Output} is nonzero, GCC will output this
9278 information not matter how you define @code{DWARF2_FRAME_INFO}.
9281 @defmac DWARF2_ASM_LINE_DEBUG_INFO
9282 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
9283 line debug info sections. This will result in much more compact line number
9284 tables, and hence is desirable if it works.
9287 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
9288 A C statement to issue assembly directives that create a difference
9289 @var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
9292 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section})
9293 A C statement to issue assembly directives that create a
9294 section-relative reference to the given @var{label}, using an integer of the
9295 given @var{size}. The label is known to be defined in the given @var{section}.
9298 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
9299 A C statement to issue assembly directives that create a self-relative
9300 reference to the given @var{label}, using an integer of the given @var{size}.
9303 @defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label})
9304 A C statement to issue assembly directives that create a reference to
9305 the DWARF table identifier @var{label} from the current section. This
9306 is used on some systems to avoid garbage collecting a DWARF table which
9307 is referenced by a function.
9310 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{file}, int @var{size}, rtx @var{x})
9311 If defined, this target hook is a function which outputs a DTP-relative
9312 reference to the given TLS symbol of the specified size.
9315 @defmac PUT_SDB_@dots{}
9316 Define these macros to override the assembler syntax for the special
9317 SDB assembler directives. See @file{sdbout.c} for a list of these
9318 macros and their arguments. If the standard syntax is used, you need
9319 not define them yourself.
9323 Some assemblers do not support a semicolon as a delimiter, even between
9324 SDB assembler directives. In that case, define this macro to be the
9325 delimiter to use (usually @samp{\n}). It is not necessary to define
9326 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
9330 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
9331 Define this macro to allow references to unknown structure,
9332 union, or enumeration tags to be emitted. Standard COFF does not
9333 allow handling of unknown references, MIPS ECOFF has support for
9337 @defmac SDB_ALLOW_FORWARD_REFERENCES
9338 Define this macro to allow references to structure, union, or
9339 enumeration tags that have not yet been seen to be handled. Some
9340 assemblers choke if forward tags are used, while some require it.
9343 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
9344 A C statement to output SDB debugging information before code for line
9345 number @var{line} of the current source file to the stdio stream
9346 @var{stream}. The default is to emit an @code{.ln} directive.
9351 @subsection Macros for VMS Debug Format
9353 @c prevent bad page break with this line
9354 Here are macros for VMS debug format.
9356 @defmac VMS_DEBUGGING_INFO
9357 Define this macro if GCC should produce debugging output for VMS
9358 in response to the @option{-g} option. The default behavior for VMS
9359 is to generate minimal debug info for a traceback in the absence of
9360 @option{-g} unless explicitly overridden with @option{-g0}. This
9361 behavior is controlled by @code{OPTIMIZATION_OPTIONS} and
9362 @code{OVERRIDE_OPTIONS}.
9365 @node Floating Point
9366 @section Cross Compilation and Floating Point
9367 @cindex cross compilation and floating point
9368 @cindex floating point and cross compilation
9370 While all modern machines use twos-complement representation for integers,
9371 there are a variety of representations for floating point numbers. This
9372 means that in a cross-compiler the representation of floating point numbers
9373 in the compiled program may be different from that used in the machine
9374 doing the compilation.
9376 Because different representation systems may offer different amounts of
9377 range and precision, all floating point constants must be represented in
9378 the target machine's format. Therefore, the cross compiler cannot
9379 safely use the host machine's floating point arithmetic; it must emulate
9380 the target's arithmetic. To ensure consistency, GCC always uses
9381 emulation to work with floating point values, even when the host and
9382 target floating point formats are identical.
9384 The following macros are provided by @file{real.h} for the compiler to
9385 use. All parts of the compiler which generate or optimize
9386 floating-point calculations must use these macros. They may evaluate
9387 their operands more than once, so operands must not have side effects.
9389 @defmac REAL_VALUE_TYPE
9390 The C data type to be used to hold a floating point value in the target
9391 machine's format. Typically this is a @code{struct} containing an
9392 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
9396 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9397 Compares for equality the two values, @var{x} and @var{y}. If the target
9398 floating point format supports negative zeroes and/or NaNs,
9399 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
9400 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
9403 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9404 Tests whether @var{x} is less than @var{y}.
9407 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
9408 Truncates @var{x} to a signed integer, rounding toward zero.
9411 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
9412 Truncates @var{x} to an unsigned integer, rounding toward zero. If
9413 @var{x} is negative, returns zero.
9416 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
9417 Converts @var{string} into a floating point number in the target machine's
9418 representation for mode @var{mode}. This routine can handle both
9419 decimal and hexadecimal floating point constants, using the syntax
9420 defined by the C language for both.
9423 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
9424 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
9427 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
9428 Determines whether @var{x} represents infinity (positive or negative).
9431 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
9432 Determines whether @var{x} represents a ``NaN'' (not-a-number).
9435 @deftypefn Macro void REAL_ARITHMETIC (REAL_VALUE_TYPE @var{output}, enum tree_code @var{code}, REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9436 Calculates an arithmetic operation on the two floating point values
9437 @var{x} and @var{y}, storing the result in @var{output} (which must be a
9440 The operation to be performed is specified by @var{code}. Only the
9441 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
9442 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
9444 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
9445 target's floating point format cannot represent infinity, it will call
9446 @code{abort}. Callers should check for this situation first, using
9447 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
9450 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
9451 Returns the negative of the floating point value @var{x}.
9454 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
9455 Returns the absolute value of @var{x}.
9458 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
9459 Truncates the floating point value @var{x} to fit in @var{mode}. The
9460 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
9461 appropriate bit pattern to be output as a floating constant whose
9462 precision accords with mode @var{mode}.
9465 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
9466 Converts a floating point value @var{x} into a double-precision integer
9467 which is then stored into @var{low} and @var{high}. If the value is not
9468 integral, it is truncated.
9471 @deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode})
9472 Converts a double-precision integer found in @var{low} and @var{high},
9473 into a floating point value which is then stored into @var{x}. The
9474 value is truncated to fit in mode @var{mode}.
9477 @node Mode Switching
9478 @section Mode Switching Instructions
9479 @cindex mode switching
9480 The following macros control mode switching optimizations:
9482 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
9483 Define this macro if the port needs extra instructions inserted for mode
9484 switching in an optimizing compilation.
9486 For an example, the SH4 can perform both single and double precision
9487 floating point operations, but to perform a single precision operation,
9488 the FPSCR PR bit has to be cleared, while for a double precision
9489 operation, this bit has to be set. Changing the PR bit requires a general
9490 purpose register as a scratch register, hence these FPSCR sets have to
9491 be inserted before reload, i.e.@: you can't put this into instruction emitting
9492 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
9494 You can have multiple entities that are mode-switched, and select at run time
9495 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
9496 return nonzero for any @var{entity} that needs mode-switching.
9497 If you define this macro, you also have to define
9498 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
9499 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
9500 @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT}
9504 @defmac NUM_MODES_FOR_MODE_SWITCHING
9505 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
9506 initializer for an array of integers. Each initializer element
9507 N refers to an entity that needs mode switching, and specifies the number
9508 of different modes that might need to be set for this entity.
9509 The position of the initializer in the initializer---starting counting at
9510 zero---determines the integer that is used to refer to the mode-switched
9512 In macros that take mode arguments / yield a mode result, modes are
9513 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
9514 switch is needed / supplied.
9517 @defmac MODE_NEEDED (@var{entity}, @var{insn})
9518 @var{entity} is an integer specifying a mode-switched entity. If
9519 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
9520 return an integer value not larger than the corresponding element in
9521 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
9522 be switched into prior to the execution of @var{insn}.
9525 @defmac MODE_AFTER (@var{mode}, @var{insn})
9526 If this macro is defined, it is evaluated for every @var{insn} during
9527 mode switching. It determines the mode that an insn results in (if
9528 different from the incoming mode).
9531 @defmac MODE_ENTRY (@var{entity})
9532 If this macro is defined, it is evaluated for every @var{entity} that needs
9533 mode switching. It should evaluate to an integer, which is a mode that
9534 @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY}
9535 is defined then @code{MODE_EXIT} must be defined.
9538 @defmac MODE_EXIT (@var{entity})
9539 If this macro is defined, it is evaluated for every @var{entity} that needs
9540 mode switching. It should evaluate to an integer, which is a mode that
9541 @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT}
9542 is defined then @code{MODE_ENTRY} must be defined.
9545 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
9546 This macro specifies the order in which modes for @var{entity} are processed.
9547 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
9548 lowest. The value of the macro should be an integer designating a mode
9549 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
9550 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
9551 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
9554 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
9555 Generate one or more insns to set @var{entity} to @var{mode}.
9556 @var{hard_reg_live} is the set of hard registers live at the point where
9557 the insn(s) are to be inserted.
