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
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 * Misc:: Everything else.
61 @node Target Structure
62 @section The Global @code{targetm} Variable
64 @cindex target functions
66 @deftypevar {struct gcc_target} targetm
67 The target @file{.c} file must define the global @code{targetm} variable
68 which contains pointers to functions and data relating to the target
69 machine. The variable is declared in @file{target.h};
70 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
71 used to initialize the variable, and macros for the default initializers
72 for elements of the structure. The @file{.c} file should override those
73 macros for which the default definition is inappropriate. For example:
76 #include "target-def.h"
78 /* @r{Initialize the GCC target structure.} */
80 #undef TARGET_COMP_TYPE_ATTRIBUTES
81 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
83 struct gcc_target targetm = TARGET_INITIALIZER;
87 Where a macro should be defined in the @file{.c} file in this manner to
88 form part of the @code{targetm} structure, it is documented below as a
89 ``Target Hook'' with a prototype. Many macros will change in future
90 from being defined in the @file{.h} file to being part of the
91 @code{targetm} structure.
94 @section Controlling the Compilation Driver, @file{gcc}
96 @cindex controlling the compilation driver
98 @c prevent bad page break with this line
99 You can control the compilation driver.
101 @defmac SWITCH_TAKES_ARG (@var{char})
102 A C expression which determines whether the option @option{-@var{char}}
103 takes arguments. The value should be the number of arguments that
104 option takes--zero, for many options.
106 By default, this macro is defined as
107 @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options
108 properly. You need not define @code{SWITCH_TAKES_ARG} unless you
109 wish to add additional options which take arguments. Any redefinition
110 should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for
114 @defmac WORD_SWITCH_TAKES_ARG (@var{name})
115 A C expression which determines whether the option @option{-@var{name}}
116 takes arguments. The value should be the number of arguments that
117 option takes--zero, for many options. This macro rather than
118 @code{SWITCH_TAKES_ARG} is used for multi-character option names.
120 By default, this macro is defined as
121 @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options
122 properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you
123 wish to add additional options which take arguments. Any redefinition
124 should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for
128 @defmac SWITCH_CURTAILS_COMPILATION (@var{char})
129 A C expression which determines whether the option @option{-@var{char}}
130 stops compilation before the generation of an executable. The value is
131 boolean, nonzero if the option does stop an executable from being
132 generated, zero otherwise.
134 By default, this macro is defined as
135 @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard
136 options properly. You need not define
137 @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional
138 options which affect the generation of an executable. Any redefinition
139 should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check
140 for additional options.
143 @defmac SWITCHES_NEED_SPACES
144 A string-valued C expression which enumerates the options for which
145 the linker needs a space between the option and its argument.
147 If this macro is not defined, the default value is @code{""}.
150 @defmac TARGET_OPTION_TRANSLATE_TABLE
151 If defined, a list of pairs of strings, the first of which is a
152 potential command line target to the @file{gcc} driver program, and the
153 second of which is a space-separated (tabs and other whitespace are not
154 supported) list of options with which to replace the first option. The
155 target defining this list is responsible for assuring that the results
156 are valid. Replacement options may not be the @code{--opt} style, they
157 must be the @code{-opt} style. It is the intention of this macro to
158 provide a mechanism for substitution that affects the multilibs chosen,
159 such as one option that enables many options, some of which select
160 multilibs. Example nonsensical definition, where @option{-malt-abi},
161 @option{-EB}, and @option{-mspoo} cause different multilibs to be chosen:
164 #define TARGET_OPTION_TRANSLATE_TABLE \
165 @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \
166 @{ "-compat", "-EB -malign=4 -mspoo" @}
170 @defmac DRIVER_SELF_SPECS
171 A list of specs for the driver itself. It should be a suitable
172 initializer for an array of strings, with no surrounding braces.
174 The driver applies these specs to its own command line between loading
175 default @file{specs} files (but not command-line specified ones) and
176 choosing the multilib directory or running any subcommands. It
177 applies them in the order given, so each spec can depend on the
178 options added by earlier ones. It is also possible to remove options
179 using @samp{%<@var{option}} in the usual way.
181 This macro can be useful when a port has several interdependent target
182 options. It provides a way of standardizing the command line so
183 that the other specs are easier to write.
185 Do not define this macro if it does not need to do anything.
188 @defmac OPTION_DEFAULT_SPECS
189 A list of specs used to support configure-time default options (i.e.@:
190 @option{--with} options) in the driver. It should be a suitable initializer
191 for an array of structures, each containing two strings, without the
192 outermost pair of surrounding braces.
194 The first item in the pair is the name of the default. This must match
195 the code in @file{config.gcc} for the target. The second item is a spec
196 to apply if a default with this name was specified. The string
197 @samp{%(VALUE)} in the spec will be replaced by the value of the default
198 everywhere it occurs.
200 The driver will apply these specs to its own command line between loading
201 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
202 the same mechanism as @code{DRIVER_SELF_SPECS}.
204 Do not define this macro if it does not need to do anything.
208 A C string constant that tells the GCC driver program options to
209 pass to CPP@. It can also specify how to translate options you
210 give to GCC into options for GCC to pass to the CPP@.
212 Do not define this macro if it does not need to do anything.
215 @defmac CPLUSPLUS_CPP_SPEC
216 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
217 than C@. If you do not define this macro, then the value of
218 @code{CPP_SPEC} (if any) will be used instead.
222 A C string constant that tells the GCC driver program options to
223 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
225 It can also specify how to translate options you give to GCC into options
226 for GCC to pass to front ends.
228 Do not define this macro if it does not need to do anything.
232 A C string constant that tells the GCC driver program options to
233 pass to @code{cc1plus}. It can also specify how to translate options you
234 give to GCC into options for GCC to pass to the @code{cc1plus}.
236 Do not define this macro if it does not need to do anything.
237 Note that everything defined in CC1_SPEC is already passed to
238 @code{cc1plus} so there is no need to duplicate the contents of
239 CC1_SPEC in CC1PLUS_SPEC@.
243 A C string constant that tells the GCC driver program options to
244 pass to the assembler. It can also specify how to translate options
245 you give to GCC into options for GCC to pass to the assembler.
246 See the file @file{sun3.h} for an example of this.
248 Do not define this macro if it does not need to do anything.
251 @defmac ASM_FINAL_SPEC
252 A C string constant that tells the GCC driver program how to
253 run any programs which cleanup after the normal assembler.
254 Normally, this is not needed. See the file @file{mips.h} for
257 Do not define this macro if it does not need to do anything.
260 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
261 Define this macro, with no value, if the driver should give the assembler
262 an argument consisting of a single dash, @option{-}, to instruct it to
263 read from its standard input (which will be a pipe connected to the
264 output of the compiler proper). This argument is given after any
265 @option{-o} option specifying the name of the output file.
267 If you do not define this macro, the assembler is assumed to read its
268 standard input if given no non-option arguments. If your assembler
269 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
270 see @file{mips.h} for instance.
274 A C string constant that tells the GCC driver program options to
275 pass to the linker. It can also specify how to translate options you
276 give to GCC into options for GCC to pass to the linker.
278 Do not define this macro if it does not need to do anything.
282 Another C string constant used much like @code{LINK_SPEC}. The difference
283 between the two is that @code{LIB_SPEC} is used at the end of the
284 command given to the linker.
286 If this macro is not defined, a default is provided that
287 loads the standard C library from the usual place. See @file{gcc.c}.
291 Another C string constant that tells the GCC driver program
292 how and when to place a reference to @file{libgcc.a} into the
293 linker command line. This constant is placed both before and after
294 the value of @code{LIB_SPEC}.
296 If this macro is not defined, the GCC driver provides a default that
297 passes the string @option{-lgcc} to the linker.
300 @defmac REAL_LIBGCC_SPEC
301 By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
302 @code{LIBGCC_SPEC} is not directly used by the driver program but is
303 instead modified to refer to different versions of @file{libgcc.a}
304 depending on the values of the command line flags @option{-static},
305 @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
306 targets where these modifications are inappropriate, define
307 @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
308 driver how to place a reference to @file{libgcc} on the link command
309 line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
312 @defmac USE_LD_AS_NEEDED
313 A macro that controls the modifications to @code{LIBGCC_SPEC}
314 mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
315 generated that uses --as-needed and the shared libgcc in place of the
316 static exception handler library, when linking without any of
317 @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
321 If defined, this C string constant is added to @code{LINK_SPEC}.
322 When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
323 the modifications to @code{LIBGCC_SPEC} mentioned in
324 @code{REAL_LIBGCC_SPEC}.
327 @defmac STARTFILE_SPEC
328 Another C string constant used much like @code{LINK_SPEC}. The
329 difference between the two is that @code{STARTFILE_SPEC} is used at
330 the very beginning of the command given to the linker.
332 If this macro is not defined, a default is provided that loads the
333 standard C startup file from the usual place. See @file{gcc.c}.
337 Another C string constant used much like @code{LINK_SPEC}. The
338 difference between the two is that @code{ENDFILE_SPEC} is used at
339 the very end of the command given to the linker.
341 Do not define this macro if it does not need to do anything.
344 @defmac THREAD_MODEL_SPEC
345 GCC @code{-v} will print the thread model GCC was configured to use.
346 However, this doesn't work on platforms that are multilibbed on thread
347 models, such as AIX 4.3. On such platforms, define
348 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
349 blanks that names one of the recognized thread models. @code{%*}, the
350 default value of this macro, will expand to the value of
351 @code{thread_file} set in @file{config.gcc}.
354 @defmac SYSROOT_SUFFIX_SPEC
355 Define this macro to add a suffix to the target sysroot when GCC is
356 configured with a sysroot. This will cause GCC to search for usr/lib,
357 et al, within sysroot+suffix.
360 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
361 Define this macro to add a headers_suffix to the target sysroot when
362 GCC is configured with a sysroot. This will cause GCC to pass the
363 updated sysroot+headers_suffix to CPP, causing it to search for
364 usr/include, et al, within sysroot+headers_suffix.
368 Define this macro to provide additional specifications to put in the
369 @file{specs} file that can be used in various specifications like
372 The definition should be an initializer for an array of structures,
373 containing a string constant, that defines the specification name, and a
374 string constant that provides the specification.
376 Do not define this macro if it does not need to do anything.
378 @code{EXTRA_SPECS} is useful when an architecture contains several
379 related targets, which have various @code{@dots{}_SPECS} which are similar
380 to each other, and the maintainer would like one central place to keep
383 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
384 define either @code{_CALL_SYSV} when the System V calling sequence is
385 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
388 The @file{config/rs6000/rs6000.h} target file defines:
391 #define EXTRA_SPECS \
392 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
394 #define CPP_SYS_DEFAULT ""
397 The @file{config/rs6000/sysv.h} target file defines:
401 "%@{posix: -D_POSIX_SOURCE @} \
402 %@{mcall-sysv: -D_CALL_SYSV @} \
403 %@{!mcall-sysv: %(cpp_sysv_default) @} \
404 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
406 #undef CPP_SYSV_DEFAULT
407 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
410 while the @file{config/rs6000/eabiaix.h} target file defines
411 @code{CPP_SYSV_DEFAULT} as:
414 #undef CPP_SYSV_DEFAULT
415 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
419 @defmac LINK_LIBGCC_SPECIAL_1
420 Define this macro if the driver program should find the library
421 @file{libgcc.a}. If you do not define this macro, the driver program will pass
422 the argument @option{-lgcc} to tell the linker to do the search.
425 @defmac LINK_GCC_C_SEQUENCE_SPEC
426 The sequence in which libgcc and libc are specified to the linker.
427 By default this is @code{%G %L %G}.
430 @defmac LINK_COMMAND_SPEC
431 A C string constant giving the complete command line need to execute the
432 linker. When you do this, you will need to update your port each time a
433 change is made to the link command line within @file{gcc.c}. Therefore,
434 define this macro only if you need to completely redefine the command
435 line for invoking the linker and there is no other way to accomplish
436 the effect you need. Overriding this macro may be avoidable by overriding
437 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
440 @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
441 A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
442 directories from linking commands. Do not give it a nonzero value if
443 removing duplicate search directories changes the linker's semantics.
446 @defmac MULTILIB_DEFAULTS
447 Define this macro as a C expression for the initializer of an array of
448 string to tell the driver program which options are defaults for this
449 target and thus do not need to be handled specially when using
450 @code{MULTILIB_OPTIONS}.
452 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
453 the target makefile fragment or if none of the options listed in
454 @code{MULTILIB_OPTIONS} are set by default.
455 @xref{Target Fragment}.
458 @defmac RELATIVE_PREFIX_NOT_LINKDIR
459 Define this macro to tell @command{gcc} that it should only translate
460 a @option{-B} prefix into a @option{-L} linker option if the prefix
461 indicates an absolute file name.
464 @defmac MD_EXEC_PREFIX
465 If defined, this macro is an additional prefix to try after
466 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
467 when the @option{-b} option is used, or the compiler is built as a cross
468 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
469 to the list of directories used to find the assembler in @file{configure.in}.
472 @defmac STANDARD_STARTFILE_PREFIX
473 Define this macro as a C string constant if you wish to override the
474 standard choice of @code{libdir} as the default prefix to
475 try when searching for startup files such as @file{crt0.o}.
476 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
477 is built as a cross compiler.
480 @defmac STANDARD_STARTFILE_PREFIX_1
481 Define this macro as a C string constant if you wish to override the
482 standard choice of @code{/lib} as a prefix to try after the default prefix
483 when searching for startup files such as @file{crt0.o}.
484 @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
485 is built as a cross compiler.
488 @defmac STANDARD_STARTFILE_PREFIX_2
489 Define this macro as a C string constant if you wish to override the
490 standard choice of @code{/lib} as yet another prefix to try after the
491 default prefix when searching for startup files such as @file{crt0.o}.
492 @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
493 is built as a cross compiler.
496 @defmac MD_STARTFILE_PREFIX
497 If defined, this macro supplies an additional prefix to try after the
498 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
499 @option{-b} option is used, or when the compiler is built as a cross
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 @option{-b} option is
506 used, or when the compiler is built as a cross compiler.
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 default definition does nothing but return false.
785 In general, you should use @code{TARGET_HANDLE_OPTION} to handle
786 options. However, if processing an option requires routines that are
787 only available in the C (and related language) front ends, then you
788 should use @code{TARGET_HANDLE_C_OPTION} instead.
791 @defmac TARGET_VERSION
792 This macro is a C statement to print on @code{stderr} a string
793 describing the particular machine description choice. Every machine
794 description should define @code{TARGET_VERSION}. For example:
798 #define TARGET_VERSION \
799 fprintf (stderr, " (68k, Motorola syntax)");
801 #define TARGET_VERSION \
802 fprintf (stderr, " (68k, MIT syntax)");
807 @defmac OVERRIDE_OPTIONS
808 Sometimes certain combinations of command options do not make sense on
809 a particular target machine. You can define a macro
810 @code{OVERRIDE_OPTIONS} to take account of this. This macro, if
811 defined, is executed once just after all the command options have been
814 Don't use this macro to turn on various extra optimizations for
815 @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for.
818 @defmac C_COMMON_OVERRIDE_OPTIONS
819 This is similar to @code{OVERRIDE_OPTIONS} but is only used in the C
820 language frontends (C, Objective-C, C++, Objective-C++) and so can be
821 used to alter option flag variables which only exist in those
825 @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size})
826 Some machines may desire to change what optimizations are performed for
827 various optimization levels. This macro, if defined, is executed once
828 just after the optimization level is determined and before the remainder
829 of the command options have been parsed. Values set in this macro are
830 used as the default values for the other command line options.
832 @var{level} is the optimization level specified; 2 if @option{-O2} is
833 specified, 1 if @option{-O} is specified, and 0 if neither is specified.
835 @var{size} is nonzero if @option{-Os} is specified and zero otherwise.
837 This macro is run once at program startup and when the optimization
838 options are changed via @code{#pragma GCC optimize} or by using the
839 @code{optimize} attribute.
841 @strong{Do not examine @code{write_symbols} in
842 this macro!} The debugging options are not supposed to alter the
846 @deftypefn {Target Hook} bool TARGET_HELP (void)
847 This hook is called in response to the user invoking
848 @option{--target-help} on the command line. It gives the target a
849 chance to display extra information on the target specific command
850 line options found in its @file{.opt} file.
853 @defmac CAN_DEBUG_WITHOUT_FP
854 Define this macro if debugging can be performed even without a frame
855 pointer. If this macro is defined, GCC will turn on the
856 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
859 @node Per-Function Data
860 @section Defining data structures for per-function information.
861 @cindex per-function data
862 @cindex data structures
864 If the target needs to store information on a per-function basis, GCC
865 provides a macro and a couple of variables to allow this. Note, just
866 using statics to store the information is a bad idea, since GCC supports
867 nested functions, so you can be halfway through encoding one function
868 when another one comes along.
870 GCC defines a data structure called @code{struct function} which
871 contains all of the data specific to an individual function. This
872 structure contains a field called @code{machine} whose type is
873 @code{struct machine_function *}, which can be used by targets to point
874 to their own specific data.
876 If a target needs per-function specific data it should define the type
877 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
878 This macro should be used to initialize the function pointer
879 @code{init_machine_status}. This pointer is explained below.
881 One typical use of per-function, target specific data is to create an
882 RTX to hold the register containing the function's return address. This
883 RTX can then be used to implement the @code{__builtin_return_address}
884 function, for level 0.
886 Note---earlier implementations of GCC used a single data area to hold
887 all of the per-function information. Thus when processing of a nested
888 function began the old per-function data had to be pushed onto a
889 stack, and when the processing was finished, it had to be popped off the
890 stack. GCC used to provide function pointers called
891 @code{save_machine_status} and @code{restore_machine_status} to handle
892 the saving and restoring of the target specific information. Since the
893 single data area approach is no longer used, these pointers are no
896 @defmac INIT_EXPANDERS
897 Macro called to initialize any target specific information. This macro
898 is called once per function, before generation of any RTL has begun.
899 The intention of this macro is to allow the initialization of the
900 function pointer @code{init_machine_status}.
903 @deftypevar {void (*)(struct function *)} init_machine_status
904 If this function pointer is non-@code{NULL} it will be called once per
905 function, before function compilation starts, in order to allow the
906 target to perform any target specific initialization of the
907 @code{struct function} structure. It is intended that this would be
908 used to initialize the @code{machine} of that structure.
910 @code{struct machine_function} structures are expected to be freed by GC@.
911 Generally, any memory that they reference must be allocated by using
912 @code{ggc_alloc}, including the structure itself.
916 @section Storage Layout
917 @cindex storage layout
919 Note that the definitions of the macros in this table which are sizes or
920 alignments measured in bits do not need to be constant. They can be C
921 expressions that refer to static variables, such as the @code{target_flags}.
922 @xref{Run-time Target}.
924 @defmac BITS_BIG_ENDIAN
925 Define this macro to have the value 1 if the most significant bit in a
926 byte has the lowest number; otherwise define it to have the value zero.
927 This means that bit-field instructions count from the most significant
928 bit. If the machine has no bit-field instructions, then this must still
929 be defined, but it doesn't matter which value it is defined to. This
930 macro need not be a constant.
932 This macro does not affect the way structure fields are packed into
933 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
936 @defmac BYTES_BIG_ENDIAN
937 Define this macro to have the value 1 if the most significant byte in a
938 word has the lowest number. This macro need not be a constant.
941 @defmac WORDS_BIG_ENDIAN
942 Define this macro to have the value 1 if, in a multiword object, the
943 most significant word has the lowest number. This applies to both
944 memory locations and registers; GCC fundamentally assumes that the
945 order of words in memory is the same as the order in registers. This
946 macro need not be a constant.
949 @defmac LIBGCC2_WORDS_BIG_ENDIAN
950 Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a
951 constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
952 used only when compiling @file{libgcc2.c}. Typically the value will be set
953 based on preprocessor defines.
956 @defmac FLOAT_WORDS_BIG_ENDIAN
957 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
958 @code{TFmode} floating point numbers are stored in memory with the word
959 containing the sign bit at the lowest address; otherwise define it to
960 have the value 0. This macro need not be a constant.
962 You need not define this macro if the ordering is the same as for
966 @defmac BITS_PER_UNIT
967 Define this macro to be the number of bits in an addressable storage
968 unit (byte). If you do not define this macro the default is 8.
971 @defmac BITS_PER_WORD
972 Number of bits in a word. If you do not define this macro, the default
973 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
976 @defmac MAX_BITS_PER_WORD
977 Maximum number of bits in a word. If this is undefined, the default is
978 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
979 largest value that @code{BITS_PER_WORD} can have at run-time.
982 @defmac UNITS_PER_WORD
983 Number of storage units in a word; normally the size of a general-purpose
984 register, a power of two from 1 or 8.
987 @defmac MIN_UNITS_PER_WORD
988 Minimum number of units in a word. If this is undefined, the default is
989 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
990 smallest value that @code{UNITS_PER_WORD} can have at run-time.
993 @defmac UNITS_PER_SIMD_WORD (@var{mode})
994 Number of units in the vectors that the vectorizer can produce for
995 scalar mode @var{mode}. The default is equal to @code{UNITS_PER_WORD},
996 because the vectorizer can do some transformations even in absence of
997 specialized @acronym{SIMD} hardware.
1000 @defmac POINTER_SIZE
1001 Width of a pointer, in bits. You must specify a value no wider than the
1002 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
1003 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
1004 a value the default is @code{BITS_PER_WORD}.
1007 @defmac POINTERS_EXTEND_UNSIGNED
1008 A C expression that determines how pointers should be extended from
1009 @code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is
1010 greater than zero if pointers should be zero-extended, zero if they
1011 should be sign-extended, and negative if some other sort of conversion
1012 is needed. In the last case, the extension is done by the target's
1013 @code{ptr_extend} instruction.
1015 You need not define this macro if the @code{ptr_mode}, @code{Pmode}
1016 and @code{word_mode} are all the same width.
1019 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
1020 A macro to update @var{m} and @var{unsignedp} when an object whose type
1021 is @var{type} and which has the specified mode and signedness is to be
1022 stored in a register. This macro is only called when @var{type} is a
1025 On most RISC machines, which only have operations that operate on a full
1026 register, define this macro to set @var{m} to @code{word_mode} if
1027 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
1028 cases, only integer modes should be widened because wider-precision
1029 floating-point operations are usually more expensive than their narrower
1032 For most machines, the macro definition does not change @var{unsignedp}.
1033 However, some machines, have instructions that preferentially handle
1034 either signed or unsigned quantities of certain modes. For example, on
1035 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
1036 sign-extend the result to 64 bits. On such machines, set
1037 @var{unsignedp} according to which kind of extension is more efficient.
1039 Do not define this macro if it would never modify @var{m}.
1042 @deftypefn {Target Hook} enum machine_mode TARGET_PROMOTE_FUNCTION_MODE (tree @var{type}, enum machine_mode @var{mode}, int *@var{punsignedp}, tree @var{funtype}, int @var{for_return})
1043 Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or
1044 function return values. The target hook should return the new mode
1045 and possibly change @code{*@var{punsignedp}} if the promotion should
1046 change signedness. This function is called only for scalar @emph{or
1049 @var{for_return} allows to distinguish the promotion of arguments and
1050 return values. If it is @code{1}, a return value is being promoted and
1051 @code{TARGET_FUNCTION_VALUE} must perform the same promotions done here.
1052 If it is @code{2}, the returned mode should be that of the register in
1053 which an incoming parameter is copied, or the outgoing result is computed;
1054 then the hook should return the same mode as @code{promote_mode}, though
1055 the signedness may be different.
1057 The default is to not promote arguments and return values. You can
1058 also define the hook to @code{default_promote_function_mode_always_promote}
1059 if you would like to apply the same rules given by @code{PROMOTE_MODE}.
1062 @defmac PARM_BOUNDARY
1063 Normal alignment required for function parameters on the stack, in
1064 bits. All stack parameters receive at least this much alignment
1065 regardless of data type. On most machines, this is the same as the
1069 @defmac STACK_BOUNDARY
1070 Define this macro to the minimum alignment enforced by hardware for the
1071 stack pointer on this machine. The definition is a C expression for the
1072 desired alignment (measured in bits). This value is used as a default
1073 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
1074 this should be the same as @code{PARM_BOUNDARY}.
1077 @defmac PREFERRED_STACK_BOUNDARY
1078 Define this macro if you wish to preserve a certain alignment for the
1079 stack pointer, greater than what the hardware enforces. The definition
1080 is a C expression for the desired alignment (measured in bits). This
1081 macro must evaluate to a value equal to or larger than
1082 @code{STACK_BOUNDARY}.
1085 @defmac INCOMING_STACK_BOUNDARY
1086 Define this macro if the incoming stack boundary may be different
1087 from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate
1088 to a value equal to or larger than @code{STACK_BOUNDARY}.
1091 @defmac FUNCTION_BOUNDARY
1092 Alignment required for a function entry point, in bits.
1095 @defmac BIGGEST_ALIGNMENT
1096 Biggest alignment that any data type can require on this machine, in
1097 bits. Note that this is not the biggest alignment that is supported,
1098 just the biggest alignment that, when violated, may cause a fault.
1101 @defmac MALLOC_ABI_ALIGNMENT
1102 Alignment, in bits, a C conformant malloc implementation has to
1103 provide. If not defined, the default value is @code{BITS_PER_WORD}.
1106 @defmac ATTRIBUTE_ALIGNED_VALUE
1107 Alignment used by the @code{__attribute__ ((aligned))} construct. If
1108 not defined, the default value is @code{BIGGEST_ALIGNMENT}.
1111 @defmac MINIMUM_ATOMIC_ALIGNMENT
1112 If defined, the smallest alignment, in bits, that can be given to an
1113 object that can be referenced in one operation, without disturbing any
1114 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1115 on machines that don't have byte or half-word store operations.
1118 @defmac BIGGEST_FIELD_ALIGNMENT
1119 Biggest alignment that any structure or union field can require on this
1120 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1121 structure and union fields only, unless the field alignment has been set
1122 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1125 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1126 An expression for the alignment of a structure field @var{field} if the
1127 alignment computed in the usual way (including applying of
1128 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1129 alignment) is @var{computed}. It overrides alignment only if the
1130 field alignment has not been set by the
1131 @code{__attribute__ ((aligned (@var{n})))} construct.
1134 @defmac MAX_STACK_ALIGNMENT
1135 Biggest stack alignment guaranteed by the backend. Use this macro
1136 to specify the maximum alignment of a variable on stack.
1138 If not defined, the default value is @code{STACK_BOUNDARY}.
1140 @c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
1141 @c But the fix for PR 32893 indicates that we can only guarantee
1142 @c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
1143 @c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
1146 @defmac MAX_OFILE_ALIGNMENT
1147 Biggest alignment supported by the object file format of this machine.
1148 Use this macro to limit the alignment which can be specified using the
1149 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1150 the default value is @code{BIGGEST_ALIGNMENT}.
1152 On systems that use ELF, the default (in @file{config/elfos.h}) is
1153 the largest supported 32-bit ELF section alignment representable on
1154 a 32-bit host e.g. @samp{(((unsigned HOST_WIDEST_INT) 1 << 28) * 8)}.
1155 On 32-bit ELF the largest supported section alignment in bits is
1156 @samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
1159 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1160 If defined, a C expression to compute the alignment for a variable in
1161 the static store. @var{type} is the data type, and @var{basic-align} is
1162 the alignment that the object would ordinarily have. The value of this
1163 macro is used instead of that alignment to align the object.
1165 If this macro is not defined, then @var{basic-align} is used.
1168 One use of this macro is to increase alignment of medium-size data to
1169 make it all fit in fewer cache lines. Another is to cause character
1170 arrays to be word-aligned so that @code{strcpy} calls that copy
1171 constants to character arrays can be done inline.
1174 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1175 If defined, a C expression to compute the alignment given to a constant
1176 that is being placed in memory. @var{constant} is the constant and
1177 @var{basic-align} is the alignment that the object would ordinarily
1178 have. The value of this macro is used instead of that alignment to
1181 If this macro is not defined, then @var{basic-align} is used.
1183 The typical use of this macro is to increase alignment for string
1184 constants to be word aligned so that @code{strcpy} calls that copy
1185 constants can be done inline.
1188 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1189 If defined, a C expression to compute the alignment for a variable in
1190 the local store. @var{type} is the data type, and @var{basic-align} is
1191 the alignment that the object would ordinarily have. The value of this
1192 macro is used instead of that alignment to align the object.
1194 If this macro is not defined, then @var{basic-align} is used.
1196 One use of this macro is to increase alignment of medium-size data to
1197 make it all fit in fewer cache lines.
1200 @defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
1201 If defined, a C expression to compute the alignment for stack slot.
1202 @var{type} is the data type, @var{mode} is the widest mode available,
1203 and @var{basic-align} is the alignment that the slot would ordinarily
1204 have. The value of this macro is used instead of that alignment to
1207 If this macro is not defined, then @var{basic-align} is used when
1208 @var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will
1211 This macro is to set alignment of stack slot to the maximum alignment
1212 of all possible modes which the slot may have.
1215 @defmac LOCAL_DECL_ALIGNMENT (@var{decl})
1216 If defined, a C expression to compute the alignment for a local
1217 variable @var{decl}.
1219 If this macro is not defined, then
1220 @code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
1223 One use of this macro is to increase alignment of medium-size data to
1224 make it all fit in fewer cache lines.
1227 @defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
1228 If defined, a C expression to compute the minimum required alignment
1229 for dynamic stack realignment purposes for @var{exp} (a type or decl),
1230 @var{mode}, assuming normal alignment @var{align}.
1232 If this macro is not defined, then @var{align} will be used.
1235 @defmac EMPTY_FIELD_BOUNDARY
1236 Alignment in bits to be given to a structure bit-field that follows an
1237 empty field such as @code{int : 0;}.
1239 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1242 @defmac STRUCTURE_SIZE_BOUNDARY
1243 Number of bits which any structure or union's size must be a multiple of.
1244 Each structure or union's size is rounded up to a multiple of this.
1246 If you do not define this macro, the default is the same as
1247 @code{BITS_PER_UNIT}.
1250 @defmac STRICT_ALIGNMENT
1251 Define this macro to be the value 1 if instructions will fail to work
1252 if given data not on the nominal alignment. If instructions will merely
1253 go slower in that case, define this macro as 0.
1256 @defmac PCC_BITFIELD_TYPE_MATTERS
1257 Define this if you wish to imitate the way many other C compilers handle
1258 alignment of bit-fields and the structures that contain them.
1260 The behavior is that the type written for a named bit-field (@code{int},
1261 @code{short}, or other integer type) imposes an alignment for the entire
1262 structure, as if the structure really did contain an ordinary field of
1263 that type. In addition, the bit-field is placed within the structure so
1264 that it would fit within such a field, not crossing a boundary for it.
1266 Thus, on most machines, a named bit-field whose type is written as
1267 @code{int} would not cross a four-byte boundary, and would force
1268 four-byte alignment for the whole structure. (The alignment used may
1269 not be four bytes; it is controlled by the other alignment parameters.)
1271 An unnamed bit-field will not affect the alignment of the containing
1274 If the macro is defined, its definition should be a C expression;
1275 a nonzero value for the expression enables this behavior.
1277 Note that if this macro is not defined, or its value is zero, some
1278 bit-fields may cross more than one alignment boundary. The compiler can
1279 support such references if there are @samp{insv}, @samp{extv}, and
1280 @samp{extzv} insns that can directly reference memory.
1282 The other known way of making bit-fields work is to define
1283 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1284 Then every structure can be accessed with fullwords.
1286 Unless the machine has bit-field instructions or you define
1287 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1288 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1290 If your aim is to make GCC use the same conventions for laying out
1291 bit-fields as are used by another compiler, here is how to investigate
1292 what the other compiler does. Compile and run this program:
1311 printf ("Size of foo1 is %d\n",
1312 sizeof (struct foo1));
1313 printf ("Size of foo2 is %d\n",
1314 sizeof (struct foo2));
1319 If this prints 2 and 5, then the compiler's behavior is what you would
1320 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1323 @defmac BITFIELD_NBYTES_LIMITED
1324 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1325 to aligning a bit-field within the structure.
1328 @deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELD (void)
1329 When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
1330 whether unnamed bitfields affect the alignment of the containing
1331 structure. The hook should return true if the structure should inherit
1332 the alignment requirements of an unnamed bitfield's type.
1335 @deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELD (void)
1336 This target hook should return @code{true} if accesses to volatile bitfields
1337 should use the narrowest mode possible. It should return @code{false} if
1338 these accesses should use the bitfield container type.
1340 The default is @code{!TARGET_STRICT_ALIGN}.
1343 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1344 Return 1 if a structure or array containing @var{field} should be accessed using
1347 If @var{field} is the only field in the structure, @var{mode} is its
1348 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1349 case where structures of one field would require the structure's mode to
1350 retain the field's mode.
1352 Normally, this is not needed.
1355 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1356 Define this macro as an expression for the alignment of a type (given
1357 by @var{type} as a tree node) if the alignment computed in the usual
1358 way is @var{computed} and the alignment explicitly specified was
1361 The default is to use @var{specified} if it is larger; otherwise, use
1362 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1365 @defmac MAX_FIXED_MODE_SIZE
1366 An integer expression for the size in bits of the largest integer
1367 machine mode that should actually be used. All integer machine modes of
1368 this size or smaller can be used for structures and unions with the
1369 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1370 (DImode)} is assumed.
1373 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1374 If defined, an expression of type @code{enum machine_mode} that
1375 specifies the mode of the save area operand of a
1376 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1377 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1378 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1379 having its mode specified.
1381 You need not define this macro if it always returns @code{Pmode}. You
1382 would most commonly define this macro if the
1383 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1387 @defmac STACK_SIZE_MODE
1388 If defined, an expression of type @code{enum machine_mode} that
1389 specifies the mode of the size increment operand of an
1390 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1392 You need not define this macro if it always returns @code{word_mode}.
1393 You would most commonly define this macro if the @code{allocate_stack}
1394 pattern needs to support both a 32- and a 64-bit mode.
1397 @deftypefn {Target Hook} {enum machine_mode} TARGET_LIBGCC_CMP_RETURN_MODE ()
1398 This target hook should return the mode to be used for the return value
1399 of compare instructions expanded to libgcc calls. If not defined
1400 @code{word_mode} is returned which is the right choice for a majority of
1404 @deftypefn {Target Hook} {enum machine_mode} TARGET_LIBGCC_SHIFT_COUNT_MODE ()
1405 This target hook should return the mode to be used for the shift count operand
1406 of shift instructions expanded to libgcc calls. If not defined
1407 @code{word_mode} is returned which is the right choice for a majority of
1411 @defmac ROUND_TOWARDS_ZERO
1412 If defined, this macro should be true if the prevailing rounding
1413 mode is towards zero.
1415 Defining this macro only affects the way @file{libgcc.a} emulates
1416 floating-point arithmetic.
1418 Not defining this macro is equivalent to returning zero.
1421 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1422 This macro should return true if floats with @var{size}
1423 bits do not have a NaN or infinity representation, but use the largest
1424 exponent for normal numbers instead.
1426 Defining this macro only affects the way @file{libgcc.a} emulates
1427 floating-point arithmetic.
1429 The default definition of this macro returns false for all sizes.
1432 @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type})
1433 This target hook returns @code{true} if bit-fields in the given
1434 @var{record_type} are to be laid out following the rules of Microsoft
1435 Visual C/C++, namely: (i) a bit-field won't share the same storage
1436 unit with the previous bit-field if their underlying types have
1437 different sizes, and the bit-field will be aligned to the highest
1438 alignment of the underlying types of itself and of the previous
1439 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1440 the whole enclosing structure, even if it is unnamed; except that
1441 (iii) a zero-sized bit-field will be disregarded unless it follows
1442 another bit-field of nonzero size. If this hook returns @code{true},
1443 other macros that control bit-field layout are ignored.
1445 When a bit-field is inserted into a packed record, the whole size
1446 of the underlying type is used by one or more same-size adjacent
1447 bit-fields (that is, if its long:3, 32 bits is used in the record,
1448 and any additional adjacent long bit-fields are packed into the same
1449 chunk of 32 bits. However, if the size changes, a new field of that
1450 size is allocated). In an unpacked record, this is the same as using
1451 alignment, but not equivalent when packing.
1453 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1454 the latter will take precedence. If @samp{__attribute__((packed))} is
1455 used on a single field when MS bit-fields are in use, it will take
1456 precedence for that field, but the alignment of the rest of the structure
1457 may affect its placement.
1460 @deftypefn {Target Hook} {bool} TARGET_DECIMAL_FLOAT_SUPPORTED_P (void)
1461 Returns true if the target supports decimal floating point.
1464 @deftypefn {Target Hook} {bool} TARGET_FIXED_POINT_SUPPORTED_P (void)
1465 Returns true if the target supports fixed-point arithmetic.
1468 @deftypefn {Target Hook} void TARGET_EXPAND_TO_RTL_HOOK (void)
1469 This hook is called just before expansion into rtl, allowing the target
1470 to perform additional initializations or analysis before the expansion.
1471 For example, the rs6000 port uses it to allocate a scratch stack slot
1472 for use in copying SDmode values between memory and floating point
1473 registers whenever the function being expanded has any SDmode
1477 @deftypefn {Target Hook} void TARGET_INSTANTIATE_DECLS (void)
1478 This hook allows the backend to perform additional instantiations on rtl
1479 that are not actually in any insns yet, but will be later.
1482 @deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (tree @var{type})
1483 If your target defines any fundamental types, or any types your target
1484 uses should be mangled differently from the default, define this hook
1485 to return the appropriate encoding for these types as part of a C++
1486 mangled name. The @var{type} argument is the tree structure representing
1487 the type to be mangled. The hook may be applied to trees which are
1488 not target-specific fundamental types; it should return @code{NULL}
1489 for all such types, as well as arguments it does not recognize. If the
1490 return value is not @code{NULL}, it must point to a statically-allocated
1493 Target-specific fundamental types might be new fundamental types or
1494 qualified versions of ordinary fundamental types. Encode new
1495 fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
1496 is the name used for the type in source code, and @var{n} is the
1497 length of @var{name} in decimal. Encode qualified versions of
1498 ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
1499 @var{name} is the name used for the type qualifier in source code,
1500 @var{n} is the length of @var{name} as above, and @var{code} is the
1501 code used to represent the unqualified version of this type. (See
1502 @code{write_builtin_type} in @file{cp/mangle.c} for the list of
1503 codes.) In both cases the spaces are for clarity; do not include any
1504 spaces in your string.
1506 This hook is applied to types prior to typedef resolution. If the mangled
1507 name for a particular type depends only on that type's main variant, you
1508 can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT}
1511 The default version of this hook always returns @code{NULL}, which is
1512 appropriate for a target that does not define any new fundamental
1517 @section Layout of Source Language Data Types
1519 These macros define the sizes and other characteristics of the standard
1520 basic data types used in programs being compiled. Unlike the macros in
1521 the previous section, these apply to specific features of C and related
1522 languages, rather than to fundamental aspects of storage layout.
1524 @defmac INT_TYPE_SIZE
1525 A C expression for the size in bits of the type @code{int} on the
1526 target machine. If you don't define this, the default is one word.
1529 @defmac SHORT_TYPE_SIZE
1530 A C expression for the size in bits of the type @code{short} on the
1531 target machine. If you don't define this, the default is half a word.
1532 (If this would be less than one storage unit, it is rounded up to one
1536 @defmac LONG_TYPE_SIZE
1537 A C expression for the size in bits of the type @code{long} on the
1538 target machine. If you don't define this, the default is one word.
1541 @defmac ADA_LONG_TYPE_SIZE
1542 On some machines, the size used for the Ada equivalent of the type
1543 @code{long} by a native Ada compiler differs from that used by C@. In
1544 that situation, define this macro to be a C expression to be used for
1545 the size of that type. If you don't define this, the default is the
1546 value of @code{LONG_TYPE_SIZE}.
1549 @defmac LONG_LONG_TYPE_SIZE
1550 A C expression for the size in bits of the type @code{long long} on the
1551 target machine. If you don't define this, the default is two
1552 words. If you want to support GNU Ada on your machine, the value of this
1553 macro must be at least 64.
1556 @defmac CHAR_TYPE_SIZE
1557 A C expression for the size in bits of the type @code{char} on the
1558 target machine. If you don't define this, the default is
1559 @code{BITS_PER_UNIT}.
1562 @defmac BOOL_TYPE_SIZE
1563 A C expression for the size in bits of the C++ type @code{bool} and
1564 C99 type @code{_Bool} on the target machine. If you don't define
1565 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1568 @defmac FLOAT_TYPE_SIZE
1569 A C expression for the size in bits of the type @code{float} on the
1570 target machine. If you don't define this, the default is one word.
1573 @defmac DOUBLE_TYPE_SIZE
1574 A C expression for the size in bits of the type @code{double} on the
1575 target machine. If you don't define this, the default is two
1579 @defmac LONG_DOUBLE_TYPE_SIZE
1580 A C expression for the size in bits of the type @code{long double} on
1581 the target machine. If you don't define this, the default is two
1585 @defmac SHORT_FRACT_TYPE_SIZE
1586 A C expression for the size in bits of the type @code{short _Fract} on
1587 the target machine. If you don't define this, the default is
1588 @code{BITS_PER_UNIT}.
1591 @defmac FRACT_TYPE_SIZE
1592 A C expression for the size in bits of the type @code{_Fract} on
1593 the target machine. If you don't define this, the default is
1594 @code{BITS_PER_UNIT * 2}.
1597 @defmac LONG_FRACT_TYPE_SIZE
1598 A C expression for the size in bits of the type @code{long _Fract} on
1599 the target machine. If you don't define this, the default is
1600 @code{BITS_PER_UNIT * 4}.
1603 @defmac LONG_LONG_FRACT_TYPE_SIZE
1604 A C expression for the size in bits of the type @code{long long _Fract} on
1605 the target machine. If you don't define this, the default is
1606 @code{BITS_PER_UNIT * 8}.
1609 @defmac SHORT_ACCUM_TYPE_SIZE
1610 A C expression for the size in bits of the type @code{short _Accum} on
1611 the target machine. If you don't define this, the default is
1612 @code{BITS_PER_UNIT * 2}.
1615 @defmac ACCUM_TYPE_SIZE
1616 A C expression for the size in bits of the type @code{_Accum} on
1617 the target machine. If you don't define this, the default is
1618 @code{BITS_PER_UNIT * 4}.
1621 @defmac LONG_ACCUM_TYPE_SIZE
1622 A C expression for the size in bits of the type @code{long _Accum} on
1623 the target machine. If you don't define this, the default is
1624 @code{BITS_PER_UNIT * 8}.
1627 @defmac LONG_LONG_ACCUM_TYPE_SIZE
1628 A C expression for the size in bits of the type @code{long long _Accum} on
1629 the target machine. If you don't define this, the default is
1630 @code{BITS_PER_UNIT * 16}.
1633 @defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE
1634 Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or
1635 if you want routines in @file{libgcc2.a} for a size other than
1636 @code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the
1637 default is @code{LONG_DOUBLE_TYPE_SIZE}.
1640 @defmac LIBGCC2_HAS_DF_MODE
1641 Define this macro if neither @code{LIBGCC2_DOUBLE_TYPE_SIZE} nor
1642 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is
1643 @code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a}
1644 anyway. If you don't define this and either @code{LIBGCC2_DOUBLE_TYPE_SIZE}
1645 or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1,
1649 @defmac LIBGCC2_HAS_XF_MODE
1650 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1651 @code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a}
1652 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1653 is 80 then the default is 1, otherwise it is 0.
1656 @defmac LIBGCC2_HAS_TF_MODE
1657 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1658 @code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a}
1659 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1660 is 128 then the default is 1, otherwise it is 0.
1667 Define these macros to be the size in bits of the mantissa of
1668 @code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values,
1669 if the defaults in @file{libgcc2.h} are inappropriate. By default,
1670 @code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG}
1671 for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or
1672 @code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether
1673 @code{LIBGCC2_DOUBLE_TYPE_SIZE} or
1674 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64.
1677 @defmac TARGET_FLT_EVAL_METHOD
1678 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1679 assuming, if applicable, that the floating-point control word is in its
1680 default state. If you do not define this macro the value of
1681 @code{FLT_EVAL_METHOD} will be zero.
1684 @defmac WIDEST_HARDWARE_FP_SIZE
1685 A C expression for the size in bits of the widest floating-point format
1686 supported by the hardware. If you define this macro, you must specify a
1687 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1688 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1692 @defmac DEFAULT_SIGNED_CHAR
1693 An expression whose value is 1 or 0, according to whether the type
1694 @code{char} should be signed or unsigned by default. The user can
1695 always override this default with the options @option{-fsigned-char}
1696 and @option{-funsigned-char}.
1699 @deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void)
1700 This target hook should return true if the compiler should give an
1701 @code{enum} type only as many bytes as it takes to represent the range
1702 of possible values of that type. It should return false if all
1703 @code{enum} types should be allocated like @code{int}.