9560 @node Target Attributes
9561 @section Defining target-specific uses of @code{__attribute__}
9562 @cindex target attributes
9563 @cindex machine attributes
9564 @cindex attributes, target-specific
9566 Target-specific attributes may be defined for functions, data and types.
9567 These are described using the following target hooks; they also need to
9568 be documented in @file{extend.texi}.
9570 @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
9571 If defined, this target hook points to an array of @samp{struct
9572 attribute_spec} (defined in @file{tree.h}) specifying the machine
9573 specific attributes for this target and some of the restrictions on the
9574 entities to which these attributes are applied and the arguments they
9578 @deftypefn {Target Hook} bool TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P (const_tree @var{name})
9579 If defined, this target hook is a function which returns true if the
9580 machine-specific attribute named @var{name} expects an identifier
9581 given as its first argument to be passed on as a plain identifier, not
9582 subjected to name lookup. If this is not defined, the default is
9583 false for all machine-specific attributes.
9586 @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (const_tree @var{type1}, const_tree @var{type2})
9587 If defined, this target hook is a function which returns zero if the attributes on
9588 @var{type1} and @var{type2} are incompatible, one if they are compatible,
9589 and two if they are nearly compatible (which causes a warning to be
9590 generated). If this is not defined, machine-specific attributes are
9591 supposed always to be compatible.
9594 @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
9595 If defined, this target hook is a function which assigns default attributes to
9596 the newly defined @var{type}.
9599 @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
9600 Define this target hook if the merging of type attributes needs special
9601 handling. If defined, the result is a list of the combined
9602 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
9603 that @code{comptypes} has already been called and returned 1. This
9604 function may call @code{merge_attributes} to handle machine-independent
9608 @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
9609 Define this target hook if the merging of decl attributes needs special
9610 handling. If defined, the result is a list of the combined
9611 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
9612 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
9613 when this is needed are when one attribute overrides another, or when an
9614 attribute is nullified by a subsequent definition. This function may
9615 call @code{merge_attributes} to handle machine-independent merging.
9617 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
9618 If the only target-specific handling you require is @samp{dllimport}
9619 for Microsoft Windows targets, you should define the macro
9620 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler
9621 will then define a function called
9622 @code{merge_dllimport_decl_attributes} which can then be defined as
9623 the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also
9624 add @code{handle_dll_attribute} in the attribute table for your port
9625 to perform initial processing of the @samp{dllimport} and
9626 @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and
9627 @file{i386/i386.c}, for example.
9630 @deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (const_tree @var{decl})
9631 @var{decl} is a variable or function with @code{__attribute__((dllimport))}
9632 specified. Use this hook if the target needs to add extra validation
9633 checks to @code{handle_dll_attribute}.
9636 @defmac TARGET_DECLSPEC
9637 Define this macro to a nonzero value if you want to treat
9638 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
9639 default, this behavior is enabled only for targets that define
9640 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
9641 of @code{__declspec} is via a built-in macro, but you should not rely
9642 on this implementation detail.
9645 @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
9646 Define this target hook if you want to be able to add attributes to a decl
9647 when it is being created. This is normally useful for back ends which
9648 wish to implement a pragma by using the attributes which correspond to
9649 the pragma's effect. The @var{node} argument is the decl which is being
9650 created. The @var{attr_ptr} argument is a pointer to the attribute list
9651 for this decl. The list itself should not be modified, since it may be
9652 shared with other decls, but attributes may be chained on the head of
9653 the list and @code{*@var{attr_ptr}} modified to point to the new
9654 attributes, or a copy of the list may be made if further changes are
9658 @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (const_tree @var{fndecl})
9660 This target hook returns @code{true} if it is ok to inline @var{fndecl}
9661 into the current function, despite its having target-specific
9662 attributes, @code{false} otherwise. By default, if a function has a
9663 target specific attribute attached to it, it will not be inlined.
9666 @deftypefn {Target Hook} bool TARGET_OPTION_VALID_ATTRIBUTE_P (tree @var{fndecl}, tree @var{name}, tree @var{args}, int @var{flags})
9667 This hook is called to parse the @code{attribute(option("..."))}, and
9668 it allows the function to set different target machine compile time
9669 options for the current function that might be different than the
9670 options specified on the command line. The hook should return
9671 @code{true} if the options are valid.
9673 The hook should set the @var{DECL_FUNCTION_SPECIFIC_TARGET} field in
9674 the function declaration to hold a pointer to a target specific
9675 @var{struct cl_target_option} structure.
9678 @deftypefn {Target Hook} void TARGET_OPTION_SAVE (struct cl_target_option *@var{ptr})
9679 This hook is called to save any additional target specific information
9680 in the @var{struct cl_target_option} structure for function specific
9682 @xref{Option file format}.
9685 @deftypefn {Target Hook} void TARGET_OPTION_RESTORE (struct cl_target_option *@var{ptr})
9686 This hook is called to restore any additional target specific
9687 information in the @var{struct cl_target_option} structure for
9688 function specific options.
9691 @deftypefn {Target Hook} void TARGET_OPTION_PRINT (FILE *@var{file}, int @var{indent}, struct cl_target_option *@var{ptr})
9692 This hook is called to print any additional target specific
9693 information in the @var{struct cl_target_option} structure for
9694 function specific options.
9697 @deftypefn {Target Hook} bool TARGET_OPTION_PRAGMA_PARSE (target @var{args})
9698 This target hook parses the options for @code{#pragma GCC option} to
9699 set the machine specific options for functions that occur later in the
9700 input stream. The options should be the same as handled by the
9701 @code{TARGET_VALID_OPTION_ATTRIBUTE_P} hook.
9704 @deftypefn {Target Hook} bool TARGET_CAN_INLINE_P (tree @var{caller}, tree @var{callee})
9705 This target hook returns @code{false} if the @var{caller} function
9706 cannot inline @var{callee}, based on target specific information. By
9707 default, inlining is not allowed if the callee function has function
9708 specific target options and the caller does not use the same options.
9712 @section Emulating TLS
9713 @cindex Emulated TLS
9715 For targets whose psABI does not provide Thread Local Storage via
9716 specific relocations and instruction sequences, an emulation layer is
9717 used. A set of target hooks allows this emulation layer to be
9718 configured for the requirements of a particular target. For instance
9719 the psABI may in fact specify TLS support in terms of an emulation
9722 The emulation layer works by creating a control object for every TLS
9723 object. To access the TLS object, a lookup function is provided
9724 which, when given the address of the control object, will return the
9725 address of the current thread's instance of the TLS object.
9727 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_GET_ADDRESS
9728 Contains the name of the helper function that uses a TLS control
9729 object to locate a TLS instance. The default causes libgcc's
9730 emulated TLS helper function to be used.
9733 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_REGISTER_COMMON
9734 Contains the name of the helper function that should be used at
9735 program startup to register TLS objects that are implicitly
9736 initialized to zero. If this is @code{NULL}, all TLS objects will
9737 have explicit initializers. The default causes libgcc's emulated TLS
9738 registration function to be used.
9741 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_SECTION
9742 Contains the name of the section in which TLS control variables should
9743 be placed. The default of @code{NULL} allows these to be placed in
9747 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_SECTION
9748 Contains the name of the section in which TLS initializers should be
9749 placed. The default of @code{NULL} allows these to be placed in any
9753 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_PREFIX
9754 Contains the prefix to be prepended to TLS control variable names.
9755 The default of @code{NULL} uses a target-specific prefix.
9758 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_PREFIX
9759 Contains the prefix to be prepended to TLS initializer objects. The
9760 default of @code{NULL} uses a target-specific prefix.
9763 @deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_FIELDS (tree @var{type}, tree *@var{name})
9764 Specifies a function that generates the FIELD_DECLs for a TLS control
9765 object type. @var{type} is the RECORD_TYPE the fields are for and
9766 @var{name} should be filled with the structure tag, if the default of
9767 @code{__emutls_object} is unsuitable. The default creates a type suitable
9768 for libgcc's emulated TLS function.
9771 @deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_INIT (tree @var{var}, tree @var{decl}, tree @var{tmpl_addr})
9772 Specifies a function that generates the CONSTRUCTOR to initialize a
9773 TLS control object. @var{var} is the TLS control object, @var{decl}
9774 is the TLS object and @var{tmpl_addr} is the address of the
9775 initializer. The default initializes libgcc's emulated TLS control object.
9778 @deftypevr {Target Hook} bool TARGET_EMUTLS_VAR_ALIGN_FIXED
9779 Specifies whether the alignment of TLS control variable objects is
9780 fixed and should not be increased as some backends may do to optimize
9781 single objects. The default is false.
9784 @deftypevr {Target Hook} bool TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
9785 Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor
9786 may be used to describe emulated TLS control objects.
9789 @node MIPS Coprocessors
9790 @section Defining coprocessor specifics for MIPS targets.
9791 @cindex MIPS coprocessor-definition macros
9793 The MIPS specification allows MIPS implementations to have as many as 4
9794 coprocessors, each with as many as 32 private registers. GCC supports
9795 accessing these registers and transferring values between the registers
9796 and memory using asm-ized variables. For example:
9799 register unsigned int cp0count asm ("c0r1");
9805 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
9806 names may be added as described below, or the default names may be
9807 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
9809 Coprocessor registers are assumed to be epilogue-used; sets to them will
9810 be preserved even if it does not appear that the register is used again
9811 later in the function.
9813 Another note: according to the MIPS spec, coprocessor 1 (if present) is
9814 the FPU@. One accesses COP1 registers through standard mips
9815 floating-point support; they are not included in this mechanism.
9817 There is one macro used in defining the MIPS coprocessor interface which
9818 you may want to override in subtargets; it is described below.
9820 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
9821 A comma-separated list (with leading comma) of pairs describing the
9822 alternate names of coprocessor registers. The format of each entry should be
9824 @{ @var{alternatename}, @var{register_number}@}
9830 @section Parameters for Precompiled Header Validity Checking
9831 @cindex parameters, precompiled headers
9833 @deftypefn {Target Hook} {void *} TARGET_GET_PCH_VALIDITY (size_t *@var{sz})
9834 This hook returns a pointer to the data needed by
9835 @code{TARGET_PCH_VALID_P} and sets
9836 @samp{*@var{sz}} to the size of the data in bytes.
9839 @deftypefn {Target Hook} {const char *} TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz})
9840 This hook checks whether the options used to create a PCH file are
9841 compatible with the current settings. It returns @code{NULL}
9842 if so and a suitable error message if not. Error messages will
9843 be presented to the user and must be localized using @samp{_(@var{msg})}.
9845 @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
9846 when the PCH file was created and @var{sz} is the size of that data in bytes.
9847 It's safe to assume that the data was created by the same version of the
9848 compiler, so no format checking is needed.
9850 The default definition of @code{default_pch_valid_p} should be
9851 suitable for most targets.
9854 @deftypefn {Target Hook} {const char *} TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags})
9855 If this hook is nonnull, the default implementation of
9856 @code{TARGET_PCH_VALID_P} will use it to check for compatible values
9857 of @code{target_flags}. @var{pch_flags} specifies the value that
9858 @code{target_flags} had when the PCH file was created. The return
9859 value is the same as for @code{TARGET_PCH_VALID_P}.
9863 @section C++ ABI parameters
9864 @cindex parameters, c++ abi
9866 @deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void)
9867 Define this hook to override the integer type used for guard variables.
9868 These are used to implement one-time construction of static objects. The
9869 default is long_long_integer_type_node.
9872 @deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void)
9873 This hook determines how guard variables are used. It should return
9874 @code{false} (the default) if the first byte should be used. A return value of
9875 @code{true} indicates that only the least significant bit should be used.
9878 @deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type})
9879 This hook returns the size of the cookie to use when allocating an array
9880 whose elements have the indicated @var{type}. Assumes that it is already
9881 known that a cookie is needed. The default is
9882 @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
9883 IA64/Generic C++ ABI@.
9886 @deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void)
9887 This hook should return @code{true} if the element size should be stored in
9888 array cookies. The default is to return @code{false}.
9891 @deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export})
9892 If defined by a backend this hook allows the decision made to export
9893 class @var{type} to be overruled. Upon entry @var{import_export}
9894 will contain 1 if the class is going to be exported, @minus{}1 if it is going
9895 to be imported and 0 otherwise. This function should return the
9896 modified value and perform any other actions necessary to support the
9897 backend's targeted operating system.
9900 @deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void)
9901 This hook should return @code{true} if constructors and destructors return
9902 the address of the object created/destroyed. The default is to return
9906 @deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void)
9907 This hook returns true if the key method for a class (i.e., the method
9908 which, if defined in the current translation unit, causes the virtual
9909 table to be emitted) may be an inline function. Under the standard
9910 Itanium C++ ABI the key method may be an inline function so long as
9911 the function is not declared inline in the class definition. Under
9912 some variants of the ABI, an inline function can never be the key
9913 method. The default is to return @code{true}.
9916 @deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl})
9917 @var{decl} is a virtual table, virtual table table, typeinfo object,
9918 or other similar implicit class data object that will be emitted with
9919 external linkage in this translation unit. No ELF visibility has been
9920 explicitly specified. If the target needs to specify a visibility
9921 other than that of the containing class, use this hook to set
9922 @code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}.
9925 @deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void)
9926 This hook returns true (the default) if virtual tables and other
9927 similar implicit class data objects are always COMDAT if they have
9928 external linkage. If this hook returns false, then class data for
9929 classes whose virtual table will be emitted in only one translation
9930 unit will not be COMDAT.
9933 @deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void)
9934 This hook returns true (the default) if the RTTI information for
9935 the basic types which is defined in the C++ runtime should always
9936 be COMDAT, false if it should not be COMDAT.
9939 @deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void)
9940 This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
9941 should be used to register static destructors when @option{-fuse-cxa-atexit}
9942 is in effect. The default is to return false to use @code{__cxa_atexit}.
9945 @deftypefn {Target Hook} bool TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT (void)
9946 This hook returns true if the target @code{atexit} function can be used
9947 in the same manner as @code{__cxa_atexit} to register C++ static
9948 destructors. This requires that @code{atexit}-registered functions in
9949 shared libraries are run in the correct order when the libraries are
9950 unloaded. The default is to return false.
9953 @deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type})
9954 @var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just been
9955 defined. Use this hook to make adjustments to the class (eg, tweak
9956 visibility or perform any other required target modifications).
9959 @node Named Address Spaces
9960 @section Adding support for named address spaces
9961 @cindex named address spaces
9963 The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
9964 standards committee, @cite{Programming Languages - C - Extensions to
9965 support embedded processors}, specifies a syntax for embedded
9966 processors to specify alternate address spaces. You can configure a
9967 GCC port to support section 5.1 of the draft report to add support for
9968 address spaces other than the default address space. These address
9969 spaces are new keywords that are similar to the @code{volatile} and
9970 @code{const} type attributes.
9972 Pointers to named address spaces can have a different size than
9973 pointers to the generic address space.
9975 For example, the SPU port uses the @code{__ea} address space to refer
9976 to memory in the host processor, rather than memory local to the SPU
9977 processor. Access to memory in the @code{__ea} address space involves
9978 issuing DMA operations to move data between the host processor and the
9979 local processor memory address space. Pointers in the @code{__ea}
9980 address space are either 32 bits or 64 bits based on the
9981 @option{-mea32} or @option{-mea64} switches (native SPU pointers are
9984 Internally, address spaces are represented as a small integer in the
9985 range 0 to 15 with address space 0 being reserved for the generic
9988 To register a named address space qualifier keyword with the C front end,
9989 the target may call the @code{c_register_addr_space} routine. For example,
9990 the SPU port uses the following to declare @code{__ea} as the keyword for
9991 named address space #1:
9993 #define ADDR_SPACE_EA 1
9994 c_register_addr_space ("__ea", ADDR_SPACE_EA);
9997 @deftypefn {Target Hook} {enum machine_mode} TARGET_ADDR_SPACE_POINTER_MODE (addr_space_t @var{address_space})
9998 Define this to return the machine mode to use for pointers to
9999 @var{address_space} if the target supports named address spaces.
10000 The default version of this hook returns @code{ptr_mode} for the
10001 generic address space only.
10004 @deftypefn {Target Hook} {enum machine_mode} TARGET_ADDR_SPACE_ADDRESS_MODE (addr_space_t @var{address_space})
10005 Define this to return the machine mode to use for addresses in
10006 @var{address_space} if the target supports named address spaces.
10007 The default version of this hook returns @code{Pmode} for the
10008 generic address space only.
10011 @deftypefn {Target Hook} bool TARGET_ADDR_SPACE_VALID_POINTER_MODE (enum machine_mode @var{mode}, addr_space_t @var{as})
10012 Define this to return nonzero if the port can handle pointers
10013 with machine mode @var{mode} to address space @var{as}. This target
10014 hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook,
10015 except that it includes explicit named address space support. The default
10016 version of this hook returns true for the modes returned by either the
10017 @code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE}
10018 target hooks for the given address space.
10021 @deftypefn {Target Hook} bool TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P (enum machine_mode @var{mode}, rtx @var{exp}, bool @var{strict}, addr_space_t @var{as})
10022 Define this to return true if @var{exp} is a valid address for mode
10023 @var{mode} in the named address space @var{as}. The @var{strict}
10024 parameter says whether strict addressing is in effect after reload has
10025 finished. This target hook is the same as the
10026 @code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes
10027 explicit named address space support.