1705 The default is to return false.
1709 A C expression for a string describing the name of the data type to use
1710 for size values. The typedef name @code{size_t} is defined using the
1711 contents of the string.
1713 The string can contain more than one keyword. If so, separate them with
1714 spaces, and write first any length keyword, then @code{unsigned} if
1715 appropriate, and finally @code{int}. The string must exactly match one
1716 of the data type names defined in the function
1717 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1718 omit @code{int} or change the order---that would cause the compiler to
1721 If you don't define this macro, the default is @code{"long unsigned
1725 @defmac PTRDIFF_TYPE
1726 A C expression for a string describing the name of the data type to use
1727 for the result of subtracting two pointers. The typedef name
1728 @code{ptrdiff_t} is defined using the contents of the string. See
1729 @code{SIZE_TYPE} above for more information.
1731 If you don't define this macro, the default is @code{"long int"}.
1735 A C expression for a string describing the name of the data type to use
1736 for wide characters. The typedef name @code{wchar_t} is defined using
1737 the contents of the string. See @code{SIZE_TYPE} above for more
1740 If you don't define this macro, the default is @code{"int"}.
1743 @defmac WCHAR_TYPE_SIZE
1744 A C expression for the size in bits of the data type for wide
1745 characters. This is used in @code{cpp}, which cannot make use of
1750 A C expression for a string describing the name of the data type to
1751 use for wide characters passed to @code{printf} and returned from
1752 @code{getwc}. The typedef name @code{wint_t} is defined using the
1753 contents of the string. See @code{SIZE_TYPE} above for more
1756 If you don't define this macro, the default is @code{"unsigned int"}.
1760 A C expression for a string describing the name of the data type that
1761 can represent any value of any standard or extended signed integer type.
1762 The typedef name @code{intmax_t} is defined using the contents of the
1763 string. See @code{SIZE_TYPE} above for more information.
1765 If you don't define this macro, the default is the first of
1766 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1767 much precision as @code{long long int}.
1770 @defmac UINTMAX_TYPE
1771 A C expression for a string describing the name of the data type that
1772 can represent any value of any standard or extended unsigned integer
1773 type. The typedef name @code{uintmax_t} is defined using the contents
1774 of the string. See @code{SIZE_TYPE} above for more information.
1776 If you don't define this macro, the default is the first of
1777 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1778 unsigned int"} that has as much precision as @code{long long unsigned
1782 @defmac SIG_ATOMIC_TYPE
1788 @defmacx UINT16_TYPE
1789 @defmacx UINT32_TYPE
1790 @defmacx UINT64_TYPE
1791 @defmacx INT_LEAST8_TYPE
1792 @defmacx INT_LEAST16_TYPE
1793 @defmacx INT_LEAST32_TYPE
1794 @defmacx INT_LEAST64_TYPE
1795 @defmacx UINT_LEAST8_TYPE
1796 @defmacx UINT_LEAST16_TYPE
1797 @defmacx UINT_LEAST32_TYPE
1798 @defmacx UINT_LEAST64_TYPE
1799 @defmacx INT_FAST8_TYPE
1800 @defmacx INT_FAST16_TYPE
1801 @defmacx INT_FAST32_TYPE
1802 @defmacx INT_FAST64_TYPE
1803 @defmacx UINT_FAST8_TYPE
1804 @defmacx UINT_FAST16_TYPE
1805 @defmacx UINT_FAST32_TYPE
1806 @defmacx UINT_FAST64_TYPE
1807 @defmacx INTPTR_TYPE
1808 @defmacx UINTPTR_TYPE
1809 C expressions for the standard types @code{sig_atomic_t},
1810 @code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
1811 @code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
1812 @code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
1813 @code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
1814 @code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
1815 @code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
1816 @code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
1817 @code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See
1818 @code{SIZE_TYPE} above for more information.
1820 If any of these macros evaluates to a null pointer, the corresponding
1821 type is not supported; if GCC is configured to provide
1822 @code{<stdint.h>} in such a case, the header provided may not conform
1823 to C99, depending on the type in question. The defaults for all of
1824 these macros are null pointers.
1827 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1828 The C++ compiler represents a pointer-to-member-function with a struct
1835 ptrdiff_t vtable_index;
1842 The C++ compiler must use one bit to indicate whether the function that
1843 will be called through a pointer-to-member-function is virtual.
1844 Normally, we assume that the low-order bit of a function pointer must
1845 always be zero. Then, by ensuring that the vtable_index is odd, we can
1846 distinguish which variant of the union is in use. But, on some
1847 platforms function pointers can be odd, and so this doesn't work. In
1848 that case, we use the low-order bit of the @code{delta} field, and shift
1849 the remainder of the @code{delta} field to the left.
1851 GCC will automatically make the right selection about where to store
1852 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1853 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1854 set such that functions always start at even addresses, but the lowest
1855 bit of pointers to functions indicate whether the function at that
1856 address is in ARM or Thumb mode. If this is the case of your
1857 architecture, you should define this macro to
1858 @code{ptrmemfunc_vbit_in_delta}.
1860 In general, you should not have to define this macro. On architectures
1861 in which function addresses are always even, according to
1862 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1863 @code{ptrmemfunc_vbit_in_pfn}.
1866 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1867 Normally, the C++ compiler uses function pointers in vtables. This
1868 macro allows the target to change to use ``function descriptors''
1869 instead. Function descriptors are found on targets for whom a
1870 function pointer is actually a small data structure. Normally the
1871 data structure consists of the actual code address plus a data
1872 pointer to which the function's data is relative.
1874 If vtables are used, the value of this macro should be the number
1875 of words that the function descriptor occupies.
1878 @defmac TARGET_VTABLE_ENTRY_ALIGN
1879 By default, the vtable entries are void pointers, the so the alignment
1880 is the same as pointer alignment. The value of this macro specifies
1881 the alignment of the vtable entry in bits. It should be defined only
1882 when special alignment is necessary. */
1885 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1886 There are a few non-descriptor entries in the vtable at offsets below
1887 zero. If these entries must be padded (say, to preserve the alignment
1888 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1889 of words in each data entry.
1893 @section Register Usage
1894 @cindex register usage
1896 This section explains how to describe what registers the target machine
1897 has, and how (in general) they can be used.
1899 The description of which registers a specific instruction can use is
1900 done with register classes; see @ref{Register Classes}. For information
1901 on using registers to access a stack frame, see @ref{Frame Registers}.
1902 For passing values in registers, see @ref{Register Arguments}.
1903 For returning values in registers, see @ref{Scalar Return}.
1906 * Register Basics:: Number and kinds of registers.
1907 * Allocation Order:: Order in which registers are allocated.
1908 * Values in Registers:: What kinds of values each reg can hold.
1909 * Leaf Functions:: Renumbering registers for leaf functions.
1910 * Stack Registers:: Handling a register stack such as 80387.
1913 @node Register Basics
1914 @subsection Basic Characteristics of Registers
1916 @c prevent bad page break with this line
1917 Registers have various characteristics.
1919 @defmac FIRST_PSEUDO_REGISTER
1920 Number of hardware registers known to the compiler. They receive
1921 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1922 pseudo register's number really is assigned the number
1923 @code{FIRST_PSEUDO_REGISTER}.
1926 @defmac FIXED_REGISTERS
1927 @cindex fixed register
1928 An initializer that says which registers are used for fixed purposes
1929 all throughout the compiled code and are therefore not available for
1930 general allocation. These would include the stack pointer, the frame
1931 pointer (except on machines where that can be used as a general
1932 register when no frame pointer is needed), the program counter on
1933 machines where that is considered one of the addressable registers,
1934 and any other numbered register with a standard use.
1936 This information is expressed as a sequence of numbers, separated by
1937 commas and surrounded by braces. The @var{n}th number is 1 if
1938 register @var{n} is fixed, 0 otherwise.
1940 The table initialized from this macro, and the table initialized by
1941 the following one, may be overridden at run time either automatically,
1942 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1943 the user with the command options @option{-ffixed-@var{reg}},
1944 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1947 @defmac CALL_USED_REGISTERS
1948 @cindex call-used register
1949 @cindex call-clobbered register
1950 @cindex call-saved register
1951 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1952 clobbered (in general) by function calls as well as for fixed
1953 registers. This macro therefore identifies the registers that are not
1954 available for general allocation of values that must live across
1957 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1958 automatically saves it on function entry and restores it on function
1959 exit, if the register is used within the function.
1962 @defmac CALL_REALLY_USED_REGISTERS
1963 @cindex call-used register
1964 @cindex call-clobbered register
1965 @cindex call-saved register
1966 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1967 that the entire set of @code{FIXED_REGISTERS} be included.
1968 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1969 This macro is optional. If not specified, it defaults to the value
1970 of @code{CALL_USED_REGISTERS}.
1973 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1974 @cindex call-used register
1975 @cindex call-clobbered register
1976 @cindex call-saved register
1977 A C expression that is nonzero if it is not permissible to store a
1978 value of mode @var{mode} in hard register number @var{regno} across a
1979 call without some part of it being clobbered. For most machines this
1980 macro need not be defined. It is only required for machines that do not
1981 preserve the entire contents of a register across a call.
1985 @findex call_used_regs
1988 @findex reg_class_contents
1989 @defmac CONDITIONAL_REGISTER_USAGE
1990 Zero or more C statements that may conditionally modify five variables
1991 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
1992 @code{reg_names}, and @code{reg_class_contents}, to take into account
1993 any dependence of these register sets on target flags. The first three
1994 of these are of type @code{char []} (interpreted as Boolean vectors).
1995 @code{global_regs} is a @code{const char *[]}, and
1996 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
1997 called, @code{fixed_regs}, @code{call_used_regs},
1998 @code{reg_class_contents}, and @code{reg_names} have been initialized
1999 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
2000 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
2001 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
2002 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
2003 command options have been applied.
2005 You need not define this macro if it has no work to do.
2007 @cindex disabling certain registers
2008 @cindex controlling register usage
2009 If the usage of an entire class of registers depends on the target
2010 flags, you may indicate this to GCC by using this macro to modify
2011 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
2012 registers in the classes which should not be used by GCC@. Also define
2013 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
2014 to return @code{NO_REGS} if it
2015 is called with a letter for a class that shouldn't be used.
2017 (However, if this class is not included in @code{GENERAL_REGS} and all
2018 of the insn patterns whose constraints permit this class are
2019 controlled by target switches, then GCC will automatically avoid using
2020 these registers when the target switches are opposed to them.)
2023 @defmac INCOMING_REGNO (@var{out})
2024 Define this macro if the target machine has register windows. This C
2025 expression returns the register number as seen by the called function
2026 corresponding to the register number @var{out} as seen by the calling
2027 function. Return @var{out} if register number @var{out} is not an
2031 @defmac OUTGOING_REGNO (@var{in})
2032 Define this macro if the target machine has register windows. This C
2033 expression returns the register number as seen by the calling function
2034 corresponding to the register number @var{in} as seen by the called
2035 function. Return @var{in} if register number @var{in} is not an inbound
2039 @defmac LOCAL_REGNO (@var{regno})
2040 Define this macro if the target machine has register windows. This C
2041 expression returns true if the register is call-saved but is in the
2042 register window. Unlike most call-saved registers, such registers
2043 need not be explicitly restored on function exit or during non-local
2048 If the program counter has a register number, define this as that
2049 register number. Otherwise, do not define it.
2052 @node Allocation Order
2053 @subsection Order of Allocation of Registers
2054 @cindex order of register allocation
2055 @cindex register allocation order
2057 @c prevent bad page break with this line
2058 Registers are allocated in order.
2060 @defmac REG_ALLOC_ORDER
2061 If defined, an initializer for a vector of integers, containing the
2062 numbers of hard registers in the order in which GCC should prefer
2063 to use them (from most preferred to least).
2065 If this macro is not defined, registers are used lowest numbered first
2066 (all else being equal).
2068 One use of this macro is on machines where the highest numbered
2069 registers must always be saved and the save-multiple-registers
2070 instruction supports only sequences of consecutive registers. On such
2071 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
2072 the highest numbered allocable register first.
2075 @defmac ORDER_REGS_FOR_LOCAL_ALLOC
2076 A C statement (sans semicolon) to choose the order in which to allocate
2077 hard registers for pseudo-registers local to a basic block.
2079 Store the desired register order in the array @code{reg_alloc_order}.
2080 Element 0 should be the register to allocate first; element 1, the next
2081 register; and so on.
2083 The macro body should not assume anything about the contents of
2084 @code{reg_alloc_order} before execution of the macro.
2086 On most machines, it is not necessary to define this macro.
2089 @defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
2090 In some case register allocation order is not enough for the
2091 Integrated Register Allocator (@acronym{IRA}) to generate a good code.
2092 If this macro is defined, it should return a floating point value
2093 based on @var{regno}. The cost of using @var{regno} for a pseudo will
2094 be increased by approximately the pseudo's usage frequency times the
2095 value returned by this macro. Not defining this macro is equivalent
2096 to having it always return @code{0.0}.
2098 On most machines, it is not necessary to define this macro.
2101 @node Values in Registers
2102 @subsection How Values Fit in Registers
2104 This section discusses the macros that describe which kinds of values
2105 (specifically, which machine modes) each register can hold, and how many
2106 consecutive registers are needed for a given mode.
2108 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
2109 A C expression for the number of consecutive hard registers, starting
2110 at register number @var{regno}, required to hold a value of mode
2111 @var{mode}. This macro must never return zero, even if a register
2112 cannot hold the requested mode - indicate that with HARD_REGNO_MODE_OK
2113 and/or CANNOT_CHANGE_MODE_CLASS instead.
2115 On a machine where all registers are exactly one word, a suitable
2116 definition of this macro is
2119 #define HARD_REGNO_NREGS(REGNO, MODE) \
2120 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
2125 @defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
2126 A C expression that is nonzero if a value of mode @var{mode}, stored
2127 in memory, ends with padding that causes it to take up more space than
2128 in registers starting at register number @var{regno} (as determined by
2129 multiplying GCC's notion of the size of the register when containing
2130 this mode by the number of registers returned by
2131 @code{HARD_REGNO_NREGS}). By default this is zero.
2133 For example, if a floating-point value is stored in three 32-bit
2134 registers but takes up 128 bits in memory, then this would be
2137 This macros only needs to be defined if there are cases where
2138 @code{subreg_get_info}
2139 would otherwise wrongly determine that a @code{subreg} can be
2140 represented by an offset to the register number, when in fact such a
2141 @code{subreg} would contain some of the padding not stored in
2142 registers and so not be representable.
2145 @defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
2146 For values of @var{regno} and @var{mode} for which
2147 @code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
2148 returning the greater number of registers required to hold the value
2149 including any padding. In the example above, the value would be four.
2152 @defmac REGMODE_NATURAL_SIZE (@var{mode})
2153 Define this macro if the natural size of registers that hold values
2154 of mode @var{mode} is not the word size. It is a C expression that
2155 should give the natural size in bytes for the specified mode. It is
2156 used by the register allocator to try to optimize its results. This
2157 happens for example on SPARC 64-bit where the natural size of
2158 floating-point registers is still 32-bit.
2161 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
2162 A C expression that is nonzero if it is permissible to store a value
2163 of mode @var{mode} in hard register number @var{regno} (or in several
2164 registers starting with that one). For a machine where all registers
2165 are equivalent, a suitable definition is
2168 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
2171 You need not include code to check for the numbers of fixed registers,
2172 because the allocation mechanism considers them to be always occupied.
2174 @cindex register pairs
2175 On some machines, double-precision values must be kept in even/odd
2176 register pairs. You can implement that by defining this macro to reject
2177 odd register numbers for such modes.
2179 The minimum requirement for a mode to be OK in a register is that the
2180 @samp{mov@var{mode}} instruction pattern support moves between the
2181 register and other hard register in the same class and that moving a
2182 value into the register and back out not alter it.
2184 Since the same instruction used to move @code{word_mode} will work for
2185 all narrower integer modes, it is not necessary on any machine for
2186 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
2187 you define patterns @samp{movhi}, etc., to take advantage of this. This
2188 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
2189 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
2192 Many machines have special registers for floating point arithmetic.
2193 Often people assume that floating point machine modes are allowed only
2194 in floating point registers. This is not true. Any registers that
2195 can hold integers can safely @emph{hold} a floating point machine
2196 mode, whether or not floating arithmetic can be done on it in those
2197 registers. Integer move instructions can be used to move the values.
2199 On some machines, though, the converse is true: fixed-point machine
2200 modes may not go in floating registers. This is true if the floating
2201 registers normalize any value stored in them, because storing a
2202 non-floating value there would garble it. In this case,
2203 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2204 floating registers. But if the floating registers do not automatically
2205 normalize, if you can store any bit pattern in one and retrieve it
2206 unchanged without a trap, then any machine mode may go in a floating
2207 register, so you can define this macro to say so.
2209 The primary significance of special floating registers is rather that
2210 they are the registers acceptable in floating point arithmetic
2211 instructions. However, this is of no concern to
2212 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2213 constraints for those instructions.
2215 On some machines, the floating registers are especially slow to access,
2216 so that it is better to store a value in a stack frame than in such a
2217 register if floating point arithmetic is not being done. As long as the
2218 floating registers are not in class @code{GENERAL_REGS}, they will not
2219 be used unless some pattern's constraint asks for one.
2222 @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
2223 A C expression that is nonzero if it is OK to rename a hard register
2224 @var{from} to another hard register @var{to}.
2226 One common use of this macro is to prevent renaming of a register to
2227 another register that is not saved by a prologue in an interrupt
2230 The default is always nonzero.
2233 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2234 A C expression that is nonzero if a value of mode
2235 @var{mode1} is accessible in mode @var{mode2} without copying.
2237 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2238 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2239 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2240 should be nonzero. If they differ for any @var{r}, you should define
2241 this macro to return zero unless some other mechanism ensures the
2242 accessibility of the value in a narrower mode.
2244 You should define this macro to return nonzero in as many cases as
2245 possible since doing so will allow GCC to perform better register
2249 @deftypefn {Target Hook} bool TARGET_HARD_REGNO_SCRATCH_OK (unsigned int @var{regno})
2250 This target hook should return @code{true} if it is OK to use a hard register
2251 @var{regno} as scratch reg in peephole2.
2253 One common use of this macro is to prevent using of a register that
2254 is not saved by a prologue in an interrupt handler.
2256 The default version of this hook always returns @code{true}.
2259 @defmac AVOID_CCMODE_COPIES
2260 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2261 registers. You should only define this macro if support for copying to/from
2262 @code{CCmode} is incomplete.
2265 @node Leaf Functions
2266 @subsection Handling Leaf Functions
2268 @cindex leaf functions
2269 @cindex functions, leaf
2270 On some machines, a leaf function (i.e., one which makes no calls) can run
2271 more efficiently if it does not make its own register window. Often this
2272 means it is required to receive its arguments in the registers where they
2273 are passed by the caller, instead of the registers where they would
2276 The special treatment for leaf functions generally applies only when
2277 other conditions are met; for example, often they may use only those
2278 registers for its own variables and temporaries. We use the term ``leaf
2279 function'' to mean a function that is suitable for this special
2280 handling, so that functions with no calls are not necessarily ``leaf
2283 GCC assigns register numbers before it knows whether the function is
2284 suitable for leaf function treatment. So it needs to renumber the
2285 registers in order to output a leaf function. The following macros
2288 @defmac LEAF_REGISTERS
2289 Name of a char vector, indexed by hard register number, which
2290 contains 1 for a register that is allowable in a candidate for leaf
2293 If leaf function treatment involves renumbering the registers, then the
2294 registers marked here should be the ones before renumbering---those that
2295 GCC would ordinarily allocate. The registers which will actually be
2296 used in the assembler code, after renumbering, should not be marked with 1
2299 Define this macro only if the target machine offers a way to optimize
2300 the treatment of leaf functions.
2303 @defmac LEAF_REG_REMAP (@var{regno})
2304 A C expression whose value is the register number to which @var{regno}
2305 should be renumbered, when a function is treated as a leaf function.
2307 If @var{regno} is a register number which should not appear in a leaf
2308 function before renumbering, then the expression should yield @minus{}1, which
2309 will cause the compiler to abort.
2311 Define this macro only if the target machine offers a way to optimize the
2312 treatment of leaf functions, and registers need to be renumbered to do
2316 @findex current_function_is_leaf
2317 @findex current_function_uses_only_leaf_regs
2318 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2319 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2320 specially. They can test the C variable @code{current_function_is_leaf}
2321 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2322 set prior to local register allocation and is valid for the remaining
2323 compiler passes. They can also test the C variable
2324 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2325 functions which only use leaf registers.
2326 @code{current_function_uses_only_leaf_regs} is valid after all passes
2327 that modify the instructions have been run and is only useful if
2328 @code{LEAF_REGISTERS} is defined.
2329 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2330 @c of the next paragraph?! --mew 2feb93
2332 @node Stack Registers
2333 @subsection Registers That Form a Stack
2335 There are special features to handle computers where some of the
2336 ``registers'' form a stack. Stack registers are normally written by
2337 pushing onto the stack, and are numbered relative to the top of the
2340 Currently, GCC can only handle one group of stack-like registers, and
2341 they must be consecutively numbered. Furthermore, the existing
2342 support for stack-like registers is specific to the 80387 floating
2343 point coprocessor. If you have a new architecture that uses
2344 stack-like registers, you will need to do substantial work on
2345 @file{reg-stack.c} and write your machine description to cooperate
2346 with it, as well as defining these macros.
2349 Define this if the machine has any stack-like registers.
2352 @defmac FIRST_STACK_REG
2353 The number of the first stack-like register. This one is the top
2357 @defmac LAST_STACK_REG
2358 The number of the last stack-like register. This one is the bottom of
2362 @node Register Classes
2363 @section Register Classes
2364 @cindex register class definitions
2365 @cindex class definitions, register
2367 On many machines, the numbered registers are not all equivalent.
2368 For example, certain registers may not be allowed for indexed addressing;
2369 certain registers may not be allowed in some instructions. These machine
2370 restrictions are described to the compiler using @dfn{register classes}.
2372 You define a number of register classes, giving each one a name and saying
2373 which of the registers belong to it. Then you can specify register classes
2374 that are allowed as operands to particular instruction patterns.
2378 In general, each register will belong to several classes. In fact, one
2379 class must be named @code{ALL_REGS} and contain all the registers. Another
2380 class must be named @code{NO_REGS} and contain no registers. Often the
2381 union of two classes will be another class; however, this is not required.
2383 @findex GENERAL_REGS
2384 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2385 terribly special about the name, but the operand constraint letters
2386 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2387 the same as @code{ALL_REGS}, just define it as a macro which expands
2390 Order the classes so that if class @var{x} is contained in class @var{y}
2391 then @var{x} has a lower class number than @var{y}.
2393 The way classes other than @code{GENERAL_REGS} are specified in operand
2394 constraints is through machine-dependent operand constraint letters.
2395 You can define such letters to correspond to various classes, then use
2396 them in operand constraints.
2398 You should define a class for the union of two classes whenever some
2399 instruction allows both classes. For example, if an instruction allows
2400 either a floating point (coprocessor) register or a general register for a
2401 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2402 which includes both of them. Otherwise you will get suboptimal code.
2404 You must also specify certain redundant information about the register
2405 classes: for each class, which classes contain it and which ones are
2406 contained in it; for each pair of classes, the largest class contained
2409 When a value occupying several consecutive registers is expected in a
2410 certain class, all the registers used must belong to that class.
2411 Therefore, register classes cannot be used to enforce a requirement for
2412 a register pair to start with an even-numbered register. The way to
2413 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2415 Register classes used for input-operands of bitwise-and or shift
2416 instructions have a special requirement: each such class must have, for
2417 each fixed-point machine mode, a subclass whose registers can transfer that
2418 mode to or from memory. For example, on some machines, the operations for
2419 single-byte values (@code{QImode}) are limited to certain registers. When
2420 this is so, each register class that is used in a bitwise-and or shift
2421 instruction must have a subclass consisting of registers from which
2422 single-byte values can be loaded or stored. This is so that
2423 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2425 @deftp {Data type} {enum reg_class}
2426 An enumerated type that must be defined with all the register class names
2427 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
2428 must be the last register class, followed by one more enumerated value,
2429 @code{LIM_REG_CLASSES}, which is not a register class but rather
2430 tells how many classes there are.
2432 Each register class has a number, which is the value of casting
2433 the class name to type @code{int}. The number serves as an index
2434 in many of the tables described below.
2437 @defmac N_REG_CLASSES
2438 The number of distinct register classes, defined as follows:
2441 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2445 @defmac REG_CLASS_NAMES
2446 An initializer containing the names of the register classes as C string
2447 constants. These names are used in writing some of the debugging dumps.
2450 @defmac REG_CLASS_CONTENTS
2451 An initializer containing the contents of the register classes, as integers
2452 which are bit masks. The @var{n}th integer specifies the contents of class
2453 @var{n}. The way the integer @var{mask} is interpreted is that
2454 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2456 When the machine has more than 32 registers, an integer does not suffice.
2457 Then the integers are replaced by sub-initializers, braced groupings containing
2458 several integers. Each sub-initializer must be suitable as an initializer
2459 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2460 In this situation, the first integer in each sub-initializer corresponds to
2461 registers 0 through 31, the second integer to registers 32 through 63, and
2465 @defmac REGNO_REG_CLASS (@var{regno})
2466 A C expression whose value is a register class containing hard register
2467 @var{regno}. In general there is more than one such class; choose a class
2468 which is @dfn{minimal}, meaning that no smaller class also contains the
2472 @defmac BASE_REG_CLASS
2473 A macro whose definition is the name of the class to which a valid
2474 base register must belong. A base register is one used in an address
2475 which is the register value plus a displacement.
2478 @defmac MODE_BASE_REG_CLASS (@var{mode})
2479 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2480 the selection of a base register in a mode dependent manner. If
2481 @var{mode} is VOIDmode then it should return the same value as
2482 @code{BASE_REG_CLASS}.
2485 @defmac MODE_BASE_REG_REG_CLASS (@var{mode})
2486 A C expression whose value is the register class to which a valid
2487 base register must belong in order to be used in a base plus index
2488 register address. You should define this macro if base plus index
2489 addresses have different requirements than other base register uses.
2492 @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code})
2493 A C expression whose value is the register class to which a valid
2494 base register must belong. @var{outer_code} and @var{index_code} define the
2495 context in which the base register occurs. @var{outer_code} is the code of
2496 the immediately enclosing expression (@code{MEM} for the top level of an
2497 address, @code{ADDRESS} for something that occurs in an
2498 @code{address_operand}). @var{index_code} is the code of the corresponding
2499 index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
2502 @defmac INDEX_REG_CLASS
2503 A macro whose definition is the name of the class to which a valid
2504 index register must belong. An index register is one used in an
2505 address where its value is either multiplied by a scale factor or
2506 added to another register (as well as added to a displacement).
2509 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2510 A C expression which is nonzero if register number @var{num} is
2511 suitable for use as a base register in operand addresses.
2512 Like @code{TARGET_LEGITIMATE_ADDRESS_P}, this macro should also
2513 define a strict and a non-strict variant. Both variants behave
2514 the same for hard register; for pseudos, the strict variant will
2515 pass only those that have been allocated to a valid hard registers,
2516 while the non-strict variant will pass all pseudos.
2518 @findex REG_OK_STRICT
2519 Compiler source files that want to use the strict variant of this and
2520 other macros define the macro @code{REG_OK_STRICT}. You should use an
2521 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant in
2522 that case and the non-strict variant otherwise.
2525 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2526 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2527 that expression may examine the mode of the memory reference in
2528 @var{mode}. You should define this macro if the mode of the memory
2529 reference affects whether a register may be used as a base register. If
2530 you define this macro, the compiler will use it instead of
2531 @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for
2532 addresses that appear outside a @code{MEM}, i.e., as an
2533 @code{address_operand}.
2535 This macro also has strict and non-strict variants.
2538 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
2539 A C expression which is nonzero if register number @var{num} is suitable for
2540 use as a base register in base plus index operand addresses, accessing
2541 memory in mode @var{mode}. It may be either a suitable hard register or a
2542 pseudo register that has been allocated such a hard register. You should
2543 define this macro if base plus index addresses have different requirements
2544 than other base register uses.
2546 Use of this macro is deprecated; please use the more general
2547 @code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
2549 This macro also has strict and non-strict variants.
2552 @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code})
2553 A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except
2554 that that expression may examine the context in which the register
2555 appears in the memory reference. @var{outer_code} is the code of the
2556 immediately enclosing expression (@code{MEM} if at the top level of the
2557 address, @code{ADDRESS} for something that occurs in an
2558 @code{address_operand}). @var{index_code} is the code of the
2559 corresponding index expression if @var{outer_code} is @code{PLUS};
2560 @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses
2561 that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
2563 This macro also has strict and non-strict variants.
2566 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2567 A C expression which is nonzero if register number @var{num} is
2568 suitable for use as an index register in operand addresses. It may be
2569 either a suitable hard register or a pseudo register that has been
2570 allocated such a hard register.
2572 The difference between an index register and a base register is that
2573 the index register may be scaled. If an address involves the sum of
2574 two registers, neither one of them scaled, then either one may be
2575 labeled the ``base'' and the other the ``index''; but whichever
2576 labeling is used must fit the machine's constraints of which registers
2577 may serve in each capacity. The compiler will try both labelings,
2578 looking for one that is valid, and will reload one or both registers
2579 only if neither labeling works.
2581 This macro also has strict and non-strict variants.
2584 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2585 A C expression that places additional restrictions on the register class
2586 to use when it is necessary to copy value @var{x} into a register in class
2587 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2588 another, smaller class. On many machines, the following definition is
2592 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2595 Sometimes returning a more restrictive class makes better code. For
2596 example, on the 68000, when @var{x} is an integer constant that is in range
2597 for a @samp{moveq} instruction, the value of this macro is always
2598 @code{DATA_REGS} as long as @var{class} includes the data registers.
2599 Requiring a data register guarantees that a @samp{moveq} will be used.
2601 One case where @code{PREFERRED_RELOAD_CLASS} must not return
2602 @var{class} is if @var{x} is a legitimate constant which cannot be
2603 loaded into some register class. By returning @code{NO_REGS} you can
2604 force @var{x} into a memory location. For example, rs6000 can load
2605 immediate values into general-purpose registers, but does not have an
2606 instruction for loading an immediate value into a floating-point
2607 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2608 @var{x} is a floating-point constant. If the constant can't be loaded
2609 into any kind of register, code generation will be better if
2610 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2611 of using @code{PREFERRED_RELOAD_CLASS}.
2613 If an insn has pseudos in it after register allocation, reload will go
2614 through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
2615 to find the best one. Returning @code{NO_REGS}, in this case, makes
2616 reload add a @code{!} in front of the constraint: the x86 back-end uses
2617 this feature to discourage usage of 387 registers when math is done in
2618 the SSE registers (and vice versa).
2621 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2622 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2623 input reloads. If you don't define this macro, the default is to use
2624 @var{class}, unchanged.
2626 You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
2627 reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}.
2630 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2631 A C expression that places additional restrictions on the register class
2632 to use when it is necessary to be able to hold a value of mode
2633 @var{mode} in a reload register for which class @var{class} would
2636 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2637 there are certain modes that simply can't go in certain reload classes.
2639 The value is a register class; perhaps @var{class}, or perhaps another,
2642 Don't define this macro unless the target machine has limitations which
2643 require the macro to do something nontrivial.
2646 @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})
2647 Many machines have some registers that cannot be copied directly to or
2648 from memory or even from other types of registers. An example is the
2649 @samp{MQ} register, which on most machines, can only be copied to or
2650 from general registers, but not memory. Below, we shall be using the
2651 term 'intermediate register' when a move operation cannot be performed
2652 directly, but has to be done by copying the source into the intermediate
2653 register first, and then copying the intermediate register to the
2654 destination. An intermediate register always has the same mode as
2655 source and destination. Since it holds the actual value being copied,
2656 reload might apply optimizations to re-use an intermediate register
2657 and eliding the copy from the source when it can determine that the
2658 intermediate register still holds the required value.
2660 Another kind of secondary reload is required on some machines which
2661 allow copying all registers to and from memory, but require a scratch
2662 register for stores to some memory locations (e.g., those with symbolic
2663 address on the RT, and those with certain symbolic address on the SPARC
2664 when compiling PIC)@. Scratch registers need not have the same mode
2665 as the value being copied, and usually hold a different value than
2666 that being copied. Special patterns in the md file are needed to
2667 describe how the copy is performed with the help of the scratch register;
2668 these patterns also describe the number, register class(es) and mode(s)
2669 of the scratch register(s).
2671 In some cases, both an intermediate and a scratch register are required.
2673 For input reloads, this target hook is called with nonzero @var{in_p},
2674 and @var{x} is an rtx that needs to be copied to a register of class
2675 @var{reload_class} in @var{reload_mode}. For output reloads, this target
2676 hook is called with zero @var{in_p}, and a register of class @var{reload_class}
2677 needs to be copied to rtx @var{x} in @var{reload_mode}.
2679 If copying a register of @var{reload_class} from/to @var{x} requires
2680 an intermediate register, the hook @code{secondary_reload} should
2681 return the register class required for this intermediate register.
2682 If no intermediate register is required, it should return NO_REGS.
2683 If more than one intermediate register is required, describe the one
2684 that is closest in the copy chain to the reload register.
2686 If scratch registers are needed, you also have to describe how to
2687 perform the copy from/to the reload register to/from this
2688 closest intermediate register. Or if no intermediate register is
2689 required, but still a scratch register is needed, describe the
2690 copy from/to the reload register to/from the reload operand @var{x}.
2692 You do this by setting @code{sri->icode} to the instruction code of a pattern
2693 in the md file which performs the move. Operands 0 and 1 are the output
2694 and input of this copy, respectively. Operands from operand 2 onward are
2695 for scratch operands. These scratch operands must have a mode, and a
2696 single-register-class
2697 @c [later: or memory]
2700 When an intermediate register is used, the @code{secondary_reload}
2701 hook will be called again to determine how to copy the intermediate
2702 register to/from the reload operand @var{x}, so your hook must also
2703 have code to handle the register class of the intermediate operand.
2705 @c [For later: maybe we'll allow multi-alternative reload patterns -
2706 @c the port maintainer could name a mov<mode> pattern that has clobbers -
2707 @c and match the constraints of input and output to determine the required
2708 @c alternative. A restriction would be that constraints used to match
2709 @c against reloads registers would have to be written as register class
2710 @c constraints, or we need a new target macro / hook that tells us if an
2711 @c arbitrary constraint can match an unknown register of a given class.
2712 @c Such a macro / hook would also be useful in other places.]
2715 @var{x} might be a pseudo-register or a @code{subreg} of a
2716 pseudo-register, which could either be in a hard register or in memory.
2717 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2718 in memory and the hard register number if it is in a register.
2720 Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are
2721 currently not supported. For the time being, you will have to continue
2722 to use @code{SECONDARY_MEMORY_NEEDED} for that purpose.
2724 @code{copy_cost} also uses this target hook to find out how values are
2725 copied. If you want it to include some extra cost for the need to allocate
2726 (a) scratch register(s), set @code{sri->extra_cost} to the additional cost.
2727 Or if two dependent moves are supposed to have a lower cost than the sum
2728 of the individual moves due to expected fortuitous scheduling and/or special
2729 forwarding logic, you can set @code{sri->extra_cost} to a negative amount.
2732 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2733 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2734 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2735 These macros are obsolete, new ports should use the target hook
2736 @code{TARGET_SECONDARY_RELOAD} instead.
2738 These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
2739 target hook. Older ports still define these macros to indicate to the
2740 reload phase that it may
2741 need to allocate at least one register for a reload in addition to the
2742 register to contain the data. Specifically, if copying @var{x} to a
2743 register @var{class} in @var{mode} requires an intermediate register,
2744 you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2745 largest register class all of whose registers can be used as
2746 intermediate registers or scratch registers.
2748 If copying a register @var{class} in @var{mode} to @var{x} requires an
2749 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2750 was supposed to be defined be defined to return the largest register
2751 class required. If the
2752 requirements for input and output reloads were the same, the macro
2753 @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
2756 The values returned by these macros are often @code{GENERAL_REGS}.
2757 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2758 can be directly copied to or from a register of @var{class} in
2759 @var{mode} without requiring a scratch register. Do not define this
2760 macro if it would always return @code{NO_REGS}.
2762 If a scratch register is required (either with or without an
2763 intermediate register), you were supposed to define patterns for
2764 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2765 (@pxref{Standard Names}. These patterns, which were normally
2766 implemented with a @code{define_expand}, should be similar to the
2767 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2770 These patterns need constraints for the reload register and scratch
2772 contain a single register class. If the original reload register (whose
2773 class is @var{class}) can meet the constraint given in the pattern, the
2774 value returned by these macros is used for the class of the scratch
2775 register. Otherwise, two additional reload registers are required.
2776 Their classes are obtained from the constraints in the insn pattern.
2778 @var{x} might be a pseudo-register or a @code{subreg} of a
2779 pseudo-register, which could either be in a hard register or in memory.
2780 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2781 in memory and the hard register number if it is in a register.
2783 These macros should not be used in the case where a particular class of
2784 registers can only be copied to memory and not to another class of
2785 registers. In that case, secondary reload registers are not needed and
2786 would not be helpful. Instead, a stack location must be used to perform
2787 the copy and the @code{mov@var{m}} pattern should use memory as an
2788 intermediate storage. This case often occurs between floating-point and
2792 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2793 Certain machines have the property that some registers cannot be copied
2794 to some other registers without using memory. Define this macro on
2795 those machines to be a C expression that is nonzero if objects of mode
2796 @var{m} in registers of @var{class1} can only be copied to registers of
2797 class @var{class2} by storing a register of @var{class1} into memory
2798 and loading that memory location into a register of @var{class2}.
2800 Do not define this macro if its value would always be zero.
2803 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2804 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2805 allocates a stack slot for a memory location needed for register copies.
2806 If this macro is defined, the compiler instead uses the memory location
2807 defined by this macro.
2809 Do not define this macro if you do not define
2810 @code{SECONDARY_MEMORY_NEEDED}.
2813 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2814 When the compiler needs a secondary memory location to copy between two
2815 registers of mode @var{mode}, it normally allocates sufficient memory to
2816 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2817 load operations in a mode that many bits wide and whose class is the
2818 same as that of @var{mode}.
2820 This is right thing to do on most machines because it ensures that all
2821 bits of the register are copied and prevents accesses to the registers
2822 in a narrower mode, which some machines prohibit for floating-point
2825 However, this default behavior is not correct on some machines, such as
2826 the DEC Alpha, that store short integers in floating-point registers
2827 differently than in integer registers. On those machines, the default
2828 widening will not work correctly and you must define this macro to
2829 suppress that widening in some cases. See the file @file{alpha.h} for
2832 Do not define this macro if you do not define
2833 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2834 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2837 @defmac SMALL_REGISTER_CLASSES
2838 On some machines, it is risky to let hard registers live across arbitrary
2839 insns. Typically, these machines have instructions that require values
2840 to be in specific registers (like an accumulator), and reload will fail
2841 if the required hard register is used for another purpose across such an
2844 Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero
2845 value on these machines. When this macro has a nonzero value, the
2846 compiler will try to minimize the lifetime of hard registers.
2848 It is always safe to define this macro with a nonzero value, but if you
2849 unnecessarily define it, you will reduce the amount of optimizations
2850 that can be performed in some cases. If you do not define this macro
2851 with a nonzero value when it is required, the compiler will run out of
2852 spill registers and print a fatal error message. For most machines, you
2853 should not define this macro at all.
2856 @defmac CLASS_LIKELY_SPILLED_P (@var{class})
2857 A C expression whose value is nonzero if pseudos that have been assigned
2858 to registers of class @var{class} would likely be spilled because
2859 registers of @var{class} are needed for spill registers.
2861 The default value of this macro returns 1 if @var{class} has exactly one
2862 register and zero otherwise. On most machines, this default should be
2863 used. Only define this macro to some other expression if pseudos
2864 allocated by @file{local-alloc.c} end up in memory because their hard
2865 registers were needed for spill registers. If this macro returns nonzero
2866 for those classes, those pseudos will only be allocated by
2867 @file{global.c}, which knows how to reallocate the pseudo to another
2868 register. If there would not be another register available for
2869 reallocation, you should not change the definition of this macro since
2870 the only effect of such a definition would be to slow down register
2874 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2875 A C expression for the maximum number of consecutive registers
2876 of class @var{class} needed to hold a value of mode @var{mode}.
2878 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2879 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2880 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2881 @var{mode})} for all @var{regno} values in the class @var{class}.
2883 This macro helps control the handling of multiple-word values
2887 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2888 If defined, a C expression that returns nonzero for a @var{class} for which
2889 a change from mode @var{from} to mode @var{to} is invalid.
2891 For the example, loading 32-bit integer or floating-point objects into
2892 floating-point registers on the Alpha extends them to 64 bits.
2893 Therefore loading a 64-bit object and then storing it as a 32-bit object
2894 does not store the low-order 32 bits, as would be the case for a normal
2895 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2899 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2900 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2901 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2905 @deftypefn {Target Hook} {const enum reg_class *} TARGET_IRA_COVER_CLASSES ()
2906 Return an array of cover classes for the Integrated Register Allocator
2907 (@acronym{IRA}). Cover classes are a set of non-intersecting register
2908 classes covering all hard registers used for register allocation
2909 purposes. If a move between two registers in the same cover class is
2910 possible, it should be cheaper than a load or store of the registers.
2911 The array is terminated by a @code{LIM_REG_CLASSES} element.
2913 The order of cover classes in the array is important. If two classes
2914 have the same cost of usage for a pseudo, the class occurred first in
2915 the array is chosen for the pseudo.
2917 This hook is called once at compiler startup, after the command-line
2918 options have been processed. It is then re-examined by every call to
2919 @code{target_reinit}.
2921 The default implementation returns @code{IRA_COVER_CLASSES}, if defined,
2922 otherwise there is no default implementation. You must define either this
2923 macro or @code{IRA_COVER_CLASSES} in order to use the integrated register
2924 allocator with Chaitin-Briggs coloring. If the macro is not defined,
2925 the only available coloring algorithm is Chow's priority coloring.
2928 @defmac IRA_COVER_CLASSES
2929 See the documentation for @code{TARGET_IRA_COVER_CLASSES}.
2932 @node Old Constraints
2933 @section Obsolete Macros for Defining Constraints
2934 @cindex defining constraints, obsolete method
2935 @cindex constraints, defining, obsolete method
2937 Machine-specific constraints can be defined with these macros instead
2938 of the machine description constructs described in @ref{Define
2939 Constraints}. This mechanism is obsolete. New ports should not use
2940 it; old ports should convert to the new mechanism.
2942 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2943 For the constraint at the start of @var{str}, which starts with the letter
2944 @var{c}, return the length. This allows you to have register class /
2945 constant / extra constraints that are longer than a single letter;
2946 you don't need to define this macro if you can do with single-letter
2947 constraints only. The definition of this macro should use
2948 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2949 to handle specially.
2950 There are some sanity checks in genoutput.c that check the constraint lengths
2951 for the md file, so you can also use this macro to help you while you are
2952 transitioning from a byzantine single-letter-constraint scheme: when you
2953 return a negative length for a constraint you want to re-use, genoutput
2954 will complain about every instance where it is used in the md file.
2957 @defmac REG_CLASS_FROM_LETTER (@var{char})
2958 A C expression which defines the machine-dependent operand constraint
2959 letters for register classes. If @var{char} is such a letter, the
2960 value should be the register class corresponding to it. Otherwise,
2961 the value should be @code{NO_REGS}. The register letter @samp{r},
2962 corresponding to class @code{GENERAL_REGS}, will not be passed
2963 to this macro; you do not need to handle it.
2966 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2967 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2968 passed in @var{str}, so that you can use suffixes to distinguish between
2972 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2973 A C expression that defines the machine-dependent operand constraint
2974 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2975 particular ranges of integer values. If @var{c} is one of those
2976 letters, the expression should check that @var{value}, an integer, is in
2977 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2978 not one of those letters, the value should be 0 regardless of
2982 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2983 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2984 string passed in @var{str}, so that you can use suffixes to distinguish
2985 between different variants.
2988 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
2989 A C expression that defines the machine-dependent operand constraint
2990 letters that specify particular ranges of @code{const_double} values
2991 (@samp{G} or @samp{H}).
2993 If @var{c} is one of those letters, the expression should check that
2994 @var{value}, an RTX of code @code{const_double}, is in the appropriate
2995 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
2996 letters, the value should be 0 regardless of @var{value}.
2998 @code{const_double} is used for all floating-point constants and for
2999 @code{DImode} fixed-point constants. A given letter can accept either
3000 or both kinds of values. It can use @code{GET_MODE} to distinguish
3001 between these kinds.
3004 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
3005 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
3006 string passed in @var{str}, so that you can use suffixes to distinguish
3007 between different variants.