10030 @deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, enum machine_mode @var{mode}, addr_space_t @var{as})
10031 Define this to modify an invalid address @var{x} to be a valid address
10032 with mode @var{mode} in the named address space @var{as}. This target
10033 hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook,
10034 except that it includes explicit named address space support.
10037 @deftypefn {Target Hook} bool TARGET_ADDR_SPACE_SUBSET_P (addr_space_t @var{superset}, addr_space_t @var{subset})
10038 Define this to return whether the @var{subset} named address space is
10039 contained within the @var{superset} named address space. Pointers to
10040 a named address space that is a subset of another named address space
10041 will be converted automatically without a cast if used together in
10042 arithmetic operations. Pointers to a superset address space can be
10043 converted to pointers to a subset address space via explicit casts.
10046 @deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_CONVERT (rtx @var{op}, tree @var{from_type}, tree @var{to_type})
10047 Define this to convert the pointer expression represented by the RTL
10048 @var{op} with type @var{from_type} that points to a named address
10049 space to a new pointer expression with type @var{to_type} that points
10050 to a different named address space. When this hook it called, it is
10051 guaranteed that one of the two address spaces is a subset of the other,
10052 as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook.
10056 @section Miscellaneous Parameters
10057 @cindex parameters, miscellaneous
10059 @c prevent bad page break with this line
10060 Here are several miscellaneous parameters.
10062 @defmac HAS_LONG_COND_BRANCH
10063 Define this boolean macro to indicate whether or not your architecture
10064 has conditional branches that can span all of memory. It is used in
10065 conjunction with an optimization that partitions hot and cold basic
10066 blocks into separate sections of the executable. If this macro is
10067 set to false, gcc will convert any conditional branches that attempt
10068 to cross between sections into unconditional branches or indirect jumps.
10071 @defmac HAS_LONG_UNCOND_BRANCH
10072 Define this boolean macro to indicate whether or not your architecture
10073 has unconditional branches that can span all of memory. It is used in
10074 conjunction with an optimization that partitions hot and cold basic
10075 blocks into separate sections of the executable. If this macro is
10076 set to false, gcc will convert any unconditional branches that attempt
10077 to cross between sections into indirect jumps.
10080 @defmac CASE_VECTOR_MODE
10081 An alias for a machine mode name. This is the machine mode that
10082 elements of a jump-table should have.
10085 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
10086 Optional: return the preferred mode for an @code{addr_diff_vec}
10087 when the minimum and maximum offset are known. If you define this,
10088 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
10089 To make this work, you also have to define @code{INSN_ALIGN} and
10090 make the alignment for @code{addr_diff_vec} explicit.
10091 The @var{body} argument is provided so that the offset_unsigned and scale
10092 flags can be updated.
10095 @defmac CASE_VECTOR_PC_RELATIVE
10096 Define this macro to be a C expression to indicate when jump-tables
10097 should contain relative addresses. You need not define this macro if
10098 jump-tables never contain relative addresses, or jump-tables should
10099 contain relative addresses only when @option{-fPIC} or @option{-fPIC}
10103 @deftypefn {Target Hook} {unsigned int} TARGET_CASE_VALUES_THRESHOLD (void)
10104 This function return the smallest number of different values for which it
10105 is best to use a jump-table instead of a tree of conditional branches.
10106 The default is four for machines with a @code{casesi} instruction and
10107 five otherwise. This is best for most machines.
10110 @defmac CASE_USE_BIT_TESTS
10111 Define this macro to be a C expression to indicate whether C switch
10112 statements may be implemented by a sequence of bit tests. This is
10113 advantageous on processors that can efficiently implement left shift
10114 of 1 by the number of bits held in a register, but inappropriate on
10115 targets that would require a loop. By default, this macro returns
10116 @code{true} if the target defines an @code{ashlsi3} pattern, and
10117 @code{false} otherwise.
10120 @defmac WORD_REGISTER_OPERATIONS
10121 Define this macro if operations between registers with integral mode
10122 smaller than a word are always performed on the entire register.
10123 Most RISC machines have this property and most CISC machines do not.
10126 @defmac LOAD_EXTEND_OP (@var{mem_mode})
10127 Define this macro to be a C expression indicating when insns that read
10128 memory in @var{mem_mode}, an integral mode narrower than a word, set the
10129 bits outside of @var{mem_mode} to be either the sign-extension or the
10130 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
10131 of @var{mem_mode} for which the
10132 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
10133 @code{UNKNOWN} for other modes.
10135 This macro is not called with @var{mem_mode} non-integral or with a width
10136 greater than or equal to @code{BITS_PER_WORD}, so you may return any
10137 value in this case. Do not define this macro if it would always return
10138 @code{UNKNOWN}. On machines where this macro is defined, you will normally
10139 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
10141 You may return a non-@code{UNKNOWN} value even if for some hard registers
10142 the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
10143 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
10144 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
10145 integral mode larger than this but not larger than @code{word_mode}.
10147 You must return @code{UNKNOWN} if for some hard registers that allow this
10148 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
10149 @code{word_mode}, but that they can change to another integral mode that
10150 is larger then @var{mem_mode} but still smaller than @code{word_mode}.
10153 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
10154 Define this macro if loading short immediate values into registers sign
10158 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
10159 Define this macro if the same instructions that convert a floating
10160 point number to a signed fixed point number also convert validly to an
10164 @deftypefn {Target Hook} {unsigned int} TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (enum machine_mode @var{mode})
10165 When @option{-ffast-math} is in effect, GCC tries to optimize
10166 divisions by the same divisor, by turning them into multiplications by
10167 the reciprocal. This target hook specifies the minimum number of divisions
10168 that should be there for GCC to perform the optimization for a variable
10169 of mode @var{mode}. The default implementation returns 3 if the machine
10170 has an instruction for the division, and 2 if it does not.
10174 The maximum number of bytes that a single instruction can move quickly
10175 between memory and registers or between two memory locations.
10178 @defmac MAX_MOVE_MAX
10179 The maximum number of bytes that a single instruction can move quickly
10180 between memory and registers or between two memory locations. If this
10181 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
10182 constant value that is the largest value that @code{MOVE_MAX} can have
10186 @defmac SHIFT_COUNT_TRUNCATED
10187 A C expression that is nonzero if on this machine the number of bits
10188 actually used for the count of a shift operation is equal to the number
10189 of bits needed to represent the size of the object being shifted. When
10190 this macro is nonzero, the compiler will assume that it is safe to omit
10191 a sign-extend, zero-extend, and certain bitwise `and' instructions that
10192 truncates the count of a shift operation. On machines that have
10193 instructions that act on bit-fields at variable positions, which may
10194 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
10195 also enables deletion of truncations of the values that serve as
10196 arguments to bit-field instructions.
10198 If both types of instructions truncate the count (for shifts) and
10199 position (for bit-field operations), or if no variable-position bit-field
10200 instructions exist, you should define this macro.
10202 However, on some machines, such as the 80386 and the 680x0, truncation
10203 only applies to shift operations and not the (real or pretended)
10204 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
10205 such machines. Instead, add patterns to the @file{md} file that include
10206 the implied truncation of the shift instructions.
10208 You need not define this macro if it would always have the value of zero.
10211 @anchor{TARGET_SHIFT_TRUNCATION_MASK}
10212 @deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_SHIFT_TRUNCATION_MASK (enum machine_mode @var{mode})
10213 This function describes how the standard shift patterns for @var{mode}
10214 deal with shifts by negative amounts or by more than the width of the mode.
10215 @xref{shift patterns}.
10217 On many machines, the shift patterns will apply a mask @var{m} to the
10218 shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
10219 equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If
10220 this is true for mode @var{mode}, the function should return @var{m},
10221 otherwise it should return 0. A return value of 0 indicates that no
10222 particular behavior is guaranteed.
10224 Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
10225 @emph{not} apply to general shift rtxes; it applies only to instructions
10226 that are generated by the named shift patterns.
10228 The default implementation of this function returns
10229 @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
10230 and 0 otherwise. This definition is always safe, but if
10231 @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
10232 nevertheless truncate the shift count, you may get better code
10236 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
10237 A C expression which is nonzero if on this machine it is safe to
10238 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
10239 bits (where @var{outprec} is smaller than @var{inprec}) by merely
10240 operating on it as if it had only @var{outprec} bits.
10242 On many machines, this expression can be 1.
10244 @c rearranged this, removed the phrase "it is reported that". this was
10245 @c to fix an overfull hbox. --mew 10feb93
10246 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
10247 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
10248 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
10249 such cases may improve things.
10252 @deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (enum machine_mode @var{mode}, enum machine_mode @var{rep_mode})
10253 The representation of an integral mode can be such that the values
10254 are always extended to a wider integral mode. Return
10255 @code{SIGN_EXTEND} if values of @var{mode} are represented in
10256 sign-extended form to @var{rep_mode}. Return @code{UNKNOWN}
10257 otherwise. (Currently, none of the targets use zero-extended
10258 representation this way so unlike @code{LOAD_EXTEND_OP},
10259 @code{TARGET_MODE_REP_EXTENDED} is expected to return either
10260 @code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends
10261 @var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next
10262 widest integral mode and currently we take advantage of this fact.)
10264 Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
10265 value even if the extension is not performed on certain hard registers
10266 as long as for the @code{REGNO_REG_CLASS} of these hard registers
10267 @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero.
10269 Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
10270 describe two related properties. If you define
10271 @code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
10272 to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
10275 In order to enforce the representation of @code{mode},
10276 @code{TRULY_NOOP_TRUNCATION} should return false when truncating to
10280 @defmac STORE_FLAG_VALUE
10281 A C expression describing the value returned by a comparison operator
10282 with an integral mode and stored by a store-flag instruction
10283 (@samp{cstore@var{mode}4}) when the condition is true. This description must
10284 apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the
10285 comparison operators whose results have a @code{MODE_INT} mode.
10287 A value of 1 or @minus{}1 means that the instruction implementing the
10288 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
10289 and 0 when the comparison is false. Otherwise, the value indicates
10290 which bits of the result are guaranteed to be 1 when the comparison is
10291 true. This value is interpreted in the mode of the comparison
10292 operation, which is given by the mode of the first operand in the
10293 @samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of
10294 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
10297 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
10298 generate code that depends only on the specified bits. It can also
10299 replace comparison operators with equivalent operations if they cause
10300 the required bits to be set, even if the remaining bits are undefined.
10301 For example, on a machine whose comparison operators return an
10302 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
10303 @samp{0x80000000}, saying that just the sign bit is relevant, the
10307 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
10311 can be converted to
10314 (ashift:SI @var{x} (const_int @var{n}))
10318 where @var{n} is the appropriate shift count to move the bit being
10319 tested into the sign bit.
10321 There is no way to describe a machine that always sets the low-order bit
10322 for a true value, but does not guarantee the value of any other bits,
10323 but we do not know of any machine that has such an instruction. If you
10324 are trying to port GCC to such a machine, include an instruction to
10325 perform a logical-and of the result with 1 in the pattern for the
10326 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
10328 Often, a machine will have multiple instructions that obtain a value
10329 from a comparison (or the condition codes). Here are rules to guide the
10330 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
10335 Use the shortest sequence that yields a valid definition for
10336 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
10337 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
10338 comparison operators to do so because there may be opportunities to
10339 combine the normalization with other operations.
10342 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
10343 slightly preferred on machines with expensive jumps and 1 preferred on
10347 As a second choice, choose a value of @samp{0x80000001} if instructions
10348 exist that set both the sign and low-order bits but do not define the
10352 Otherwise, use a value of @samp{0x80000000}.
10355 Many machines can produce both the value chosen for
10356 @code{STORE_FLAG_VALUE} and its negation in the same number of
10357 instructions. On those machines, you should also define a pattern for
10358 those cases, e.g., one matching
10361 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
10364 Some machines can also perform @code{and} or @code{plus} operations on
10365 condition code values with less instructions than the corresponding
10366 @samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those
10367 machines, define the appropriate patterns. Use the names @code{incscc}
10368 and @code{decscc}, respectively, for the patterns which perform
10369 @code{plus} or @code{minus} operations on condition code values. See
10370 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
10371 find such instruction sequences on other machines.
10373 If this macro is not defined, the default value, 1, is used. You need
10374 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
10375 instructions, or if the value generated by these instructions is 1.
10378 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
10379 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
10380 returned when comparison operators with floating-point results are true.
10381 Define this macro on machines that have comparison operations that return
10382 floating-point values. If there are no such operations, do not define
10386 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
10387 A C expression that gives a rtx representing the nonzero true element
10388 for vector comparisons. The returned rtx should be valid for the inner
10389 mode of @var{mode} which is guaranteed to be a vector mode. Define
10390 this macro on machines that have vector comparison operations that
10391 return a vector result. If there are no such operations, do not define
10392 this macro. Typically, this macro is defined as @code{const1_rtx} or
10393 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
10394 the compiler optimizing such vector comparison operations for the
10398 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10399 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10400 A C expression that indicates whether the architecture defines a value
10401 for @code{clz} or @code{ctz} with a zero operand.
10402 A result of @code{0} indicates the value is undefined.
10403 If the value is defined for only the RTL expression, the macro should
10404 evaluate to @code{1}; if the value applies also to the corresponding optab
10405 entry (which is normally the case if it expands directly into
10406 the corresponding RTL), then the macro should evaluate to @code{2}.
10407 In the cases where the value is defined, @var{value} should be set to
10410 If this macro is not defined, the value of @code{clz} or
10411 @code{ctz} at zero is assumed to be undefined.
10413 This macro must be defined if the target's expansion for @code{ffs}
10414 relies on a particular value to get correct results. Otherwise it
10415 is not necessary, though it may be used to optimize some corner cases, and
10416 to provide a default expansion for the @code{ffs} optab.
10418 Note that regardless of this macro the ``definedness'' of @code{clz}
10419 and @code{ctz} at zero do @emph{not} extend to the builtin functions
10420 visible to the user. Thus one may be free to adjust the value at will
10421 to match the target expansion of these operations without fear of
10426 An alias for the machine mode for pointers. On most machines, define
10427 this to be the integer mode corresponding to the width of a hardware
10428 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
10429 On some machines you must define this to be one of the partial integer
10430 modes, such as @code{PSImode}.
10432 The width of @code{Pmode} must be at least as large as the value of
10433 @code{POINTER_SIZE}. If it is not equal, you must define the macro
10434 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
10438 @defmac FUNCTION_MODE
10439 An alias for the machine mode used for memory references to functions
10440 being called, in @code{call} RTL expressions. On most CISC machines,
10441 where an instruction can begin at any byte address, this should be
10442 @code{QImode}. On most RISC machines, where all instructions have fixed
10443 size and alignment, this should be a mode with the same size and alignment
10444 as the machine instruction words - typically @code{SImode} or @code{HImode}.
10447 @defmac STDC_0_IN_SYSTEM_HEADERS
10448 In normal operation, the preprocessor expands @code{__STDC__} to the
10449 constant 1, to signify that GCC conforms to ISO Standard C@. On some
10450 hosts, like Solaris, the system compiler uses a different convention,
10451 where @code{__STDC__} is normally 0, but is 1 if the user specifies
10452 strict conformance to the C Standard.
10454 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
10455 convention when processing system header files, but when processing user
10456 files @code{__STDC__} will always expand to 1.
10459 @defmac NO_IMPLICIT_EXTERN_C
10460 Define this macro if the system header files support C++ as well as C@.
10461 This macro inhibits the usual method of using system header files in
10462 C++, which is to pretend that the file's contents are enclosed in
10463 @samp{extern "C" @{@dots{}@}}.
10468 @defmac REGISTER_TARGET_PRAGMAS ()
10469 Define this macro if you want to implement any target-specific pragmas.
10470 If defined, it is a C expression which makes a series of calls to
10471 @code{c_register_pragma} or @code{c_register_pragma_with_expansion}
10472 for each pragma. The macro may also do any
10473 setup required for the pragmas.
10475 The primary reason to define this macro is to provide compatibility with
10476 other compilers for the same target. In general, we discourage
10477 definition of target-specific pragmas for GCC@.
10479 If the pragma can be implemented by attributes then you should consider
10480 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
10482 Preprocessor macros that appear on pragma lines are not expanded. All
10483 @samp{#pragma} directives that do not match any registered pragma are
10484 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
10487 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10488 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10490 Each call to @code{c_register_pragma} or
10491 @code{c_register_pragma_with_expansion} establishes one pragma. The
10492 @var{callback} routine will be called when the preprocessor encounters a
10496 #pragma [@var{space}] @var{name} @dots{}
10499 @var{space} is the case-sensitive namespace of the pragma, or
10500 @code{NULL} to put the pragma in the global namespace. The callback
10501 routine receives @var{pfile} as its first argument, which can be passed
10502 on to cpplib's functions if necessary. You can lex tokens after the
10503 @var{name} by calling @code{pragma_lex}. Tokens that are not read by the
10504 callback will be silently ignored. The end of the line is indicated by
10505 a token of type @code{CPP_EOF}. Macro expansion occurs on the
10506 arguments of pragmas registered with
10507 @code{c_register_pragma_with_expansion} but not on the arguments of
10508 pragmas registered with @code{c_register_pragma}.