3010 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
3011 A C expression that defines the optional machine-dependent constraint
3012 letters that can be used to segregate specific types of operands, usually
3013 memory references, for the target machine. Any letter that is not
3014 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
3015 @code{REG_CLASS_FROM_CONSTRAINT}
3016 may be used. Normally this macro will not be defined.
3018 If it is required for a particular target machine, it should return 1
3019 if @var{value} corresponds to the operand type represented by the
3020 constraint letter @var{c}. If @var{c} is not defined as an extra
3021 constraint, the value returned should be 0 regardless of @var{value}.
3023 For example, on the ROMP, load instructions cannot have their output
3024 in r0 if the memory reference contains a symbolic address. Constraint
3025 letter @samp{Q} is defined as representing a memory address that does
3026 @emph{not} contain a symbolic address. An alternative is specified with
3027 a @samp{Q} constraint on the input and @samp{r} on the output. The next
3028 alternative specifies @samp{m} on the input and a register class that
3029 does not include r0 on the output.
3032 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
3033 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
3034 in @var{str}, so that you can use suffixes to distinguish between different
3038 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
3039 A C expression that defines the optional machine-dependent constraint
3040 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
3041 be treated like memory constraints by the reload pass.
3043 It should return 1 if the operand type represented by the constraint
3044 at the start of @var{str}, the first letter of which is the letter @var{c},
3045 comprises a subset of all memory references including
3046 all those whose address is simply a base register. This allows the reload
3047 pass to reload an operand, if it does not directly correspond to the operand
3048 type of @var{c}, by copying its address into a base register.
3050 For example, on the S/390, some instructions do not accept arbitrary
3051 memory references, but only those that do not make use of an index
3052 register. The constraint letter @samp{Q} is defined via
3053 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
3054 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
3055 a @samp{Q} constraint can handle any memory operand, because the
3056 reload pass knows it can be reloaded by copying the memory address
3057 into a base register if required. This is analogous to the way
3058 an @samp{o} constraint can handle any memory operand.
3061 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
3062 A C expression that defines the optional machine-dependent constraint
3063 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
3064 @code{EXTRA_CONSTRAINT_STR}, that should
3065 be treated like address constraints by the reload pass.
3067 It should return 1 if the operand type represented by the constraint
3068 at the start of @var{str}, which starts with the letter @var{c}, comprises
3069 a subset of all memory addresses including
3070 all those that consist of just a base register. This allows the reload
3071 pass to reload an operand, if it does not directly correspond to the operand
3072 type of @var{str}, by copying it into a base register.
3074 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
3075 be used with the @code{address_operand} predicate. It is treated
3076 analogously to the @samp{p} constraint.
3079 @node Stack and Calling
3080 @section Stack Layout and Calling Conventions
3081 @cindex calling conventions
3083 @c prevent bad page break with this line
3084 This describes the stack layout and calling conventions.
3088 * Exception Handling::
3093 * Register Arguments::
3095 * Aggregate Return::
3100 * Stack Smashing Protection::
3104 @subsection Basic Stack Layout
3105 @cindex stack frame layout
3106 @cindex frame layout
3108 @c prevent bad page break with this line
3109 Here is the basic stack layout.
3111 @defmac STACK_GROWS_DOWNWARD
3112 Define this macro if pushing a word onto the stack moves the stack
3113 pointer to a smaller address.
3115 When we say, ``define this macro if @dots{}'', it means that the
3116 compiler checks this macro only with @code{#ifdef} so the precise
3117 definition used does not matter.
3120 @defmac STACK_PUSH_CODE
3121 This macro defines the operation used when something is pushed
3122 on the stack. In RTL, a push operation will be
3123 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
3125 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
3126 and @code{POST_INC}. Which of these is correct depends on
3127 the stack direction and on whether the stack pointer points
3128 to the last item on the stack or whether it points to the
3129 space for the next item on the stack.
3131 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
3132 defined, which is almost always right, and @code{PRE_INC} otherwise,
3133 which is often wrong.
3136 @defmac FRAME_GROWS_DOWNWARD
3137 Define this macro to nonzero value if the addresses of local variable slots
3138 are at negative offsets from the frame pointer.
3141 @defmac ARGS_GROW_DOWNWARD
3142 Define this macro if successive arguments to a function occupy decreasing
3143 addresses on the stack.
3146 @defmac STARTING_FRAME_OFFSET
3147 Offset from the frame pointer to the first local variable slot to be allocated.
3149 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
3150 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
3151 Otherwise, it is found by adding the length of the first slot to the
3152 value @code{STARTING_FRAME_OFFSET}.
3153 @c i'm not sure if the above is still correct.. had to change it to get
3154 @c rid of an overfull. --mew 2feb93
3157 @defmac STACK_ALIGNMENT_NEEDED
3158 Define to zero to disable final alignment of the stack during reload.
3159 The nonzero default for this macro is suitable for most ports.
3161 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
3162 is a register save block following the local block that doesn't require
3163 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
3164 stack alignment and do it in the backend.
3167 @defmac STACK_POINTER_OFFSET
3168 Offset from the stack pointer register to the first location at which
3169 outgoing arguments are placed. If not specified, the default value of
3170 zero is used. This is the proper value for most machines.
3172 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3173 the first location at which outgoing arguments are placed.
3176 @defmac FIRST_PARM_OFFSET (@var{fundecl})
3177 Offset from the argument pointer register to the first argument's
3178 address. On some machines it may depend on the data type of the
3181 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3182 the first argument's address.
3185 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
3186 Offset from the stack pointer register to an item dynamically allocated
3187 on the stack, e.g., by @code{alloca}.
3189 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
3190 length of the outgoing arguments. The default is correct for most
3191 machines. See @file{function.c} for details.
3194 @defmac INITIAL_FRAME_ADDRESS_RTX
3195 A C expression whose value is RTL representing the address of the initial
3196 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
3197 @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable
3198 default value will be used. Define this macro in order to make frame pointer
3199 elimination work in the presence of @code{__builtin_frame_address (count)} and
3200 @code{__builtin_return_address (count)} for @code{count} not equal to zero.
3203 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
3204 A C expression whose value is RTL representing the address in a stack
3205 frame where the pointer to the caller's frame is stored. Assume that
3206 @var{frameaddr} is an RTL expression for the address of the stack frame
3209 If you don't define this macro, the default is to return the value
3210 of @var{frameaddr}---that is, the stack frame address is also the
3211 address of the stack word that points to the previous frame.
3214 @defmac SETUP_FRAME_ADDRESSES
3215 If defined, a C expression that produces the machine-specific code to
3216 setup the stack so that arbitrary frames can be accessed. For example,
3217 on the SPARC, we must flush all of the register windows to the stack
3218 before we can access arbitrary stack frames. You will seldom need to
3222 @deftypefn {Target Hook} bool TARGET_BUILTIN_SETJMP_FRAME_VALUE ()
3223 This target hook should return an rtx that is used to store
3224 the address of the current frame into the built in @code{setjmp} buffer.
3225 The default value, @code{virtual_stack_vars_rtx}, is correct for most
3226 machines. One reason you may need to define this target hook is if
3227 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
3230 @defmac FRAME_ADDR_RTX (@var{frameaddr})
3231 A C expression whose value is RTL representing the value of the frame
3232 address for the current frame. @var{frameaddr} is the frame pointer
3233 of the current frame. This is used for __builtin_frame_address.
3234 You need only define this macro if the frame address is not the same
3235 as the frame pointer. Most machines do not need to define it.
3238 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
3239 A C expression whose value is RTL representing the value of the return
3240 address for the frame @var{count} steps up from the current frame, after
3241 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
3242 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
3243 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
3245 The value of the expression must always be the correct address when
3246 @var{count} is zero, but may be @code{NULL_RTX} if there is no way to
3247 determine the return address of other frames.
3250 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
3251 Define this if the return address of a particular stack frame is accessed
3252 from the frame pointer of the previous stack frame.
3255 @defmac INCOMING_RETURN_ADDR_RTX
3256 A C expression whose value is RTL representing the location of the
3257 incoming return address at the beginning of any function, before the
3258 prologue. This RTL is either a @code{REG}, indicating that the return
3259 value is saved in @samp{REG}, or a @code{MEM} representing a location in
3262 You only need to define this macro if you want to support call frame
3263 debugging information like that provided by DWARF 2.
3265 If this RTL is a @code{REG}, you should also define
3266 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
3269 @defmac DWARF_ALT_FRAME_RETURN_COLUMN
3270 A C expression whose value is an integer giving a DWARF 2 column
3271 number that may be used as an alternative return column. The column
3272 must not correspond to any gcc hard register (that is, it must not
3273 be in the range of @code{DWARF_FRAME_REGNUM}).
3275 This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
3276 general register, but an alternative column needs to be used for signal
3277 frames. Some targets have also used different frame return columns
3281 @defmac DWARF_ZERO_REG
3282 A C expression whose value is an integer giving a DWARF 2 register
3283 number that is considered to always have the value zero. This should
3284 only be defined if the target has an architected zero register, and
3285 someone decided it was a good idea to use that register number to
3286 terminate the stack backtrace. New ports should avoid this.
3289 @deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index})
3290 This target hook allows the backend to emit frame-related insns that
3291 contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
3292 info engine will invoke it on insns of the form
3294 (set (reg) (unspec [@dots{}] UNSPEC_INDEX))
3298 (set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)).
3300 to let the backend emit the call frame instructions. @var{label} is
3301 the CFI label attached to the insn, @var{pattern} is the pattern of
3302 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
3305 @defmac INCOMING_FRAME_SP_OFFSET
3306 A C expression whose value is an integer giving the offset, in bytes,
3307 from the value of the stack pointer register to the top of the stack
3308 frame at the beginning of any function, before the prologue. The top of
3309 the frame is defined to be the value of the stack pointer in the
3310 previous frame, just before the call instruction.
3312 You only need to define this macro if you want to support call frame
3313 debugging information like that provided by DWARF 2.
3316 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
3317 A C expression whose value is an integer giving the offset, in bytes,
3318 from the argument pointer to the canonical frame address (cfa). The
3319 final value should coincide with that calculated by
3320 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
3321 during virtual register instantiation.
3323 The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)},
3324 which is correct for most machines; in general, the arguments are found
3325 immediately before the stack frame. Note that this is not the case on
3326 some targets that save registers into the caller's frame, such as SPARC
3327 and rs6000, and so such targets need to define this macro.
3329 You only need to define this macro if the default is incorrect, and you
3330 want to support call frame debugging information like that provided by
3334 @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
3335 If defined, a C expression whose value is an integer giving the offset
3336 in bytes from the frame pointer to the canonical frame address (cfa).
3337 The final value should coincide with that calculated by
3338 @code{INCOMING_FRAME_SP_OFFSET}.
3340 Normally the CFA is calculated as an offset from the argument pointer,
3341 via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
3342 variable due to the ABI, this may not be possible. If this macro is
3343 defined, it implies that the virtual register instantiation should be
3344 based on the frame pointer instead of the argument pointer. Only one
3345 of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
3349 @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
3350 If defined, a C expression whose value is an integer giving the offset
3351 in bytes from the canonical frame address (cfa) to the frame base used
3352 in DWARF 2 debug information. The default is zero. A different value
3353 may reduce the size of debug information on some ports.
3356 @node Exception Handling
3357 @subsection Exception Handling Support
3358 @cindex exception handling
3360 @defmac EH_RETURN_DATA_REGNO (@var{N})
3361 A C expression whose value is the @var{N}th register number used for
3362 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
3363 @var{N} registers are usable.
3365 The exception handling library routines communicate with the exception
3366 handlers via a set of agreed upon registers. Ideally these registers
3367 should be call-clobbered; it is possible to use call-saved registers,
3368 but may negatively impact code size. The target must support at least
3369 2 data registers, but should define 4 if there are enough free registers.
3371 You must define this macro if you want to support call frame exception
3372 handling like that provided by DWARF 2.
3375 @defmac EH_RETURN_STACKADJ_RTX
3376 A C expression whose value is RTL representing a location in which
3377 to store a stack adjustment to be applied before function return.
3378 This is used to unwind the stack to an exception handler's call frame.
3379 It will be assigned zero on code paths that return normally.
3381 Typically this is a call-clobbered hard register that is otherwise
3382 untouched by the epilogue, but could also be a stack slot.
3384 Do not define this macro if the stack pointer is saved and restored
3385 by the regular prolog and epilog code in the call frame itself; in
3386 this case, the exception handling library routines will update the
3387 stack location to be restored in place. Otherwise, you must define
3388 this macro if you want to support call frame exception handling like
3389 that provided by DWARF 2.
3392 @defmac EH_RETURN_HANDLER_RTX
3393 A C expression whose value is RTL representing a location in which
3394 to store the address of an exception handler to which we should
3395 return. It will not be assigned on code paths that return normally.
3397 Typically this is the location in the call frame at which the normal
3398 return address is stored. For targets that return by popping an
3399 address off the stack, this might be a memory address just below
3400 the @emph{target} call frame rather than inside the current call
3401 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
3402 been assigned, so it may be used to calculate the location of the
3405 Some targets have more complex requirements than storing to an
3406 address calculable during initial code generation. In that case
3407 the @code{eh_return} instruction pattern should be used instead.
3409 If you want to support call frame exception handling, you must
3410 define either this macro or the @code{eh_return} instruction pattern.
3413 @defmac RETURN_ADDR_OFFSET
3414 If defined, an integer-valued C expression for which rtl will be generated
3415 to add it to the exception handler address before it is searched in the
3416 exception handling tables, and to subtract it again from the address before
3417 using it to return to the exception handler.
3420 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3421 This macro chooses the encoding of pointers embedded in the exception
3422 handling sections. If at all possible, this should be defined such
3423 that the exception handling section will not require dynamic relocations,
3424 and so may be read-only.
3426 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3427 @var{global} is true if the symbol may be affected by dynamic relocations.
3428 The macro should return a combination of the @code{DW_EH_PE_*} defines
3429 as found in @file{dwarf2.h}.
3431 If this macro is not defined, pointers will not be encoded but
3432 represented directly.
3435 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3436 This macro allows the target to emit whatever special magic is required
3437 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3438 Generic code takes care of pc-relative and indirect encodings; this must
3439 be defined if the target uses text-relative or data-relative encodings.
3441 This is a C statement that branches to @var{done} if the format was
3442 handled. @var{encoding} is the format chosen, @var{size} is the number
3443 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3447 @defmac MD_UNWIND_SUPPORT
3448 A string specifying a file to be #include'd in unwind-dw2.c. The file
3449 so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}.
3452 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
3453 This macro allows the target to add CPU and operating system specific
3454 code to the call-frame unwinder for use when there is no unwind data
3455 available. The most common reason to implement this macro is to unwind
3456 through signal frames.
3458 This macro is called from @code{uw_frame_state_for} in
3459 @file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
3460 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3461 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3462 for the address of the code being executed and @code{context->cfa} for
3463 the stack pointer value. If the frame can be decoded, the register
3464 save addresses should be updated in @var{fs} and the macro should
3465 evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded,
3466 the macro should evaluate to @code{_URC_END_OF_STACK}.
3468 For proper signal handling in Java this macro is accompanied by
3469 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3472 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
3473 This macro allows the target to add operating system specific code to the
3474 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
3475 usually used for signal or interrupt frames.
3477 This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}.
3478 @var{context} is an @code{_Unwind_Context};
3479 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
3480 for the abi and context in the @code{.unwabi} directive. If the
3481 @code{.unwabi} directive can be handled, the register save addresses should
3482 be updated in @var{fs}.
3485 @defmac TARGET_USES_WEAK_UNWIND_INFO
3486 A C expression that evaluates to true if the target requires unwind
3487 info to be given comdat linkage. Define it to be @code{1} if comdat
3488 linkage is necessary. The default is @code{0}.
3491 @node Stack Checking
3492 @subsection Specifying How Stack Checking is Done
3494 GCC will check that stack references are within the boundaries of the
3495 stack, if the option @option{-fstack-check} is specified, in one of
3500 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3501 will assume that you have arranged for full stack checking to be done
3502 at appropriate places in the configuration files. GCC will not do
3503 other special processing.
3506 If @code{STACK_CHECK_BUILTIN} is zero and the value of the
3507 @code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
3508 that you have arranged for static stack checking (checking of the
3509 static stack frame of functions) to be done at appropriate places
3510 in the configuration files. GCC will only emit code to do dynamic
3511 stack checking (checking on dynamic stack allocations) using the third
3515 If neither of the above are true, GCC will generate code to periodically
3516 ``probe'' the stack pointer using the values of the macros defined below.
3519 If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
3520 GCC will change its allocation strategy for large objects if the option
3521 @option{-fstack-check} is specified: they will always be allocated
3522 dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
3524 @defmac STACK_CHECK_BUILTIN
3525 A nonzero value if stack checking is done by the configuration files in a
3526 machine-dependent manner. You should define this macro if stack checking
3527 is require by the ABI of your machine or if you would like to do stack
3528 checking in some more efficient way than the generic approach. The default
3529 value of this macro is zero.
3532 @defmac STACK_CHECK_STATIC_BUILTIN
3533 A nonzero value if static stack checking is done by the configuration files
3534 in a machine-dependent manner. You should define this macro if you would
3535 like to do static stack checking in some more efficient way than the generic
3536 approach. The default value of this macro is zero.
3539 @defmac STACK_CHECK_PROBE_INTERVAL
3540 An integer representing the interval at which GCC must generate stack
3541 probe instructions. You will normally define this macro to be no larger
3542 than the size of the ``guard pages'' at the end of a stack area. The
3543 default value of 4096 is suitable for most systems.
3546 @defmac STACK_CHECK_PROBE_LOAD
3547 An integer which is nonzero if GCC should perform the stack probe
3548 as a load instruction and zero if GCC should use a store instruction.
3549 The default is zero, which is the most efficient choice on most systems.
3552 @defmac STACK_CHECK_PROTECT
3553 The number of bytes of stack needed to recover from a stack overflow,
3554 for languages where such a recovery is supported. The default value of
3555 75 words should be adequate for most machines.
3558 The following macros are relevant only if neither STACK_CHECK_BUILTIN
3559 nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
3560 in the opposite case.
3562 @defmac STACK_CHECK_MAX_FRAME_SIZE
3563 The maximum size of a stack frame, in bytes. GCC will generate probe
3564 instructions in non-leaf functions to ensure at least this many bytes of
3565 stack are available. If a stack frame is larger than this size, stack
3566 checking will not be reliable and GCC will issue a warning. The
3567 default is chosen so that GCC only generates one instruction on most
3568 systems. You should normally not change the default value of this macro.
3571 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3572 GCC uses this value to generate the above warning message. It
3573 represents the amount of fixed frame used by a function, not including
3574 space for any callee-saved registers, temporaries and user variables.
3575 You need only specify an upper bound for this amount and will normally
3576 use the default of four words.
3579 @defmac STACK_CHECK_MAX_VAR_SIZE
3580 The maximum size, in bytes, of an object that GCC will place in the
3581 fixed area of the stack frame when the user specifies
3582 @option{-fstack-check}.
3583 GCC computed the default from the values of the above macros and you will
3584 normally not need to override that default.
3588 @node Frame Registers
3589 @subsection Registers That Address the Stack Frame
3591 @c prevent bad page break with this line
3592 This discusses registers that address the stack frame.
3594 @defmac STACK_POINTER_REGNUM
3595 The register number of the stack pointer register, which must also be a
3596 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3597 the hardware determines which register this is.
3600 @defmac FRAME_POINTER_REGNUM
3601 The register number of the frame pointer register, which is used to
3602 access automatic variables in the stack frame. On some machines, the
3603 hardware determines which register this is. On other machines, you can
3604 choose any register you wish for this purpose.
3607 @defmac HARD_FRAME_POINTER_REGNUM
3608 On some machines the offset between the frame pointer and starting
3609 offset of the automatic variables is not known until after register
3610 allocation has been done (for example, because the saved registers are
3611 between these two locations). On those machines, define
3612 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3613 be used internally until the offset is known, and define
3614 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3615 used for the frame pointer.
3617 You should define this macro only in the very rare circumstances when it
3618 is not possible to calculate the offset between the frame pointer and
3619 the automatic variables until after register allocation has been
3620 completed. When this macro is defined, you must also indicate in your
3621 definition of @code{ELIMINABLE_REGS} how to eliminate
3622 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3623 or @code{STACK_POINTER_REGNUM}.
3625 Do not define this macro if it would be the same as
3626 @code{FRAME_POINTER_REGNUM}.
3629 @defmac ARG_POINTER_REGNUM
3630 The register number of the arg pointer register, which is used to access
3631 the function's argument list. On some machines, this is the same as the
3632 frame pointer register. On some machines, the hardware determines which
3633 register this is. On other machines, you can choose any register you
3634 wish for this purpose. If this is not the same register as the frame
3635 pointer register, then you must mark it as a fixed register according to
3636 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3637 (@pxref{Elimination}).
3640 @defmac RETURN_ADDRESS_POINTER_REGNUM
3641 The register number of the return address pointer register, which is used to
3642 access the current function's return address from the stack. On some
3643 machines, the return address is not at a fixed offset from the frame
3644 pointer or stack pointer or argument pointer. This register can be defined
3645 to point to the return address on the stack, and then be converted by
3646 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3648 Do not define this macro unless there is no other way to get the return
3649 address from the stack.
3652 @defmac STATIC_CHAIN_REGNUM
3653 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3654 Register numbers used for passing a function's static chain pointer. If
3655 register windows are used, the register number as seen by the called
3656 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3657 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3658 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3661 The static chain register need not be a fixed register.
3663 If the static chain is passed in memory, these macros should not be
3664 defined; instead, the next two macros should be defined.
3667 @defmac STATIC_CHAIN
3668 @defmacx STATIC_CHAIN_INCOMING
3669 If the static chain is passed in memory, these macros provide rtx giving
3670 @code{mem} expressions that denote where they are stored.
3671 @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations
3672 as seen by the calling and called functions, respectively. Often the former
3673 will be at an offset from the stack pointer and the latter at an offset from
3676 @findex stack_pointer_rtx
3677 @findex frame_pointer_rtx
3678 @findex arg_pointer_rtx
3679 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3680 @code{arg_pointer_rtx} will have been initialized prior to the use of these
3681 macros and should be used to refer to those items.
3683 If the static chain is passed in a register, the two previous macros should
3687 @defmac DWARF_FRAME_REGISTERS
3688 This macro specifies the maximum number of hard registers that can be
3689 saved in a call frame. This is used to size data structures used in
3690 DWARF2 exception handling.
3692 Prior to GCC 3.0, this macro was needed in order to establish a stable
3693 exception handling ABI in the face of adding new hard registers for ISA
3694 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3695 in the number of hard registers. Nevertheless, this macro can still be
3696 used to reduce the runtime memory requirements of the exception handling
3697 routines, which can be substantial if the ISA contains a lot of
3698 registers that are not call-saved.
3700 If this macro is not defined, it defaults to
3701 @code{FIRST_PSEUDO_REGISTER}.
3704 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3706 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3707 for backward compatibility in pre GCC 3.0 compiled code.
3709 If this macro is not defined, it defaults to
3710 @code{DWARF_FRAME_REGISTERS}.
3713 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3715 Define this macro if the target's representation for dwarf registers
3716 is different than the internal representation for unwind column.
3717 Given a dwarf register, this macro should return the internal unwind
3718 column number to use instead.
3720 See the PowerPC's SPE target for an example.
3723 @defmac DWARF_FRAME_REGNUM (@var{regno})
3725 Define this macro if the target's representation for dwarf registers
3726 used in .eh_frame or .debug_frame is different from that used in other
3727 debug info sections. Given a GCC hard register number, this macro
3728 should return the .eh_frame register number. The default is
3729 @code{DBX_REGISTER_NUMBER (@var{regno})}.
3733 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
3735 Define this macro to map register numbers held in the call frame info
3736 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
3737 should be output in .debug_frame (@code{@var{for_eh}} is zero) and
3738 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to
3739 return @code{@var{regno}}.
3744 @subsection Eliminating Frame Pointer and Arg Pointer
3746 @c prevent bad page break with this line
3747 This is about eliminating the frame pointer and arg pointer.
3749 @deftypefn {Target Hook} bool TARGET_FRAME_POINTER_REQUIRED (void)
3750 This target hook should return @code{true} if a function must have and use
3751 a frame pointer. This target hook is called in the reload pass. If its return
3752 value is @code{true} the function will have a frame pointer.
3754 This target hook can in principle examine the current function and decide
3755 according to the facts, but on most machines the constant @code{false} or the
3756 constant @code{true} suffices. Use @code{false} when the machine allows code
3757 to be generated with no frame pointer, and doing so saves some time or space.
3758 Use @code{true} when there is no possible advantage to avoiding a frame
3761 In certain cases, the compiler does not know how to produce valid code
3762 without a frame pointer. The compiler recognizes those cases and
3763 automatically gives the function a frame pointer regardless of what
3764 @code{TARGET_FRAME_POINTER_REQUIRED} returns. You don't need to worry about
3767 In a function that does not require a frame pointer, the frame pointer
3768 register can be allocated for ordinary usage, unless you mark it as a
3769 fixed register. See @code{FIXED_REGISTERS} for more information.
3771 Default return value is @code{false}.
3774 @findex get_frame_size
3775 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3776 A C statement to store in the variable @var{depth-var} the difference
3777 between the frame pointer and the stack pointer values immediately after
3778 the function prologue. The value would be computed from information
3779 such as the result of @code{get_frame_size ()} and the tables of
3780 registers @code{regs_ever_live} and @code{call_used_regs}.
3782 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3783 need not be defined. Otherwise, it must be defined even if
3784 @code{TARGET_FRAME_POINTER_REQUIRED} is always return true; in that
3785 case, you may set @var{depth-var} to anything.
3788 @defmac ELIMINABLE_REGS
3789 If defined, this macro specifies a table of register pairs used to
3790 eliminate unneeded registers that point into the stack frame. If it is not
3791 defined, the only elimination attempted by the compiler is to replace
3792 references to the frame pointer with references to the stack pointer.
3794 The definition of this macro is a list of structure initializations, each
3795 of which specifies an original and replacement register.
3797 On some machines, the position of the argument pointer is not known until
3798 the compilation is completed. In such a case, a separate hard register
3799 must be used for the argument pointer. This register can be eliminated by
3800 replacing it with either the frame pointer or the argument pointer,
3801 depending on whether or not the frame pointer has been eliminated.
3803 In this case, you might specify:
3805 #define ELIMINABLE_REGS \
3806 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3807 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3808 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3811 Note that the elimination of the argument pointer with the stack pointer is
3812 specified first since that is the preferred elimination.
3815 @defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg})
3816 A C expression that returns @code{true} if the compiler is allowed to try
3817 to replace register number @var{from-reg} with register number
3818 @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS}
3819 is defined, and will usually be @code{true}, since most of the cases
3820 preventing register elimination are things that the compiler already
3823 Default value is @code{true}.
3826 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3827 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3828 specifies the initial difference between the specified pair of
3829 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3833 @node Stack Arguments
3834 @subsection Passing Function Arguments on the Stack
3835 @cindex arguments on stack
3836 @cindex stack arguments
3838 The macros in this section control how arguments are passed
3839 on the stack. See the following section for other macros that
3840 control passing certain arguments in registers.
3842 @deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (tree @var{fntype})
3843 This target hook returns @code{true} if an argument declared in a
3844 prototype as an integral type smaller than @code{int} should actually be
3845 passed as an @code{int}. In addition to avoiding errors in certain
3846 cases of mismatch, it also makes for better code on certain machines.
3847 The default is to not promote prototypes.
3851 A C expression. If nonzero, push insns will be used to pass
3853 If the target machine does not have a push instruction, set it to zero.
3854 That directs GCC to use an alternate strategy: to
3855 allocate the entire argument block and then store the arguments into
3856 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3859 @defmac PUSH_ARGS_REVERSED
3860 A C expression. If nonzero, function arguments will be evaluated from
3861 last to first, rather than from first to last. If this macro is not
3862 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3863 and args grow in opposite directions, and 0 otherwise.
3866 @defmac PUSH_ROUNDING (@var{npushed})
3867 A C expression that is the number of bytes actually pushed onto the
3868 stack when an instruction attempts to push @var{npushed} bytes.
3870 On some machines, the definition
3873 #define PUSH_ROUNDING(BYTES) (BYTES)
3877 will suffice. But on other machines, instructions that appear
3878 to push one byte actually push two bytes in an attempt to maintain
3879 alignment. Then the definition should be
3882 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3886 @findex current_function_outgoing_args_size
3887 @defmac ACCUMULATE_OUTGOING_ARGS
3888 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3889 will be computed and placed into the variable
3890 @code{current_function_outgoing_args_size}. No space will be pushed
3891 onto the stack for each call; instead, the function prologue should
3892 increase the stack frame size by this amount.
3894 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3898 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3899 Define this macro if functions should assume that stack space has been
3900 allocated for arguments even when their values are passed in
3903 The value of this macro is the size, in bytes, of the area reserved for
3904 arguments passed in registers for the function represented by @var{fndecl},
3905 which can be zero if GCC is calling a library function.
3906 The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
3909 This space can be allocated by the caller, or be a part of the
3910 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3913 @c above is overfull. not sure what to do. --mew 5feb93 did
3914 @c something, not sure if it looks good. --mew 10feb93
3916 @defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
3917 Define this to a nonzero value if it is the responsibility of the
3918 caller to allocate the area reserved for arguments passed in registers
3919 when calling a function of @var{fntype}. @var{fntype} may be NULL
3920 if the function called is a library function.
3922 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3923 whether the space for these arguments counts in the value of
3924 @code{current_function_outgoing_args_size}.
3927 @defmac STACK_PARMS_IN_REG_PARM_AREA
3928 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3929 stack parameters don't skip the area specified by it.
3930 @c i changed this, makes more sens and it should have taken care of the
3931 @c overfull.. not as specific, tho. --mew 5feb93
3933 Normally, when a parameter is not passed in registers, it is placed on the
3934 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3935 suppresses this behavior and causes the parameter to be passed on the
3936 stack in its natural location.
3939 @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size})
3940 A C expression that should indicate the number of bytes of its own
3941 arguments that a function pops on returning, or 0 if the
3942 function pops no arguments and the caller must therefore pop them all
3943 after the function returns.
3945 @var{fundecl} is a C variable whose value is a tree node that describes
3946 the function in question. Normally it is a node of type
3947 @code{FUNCTION_DECL} that describes the declaration of the function.
3948 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3950 @var{funtype} is a C variable whose value is a tree node that
3951 describes the function in question. Normally it is a node of type
3952 @code{FUNCTION_TYPE} that describes the data type of the function.
3953 From this it is possible to obtain the data types of the value and
3954 arguments (if known).
3956 When a call to a library function is being considered, @var{fundecl}
3957 will contain an identifier node for the library function. Thus, if
3958 you need to distinguish among various library functions, you can do so
3959 by their names. Note that ``library function'' in this context means
3960 a function used to perform arithmetic, whose name is known specially
3961 in the compiler and was not mentioned in the C code being compiled.
3963 @var{stack-size} is the number of bytes of arguments passed on the
3964 stack. If a variable number of bytes is passed, it is zero, and
3965 argument popping will always be the responsibility of the calling function.
3967 On the VAX, all functions always pop their arguments, so the definition
3968 of this macro is @var{stack-size}. On the 68000, using the standard
3969 calling convention, no functions pop their arguments, so the value of
3970 the macro is always 0 in this case. But an alternative calling
3971 convention is available in which functions that take a fixed number of
3972 arguments pop them but other functions (such as @code{printf}) pop
3973 nothing (the caller pops all). When this convention is in use,
3974 @var{funtype} is examined to determine whether a function takes a fixed
3975 number of arguments.
3978 @defmac CALL_POPS_ARGS (@var{cum})
3979 A C expression that should indicate the number of bytes a call sequence
3980 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3981 when compiling a function call.
3983 @var{cum} is the variable in which all arguments to the called function
3984 have been accumulated.
3986 On certain architectures, such as the SH5, a call trampoline is used
3987 that pops certain registers off the stack, depending on the arguments
3988 that have been passed to the function. Since this is a property of the
3989 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3993 @node Register Arguments
3994 @subsection Passing Arguments in Registers
3995 @cindex arguments in registers
3996 @cindex registers arguments
3998 This section describes the macros which let you control how various
3999 types of arguments are passed in registers or how they are arranged in
4002 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
4003 A C expression that controls whether a function argument is passed
4004 in a register, and which register.
4006 The arguments are @var{cum}, which summarizes all the previous
4007 arguments; @var{mode}, the machine mode of the argument; @var{type},
4008 the data type of the argument as a tree node or 0 if that is not known
4009 (which happens for C support library functions); and @var{named},
4010 which is 1 for an ordinary argument and 0 for nameless arguments that
4011 correspond to @samp{@dots{}} in the called function's prototype.
4012 @var{type} can be an incomplete type if a syntax error has previously
4015 The value of the expression is usually either a @code{reg} RTX for the
4016 hard register in which to pass the argument, or zero to pass the
4017 argument on the stack.
4019 For machines like the VAX and 68000, where normally all arguments are
4020 pushed, zero suffices as a definition.
4022 The value of the expression can also be a @code{parallel} RTX@. This is
4023 used when an argument is passed in multiple locations. The mode of the
4024 @code{parallel} should be the mode of the entire argument. The
4025 @code{parallel} holds any number of @code{expr_list} pairs; each one
4026 describes where part of the argument is passed. In each
4027 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
4028 register in which to pass this part of the argument, and the mode of the
4029 register RTX indicates how large this part of the argument is. The
4030 second operand of the @code{expr_list} is a @code{const_int} which gives
4031 the offset in bytes into the entire argument of where this part starts.
4032 As a special exception the first @code{expr_list} in the @code{parallel}
4033 RTX may have a first operand of zero. This indicates that the entire
4034 argument is also stored on the stack.
4036 The last time this macro is called, it is called with @code{MODE ==
4037 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
4038 pattern as operands 2 and 3 respectively.
4040 @cindex @file{stdarg.h} and register arguments
4041 The usual way to make the ISO library @file{stdarg.h} work on a machine
4042 where some arguments are usually passed in registers, is to cause
4043 nameless arguments to be passed on the stack instead. This is done
4044 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
4046 @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
4047 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
4048 You may use the hook @code{targetm.calls.must_pass_in_stack}
4049 in the definition of this macro to determine if this argument is of a
4050 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
4051 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
4052 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
4053 defined, the argument will be computed in the stack and then loaded into
4057 @deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (enum machine_mode @var{mode}, tree @var{type})
4058 This target hook should return @code{true} if we should not pass @var{type}
4059 solely in registers. The file @file{expr.h} defines a
4060 definition that is usually appropriate, refer to @file{expr.h} for additional
4064 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
4065 Define this macro if the target machine has ``register windows'', so
4066 that the register in which a function sees an arguments is not
4067 necessarily the same as the one in which the caller passed the
4070 For such machines, @code{FUNCTION_ARG} computes the register in which
4071 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
4072 be defined in a similar fashion to tell the function being called
4073 where the arguments will arrive.
4075 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
4076 serves both purposes.
4079 @deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
4080 This target hook returns the number of bytes at the beginning of an
4081 argument that must be put in registers. The value must be zero for
4082 arguments that are passed entirely in registers or that are entirely
4083 pushed on the stack.
4085 On some machines, certain arguments must be passed partially in
4086 registers and partially in memory. On these machines, typically the
4087 first few words of arguments are passed in registers, and the rest
4088 on the stack. If a multi-word argument (a @code{double} or a
4089 structure) crosses that boundary, its first few words must be passed
4090 in registers and the rest must be pushed. This macro tells the
4091 compiler when this occurs, and how many bytes should go in registers.
4093 @code{FUNCTION_ARG} for these arguments should return the first
4094 register to be used by the caller for this argument; likewise
4095 @code{FUNCTION_INCOMING_ARG}, for the called function.
4098 @deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
4099 This target hook should return @code{true} if an argument at the
4100 position indicated by @var{cum} should be passed by reference. This
4101 predicate is queried after target independent reasons for being
4102 passed by reference, such as @code{TREE_ADDRESSABLE (type)}.
4104 If the hook returns true, a copy of that argument is made in memory and a
4105 pointer to the argument is passed instead of the argument itself.
4106 The pointer is passed in whatever way is appropriate for passing a pointer
4110 @deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
4111 The function argument described by the parameters to this hook is
4112 known to be passed by reference. The hook should return true if the
4113 function argument should be copied by the callee instead of copied
4116 For any argument for which the hook returns true, if it can be
4117 determined that the argument is not modified, then a copy need
4120 The default version of this hook always returns false.
4123 @defmac CUMULATIVE_ARGS
4124 A C type for declaring a variable that is used as the first argument of
4125 @code{FUNCTION_ARG} and other related values. For some target machines,
4126 the type @code{int} suffices and can hold the number of bytes of
4129 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
4130 arguments that have been passed on the stack. The compiler has other
4131 variables to keep track of that. For target machines on which all
4132 arguments are passed on the stack, there is no need to store anything in
4133 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
4134 should not be empty, so use @code{int}.
4137 @defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
4138 If defined, this macro is called before generating any code for a
4139 function, but after the @var{cfun} descriptor for the function has been
4140 created. The back end may use this macro to update @var{cfun} to
4141 reflect an ABI other than that which would normally be used by default.
4142 If the compiler is generating code for a compiler-generated function,
4143 @var{fndecl} may be @code{NULL}.
4146 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
4147 A C statement (sans semicolon) for initializing the variable
4148 @var{cum} for the state at the beginning of the argument list. The
4149 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
4150 is the tree node for the data type of the function which will receive
4151 the args, or 0 if the args are to a compiler support library function.
4152 For direct calls that are not libcalls, @var{fndecl} contain the
4153 declaration node of the function. @var{fndecl} is also set when
4154 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
4155 being compiled. @var{n_named_args} is set to the number of named
4156 arguments, including a structure return address if it is passed as a
4157 parameter, when making a call. When processing incoming arguments,
4158 @var{n_named_args} is set to @minus{}1.
4160 When processing a call to a compiler support library function,
4161 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
4162 contains the name of the function, as a string. @var{libname} is 0 when
4163 an ordinary C function call is being processed. Thus, each time this
4164 macro is called, either @var{libname} or @var{fntype} is nonzero, but
4165 never both of them at once.
4168 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
4169 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
4170 it gets a @code{MODE} argument instead of @var{fntype}, that would be
4171 @code{NULL}. @var{indirect} would always be zero, too. If this macro
4172 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
4173 0)} is used instead.
4176 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
4177 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
4178 finding the arguments for the function being compiled. If this macro is
4179 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
4181 The value passed for @var{libname} is always 0, since library routines
4182 with special calling conventions are never compiled with GCC@. The
4183 argument @var{libname} exists for symmetry with
4184 @code{INIT_CUMULATIVE_ARGS}.
4185 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
4186 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
4189 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
4190 A C statement (sans semicolon) to update the summarizer variable
4191 @var{cum} to advance past an argument in the argument list. The
4192 values @var{mode}, @var{type} and @var{named} describe that argument.
4193 Once this is done, the variable @var{cum} is suitable for analyzing
4194 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
4196 This macro need not do anything if the argument in question was passed
4197 on the stack. The compiler knows how to track the amount of stack space
4198 used for arguments without any special help.
4202 @defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type})
4203 If defined, a C expression that is the number of bytes to add to the
4204 offset of the argument passed in memory. This is needed for the SPU,
4205 which passes @code{char} and @code{short} arguments in the preferred
4206 slot that is in the middle of the quad word instead of starting at the
4210 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
4211 If defined, a C expression which determines whether, and in which direction,
4212 to pad out an argument with extra space. The value should be of type
4213 @code{enum direction}: either @code{upward} to pad above the argument,
4214 @code{downward} to pad below, or @code{none} to inhibit padding.
4216 The @emph{amount} of padding is always just enough to reach the next
4217 multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control
4220 This macro has a default definition which is right for most systems.
4221 For little-endian machines, the default is to pad upward. For
4222 big-endian machines, the default is to pad downward for an argument of
4223 constant size shorter than an @code{int}, and upward otherwise.
4226 @defmac PAD_VARARGS_DOWN
4227 If defined, a C expression which determines whether the default
4228 implementation of va_arg will attempt to pad down before reading the
4229 next argument, if that argument is smaller than its aligned space as
4230 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
4231 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
4234 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
4235 Specify padding for the last element of a block move between registers and
4236 memory. @var{first} is nonzero if this is the only element. Defining this
4237 macro allows better control of register function parameters on big-endian
4238 machines, without using @code{PARALLEL} rtl. In particular,
4239 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
4240 registers, as there is no longer a "wrong" part of a register; For example,
4241 a three byte aggregate may be passed in the high part of a register if so
4245 @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type})
4246 If defined, a C expression that gives the alignment boundary, in bits,
4247 of an argument with the specified mode and type. If it is not defined,
4248 @code{PARM_BOUNDARY} is used for all arguments.
4251 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
4252 A C expression that is nonzero if @var{regno} is the number of a hard
4253 register in which function arguments are sometimes passed. This does
4254 @emph{not} include implicit arguments such as the static chain and
4255 the structure-value address. On many machines, no registers can be
4256 used for this purpose since all function arguments are pushed on the
4260 @deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (tree @var{type})
4261 This hook should return true if parameter of type @var{type} are passed
4262 as two scalar parameters. By default, GCC will attempt to pack complex
4263 arguments into the target's word size. Some ABIs require complex arguments
4264 to be split and treated as their individual components. For example, on
4265 AIX64, complex floats should be passed in a pair of floating point
4266 registers, even though a complex float would fit in one 64-bit floating
4269 The default value of this hook is @code{NULL}, which is treated as always
4273 @deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void)
4274 This hook returns a type node for @code{va_list} for the target.
4275 The default version of the hook returns @code{void*}.
4278 @deftypefn {Target Hook} tree TARGET_FN_ABI_VA_LIST (tree @var{fndecl})
4279 This hook returns the va_list type of the calling convention specified by
4281 The default version of this hook returns @code{va_list_type_node}.
4284 @deftypefn {Target Hook} tree TARGET_CANONICAL_VA_LIST_TYPE (tree @var{type})
4285 This hook returns the va_list type of the calling convention specified by the
4286 type of @var{type}. If @var{type} is not a valid va_list type, it returns
4290 @deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, tree *@var{pre_p}, tree *@var{post_p})
4291 This hook performs target-specific gimplification of
4292 @code{VA_ARG_EXPR}. The first two parameters correspond to the
4293 arguments to @code{va_arg}; the latter two are as in
4294 @code{gimplify.c:gimplify_expr}.
4297 @deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (enum machine_mode @var{mode})
4298 Define this to return nonzero if the port can handle pointers
4299 with machine mode @var{mode}. The default version of this
4300 hook returns true for both @code{ptr_mode} and @code{Pmode}.
4303 @deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
4304 Define this to return nonzero if the port is prepared to handle
4305 insns involving scalar mode @var{mode}. For a scalar mode to be
4306 considered supported, all the basic arithmetic and comparisons
4309 The default version of this hook returns true for any mode
4310 required to handle the basic C types (as defined by the port).
4311 Included here are the double-word arithmetic supported by the
4312 code in @file{optabs.c}.
4315 @deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
4316 Define this to return nonzero if the port is prepared to handle
4317 insns involving vector mode @var{mode}. At the very least, it
4318 must have move patterns for this mode.
4322 @subsection How Scalar Function Values Are Returned
4323 @cindex return values in registers
4324 @cindex values, returned by functions
4325 @cindex scalars, returned as values
4327 This section discusses the macros that control returning scalars as
4328 values---values that can fit in registers.
4330 @deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (tree @var{ret_type}, tree @var{fn_decl_or_type}, bool @var{outgoing})
4332 Define this to return an RTX representing the place where a function
4333 returns or receives a value of data type @var{ret_type}, a tree node
4334 representing a data type. @var{fn_decl_or_type} is a tree node
4335 representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a
4336 function being called. If @var{outgoing} is false, the hook should
4337 compute the register in which the caller will see the return value.
4338 Otherwise, the hook should return an RTX representing the place where
4339 a function returns a value.
4341 On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant.
4342 (Actually, on most machines, scalar values are returned in the same
4343 place regardless of mode.) The value of the expression is usually a
4344 @code{reg} RTX for the hard register where the return value is stored.
4345 The value can also be a @code{parallel} RTX, if the return value is in
4346 multiple places. See @code{FUNCTION_ARG} for an explanation of the
4347 @code{parallel} form. Note that the callee will populate every
4348 location specified in the @code{parallel}, but if the first element of
4349 the @code{parallel} contains the whole return value, callers will use
4350 that element as the canonical location and ignore the others. The m68k
4351 port uses this type of @code{parallel} to return pointers in both
4352 @samp{%a0} (the canonical location) and @samp{%d0}.
4354 If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply
4355 the same promotion rules specified in @code{PROMOTE_MODE} if
4356 @var{valtype} is a scalar type.