10510 Note that the use of @code{pragma_lex} is specific to the C and C++
10511 compilers. It will not work in the Java or Fortran compilers, or any
10512 other language compilers for that matter. Thus if @code{pragma_lex} is going
10513 to be called from target-specific code, it must only be done so when
10514 building the C and C++ compilers. This can be done by defining the
10515 variables @code{c_target_objs} and @code{cxx_target_objs} in the
10516 target entry in the @file{config.gcc} file. These variables should name
10517 the target-specific, language-specific object file which contains the
10518 code that uses @code{pragma_lex}. Note it will also be necessary to add a
10519 rule to the makefile fragment pointed to by @code{tmake_file} that shows
10520 how to build this object file.
10525 @defmac HANDLE_SYSV_PRAGMA
10526 Define this macro (to a value of 1) if you want the System V style
10527 pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name>
10528 [=<value>]} to be supported by gcc.
10530 The pack pragma specifies the maximum alignment (in bytes) of fields
10531 within a structure, in much the same way as the @samp{__aligned__} and
10532 @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets
10533 the behavior to the default.
10535 A subtlety for Microsoft Visual C/C++ style bit-field packing
10536 (e.g.@: -mms-bitfields) for targets that support it:
10537 When a bit-field is inserted into a packed record, the whole size
10538 of the underlying type is used by one or more same-size adjacent
10539 bit-fields (that is, if its long:3, 32 bits is used in the record,
10540 and any additional adjacent long bit-fields are packed into the same
10541 chunk of 32 bits. However, if the size changes, a new field of that
10542 size is allocated).
10544 If both MS bit-fields and @samp{__attribute__((packed))} are used,
10545 the latter will take precedence. If @samp{__attribute__((packed))} is
10546 used on a single field when MS bit-fields are in use, it will take
10547 precedence for that field, but the alignment of the rest of the structure
10548 may affect its placement.
10550 The weak pragma only works if @code{SUPPORTS_WEAK} and
10551 @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation
10552 of specifically named weak labels, optionally with a value.
10557 @defmac HANDLE_PRAGMA_PACK_PUSH_POP
10558 Define this macro (to a value of 1) if you want to support the Win32
10559 style pragmas @samp{#pragma pack(push[,@var{n}])} and @samp{#pragma
10560 pack(pop)}. The @samp{pack(push,[@var{n}])} pragma specifies the maximum
10561 alignment (in bytes) of fields within a structure, in much the same way as
10562 the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A
10563 pack value of zero resets the behavior to the default. Successive
10564 invocations of this pragma cause the previous values to be stacked, so
10565 that invocations of @samp{#pragma pack(pop)} will return to the previous
10569 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
10570 Define this macro, as well as
10571 @code{HANDLE_SYSV_PRAGMA}, if macros should be expanded in the
10572 arguments of @samp{#pragma pack}.
10575 @deftypevr {Target Hook} bool TARGET_HANDLE_PRAGMA_EXTERN_PREFIX
10576 True if @code{#pragma extern_prefix} is to be supported.
10579 @defmac TARGET_DEFAULT_PACK_STRUCT
10580 If your target requires a structure packing default other than 0 (meaning
10581 the machine default), define this macro to the necessary value (in bytes).
10582 This must be a value that would also be valid to use with
10583 @samp{#pragma pack()} (that is, a small power of two).
10586 @defmac DOLLARS_IN_IDENTIFIERS
10587 Define this macro to control use of the character @samp{$} in
10588 identifier names for the C family of languages. 0 means @samp{$} is
10589 not allowed by default; 1 means it is allowed. 1 is the default;
10590 there is no need to define this macro in that case.
10593 @defmac NO_DOLLAR_IN_LABEL
10594 Define this macro if the assembler does not accept the character
10595 @samp{$} in label names. By default constructors and destructors in
10596 G++ have @samp{$} in the identifiers. If this macro is defined,
10597 @samp{.} is used instead.
10600 @defmac NO_DOT_IN_LABEL
10601 Define this macro if the assembler does not accept the character
10602 @samp{.} in label names. By default constructors and destructors in G++
10603 have names that use @samp{.}. If this macro is defined, these names
10604 are rewritten to avoid @samp{.}.
10607 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
10608 Define this macro as a C expression that is nonzero if it is safe for the
10609 delay slot scheduler to place instructions in the delay slot of @var{insn},
10610 even if they appear to use a resource set or clobbered in @var{insn}.
10611 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
10612 every @code{call_insn} has this behavior. On machines where some @code{insn}
10613 or @code{jump_insn} is really a function call and hence has this behavior,
10614 you should define this macro.
10616 You need not define this macro if it would always return zero.
10619 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
10620 Define this macro as a C expression that is nonzero if it is safe for the
10621 delay slot scheduler to place instructions in the delay slot of @var{insn},
10622 even if they appear to set or clobber a resource referenced in @var{insn}.
10623 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
10624 some @code{insn} or @code{jump_insn} is really a function call and its operands
10625 are registers whose use is actually in the subroutine it calls, you should
10626 define this macro. Doing so allows the delay slot scheduler to move
10627 instructions which copy arguments into the argument registers into the delay
10628 slot of @var{insn}.
10630 You need not define this macro if it would always return zero.
10633 @defmac MULTIPLE_SYMBOL_SPACES
10634 Define this macro as a C expression that is nonzero if, in some cases,
10635 global symbols from one translation unit may not be bound to undefined
10636 symbols in another translation unit without user intervention. For
10637 instance, under Microsoft Windows symbols must be explicitly imported
10638 from shared libraries (DLLs).
10640 You need not define this macro if it would always evaluate to zero.
10643 @deftypefn {Target Hook} tree TARGET_MD_ASM_CLOBBERS (tree @var{outputs}, tree @var{inputs}, tree @var{clobbers})
10644 This target hook should add to @var{clobbers} @code{STRING_CST} trees for
10645 any hard regs the port wishes to automatically clobber for an asm.
10646 It should return the result of the last @code{tree_cons} used to add a
10647 clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the
10648 corresponding parameters to the asm and may be inspected to avoid
10649 clobbering a register that is an input or output of the asm. You can use
10650 @code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test
10651 for overlap with regards to asm-declared registers.
10654 @defmac MATH_LIBRARY
10655 Define this macro as a C string constant for the linker argument to link
10656 in the system math library, or @samp{""} if the target does not have a
10657 separate math library.
10659 You need only define this macro if the default of @samp{"-lm"} is wrong.
10662 @defmac LIBRARY_PATH_ENV
10663 Define this macro as a C string constant for the environment variable that
10664 specifies where the linker should look for libraries.
10666 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
10670 @defmac TARGET_POSIX_IO
10671 Define this macro if the target supports the following POSIX@ file
10672 functions, access, mkdir and file locking with fcntl / F_SETLKW@.
10673 Defining @code{TARGET_POSIX_IO} will enable the test coverage code
10674 to use file locking when exiting a program, which avoids race conditions
10675 if the program has forked. It will also create directories at run-time
10676 for cross-profiling.
10679 @defmac MAX_CONDITIONAL_EXECUTE
10681 A C expression for the maximum number of instructions to execute via
10682 conditional execution instructions instead of a branch. A value of
10683 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
10684 1 if it does use cc0.
10687 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
10688 Used if the target needs to perform machine-dependent modifications on the
10689 conditionals used for turning basic blocks into conditionally executed code.
10690 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
10691 contains information about the currently processed blocks. @var{true_expr}
10692 and @var{false_expr} are the tests that are used for converting the
10693 then-block and the else-block, respectively. Set either @var{true_expr} or
10694 @var{false_expr} to a null pointer if the tests cannot be converted.
10697 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
10698 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
10699 if-statements into conditions combined by @code{and} and @code{or} operations.
10700 @var{bb} contains the basic block that contains the test that is currently
10701 being processed and about to be turned into a condition.
10704 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
10705 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
10706 be converted to conditional execution format. @var{ce_info} points to
10707 a data structure, @code{struct ce_if_block}, which contains information
10708 about the currently processed blocks.
10711 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
10712 A C expression to perform any final machine dependent modifications in
10713 converting code to conditional execution. The involved basic blocks
10714 can be found in the @code{struct ce_if_block} structure that is pointed
10715 to by @var{ce_info}.
10718 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
10719 A C expression to cancel any machine dependent modifications in
10720 converting code to conditional execution. The involved basic blocks
10721 can be found in the @code{struct ce_if_block} structure that is pointed
10722 to by @var{ce_info}.
10725 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
10726 A C expression to initialize any extra fields in a @code{struct ce_if_block}
10727 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
10730 @defmac IFCVT_EXTRA_FIELDS
10731 If defined, it should expand to a set of field declarations that will be
10732 added to the @code{struct ce_if_block} structure. These should be initialized
10733 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
10736 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG (void)
10737 If non-null, this hook performs a target-specific pass over the
10738 instruction stream. The compiler will run it at all optimization levels,
10739 just before the point at which it normally does delayed-branch scheduling.
10741 The exact purpose of the hook varies from target to target. Some use
10742 it to do transformations that are necessary for correctness, such as
10743 laying out in-function constant pools or avoiding hardware hazards.
10744 Others use it as an opportunity to do some machine-dependent optimizations.
10746 You need not implement the hook if it has nothing to do. The default
10747 definition is null.
10750 @deftypefn {Target Hook} void TARGET_INIT_BUILTINS (void)
10751 Define this hook if you have any machine-specific built-in functions
10752 that need to be defined. It should be a function that performs the
10755 Machine specific built-in functions can be useful to expand special machine
10756 instructions that would otherwise not normally be generated because
10757 they have no equivalent in the source language (for example, SIMD vector
10758 instructions or prefetch instructions).
10760 To create a built-in function, call the function
10761 @code{lang_hooks.builtin_function}
10762 which is defined by the language front end. You can use any type nodes set
10763 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
10764 only language front ends that use those two functions will call
10765 @samp{TARGET_INIT_BUILTINS}.
10768 @deftypefn {Target Hook} tree TARGET_BUILTIN_DECL (unsigned @var{code}, bool @var{initialize_p})
10769 Define this hook if you have any machine-specific built-in functions
10770 that need to be defined. It should be a function that returns the
10771 builtin function declaration for the builtin function code @var{code}.
10772 If there is no such builtin and it cannot be initialized at this time
10773 if @var{initialize_p} is true the function should return @code{NULL_TREE}.
10774 If @var{code} is out of range the function should return
10775 @code{error_mark_node}.
10778 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore})
10780 Expand a call to a machine specific built-in function that was set up by
10781 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
10782 function call; the result should go to @var{target} if that is
10783 convenient, and have mode @var{mode} if that is convenient.
10784 @var{subtarget} may be used as the target for computing one of
10785 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
10786 ignored. This function should return the result of the call to the
10790 @deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (unsigned int @var{loc}, tree @var{fndecl}, void *@var{arglist})
10792 Select a replacement for a machine specific built-in function that
10793 was set up by @samp{TARGET_INIT_BUILTINS}. This is done
10794 @emph{before} regular type checking, and so allows the target to
10795 implement a crude form of function overloading. @var{fndecl} is the
10796 declaration of the built-in function. @var{arglist} is the list of
10797 arguments passed to the built-in function. The result is a
10798 complete expression that implements the operation, usually
10799 another @code{CALL_EXPR}.
10800 @var{arglist} really has type @samp{VEC(tree,gc)*}
10803 @deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, int @var{n_args}, tree *@var{argp}, bool @var{ignore})
10805 Fold a call to a machine specific built-in function that was set up by
10806 @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the
10807 built-in function. @var{n_args} is the number of arguments passed to
10808 the function; the arguments themselves are pointed to by @var{argp}.
10809 The result is another tree containing a simplified expression for the
10810 call's result. If @var{ignore} is true the value will be ignored.
10813 @deftypefn {Target Hook} {const char *} TARGET_INVALID_WITHIN_DOLOOP (const_rtx @var{insn})
10815 Take an instruction in @var{insn} and return NULL if it is valid within a
10816 low-overhead loop, otherwise return a string explaining why doloop
10817 could not be applied.
10819 Many targets use special registers for low-overhead looping. For any
10820 instruction that clobbers these this function should return a string indicating
10821 the reason why the doloop could not be applied.
10822 By default, the RTL loop optimizer does not use a present doloop pattern for
10823 loops containing function calls or branch on table instructions.
10826 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
10828 Take a branch insn in @var{branch1} and another in @var{branch2}.
10829 Return true if redirecting @var{branch1} to the destination of
10830 @var{branch2} is possible.
10832 On some targets, branches may have a limited range. Optimizing the
10833 filling of delay slots can result in branches being redirected, and this
10834 may in turn cause a branch offset to overflow.
10837 @deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (const_rtx @var{x}, int @var{outer_code})
10838 This target hook returns @code{true} if @var{x} is considered to be commutative.
10839 Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider
10840 PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code
10841 of the enclosing rtl, if known, otherwise it is UNKNOWN.
10844 @deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg})
10846 When the initial value of a hard register has been copied in a pseudo
10847 register, it is often not necessary to actually allocate another register
10848 to this pseudo register, because the original hard register or a stack slot
10849 it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE}
10850 is called at the start of register allocation once for each hard register
10851 that had its initial value copied by using
10852 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
10853 Possible values are @code{NULL_RTX}, if you don't want
10854 to do any special allocation, a @code{REG} rtx---that would typically be
10855 the hard register itself, if it is known not to be clobbered---or a
10857 If you are returning a @code{MEM}, this is only a hint for the allocator;
10858 it might decide to use another register anyways.
10859 You may use @code{current_function_leaf_function} in the hook, functions
10860 that use @code{REG_N_SETS}, to determine if the hard
10861 register in question will not be clobbered.
10862 The default value of this hook is @code{NULL}, which disables any special
10866 @deftypefn {Target Hook} int TARGET_UNSPEC_MAY_TRAP_P (const_rtx @var{x}, unsigned @var{flags})
10867 This target hook returns nonzero if @var{x}, an @code{unspec} or
10868 @code{unspec_volatile} operation, might cause a trap. Targets can use
10869 this hook to enhance precision of analysis for @code{unspec} and
10870 @code{unspec_volatile} operations. You may call @code{may_trap_p_1}
10871 to analyze inner elements of @var{x} in which case @var{flags} should be
10875 @deftypefn {Target Hook} void TARGET_SET_CURRENT_FUNCTION (tree @var{decl})
10876 The compiler invokes this hook whenever it changes its current function
10877 context (@code{cfun}). You can define this function if
10878 the back end needs to perform any initialization or reset actions on a
10879 per-function basis. For example, it may be used to implement function
10880 attributes that affect register usage or code generation patterns.
10881 The argument @var{decl} is the declaration for the new function context,
10882 and may be null to indicate that the compiler has left a function context
10883 and is returning to processing at the top level.
10884 The default hook function does nothing.
10886 GCC sets @code{cfun} to a dummy function context during initialization of
10887 some parts of the back end. The hook function is not invoked in this
10888 situation; you need not worry about the hook being invoked recursively,
10889 or when the back end is in a partially-initialized state.
10890 @code{cfun} might be @code{NULL} to indicate processing at top level,
10891 outside of any function scope.
10894 @defmac TARGET_OBJECT_SUFFIX
10895 Define this macro to be a C string representing the suffix for object
10896 files on your target machine. If you do not define this macro, GCC will
10897 use @samp{.o} as the suffix for object files.
10900 @defmac TARGET_EXECUTABLE_SUFFIX
10901 Define this macro to be a C string representing the suffix to be
10902 automatically added to executable files on your target machine. If you
10903 do not define this macro, GCC will use the null string as the suffix for
10907 @defmac COLLECT_EXPORT_LIST
10908 If defined, @code{collect2} will scan the individual object files
10909 specified on its command line and create an export list for the linker.
10910 Define this macro for systems like AIX, where the linker discards
10911 object files that are not referenced from @code{main} and uses export
10915 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
10916 Define this macro to a C expression representing a variant of the
10917 method call @var{mdecl}, if Java Native Interface (JNI) methods
10918 must be invoked differently from other methods on your target.
10919 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
10920 the @code{stdcall} calling convention and this macro is then
10921 defined as this expression:
10924 build_type_attribute_variant (@var{mdecl},
10926 (get_identifier ("stdcall"),
10931 @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
10932 This target hook returns @code{true} past the point in which new jump
10933 instructions could be created. On machines that require a register for
10934 every jump such as the SHmedia ISA of SH5, this point would typically be
10935 reload, so this target hook should be defined to a function such as:
10939 cannot_modify_jumps_past_reload_p ()
10941 return (reload_completed || reload_in_progress);
10946 @deftypefn {Target Hook} {enum reg_class} TARGET_BRANCH_TARGET_REGISTER_CLASS (void)
10947 This target hook returns a register class for which branch target register
10948 optimizations should be applied. All registers in this class should be
10949 usable interchangeably. After reload, registers in this class will be
10950 re-allocated and loads will be hoisted out of loops and be subjected
10951 to inter-block scheduling.
10954 @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen})
10955 Branch target register optimization will by default exclude callee-saved
10957 that are not already live during the current function; if this target hook
10958 returns true, they will be included. The target code must than make sure
10959 that all target registers in the class returned by
10960 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
10961 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
10962 epilogues have already been generated. Note, even if you only return
10963 true when @var{after_prologue_epilogue_gen} is false, you still are likely
10964 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
10965 to reserve space for caller-saved target registers.