4358 If the precise function being called is known, @var{func} is a tree
4359 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
4360 pointer. This makes it possible to use a different value-returning
4361 convention for specific functions when all their calls are
4364 Some target machines have ``register windows'' so that the register in
4365 which a function returns its value is not the same as the one in which
4366 the caller sees the value. For such machines, you should return
4367 different RTX depending on @var{outgoing}.
4369 @code{TARGET_FUNCTION_VALUE} is not used for return values with
4370 aggregate data types, because these are returned in another way. See
4371 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
4374 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
4375 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
4376 a new target instead.
4379 @defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func})
4380 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
4381 a new target instead.
4384 @defmac LIBCALL_VALUE (@var{mode})
4385 A C expression to create an RTX representing the place where a library
4386 function returns a value of mode @var{mode}.
4388 Note that ``library function'' in this context means a compiler
4389 support routine, used to perform arithmetic, whose name is known
4390 specially by the compiler and was not mentioned in the C code being
4394 @deftypefn {Target Hook} rtx TARGET_LIBCALL_VALUE (enum machine_mode
4395 @var{mode}, rtx @var{fun})
4396 Define this hook if the back-end needs to know the name of the libcall
4397 function in order to determine where the result should be returned.
4399 The mode of the result is given by @var{mode} and the name of the called
4400 library function is given by @var{fun}. The hook should return an RTX
4401 representing the place where the library function result will be returned.
4403 If this hook is not defined, then LIBCALL_VALUE will be used.
4406 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
4407 A C expression that is nonzero if @var{regno} is the number of a hard
4408 register in which the values of called function may come back.
4410 A register whose use for returning values is limited to serving as the
4411 second of a pair (for a value of type @code{double}, say) need not be
4412 recognized by this macro. So for most machines, this definition
4416 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
4419 If the machine has register windows, so that the caller and the called
4420 function use different registers for the return value, this macro
4421 should recognize only the caller's register numbers.
4424 @defmac TARGET_ENUM_VA_LIST (@var{idx}, @var{pname}, @var{ptype})
4425 This target macro is used in function @code{c_common_nodes_and_builtins}
4426 to iterate through the target specific builtin types for va_list. The
4427 variable @var{idx} is used as iterator. @var{pname} has to be a pointer
4428 to a @code{const char *} and @var{ptype} a pointer to a @code{tree} typed
4430 The arguments @var{pname} and @var{ptype} are used to store the result of
4431 this macro and are set to the name of the va_list builtin type and its
4433 If the return value of this macro is zero, then there is no more element.
4434 Otherwise the @var{IDX} should be increased for the next call of this
4435 macro to iterate through all types.
4438 @defmac APPLY_RESULT_SIZE
4439 Define this macro if @samp{untyped_call} and @samp{untyped_return}
4440 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
4441 saving and restoring an arbitrary return value.
4444 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (tree @var{type})
4445 This hook should return true if values of type @var{type} are returned
4446 at the most significant end of a register (in other words, if they are
4447 padded at the least significant end). You can assume that @var{type}
4448 is returned in a register; the caller is required to check this.
4450 Note that the register provided by @code{TARGET_FUNCTION_VALUE} must
4451 be able to hold the complete return value. For example, if a 1-, 2-
4452 or 3-byte structure is returned at the most significant end of a
4453 4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an
4457 @node Aggregate Return
4458 @subsection How Large Values Are Returned
4459 @cindex aggregates as return values
4460 @cindex large return values
4461 @cindex returning aggregate values
4462 @cindex structure value address
4464 When a function value's mode is @code{BLKmode} (and in some other
4465 cases), the value is not returned according to
4466 @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the
4467 caller passes the address of a block of memory in which the value
4468 should be stored. This address is called the @dfn{structure value
4471 This section describes how to control returning structure values in
4474 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (tree @var{type}, tree @var{fntype})
4475 This target hook should return a nonzero value to say to return the
4476 function value in memory, just as large structures are always returned.
4477 Here @var{type} will be the data type of the value, and @var{fntype}
4478 will be the type of the function doing the returning, or @code{NULL} for
4481 Note that values of mode @code{BLKmode} must be explicitly handled
4482 by this function. Also, the option @option{-fpcc-struct-return}
4483 takes effect regardless of this macro. On most systems, it is
4484 possible to leave the hook undefined; this causes a default
4485 definition to be used, whose value is the constant 1 for @code{BLKmode}
4486 values, and 0 otherwise.
4488 Do not use this hook to indicate that structures and unions should always
4489 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
4493 @defmac DEFAULT_PCC_STRUCT_RETURN
4494 Define this macro to be 1 if all structure and union return values must be
4495 in memory. Since this results in slower code, this should be defined
4496 only if needed for compatibility with other compilers or with an ABI@.
4497 If you define this macro to be 0, then the conventions used for structure
4498 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
4501 If not defined, this defaults to the value 1.
4504 @deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming})
4505 This target hook should return the location of the structure value
4506 address (normally a @code{mem} or @code{reg}), or 0 if the address is
4507 passed as an ``invisible'' first argument. Note that @var{fndecl} may
4508 be @code{NULL}, for libcalls. You do not need to define this target
4509 hook if the address is always passed as an ``invisible'' first
4512 On some architectures the place where the structure value address
4513 is found by the called function is not the same place that the
4514 caller put it. This can be due to register windows, or it could
4515 be because the function prologue moves it to a different place.
4516 @var{incoming} is @code{1} or @code{2} when the location is needed in
4517 the context of the called function, and @code{0} in the context of
4520 If @var{incoming} is nonzero and the address is to be found on the
4521 stack, return a @code{mem} which refers to the frame pointer. If
4522 @var{incoming} is @code{2}, the result is being used to fetch the
4523 structure value address at the beginning of a function. If you need
4524 to emit adjusting code, you should do it at this point.
4527 @defmac PCC_STATIC_STRUCT_RETURN
4528 Define this macro if the usual system convention on the target machine
4529 for returning structures and unions is for the called function to return
4530 the address of a static variable containing the value.
4532 Do not define this if the usual system convention is for the caller to
4533 pass an address to the subroutine.
4535 This macro has effect in @option{-fpcc-struct-return} mode, but it does
4536 nothing when you use @option{-freg-struct-return} mode.
4540 @subsection Caller-Saves Register Allocation
4542 If you enable it, GCC can save registers around function calls. This
4543 makes it possible to use call-clobbered registers to hold variables that
4544 must live across calls.
4546 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
4547 A C expression to determine whether it is worthwhile to consider placing
4548 a pseudo-register in a call-clobbered hard register and saving and
4549 restoring it around each function call. The expression should be 1 when
4550 this is worth doing, and 0 otherwise.
4552 If you don't define this macro, a default is used which is good on most
4553 machines: @code{4 * @var{calls} < @var{refs}}.
4556 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
4557 A C expression specifying which mode is required for saving @var{nregs}
4558 of a pseudo-register in call-clobbered hard register @var{regno}. If
4559 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4560 returned. For most machines this macro need not be defined since GCC
4561 will select the smallest suitable mode.
4564 @node Function Entry
4565 @subsection Function Entry and Exit
4566 @cindex function entry and exit
4570 This section describes the macros that output function entry
4571 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4573 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4574 If defined, a function that outputs the assembler code for entry to a
4575 function. The prologue is responsible for setting up the stack frame,
4576 initializing the frame pointer register, saving registers that must be
4577 saved, and allocating @var{size} additional bytes of storage for the
4578 local variables. @var{size} is an integer. @var{file} is a stdio
4579 stream to which the assembler code should be output.
4581 The label for the beginning of the function need not be output by this
4582 macro. That has already been done when the macro is run.
4584 @findex regs_ever_live
4585 To determine which registers to save, the macro can refer to the array
4586 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4587 @var{r} is used anywhere within the function. This implies the function
4588 prologue should save register @var{r}, provided it is not one of the
4589 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4590 @code{regs_ever_live}.)
4592 On machines that have ``register windows'', the function entry code does
4593 not save on the stack the registers that are in the windows, even if
4594 they are supposed to be preserved by function calls; instead it takes
4595 appropriate steps to ``push'' the register stack, if any non-call-used
4596 registers are used in the function.
4598 @findex frame_pointer_needed
4599 On machines where functions may or may not have frame-pointers, the
4600 function entry code must vary accordingly; it must set up the frame
4601 pointer if one is wanted, and not otherwise. To determine whether a
4602 frame pointer is in wanted, the macro can refer to the variable
4603 @code{frame_pointer_needed}. The variable's value will be 1 at run
4604 time in a function that needs a frame pointer. @xref{Elimination}.
4606 The function entry code is responsible for allocating any stack space
4607 required for the function. This stack space consists of the regions
4608 listed below. In most cases, these regions are allocated in the
4609 order listed, with the last listed region closest to the top of the
4610 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4611 the highest address if it is not defined). You can use a different order
4612 for a machine if doing so is more convenient or required for
4613 compatibility reasons. Except in cases where required by standard
4614 or by a debugger, there is no reason why the stack layout used by GCC
4615 need agree with that used by other compilers for a machine.
4618 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
4619 If defined, a function that outputs assembler code at the end of a
4620 prologue. This should be used when the function prologue is being
4621 emitted as RTL, and you have some extra assembler that needs to be
4622 emitted. @xref{prologue instruction pattern}.
4625 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
4626 If defined, a function that outputs assembler code at the start of an
4627 epilogue. This should be used when the function epilogue is being
4628 emitted as RTL, and you have some extra assembler that needs to be
4629 emitted. @xref{epilogue instruction pattern}.
4632 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4633 If defined, a function that outputs the assembler code for exit from a
4634 function. The epilogue is responsible for restoring the saved
4635 registers and stack pointer to their values when the function was
4636 called, and returning control to the caller. This macro takes the
4637 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4638 registers to restore are determined from @code{regs_ever_live} and
4639 @code{CALL_USED_REGISTERS} in the same way.
4641 On some machines, there is a single instruction that does all the work
4642 of returning from the function. On these machines, give that
4643 instruction the name @samp{return} and do not define the macro
4644 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4646 Do not define a pattern named @samp{return} if you want the
4647 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4648 switches to control whether return instructions or epilogues are used,
4649 define a @samp{return} pattern with a validity condition that tests the
4650 target switches appropriately. If the @samp{return} pattern's validity
4651 condition is false, epilogues will be used.
4653 On machines where functions may or may not have frame-pointers, the
4654 function exit code must vary accordingly. Sometimes the code for these
4655 two cases is completely different. To determine whether a frame pointer
4656 is wanted, the macro can refer to the variable
4657 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4658 a function that needs a frame pointer.
4660 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4661 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4662 The C variable @code{current_function_is_leaf} is nonzero for such a
4663 function. @xref{Leaf Functions}.
4665 On some machines, some functions pop their arguments on exit while
4666 others leave that for the caller to do. For example, the 68020 when
4667 given @option{-mrtd} pops arguments in functions that take a fixed
4668 number of arguments.
4670 @findex current_function_pops_args
4671 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4672 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4673 needs to know what was decided. The variable that is called
4674 @code{current_function_pops_args} is the number of bytes of its
4675 arguments that a function should pop. @xref{Scalar Return}.
4676 @c what is the "its arguments" in the above sentence referring to, pray
4677 @c tell? --mew 5feb93
4682 @findex current_function_pretend_args_size
4683 A region of @code{current_function_pretend_args_size} bytes of
4684 uninitialized space just underneath the first argument arriving on the
4685 stack. (This may not be at the very start of the allocated stack region
4686 if the calling sequence has pushed anything else since pushing the stack
4687 arguments. But usually, on such machines, nothing else has been pushed
4688 yet, because the function prologue itself does all the pushing.) This
4689 region is used on machines where an argument may be passed partly in
4690 registers and partly in memory, and, in some cases to support the
4691 features in @code{<stdarg.h>}.
4694 An area of memory used to save certain registers used by the function.
4695 The size of this area, which may also include space for such things as
4696 the return address and pointers to previous stack frames, is
4697 machine-specific and usually depends on which registers have been used
4698 in the function. Machines with register windows often do not require
4702 A region of at least @var{size} bytes, possibly rounded up to an allocation
4703 boundary, to contain the local variables of the function. On some machines,
4704 this region and the save area may occur in the opposite order, with the
4705 save area closer to the top of the stack.
4708 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4709 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4710 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4711 argument lists of the function. @xref{Stack Arguments}.
4714 @defmac EXIT_IGNORE_STACK
4715 Define this macro as a C expression that is nonzero if the return
4716 instruction or the function epilogue ignores the value of the stack
4717 pointer; in other words, if it is safe to delete an instruction to
4718 adjust the stack pointer before a return from the function. The
4721 Note that this macro's value is relevant only for functions for which
4722 frame pointers are maintained. It is never safe to delete a final
4723 stack adjustment in a function that has no frame pointer, and the
4724 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4727 @defmac EPILOGUE_USES (@var{regno})
4728 Define this macro as a C expression that is nonzero for registers that are
4729 used by the epilogue or the @samp{return} pattern. The stack and frame
4730 pointer registers are already assumed to be used as needed.
4733 @defmac EH_USES (@var{regno})
4734 Define this macro as a C expression that is nonzero for registers that are
4735 used by the exception handling mechanism, and so should be considered live
4736 on entry to an exception edge.
4739 @defmac DELAY_SLOTS_FOR_EPILOGUE
4740 Define this macro if the function epilogue contains delay slots to which
4741 instructions from the rest of the function can be ``moved''. The
4742 definition should be a C expression whose value is an integer
4743 representing the number of delay slots there.
4746 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4747 A C expression that returns 1 if @var{insn} can be placed in delay
4748 slot number @var{n} of the epilogue.
4750 The argument @var{n} is an integer which identifies the delay slot now
4751 being considered (since different slots may have different rules of
4752 eligibility). It is never negative and is always less than the number
4753 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4754 If you reject a particular insn for a given delay slot, in principle, it
4755 may be reconsidered for a subsequent delay slot. Also, other insns may
4756 (at least in principle) be considered for the so far unfilled delay
4759 @findex current_function_epilogue_delay_list
4760 @findex final_scan_insn
4761 The insns accepted to fill the epilogue delay slots are put in an RTL
4762 list made with @code{insn_list} objects, stored in the variable
4763 @code{current_function_epilogue_delay_list}. The insn for the first
4764 delay slot comes first in the list. Your definition of the macro
4765 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4766 outputting the insns in this list, usually by calling
4767 @code{final_scan_insn}.
4769 You need not define this macro if you did not define
4770 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4773 @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})
4774 A function that outputs the assembler code for a thunk
4775 function, used to implement C++ virtual function calls with multiple
4776 inheritance. The thunk acts as a wrapper around a virtual function,
4777 adjusting the implicit object parameter before handing control off to
4780 First, emit code to add the integer @var{delta} to the location that
4781 contains the incoming first argument. Assume that this argument
4782 contains a pointer, and is the one used to pass the @code{this} pointer
4783 in C++. This is the incoming argument @emph{before} the function prologue,
4784 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4785 all other incoming arguments.
4787 Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
4788 made after adding @code{delta}. In particular, if @var{p} is the
4789 adjusted pointer, the following adjustment should be made:
4792 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4795 After the additions, emit code to jump to @var{function}, which is a
4796 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4797 not touch the return address. Hence returning from @var{FUNCTION} will
4798 return to whoever called the current @samp{thunk}.
4800 The effect must be as if @var{function} had been called directly with
4801 the adjusted first argument. This macro is responsible for emitting all
4802 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4803 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4805 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4806 have already been extracted from it.) It might possibly be useful on
4807 some targets, but probably not.
4809 If you do not define this macro, the target-independent code in the C++
4810 front end will generate a less efficient heavyweight thunk that calls
4811 @var{function} instead of jumping to it. The generic approach does
4812 not support varargs.
4815 @deftypefn {Target Hook} bool TARGET_ASM_CAN_OUTPUT_MI_THUNK (tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function})
4816 A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
4817 to output the assembler code for the thunk function specified by the
4818 arguments it is passed, and false otherwise. In the latter case, the
4819 generic approach will be used by the C++ front end, with the limitations
4824 @subsection Generating Code for Profiling
4825 @cindex profiling, code generation
4827 These macros will help you generate code for profiling.
4829 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4830 A C statement or compound statement to output to @var{file} some
4831 assembler code to call the profiling subroutine @code{mcount}.
4834 The details of how @code{mcount} expects to be called are determined by
4835 your operating system environment, not by GCC@. To figure them out,
4836 compile a small program for profiling using the system's installed C
4837 compiler and look at the assembler code that results.
4839 Older implementations of @code{mcount} expect the address of a counter
4840 variable to be loaded into some register. The name of this variable is
4841 @samp{LP} followed by the number @var{labelno}, so you would generate
4842 the name using @samp{LP%d} in a @code{fprintf}.
4845 @defmac PROFILE_HOOK
4846 A C statement or compound statement to output to @var{file} some assembly
4847 code to call the profiling subroutine @code{mcount} even the target does
4848 not support profiling.
4851 @defmac NO_PROFILE_COUNTERS
4852 Define this macro to be an expression with a nonzero value if the
4853 @code{mcount} subroutine on your system does not need a counter variable
4854 allocated for each function. This is true for almost all modern
4855 implementations. If you define this macro, you must not use the
4856 @var{labelno} argument to @code{FUNCTION_PROFILER}.
4859 @defmac PROFILE_BEFORE_PROLOGUE
4860 Define this macro if the code for function profiling should come before
4861 the function prologue. Normally, the profiling code comes after.
4865 @subsection Permitting tail calls
4868 @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
4869 True if it is ok to do sibling call optimization for the specified
4870 call expression @var{exp}. @var{decl} will be the called function,
4871 or @code{NULL} if this is an indirect call.
4873 It is not uncommon for limitations of calling conventions to prevent
4874 tail calls to functions outside the current unit of translation, or
4875 during PIC compilation. The hook is used to enforce these restrictions,
4876 as the @code{sibcall} md pattern can not fail, or fall over to a
4877 ``normal'' call. The criteria for successful sibling call optimization
4878 may vary greatly between different architectures.
4881 @deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap *@var{regs})
4882 Add any hard registers to @var{regs} that are live on entry to the
4883 function. This hook only needs to be defined to provide registers that
4884 cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved
4885 registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM,
4886 TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES,
4887 FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.
4890 @node Stack Smashing Protection
4891 @subsection Stack smashing protection
4892 @cindex stack smashing protection
4894 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void)
4895 This hook returns a @code{DECL} node for the external variable to use
4896 for the stack protection guard. This variable is initialized by the
4897 runtime to some random value and is used to initialize the guard value
4898 that is placed at the top of the local stack frame. The type of this
4899 variable must be @code{ptr_type_node}.
4901 The default version of this hook creates a variable called
4902 @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
4905 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void)
4906 This hook returns a tree expression that alerts the runtime that the
4907 stack protect guard variable has been modified. This expression should
4908 involve a call to a @code{noreturn} function.
4910 The default version of this hook invokes a function called
4911 @samp{__stack_chk_fail}, taking no arguments. This function is
4912 normally defined in @file{libgcc2.c}.
4916 @section Implementing the Varargs Macros
4917 @cindex varargs implementation
4919 GCC comes with an implementation of @code{<varargs.h>} and
4920 @code{<stdarg.h>} that work without change on machines that pass arguments
4921 on the stack. Other machines require their own implementations of
4922 varargs, and the two machine independent header files must have
4923 conditionals to include it.
4925 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4926 the calling convention for @code{va_start}. The traditional
4927 implementation takes just one argument, which is the variable in which
4928 to store the argument pointer. The ISO implementation of
4929 @code{va_start} takes an additional second argument. The user is
4930 supposed to write the last named argument of the function here.
4932 However, @code{va_start} should not use this argument. The way to find
4933 the end of the named arguments is with the built-in functions described
4936 @defmac __builtin_saveregs ()
4937 Use this built-in function to save the argument registers in memory so
4938 that the varargs mechanism can access them. Both ISO and traditional
4939 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
4940 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
4942 On some machines, @code{__builtin_saveregs} is open-coded under the
4943 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
4944 other machines, it calls a routine written in assembler language,
4945 found in @file{libgcc2.c}.
4947 Code generated for the call to @code{__builtin_saveregs} appears at the
4948 beginning of the function, as opposed to where the call to
4949 @code{__builtin_saveregs} is written, regardless of what the code is.
4950 This is because the registers must be saved before the function starts
4951 to use them for its own purposes.
4952 @c i rewrote the first sentence above to fix an overfull hbox. --mew
4956 @defmac __builtin_args_info (@var{category})
4957 Use this built-in function to find the first anonymous arguments in
4960 In general, a machine may have several categories of registers used for
4961 arguments, each for a particular category of data types. (For example,
4962 on some machines, floating-point registers are used for floating-point
4963 arguments while other arguments are passed in the general registers.)
4964 To make non-varargs functions use the proper calling convention, you
4965 have defined the @code{CUMULATIVE_ARGS} data type to record how many
4966 registers in each category have been used so far
4968 @code{__builtin_args_info} accesses the same data structure of type
4969 @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished
4970 with it, with @var{category} specifying which word to access. Thus, the
4971 value indicates the first unused register in a given category.
4973 Normally, you would use @code{__builtin_args_info} in the implementation
4974 of @code{va_start}, accessing each category just once and storing the
4975 value in the @code{va_list} object. This is because @code{va_list} will
4976 have to update the values, and there is no way to alter the
4977 values accessed by @code{__builtin_args_info}.
4980 @defmac __builtin_next_arg (@var{lastarg})
4981 This is the equivalent of @code{__builtin_args_info}, for stack
4982 arguments. It returns the address of the first anonymous stack
4983 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
4984 returns the address of the location above the first anonymous stack
4985 argument. Use it in @code{va_start} to initialize the pointer for
4986 fetching arguments from the stack. Also use it in @code{va_start} to
4987 verify that the second parameter @var{lastarg} is the last named argument
4988 of the current function.
4991 @defmac __builtin_classify_type (@var{object})
4992 Since each machine has its own conventions for which data types are
4993 passed in which kind of register, your implementation of @code{va_arg}
4994 has to embody these conventions. The easiest way to categorize the
4995 specified data type is to use @code{__builtin_classify_type} together
4996 with @code{sizeof} and @code{__alignof__}.
4998 @code{__builtin_classify_type} ignores the value of @var{object},
4999 considering only its data type. It returns an integer describing what
5000 kind of type that is---integer, floating, pointer, structure, and so on.
5002 The file @file{typeclass.h} defines an enumeration that you can use to
5003 interpret the values of @code{__builtin_classify_type}.
5006 These machine description macros help implement varargs:
5008 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void)
5009 If defined, this hook produces the machine-specific code for a call to
5010 @code{__builtin_saveregs}. This code will be moved to the very
5011 beginning of the function, before any parameter access are made. The
5012 return value of this function should be an RTX that contains the value
5013 to use as the return of @code{__builtin_saveregs}.
5016 @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})
5017 This target hook offers an alternative to using
5018 @code{__builtin_saveregs} and defining the hook
5019 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
5020 register arguments into the stack so that all the arguments appear to
5021 have been passed consecutively on the stack. Once this is done, you can
5022 use the standard implementation of varargs that works for machines that
5023 pass all their arguments on the stack.
5025 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
5026 structure, containing the values that are obtained after processing the
5027 named arguments. The arguments @var{mode} and @var{type} describe the
5028 last named argument---its machine mode and its data type as a tree node.
5030 The target hook should do two things: first, push onto the stack all the
5031 argument registers @emph{not} used for the named arguments, and second,
5032 store the size of the data thus pushed into the @code{int}-valued
5033 variable pointed to by @var{pretend_args_size}. The value that you
5034 store here will serve as additional offset for setting up the stack
5037 Because you must generate code to push the anonymous arguments at
5038 compile time without knowing their data types,
5039 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
5040 have just a single category of argument register and use it uniformly
5043 If the argument @var{second_time} is nonzero, it means that the
5044 arguments of the function are being analyzed for the second time. This
5045 happens for an inline function, which is not actually compiled until the
5046 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
5047 not generate any instructions in this case.
5050 @deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca})
5051 Define this hook to return @code{true} if the location where a function
5052 argument is passed depends on whether or not it is a named argument.
5054 This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
5055 is set for varargs and stdarg functions. If this hook returns
5056 @code{true}, the @var{named} argument is always true for named
5057 arguments, and false for unnamed arguments. If it returns @code{false},
5058 but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
5059 then all arguments are treated as named. Otherwise, all named arguments
5060 except the last are treated as named.
5062 You need not define this hook if it always returns zero.
5065 @deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED
5066 If you need to conditionally change ABIs so that one works with
5067 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
5068 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
5069 defined, then define this hook to return @code{true} if
5070 @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
5071 Otherwise, you should not define this hook.
5075 @section Trampolines for Nested Functions
5076 @cindex trampolines for nested functions
5077 @cindex nested functions, trampolines for
5079 A @dfn{trampoline} is a small piece of code that is created at run time
5080 when the address of a nested function is taken. It normally resides on
5081 the stack, in the stack frame of the containing function. These macros
5082 tell GCC how to generate code to allocate and initialize a
5085 The instructions in the trampoline must do two things: load a constant
5086 address into the static chain register, and jump to the real address of
5087 the nested function. On CISC machines such as the m68k, this requires
5088 two instructions, a move immediate and a jump. Then the two addresses
5089 exist in the trampoline as word-long immediate operands. On RISC
5090 machines, it is often necessary to load each address into a register in
5091 two parts. Then pieces of each address form separate immediate
5094 The code generated to initialize the trampoline must store the variable
5095 parts---the static chain value and the function address---into the
5096 immediate operands of the instructions. On a CISC machine, this is
5097 simply a matter of copying each address to a memory reference at the
5098 proper offset from the start of the trampoline. On a RISC machine, it
5099 may be necessary to take out pieces of the address and store them
5102 @defmac TRAMPOLINE_TEMPLATE (@var{file})
5103 A C statement to output, on the stream @var{file}, assembler code for a
5104 block of data that contains the constant parts of a trampoline. This
5105 code should not include a label---the label is taken care of
5108 If you do not define this macro, it means no template is needed
5109 for the target. Do not define this macro on systems where the block move
5110 code to copy the trampoline into place would be larger than the code
5111 to generate it on the spot.
5114 @defmac TRAMPOLINE_SECTION
5115 Return the section into which the trampoline template is to be placed
5116 (@pxref{Sections}). The default value is @code{readonly_data_section}.
5119 @defmac TRAMPOLINE_SIZE
5120 A C expression for the size in bytes of the trampoline, as an integer.
5123 @defmac TRAMPOLINE_ALIGNMENT
5124 Alignment required for trampolines, in bits.
5126 If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT}
5127 is used for aligning trampolines.
5130 @defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain})
5131 A C statement to initialize the variable parts of a trampoline.
5132 @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is
5133 an RTX for the address of the nested function; @var{static_chain} is an
5134 RTX for the static chain value that should be passed to the function
5138 @defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr})
5139 A C statement that should perform any machine-specific adjustment in
5140 the address of the trampoline. Its argument contains the address that
5141 was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be
5142 used for a function call should be different from the address in which
5143 the template was stored, the different address should be assigned to
5144 @var{addr}. If this macro is not defined, @var{addr} will be used for
5147 @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines
5148 @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines
5149 If this macro is not defined, by default the trampoline is allocated as
5150 a stack slot. This default is right for most machines. The exceptions
5151 are machines where it is impossible to execute instructions in the stack
5152 area. On such machines, you may have to implement a separate stack,
5153 using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE}
5154 and @code{TARGET_ASM_FUNCTION_EPILOGUE}.
5156 @var{fp} points to a data structure, a @code{struct function}, which
5157 describes the compilation status of the immediate containing function of
5158 the function which the trampoline is for. The stack slot for the
5159 trampoline is in the stack frame of this containing function. Other
5160 allocation strategies probably must do something analogous with this
5164 Implementing trampolines is difficult on many machines because they have
5165 separate instruction and data caches. Writing into a stack location
5166 fails to clear the memory in the instruction cache, so when the program
5167 jumps to that location, it executes the old contents.
5169 Here are two possible solutions. One is to clear the relevant parts of
5170 the instruction cache whenever a trampoline is set up. The other is to
5171 make all trampolines identical, by having them jump to a standard
5172 subroutine. The former technique makes trampoline execution faster; the
5173 latter makes initialization faster.
5175 To clear the instruction cache when a trampoline is initialized, define
5176 the following macro.
5178 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
5179 If defined, expands to a C expression clearing the @emph{instruction
5180 cache} in the specified interval. The definition of this macro would
5181 typically be a series of @code{asm} statements. Both @var{beg} and
5182 @var{end} are both pointer expressions.
5185 The operating system may also require the stack to be made executable
5186 before calling the trampoline. To implement this requirement, define
5187 the following macro.
5189 @defmac ENABLE_EXECUTE_STACK
5190 Define this macro if certain operations must be performed before executing
5191 code located on the stack. The macro should expand to a series of C
5192 file-scope constructs (e.g.@: functions) and provide a unique entry point
5193 named @code{__enable_execute_stack}. The target is responsible for
5194 emitting calls to the entry point in the code, for example from the
5195 @code{INITIALIZE_TRAMPOLINE} macro.
5198 To use a standard subroutine, define the following macro. In addition,
5199 you must make sure that the instructions in a trampoline fill an entire
5200 cache line with identical instructions, or else ensure that the
5201 beginning of the trampoline code is always aligned at the same point in
5202 its cache line. Look in @file{m68k.h} as a guide.
5204 @defmac TRANSFER_FROM_TRAMPOLINE
5205 Define this macro if trampolines need a special subroutine to do their
5206 work. The macro should expand to a series of @code{asm} statements
5207 which will be compiled with GCC@. They go in a library function named
5208 @code{__transfer_from_trampoline}.
5210 If you need to avoid executing the ordinary prologue code of a compiled
5211 C function when you jump to the subroutine, you can do so by placing a
5212 special label of your own in the assembler code. Use one @code{asm}
5213 statement to generate an assembler label, and another to make the label
5214 global. Then trampolines can use that label to jump directly to your
5215 special assembler code.
5219 @section Implicit Calls to Library Routines
5220 @cindex library subroutine names
5221 @cindex @file{libgcc.a}
5223 @c prevent bad page break with this line
5224 Here is an explanation of implicit calls to library routines.
5226 @defmac DECLARE_LIBRARY_RENAMES
5227 This macro, if defined, should expand to a piece of C code that will get
5228 expanded when compiling functions for libgcc.a. It can be used to
5229 provide alternate names for GCC's internal library functions if there
5230 are ABI-mandated names that the compiler should provide.
5233 @findex init_one_libfunc
5234 @findex set_optab_libfunc
5235 @deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void)
5236 This hook should declare additional library routines or rename
5237 existing ones, using the functions @code{set_optab_libfunc} and
5238 @code{init_one_libfunc} defined in @file{optabs.c}.
5239 @code{init_optabs} calls this macro after initializing all the normal
5242 The default is to do nothing. Most ports don't need to define this hook.
5245 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
5246 This macro should return @code{true} if the library routine that
5247 implements the floating point comparison operator @var{comparison} in
5248 mode @var{mode} will return a boolean, and @var{false} if it will
5251 GCC's own floating point libraries return tristates from the
5252 comparison operators, so the default returns false always. Most ports
5253 don't need to define this macro.
5256 @defmac TARGET_LIB_INT_CMP_BIASED
5257 This macro should evaluate to @code{true} if the integer comparison
5258 functions (like @code{__cmpdi2}) return 0 to indicate that the first
5259 operand is smaller than the second, 1 to indicate that they are equal,
5260 and 2 to indicate that the first operand is greater than the second.
5261 If this macro evaluates to @code{false} the comparison functions return
5262 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
5263 in @file{libgcc.a}, you do not need to define this macro.
5266 @cindex US Software GOFAST, floating point emulation library
5267 @cindex floating point emulation library, US Software GOFAST
5268 @cindex GOFAST, floating point emulation library
5269 @findex gofast_maybe_init_libfuncs
5270 @defmac US_SOFTWARE_GOFAST
5271 Define this macro if your system C library uses the US Software GOFAST
5272 library to provide floating point emulation.
5274 In addition to defining this macro, your architecture must set
5275 @code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or
5276 else call that function from its version of that hook. It is defined
5277 in @file{config/gofast.h}, which must be included by your
5278 architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for
5281 If this macro is defined, the
5282 @code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return
5283 false for @code{SFmode} and @code{DFmode} comparisons.
5286 @cindex @code{EDOM}, implicit usage
5289 The value of @code{EDOM} on the target machine, as a C integer constant
5290 expression. If you don't define this macro, GCC does not attempt to
5291 deposit the value of @code{EDOM} into @code{errno} directly. Look in
5292 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
5295 If you do not define @code{TARGET_EDOM}, then compiled code reports
5296 domain errors by calling the library function and letting it report the
5297 error. If mathematical functions on your system use @code{matherr} when
5298 there is an error, then you should leave @code{TARGET_EDOM} undefined so
5299 that @code{matherr} is used normally.
5302 @cindex @code{errno}, implicit usage
5303 @defmac GEN_ERRNO_RTX
5304 Define this macro as a C expression to create an rtl expression that
5305 refers to the global ``variable'' @code{errno}. (On certain systems,
5306 @code{errno} may not actually be a variable.) If you don't define this
5307 macro, a reasonable default is used.
5310 @cindex C99 math functions, implicit usage
5311 @defmac TARGET_C99_FUNCTIONS
5312 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
5313 @code{sinf} and similarly for other functions defined by C99 standard. The
5314 default is zero because a number of existing systems lack support for these
5315 functions in their runtime so this macro needs to be redefined to one on
5316 systems that do support the C99 runtime.
5319 @cindex sincos math function, implicit usage
5320 @defmac TARGET_HAS_SINCOS
5321 When this macro is nonzero, GCC will implicitly optimize calls to @code{sin}
5322 and @code{cos} with the same argument to a call to @code{sincos}. The
5323 default is zero. The target has to provide the following functions:
5325 void sincos(double x, double *sin, double *cos);
5326 void sincosf(float x, float *sin, float *cos);
5327 void sincosl(long double x, long double *sin, long double *cos);
5331 @defmac NEXT_OBJC_RUNTIME
5332 Define this macro to generate code for Objective-C message sending using
5333 the calling convention of the NeXT system. This calling convention
5334 involves passing the object, the selector and the method arguments all
5335 at once to the method-lookup library function.
5337 The default calling convention passes just the object and the selector
5338 to the lookup function, which returns a pointer to the method.
5341 @node Addressing Modes
5342 @section Addressing Modes
5343 @cindex addressing modes
5345 @c prevent bad page break with this line
5346 This is about addressing modes.
5348 @defmac HAVE_PRE_INCREMENT
5349 @defmacx HAVE_PRE_DECREMENT
5350 @defmacx HAVE_POST_INCREMENT
5351 @defmacx HAVE_POST_DECREMENT
5352 A C expression that is nonzero if the machine supports pre-increment,
5353 pre-decrement, post-increment, or post-decrement addressing respectively.
5356 @defmac HAVE_PRE_MODIFY_DISP
5357 @defmacx HAVE_POST_MODIFY_DISP
5358 A C expression that is nonzero if the machine supports pre- or
5359 post-address side-effect generation involving constants other than
5360 the size of the memory operand.
5363 @defmac HAVE_PRE_MODIFY_REG
5364 @defmacx HAVE_POST_MODIFY_REG
5365 A C expression that is nonzero if the machine supports pre- or
5366 post-address side-effect generation involving a register displacement.
5369 @defmac CONSTANT_ADDRESS_P (@var{x})
5370 A C expression that is 1 if the RTX @var{x} is a constant which
5371 is a valid address. On most machines, this can be defined as
5372 @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive
5373 in which constant addresses are supported.
5376 @defmac CONSTANT_P (@var{x})
5377 @code{CONSTANT_P}, which is defined by target-independent code,
5378 accepts integer-values expressions whose values are not explicitly
5379 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
5380 expressions and @code{const} arithmetic expressions, in addition to
5381 @code{const_int} and @code{const_double} expressions.
5384 @defmac MAX_REGS_PER_ADDRESS
5385 A number, the maximum number of registers that can appear in a valid
5386 memory address. Note that it is up to you to specify a value equal to
5387 the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
5391 @deftypefn {Target Hook} TARGET_LEGITIMATE_ADDRESS_P (enum machine_mode @var{mode}, rtx @var{x}, bool @var{strict})
5392 A function that returns whether @var{x} (an RTX) is a legitimate memory
5393 address on the target machine for a memory operand of mode @var{mode}.
5395 Legitimate addresses are defined in two variants: a strict variant and a
5396 non-strict one. The @code{strict} parameter chooses which variant is
5397 desired by the caller.
5399 The strict variant is used in the reload pass. It must be defined so
5400 that any pseudo-register that has not been allocated a hard register is
5401 considered a memory reference. This is because in contexts where some
5402 kind of register is required, a pseudo-register with no hard register
5403 must be rejected. For non-hard registers, the strict variant should look
5404 up the @code{reg_renumber} array; it should then proceed using the hard
5405 register number in the array, or treat the pseudo as a memory reference
5406 if the array holds @code{-1}.
5408 The non-strict variant is used in other passes. It must be defined to
5409 accept all pseudo-registers in every context where some kind of
5410 register is required.
5412 Normally, constant addresses which are the sum of a @code{symbol_ref}
5413 and an integer are stored inside a @code{const} RTX to mark them as
5414 constant. Therefore, there is no need to recognize such sums
5415 specifically as legitimate addresses. Normally you would simply
5416 recognize any @code{const} as legitimate.
5418 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
5419 sums that are not marked with @code{const}. It assumes that a naked
5420 @code{plus} indicates indexing. If so, then you @emph{must} reject such
5421 naked constant sums as illegitimate addresses, so that none of them will
5422 be given to @code{PRINT_OPERAND_ADDRESS}.
5424 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
5425 On some machines, whether a symbolic address is legitimate depends on
5426 the section that the address refers to. On these machines, define the
5427 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
5428 into the @code{symbol_ref}, and then check for it here. When you see a
5429 @code{const}, you will have to look inside it to find the
5430 @code{symbol_ref} in order to determine the section. @xref{Assembler
5433 @cindex @code{GO_IF_LEGITIMATE_ADDRESS}
5434 Some ports are still using a deprecated legacy substitute for
5435 this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro
5439 #define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
5443 and should @code{goto @var{label}} if the address @var{x} is a valid
5444 address on the target machine for a memory operand of mode @var{mode}.
5445 Whether the strict or non-strict variants are desired is defined by
5446 the @code{REG_OK_STRICT} macro introduced earlier in this section.
5447 Using the hook is usually simpler because it limits the number of
5448 files that are recompiled when changes are made.
5451 @defmac TARGET_MEM_CONSTRAINT
5452 A single character to be used instead of the default @code{'m'}
5453 character for general memory addresses. This defines the constraint
5454 letter which matches the memory addresses accepted by
5455 @code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to
5456 support new address formats in your back end without changing the
5457 semantics of the @code{'m'} constraint. This is necessary in order to
5458 preserve functionality of inline assembly constructs using the
5459 @code{'m'} constraint.
5462 @defmac FIND_BASE_TERM (@var{x})
5463 A C expression to determine the base term of address @var{x},
5464 or to provide a simplified version of @var{x} from which @file{alias.c}
5465 can easily find the base term. This macro is used in only two places:
5466 @code{find_base_value} and @code{find_base_term} in @file{alias.c}.
5468 It is always safe for this macro to not be defined. It exists so
5469 that alias analysis can understand machine-dependent addresses.
5471 The typical use of this macro is to handle addresses containing
5472 a label_ref or symbol_ref within an UNSPEC@.
5475 @deftypefn {Target Hook} rtx TARGET_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, enum machine_mode @var{mode})
5476 This hook is given an invalid memory address @var{x} for an
5477 operand of mode @var{mode} and should try to return a valid memory
5480 @findex break_out_memory_refs
5481 @var{x} will always be the result of a call to @code{break_out_memory_refs},
5482 and @var{oldx} will be the operand that was given to that function to produce
5485 The code of the hook should not alter the substructure of
5486 @var{x}. If it transforms @var{x} into a more legitimate form, it
5487 should return the new @var{x}.
5489 It is not necessary for this hook to come up with a legitimate address.
5490 The compiler has standard ways of doing so in all cases. In fact, it
5491 is safe to omit this hook or make it return @var{x} if it cannot find
5492 a valid way to legitimize the address. But often a machine-dependent
5493 strategy can generate better code.
5496 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
5497 A C compound statement that attempts to replace @var{x}, which is an address
5498 that needs reloading, with a valid memory address for an operand of mode
5499 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
5500 It is not necessary to define this macro, but it might be useful for
5501 performance reasons.
5503 For example, on the i386, it is sometimes possible to use a single
5504 reload register instead of two by reloading a sum of two pseudo
5505 registers into a register. On the other hand, for number of RISC
5506 processors offsets are limited so that often an intermediate address
5507 needs to be generated in order to address a stack slot. By defining
5508 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
5509 generated for adjacent some stack slots can be made identical, and thus
5512 @emph{Note}: This macro should be used with caution. It is necessary
5513 to know something of how reload works in order to effectively use this,
5514 and it is quite easy to produce macros that build in too much knowledge
5515 of reload internals.
5517 @emph{Note}: This macro must be able to reload an address created by a
5518 previous invocation of this macro. If it fails to handle such addresses
5519 then the compiler may generate incorrect code or abort.
5522 The macro definition should use @code{push_reload} to indicate parts that
5523 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
5524 suitable to be passed unaltered to @code{push_reload}.
5526 The code generated by this macro must not alter the substructure of
5527 @var{x}. If it transforms @var{x} into a more legitimate form, it
5528 should assign @var{x} (which will always be a C variable) a new value.
5529 This also applies to parts that you change indirectly by calling
5532 @findex strict_memory_address_p
5533 The macro definition may use @code{strict_memory_address_p} to test if
5534 the address has become legitimate.
5537 If you want to change only a part of @var{x}, one standard way of doing
5538 this is to use @code{copy_rtx}. Note, however, that it unshares only a
5539 single level of rtl. Thus, if the part to be changed is not at the
5540 top level, you'll need to replace first the top level.
5541 It is not necessary for this macro to come up with a legitimate
5542 address; but often a machine-dependent strategy can generate better code.
5545 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
5546 A C statement or compound statement with a conditional @code{goto
5547 @var{label};} executed if memory address @var{x} (an RTX) can have
5548 different meanings depending on the machine mode of the memory
5549 reference it is used for or if the address is valid for some modes
5552 Autoincrement and autodecrement addresses typically have mode-dependent
5553 effects because the amount of the increment or decrement is the size
5554 of the operand being addressed. Some machines have other mode-dependent
5555 addresses. Many RISC machines have no mode-dependent addresses.
5557 You may assume that @var{addr} is a valid address for the machine.
5560 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5561 A C expression that is nonzero if @var{x} is a legitimate constant for
5562 an immediate operand on the target machine. You can assume that
5563 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5564 @samp{1} is a suitable definition for this macro on machines where
5565 anything @code{CONSTANT_P} is valid.
5568 @deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x})
5569 This hook is used to undo the possibly obfuscating effects of the
5570 @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
5571 macros. Some backend implementations of these macros wrap symbol
5572 references inside an @code{UNSPEC} rtx to represent PIC or similar
5573 addressing modes. This target hook allows GCC's optimizers to understand
5574 the semantics of these opaque @code{UNSPEC}s by converting them back
5575 into their original form.
5578 @deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (rtx @var{x})
5579 This hook should return true if @var{x} is of a form that cannot (or
5580 should not) be spilled to the constant pool. The default version of
5581 this hook returns false.
5583 The primary reason to define this hook is to prevent reload from
5584 deciding that a non-legitimate constant would be better reloaded
5585 from the constant pool instead of spilling and reloading a register
5586 holding the constant. This restriction is often true of addresses
5587 of TLS symbols for various targets.
5590 @deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (enum machine_mode @var{mode}, rtx @var{x})
5591 This hook should return true if pool entries for constant @var{x} can
5592 be placed in an @code{object_block} structure. @var{mode} is the mode
5595 The default version returns false for all constants.
5598 @deftypefn {Target Hook} tree TARGET_BUILTIN_RECIPROCAL (enum tree_code @var{fn}, bool @var{tm_fn}, bool @var{sqrt})
5599 This hook should return the DECL of a function that implements reciprocal of
5600 the builtin function with builtin function code @var{fn}, or
5601 @code{NULL_TREE} if such a function is not available. @var{tm_fn} is true
5602 when @var{fn} is a code of a machine-dependent builtin function. When
5603 @var{sqrt} is true, additional optimizations that apply only to the reciprocal
5604 of a square root function are performed, and only reciprocals of @code{sqrt}
5608 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void)
5609 This hook should return the DECL of a function @var{f} that given an
5610 address @var{addr} as an argument returns a mask @var{m} that can be
5611 used to extract from two vectors the relevant data that resides in
5612 @var{addr} in case @var{addr} is not properly aligned.