10968 @deftypefn {Target Hook} bool TARGET_HAVE_CONDITIONAL_EXECUTION (void)
10969 This target hook returns true if the target supports conditional execution.
10970 This target hook is required only when the target has several different
10971 modes and they have different conditional execution capability, such as ARM.
10974 @deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, struct loop *@var{loop})
10975 This target hook returns a new value for the number of times @var{loop}
10976 should be unrolled. The parameter @var{nunroll} is the number of times
10977 the loop is to be unrolled. The parameter @var{loop} is a pointer to
10978 the loop, which is going to be checked for unrolling. This target hook
10979 is required only when the target has special constraints like maximum
10980 number of memory accesses.
10983 @defmac POWI_MAX_MULTS
10984 If defined, this macro is interpreted as a signed integer C expression
10985 that specifies the maximum number of floating point multiplications
10986 that should be emitted when expanding exponentiation by an integer
10987 constant inline. When this value is defined, exponentiation requiring
10988 more than this number of multiplications is implemented by calling the
10989 system library's @code{pow}, @code{powf} or @code{powl} routines.
10990 The default value places no upper bound on the multiplication count.
10993 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
10994 This target hook should register any extra include files for the
10995 target. The parameter @var{stdinc} indicates if normal include files
10996 are present. The parameter @var{sysroot} is the system root directory.
10997 The parameter @var{iprefix} is the prefix for the gcc directory.
11000 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
11001 This target hook should register any extra include files for the
11002 target before any standard headers. The parameter @var{stdinc}
11003 indicates if normal include files are present. The parameter
11004 @var{sysroot} is the system root directory. The parameter
11005 @var{iprefix} is the prefix for the gcc directory.
11008 @deftypefn Macro void TARGET_OPTF (char *@var{path})
11009 This target hook should register special include paths for the target.
11010 The parameter @var{path} is the include to register. On Darwin
11011 systems, this is used for Framework includes, which have semantics
11012 that are different from @option{-I}.
11015 @defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
11016 This target macro returns @code{true} if it is safe to use a local alias
11017 for a virtual function @var{fndecl} when constructing thunks,
11018 @code{false} otherwise. By default, the macro returns @code{true} for all
11019 functions, if a target supports aliases (i.e.@: defines
11020 @code{ASM_OUTPUT_DEF}), @code{false} otherwise,
11023 @defmac TARGET_FORMAT_TYPES
11024 If defined, this macro is the name of a global variable containing
11025 target-specific format checking information for the @option{-Wformat}
11026 option. The default is to have no target-specific format checks.
11029 @defmac TARGET_N_FORMAT_TYPES
11030 If defined, this macro is the number of entries in
11031 @code{TARGET_FORMAT_TYPES}.
11034 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
11035 If defined, this macro is the name of a global variable containing
11036 target-specific format overrides for the @option{-Wformat} option. The
11037 default is to have no target-specific format overrides. If defined,
11038 @code{TARGET_FORMAT_TYPES} must be defined, too.
11041 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
11042 If defined, this macro specifies the number of entries in
11043 @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
11046 @defmac TARGET_OVERRIDES_FORMAT_INIT
11047 If defined, this macro specifies the optional initialization
11048 routine for target specific customizations of the system printf
11049 and scanf formatter settings.
11052 @deftypevr {Target Hook} bool TARGET_RELAXED_ORDERING
11053 If set to @code{true}, means that the target's memory model does not
11054 guarantee that loads which do not depend on one another will access
11055 main memory in the order of the instruction stream; if ordering is
11056 important, an explicit memory barrier must be used. This is true of
11057 many recent processors which implement a policy of ``relaxed,''
11058 ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC,
11059 and ia64. The default is @code{false}.
11062 @deftypefn {Target Hook} {const char *} TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (const_tree @var{typelist}, const_tree @var{funcdecl}, const_tree @var{val})
11063 If defined, this macro returns the diagnostic message when it is
11064 illegal to pass argument @var{val} to function @var{funcdecl}
11065 with prototype @var{typelist}.
11068 @deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (const_tree @var{fromtype}, const_tree @var{totype})
11069 If defined, this macro returns the diagnostic message when it is
11070 invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL}
11071 if validity should be determined by the front end.
11074 @deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, const_tree @var{type})
11075 If defined, this macro returns the diagnostic message when it is
11076 invalid to apply operation @var{op} (where unary plus is denoted by
11077 @code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL}
11078 if validity should be determined by the front end.
11081 @deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, const_tree @var{type1}, const_tree @var{type2})
11082 If defined, this macro returns the diagnostic message when it is
11083 invalid to apply operation @var{op} to operands of types @var{type1}
11084 and @var{type2}, or @code{NULL} if validity should be determined by
11088 @deftypefn {Target Hook} {const char *} TARGET_INVALID_PARAMETER_TYPE (const_tree @var{type})
11089 If defined, this macro returns the diagnostic message when it is
11090 invalid for functions to include parameters of type @var{type},
11091 or @code{NULL} if validity should be determined by
11092 the front end. This is currently used only by the C and C++ front ends.
11095 @deftypefn {Target Hook} {const char *} TARGET_INVALID_RETURN_TYPE (const_tree @var{type})
11096 If defined, this macro returns the diagnostic message when it is
11097 invalid for functions to have return type @var{type},
11098 or @code{NULL} if validity should be determined by
11099 the front end. This is currently used only by the C and C++ front ends.
11102 @deftypefn {Target Hook} tree TARGET_PROMOTED_TYPE (const_tree @var{type})
11103 If defined, this target hook returns the type to which values of
11104 @var{type} should be promoted when they appear in expressions,
11105 analogous to the integer promotions, or @code{NULL_TREE} to use the
11106 front end's normal promotion rules. This hook is useful when there are
11107 target-specific types with special promotion rules.
11108 This is currently used only by the C and C++ front ends.
11111 @deftypefn {Target Hook} tree TARGET_CONVERT_TO_TYPE (tree @var{type}, tree @var{expr})
11112 If defined, this hook returns the result of converting @var{expr} to
11113 @var{type}. It should return the converted expression,
11114 or @code{NULL_TREE} to apply the front end's normal conversion rules.
11115 This hook is useful when there are target-specific types with special
11117 This is currently used only by the C and C++ front ends.
11120 @defmac TARGET_USE_JCR_SECTION
11121 This macro determines whether to use the JCR section to register Java
11122 classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both
11123 SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0.
11127 This macro determines the size of the objective C jump buffer for the
11128 NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
11131 @defmac LIBGCC2_UNWIND_ATTRIBUTE
11132 Define this macro if any target-specific attributes need to be attached
11133 to the functions in @file{libgcc} that provide low-level support for
11134 call stack unwinding. It is used in declarations in @file{unwind-generic.h}
11135 and the associated definitions of those functions.
11138 @deftypefn {Target Hook} void TARGET_UPDATE_STACK_BOUNDARY (void)
11139 Define this macro to update the current function stack boundary if
11143 @deftypefn {Target Hook} rtx TARGET_GET_DRAP_RTX (void)
11144 This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a
11145 different argument pointer register is needed to access the function's
11146 argument list due to stack realignment. Return @code{NULL} if no DRAP
11150 @deftypefn {Target Hook} bool TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS (void)
11151 When optimization is disabled, this hook indicates whether or not
11152 arguments should be allocated to stack slots. Normally, GCC allocates
11153 stacks slots for arguments when not optimizing in order to make
11154 debugging easier. However, when a function is declared with
11155 @code{__attribute__((naked))}, there is no stack frame, and the compiler
11156 cannot safely move arguments from the registers in which they are passed
11157 to the stack. Therefore, this hook should return true in general, but
11158 false for naked functions. The default implementation always returns true.
11161 @deftypevr {Target Hook} {unsigned HOST_WIDE_INT} TARGET_CONST_ANCHOR
11162 On some architectures it can take multiple instructions to synthesize
11163 a constant. If there is another constant already in a register that
11164 is close enough in value then it is preferable that the new constant
11165 is computed from this register using immediate addition or
11166 subtraction. We accomplish this through CSE. Besides the value of
11167 the constant we also add a lower and an upper constant anchor to the
11168 available expressions. These are then queried when encountering new
11169 constants. The anchors are computed by rounding the constant up and
11170 down to a multiple of the value of @code{TARGET_CONST_ANCHOR}.
11171 @code{TARGET_CONST_ANCHOR} should be the maximum positive value
11172 accepted by immediate-add plus one. We currently assume that the
11173 value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on
11174 MIPS, where add-immediate takes a 16-bit signed value,
11175 @code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value
11176 is zero, which disables this optimization. @end deftypevr