5614 The autovectorizer, when vectorizing a load operation from an address
5615 @var{addr} that may be unaligned, will generate two vector loads from
5616 the two aligned addresses around @var{addr}. It then generates a
5617 @code{REALIGN_LOAD} operation to extract the relevant data from the
5618 two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
5619 @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
5620 the third argument, @var{OFF}, defines how the data will be extracted
5621 from these two vectors: if @var{OFF} is 0, then the returned vector is
5622 @var{v2}; otherwise, the returned vector is composed from the last
5623 @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
5624 @var{OFF} elements of @var{v2}.
5626 If this hook is defined, the autovectorizer will generate a call
5627 to @var{f} (using the DECL tree that this hook returns) and will
5628 use the return value of @var{f} as the argument @var{OFF} to
5629 @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
5630 should comply with the semantics expected by @code{REALIGN_LOAD}
5632 If this hook is not defined, then @var{addr} will be used as
5633 the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
5634 log2(@var{VS})-1 bits of @var{addr} will be considered.
5637 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN (tree @var{x})
5638 This hook should return the DECL of a function @var{f} that implements
5639 widening multiplication of the even elements of two input vectors of type @var{x}.
5641 If this hook is defined, the autovectorizer will use it along with the
5642 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD} target hook when vectorizing
5643 widening multiplication in cases that the order of the results does not have to be
5644 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5645 @code{widen_mult_hi/lo} idioms will be used.
5648 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD (tree @var{x})
5649 This hook should return the DECL of a function @var{f} that implements
5650 widening multiplication of the odd elements of two input vectors of type @var{x}.
5652 If this hook is defined, the autovectorizer will use it along with the
5653 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN} target hook when vectorizing
5654 widening multiplication in cases that the order of the results does not have to be
5655 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5656 @code{widen_mult_hi/lo} idioms will be used.
5659 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_CONVERSION (enum tree_code @var{code}, tree @var{type})
5660 This hook should return the DECL of a function that implements conversion of the
5661 input vector of type @var{type}.
5662 If @var{type} is an integral type, the result of the conversion is a vector of
5663 floating-point type of the same size.
5664 If @var{type} is a floating-point type, the result of the conversion is a vector
5665 of integral type of the same size.
5666 @var{code} specifies how the conversion is to be applied
5667 (truncation, rounding, etc.).
5669 If this hook is defined, the autovectorizer will use the
5670 @code{TARGET_VECTORIZE_BUILTIN_CONVERSION} target hook when vectorizing
5671 conversion. Otherwise, it will return @code{NULL_TREE}.
5674 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION (enum built_in_function @var{code}, tree @var{vec_type_out}, tree @var{vec_type_in})
5675 This hook should return the decl of a function that implements the vectorized
5676 variant of the builtin function with builtin function code @var{code} or
5677 @code{NULL_TREE} if such a function is not available. The return type of
5678 the vectorized function shall be of vector type @var{vec_type_out} and the
5679 argument types should be @var{vec_type_in}.
5682 @node Anchored Addresses
5683 @section Anchored Addresses
5684 @cindex anchored addresses
5685 @cindex @option{-fsection-anchors}
5687 GCC usually addresses every static object as a separate entity.
5688 For example, if we have:
5692 int foo (void) @{ return a + b + c; @}
5695 the code for @code{foo} will usually calculate three separate symbolic
5696 addresses: those of @code{a}, @code{b} and @code{c}. On some targets,
5697 it would be better to calculate just one symbolic address and access
5698 the three variables relative to it. The equivalent pseudocode would
5704 register int *xr = &x;
5705 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
5709 (which isn't valid C). We refer to shared addresses like @code{x} as
5710 ``section anchors''. Their use is controlled by @option{-fsection-anchors}.
5712 The hooks below describe the target properties that GCC needs to know
5713 in order to make effective use of section anchors. It won't use
5714 section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
5715 or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
5717 @deftypevr {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET
5718 The minimum offset that should be applied to a section anchor.
5719 On most targets, it should be the smallest offset that can be
5720 applied to a base register while still giving a legitimate address
5721 for every mode. The default value is 0.
5724 @deftypevr {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET
5725 Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive)
5726 offset that should be applied to section anchors. The default
5730 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x})
5731 Write the assembly code to define section anchor @var{x}, which is a
5732 @code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true.
5733 The hook is called with the assembly output position set to the beginning
5734 of @code{SYMBOL_REF_BLOCK (@var{x})}.
5736 If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses
5737 it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}.
5738 If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition
5739 is @code{NULL}, which disables the use of section anchors altogether.
5742 @deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (rtx @var{x})
5743 Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF}
5744 @var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and
5745 @samp{!SYMBOL_REF_ANCHOR_P (@var{x})}.
5747 The default version is correct for most targets, but you might need to
5748 intercept this hook to handle things like target-specific attributes
5749 or target-specific sections.
5752 @node Condition Code
5753 @section Condition Code Status
5754 @cindex condition code status
5756 The macros in this section can be split in two families, according to the
5757 two ways of representing condition codes in GCC.
5759 The first representation is the so called @code{(cc0)} representation
5760 (@pxref{Jump Patterns}), where all instructions can have an implicit
5761 clobber of the condition codes. The second is the condition code
5762 register representation, which provides better schedulability for
5763 architectures that do have a condition code register, but on which
5764 most instructions do not affect it. The latter category includes
5767 The implicit clobbering poses a strong restriction on the placement of
5768 the definition and use of the condition code, which need to be in adjacent
5769 insns for machines using @code{(cc0)}. This can prevent important
5770 optimizations on some machines. For example, on the IBM RS/6000, there
5771 is a delay for taken branches unless the condition code register is set
5772 three instructions earlier than the conditional branch. The instruction
5773 scheduler cannot perform this optimization if it is not permitted to
5774 separate the definition and use of the condition code register.
5776 For this reason, it is possible and suggested to use a register to
5777 represent the condition code for new ports. If there is a specific
5778 condition code register in the machine, use a hard register. If the
5779 condition code or comparison result can be placed in any general register,
5780 or if there are multiple condition registers, use a pseudo register.
5781 Registers used to store the condition code value will usually have a mode
5782 that is in class @code{MODE_CC}.
5784 Alternatively, you can use @code{BImode} if the comparison operator is
5785 specified already in the compare instruction. In this case, you are not
5786 interested in most macros in this section.
5789 * CC0 Condition Codes:: Old style representation of condition codes.
5790 * MODE_CC Condition Codes:: Modern representation of condition codes.
5791 * Cond. Exec. Macros:: Macros to control conditional execution.
5794 @node CC0 Condition Codes
5795 @subsection Representation of condition codes using @code{(cc0)}
5799 The file @file{conditions.h} defines a variable @code{cc_status} to
5800 describe how the condition code was computed (in case the interpretation of
5801 the condition code depends on the instruction that it was set by). This
5802 variable contains the RTL expressions on which the condition code is
5803 currently based, and several standard flags.
5805 Sometimes additional machine-specific flags must be defined in the machine
5806 description header file. It can also add additional machine-specific
5807 information by defining @code{CC_STATUS_MDEP}.
5809 @defmac CC_STATUS_MDEP
5810 C code for a data type which is used for declaring the @code{mdep}
5811 component of @code{cc_status}. It defaults to @code{int}.
5813 This macro is not used on machines that do not use @code{cc0}.
5816 @defmac CC_STATUS_MDEP_INIT
5817 A C expression to initialize the @code{mdep} field to ``empty''.
5818 The default definition does nothing, since most machines don't use
5819 the field anyway. If you want to use the field, you should probably
5820 define this macro to initialize it.
5822 This macro is not used on machines that do not use @code{cc0}.
5825 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5826 A C compound statement to set the components of @code{cc_status}
5827 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5828 this macro's responsibility to recognize insns that set the condition
5829 code as a byproduct of other activity as well as those that explicitly
5832 This macro is not used on machines that do not use @code{cc0}.
5834 If there are insns that do not set the condition code but do alter
5835 other machine registers, this macro must check to see whether they
5836 invalidate the expressions that the condition code is recorded as
5837 reflecting. For example, on the 68000, insns that store in address
5838 registers do not set the condition code, which means that usually
5839 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5840 insns. But suppose that the previous insn set the condition code
5841 based on location @samp{a4@@(102)} and the current insn stores a new
5842 value in @samp{a4}. Although the condition code is not changed by
5843 this, it will no longer be true that it reflects the contents of
5844 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5845 @code{cc_status} in this case to say that nothing is known about the
5846 condition code value.
5848 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5849 with the results of peephole optimization: insns whose patterns are
5850 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5851 constants which are just the operands. The RTL structure of these
5852 insns is not sufficient to indicate what the insns actually do. What
5853 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5854 @code{CC_STATUS_INIT}.
5856 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5857 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5858 @samp{cc}. This avoids having detailed information about patterns in
5859 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5862 @node MODE_CC Condition Codes
5863 @subsection Representation of condition codes using registers
5867 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5868 On many machines, the condition code may be produced by other instructions
5869 than compares, for example the branch can use directly the condition
5870 code set by a subtract instruction. However, on some machines
5871 when the condition code is set this way some bits (such as the overflow
5872 bit) are not set in the same way as a test instruction, so that a different
5873 branch instruction must be used for some conditional branches. When
5874 this happens, use the machine mode of the condition code register to
5875 record different formats of the condition code register. Modes can
5876 also be used to record which compare instruction (e.g. a signed or an
5877 unsigned comparison) produced the condition codes.
5879 If other modes than @code{CCmode} are required, add them to
5880 @file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
5881 a mode given an operand of a compare. This is needed because the modes
5882 have to be chosen not only during RTL generation but also, for example,
5883 by instruction combination. The result of @code{SELECT_CC_MODE} should
5884 be consistent with the mode used in the patterns; for example to support
5885 the case of the add on the SPARC discussed above, we have the pattern
5889 [(set (reg:CC_NOOV 0)
5891 (plus:SI (match_operand:SI 0 "register_operand" "%r")
5892 (match_operand:SI 1 "arith_operand" "rI"))
5899 together with a @code{SELECT_CC_MODE} that returns @code{CC_NOOVmode}
5900 for comparisons whose argument is a @code{plus}:
5903 #define SELECT_CC_MODE(OP,X,Y) \
5904 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
5905 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
5906 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
5907 || GET_CODE (X) == NEG) \
5908 ? CC_NOOVmode : CCmode))
5911 Another reason to use modes is to retain information on which operands
5912 were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
5915 You should define this macro if and only if you define extra CC modes
5916 in @file{@var{machine}-modes.def}.
5919 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
5920 On some machines not all possible comparisons are defined, but you can
5921 convert an invalid comparison into a valid one. For example, the Alpha
5922 does not have a @code{GT} comparison, but you can use an @code{LT}
5923 comparison instead and swap the order of the operands.
5925 On such machines, define this macro to be a C statement to do any
5926 required conversions. @var{code} is the initial comparison code
5927 and @var{op0} and @var{op1} are the left and right operands of the
5928 comparison, respectively. You should modify @var{code}, @var{op0}, and
5929 @var{op1} as required.
5931 GCC will not assume that the comparison resulting from this macro is
5932 valid but will see if the resulting insn matches a pattern in the
5935 You need not define this macro if it would never change the comparison
5939 @defmac REVERSIBLE_CC_MODE (@var{mode})
5940 A C expression whose value is one if it is always safe to reverse a
5941 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
5942 can ever return @var{mode} for a floating-point inequality comparison,
5943 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
5945 You need not define this macro if it would always returns zero or if the
5946 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
5947 For example, here is the definition used on the SPARC, where floating-point
5948 inequality comparisons are always given @code{CCFPEmode}:
5951 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
5955 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
5956 A C expression whose value is reversed condition code of the @var{code} for
5957 comparison done in CC_MODE @var{mode}. The macro is used only in case
5958 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
5959 machine has some non-standard way how to reverse certain conditionals. For
5960 instance in case all floating point conditions are non-trapping, compiler may
5961 freely convert unordered compares to ordered one. Then definition may look
5965 #define REVERSE_CONDITION(CODE, MODE) \
5966 ((MODE) != CCFPmode ? reverse_condition (CODE) \
5967 : reverse_condition_maybe_unordered (CODE))
5971 @deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *, unsigned int *)
5972 On targets which do not use @code{(cc0)}, and which use a hard
5973 register rather than a pseudo-register to hold condition codes, the
5974 regular CSE passes are often not able to identify cases in which the
5975 hard register is set to a common value. Use this hook to enable a
5976 small pass which optimizes such cases. This hook should return true
5977 to enable this pass, and it should set the integers to which its
5978 arguments point to the hard register numbers used for condition codes.
5979 When there is only one such register, as is true on most systems, the
5980 integer pointed to by the second argument should be set to
5981 @code{INVALID_REGNUM}.
5983 The default version of this hook returns false.
5986 @deftypefn {Target Hook} enum machine_mode TARGET_CC_MODES_COMPATIBLE (enum machine_mode, enum machine_mode)
5987 On targets which use multiple condition code modes in class
5988 @code{MODE_CC}, it is sometimes the case that a comparison can be
5989 validly done in more than one mode. On such a system, define this
5990 target hook to take two mode arguments and to return a mode in which
5991 both comparisons may be validly done. If there is no such mode,
5992 return @code{VOIDmode}.
5994 The default version of this hook checks whether the modes are the
5995 same. If they are, it returns that mode. If they are different, it
5996 returns @code{VOIDmode}.
5999 @node Cond. Exec. Macros
6000 @subsection Macros to control conditional execution
6001 @findex conditional execution
6004 There is one macro that may need to be defined for targets
6005 supporting conditional execution, independent of how they
6006 represent conditional branches.
6008 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2})
6009 A C expression that returns true if the conditional execution predicate
6010 @var{op1}, a comparison operation, is the inverse of @var{op2} and vice
6011 versa. Define this to return 0 if the target has conditional execution
6012 predicates that cannot be reversed safely. There is no need to validate
6013 that the arguments of op1 and op2 are the same, this is done separately.
6014 If no expansion is specified, this macro is defined as follows:
6017 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
6018 (GET_CODE ((x)) == reversed_comparison_code ((y), NULL))
6023 @section Describing Relative Costs of Operations
6024 @cindex costs of instructions
6025 @cindex relative costs
6026 @cindex speed of instructions
6028 These macros let you describe the relative speed of various operations
6029 on the target machine.
6031 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
6032 A C expression for the cost of moving data of mode @var{mode} from a
6033 register in class @var{from} to one in class @var{to}. The classes are
6034 expressed using the enumeration values such as @code{GENERAL_REGS}. A
6035 value of 2 is the default; other values are interpreted relative to
6038 It is not required that the cost always equal 2 when @var{from} is the
6039 same as @var{to}; on some machines it is expensive to move between
6040 registers if they are not general registers.
6042 If reload sees an insn consisting of a single @code{set} between two
6043 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
6044 classes returns a value of 2, reload does not check to ensure that the
6045 constraints of the insn are met. Setting a cost of other than 2 will
6046 allow reload to verify that the constraints are met. You should do this
6047 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
6050 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
6051 A C expression for the cost of moving data of mode @var{mode} between a
6052 register of class @var{class} and memory; @var{in} is zero if the value
6053 is to be written to memory, nonzero if it is to be read in. This cost
6054 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
6055 registers and memory is more expensive than between two registers, you
6056 should define this macro to express the relative cost.
6058 If you do not define this macro, GCC uses a default cost of 4 plus
6059 the cost of copying via a secondary reload register, if one is
6060 needed. If your machine requires a secondary reload register to copy
6061 between memory and a register of @var{class} but the reload mechanism is
6062 more complex than copying via an intermediate, define this macro to
6063 reflect the actual cost of the move.
6065 GCC defines the function @code{memory_move_secondary_cost} if
6066 secondary reloads are needed. It computes the costs due to copying via
6067 a secondary register. If your machine copies from memory using a
6068 secondary register in the conventional way but the default base value of
6069 4 is not correct for your machine, define this macro to add some other
6070 value to the result of that function. The arguments to that function
6071 are the same as to this macro.
6074 @defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
6075 A C expression for the cost of a branch instruction. A value of 1 is the
6076 default; other values are interpreted relative to that. Parameter @var{speed_p}
6077 is true when the branch in question should be optimized for speed. When
6078 it is false, @code{BRANCH_COST} should be returning value optimal for code size
6079 rather then performance considerations. @var{predictable_p} is true for well
6080 predictable branches. On many architectures the @code{BRANCH_COST} can be
6084 Here are additional macros which do not specify precise relative costs,
6085 but only that certain actions are more expensive than GCC would
6088 @defmac SLOW_BYTE_ACCESS
6089 Define this macro as a C expression which is nonzero if accessing less
6090 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
6091 faster than accessing a word of memory, i.e., if such access
6092 require more than one instruction or if there is no difference in cost
6093 between byte and (aligned) word loads.
6095 When this macro is not defined, the compiler will access a field by
6096 finding the smallest containing object; when it is defined, a fullword
6097 load will be used if alignment permits. Unless bytes accesses are
6098 faster than word accesses, using word accesses is preferable since it
6099 may eliminate subsequent memory access if subsequent accesses occur to
6100 other fields in the same word of the structure, but to different bytes.
6103 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
6104 Define this macro to be the value 1 if memory accesses described by the
6105 @var{mode} and @var{alignment} parameters have a cost many times greater
6106 than aligned accesses, for example if they are emulated in a trap
6109 When this macro is nonzero, the compiler will act as if
6110 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
6111 moves. This can cause significantly more instructions to be produced.
6112 Therefore, do not set this macro nonzero if unaligned accesses only add a
6113 cycle or two to the time for a memory access.
6115 If the value of this macro is always zero, it need not be defined. If
6116 this macro is defined, it should produce a nonzero value when
6117 @code{STRICT_ALIGNMENT} is nonzero.
6121 The threshold of number of scalar memory-to-memory move insns, @emph{below}
6122 which a sequence of insns should be generated instead of a
6123 string move insn or a library call. Increasing the value will always
6124 make code faster, but eventually incurs high cost in increased code size.
6126 Note that on machines where the corresponding move insn is a
6127 @code{define_expand} that emits a sequence of insns, this macro counts
6128 the number of such sequences.
6130 If you don't define this, a reasonable default is used.
6133 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
6134 A C expression used to determine whether @code{move_by_pieces} will be used to
6135 copy a chunk of memory, or whether some other block move mechanism
6136 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6137 than @code{MOVE_RATIO}.
6140 @defmac MOVE_MAX_PIECES
6141 A C expression used by @code{move_by_pieces} to determine the largest unit
6142 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
6146 The threshold of number of scalar move insns, @emph{below} which a sequence
6147 of insns should be generated to clear memory instead of a string clear insn
6148 or a library call. Increasing the value will always make code faster, but
6149 eventually incurs high cost in increased code size.
6151 If you don't define this, a reasonable default is used.
6154 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
6155 A C expression used to determine whether @code{clear_by_pieces} will be used
6156 to clear a chunk of memory, or whether some other block clear mechanism
6157 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6158 than @code{CLEAR_RATIO}.
6162 The threshold of number of scalar move insns, @emph{below} which a sequence
6163 of insns should be generated to set memory to a constant value, instead of
6164 a block set insn or a library call.
6165 Increasing the value will always make code faster, but
6166 eventually incurs high cost in increased code size.
6168 If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
6171 @defmac SET_BY_PIECES_P (@var{size}, @var{alignment})
6172 A C expression used to determine whether @code{store_by_pieces} will be
6173 used to set a chunk of memory to a constant value, or whether some
6174 other mechanism will be used. Used by @code{__builtin_memset} when
6175 storing values other than constant zero.
6176 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6177 than @code{SET_RATIO}.
6180 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
6181 A C expression used to determine whether @code{store_by_pieces} will be
6182 used to set a chunk of memory to a constant string value, or whether some
6183 other mechanism will be used. Used by @code{__builtin_strcpy} when
6184 called with a constant source string.
6185 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6186 than @code{MOVE_RATIO}.
6189 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
6190 A C expression used to determine whether a load postincrement is a good
6191 thing to use for a given mode. Defaults to the value of
6192 @code{HAVE_POST_INCREMENT}.
6195 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
6196 A C expression used to determine whether a load postdecrement is a good
6197 thing to use for a given mode. Defaults to the value of
6198 @code{HAVE_POST_DECREMENT}.
6201 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
6202 A C expression used to determine whether a load preincrement is a good
6203 thing to use for a given mode. Defaults to the value of
6204 @code{HAVE_PRE_INCREMENT}.
6207 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
6208 A C expression used to determine whether a load predecrement is a good
6209 thing to use for a given mode. Defaults to the value of
6210 @code{HAVE_PRE_DECREMENT}.
6213 @defmac USE_STORE_POST_INCREMENT (@var{mode})
6214 A C expression used to determine whether a store postincrement is a good
6215 thing to use for a given mode. Defaults to the value of
6216 @code{HAVE_POST_INCREMENT}.
6219 @defmac USE_STORE_POST_DECREMENT (@var{mode})
6220 A C expression used to determine whether a store postdecrement is a good
6221 thing to use for a given mode. Defaults to the value of
6222 @code{HAVE_POST_DECREMENT}.
6225 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
6226 This macro is used to determine whether a store preincrement is a good
6227 thing to use for a given mode. Defaults to the value of
6228 @code{HAVE_PRE_INCREMENT}.
6231 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
6232 This macro is used to determine whether a store predecrement is a good
6233 thing to use for a given mode. Defaults to the value of
6234 @code{HAVE_PRE_DECREMENT}.
6237 @defmac NO_FUNCTION_CSE
6238 Define this macro if it is as good or better to call a constant
6239 function address than to call an address kept in a register.
6242 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
6243 Define this macro if a non-short-circuit operation produced by
6244 @samp{fold_range_test ()} is optimal. This macro defaults to true if
6245 @code{BRANCH_COST} is greater than or equal to the value 2.
6248 @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total})
6249 This target hook describes the relative costs of RTL expressions.
6251 The cost may depend on the precise form of the expression, which is
6252 available for examination in @var{x}, and the rtx code of the expression
6253 in which it is contained, found in @var{outer_code}. @var{code} is the
6254 expression code---redundant, since it can be obtained with
6255 @code{GET_CODE (@var{x})}.
6257 In implementing this hook, you can use the construct
6258 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
6261 On entry to the hook, @code{*@var{total}} contains a default estimate
6262 for the cost of the expression. The hook should modify this value as
6263 necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
6264 for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
6265 operations, and @code{COSTS_N_INSNS (1)} for all other operations.
6267 When optimizing for code size, i.e.@: when @code{optimize_size} is
6268 nonzero, this target hook should be used to estimate the relative
6269 size cost of an expression, again relative to @code{COSTS_N_INSNS}.
6271 The hook returns true when all subexpressions of @var{x} have been
6272 processed, and false when @code{rtx_cost} should recurse.
6275 @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address})
6276 This hook computes the cost of an addressing mode that contains
6277 @var{address}. If not defined, the cost is computed from
6278 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
6280 For most CISC machines, the default cost is a good approximation of the
6281 true cost of the addressing mode. However, on RISC machines, all
6282 instructions normally have the same length and execution time. Hence
6283 all addresses will have equal costs.
6285 In cases where more than one form of an address is known, the form with
6286 the lowest cost will be used. If multiple forms have the same, lowest,
6287 cost, the one that is the most complex will be used.
6289 For example, suppose an address that is equal to the sum of a register
6290 and a constant is used twice in the same basic block. When this macro
6291 is not defined, the address will be computed in a register and memory
6292 references will be indirect through that register. On machines where
6293 the cost of the addressing mode containing the sum is no higher than
6294 that of a simple indirect reference, this will produce an additional
6295 instruction and possibly require an additional register. Proper
6296 specification of this macro eliminates this overhead for such machines.
6298 This hook is never called with an invalid address.
6300 On machines where an address involving more than one register is as
6301 cheap as an address computation involving only one register, defining
6302 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
6303 be live over a region of code where only one would have been if
6304 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
6305 should be considered in the definition of this macro. Equivalent costs
6306 should probably only be given to addresses with different numbers of
6307 registers on machines with lots of registers.
6311 @section Adjusting the Instruction Scheduler
6313 The instruction scheduler may need a fair amount of machine-specific
6314 adjustment in order to produce good code. GCC provides several target
6315 hooks for this purpose. It is usually enough to define just a few of
6316 them: try the first ones in this list first.
6318 @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
6319 This hook returns the maximum number of instructions that can ever
6320 issue at the same time on the target machine. The default is one.
6321 Although the insn scheduler can define itself the possibility of issue
6322 an insn on the same cycle, the value can serve as an additional
6323 constraint to issue insns on the same simulated processor cycle (see
6324 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
6325 This value must be constant over the entire compilation. If you need
6326 it to vary depending on what the instructions are, you must use
6327 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
6330 @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
6331 This hook is executed by the scheduler after it has scheduled an insn
6332 from the ready list. It should return the number of insns which can
6333 still be issued in the current cycle. The default is
6334 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
6335 @code{USE}, which normally are not counted against the issue rate.
6336 You should define this hook if some insns take more machine resources
6337 than others, so that fewer insns can follow them in the same cycle.
6338 @var{file} is either a null pointer, or a stdio stream to write any
6339 debug output to. @var{verbose} is the verbose level provided by
6340 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
6344 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
6345 This function corrects the value of @var{cost} based on the
6346 relationship between @var{insn} and @var{dep_insn} through the
6347 dependence @var{link}. It should return the new value. The default
6348 is to make no adjustment to @var{cost}. This can be used for example
6349 to specify to the scheduler using the traditional pipeline description
6350 that an output- or anti-dependence does not incur the same cost as a
6351 data-dependence. If the scheduler using the automaton based pipeline
6352 description, the cost of anti-dependence is zero and the cost of
6353 output-dependence is maximum of one and the difference of latency
6354 times of the first and the second insns. If these values are not
6355 acceptable, you could use the hook to modify them too. See also
6356 @pxref{Processor pipeline description}.
6359 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
6360 This hook adjusts the integer scheduling priority @var{priority} of
6361 @var{insn}. It should return the new priority. Increase the priority to
6362 execute @var{insn} earlier, reduce the priority to execute @var{insn}
6363 later. Do not define this hook if you do not need to adjust the
6364 scheduling priorities of insns.
6367 @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
6368 This hook is executed by the scheduler after it has scheduled the ready
6369 list, to allow the machine description to reorder it (for example to
6370 combine two small instructions together on @samp{VLIW} machines).
6371 @var{file} is either a null pointer, or a stdio stream to write any
6372 debug output to. @var{verbose} is the verbose level provided by
6373 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
6374 list of instructions that are ready to be scheduled. @var{n_readyp} is
6375 a pointer to the number of elements in the ready list. The scheduler
6376 reads the ready list in reverse order, starting with
6377 @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock}
6378 is the timer tick of the scheduler. You may modify the ready list and
6379 the number of ready insns. The return value is the number of insns that
6380 can issue this cycle; normally this is just @code{issue_rate}. See also
6381 @samp{TARGET_SCHED_REORDER2}.
6384 @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock})
6385 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
6386 function is called whenever the scheduler starts a new cycle. This one
6387 is called once per iteration over a cycle, immediately after
6388 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
6389 return the number of insns to be scheduled in the same cycle. Defining
6390 this hook can be useful if there are frequent situations where
6391 scheduling one insn causes other insns to become ready in the same
6392 cycle. These other insns can then be taken into account properly.
6395 @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail})
6396 This hook is called after evaluation forward dependencies of insns in
6397 chain given by two parameter values (@var{head} and @var{tail}
6398 correspondingly) but before insns scheduling of the insn chain. For
6399 example, it can be used for better insn classification if it requires
6400 analysis of dependencies. This hook can use backward and forward
6401 dependencies of the insn scheduler because they are already
6405 @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
6406 This hook is executed by the scheduler at the beginning of each block of
6407 instructions that are to be scheduled. @var{file} is either a null
6408 pointer, or a stdio stream to write any debug output to. @var{verbose}
6409 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6410 @var{max_ready} is the maximum number of insns in the current scheduling
6411 region that can be live at the same time. This can be used to allocate
6412 scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
6415 @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
6416 This hook is executed by the scheduler at the end of each block of
6417 instructions that are to be scheduled. It can be used to perform
6418 cleanup of any actions done by the other scheduling hooks. @var{file}
6419 is either a null pointer, or a stdio stream to write any debug output
6420 to. @var{verbose} is the verbose level provided by
6421 @option{-fsched-verbose-@var{n}}.
6424 @deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid})
6425 This hook is executed by the scheduler after function level initializations.
6426 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6427 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6428 @var{old_max_uid} is the maximum insn uid when scheduling begins.
6431 @deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose})
6432 This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
6433 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6434 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6437 @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
6438 The hook returns an RTL insn. The automaton state used in the
6439 pipeline hazard recognizer is changed as if the insn were scheduled
6440 when the new simulated processor cycle starts. Usage of the hook may
6441 simplify the automaton pipeline description for some @acronym{VLIW}
6442 processors. If the hook is defined, it is used only for the automaton
6443 based pipeline description. The default is not to change the state
6444 when the new simulated processor cycle starts.
6447 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
6448 The hook can be used to initialize data used by the previous hook.
6451 @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
6452 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6453 to changed the state as if the insn were scheduled when the new
6454 simulated processor cycle finishes.
6457 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
6458 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
6459 used to initialize data used by the previous hook.
6462 @deftypefn {Target Hook} void TARGET_SCHED_DFA_PRE_CYCLE_ADVANCE (void)
6463 The hook to notify target that the current simulated cycle is about to finish.
6464 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6465 to change the state in more complicated situations - e.g., when advancing
6466 state on a single insn is not enough.
6469 @deftypefn {Target Hook} void TARGET_SCHED_DFA_POST_CYCLE_ADVANCE (void)
6470 The hook to notify target that new simulated cycle has just started.
6471 The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used
6472 to change the state in more complicated situations - e.g., when advancing
6473 state on a single insn is not enough.
6476 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
6477 This hook controls better choosing an insn from the ready insn queue
6478 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
6479 chooses the first insn from the queue. If the hook returns a positive
6480 value, an additional scheduler code tries all permutations of
6481 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
6482 subsequent ready insns to choose an insn whose issue will result in
6483 maximal number of issued insns on the same cycle. For the
6484 @acronym{VLIW} processor, the code could actually solve the problem of
6485 packing simple insns into the @acronym{VLIW} insn. Of course, if the
6486 rules of @acronym{VLIW} packing are described in the automaton.
6488 This code also could be used for superscalar @acronym{RISC}
6489 processors. Let us consider a superscalar @acronym{RISC} processor
6490 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
6491 @var{B}, some insns can be executed only in pipelines @var{B} or
6492 @var{C}, and one insn can be executed in pipeline @var{B}. The
6493 processor may issue the 1st insn into @var{A} and the 2nd one into
6494 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
6495 until the next cycle. If the scheduler issues the 3rd insn the first,
6496 the processor could issue all 3 insns per cycle.
6498 Actually this code demonstrates advantages of the automaton based
6499 pipeline hazard recognizer. We try quickly and easy many insn
6500 schedules to choose the best one.
6502 The default is no multipass scheduling.
6505 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx)
6507 This hook controls what insns from the ready insn queue will be
6508 considered for the multipass insn scheduling. If the hook returns
6509 zero for insn passed as the parameter, the insn will be not chosen to
6512 The default is that any ready insns can be chosen to be issued.
6515 @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *)
6517 This hook is called by the insn scheduler before issuing insn passed
6518 as the third parameter on given cycle. If the hook returns nonzero,
6519 the insn is not issued on given processors cycle. Instead of that,
6520 the processor cycle is advanced. If the value passed through the last
6521 parameter is zero, the insn ready queue is not sorted on the new cycle
6522 start as usually. The first parameter passes file for debugging
6523 output. The second one passes the scheduler verbose level of the
6524 debugging output. The forth and the fifth parameter values are
6525 correspondingly processor cycle on which the previous insn has been
6526 issued and the current processor cycle.
6529 @deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (struct dep_def *@var{_dep}, int @var{cost}, int @var{distance})
6530 This hook is used to define which dependences are considered costly by
6531 the target, so costly that it is not advisable to schedule the insns that
6532 are involved in the dependence too close to one another. The parameters
6533 to this hook are as follows: The first parameter @var{_dep} is the dependence
6534 being evaluated. The second parameter @var{cost} is the cost of the
6535 dependence, and the third
6536 parameter @var{distance} is the distance in cycles between the two insns.
6537 The hook returns @code{true} if considering the distance between the two
6538 insns the dependence between them is considered costly by the target,
6539 and @code{false} otherwise.
6541 Defining this hook can be useful in multiple-issue out-of-order machines,
6542 where (a) it's practically hopeless to predict the actual data/resource
6543 delays, however: (b) there's a better chance to predict the actual grouping
6544 that will be formed, and (c) correctly emulating the grouping can be very
6545 important. In such targets one may want to allow issuing dependent insns
6546 closer to one another---i.e., closer than the dependence distance; however,
6547 not in cases of "costly dependences", which this hooks allows to define.
6550 @deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void)
6551 This hook is called by the insn scheduler after emitting a new instruction to
6552 the instruction stream. The hook notifies a target backend to extend its
6553 per instruction data structures.
6556 @deftypefn {Target Hook} void * TARGET_SCHED_ALLOC_SCHED_CONTEXT (void)
6557 Return a pointer to a store large enough to hold target scheduling context.
6560 @deftypefn {Target Hook} void TARGET_SCHED_INIT_SCHED_CONTEXT (void *@var{tc}, bool @var{clean_p})
6561 Initialize store pointed to by @var{tc} to hold target scheduling context.
6562 It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
6563 beginning of the block. Otherwise, make a copy of the current context in
6567 @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_CONTEXT (void *@var{tc})
6568 Copy target scheduling context pointer to by @var{tc} to the current context.
6571 @deftypefn {Target Hook} void TARGET_SCHED_CLEAR_SCHED_CONTEXT (void *@var{tc})
6572 Deallocate internal data in target scheduling context pointed to by @var{tc}.
6575 @deftypefn {Target Hook} void TARGET_SCHED_FREE_SCHED_CONTEXT (void *@var{tc})
6576 Deallocate a store for target scheduling context pointed to by @var{tc}.
6579 @deftypefn {Target Hook} void * TARGET_SCHED_ALLOC_SCHED_CONTEXT (void)
6580 Return a pointer to a store large enough to hold target scheduling context.
6583 @deftypefn {Target Hook} void TARGET_SCHED_INIT_SCHED_CONTEXT (void *@var{tc}, bool @var{clean_p})
6584 Initialize store pointed to by @var{tc} to hold target scheduling context.
6585 It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
6586 beginning of the block. Otherwise, make a copy of the current context in
6590 @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_CONTEXT (void *@var{tc})
6591 Copy target scheduling context pointer to by @var{tc} to the current context.
6594 @deftypefn {Target Hook} void TARGET_SCHED_CLEAR_SCHED_CONTEXT (void *@var{tc})
6595 Deallocate internal data in target scheduling context pointed to by @var{tc}.
6598 @deftypefn {Target Hook} void TARGET_SCHED_FREE_SCHED_CONTEXT (void *@var{tc})
6599 Deallocate a store for target scheduling context pointed to by @var{tc}.
6602 @deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx @var{insn}, int @var{request}, rtx *@var{new_pat})
6603 This hook is called by the insn scheduler when @var{insn} has only
6604 speculative dependencies and therefore can be scheduled speculatively.
6605 The hook is used to check if the pattern of @var{insn} has a speculative
6606 version and, in case of successful check, to generate that speculative
6607 pattern. The hook should return 1, if the instruction has a speculative form,
6608 or -1, if it doesn't. @var{request} describes the type of requested
6609 speculation. If the return value equals 1 then @var{new_pat} is assigned
6610 the generated speculative pattern.
6613 @deftypefn {Target Hook} int TARGET_SCHED_NEEDS_BLOCK_P (rtx @var{insn})
6614 This hook is called by the insn scheduler during generation of recovery code
6615 for @var{insn}. It should return nonzero, if the corresponding check
6616 instruction should branch to recovery code, or zero otherwise.
6619 @deftypefn {Target Hook} rtx TARGET_SCHED_GEN_CHECK (rtx @var{insn}, rtx @var{label}, int @var{mutate_p})
6620 This hook is called by the insn scheduler to generate a pattern for recovery
6621 check instruction. If @var{mutate_p} is zero, then @var{insn} is a
6622 speculative instruction for which the check should be generated.
6623 @var{label} is either a label of a basic block, where recovery code should
6624 be emitted, or a null pointer, when requested check doesn't branch to
6625 recovery code (a simple check). If @var{mutate_p} is nonzero, then
6626 a pattern for a branchy check corresponding to a simple check denoted by
6627 @var{insn} should be generated. In this case @var{label} can't be null.
6630 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC (rtx @var{insn})
6631 This hook is used as a workaround for
6632 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being
6633 called on the first instruction of the ready list. The hook is used to
6634 discard speculative instruction that stand first in the ready list from
6635 being scheduled on the current cycle. For non-speculative instructions,
6636 the hook should always return nonzero. For example, in the ia64 backend
6637 the hook is used to cancel data speculative insns when the ALAT table
6641 @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (unsigned int *@var{flags}, spec_info_t @var{spec_info})
6642 This hook is used by the insn scheduler to find out what features should be
6643 enabled/used. @var{flags} initially may have either the SCHED_RGN or SCHED_EBB
6644 bit set. This denotes the scheduler pass for which the data should be
6645 provided. The target backend should modify @var{flags} by modifying
6646 the bits corresponding to the following features: USE_DEPS_LIST, USE_GLAT,
6647 DETACH_LIFE_INFO, and DO_SPECULATION@. For the DO_SPECULATION feature
6648 an additional structure @var{spec_info} should be filled by the target.
6649 The structure describes speculation types that can be used in the scheduler.
6652 @deftypefn {Target Hook} int TARGET_SCHED_SMS_RES_MII (struct ddg *@var{g})
6653 This hook is called by the swing modulo scheduler to calculate a
6654 resource-based lower bound which is based on the resources available in
6655 the machine and the resources required by each instruction. The target
6656 backend can use @var{g} to calculate such bound. A very simple lower
6657 bound will be used in case this hook is not implemented: the total number
6658 of instructions divided by the issue rate.
6662 @section Dividing the Output into Sections (Texts, Data, @dots{})
6663 @c the above section title is WAY too long. maybe cut the part between
6664 @c the (...)? --mew 10feb93
6666 An object file is divided into sections containing different types of
6667 data. In the most common case, there are three sections: the @dfn{text
6668 section}, which holds instructions and read-only data; the @dfn{data
6669 section}, which holds initialized writable data; and the @dfn{bss
6670 section}, which holds uninitialized data. Some systems have other kinds
6673 @file{varasm.c} provides several well-known sections, such as
6674 @code{text_section}, @code{data_section} and @code{bss_section}.
6675 The normal way of controlling a @code{@var{foo}_section} variable
6676 is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
6677 as described below. The macros are only read once, when @file{varasm.c}
6678 initializes itself, so their values must be run-time constants.
6679 They may however depend on command-line flags.
6681 @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
6682 use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
6683 to be string literals.
6685 Some assemblers require a different string to be written every time a
6686 section is selected. If your assembler falls into this category, you
6687 should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
6688 @code{get_unnamed_section} to set up the sections.
6690 You must always create a @code{text_section}, either by defining
6691 @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
6692 in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of
6693 @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not
6694 create a distinct @code{readonly_data_section}, the default is to
6695 reuse @code{text_section}.
6697 All the other @file{varasm.c} sections are optional, and are null
6698 if the target does not provide them.
6700 @defmac TEXT_SECTION_ASM_OP
6701 A C expression whose value is a string, including spacing, containing the
6702 assembler operation that should precede instructions and read-only data.
6703 Normally @code{"\t.text"} is right.
6706 @defmac HOT_TEXT_SECTION_NAME
6707 If defined, a C string constant for the name of the section containing most
6708 frequently executed functions of the program. If not defined, GCC will provide
6709 a default definition if the target supports named sections.
6712 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
6713 If defined, a C string constant for the name of the section containing unlikely
6714 executed functions in the program.
6717 @defmac DATA_SECTION_ASM_OP
6718 A C expression whose value is a string, including spacing, containing the
6719 assembler operation to identify the following data as writable initialized
6720 data. Normally @code{"\t.data"} is right.
6723 @defmac SDATA_SECTION_ASM_OP
6724 If defined, a C expression whose value is a string, including spacing,
6725 containing the assembler operation to identify the following data as
6726 initialized, writable small data.
6729 @defmac READONLY_DATA_SECTION_ASM_OP
6730 A C expression whose value is a string, including spacing, containing the
6731 assembler operation to identify the following data as read-only initialized
6735 @defmac BSS_SECTION_ASM_OP
6736 If defined, a C expression whose value is a string, including spacing,
6737 containing the assembler operation to identify the following data as
6738 uninitialized global data. If not defined, and neither
6739 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
6740 uninitialized global data will be output in the data section if
6741 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
6745 @defmac SBSS_SECTION_ASM_OP
6746 If defined, a C expression whose value is a string, including spacing,
6747 containing the assembler operation to identify the following data as
6748 uninitialized, writable small data.
6751 @defmac INIT_SECTION_ASM_OP
6752 If defined, a C expression whose value is a string, including spacing,
6753 containing the assembler operation to identify the following data as
6754 initialization code. If not defined, GCC will assume such a section does
6755 not exist. This section has no corresponding @code{init_section}
6756 variable; it is used entirely in runtime code.
6759 @defmac FINI_SECTION_ASM_OP
6760 If defined, a C expression whose value is a string, including spacing,
6761 containing the assembler operation to identify the following data as
6762 finalization code. If not defined, GCC will assume such a section does
6763 not exist. This section has no corresponding @code{fini_section}
6764 variable; it is used entirely in runtime code.
6767 @defmac INIT_ARRAY_SECTION_ASM_OP
6768 If defined, a C expression whose value is a string, including spacing,
6769 containing the assembler operation to identify the following data as
6770 part of the @code{.init_array} (or equivalent) section. If not
6771 defined, GCC will assume such a section does not exist. Do not define
6772 both this macro and @code{INIT_SECTION_ASM_OP}.
6775 @defmac FINI_ARRAY_SECTION_ASM_OP
6776 If defined, a C expression whose value is a string, including spacing,
6777 containing the assembler operation to identify the following data as
6778 part of the @code{.fini_array} (or equivalent) section. If not
6779 defined, GCC will assume such a section does not exist. Do not define
6780 both this macro and @code{FINI_SECTION_ASM_OP}.
6783 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
6784 If defined, an ASM statement that switches to a different section
6785 via @var{section_op}, calls @var{function}, and switches back to
6786 the text section. This is used in @file{crtstuff.c} if
6787 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
6788 to initialization and finalization functions from the init and fini
6789 sections. By default, this macro uses a simple function call. Some
6790 ports need hand-crafted assembly code to avoid dependencies on
6791 registers initialized in the function prologue or to ensure that
6792 constant pools don't end up too far way in the text section.
6795 @defmac TARGET_LIBGCC_SDATA_SECTION
6796 If defined, a string which names the section into which small
6797 variables defined in crtstuff and libgcc should go. This is useful
6798 when the target has options for optimizing access to small data, and
6799 you want the crtstuff and libgcc routines to be conservative in what
6800 they expect of your application yet liberal in what your application
6801 expects. For example, for targets with a @code{.sdata} section (like
6802 MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
6803 require small data support from your application, but use this macro
6804 to put small data into @code{.sdata} so that your application can
6805 access these variables whether it uses small data or not.
6808 @defmac FORCE_CODE_SECTION_ALIGN
6809 If defined, an ASM statement that aligns a code section to some
6810 arbitrary boundary. This is used to force all fragments of the
6811 @code{.init} and @code{.fini} sections to have to same alignment
6812 and thus prevent the linker from having to add any padding.
6815 @defmac JUMP_TABLES_IN_TEXT_SECTION
6816 Define this macro to be an expression with a nonzero value if jump
6817 tables (for @code{tablejump} insns) should be output in the text
6818 section, along with the assembler instructions. Otherwise, the
6819 readonly data section is used.
6821 This macro is irrelevant if there is no separate readonly data section.
6824 @deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void)
6825 Define this hook if you need to do something special to set up the
6826 @file{varasm.c} sections, or if your target has some special sections
6827 of its own that you need to create.
6829 GCC calls this hook after processing the command line, but before writing
6830 any assembly code, and before calling any of the section-returning hooks
6834 @deftypefn {Target Hook} TARGET_ASM_RELOC_RW_MASK (void)
6835 Return a mask describing how relocations should be treated when
6836 selecting sections. Bit 1 should be set if global relocations
6837 should be placed in a read-write section; bit 0 should be set if
6838 local relocations should be placed in a read-write section.
6840 The default version of this function returns 3 when @option{-fpic}
6841 is in effect, and 0 otherwise. The hook is typically redefined
6842 when the target cannot support (some kinds of) dynamic relocations
6843 in read-only sections even in executables.
6846 @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
6847 Return the section into which @var{exp} should be placed. You can
6848 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
6849 some sort. @var{reloc} indicates whether the initial value of @var{exp}
6850 requires link-time relocations. Bit 0 is set when variable contains
6851 local relocations only, while bit 1 is set for global relocations.
6852 @var{align} is the constant alignment in bits.
6854 The default version of this function takes care of putting read-only
6855 variables in @code{readonly_data_section}.
6857 See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
6860 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS
6861 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
6862 for @code{FUNCTION_DECL}s as well as for variables and constants.
6864 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
6865 function has been determined to be likely to be called, and nonzero if
6866 it is unlikely to be called.
6869 @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
6870 Build up a unique section name, expressed as a @code{STRING_CST} node,
6871 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
6872 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
6873 the initial value of @var{exp} requires link-time relocations.
6875 The default version of this function appends the symbol name to the
6876 ELF section name that would normally be used for the symbol. For
6877 example, the function @code{foo} would be placed in @code{.text.foo}.
6878 Whatever the actual target object format, this is often good enough.
6881 @deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl})
6882 Return the readonly data section associated with
6883 @samp{DECL_SECTION_NAME (@var{decl})}.
6884 The default version of this function selects @code{.gnu.linkonce.r.name} if
6885 the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name}
6886 if function is in @code{.text.name}, and the normal readonly-data section
6890 @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
6891 Return the section into which a constant @var{x}, of mode @var{mode},
6892 should be placed. You can assume that @var{x} is some kind of
6893 constant in RTL@. The argument @var{mode} is redundant except in the
6894 case of a @code{const_int} rtx. @var{align} is the constant alignment
6897 The default version of this function takes care of putting symbolic
6898 constants in @code{flag_pic} mode in @code{data_section} and everything
6899 else in @code{readonly_data_section}.
6902 @deftypefn {Target Hook} void TARGET_MANGLE_DECL_ASSEMBLER_NAME (tree @var{decl}, tree @var{id})
6903 Define this hook if you need to postprocess the assembler name generated
6904 by target-independent code. The @var{id} provided to this hook will be
6905 the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C,
6906 or the mangled name of the @var{decl} in C++). The return value of the
6907 hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on
6908 your target system. The default implementation of this hook just
6909 returns the @var{id} provided.
6912 @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
6913 Define this hook if references to a symbol or a constant must be
6914 treated differently depending on something about the variable or
6915 function named by the symbol (such as what section it is in).
6917 The hook is executed immediately after rtl has been created for
6918 @var{decl}, which may be a variable or function declaration or
6919 an entry in the constant pool. In either case, @var{rtl} is the
6920 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
6921 in this hook; that field may not have been initialized yet.
6923 In the case of a constant, it is safe to assume that the rtl is
6924 a @code{mem} whose address is a @code{symbol_ref}. Most decls
6925 will also have this form, but that is not guaranteed. Global
6926 register variables, for instance, will have a @code{reg} for their
6927 rtl. (Normally the right thing to do with such unusual rtl is
6930 The @var{new_decl_p} argument will be true if this is the first time
6931 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
6932 be false for subsequent invocations, which will happen for duplicate
6933 declarations. Whether or not anything must be done for the duplicate
6934 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
6935 @var{new_decl_p} is always true when the hook is called for a constant.
6937 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
6938 The usual thing for this hook to do is to record flags in the
6939 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
6940 Historically, the name string was modified if it was necessary to
6941 encode more than one bit of information, but this practice is now
6942 discouraged; use @code{SYMBOL_REF_FLAGS}.
6944 The default definition of this hook, @code{default_encode_section_info}
6945 in @file{varasm.c}, sets a number of commonly-useful bits in
6946 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
6947 before overriding it.
6950 @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name)
6951 Decode @var{name} and return the real name part, sans
6952 the characters that @code{TARGET_ENCODE_SECTION_INFO}
6956 @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp})
6957 Returns true if @var{exp} should be placed into a ``small data'' section.
6958 The default version of this hook always returns false.
6961 @deftypevr {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
6962 Contains the value true if the target places read-only
6963 ``small data'' into a separate section. The default value is false.
6966 @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp})
6967 Returns true if @var{exp} names an object for which name resolution
6968 rules must resolve to the current ``module'' (dynamic shared library
6969 or executable image).
6971 The default version of this hook implements the name resolution rules
6972 for ELF, which has a looser model of global name binding than other
6973 currently supported object file formats.
6976 @deftypevr {Target Hook} bool TARGET_HAVE_TLS
6977 Contains the value true if the target supports thread-local storage.
6978 The default value is false.
6983 @section Position Independent Code
6984 @cindex position independent code
6987 This section describes macros that help implement generation of position
6988 independent code. Simply defining these macros is not enough to
6989 generate valid PIC; you must also add support to the hook
6990 @code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
6991 @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You
6992 must modify the definition of @samp{movsi} to do something appropriate
6993 when the source operand contains a symbolic address. You may also
6994 need to alter the handling of switch statements so that they use
6996 @c i rearranged the order of the macros above to try to force one of
6997 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
6999 @defmac PIC_OFFSET_TABLE_REGNUM
7000 The register number of the register used to address a table of static
7001 data addresses in memory. In some cases this register is defined by a
7002 processor's ``application binary interface'' (ABI)@. When this macro
7003 is defined, RTL is generated for this register once, as with the stack
7004 pointer and frame pointer registers. If this macro is not defined, it
7005 is up to the machine-dependent files to allocate such a register (if
7006 necessary). Note that this register must be fixed when in use (e.g.@:
7007 when @code{flag_pic} is true).
7010 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
7011 Define this macro if the register defined by
7012 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define
7013 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
7016 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
7017 A C expression that is nonzero if @var{x} is a legitimate immediate
7018 operand on the target machine when generating position independent code.
7019 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
7020 check this. You can also assume @var{flag_pic} is true, so you need not
7021 check it either. You need not define this macro if all constants
7022 (including @code{SYMBOL_REF}) can be immediate operands when generating
7023 position independent code.
7026 @node Assembler Format
7027 @section Defining the Output Assembler Language
7029 This section describes macros whose principal purpose is to describe how
7030 to write instructions in assembler language---rather than what the
7034 * File Framework:: Structural information for the assembler file.
7035 * Data Output:: Output of constants (numbers, strings, addresses).
7036 * Uninitialized Data:: Output of uninitialized variables.
7037 * Label Output:: Output and generation of labels.
7038 * Initialization:: General principles of initialization
7039 and termination routines.
7040 * Macros for Initialization::
7041 Specific macros that control the handling of
7042 initialization and termination routines.
7043 * Instruction Output:: Output of actual instructions.
7044 * Dispatch Tables:: Output of jump tables.
7045 * Exception Region Output:: Output of exception region code.
7046 * Alignment Output:: Pseudo ops for alignment and skipping data.
7049 @node File Framework
7050 @subsection The Overall Framework of an Assembler File
7051 @cindex assembler format
7052 @cindex output of assembler code
7054 @c prevent bad page break with this line
7055 This describes the overall framework of an assembly file.
7057 @deftypefn {Target Hook} void TARGET_ASM_FILE_START ()
7058 @findex default_file_start
7059 Output to @code{asm_out_file} any text which the assembler expects to
7060 find at the beginning of a file. The default behavior is controlled
7061 by two flags, documented below. Unless your target's assembler is
7062 quite unusual, if you override the default, you should call
7063 @code{default_file_start} at some point in your target hook. This
7064 lets other target files rely on these variables.
7067 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
7068 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
7069 printed as the very first line in the assembly file, unless
7070 @option{-fverbose-asm} is in effect. (If that macro has been defined
7071 to the empty string, this variable has no effect.) With the normal
7072 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
7073 assembler that it need not bother stripping comments or extra
7074 whitespace from its input. This allows it to work a bit faster.
7076 The default is false. You should not set it to true unless you have
7077 verified that your port does not generate any extra whitespace or
7078 comments that will cause GAS to issue errors in NO_APP mode.
7081 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
7082 If this flag is true, @code{output_file_directive} will be called
7083 for the primary source file, immediately after printing
7084 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
7085 this to be done. The default is false.
7088 @deftypefn {Target Hook} void TARGET_ASM_FILE_END ()
7089 Output to @code{asm_out_file} any text which the assembler expects
7090 to find at the end of a file. The default is to output nothing.
7093 @deftypefun void file_end_indicate_exec_stack ()
7094 Some systems use a common convention, the @samp{.note.GNU-stack}
7095 special section, to indicate whether or not an object file relies on
7096 the stack being executable. If your system uses this convention, you
7097 should define @code{TARGET_ASM_FILE_END} to this function. If you
7098 need to do other things in that hook, have your hook function call
7102 @defmac ASM_COMMENT_START
7103 A C string constant describing how to begin a comment in the target
7104 assembler language. The compiler assumes that the comment will end at
7105 the end of the line.
7109 A C string constant for text to be output before each @code{asm}
7110 statement or group of consecutive ones. Normally this is
7111 @code{"#APP"}, which is a comment that has no effect on most
7112 assemblers but tells the GNU assembler that it must check the lines
7113 that follow for all valid assembler constructs.
7117 A C string constant for text to be output after each @code{asm}
7118 statement or group of consecutive ones. Normally this is
7119 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
7120 time-saving assumptions that are valid for ordinary compiler output.
7123 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
7124 A C statement to output COFF information or DWARF debugging information
7125 which indicates that filename @var{name} is the current source file to
7126 the stdio stream @var{stream}.
7128 This macro need not be defined if the standard form of output
7129 for the file format in use is appropriate.
7132 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
7133 A C statement to output the string @var{string} to the stdio stream
7134 @var{stream}. If you do not call the function @code{output_quoted_string}
7135 in your config files, GCC will only call it to output filenames to
7136 the assembler source. So you can use it to canonicalize the format
7137 of the filename using this macro.
7140 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
7141 A C statement to output something to the assembler file to handle a
7142 @samp{#ident} directive containing the text @var{string}. If this
7143 macro is not defined, nothing is output for a @samp{#ident} directive.
7146 @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align})
7147 Output assembly directives to switch to section @var{name}. The section
7148 should have attributes as specified by @var{flags}, which is a bit mask
7149 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align}
7150 is nonzero, it contains an alignment in bytes to be used for the section,
7151 otherwise some target default should be used. Only targets that must
7152 specify an alignment within the section directive need pay attention to
7153 @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}.
7156 @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
7157 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
7160 @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
7161 @deftypefn {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
7162 This flag is true if we can create zeroed data by switching to a BSS
7163 section and then using @code{ASM_OUTPUT_SKIP} to allocate the space.
7164 This is true on most ELF targets.
7167 @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
7168 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
7169 based on a variable or function decl, a section name, and whether or not the
7170 declaration's initializer may contain runtime relocations. @var{decl} may be
7171 null, in which case read-write data should be assumed.
7173 The default version of this function handles choosing code vs data,
7174 read-only vs read-write data, and @code{flag_pic}. You should only
7175 need to override this if your target has special flags that might be
7176 set via @code{__attribute__}.
7179 @deftypefn {Target Hook} {int} TARGET_ASM_RECORD_GCC_SWITCHES (print_switch_type @var{type}, const char * @var{text})
7180 Provides the target with the ability to record the gcc command line
7181 switches that have been passed to the compiler, and options that are
7182 enabled. The @var{type} argument specifies what is being recorded.
7183 It can take the following values:
7186 @item SWITCH_TYPE_PASSED
7187 @var{text} is a command line switch that has been set by the user.
7189 @item SWITCH_TYPE_ENABLED
7190 @var{text} is an option which has been enabled. This might be as a
7191 direct result of a command line switch, or because it is enabled by
7192 default or because it has been enabled as a side effect of a different
7193 command line switch. For example, the @option{-O2} switch enables
7194 various different individual optimization passes.
7196 @item SWITCH_TYPE_DESCRIPTIVE
7197 @var{text} is either NULL or some descriptive text which should be
7198 ignored. If @var{text} is NULL then it is being used to warn the
7199 target hook that either recording is starting or ending. The first
7200 time @var{type} is SWITCH_TYPE_DESCRIPTIVE and @var{text} is NULL, the
7201 warning is for start up and the second time the warning is for
7202 wind down. This feature is to allow the target hook to make any
7203 necessary preparations before it starts to record switches and to
7204 perform any necessary tidying up after it has finished recording
7207 @item SWITCH_TYPE_LINE_START
7208 This option can be ignored by this target hook.
7210 @item SWITCH_TYPE_LINE_END
7211 This option can be ignored by this target hook.
7214 The hook's return value must be zero. Other return values may be
7215 supported in the future.
7217 By default this hook is set to NULL, but an example implementation is
7218 provided for ELF based targets. Called @var{elf_record_gcc_switches},
7219 it records the switches as ASCII text inside a new, string mergeable
7220 section in the assembler output file. The name of the new section is
7221 provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target
7225 @deftypefn {Target Hook} {const char *} TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
7226 This is the name of the section that will be created by the example
7227 ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target
7233 @subsection Output of Data
7236 @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
7237 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
7238 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
7239 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
7240 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
7241 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
7242 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
7243 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
7244 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
7245 These hooks specify assembly directives for creating certain kinds
7246 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
7247 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
7248 aligned two-byte object, and so on. Any of the hooks may be
7249 @code{NULL}, indicating that no suitable directive is available.
7251 The compiler will print these strings at the start of a new line,
7252 followed immediately by the object's initial value. In most cases,
7253 the string should contain a tab, a pseudo-op, and then another tab.
7256 @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
7257 The @code{assemble_integer} function uses this hook to output an
7258 integer object. @var{x} is the object's value, @var{size} is its size
7259 in bytes and @var{aligned_p} indicates whether it is aligned. The
7260 function should return @code{true} if it was able to output the
7261 object. If it returns false, @code{assemble_integer} will try to
7262 split the object into smaller parts.
7264 The default implementation of this hook will use the
7265 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
7266 when the relevant string is @code{NULL}.
7269 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
7270 A C statement to recognize @var{rtx} patterns that
7271 @code{output_addr_const} can't deal with, and output assembly code to
7272 @var{stream} corresponding to the pattern @var{x}. This may be used to
7273 allow machine-dependent @code{UNSPEC}s to appear within constants.
7275 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
7276 @code{goto fail}, so that a standard error message is printed. If it
7277 prints an error message itself, by calling, for example,
7278 @code{output_operand_lossage}, it may just complete normally.
7281 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
7282 A C statement to output to the stdio stream @var{stream} an assembler
7283 instruction to assemble a string constant containing the @var{len}
7284 bytes at @var{ptr}. @var{ptr} will be a C expression of type
7285 @code{char *} and @var{len} a C expression of type @code{int}.
7287 If the assembler has a @code{.ascii} pseudo-op as found in the
7288 Berkeley Unix assembler, do not define the macro
7289 @code{ASM_OUTPUT_ASCII}.
7292 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
7293 A C statement to output word @var{n} of a function descriptor for
7294 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
7295 is defined, and is otherwise unused.
7298 @defmac CONSTANT_POOL_BEFORE_FUNCTION
7299 You may define this macro as a C expression. You should define the
7300 expression to have a nonzero value if GCC should output the constant
7301 pool for a function before the code for the function, or a zero value if
7302 GCC should output the constant pool after the function. If you do
7303 not define this macro, the usual case, GCC will output the constant
7304 pool before the function.
7307 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
7308 A C statement to output assembler commands to define the start of the
7309 constant pool for a function. @var{funname} is a string giving
7310 the name of the function. Should the return type of the function
7311 be required, it can be obtained via @var{fundecl}. @var{size}
7312 is the size, in bytes, of the constant pool that will be written
7313 immediately after this call.
7315 If no constant-pool prefix is required, the usual case, this macro need
7319 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
7320 A C statement (with or without semicolon) to output a constant in the
7321 constant pool, if it needs special treatment. (This macro need not do
7322 anything for RTL expressions that can be output normally.)
7324 The argument @var{file} is the standard I/O stream to output the
7325 assembler code on. @var{x} is the RTL expression for the constant to
7326 output, and @var{mode} is the machine mode (in case @var{x} is a
7327 @samp{const_int}). @var{align} is the required alignment for the value
7328 @var{x}; you should output an assembler directive to force this much
7331 The argument @var{labelno} is a number to use in an internal label for
7332 the address of this pool entry. The definition of this macro is
7333 responsible for outputting the label definition at the proper place.
7334 Here is how to do this:
7337 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
7340 When you output a pool entry specially, you should end with a
7341 @code{goto} to the label @var{jumpto}. This will prevent the same pool
7342 entry from being output a second time in the usual manner.
7344 You need not define this macro if it would do nothing.
7347 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
7348 A C statement to output assembler commands to at the end of the constant
7349 pool for a function. @var{funname} is a string giving the name of the
7350 function. Should the return type of the function be required, you can
7351 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
7352 constant pool that GCC wrote immediately before this call.
7354 If no constant-pool epilogue is required, the usual case, you need not
7358 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
7359 Define this macro as a C expression which is nonzero if @var{C} is
7360 used as a logical line separator by the assembler. @var{STR} points
7361 to the position in the string where @var{C} was found; this can be used if
7362 a line separator uses multiple characters.
7364 If you do not define this macro, the default is that only
7365 the character @samp{;} is treated as a logical line separator.
7368 @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
7369 @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
7370 These target hooks are C string constants, describing the syntax in the
7371 assembler for grouping arithmetic expressions. If not overridden, they
7372 default to normal parentheses, which is correct for most assemblers.
7375 These macros are provided by @file{real.h} for writing the definitions
7376 of @code{ASM_OUTPUT_DOUBLE} and the like:
7378 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
7379 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
7380 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
7381 @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
7382 @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
7383 @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
7384 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
7385 target's floating point representation, and store its bit pattern in
7386 the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and
7387 @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
7388 simple @code{long int}. For the others, it should be an array of
7389 @code{long int}. The number of elements in this array is determined
7390 by the size of the desired target floating point data type: 32 bits of
7391 it go in each @code{long int} array element. Each array element holds
7392 32 bits of the result, even if @code{long int} is wider than 32 bits
7393 on the host machine.
7395 The array element values are designed so that you can print them out
7396 using @code{fprintf} in the order they should appear in the target
7400 @node Uninitialized Data
7401 @subsection Output of Uninitialized Variables
7403 Each of the macros in this section is used to do the whole job of
7404 outputting a single uninitialized variable.
7406 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
7407 A C statement (sans semicolon) to output to the stdio stream
7408 @var{stream} the assembler definition of a common-label named
7409 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7410 is the size rounded up to whatever alignment the caller wants. It is
7411 possible that @var{size} may be zero, for instance if a struct with no
7412 other member than a zero-length array is defined. In this case, the
7413 backend must output a symbol definition that allocates at least one
7414 byte, both so that the address of the resulting object does not compare
7415 equal to any other, and because some object formats cannot even express
7416 the concept of a zero-sized common symbol, as that is how they represent
7417 an ordinary undefined external.
7419 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7420 output the name itself; before and after that, output the additional
7421 assembler syntax for defining the name, and a newline.
7423 This macro controls how the assembler definitions of uninitialized
7424 common global variables are output.
7427 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
7428 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
7429 separate, explicit argument. If you define this macro, it is used in
7430 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
7431 handling the required alignment of the variable. The alignment is specified
7432 as the number of bits.
7435 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7436 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
7437 variable to be output, if there is one, or @code{NULL_TREE} if there
7438 is no corresponding variable. If you define this macro, GCC will use it
7439 in place of both @code{ASM_OUTPUT_COMMON} and
7440 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
7441 the variable's decl in order to chose what to output.
7444 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
7445 A C statement (sans semicolon) to output to the stdio stream
7446 @var{stream} the assembler definition of uninitialized global @var{decl} named
7447 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7448 is the size rounded up to whatever alignment the caller wants.
7450 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
7451 defining this macro. If unable, use the expression
7452 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
7453 before and after that, output the additional assembler syntax for defining
7454 the name, and a newline.
7456 There are two ways of handling global BSS@. One is to define either
7457 this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}.
7458 The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
7459 switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
7460 You do not need to do both.
7462 Some languages do not have @code{common} data, and require a
7463 non-common form of global BSS in order to handle uninitialized globals
7464 efficiently. C++ is one example of this. However, if the target does
7465 not support global BSS, the front end may choose to make globals
7466 common in order to save space in the object file.
7469 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7470 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
7471 separate, explicit argument. If you define this macro, it is used in
7472 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
7473 handling the required alignment of the variable. The alignment is specified
7474 as the number of bits.
7476 Try to use function @code{asm_output_aligned_bss} defined in file
7477 @file{varasm.c} when defining this macro.
7480 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
7481 A C statement (sans semicolon) to output to the stdio stream
7482 @var{stream} the assembler definition of a local-common-label named
7483 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7484 is the size rounded up to whatever alignment the caller wants.
7486 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7487 output the name itself; before and after that, output the additional
7488 assembler syntax for defining the name, and a newline.
7490 This macro controls how the assembler definitions of uninitialized
7491 static variables are output.
7494 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
7495 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
7496 separate, explicit argument. If you define this macro, it is used in
7497 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
7498 handling the required alignment of the variable. The alignment is specified
7499 as the number of bits.
7502 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7503 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
7504 variable to be output, if there is one, or @code{NULL_TREE} if there
7505 is no corresponding variable. If you define this macro, GCC will use it
7506 in place of both @code{ASM_OUTPUT_DECL} and
7507 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
7508 the variable's decl in order to chose what to output.
7512 @subsection Output and Generation of Labels
7514 @c prevent bad page break with this line
7515 This is about outputting labels.
7517 @findex assemble_name
7518 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
7519 A C statement (sans semicolon) to output to the stdio stream
7520 @var{stream} the assembler definition of a label named @var{name}.
7521 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7522 output the name itself; before and after that, output the additional
7523 assembler syntax for defining the name, and a newline. A default
7524 definition of this macro is provided which is correct for most systems.
7527 @findex assemble_name_raw
7528 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
7529 Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
7530 to refer to a compiler-generated label. The default definition uses
7531 @code{assemble_name_raw}, which is like @code{assemble_name} except
7532 that it is more efficient.
7536 A C string containing the appropriate assembler directive to specify the
7537 size of a symbol, without any arguments. On systems that use ELF, the
7538 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
7539 systems, the default is not to define this macro.
7541 Define this macro only if it is correct to use the default definitions
7542 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
7543 for your system. If you need your own custom definitions of those
7544 macros, or if you do not need explicit symbol sizes at all, do not
7548 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
7549 A C statement (sans semicolon) to output to the stdio stream
7550 @var{stream} a directive telling the assembler that the size of the
7551 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
7552 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7556 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
7557 A C statement (sans semicolon) to output to the stdio stream
7558 @var{stream} a directive telling the assembler to calculate the size of
7559 the symbol @var{name} by subtracting its address from the current
7562 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7563 provided. The default assumes that the assembler recognizes a special
7564 @samp{.} symbol as referring to the current address, and can calculate
7565 the difference between this and another symbol. If your assembler does
7566 not recognize @samp{.} or cannot do calculations with it, you will need
7567 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
7571 A C string containing the appropriate assembler directive to specify the
7572 type of a symbol, without any arguments. On systems that use ELF, the
7573 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
7574 systems, the default is not to define this macro.
7576 Define this macro only if it is correct to use the default definition of
7577 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7578 custom definition of this macro, or if you do not need explicit symbol
7579 types at all, do not define this macro.
7582 @defmac TYPE_OPERAND_FMT
7583 A C string which specifies (using @code{printf} syntax) the format of
7584 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
7585 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
7586 the default is not to define this macro.
7588 Define this macro only if it is correct to use the default definition of
7589 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7590 custom definition of this macro, or if you do not need explicit symbol
7591 types at all, do not define this macro.
7594 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
7595 A C statement (sans semicolon) to output to the stdio stream
7596 @var{stream} a directive telling the assembler that the type of the
7597 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
7598 that string is always either @samp{"function"} or @samp{"object"}, but
7599 you should not count on this.
7601 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
7602 definition of this macro is provided.
7605 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
7606 A C statement (sans semicolon) to output to the stdio stream
7607 @var{stream} any text necessary for declaring the name @var{name} of a
7608 function which is being defined. This macro is responsible for
7609 outputting the label definition (perhaps using
7610 @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the
7611 @code{FUNCTION_DECL} tree node representing the function.
7613 If this macro is not defined, then the function name is defined in the
7614 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7616 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
7620 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
7621 A C statement (sans semicolon) to output to the stdio stream
7622 @var{stream} any text necessary for declaring the size of a function
7623 which is being defined. The argument @var{name} is the name of the
7624 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
7625 representing the function.
7627 If this macro is not defined, then the function size is not defined.
7629 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
7633 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
7634 A C statement (sans semicolon) to output to the stdio stream
7635 @var{stream} any text necessary for declaring the name @var{name} of an
7636 initialized variable which is being defined. This macro must output the
7637 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
7638 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
7640 If this macro is not defined, then the variable name is defined in the
7641 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7643 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
7644 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
7647 @defmac ASM_DECLARE_CONSTANT_NAME (@var{stream}, @var{name}, @var{exp}, @var{size})
7648 A C statement (sans semicolon) to output to the stdio stream
7649 @var{stream} any text necessary for declaring the name @var{name} of a
7650 constant which is being defined. This macro is responsible for
7651 outputting the label definition (perhaps using
7652 @code{ASM_OUTPUT_LABEL}). The argument @var{exp} is the
7653 value of the constant, and @var{size} is the size of the constant
7654 in bytes. @var{name} will be an internal label.
7656 If this macro is not defined, then the @var{name} is defined in the
7657 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7659 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
7663 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
7664 A C statement (sans semicolon) to output to the stdio stream
7665 @var{stream} any text necessary for claiming a register @var{regno}
7666 for a global variable @var{decl} with name @var{name}.
7668 If you don't define this macro, that is equivalent to defining it to do
7672 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
7673 A C statement (sans semicolon) to finish up declaring a variable name
7674 once the compiler has processed its initializer fully and thus has had a
7675 chance to determine the size of an array when controlled by an
7676 initializer. This is used on systems where it's necessary to declare
7677 something about the size of the object.
7679 If you don't define this macro, that is equivalent to defining it to do
7682 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
7683 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
7686 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
7687 This target hook is a function to output to the stdio stream
7688 @var{stream} some commands that will make the label @var{name} global;
7689 that is, available for reference from other files.
7691 The default implementation relies on a proper definition of
7692 @code{GLOBAL_ASM_OP}.
7695 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_DECL_NAME (FILE *@var{stream}, tree @var{decl})
7696 This target hook is a function to output to the stdio stream
7697 @var{stream} some commands that will make the name associated with @var{decl}
7698 global; that is, available for reference from other files.
7700 The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.
7703 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
7704 A C statement (sans semicolon) to output to the stdio stream
7705 @var{stream} some commands that will make the label @var{name} weak;
7706 that is, available for reference from other files but only used if
7707 no other definition is available. Use the expression
7708 @code{assemble_name (@var{stream}, @var{name})} to output the name
7709 itself; before and after that, output the additional assembler syntax
7710 for making that name weak, and a newline.
7712 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
7713 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
7717 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
7718 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
7719 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
7720 or variable decl. If @var{value} is not @code{NULL}, this C statement
7721 should output to the stdio stream @var{stream} assembler code which
7722 defines (equates) the weak symbol @var{name} to have the value
7723 @var{value}. If @var{value} is @code{NULL}, it should output commands
7724 to make @var{name} weak.
7727 @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
7728 Outputs a directive that enables @var{name} to be used to refer to
7729 symbol @var{value} with weak-symbol semantics. @code{decl} is the
7730 declaration of @code{name}.
7733 @defmac SUPPORTS_WEAK
7734 A C expression which evaluates to true if the target supports weak symbols.
7736 If you don't define this macro, @file{defaults.h} provides a default
7737 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
7738 is defined, the default definition is @samp{1}; otherwise, it is
7739 @samp{0}. Define this macro if you want to control weak symbol support
7740 with a compiler flag such as @option{-melf}.
7743 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
7744 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
7745 public symbol such that extra copies in multiple translation units will
7746 be discarded by the linker. Define this macro if your object file
7747 format provides support for this concept, such as the @samp{COMDAT}
7748 section flags in the Microsoft Windows PE/COFF format, and this support
7749 requires changes to @var{decl}, such as putting it in a separate section.
7752 @defmac SUPPORTS_ONE_ONLY
7753 A C expression which evaluates to true if the target supports one-only
7756 If you don't define this macro, @file{varasm.c} provides a default
7757 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
7758 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
7759 you want to control one-only symbol support with a compiler flag, or if
7760 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
7761 be emitted as one-only.
7764 @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility})
7765 This target hook is a function to output to @var{asm_out_file} some
7766 commands that will make the symbol(s) associated with @var{decl} have
7767 hidden, protected or internal visibility as specified by @var{visibility}.
7770 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
7771 A C expression that evaluates to true if the target's linker expects
7772 that weak symbols do not appear in a static archive's table of contents.
7773 The default is @code{0}.
7775 Leaving weak symbols out of an archive's table of contents means that,
7776 if a symbol will only have a definition in one translation unit and
7777 will have undefined references from other translation units, that
7778 symbol should not be weak. Defining this macro to be nonzero will
7779 thus have the effect that certain symbols that would normally be weak
7780 (explicit template instantiations, and vtables for polymorphic classes
7781 with noninline key methods) will instead be nonweak.
7783 The C++ ABI requires this macro to be zero. Define this macro for
7784 targets where full C++ ABI compliance is impossible and where linker
7785 restrictions require weak symbols to be left out of a static archive's
7789 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
7790 A C statement (sans semicolon) to output to the stdio stream
7791 @var{stream} any text necessary for declaring the name of an external
7792 symbol named @var{name} which is referenced in this compilation but
7793 not defined. The value of @var{decl} is the tree node for the
7796 This macro need not be defined if it does not need to output anything.
7797 The GNU assembler and most Unix assemblers don't require anything.
7800 @deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref})
7801 This target hook is a function to output to @var{asm_out_file} an assembler
7802 pseudo-op to declare a library function name external. The name of the
7803 library function is given by @var{symref}, which is a @code{symbol_ref}.
7806 @deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (tree @var{decl})
7807 This target hook is a function to output to @var{asm_out_file} an assembler
7808 directive to annotate used symbol. Darwin target use .no_dead_code_strip
7812 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
7813 A C statement (sans semicolon) to output to the stdio stream
7814 @var{stream} a reference in assembler syntax to a label named
7815 @var{name}. This should add @samp{_} to the front of the name, if that
7816 is customary on your operating system, as it is in most Berkeley Unix
7817 systems. This macro is used in @code{assemble_name}.
7820 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
7821 A C statement (sans semicolon) to output a reference to
7822 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
7823 will be used to output the name of the symbol. This macro may be used
7824 to modify the way a symbol is referenced depending on information
7825 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
7828 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
7829 A C statement (sans semicolon) to output a reference to @var{buf}, the
7830 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
7831 @code{assemble_name} will be used to output the name of the symbol.
7832 This macro is not used by @code{output_asm_label}, or the @code{%l}
7833 specifier that calls it; the intention is that this macro should be set
7834 when it is necessary to output a label differently when its address is
7838 @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
7839 A function to output to the stdio stream @var{stream} a label whose
7840 name is made from the string @var{prefix} and the number @var{labelno}.
7842 It is absolutely essential that these labels be distinct from the labels
7843 used for user-level functions and variables. Otherwise, certain programs
7844 will have name conflicts with internal labels.
7846 It is desirable to exclude internal labels from the symbol table of the
7847 object file. Most assemblers have a naming convention for labels that
7848 should be excluded; on many systems, the letter @samp{L} at the
7849 beginning of a label has this effect. You should find out what
7850 convention your system uses, and follow it.
7852 The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
7855 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
7856 A C statement to output to the stdio stream @var{stream} a debug info
7857 label whose name is made from the string @var{prefix} and the number
7858 @var{num}. This is useful for VLIW targets, where debug info labels
7859 may need to be treated differently than branch target labels. On some
7860 systems, branch target labels must be at the beginning of instruction
7861 bundles, but debug info labels can occur in the middle of instruction
7864 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
7868 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
7869 A C statement to store into the string @var{string} a label whose name
7870 is made from the string @var{prefix} and the number @var{num}.
7872 This string, when output subsequently by @code{assemble_name}, should
7873 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
7874 with the same @var{prefix} and @var{num}.
7876 If the string begins with @samp{*}, then @code{assemble_name} will
7877 output the rest of the string unchanged. It is often convenient for
7878 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
7879 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
7880 to output the string, and may change it. (Of course,
7881 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
7882 you should know what it does on your machine.)
7885 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
7886 A C expression to assign to @var{outvar} (which is a variable of type
7887 @code{char *}) a newly allocated string made from the string
7888 @var{name} and the number @var{number}, with some suitable punctuation
7889 added. Use @code{alloca} to get space for the string.
7891 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
7892 produce an assembler label for an internal static variable whose name is
7893 @var{name}. Therefore, the string must be such as to result in valid
7894 assembler code. The argument @var{number} is different each time this
7895 macro is executed; it prevents conflicts between similarly-named
7896 internal static variables in different scopes.
7898 Ideally this string should not be a valid C identifier, to prevent any
7899 conflict with the user's own symbols. Most assemblers allow periods
7900 or percent signs in assembler symbols; putting at least one of these
7901 between the name and the number will suffice.
7903 If this macro is not defined, a default definition will be provided
7904 which is correct for most systems.
7907 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
7908 A C statement to output to the stdio stream @var{stream} assembler code
7909 which defines (equates) the symbol @var{name} to have the value @var{value}.
7912 If @code{SET_ASM_OP} is defined, a default definition is provided which is
7913 correct for most systems.
7916 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
7917 A C statement to output to the stdio stream @var{stream} assembler code
7918 which defines (equates) the symbol whose tree node is @var{decl_of_name}
7919 to have the value of the tree node @var{decl_of_value}. This macro will
7920 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
7921 the tree nodes are available.
7924 If @code{SET_ASM_OP} is defined, a default definition is provided which is
7925 correct for most systems.
7928 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
7929 A C statement that evaluates to true if the assembler code which defines
7930 (equates) the symbol whose tree node is @var{decl_of_name} to have the value
7931 of the tree node @var{decl_of_value} should be emitted near the end of the
7932 current compilation unit. The default is to not defer output of defines.
7933 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
7934 @samp{ASM_OUTPUT_DEF_FROM_DECLS}.
7937 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
7938 A C statement to output to the stdio stream @var{stream} assembler code
7939 which defines (equates) the weak symbol @var{name} to have the value
7940 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
7941 an undefined weak symbol.
7943 Define this macro if the target only supports weak aliases; define
7944 @code{ASM_OUTPUT_DEF} instead if possible.
7947 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
7948 Define this macro to override the default assembler names used for
7949 Objective-C methods.
7951 The default name is a unique method number followed by the name of the
7952 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
7953 the category is also included in the assembler name (e.g.@:
7956 These names are safe on most systems, but make debugging difficult since
7957 the method's selector is not present in the name. Therefore, particular
7958 systems define other ways of computing names.
7960 @var{buf} is an expression of type @code{char *} which gives you a
7961 buffer in which to store the name; its length is as long as
7962 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
7963 50 characters extra.
7965 The argument @var{is_inst} specifies whether the method is an instance
7966 method or a class method; @var{class_name} is the name of the class;
7967 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
7968 in a category); and @var{sel_name} is the name of the selector.
7970 On systems where the assembler can handle quoted names, you can use this
7971 macro to provide more human-readable names.
7974 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
7975 A C statement (sans semicolon) to output to the stdio stream
7976 @var{stream} commands to declare that the label @var{name} is an
7977 Objective-C class reference. This is only needed for targets whose
7978 linkers have special support for NeXT-style runtimes.
7981 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
7982 A C statement (sans semicolon) to output to the stdio stream
7983 @var{stream} commands to declare that the label @var{name} is an
7984 unresolved Objective-C class reference. This is only needed for targets
7985 whose linkers have special support for NeXT-style runtimes.
7988 @node Initialization
7989 @subsection How Initialization Functions Are Handled
7990 @cindex initialization routines
7991 @cindex termination routines
7992 @cindex constructors, output of
7993 @cindex destructors, output of
7995 The compiled code for certain languages includes @dfn{constructors}
7996 (also called @dfn{initialization routines})---functions to initialize
7997 data in the program when the program is started. These functions need
7998 to be called before the program is ``started''---that is to say, before
7999 @code{main} is called.
8001 Compiling some languages generates @dfn{destructors} (also called
8002 @dfn{termination routines}) that should be called when the program
8005 To make the initialization and termination functions work, the compiler
8006 must output something in the assembler code to cause those functions to
8007 be called at the appropriate time. When you port the compiler to a new
8008 system, you need to specify how to do this.
8010 There are two major ways that GCC currently supports the execution of
8011 initialization and termination functions. Each way has two variants.
8012 Much of the structure is common to all four variations.
8014 @findex __CTOR_LIST__
8015 @findex __DTOR_LIST__
8016 The linker must build two lists of these functions---a list of
8017 initialization functions, called @code{__CTOR_LIST__}, and a list of
8018 termination functions, called @code{__DTOR_LIST__}.
8020 Each list always begins with an ignored function pointer (which may hold
8021 0, @minus{}1, or a count of the function pointers after it, depending on
8022 the environment). This is followed by a series of zero or more function
8023 pointers to constructors (or destructors), followed by a function
8024 pointer containing zero.
8026 Depending on the operating system and its executable file format, either
8027 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
8028 time and exit time. Constructors are called in reverse order of the
8029 list; destructors in forward order.
8031 The best way to handle static constructors works only for object file
8032 formats which provide arbitrarily-named sections. A section is set
8033 aside for a list of constructors, and another for a list of destructors.
8034 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
8035 object file that defines an initialization function also puts a word in
8036 the constructor section to point to that function. The linker
8037 accumulates all these words into one contiguous @samp{.ctors} section.
8038 Termination functions are handled similarly.
8040 This method will be chosen as the default by @file{target-def.h} if
8041 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
8042 support arbitrary sections, but does support special designated
8043 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
8044 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
8046 When arbitrary sections are available, there are two variants, depending
8047 upon how the code in @file{crtstuff.c} is called. On systems that
8048 support a @dfn{.init} section which is executed at program startup,
8049 parts of @file{crtstuff.c} are compiled into that section. The
8050 program is linked by the @command{gcc} driver like this:
8053 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
8056 The prologue of a function (@code{__init}) appears in the @code{.init}
8057 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
8058 for the function @code{__fini} in the @dfn{.fini} section. Normally these
8059 files are provided by the operating system or by the GNU C library, but
8060 are provided by GCC for a few targets.
8062 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
8063 compiled from @file{crtstuff.c}. They contain, among other things, code
8064 fragments within the @code{.init} and @code{.fini} sections that branch
8065 to routines in the @code{.text} section. The linker will pull all parts
8066 of a section together, which results in a complete @code{__init} function
8067 that invokes the routines we need at startup.
8069 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
8072 If no init section is available, when GCC compiles any function called
8073 @code{main} (or more accurately, any function designated as a program
8074 entry point by the language front end calling @code{expand_main_function}),
8075 it inserts a procedure call to @code{__main} as the first executable code
8076 after the function prologue. The @code{__main} function is defined
8077 in @file{libgcc2.c} and runs the global constructors.
8079 In file formats that don't support arbitrary sections, there are again
8080 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
8081 and an `a.out' format must be used. In this case,
8082 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
8083 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
8084 and with the address of the void function containing the initialization
8085 code as its value. The GNU linker recognizes this as a request to add
8086 the value to a @dfn{set}; the values are accumulated, and are eventually
8087 placed in the executable as a vector in the format described above, with
8088 a leading (ignored) count and a trailing zero element.
8089 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
8090 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
8091 the compilation of @code{main} to call @code{__main} as above, starting
8092 the initialization process.
8094 The last variant uses neither arbitrary sections nor the GNU linker.
8095 This is preferable when you want to do dynamic linking and when using
8096 file formats which the GNU linker does not support, such as `ECOFF'@. In
8097 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
8098 termination functions are recognized simply by their names. This requires
8099 an extra program in the linkage step, called @command{collect2}. This program
8100 pretends to be the linker, for use with GCC; it does its job by running
8101 the ordinary linker, but also arranges to include the vectors of
8102 initialization and termination functions. These functions are called
8103 via @code{__main} as described above. In order to use this method,
8104 @code{use_collect2} must be defined in the target in @file{config.gcc}.
8107 The following section describes the specific macros that control and
8108 customize the handling of initialization and termination functions.
8111 @node Macros for Initialization
8112 @subsection Macros Controlling Initialization Routines
8114 Here are the macros that control how the compiler handles initialization
8115 and termination functions:
8117 @defmac INIT_SECTION_ASM_OP
8118 If defined, a C string constant, including spacing, for the assembler
8119 operation to identify the following data as initialization code. If not
8120 defined, GCC will assume such a section does not exist. When you are
8121 using special sections for initialization and termination functions, this
8122 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
8123 run the initialization functions.
8126 @defmac HAS_INIT_SECTION
8127 If defined, @code{main} will not call @code{__main} as described above.
8128 This macro should be defined for systems that control start-up code
8129 on a symbol-by-symbol basis, such as OSF/1, and should not
8130 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
8133 @defmac LD_INIT_SWITCH
8134 If defined, a C string constant for a switch that tells the linker that
8135 the following symbol is an initialization routine.
8138 @defmac LD_FINI_SWITCH
8139 If defined, a C string constant for a switch that tells the linker that
8140 the following symbol is a finalization routine.
8143 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
8144 If defined, a C statement that will write a function that can be
8145 automatically called when a shared library is loaded. The function
8146 should call @var{func}, which takes no arguments. If not defined, and
8147 the object format requires an explicit initialization function, then a
8148 function called @code{_GLOBAL__DI} will be generated.
8150 This function and the following one are used by collect2 when linking a
8151 shared library that needs constructors or destructors, or has DWARF2
8152 exception tables embedded in the code.
8155 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
8156 If defined, a C statement that will write a function that can be
8157 automatically called when a shared library is unloaded. The function
8158 should call @var{func}, which takes no arguments. If not defined, and
8159 the object format requires an explicit finalization function, then a
8160 function called @code{_GLOBAL__DD} will be generated.
8163 @defmac INVOKE__main
8164 If defined, @code{main} will call @code{__main} despite the presence of
8165 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
8166 where the init section is not actually run automatically, but is still
8167 useful for collecting the lists of constructors and destructors.
8170 @defmac SUPPORTS_INIT_PRIORITY
8171 If nonzero, the C++ @code{init_priority} attribute is supported and the
8172 compiler should emit instructions to control the order of initialization
8173 of objects. If zero, the compiler will issue an error message upon
8174 encountering an @code{init_priority} attribute.
8177 @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS
8178 This value is true if the target supports some ``native'' method of
8179 collecting constructors and destructors to be run at startup and exit.
8180 It is false if we must use @command{collect2}.
8183 @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
8184 If defined, a function that outputs assembler code to arrange to call
8185 the function referenced by @var{symbol} at initialization time.
8187 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
8188 no arguments and with no return value. If the target supports initialization
8189 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
8190 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
8192 If this macro is not defined by the target, a suitable default will
8193 be chosen if (1) the target supports arbitrary section names, (2) the
8194 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
8198 @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
8199 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
8200 functions rather than initialization functions.
8203 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
8204 generated for the generated object file will have static linkage.
8206 If your system uses @command{collect2} as the means of processing
8207 constructors, then that program normally uses @command{nm} to scan
8208 an object file for constructor functions to be called.
8210 On certain kinds of systems, you can define this macro to make
8211 @command{collect2} work faster (and, in some cases, make it work at all):
8213 @defmac OBJECT_FORMAT_COFF
8214 Define this macro if the system uses COFF (Common Object File Format)
8215 object files, so that @command{collect2} can assume this format and scan
8216 object files directly for dynamic constructor/destructor functions.
8218 This macro is effective only in a native compiler; @command{collect2} as
8219 part of a cross compiler always uses @command{nm} for the target machine.
8222 @defmac REAL_NM_FILE_NAME
8223 Define this macro as a C string constant containing the file name to use
8224 to execute @command{nm}. The default is to search the path normally for
8227 If your system supports shared libraries and has a program to list the
8228 dynamic dependencies of a given library or executable, you can define
8229 these macros to enable support for running initialization and
8230 termination functions in shared libraries:
8234 Define this macro to a C string constant containing the name of the program
8235 which lists dynamic dependencies, like @command{"ldd"} under SunOS 4.
8238 @defmac PARSE_LDD_OUTPUT (@var{ptr})
8239 Define this macro to be C code that extracts filenames from the output
8240 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
8241 of type @code{char *} that points to the beginning of a line of output
8242 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
8243 code must advance @var{ptr} to the beginning of the filename on that
8244 line. Otherwise, it must set @var{ptr} to @code{NULL}.
8247 @defmac SHLIB_SUFFIX
8248 Define this macro to a C string constant containing the default shared
8249 library extension of the target (e.g., @samp{".so"}). @command{collect2}
8250 strips version information after this suffix when generating global
8251 constructor and destructor names. This define is only needed on targets
8252 that use @command{collect2} to process constructors and destructors.
8255 @node Instruction Output
8256 @subsection Output of Assembler Instructions
8258 @c prevent bad page break with this line
8259 This describes assembler instruction output.
8261 @defmac REGISTER_NAMES
8262 A C initializer containing the assembler's names for the machine
8263 registers, each one as a C string constant. This is what translates
8264 register numbers in the compiler into assembler language.
8267 @defmac ADDITIONAL_REGISTER_NAMES
8268 If defined, a C initializer for an array of structures containing a name
8269 and a register number. This macro defines additional names for hard
8270 registers, thus allowing the @code{asm} option in declarations to refer
8271 to registers using alternate names.
8274 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
8275 Define this macro if you are using an unusual assembler that
8276 requires different names for the machine instructions.
8278 The definition is a C statement or statements which output an
8279 assembler instruction opcode to the stdio stream @var{stream}. The
8280 macro-operand @var{ptr} is a variable of type @code{char *} which
8281 points to the opcode name in its ``internal'' form---the form that is
8282 written in the machine description. The definition should output the
8283 opcode name to @var{stream}, performing any translation you desire, and
8284 increment the variable @var{ptr} to point at the end of the opcode
8285 so that it will not be output twice.
8287 In fact, your macro definition may process less than the entire opcode
8288 name, or more than the opcode name; but if you want to process text
8289 that includes @samp{%}-sequences to substitute operands, you must take
8290 care of the substitution yourself. Just be sure to increment
8291 @var{ptr} over whatever text should not be output normally.
8293 @findex recog_data.operand
8294 If you need to look at the operand values, they can be found as the
8295 elements of @code{recog_data.operand}.
8297 If the macro definition does nothing, the instruction is output
8301 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
8302 If defined, a C statement to be executed just prior to the output of
8303 assembler code for @var{insn}, to modify the extracted operands so
8304 they will be output differently.
8306 Here the argument @var{opvec} is the vector containing the operands
8307 extracted from @var{insn}, and @var{noperands} is the number of
8308 elements of the vector which contain meaningful data for this insn.
8309 The contents of this vector are what will be used to convert the insn
8310 template into assembler code, so you can change the assembler output
8311 by changing the contents of the vector.
8313 This macro is useful when various assembler syntaxes share a single
8314 file of instruction patterns; by defining this macro differently, you
8315 can cause a large class of instructions to be output differently (such
8316 as with rearranged operands). Naturally, variations in assembler
8317 syntax affecting individual insn patterns ought to be handled by
8318 writing conditional output routines in those patterns.
8320 If this macro is not defined, it is equivalent to a null statement.
8323 @deftypefn {Target Hook} void TARGET_ASM_FINAL_POSTSCAN_INSN (FILE *@var{FILE}, rtx @var{insn}, rtx *@var{opvec}, int @var{noperands})
8324 If defined, this target hook is a function which is executed just after the
8325 output of assembler code for @var{insn}, to change the mode of the assembler
8328 Here the argument @var{opvec} is the vector containing the operands
8329 extracted from @var{insn}, and @var{noperands} is the number of
8330 elements of the vector which contain meaningful data for this insn.
8331 The contents of this vector are what was used to convert the insn
8332 template into assembler code, so you can change the assembler mode
8333 by checking the contents of the vector.
8336 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
8337 A C compound statement to output to stdio stream @var{stream} the
8338 assembler syntax for an instruction operand @var{x}. @var{x} is an
8341 @var{code} is a value that can be used to specify one of several ways
8342 of printing the operand. It is used when identical operands must be
8343 printed differently depending on the context. @var{code} comes from
8344 the @samp{%} specification that was used to request printing of the
8345 operand. If the specification was just @samp{%@var{digit}} then
8346 @var{code} is 0; if the specification was @samp{%@var{ltr}
8347 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
8350 If @var{x} is a register, this macro should print the register's name.
8351 The names can be found in an array @code{reg_names} whose type is
8352 @code{char *[]}. @code{reg_names} is initialized from
8353 @code{REGISTER_NAMES}.
8355 When the machine description has a specification @samp{%@var{punct}}
8356 (a @samp{%} followed by a punctuation character), this macro is called
8357 with a null pointer for @var{x} and the punctuation character for
8361 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
8362 A C expression which evaluates to true if @var{code} is a valid
8363 punctuation character for use in the @code{PRINT_OPERAND} macro. If
8364 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
8365 punctuation characters (except for the standard one, @samp{%}) are used
8369 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
8370 A C compound statement to output to stdio stream @var{stream} the
8371 assembler syntax for an instruction operand that is a memory reference
8372 whose address is @var{x}. @var{x} is an RTL expression.
8374 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
8375 On some machines, the syntax for a symbolic address depends on the
8376 section that the address refers to. On these machines, define the hook
8377 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
8378 @code{symbol_ref}, and then check for it here. @xref{Assembler
8382 @findex dbr_sequence_length
8383 @defmac DBR_OUTPUT_SEQEND (@var{file})
8384 A C statement, to be executed after all slot-filler instructions have
8385 been output. If necessary, call @code{dbr_sequence_length} to
8386 determine the number of slots filled in a sequence (zero if not
8387 currently outputting a sequence), to decide how many no-ops to output,
8390 Don't define this macro if it has nothing to do, but it is helpful in
8391 reading assembly output if the extent of the delay sequence is made
8392 explicit (e.g.@: with white space).
8395 @findex final_sequence
8396 Note that output routines for instructions with delay slots must be
8397 prepared to deal with not being output as part of a sequence
8398 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
8399 found.) The variable @code{final_sequence} is null when not
8400 processing a sequence, otherwise it contains the @code{sequence} rtx
8404 @defmac REGISTER_PREFIX
8405 @defmacx LOCAL_LABEL_PREFIX
8406 @defmacx USER_LABEL_PREFIX
8407 @defmacx IMMEDIATE_PREFIX
8408 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
8409 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
8410 @file{final.c}). These are useful when a single @file{md} file must
8411 support multiple assembler formats. In that case, the various @file{tm.h}
8412 files can define these macros differently.
8415 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
8416 If defined this macro should expand to a series of @code{case}
8417 statements which will be parsed inside the @code{switch} statement of
8418 the @code{asm_fprintf} function. This allows targets to define extra
8419 printf formats which may useful when generating their assembler
8420 statements. Note that uppercase letters are reserved for future
8421 generic extensions to asm_fprintf, and so are not available to target
8422 specific code. The output file is given by the parameter @var{file}.
8423 The varargs input pointer is @var{argptr} and the rest of the format
8424 string, starting the character after the one that is being switched
8425 upon, is pointed to by @var{format}.
8428 @defmac ASSEMBLER_DIALECT
8429 If your target supports multiple dialects of assembler language (such as
8430 different opcodes), define this macro as a C expression that gives the
8431 numeric index of the assembler language dialect to use, with zero as the
8434 If this macro is defined, you may use constructs of the form
8436 @samp{@{option0|option1|option2@dots{}@}}
8439 in the output templates of patterns (@pxref{Output Template}) or in the
8440 first argument of @code{asm_fprintf}. This construct outputs
8441 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
8442 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
8443 within these strings retain their usual meaning. If there are fewer
8444 alternatives within the braces than the value of
8445 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
8447 If you do not define this macro, the characters @samp{@{}, @samp{|} and
8448 @samp{@}} do not have any special meaning when used in templates or
8449 operands to @code{asm_fprintf}.
8451 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
8452 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
8453 the variations in assembler language syntax with that mechanism. Define
8454 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
8455 if the syntax variant are larger and involve such things as different
8456 opcodes or operand order.
8459 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
8460 A C expression to output to @var{stream} some assembler code
8461 which will push hard register number @var{regno} onto the stack.
8462 The code need not be optimal, since this macro is used only when
8466 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
8467 A C expression to output to @var{stream} some assembler code
8468 which will pop hard register number @var{regno} off of the stack.
8469 The code need not be optimal, since this macro is used only when
8473 @node Dispatch Tables
8474 @subsection Output of Dispatch Tables
8476 @c prevent bad page break with this line
8477 This concerns dispatch tables.
8479 @cindex dispatch table
8480 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
8481 A C statement to output to the stdio stream @var{stream} an assembler
8482 pseudo-instruction to generate a difference between two labels.
8483 @var{value} and @var{rel} are the numbers of two internal labels. The
8484 definitions of these labels are output using
8485 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
8486 way here. For example,
8489 fprintf (@var{stream}, "\t.word L%d-L%d\n",
8490 @var{value}, @var{rel})
8493 You must provide this macro on machines where the addresses in a
8494 dispatch table are relative to the table's own address. If defined, GCC
8495 will also use this macro on all machines when producing PIC@.
8496 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
8497 mode and flags can be read.
8500 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
8501 This macro should be provided on machines where the addresses
8502 in a dispatch table are absolute.
8504 The definition should be a C statement to output to the stdio stream
8505 @var{stream} an assembler pseudo-instruction to generate a reference to
8506 a label. @var{value} is the number of an internal label whose
8507 definition is output using @code{(*targetm.asm_out.internal_label)}.
8511 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
8515 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
8516 Define this if the label before a jump-table needs to be output
8517 specially. The first three arguments are the same as for
8518 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
8519 jump-table which follows (a @code{jump_insn} containing an
8520 @code{addr_vec} or @code{addr_diff_vec}).
8522 This feature is used on system V to output a @code{swbeg} statement
8525 If this macro is not defined, these labels are output with
8526 @code{(*targetm.asm_out.internal_label)}.
8529 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
8530 Define this if something special must be output at the end of a
8531 jump-table. The definition should be a C statement to be executed
8532 after the assembler code for the table is written. It should write
8533 the appropriate code to stdio stream @var{stream}. The argument
8534 @var{table} is the jump-table insn, and @var{num} is the label-number
8535 of the preceding label.
8537 If this macro is not defined, nothing special is output at the end of
8541 @deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (@var{stream}, @var{decl}, @var{for_eh}, @var{empty})
8542 This target hook emits a label at the beginning of each FDE@. It
8543 should be defined on targets where FDEs need special labels, and it
8544 should write the appropriate label, for the FDE associated with the
8545 function declaration @var{decl}, to the stdio stream @var{stream}.
8546 The third argument, @var{for_eh}, is a boolean: true if this is for an
8547 exception table. The fourth argument, @var{empty}, is a boolean:
8548 true if this is a placeholder label for an omitted FDE@.
8550 The default is that FDEs are not given nonlocal labels.
8553 @deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (@var{stream})
8554 This target hook emits a label at the beginning of the exception table.
8555 It should be defined on targets where it is desirable for the table
8556 to be broken up according to function.
8558 The default is that no label is emitted.
8561 @deftypefn {Target Hook} void TARGET_UNWIND_EMIT (FILE * @var{stream}, rtx @var{insn})
8562 This target hook emits and assembly directives required to unwind the
8563 given instruction. This is only used when TARGET_UNWIND_INFO is set.
8566 @node Exception Region Output
8567 @subsection Assembler Commands for Exception Regions
8569 @c prevent bad page break with this line
8571 This describes commands marking the start and the end of an exception
8574 @defmac EH_FRAME_SECTION_NAME
8575 If defined, a C string constant for the name of the section containing
8576 exception handling frame unwind information. If not defined, GCC will
8577 provide a default definition if the target supports named sections.
8578 @file{crtstuff.c} uses this macro to switch to the appropriate section.
8580 You should define this symbol if your target supports DWARF 2 frame
8581 unwind information and the default definition does not work.
8584 @defmac EH_FRAME_IN_DATA_SECTION
8585 If defined, DWARF 2 frame unwind information will be placed in the
8586 data section even though the target supports named sections. This
8587 might be necessary, for instance, if the system linker does garbage
8588 collection and sections cannot be marked as not to be collected.
8590 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
8594 @defmac EH_TABLES_CAN_BE_READ_ONLY
8595 Define this macro to 1 if your target is such that no frame unwind
8596 information encoding used with non-PIC code will ever require a
8597 runtime relocation, but the linker may not support merging read-only
8598 and read-write sections into a single read-write section.
8601 @defmac MASK_RETURN_ADDR
8602 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
8603 that it does not contain any extraneous set bits in it.
8606 @defmac DWARF2_UNWIND_INFO
8607 Define this macro to 0 if your target supports DWARF 2 frame unwind
8608 information, but it does not yet work with exception handling.
8609 Otherwise, if your target supports this information (if it defines
8610 @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP}
8611 or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1.
8613 If @code{TARGET_UNWIND_INFO} is defined, the target specific unwinder
8614 will be used in all cases. Defining this macro will enable the generation
8615 of DWARF 2 frame debugging information.
8617 If @code{TARGET_UNWIND_INFO} is not defined, and this macro is defined to 1,
8618 the DWARF 2 unwinder will be the default exception handling mechanism;
8619 otherwise, the @code{setjmp}/@code{longjmp}-based scheme will be used by
8623 @defmac TARGET_UNWIND_INFO
8624 Define this macro if your target has ABI specified unwind tables. Usually
8625 these will be output by @code{TARGET_UNWIND_EMIT}.
8628 @deftypevr {Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT
8629 This variable should be set to @code{true} if the target ABI requires unwinding
8630 tables even when exceptions are not used.
8633 @defmac MUST_USE_SJLJ_EXCEPTIONS
8634 This macro need only be defined if @code{DWARF2_UNWIND_INFO} is
8635 runtime-variable. In that case, @file{except.h} cannot correctly
8636 determine the corresponding definition of @code{MUST_USE_SJLJ_EXCEPTIONS},
8637 so the target must provide it directly.
8640 @defmac DONT_USE_BUILTIN_SETJMP
8641 Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
8642 should use the @code{setjmp}/@code{longjmp} functions from the C library
8643 instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
8646 @defmac DWARF_CIE_DATA_ALIGNMENT
8647 This macro need only be defined if the target might save registers in the
8648 function prologue at an offset to the stack pointer that is not aligned to
8649 @code{UNITS_PER_WORD}. The definition should be the negative minimum
8650 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
8651 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
8652 the target supports DWARF 2 frame unwind information.
8655 @deftypevr {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
8656 Contains the value true if the target should add a zero word onto the
8657 end of a Dwarf-2 frame info section when used for exception handling.
8658 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
8662 @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
8663 Given a register, this hook should return a parallel of registers to
8664 represent where to find the register pieces. Define this hook if the
8665 register and its mode are represented in Dwarf in non-contiguous
8666 locations, or if the register should be represented in more than one
8667 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
8668 If not defined, the default is to return @code{NULL_RTX}.
8671 @deftypefn {Target Hook} void TARGET_INIT_DWARF_REG_SIZES_EXTRA (tree @var{address})
8672 If some registers are represented in Dwarf-2 unwind information in
8673 multiple pieces, define this hook to fill in information about the
8674 sizes of those pieces in the table used by the unwinder at runtime.
8675 It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after
8676 filling in a single size corresponding to each hard register;
8677 @var{address} is the address of the table.
8680 @deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym})
8681 This hook is used to output a reference from a frame unwinding table to
8682 the type_info object identified by @var{sym}. It should return @code{true}
8683 if the reference was output. Returning @code{false} will cause the
8684 reference to be output using the normal Dwarf2 routines.
8687 @deftypefn {Target Hook} bool TARGET_ARM_EABI_UNWINDER
8688 This hook should be set to @code{true} on targets that use an ARM EABI
8689 based unwinding library, and @code{false} on other targets. This effects
8690 the format of unwinding tables, and how the unwinder in entered after
8691 running a cleanup. The default is @code{false}.
8694 @node Alignment Output
8695 @subsection Assembler Commands for Alignment
8697 @c prevent bad page break with this line
8698 This describes commands for alignment.
8700 @defmac JUMP_ALIGN (@var{label})
8701 The alignment (log base 2) to put in front of @var{label}, which is
8702 a common destination of jumps and has no fallthru incoming edge.
8704 This macro need not be defined if you don't want any special alignment
8705 to be done at such a time. Most machine descriptions do not currently
8708 Unless it's necessary to inspect the @var{label} parameter, it is better
8709 to set the variable @var{align_jumps} in the target's
8710 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8711 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
8714 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
8715 The alignment (log base 2) to put in front of @var{label}, which follows
8718 This macro need not be defined if you don't want any special alignment
8719 to be done at such a time. Most machine descriptions do not currently
8723 @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
8724 The maximum number of bytes to skip when applying
8725 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
8726 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8729 @defmac LOOP_ALIGN (@var{label})
8730 The alignment (log base 2) to put in front of @var{label}, which follows
8731 a @code{NOTE_INSN_LOOP_BEG} note.
8733 This macro need not be defined if you don't want any special alignment
8734 to be done at such a time. Most machine descriptions do not currently
8737 Unless it's necessary to inspect the @var{label} parameter, it is better
8738 to set the variable @code{align_loops} in the target's
8739 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8740 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
8743 @defmac LOOP_ALIGN_MAX_SKIP
8744 The maximum number of bytes to skip when applying @code{LOOP_ALIGN}.
8745 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8748 @defmac LABEL_ALIGN (@var{label})
8749 The alignment (log base 2) to put in front of @var{label}.
8750 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
8751 the maximum of the specified values is used.
8753 Unless it's necessary to inspect the @var{label} parameter, it is better
8754 to set the variable @code{align_labels} in the target's
8755 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
8756 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
8759 @defmac LABEL_ALIGN_MAX_SKIP
8760 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}.
8761 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8764 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
8765 A C statement to output to the stdio stream @var{stream} an assembler
8766 instruction to advance the location counter by @var{nbytes} bytes.
8767 Those bytes should be zero when loaded. @var{nbytes} will be a C
8768 expression of type @code{unsigned HOST_WIDE_INT}.
8771 @defmac ASM_NO_SKIP_IN_TEXT
8772 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
8773 text section because it fails to put zeros in the bytes that are skipped.
8774 This is true on many Unix systems, where the pseudo--op to skip bytes
8775 produces no-op instructions rather than zeros when used in the text
8779 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
8780 A C statement to output to the stdio stream @var{stream} an assembler
8781 command to advance the location counter to a multiple of 2 to the
8782 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
8785 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
8786 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
8787 for padding, if necessary.
8790 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
8791 A C statement to output to the stdio stream @var{stream} an assembler
8792 command to advance the location counter to a multiple of 2 to the
8793 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
8794 satisfy the alignment request. @var{power} and @var{max_skip} will be
8795 a C expression of type @code{int}.
8799 @node Debugging Info
8800 @section Controlling Debugging Information Format
8802 @c prevent bad page break with this line
8803 This describes how to specify debugging information.
8806 * All Debuggers:: Macros that affect all debugging formats uniformly.
8807 * DBX Options:: Macros enabling specific options in DBX format.
8808 * DBX Hooks:: Hook macros for varying DBX format.
8809 * File Names and DBX:: Macros controlling output of file names in DBX format.
8810 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
8811 * VMS Debug:: Macros for VMS debug format.
8815 @subsection Macros Affecting All Debugging Formats
8817 @c prevent bad page break with this line
8818 These macros affect all debugging formats.
8820 @defmac DBX_REGISTER_NUMBER (@var{regno})
8821 A C expression that returns the DBX register number for the compiler
8822 register number @var{regno}. In the default macro provided, the value
8823 of this expression will be @var{regno} itself. But sometimes there are
8824 some registers that the compiler knows about and DBX does not, or vice
8825 versa. In such cases, some register may need to have one number in the
8826 compiler and another for DBX@.
8828 If two registers have consecutive numbers inside GCC, and they can be
8829 used as a pair to hold a multiword value, then they @emph{must} have
8830 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
8831 Otherwise, debuggers will be unable to access such a pair, because they
8832 expect register pairs to be consecutive in their own numbering scheme.
8834 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
8835 does not preserve register pairs, then what you must do instead is
8836 redefine the actual register numbering scheme.
8839 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
8840 A C expression that returns the integer offset value for an automatic
8841 variable having address @var{x} (an RTL expression). The default
8842 computation assumes that @var{x} is based on the frame-pointer and
8843 gives the offset from the frame-pointer. This is required for targets
8844 that produce debugging output for DBX or COFF-style debugging output
8845 for SDB and allow the frame-pointer to be eliminated when the
8846 @option{-g} options is used.
8849 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
8850 A C expression that returns the integer offset value for an argument
8851 having address @var{x} (an RTL expression). The nominal offset is
8855 @defmac PREFERRED_DEBUGGING_TYPE
8856 A C expression that returns the type of debugging output GCC should
8857 produce when the user specifies just @option{-g}. Define
8858 this if you have arranged for GCC to support more than one format of
8859 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
8860 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
8861 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
8863 When the user specifies @option{-ggdb}, GCC normally also uses the
8864 value of this macro to select the debugging output format, but with two
8865 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
8866 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
8867 defined, GCC uses @code{DBX_DEBUG}.
8869 The value of this macro only affects the default debugging output; the
8870 user can always get a specific type of output by using @option{-gstabs},
8871 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
8875 @subsection Specific Options for DBX Output
8877 @c prevent bad page break with this line
8878 These are specific options for DBX output.
8880 @defmac DBX_DEBUGGING_INFO
8881 Define this macro if GCC should produce debugging output for DBX
8882 in response to the @option{-g} option.
8885 @defmac XCOFF_DEBUGGING_INFO
8886 Define this macro if GCC should produce XCOFF format debugging output
8887 in response to the @option{-g} option. This is a variant of DBX format.
8890 @defmac DEFAULT_GDB_EXTENSIONS
8891 Define this macro to control whether GCC should by default generate
8892 GDB's extended version of DBX debugging information (assuming DBX-format
8893 debugging information is enabled at all). If you don't define the
8894 macro, the default is 1: always generate the extended information
8895 if there is any occasion to.
8898 @defmac DEBUG_SYMS_TEXT
8899 Define this macro if all @code{.stabs} commands should be output while
8900 in the text section.
8903 @defmac ASM_STABS_OP
8904 A C string constant, including spacing, naming the assembler pseudo op to
8905 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
8906 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
8907 applies only to DBX debugging information format.
8910 @defmac ASM_STABD_OP
8911 A C string constant, including spacing, naming the assembler pseudo op to
8912 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
8913 value is the current location. If you don't define this macro,
8914 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
8918 @defmac ASM_STABN_OP
8919 A C string constant, including spacing, naming the assembler pseudo op to
8920 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
8921 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
8922 macro applies only to DBX debugging information format.
8925 @defmac DBX_NO_XREFS
8926 Define this macro if DBX on your system does not support the construct
8927 @samp{xs@var{tagname}}. On some systems, this construct is used to
8928 describe a forward reference to a structure named @var{tagname}.
8929 On other systems, this construct is not supported at all.
8932 @defmac DBX_CONTIN_LENGTH
8933 A symbol name in DBX-format debugging information is normally
8934 continued (split into two separate @code{.stabs} directives) when it
8935 exceeds a certain length (by default, 80 characters). On some
8936 operating systems, DBX requires this splitting; on others, splitting
8937 must not be done. You can inhibit splitting by defining this macro
8938 with the value zero. You can override the default splitting-length by
8939 defining this macro as an expression for the length you desire.
8942 @defmac DBX_CONTIN_CHAR
8943 Normally continuation is indicated by adding a @samp{\} character to
8944 the end of a @code{.stabs} string when a continuation follows. To use
8945 a different character instead, define this macro as a character
8946 constant for the character you want to use. Do not define this macro
8947 if backslash is correct for your system.
8950 @defmac DBX_STATIC_STAB_DATA_SECTION
8951 Define this macro if it is necessary to go to the data section before
8952 outputting the @samp{.stabs} pseudo-op for a non-global static
8956 @defmac DBX_TYPE_DECL_STABS_CODE
8957 The value to use in the ``code'' field of the @code{.stabs} directive
8958 for a typedef. The default is @code{N_LSYM}.
8961 @defmac DBX_STATIC_CONST_VAR_CODE
8962 The value to use in the ``code'' field of the @code{.stabs} directive
8963 for a static variable located in the text section. DBX format does not
8964 provide any ``right'' way to do this. The default is @code{N_FUN}.
8967 @defmac DBX_REGPARM_STABS_CODE
8968 The value to use in the ``code'' field of the @code{.stabs} directive
8969 for a parameter passed in registers. DBX format does not provide any
8970 ``right'' way to do this. The default is @code{N_RSYM}.
8973 @defmac DBX_REGPARM_STABS_LETTER
8974 The letter to use in DBX symbol data to identify a symbol as a parameter
8975 passed in registers. DBX format does not customarily provide any way to
8976 do this. The default is @code{'P'}.
8979 @defmac DBX_FUNCTION_FIRST
8980 Define this macro if the DBX information for a function and its
8981 arguments should precede the assembler code for the function. Normally,
8982 in DBX format, the debugging information entirely follows the assembler
8986 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
8987 Define this macro, with value 1, if the value of a symbol describing
8988 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
8989 relative to the start of the enclosing function. Normally, GCC uses
8990 an absolute address.
8993 @defmac DBX_LINES_FUNCTION_RELATIVE
8994 Define this macro, with value 1, if the value of a symbol indicating
8995 the current line number (@code{N_SLINE}) should be relative to the
8996 start of the enclosing function. Normally, GCC uses an absolute address.
8999 @defmac DBX_USE_BINCL
9000 Define this macro if GCC should generate @code{N_BINCL} and
9001 @code{N_EINCL} stabs for included header files, as on Sun systems. This
9002 macro also directs GCC to output a type number as a pair of a file
9003 number and a type number within the file. Normally, GCC does not
9004 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
9005 number for a type number.
9009 @subsection Open-Ended Hooks for DBX Format
9011 @c prevent bad page break with this line
9012 These are hooks for DBX format.
9014 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
9015 Define this macro to say how to output to @var{stream} the debugging
9016 information for the start of a scope level for variable names. The
9017 argument @var{name} is the name of an assembler symbol (for use with
9018 @code{assemble_name}) whose value is the address where the scope begins.
9021 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
9022 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
9025 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
9026 Define this macro if the target machine requires special handling to
9027 output an @code{N_FUN} entry for the function @var{decl}.
9030 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
9031 A C statement to output DBX debugging information before code for line
9032 number @var{line} of the current source file to the stdio stream
9033 @var{stream}. @var{counter} is the number of time the macro was
9034 invoked, including the current invocation; it is intended to generate
9035 unique labels in the assembly output.
9037 This macro should not be defined if the default output is correct, or
9038 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
9041 @defmac NO_DBX_FUNCTION_END
9042 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
9043 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
9044 On those machines, define this macro to turn this feature off without
9045 disturbing the rest of the gdb extensions.
9048 @defmac NO_DBX_BNSYM_ENSYM
9049 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
9050 extension construct. On those machines, define this macro to turn this
9051 feature off without disturbing the rest of the gdb extensions.
9054 @node File Names and DBX
9055 @subsection File Names in DBX Format
9057 @c prevent bad page break with this line
9058 This describes file names in DBX format.
9060 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
9061 A C statement to output DBX debugging information to the stdio stream
9062 @var{stream}, which indicates that file @var{name} is the main source
9063 file---the file specified as the input file for compilation.
9064 This macro is called only once, at the beginning of compilation.
9066 This macro need not be defined if the standard form of output
9067 for DBX debugging information is appropriate.
9069 It may be necessary to refer to a label equal to the beginning of the
9070 text section. You can use @samp{assemble_name (stream, ltext_label_name)}
9071 to do so. If you do this, you must also set the variable
9072 @var{used_ltext_label_name} to @code{true}.
9075 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY
9076 Define this macro, with value 1, if GCC should not emit an indication
9077 of the current directory for compilation and current source language at
9078 the beginning of the file.
9081 @defmac NO_DBX_GCC_MARKER
9082 Define this macro, with value 1, if GCC should not emit an indication
9083 that this object file was compiled by GCC@. The default is to emit
9084 an @code{N_OPT} stab at the beginning of every source file, with
9085 @samp{gcc2_compiled.} for the string and value 0.
9088 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
9089 A C statement to output DBX debugging information at the end of
9090 compilation of the main source file @var{name}. Output should be
9091 written to the stdio stream @var{stream}.
9093 If you don't define this macro, nothing special is output at the end
9094 of compilation, which is correct for most machines.
9097 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
9098 Define this macro @emph{instead of} defining
9099 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
9100 the end of compilation is an @code{N_SO} stab with an empty string,
9101 whose value is the highest absolute text address in the file.
9106 @subsection Macros for SDB and DWARF Output
9108 @c prevent bad page break with this line
9109 Here are macros for SDB and DWARF output.
9111 @defmac SDB_DEBUGGING_INFO
9112 Define this macro if GCC should produce COFF-style debugging output
9113 for SDB in response to the @option{-g} option.
9116 @defmac DWARF2_DEBUGGING_INFO
9117 Define this macro if GCC should produce dwarf version 2 format
9118 debugging output in response to the @option{-g} option.
9120 @deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (tree @var{function})
9121 Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
9122 be emitted for each function. Instead of an integer return the enum
9123 value for the @code{DW_CC_} tag.
9126 To support optional call frame debugging information, you must also
9127 define @code{INCOMING_RETURN_ADDR_RTX} and either set
9128 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
9129 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
9130 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
9133 @defmac DWARF2_FRAME_INFO
9134 Define this macro to a nonzero value if GCC should always output
9135 Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO}
9136 (@pxref{Exception Region Output} is nonzero, GCC will output this
9137 information not matter how you define @code{DWARF2_FRAME_INFO}.
9140 @defmac DWARF2_ASM_LINE_DEBUG_INFO
9141 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
9142 line debug info sections. This will result in much more compact line number
9143 tables, and hence is desirable if it works.
9146 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
9147 A C statement to issue assembly directives that create a difference
9148 @var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
9151 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section})
9152 A C statement to issue assembly directives that create a
9153 section-relative reference to the given @var{label}, using an integer of the
9154 given @var{size}. The label is known to be defined in the given @var{section}.
9157 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
9158 A C statement to issue assembly directives that create a self-relative
9159 reference to the given @var{label}, using an integer of the given @var{size}.
9162 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{FILE}, int @var{size}, rtx @var{x})
9163 If defined, this target hook is a function which outputs a DTP-relative
9164 reference to the given TLS symbol of the specified size.
9167 @defmac PUT_SDB_@dots{}
9168 Define these macros to override the assembler syntax for the special
9169 SDB assembler directives. See @file{sdbout.c} for a list of these
9170 macros and their arguments. If the standard syntax is used, you need
9171 not define them yourself.
9175 Some assemblers do not support a semicolon as a delimiter, even between
9176 SDB assembler directives. In that case, define this macro to be the
9177 delimiter to use (usually @samp{\n}). It is not necessary to define
9178 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
9182 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
9183 Define this macro to allow references to unknown structure,
9184 union, or enumeration tags to be emitted. Standard COFF does not
9185 allow handling of unknown references, MIPS ECOFF has support for
9189 @defmac SDB_ALLOW_FORWARD_REFERENCES
9190 Define this macro to allow references to structure, union, or
9191 enumeration tags that have not yet been seen to be handled. Some
9192 assemblers choke if forward tags are used, while some require it.
9195 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
9196 A C statement to output SDB debugging information before code for line
9197 number @var{line} of the current source file to the stdio stream
9198 @var{stream}. The default is to emit an @code{.ln} directive.
9203 @subsection Macros for VMS Debug Format
9205 @c prevent bad page break with this line
9206 Here are macros for VMS debug format.
9208 @defmac VMS_DEBUGGING_INFO
9209 Define this macro if GCC should produce debugging output for VMS
9210 in response to the @option{-g} option. The default behavior for VMS
9211 is to generate minimal debug info for a traceback in the absence of
9212 @option{-g} unless explicitly overridden with @option{-g0}. This
9213 behavior is controlled by @code{OPTIMIZATION_OPTIONS} and
9214 @code{OVERRIDE_OPTIONS}.
9217 @node Floating Point
9218 @section Cross Compilation and Floating Point
9219 @cindex cross compilation and floating point
9220 @cindex floating point and cross compilation
9222 While all modern machines use twos-complement representation for integers,
9223 there are a variety of representations for floating point numbers. This
9224 means that in a cross-compiler the representation of floating point numbers
9225 in the compiled program may be different from that used in the machine
9226 doing the compilation.
9228 Because different representation systems may offer different amounts of
9229 range and precision, all floating point constants must be represented in
9230 the target machine's format. Therefore, the cross compiler cannot
9231 safely use the host machine's floating point arithmetic; it must emulate
9232 the target's arithmetic. To ensure consistency, GCC always uses
9233 emulation to work with floating point values, even when the host and
9234 target floating point formats are identical.
9236 The following macros are provided by @file{real.h} for the compiler to
9237 use. All parts of the compiler which generate or optimize
9238 floating-point calculations must use these macros. They may evaluate
9239 their operands more than once, so operands must not have side effects.
9241 @defmac REAL_VALUE_TYPE
9242 The C data type to be used to hold a floating point value in the target
9243 machine's format. Typically this is a @code{struct} containing an
9244 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
9248 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9249 Compares for equality the two values, @var{x} and @var{y}. If the target
9250 floating point format supports negative zeroes and/or NaNs,
9251 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
9252 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
9255 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9256 Tests whether @var{x} is less than @var{y}.
9259 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
9260 Truncates @var{x} to a signed integer, rounding toward zero.
9263 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
9264 Truncates @var{x} to an unsigned integer, rounding toward zero. If
9265 @var{x} is negative, returns zero.
9268 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
9269 Converts @var{string} into a floating point number in the target machine's
9270 representation for mode @var{mode}. This routine can handle both
9271 decimal and hexadecimal floating point constants, using the syntax
9272 defined by the C language for both.
9275 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
9276 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
9279 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
9280 Determines whether @var{x} represents infinity (positive or negative).
9283 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
9284 Determines whether @var{x} represents a ``NaN'' (not-a-number).
9287 @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})
9288 Calculates an arithmetic operation on the two floating point values
9289 @var{x} and @var{y}, storing the result in @var{output} (which must be a
9292 The operation to be performed is specified by @var{code}. Only the
9293 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
9294 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
9296 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
9297 target's floating point format cannot represent infinity, it will call
9298 @code{abort}. Callers should check for this situation first, using
9299 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
9302 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
9303 Returns the negative of the floating point value @var{x}.
9306 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
9307 Returns the absolute value of @var{x}.
9310 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
9311 Truncates the floating point value @var{x} to fit in @var{mode}. The
9312 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
9313 appropriate bit pattern to be output as a floating constant whose
9314 precision accords with mode @var{mode}.
9317 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
9318 Converts a floating point value @var{x} into a double-precision integer
9319 which is then stored into @var{low} and @var{high}. If the value is not
9320 integral, it is truncated.
9323 @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})
9324 Converts a double-precision integer found in @var{low} and @var{high},
9325 into a floating point value which is then stored into @var{x}. The
9326 value is truncated to fit in mode @var{mode}.
9329 @node Mode Switching
9330 @section Mode Switching Instructions
9331 @cindex mode switching
9332 The following macros control mode switching optimizations:
9334 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
9335 Define this macro if the port needs extra instructions inserted for mode
9336 switching in an optimizing compilation.
9338 For an example, the SH4 can perform both single and double precision
9339 floating point operations, but to perform a single precision operation,
9340 the FPSCR PR bit has to be cleared, while for a double precision
9341 operation, this bit has to be set. Changing the PR bit requires a general
9342 purpose register as a scratch register, hence these FPSCR sets have to
9343 be inserted before reload, i.e.@: you can't put this into instruction emitting
9344 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
9346 You can have multiple entities that are mode-switched, and select at run time
9347 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
9348 return nonzero for any @var{entity} that needs mode-switching.
9349 If you define this macro, you also have to define
9350 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
9351 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
9352 @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT}
9356 @defmac NUM_MODES_FOR_MODE_SWITCHING
9357 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
9358 initializer for an array of integers. Each initializer element
9359 N refers to an entity that needs mode switching, and specifies the number
9360 of different modes that might need to be set for this entity.
9361 The position of the initializer in the initializer---starting counting at
9362 zero---determines the integer that is used to refer to the mode-switched
9364 In macros that take mode arguments / yield a mode result, modes are
9365 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
9366 switch is needed / supplied.
9369 @defmac MODE_NEEDED (@var{entity}, @var{insn})
9370 @var{entity} is an integer specifying a mode-switched entity. If
9371 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
9372 return an integer value not larger than the corresponding element in
9373 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
9374 be switched into prior to the execution of @var{insn}.
9377 @defmac MODE_AFTER (@var{mode}, @var{insn})
9378 If this macro is defined, it is evaluated for every @var{insn} during
9379 mode switching. It determines the mode that an insn results in (if
9380 different from the incoming mode).
9383 @defmac MODE_ENTRY (@var{entity})
9384 If this macro is defined, it is evaluated for every @var{entity} that needs
9385 mode switching. It should evaluate to an integer, which is a mode that
9386 @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY}
9387 is defined then @code{MODE_EXIT} must be defined.
9390 @defmac MODE_EXIT (@var{entity})
9391 If this macro is defined, it is evaluated for every @var{entity} that needs
9392 mode switching. It should evaluate to an integer, which is a mode that
9393 @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT}
9394 is defined then @code{MODE_ENTRY} must be defined.
9397 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
9398 This macro specifies the order in which modes for @var{entity} are processed.
9399 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
9400 lowest. The value of the macro should be an integer designating a mode
9401 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
9402 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
9403 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
9406 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
9407 Generate one or more insns to set @var{entity} to @var{mode}.
9408 @var{hard_reg_live} is the set of hard registers live at the point where
9409 the insn(s) are to be inserted.
9412 @node Target Attributes
9413 @section Defining target-specific uses of @code{__attribute__}
9414 @cindex target attributes
9415 @cindex machine attributes
9416 @cindex attributes, target-specific
9418 Target-specific attributes may be defined for functions, data and types.
9419 These are described using the following target hooks; they also need to
9420 be documented in @file{extend.texi}.
9422 @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
9423 If defined, this target hook points to an array of @samp{struct
9424 attribute_spec} (defined in @file{tree.h}) specifying the machine
9425 specific attributes for this target and some of the restrictions on the
9426 entities to which these attributes are applied and the arguments they
9430 @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
9431 If defined, this target hook is a function which returns zero if the attributes on
9432 @var{type1} and @var{type2} are incompatible, one if they are compatible,
9433 and two if they are nearly compatible (which causes a warning to be
9434 generated). If this is not defined, machine-specific attributes are
9435 supposed always to be compatible.
9438 @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
9439 If defined, this target hook is a function which assigns default attributes to
9440 newly defined @var{type}.
9443 @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
9444 Define this target hook if the merging of type attributes needs special
9445 handling. If defined, the result is a list of the combined
9446 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
9447 that @code{comptypes} has already been called and returned 1. This
9448 function may call @code{merge_attributes} to handle machine-independent
9452 @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
9453 Define this target hook if the merging of decl attributes needs special
9454 handling. If defined, the result is a list of the combined
9455 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
9456 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
9457 when this is needed are when one attribute overrides another, or when an
9458 attribute is nullified by a subsequent definition. This function may
9459 call @code{merge_attributes} to handle machine-independent merging.
9461 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
9462 If the only target-specific handling you require is @samp{dllimport}
9463 for Microsoft Windows targets, you should define the macro
9464 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler
9465 will then define a function called
9466 @code{merge_dllimport_decl_attributes} which can then be defined as
9467 the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also
9468 add @code{handle_dll_attribute} in the attribute table for your port
9469 to perform initial processing of the @samp{dllimport} and
9470 @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and
9471 @file{i386/i386.c}, for example.
9474 @deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (tree @var{decl})
9475 @var{decl} is a variable or function with @code{__attribute__((dllimport))}
9476 specified. Use this hook if the target needs to add extra validation
9477 checks to @code{handle_dll_attribute}.
9480 @defmac TARGET_DECLSPEC
9481 Define this macro to a nonzero value if you want to treat
9482 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
9483 default, this behavior is enabled only for targets that define
9484 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
9485 of @code{__declspec} is via a built-in macro, but you should not rely
9486 on this implementation detail.
9489 @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
9490 Define this target hook if you want to be able to add attributes to a decl
9491 when it is being created. This is normally useful for back ends which
9492 wish to implement a pragma by using the attributes which correspond to
9493 the pragma's effect. The @var{node} argument is the decl which is being
9494 created. The @var{attr_ptr} argument is a pointer to the attribute list
9495 for this decl. The list itself should not be modified, since it may be
9496 shared with other decls, but attributes may be chained on the head of
9497 the list and @code{*@var{attr_ptr}} modified to point to the new
9498 attributes, or a copy of the list may be made if further changes are
9502 @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl})
9504 This target hook returns @code{true} if it is ok to inline @var{fndecl}
9505 into the current function, despite its having target-specific
9506 attributes, @code{false} otherwise. By default, if a function has a
9507 target specific attribute attached to it, it will not be inlined.
9510 @deftypefn {Target Hook} bool TARGET_VALID_OPTION_ATTRIBUTE_P (tree @var{fndecl}, tree @var{name}, tree @var{args}, int @var{flags})
9511 This hook is called to parse the @code{attribute(option("..."))}, and
9512 it allows the function to set different target machine compile time
9513 options for the current function that might be different than the
9514 options specified on the command line. The hook should return
9515 @code{true} if the options are valid.
9517 The hook should set the @var{DECL_FUNCTION_SPECIFIC_TARGET} field in
9518 the function declaration to hold a pointer to a target specific
9519 @var{struct cl_target_option} structure.
9522 @deftypefn {Target Hook} void TARGET_OPTION_SAVE (struct cl_target_option *@var{ptr})
9523 This hook is called to save any additional target specific information
9524 in the @var{struct cl_target_option} structure for function specific
9526 @xref{Option file format}.
9529 @deftypefn {Target Hook} void TARGET_OPTION_RESTORE (struct cl_target_option *@var{ptr})
9530 This hook is called to restore any additional target specific
9531 information in the @var{struct cl_target_option} structure for
9532 function specific options.
9535 @deftypefn {Target Hook} void TARGET_OPTION_PRINT (struct cl_target_option *@var{ptr})
9536 This hook is called to print any additional target specific
9537 information in the @var{struct cl_target_option} structure for
9538 function specific options.
9541 @deftypefn {Target Hook} bool TARGET_OPTION_PRAGMA_PARSE (target @var{args})
9542 This target hook parses the options for @code{#pragma GCC option} to
9543 set the machine specific options for functions that occur later in the
9544 input stream. The options should be the same as handled by the
9545 @code{TARGET_VALID_OPTION_ATTRIBUTE_P} hook.
9548 @deftypefn {Target Hook} bool TARGET_CAN_INLINE_P (tree @var{caller}, tree @var{callee})
9549 This target hook returns @code{false} if the @var{caller} function
9550 cannot inline @var{callee}, based on target specific information. By
9551 default, inlining is not allowed if the callee function has function
9552 specific target options and the caller does not use the same options.
9556 @section Emulating TLS
9557 @cindex Emulated TLS
9559 For targets whose psABI does not provide Thread Local Storage via
9560 specific relocations and instruction sequences, an emulation layer is
9561 used. A set of target hooks allows this emulation layer to be
9562 configured for the requirements of a particular target. For instance
9563 the psABI may in fact specify TLS support in terms of an emulation
9566 The emulation layer works by creating a control object for every TLS
9567 object. To access the TLS object, a lookup function is provided
9568 which, when given the address of the control object, will return the
9569 address of the current thread's instance of the TLS object.
9571 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_GET_ADDRESS
9572 Contains the name of the helper function that uses a TLS control
9573 object to locate a TLS instance. The default causes libgcc's
9574 emulated TLS helper function to be used.
9577 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_REGISTER_COMMON
9578 Contains the name of the helper function that should be used at
9579 program startup to register TLS objects that are implicitly
9580 initialized to zero. If this is @code{NULL}, all TLS objects will
9581 have explicit initializers. The default causes libgcc's emulated TLS
9582 registration function to be used.
9585 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_SECTION
9586 Contains the name of the section in which TLS control variables should
9587 be placed. The default of @code{NULL} allows these to be placed in
9591 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_SECTION
9592 Contains the name of the section in which TLS initializers should be
9593 placed. The default of @code{NULL} allows these to be placed in any
9597 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_PREFIX
9598 Contains the prefix to be prepended to TLS control variable names.
9599 The default of @code{NULL} uses a target-specific prefix.
9602 @deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_PREFIX
9603 Contains the prefix to be prepended to TLS initializer objects. The
9604 default of @code{NULL} uses a target-specific prefix.
9607 @deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_FIELDS (tree @var{type}, tree *@var{name})
9608 Specifies a function that generates the FIELD_DECLs for a TLS control
9609 object type. @var{type} is the RECORD_TYPE the fields are for and
9610 @var{name} should be filled with the structure tag, if the default of
9611 @code{__emutls_object} is unsuitable. The default creates a type suitable
9612 for libgcc's emulated TLS function.
9615 @deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_INIT (tree @var{var}, tree @var{decl}, tree @var{tmpl_addr})
9616 Specifies a function that generates the CONSTRUCTOR to initialize a
9617 TLS control object. @var{var} is the TLS control object, @var{decl}
9618 is the TLS object and @var{tmpl_addr} is the address of the
9619 initializer. The default initializes libgcc's emulated TLS control object.
9622 @deftypevr {Target Hook} {bool} TARGET_EMUTLS_VAR_ALIGN_FIXED
9623 Specifies whether the alignment of TLS control variable objects is
9624 fixed and should not be increased as some backends may do to optimize
9625 single objects. The default is false.
9628 @deftypevr {Target Hook} {bool} TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
9629 Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor
9630 may be used to describe emulated TLS control objects.
9633 @node MIPS Coprocessors
9634 @section Defining coprocessor specifics for MIPS targets.
9635 @cindex MIPS coprocessor-definition macros
9637 The MIPS specification allows MIPS implementations to have as many as 4
9638 coprocessors, each with as many as 32 private registers. GCC supports
9639 accessing these registers and transferring values between the registers
9640 and memory using asm-ized variables. For example:
9643 register unsigned int cp0count asm ("c0r1");
9649 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
9650 names may be added as described below, or the default names may be
9651 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
9653 Coprocessor registers are assumed to be epilogue-used; sets to them will
9654 be preserved even if it does not appear that the register is used again
9655 later in the function.
9657 Another note: according to the MIPS spec, coprocessor 1 (if present) is
9658 the FPU@. One accesses COP1 registers through standard mips
9659 floating-point support; they are not included in this mechanism.
9661 There is one macro used in defining the MIPS coprocessor interface which
9662 you may want to override in subtargets; it is described below.
9664 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
9665 A comma-separated list (with leading comma) of pairs describing the
9666 alternate names of coprocessor registers. The format of each entry should be
9668 @{ @var{alternatename}, @var{register_number}@}
9674 @section Parameters for Precompiled Header Validity Checking
9675 @cindex parameters, precompiled headers
9677 @deftypefn {Target Hook} void *TARGET_GET_PCH_VALIDITY (size_t *@var{sz})
9678 This hook returns the data needed by @code{TARGET_PCH_VALID_P} and sets
9679 @samp{*@var{sz}} to the size of the data in bytes.
9682 @deftypefn {Target Hook} const char *TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz})
9683 This hook checks whether the options used to create a PCH file are
9684 compatible with the current settings. It returns @code{NULL}
9685 if so and a suitable error message if not. Error messages will
9686 be presented to the user and must be localized using @samp{_(@var{msg})}.
9688 @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
9689 when the PCH file was created and @var{sz} is the size of that data in bytes.
9690 It's safe to assume that the data was created by the same version of the
9691 compiler, so no format checking is needed.
9693 The default definition of @code{default_pch_valid_p} should be
9694 suitable for most targets.
9697 @deftypefn {Target Hook} const char *TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags})
9698 If this hook is nonnull, the default implementation of
9699 @code{TARGET_PCH_VALID_P} will use it to check for compatible values
9700 of @code{target_flags}. @var{pch_flags} specifies the value that
9701 @code{target_flags} had when the PCH file was created. The return
9702 value is the same as for @code{TARGET_PCH_VALID_P}.
9706 @section C++ ABI parameters
9707 @cindex parameters, c++ abi
9709 @deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void)
9710 Define this hook to override the integer type used for guard variables.
9711 These are used to implement one-time construction of static objects. The
9712 default is long_long_integer_type_node.
9715 @deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void)
9716 This hook determines how guard variables are used. It should return
9717 @code{false} (the default) if first byte should be used. A return value of
9718 @code{true} indicates the least significant bit should be used.
9721 @deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type})
9722 This hook returns the size of the cookie to use when allocating an array
9723 whose elements have the indicated @var{type}. Assumes that it is already
9724 known that a cookie is needed. The default is
9725 @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
9726 IA64/Generic C++ ABI@.
9729 @deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void)
9730 This hook should return @code{true} if the element size should be stored in
9731 array cookies. The default is to return @code{false}.
9734 @deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export})
9735 If defined by a backend this hook allows the decision made to export
9736 class @var{type} to be overruled. Upon entry @var{import_export}
9737 will contain 1 if the class is going to be exported, @minus{}1 if it is going
9738 to be imported and 0 otherwise. This function should return the
9739 modified value and perform any other actions necessary to support the
9740 backend's targeted operating system.
9743 @deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void)
9744 This hook should return @code{true} if constructors and destructors return
9745 the address of the object created/destroyed. The default is to return
9749 @deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void)
9750 This hook returns true if the key method for a class (i.e., the method
9751 which, if defined in the current translation unit, causes the virtual
9752 table to be emitted) may be an inline function. Under the standard
9753 Itanium C++ ABI the key method may be an inline function so long as
9754 the function is not declared inline in the class definition. Under
9755 some variants of the ABI, an inline function can never be the key
9756 method. The default is to return @code{true}.
9759 @deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl})
9760 @var{decl} is a virtual table, virtual table table, typeinfo object,
9761 or other similar implicit class data object that will be emitted with
9762 external linkage in this translation unit. No ELF visibility has been
9763 explicitly specified. If the target needs to specify a visibility
9764 other than that of the containing class, use this hook to set
9765 @code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}.
9768 @deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void)
9769 This hook returns true (the default) if virtual tables and other
9770 similar implicit class data objects are always COMDAT if they have
9771 external linkage. If this hook returns false, then class data for
9772 classes whose virtual table will be emitted in only one translation
9773 unit will not be COMDAT.
9776 @deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void)
9777 This hook returns true (the default) if the RTTI information for
9778 the basic types which is defined in the C++ runtime should always
9779 be COMDAT, false if it should not be COMDAT.
9782 @deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void)
9783 This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
9784 should be used to register static destructors when @option{-fuse-cxa-atexit}
9785 is in effect. The default is to return false to use @code{__cxa_atexit}.
9788 @deftypefn {Target Hook} bool TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT (void)
9789 This hook returns true if the target @code{atexit} function can be used
9790 in the same manner as @code{__cxa_atexit} to register C++ static
9791 destructors. This requires that @code{atexit}-registered functions in
9792 shared libraries are run in the correct order when the libraries are
9793 unloaded. The default is to return false.
9796 @deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type})
9797 @var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just been
9798 defined. Use this hook to make adjustments to the class (eg, tweak
9799 visibility or perform any other required target modifications).
9803 @section Miscellaneous Parameters
9804 @cindex parameters, miscellaneous
9806 @c prevent bad page break with this line
9807 Here are several miscellaneous parameters.
9809 @defmac HAS_LONG_COND_BRANCH
9810 Define this boolean macro to indicate whether or not your architecture
9811 has conditional branches that can span all of memory. It is used in
9812 conjunction with an optimization that partitions hot and cold basic
9813 blocks into separate sections of the executable. If this macro is
9814 set to false, gcc will convert any conditional branches that attempt
9815 to cross between sections into unconditional branches or indirect jumps.
9818 @defmac HAS_LONG_UNCOND_BRANCH
9819 Define this boolean macro to indicate whether or not your architecture
9820 has unconditional branches that can span all of memory. It is used in
9821 conjunction with an optimization that partitions hot and cold basic
9822 blocks into separate sections of the executable. If this macro is
9823 set to false, gcc will convert any unconditional branches that attempt
9824 to cross between sections into indirect jumps.
9827 @defmac CASE_VECTOR_MODE
9828 An alias for a machine mode name. This is the machine mode that
9829 elements of a jump-table should have.
9832 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
9833 Optional: return the preferred mode for an @code{addr_diff_vec}
9834 when the minimum and maximum offset are known. If you define this,
9835 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
9836 To make this work, you also have to define @code{INSN_ALIGN} and
9837 make the alignment for @code{addr_diff_vec} explicit.
9838 The @var{body} argument is provided so that the offset_unsigned and scale
9839 flags can be updated.
9842 @defmac CASE_VECTOR_PC_RELATIVE
9843 Define this macro to be a C expression to indicate when jump-tables
9844 should contain relative addresses. You need not define this macro if
9845 jump-tables never contain relative addresses, or jump-tables should
9846 contain relative addresses only when @option{-fPIC} or @option{-fPIC}
9850 @deftypefn {Target Hook} unsigned int TARGET_CASE_VALUES_THRESHOLD (void)
9851 This function return the smallest number of different values for which it
9852 is best to use a jump-table instead of a tree of conditional branches.
9853 The default is four for machines with a @code{casesi} instruction and
9854 five otherwise. This is best for most machines.
9857 @defmac CASE_USE_BIT_TESTS
9858 Define this macro to be a C expression to indicate whether C switch
9859 statements may be implemented by a sequence of bit tests. This is
9860 advantageous on processors that can efficiently implement left shift
9861 of 1 by the number of bits held in a register, but inappropriate on
9862 targets that would require a loop. By default, this macro returns
9863 @code{true} if the target defines an @code{ashlsi3} pattern, and
9864 @code{false} otherwise.
9867 @defmac WORD_REGISTER_OPERATIONS
9868 Define this macro if operations between registers with integral mode
9869 smaller than a word are always performed on the entire register.
9870 Most RISC machines have this property and most CISC machines do not.
9873 @defmac LOAD_EXTEND_OP (@var{mem_mode})
9874 Define this macro to be a C expression indicating when insns that read
9875 memory in @var{mem_mode}, an integral mode narrower than a word, set the
9876 bits outside of @var{mem_mode} to be either the sign-extension or the
9877 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
9878 of @var{mem_mode} for which the
9879 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
9880 @code{UNKNOWN} for other modes.
9882 This macro is not called with @var{mem_mode} non-integral or with a width
9883 greater than or equal to @code{BITS_PER_WORD}, so you may return any
9884 value in this case. Do not define this macro if it would always return
9885 @code{UNKNOWN}. On machines where this macro is defined, you will normally
9886 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
9888 You may return a non-@code{UNKNOWN} value even if for some hard registers
9889 the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
9890 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
9891 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
9892 integral mode larger than this but not larger than @code{word_mode}.
9894 You must return @code{UNKNOWN} if for some hard registers that allow this
9895 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
9896 @code{word_mode}, but that they can change to another integral mode that
9897 is larger then @var{mem_mode} but still smaller than @code{word_mode}.
9900 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
9901 Define this macro if loading short immediate values into registers sign
9905 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
9906 Define this macro if the same instructions that convert a floating
9907 point number to a signed fixed point number also convert validly to an
9911 @deftypefn {Target Hook} int TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (enum machine_mode @var{mode})
9912 When @option{-ffast-math} is in effect, GCC tries to optimize
9913 divisions by the same divisor, by turning them into multiplications by
9914 the reciprocal. This target hook specifies the minimum number of divisions
9915 that should be there for GCC to perform the optimization for a variable
9916 of mode @var{mode}. The default implementation returns 3 if the machine
9917 has an instruction for the division, and 2 if it does not.
9921 The maximum number of bytes that a single instruction can move quickly
9922 between memory and registers or between two memory locations.
9925 @defmac MAX_MOVE_MAX
9926 The maximum number of bytes that a single instruction can move quickly
9927 between memory and registers or between two memory locations. If this
9928 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
9929 constant value that is the largest value that @code{MOVE_MAX} can have
9933 @defmac SHIFT_COUNT_TRUNCATED
9934 A C expression that is nonzero if on this machine the number of bits
9935 actually used for the count of a shift operation is equal to the number
9936 of bits needed to represent the size of the object being shifted. When
9937 this macro is nonzero, the compiler will assume that it is safe to omit
9938 a sign-extend, zero-extend, and certain bitwise `and' instructions that
9939 truncates the count of a shift operation. On machines that have
9940 instructions that act on bit-fields at variable positions, which may
9941 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
9942 also enables deletion of truncations of the values that serve as
9943 arguments to bit-field instructions.
9945 If both types of instructions truncate the count (for shifts) and
9946 position (for bit-field operations), or if no variable-position bit-field
9947 instructions exist, you should define this macro.
9949 However, on some machines, such as the 80386 and the 680x0, truncation
9950 only applies to shift operations and not the (real or pretended)
9951 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
9952 such machines. Instead, add patterns to the @file{md} file that include
9953 the implied truncation of the shift instructions.
9955 You need not define this macro if it would always have the value of zero.
9958 @anchor{TARGET_SHIFT_TRUNCATION_MASK}
9959 @deftypefn {Target Hook} int TARGET_SHIFT_TRUNCATION_MASK (enum machine_mode @var{mode})
9960 This function describes how the standard shift patterns for @var{mode}
9961 deal with shifts by negative amounts or by more than the width of the mode.
9962 @xref{shift patterns}.
9964 On many machines, the shift patterns will apply a mask @var{m} to the
9965 shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
9966 equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If
9967 this is true for mode @var{mode}, the function should return @var{m},
9968 otherwise it should return 0. A return value of 0 indicates that no
9969 particular behavior is guaranteed.
9971 Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
9972 @emph{not} apply to general shift rtxes; it applies only to instructions
9973 that are generated by the named shift patterns.
9975 The default implementation of this function returns
9976 @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
9977 and 0 otherwise. This definition is always safe, but if
9978 @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
9979 nevertheless truncate the shift count, you may get better code
9983 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
9984 A C expression which is nonzero if on this machine it is safe to
9985 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
9986 bits (where @var{outprec} is smaller than @var{inprec}) by merely
9987 operating on it as if it had only @var{outprec} bits.
9989 On many machines, this expression can be 1.
9991 @c rearranged this, removed the phrase "it is reported that". this was
9992 @c to fix an overfull hbox. --mew 10feb93
9993 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
9994 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
9995 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
9996 such cases may improve things.
9999 @deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (enum machine_mode @var{mode}, enum machine_mode @var{rep_mode})
10000 The representation of an integral mode can be such that the values
10001 are always extended to a wider integral mode. Return
10002 @code{SIGN_EXTEND} if values of @var{mode} are represented in
10003 sign-extended form to @var{rep_mode}. Return @code{UNKNOWN}
10004 otherwise. (Currently, none of the targets use zero-extended
10005 representation this way so unlike @code{LOAD_EXTEND_OP},
10006 @code{TARGET_MODE_REP_EXTENDED} is expected to return either
10007 @code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends
10008 @var{mode} to @var{mode_rep} so that @var{mode_rep} is not the next
10009 widest integral mode and currently we take advantage of this fact.)
10011 Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
10012 value even if the extension is not performed on certain hard registers
10013 as long as for the @code{REGNO_REG_CLASS} of these hard registers
10014 @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero.
10016 Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
10017 describe two related properties. If you define
10018 @code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
10019 to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
10022 In order to enforce the representation of @code{mode},
10023 @code{TRULY_NOOP_TRUNCATION} should return false when truncating to
10027 @defmac STORE_FLAG_VALUE
10028 A C expression describing the value returned by a comparison operator
10029 with an integral mode and stored by a store-flag instruction
10030 (@samp{s@var{cond}}) when the condition is true. This description must
10031 apply to @emph{all} the @samp{s@var{cond}} patterns and all the
10032 comparison operators whose results have a @code{MODE_INT} mode.
10034 A value of 1 or @minus{}1 means that the instruction implementing the
10035 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
10036 and 0 when the comparison is false. Otherwise, the value indicates
10037 which bits of the result are guaranteed to be 1 when the comparison is
10038 true. This value is interpreted in the mode of the comparison
10039 operation, which is given by the mode of the first operand in the
10040 @samp{s@var{cond}} pattern. Either the low bit or the sign bit of
10041 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
10044 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
10045 generate code that depends only on the specified bits. It can also
10046 replace comparison operators with equivalent operations if they cause
10047 the required bits to be set, even if the remaining bits are undefined.
10048 For example, on a machine whose comparison operators return an
10049 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
10050 @samp{0x80000000}, saying that just the sign bit is relevant, the
10054 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
10058 can be converted to
10061 (ashift:SI @var{x} (const_int @var{n}))
10065 where @var{n} is the appropriate shift count to move the bit being
10066 tested into the sign bit.
10068 There is no way to describe a machine that always sets the low-order bit
10069 for a true value, but does not guarantee the value of any other bits,
10070 but we do not know of any machine that has such an instruction. If you
10071 are trying to port GCC to such a machine, include an instruction to
10072 perform a logical-and of the result with 1 in the pattern for the
10073 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
10075 Often, a machine will have multiple instructions that obtain a value
10076 from a comparison (or the condition codes). Here are rules to guide the
10077 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
10082 Use the shortest sequence that yields a valid definition for
10083 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
10084 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
10085 comparison operators to do so because there may be opportunities to
10086 combine the normalization with other operations.
10089 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
10090 slightly preferred on machines with expensive jumps and 1 preferred on
10094 As a second choice, choose a value of @samp{0x80000001} if instructions
10095 exist that set both the sign and low-order bits but do not define the
10099 Otherwise, use a value of @samp{0x80000000}.
10102 Many machines can produce both the value chosen for
10103 @code{STORE_FLAG_VALUE} and its negation in the same number of
10104 instructions. On those machines, you should also define a pattern for
10105 those cases, e.g., one matching
10108 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
10111 Some machines can also perform @code{and} or @code{plus} operations on
10112 condition code values with less instructions than the corresponding
10113 @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those
10114 machines, define the appropriate patterns. Use the names @code{incscc}
10115 and @code{decscc}, respectively, for the patterns which perform
10116 @code{plus} or @code{minus} operations on condition code values. See
10117 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
10118 find such instruction sequences on other machines.
10120 If this macro is not defined, the default value, 1, is used. You need
10121 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
10122 instructions, or if the value generated by these instructions is 1.
10125 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
10126 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
10127 returned when comparison operators with floating-point results are true.
10128 Define this macro on machines that have comparison operations that return
10129 floating-point values. If there are no such operations, do not define
10133 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
10134 A C expression that gives a rtx representing the nonzero true element
10135 for vector comparisons. The returned rtx should be valid for the inner
10136 mode of @var{mode} which is guaranteed to be a vector mode. Define
10137 this macro on machines that have vector comparison operations that
10138 return a vector result. If there are no such operations, do not define
10139 this macro. Typically, this macro is defined as @code{const1_rtx} or
10140 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
10141 the compiler optimizing such vector comparison operations for the
10145 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10146 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10147 A C expression that indicates whether the architecture defines a value
10148 for @code{clz} or @code{ctz} with a zero operand.
10149 A result of @code{0} indicates the value is undefined.
10150 If the value is defined for only the RTL expression, the macro should
10151 evaluate to @code{1}; if the value applies also to the corresponding optab
10152 entry (which is normally the case if it expands directly into
10153 the corresponding RTL), then the macro should evaluate to @code{2}.
10154 In the cases where the value is defined, @var{value} should be set to
10157 If this macro is not defined, the value of @code{clz} or
10158 @code{ctz} at zero is assumed to be undefined.
10160 This macro must be defined if the target's expansion for @code{ffs}
10161 relies on a particular value to get correct results. Otherwise it
10162 is not necessary, though it may be used to optimize some corner cases, and
10163 to provide a default expansion for the @code{ffs} optab.
10165 Note that regardless of this macro the ``definedness'' of @code{clz}
10166 and @code{ctz} at zero do @emph{not} extend to the builtin functions
10167 visible to the user. Thus one may be free to adjust the value at will
10168 to match the target expansion of these operations without fear of
10173 An alias for the machine mode for pointers. On most machines, define
10174 this to be the integer mode corresponding to the width of a hardware
10175 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
10176 On some machines you must define this to be one of the partial integer
10177 modes, such as @code{PSImode}.
10179 The width of @code{Pmode} must be at least as large as the value of
10180 @code{POINTER_SIZE}. If it is not equal, you must define the macro
10181 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
10185 @defmac FUNCTION_MODE
10186 An alias for the machine mode used for memory references to functions
10187 being called, in @code{call} RTL expressions. On most CISC machines,
10188 where an instruction can begin at any byte address, this should be
10189 @code{QImode}. On most RISC machines, where all instructions have fixed
10190 size and alignment, this should be a mode with the same size and alignment
10191 as the machine instruction words - typically @code{SImode} or @code{HImode}.
10194 @defmac STDC_0_IN_SYSTEM_HEADERS
10195 In normal operation, the preprocessor expands @code{__STDC__} to the
10196 constant 1, to signify that GCC conforms to ISO Standard C@. On some
10197 hosts, like Solaris, the system compiler uses a different convention,
10198 where @code{__STDC__} is normally 0, but is 1 if the user specifies
10199 strict conformance to the C Standard.
10201 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
10202 convention when processing system header files, but when processing user
10203 files @code{__STDC__} will always expand to 1.
10206 @defmac NO_IMPLICIT_EXTERN_C
10207 Define this macro if the system header files support C++ as well as C@.
10208 This macro inhibits the usual method of using system header files in
10209 C++, which is to pretend that the file's contents are enclosed in
10210 @samp{extern "C" @{@dots{}@}}.
10215 @defmac REGISTER_TARGET_PRAGMAS ()
10216 Define this macro if you want to implement any target-specific pragmas.
10217 If defined, it is a C expression which makes a series of calls to
10218 @code{c_register_pragma} or @code{c_register_pragma_with_expansion}
10219 for each pragma. The macro may also do any
10220 setup required for the pragmas.
10222 The primary reason to define this macro is to provide compatibility with
10223 other compilers for the same target. In general, we discourage
10224 definition of target-specific pragmas for GCC@.
10226 If the pragma can be implemented by attributes then you should consider
10227 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
10229 Preprocessor macros that appear on pragma lines are not expanded. All
10230 @samp{#pragma} directives that do not match any registered pragma are
10231 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
10234 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10235 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10237 Each call to @code{c_register_pragma} or
10238 @code{c_register_pragma_with_expansion} establishes one pragma. The
10239 @var{callback} routine will be called when the preprocessor encounters a
10243 #pragma [@var{space}] @var{name} @dots{}
10246 @var{space} is the case-sensitive namespace of the pragma, or
10247 @code{NULL} to put the pragma in the global namespace. The callback
10248 routine receives @var{pfile} as its first argument, which can be passed
10249 on to cpplib's functions if necessary. You can lex tokens after the
10250 @var{name} by calling @code{pragma_lex}. Tokens that are not read by the
10251 callback will be silently ignored. The end of the line is indicated by
10252 a token of type @code{CPP_EOF}. Macro expansion occurs on the
10253 arguments of pragmas registered with
10254 @code{c_register_pragma_with_expansion} but not on the arguments of
10255 pragmas registered with @code{c_register_pragma}.
10257 Note that the use of @code{pragma_lex} is specific to the C and C++
10258 compilers. It will not work in the Java or Fortran compilers, or any
10259 other language compilers for that matter. Thus if @code{pragma_lex} is going
10260 to be called from target-specific code, it must only be done so when
10261 building the C and C++ compilers. This can be done by defining the
10262 variables @code{c_target_objs} and @code{cxx_target_objs} in the
10263 target entry in the @file{config.gcc} file. These variables should name
10264 the target-specific, language-specific object file which contains the
10265 code that uses @code{pragma_lex}. Note it will also be necessary to add a
10266 rule to the makefile fragment pointed to by @code{tmake_file} that shows
10267 how to build this object file.
10272 @defmac HANDLE_SYSV_PRAGMA
10273 Define this macro (to a value of 1) if you want the System V style
10274 pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name>
10275 [=<value>]} to be supported by gcc.
10277 The pack pragma specifies the maximum alignment (in bytes) of fields
10278 within a structure, in much the same way as the @samp{__aligned__} and
10279 @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets
10280 the behavior to the default.
10282 A subtlety for Microsoft Visual C/C++ style bit-field packing
10283 (e.g.@: -mms-bitfields) for targets that support it:
10284 When a bit-field is inserted into a packed record, the whole size
10285 of the underlying type is used by one or more same-size adjacent
10286 bit-fields (that is, if its long:3, 32 bits is used in the record,
10287 and any additional adjacent long bit-fields are packed into the same
10288 chunk of 32 bits. However, if the size changes, a new field of that
10289 size is allocated).
10291 If both MS bit-fields and @samp{__attribute__((packed))} are used,
10292 the latter will take precedence. If @samp{__attribute__((packed))} is
10293 used on a single field when MS bit-fields are in use, it will take
10294 precedence for that field, but the alignment of the rest of the structure
10295 may affect its placement.
10297 The weak pragma only works if @code{SUPPORTS_WEAK} and
10298 @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation
10299 of specifically named weak labels, optionally with a value.
10304 @defmac HANDLE_PRAGMA_PACK_PUSH_POP
10305 Define this macro (to a value of 1) if you want to support the Win32
10306 style pragmas @samp{#pragma pack(push[,@var{n}])} and @samp{#pragma
10307 pack(pop)}. The @samp{pack(push,[@var{n}])} pragma specifies the maximum
10308 alignment (in bytes) of fields within a structure, in much the same way as
10309 the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A
10310 pack value of zero resets the behavior to the default. Successive
10311 invocations of this pragma cause the previous values to be stacked, so
10312 that invocations of @samp{#pragma pack(pop)} will return to the previous
10316 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
10317 Define this macro, as well as
10318 @code{HANDLE_SYSV_PRAGMA}, if macros should be expanded in the
10319 arguments of @samp{#pragma pack}.
10322 @defmac TARGET_DEFAULT_PACK_STRUCT
10323 If your target requires a structure packing default other than 0 (meaning
10324 the machine default), define this macro to the necessary value (in bytes).
10325 This must be a value that would also be valid to use with
10326 @samp{#pragma pack()} (that is, a small power of two).
10331 @defmac HANDLE_PRAGMA_PUSH_POP_MACRO
10332 Define this macro if you want to support the Win32 style pragmas
10333 @samp{#pragma push_macro(macro-name-as-string)} and @samp{#pragma
10334 pop_macro(macro-name-as-string)}. The @samp{#pragma push_macro(
10335 macro-name-as-string)} pragma saves the named macro and via
10336 @samp{#pragma pop_macro(macro-name-as-string)} it will return to the
10341 @defmac DOLLARS_IN_IDENTIFIERS
10342 Define this macro to control use of the character @samp{$} in
10343 identifier names for the C family of languages. 0 means @samp{$} is
10344 not allowed by default; 1 means it is allowed. 1 is the default;
10345 there is no need to define this macro in that case.
10348 @defmac NO_DOLLAR_IN_LABEL
10349 Define this macro if the assembler does not accept the character
10350 @samp{$} in label names. By default constructors and destructors in
10351 G++ have @samp{$} in the identifiers. If this macro is defined,
10352 @samp{.} is used instead.
10355 @defmac NO_DOT_IN_LABEL
10356 Define this macro if the assembler does not accept the character
10357 @samp{.} in label names. By default constructors and destructors in G++
10358 have names that use @samp{.}. If this macro is defined, these names
10359 are rewritten to avoid @samp{.}.
10362 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
10363 Define this macro as a C expression that is nonzero if it is safe for the
10364 delay slot scheduler to place instructions in the delay slot of @var{insn},
10365 even if they appear to use a resource set or clobbered in @var{insn}.
10366 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
10367 every @code{call_insn} has this behavior. On machines where some @code{insn}
10368 or @code{jump_insn} is really a function call and hence has this behavior,
10369 you should define this macro.
10371 You need not define this macro if it would always return zero.
10374 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
10375 Define this macro as a C expression that is nonzero if it is safe for the
10376 delay slot scheduler to place instructions in the delay slot of @var{insn},
10377 even if they appear to set or clobber a resource referenced in @var{insn}.
10378 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
10379 some @code{insn} or @code{jump_insn} is really a function call and its operands
10380 are registers whose use is actually in the subroutine it calls, you should
10381 define this macro. Doing so allows the delay slot scheduler to move
10382 instructions which copy arguments into the argument registers into the delay
10383 slot of @var{insn}.
10385 You need not define this macro if it would always return zero.
10388 @defmac MULTIPLE_SYMBOL_SPACES
10389 Define this macro as a C expression that is nonzero if, in some cases,
10390 global symbols from one translation unit may not be bound to undefined
10391 symbols in another translation unit without user intervention. For
10392 instance, under Microsoft Windows symbols must be explicitly imported
10393 from shared libraries (DLLs).
10395 You need not define this macro if it would always evaluate to zero.
10398 @deftypefn {Target Hook} tree TARGET_MD_ASM_CLOBBERS (tree @var{outputs}, tree @var{inputs}, tree @var{clobbers})
10399 This target hook should add to @var{clobbers} @code{STRING_CST} trees for
10400 any hard regs the port wishes to automatically clobber for an asm.
10401 It should return the result of the last @code{tree_cons} used to add a
10402 clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the
10403 corresponding parameters to the asm and may be inspected to avoid
10404 clobbering a register that is an input or output of the asm. You can use
10405 @code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test
10406 for overlap with regards to asm-declared registers.
10409 @defmac MATH_LIBRARY
10410 Define this macro as a C string constant for the linker argument to link
10411 in the system math library, or @samp{""} if the target does not have a
10412 separate math library.
10414 You need only define this macro if the default of @samp{"-lm"} is wrong.
10417 @defmac LIBRARY_PATH_ENV
10418 Define this macro as a C string constant for the environment variable that
10419 specifies where the linker should look for libraries.
10421 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
10425 @defmac TARGET_POSIX_IO
10426 Define this macro if the target supports the following POSIX@ file
10427 functions, access, mkdir and file locking with fcntl / F_SETLKW@.
10428 Defining @code{TARGET_POSIX_IO} will enable the test coverage code
10429 to use file locking when exiting a program, which avoids race conditions
10430 if the program has forked. It will also create directories at run-time
10431 for cross-profiling.
10434 @defmac MAX_CONDITIONAL_EXECUTE
10436 A C expression for the maximum number of instructions to execute via
10437 conditional execution instructions instead of a branch. A value of
10438 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
10439 1 if it does use cc0.
10442 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
10443 Used if the target needs to perform machine-dependent modifications on the
10444 conditionals used for turning basic blocks into conditionally executed code.
10445 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
10446 contains information about the currently processed blocks. @var{true_expr}
10447 and @var{false_expr} are the tests that are used for converting the
10448 then-block and the else-block, respectively. Set either @var{true_expr} or
10449 @var{false_expr} to a null pointer if the tests cannot be converted.
10452 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
10453 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
10454 if-statements into conditions combined by @code{and} and @code{or} operations.
10455 @var{bb} contains the basic block that contains the test that is currently
10456 being processed and about to be turned into a condition.
10459 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
10460 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
10461 be converted to conditional execution format. @var{ce_info} points to
10462 a data structure, @code{struct ce_if_block}, which contains information
10463 about the currently processed blocks.
10466 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
10467 A C expression to perform any final machine dependent modifications in
10468 converting code to conditional execution. The involved basic blocks
10469 can be found in the @code{struct ce_if_block} structure that is pointed
10470 to by @var{ce_info}.
10473 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
10474 A C expression to cancel any machine dependent modifications in
10475 converting code to conditional execution. The involved basic blocks
10476 can be found in the @code{struct ce_if_block} structure that is pointed
10477 to by @var{ce_info}.
10480 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
10481 A C expression to initialize any extra fields in a @code{struct ce_if_block}
10482 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
10485 @defmac IFCVT_EXTRA_FIELDS
10486 If defined, it should expand to a set of field declarations that will be
10487 added to the @code{struct ce_if_block} structure. These should be initialized
10488 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
10491 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG ()
10492 If non-null, this hook performs a target-specific pass over the
10493 instruction stream. The compiler will run it at all optimization levels,
10494 just before the point at which it normally does delayed-branch scheduling.
10496 The exact purpose of the hook varies from target to target. Some use
10497 it to do transformations that are necessary for correctness, such as
10498 laying out in-function constant pools or avoiding hardware hazards.
10499 Others use it as an opportunity to do some machine-dependent optimizations.
10501 You need not implement the hook if it has nothing to do. The default
10502 definition is null.
10505 @deftypefn {Target Hook} void TARGET_INIT_BUILTINS ()
10506 Define this hook if you have any machine-specific built-in functions
10507 that need to be defined. It should be a function that performs the
10510 Machine specific built-in functions can be useful to expand special machine
10511 instructions that would otherwise not normally be generated because
10512 they have no equivalent in the source language (for example, SIMD vector
10513 instructions or prefetch instructions).
10515 To create a built-in function, call the function
10516 @code{lang_hooks.builtin_function}
10517 which is defined by the language front end. You can use any type nodes set
10518 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
10519 only language front ends that use those two functions will call
10520 @samp{TARGET_INIT_BUILTINS}.
10523 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore})
10525 Expand a call to a machine specific built-in function that was set up by
10526 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
10527 function call; the result should go to @var{target} if that is
10528 convenient, and have mode @var{mode} if that is convenient.
10529 @var{subtarget} may be used as the target for computing one of
10530 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
10531 ignored. This function should return the result of the call to the
10535 @deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (tree @var{fndecl}, tree @var{arglist})
10537 Select a replacement for a machine specific built-in function that
10538 was set up by @samp{TARGET_INIT_BUILTINS}. This is done
10539 @emph{before} regular type checking, and so allows the target to
10540 implement a crude form of function overloading. @var{fndecl} is the
10541 declaration of the built-in function. @var{arglist} is the list of
10542 arguments passed to the built-in function. The result is a
10543 complete expression that implements the operation, usually
10544 another @code{CALL_EXPR}.
10547 @deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, tree @var{arglist}, bool @var{ignore})
10549 Fold a call to a machine specific built-in function that was set up by
10550 @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the
10551 built-in function. @var{arglist} is the list of arguments passed to
10552 the built-in function. The result is another tree containing a
10553 simplified expression for the call's result. If @var{ignore} is true
10554 the value will be ignored.
10557 @deftypefn {Target Hook} const char * TARGET_INVALID_WITHIN_DOLOOP (rtx @var{insn})
10559 Take an instruction in @var{insn} and return NULL if it is valid within a
10560 low-overhead loop, otherwise return a string why doloop could not be applied.
10562 Many targets use special registers for low-overhead looping. For any
10563 instruction that clobbers these this function should return a string indicating
10564 the reason why the doloop could not be applied.
10565 By default, the RTL loop optimizer does not use a present doloop pattern for
10566 loops containing function calls or branch on table instructions.
10569 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
10571 Take a branch insn in @var{branch1} and another in @var{branch2}.
10572 Return true if redirecting @var{branch1} to the destination of
10573 @var{branch2} is possible.
10575 On some targets, branches may have a limited range. Optimizing the
10576 filling of delay slots can result in branches being redirected, and this
10577 may in turn cause a branch offset to overflow.
10580 @deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (rtx @var{x}, @var{outer_code})
10581 This target hook returns @code{true} if @var{x} is considered to be commutative.
10582 Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider
10583 PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code
10584 of the enclosing rtl, if known, otherwise it is UNKNOWN.
10587 @deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg})
10589 When the initial value of a hard register has been copied in a pseudo
10590 register, it is often not necessary to actually allocate another register
10591 to this pseudo register, because the original hard register or a stack slot
10592 it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE}
10593 is called at the start of register allocation once for each hard register
10594 that had its initial value copied by using
10595 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
10596 Possible values are @code{NULL_RTX}, if you don't want
10597 to do any special allocation, a @code{REG} rtx---that would typically be
10598 the hard register itself, if it is known not to be clobbered---or a
10600 If you are returning a @code{MEM}, this is only a hint for the allocator;
10601 it might decide to use another register anyways.
10602 You may use @code{current_function_leaf_function} in the hook, functions
10603 that use @code{REG_N_SETS}, to determine if the hard
10604 register in question will not be clobbered.
10605 The default value of this hook is @code{NULL}, which disables any special
10609 @deftypefn {Target Hook} int TARGET_UNSPEC_MAY_TRAP_P (const_rtx @var{x}, unsigned @var{flags})
10610 This target hook returns nonzero if @var{x}, an @code{unspec} or
10611 @code{unspec_volatile} operation, might cause a trap. Targets can use
10612 this hook to enhance precision of analysis for @code{unspec} and
10613 @code{unspec_volatile} operations. You may call @code{may_trap_p_1}
10614 to analyze inner elements of @var{x} in which case @var{flags} should be
10618 @deftypefn {Target Hook} void TARGET_SET_CURRENT_FUNCTION (tree @var{decl})
10619 The compiler invokes this hook whenever it changes its current function
10620 context (@code{cfun}). You can define this function if
10621 the back end needs to perform any initialization or reset actions on a
10622 per-function basis. For example, it may be used to implement function
10623 attributes that affect register usage or code generation patterns.
10624 The argument @var{decl} is the declaration for the new function context,
10625 and may be null to indicate that the compiler has left a function context
10626 and is returning to processing at the top level.
10627 The default hook function does nothing.
10629 GCC sets @code{cfun} to a dummy function context during initialization of
10630 some parts of the back end. The hook function is not invoked in this
10631 situation; you need not worry about the hook being invoked recursively,
10632 or when the back end is in a partially-initialized state.
10635 @defmac TARGET_OBJECT_SUFFIX
10636 Define this macro to be a C string representing the suffix for object
10637 files on your target machine. If you do not define this macro, GCC will
10638 use @samp{.o} as the suffix for object files.
10641 @defmac TARGET_EXECUTABLE_SUFFIX
10642 Define this macro to be a C string representing the suffix to be
10643 automatically added to executable files on your target machine. If you
10644 do not define this macro, GCC will use the null string as the suffix for
10648 @defmac COLLECT_EXPORT_LIST
10649 If defined, @code{collect2} will scan the individual object files
10650 specified on its command line and create an export list for the linker.
10651 Define this macro for systems like AIX, where the linker discards
10652 object files that are not referenced from @code{main} and uses export
10656 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
10657 Define this macro to a C expression representing a variant of the
10658 method call @var{mdecl}, if Java Native Interface (JNI) methods
10659 must be invoked differently from other methods on your target.
10660 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
10661 the @code{stdcall} calling convention and this macro is then
10662 defined as this expression:
10665 build_type_attribute_variant (@var{mdecl},
10667 (get_identifier ("stdcall"),
10672 @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
10673 This target hook returns @code{true} past the point in which new jump
10674 instructions could be created. On machines that require a register for
10675 every jump such as the SHmedia ISA of SH5, this point would typically be
10676 reload, so this target hook should be defined to a function such as:
10680 cannot_modify_jumps_past_reload_p ()
10682 return (reload_completed || reload_in_progress);
10687 @deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void)
10688 This target hook returns a register class for which branch target register
10689 optimizations should be applied. All registers in this class should be
10690 usable interchangeably. After reload, registers in this class will be
10691 re-allocated and loads will be hoisted out of loops and be subjected
10692 to inter-block scheduling.
10695 @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen})
10696 Branch target register optimization will by default exclude callee-saved
10698 that are not already live during the current function; if this target hook
10699 returns true, they will be included. The target code must than make sure
10700 that all target registers in the class returned by
10701 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
10702 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
10703 epilogues have already been generated. Note, even if you only return
10704 true when @var{after_prologue_epilogue_gen} is false, you still are likely
10705 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
10706 to reserve space for caller-saved target registers.
10709 @defmac POWI_MAX_MULTS
10710 If defined, this macro is interpreted as a signed integer C expression
10711 that specifies the maximum number of floating point multiplications
10712 that should be emitted when expanding exponentiation by an integer
10713 constant inline. When this value is defined, exponentiation requiring
10714 more than this number of multiplications is implemented by calling the
10715 system library's @code{pow}, @code{powf} or @code{powl} routines.
10716 The default value places no upper bound on the multiplication count.
10719 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
10720 This target hook should register any extra include files for the
10721 target. The parameter @var{stdinc} indicates if normal include files
10722 are present. The parameter @var{sysroot} is the system root directory.
10723 The parameter @var{iprefix} is the prefix for the gcc directory.
10726 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
10727 This target hook should register any extra include files for the
10728 target before any standard headers. The parameter @var{stdinc}
10729 indicates if normal include files are present. The parameter
10730 @var{sysroot} is the system root directory. The parameter
10731 @var{iprefix} is the prefix for the gcc directory.
10734 @deftypefn Macro void TARGET_OPTF (char *@var{path})
10735 This target hook should register special include paths for the target.
10736 The parameter @var{path} is the include to register. On Darwin
10737 systems, this is used for Framework includes, which have semantics
10738 that are different from @option{-I}.
10741 @deftypefn {Target Hook} bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
10742 This target hook returns @code{true} if it is safe to use a local alias
10743 for a virtual function @var{fndecl} when constructing thunks,
10744 @code{false} otherwise. By default, the hook returns @code{true} for all
10745 functions, if a target supports aliases (i.e.@: defines
10746 @code{ASM_OUTPUT_DEF}), @code{false} otherwise,
10749 @defmac TARGET_FORMAT_TYPES
10750 If defined, this macro is the name of a global variable containing
10751 target-specific format checking information for the @option{-Wformat}
10752 option. The default is to have no target-specific format checks.
10755 @defmac TARGET_N_FORMAT_TYPES
10756 If defined, this macro is the number of entries in
10757 @code{TARGET_FORMAT_TYPES}.
10760 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
10761 If defined, this macro is the name of a global variable containing
10762 target-specific format overrides for the @option{-Wformat} option. The
10763 default is to have no target-specific format overrides. If defined,
10764 @code{TARGET_FORMAT_TYPES} must be defined, too.
10767 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
10768 If defined, this macro specifies the number of entries in
10769 @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
10772 @defmac TARGET_OVERRIDES_FORMAT_INIT
10773 If defined, this macro specifies the optional initialization
10774 routine for target specific customizations of the system printf
10775 and scanf formatter settings.
10778 @deftypefn {Target Hook} bool TARGET_RELAXED_ORDERING
10779 If set to @code{true}, means that the target's memory model does not
10780 guarantee that loads which do not depend on one another will access
10781 main memory in the order of the instruction stream; if ordering is
10782 important, an explicit memory barrier must be used. This is true of
10783 many recent processors which implement a policy of ``relaxed,''
10784 ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC,
10785 and ia64. The default is @code{false}.
10788 @deftypefn {Target Hook} const char *TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (tree @var{typelist}, tree @var{funcdecl}, tree @var{val})
10789 If defined, this macro returns the diagnostic message when it is
10790 illegal to pass argument @var{val} to function @var{funcdecl}
10791 with prototype @var{typelist}.
10794 @deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (tree @var{fromtype}, tree @var{totype})
10795 If defined, this macro returns the diagnostic message when it is
10796 invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL}
10797 if validity should be determined by the front end.
10800 @deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, tree @var{type})
10801 If defined, this macro returns the diagnostic message when it is
10802 invalid to apply operation @var{op} (where unary plus is denoted by
10803 @code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL}
10804 if validity should be determined by the front end.
10807 @deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, tree @var{type1}, tree @var{type2})
10808 If defined, this macro returns the diagnostic message when it is
10809 invalid to apply operation @var{op} to operands of types @var{type1}
10810 and @var{type2}, or @code{NULL} if validity should be determined by
10814 @deftypefn {Target Hook} {const char *} TARGET_INVALID_PARAMETER_TYPE (tree @var{type})
10815 If defined, this macro returns the diagnostic message when it is
10816 invalid for functions to include parameters of type @var{type},
10817 or @code{NULL} if validity should be determined by
10818 the front end. This is currently used only by the C and C++ front ends.
10821 @deftypefn {Target Hook} {const char *} TARGET_INVALID_RETURN_TYPE (tree @var{type})
10822 If defined, this macro returns the diagnostic message when it is
10823 invalid for functions to have return type @var{type},
10824 or @code{NULL} if validity should be determined by
10825 the front end. This is currently used only by the C and C++ front ends.
10828 @deftypefn {Target Hook} {tree} TARGET_PROMOTED_TYPE (tree @var{type})
10829 If defined, this target hook returns the type to which values of
10830 @var{type} should be promoted when they appear in expressions,
10831 analogous to the integer promotions, or @code{NULL_TREE} to use the
10832 front end's normal promotion rules. This hook is useful when there are
10833 target-specific types with special promotion rules.
10834 This is currently used only by the C and C++ front ends.
10837 @deftypefn {Target Hook} {tree} TARGET_CONVERT_TO_TYPE (tree @var{type}, tree @var{expr})
10838 If defined, this hook returns the result of converting @var{expr} to
10839 @var{type}. It should return the converted expression,
10840 or @code{NULL_TREE} to apply the front end's normal conversion rules.
10841 This hook is useful when there are target-specific types with special
10843 This is currently used only by the C and C++ front ends.
10846 @defmac TARGET_USE_JCR_SECTION
10847 This macro determines whether to use the JCR section to register Java
10848 classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both
10849 SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0.
10853 This macro determines the size of the objective C jump buffer for the
10854 NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
10857 @defmac LIBGCC2_UNWIND_ATTRIBUTE
10858 Define this macro if any target-specific attributes need to be attached
10859 to the functions in @file{libgcc} that provide low-level support for
10860 call stack unwinding. It is used in declarations in @file{unwind-generic.h}
10861 and the associated definitions of those functions.
10864 @deftypefn {Target Hook} void TARGET_UPDATE_STACK_BOUNDARY (void)
10865 Define this macro to update the current function stack boundary if
10869 @deftypefn {Target Hook} rtx TARGET_GET_DRAP_RTX (void)
10870 Define this macro to an rtx for Dynamic Realign Argument Pointer if a
10871 different argument pointer register is needed to access the function's
10872 argument list when stack is aligned.
10875 @deftypefn {Target Hook} {bool} TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS (void)
10876 When optimization is disabled, this hook indicates whether or not
10877 arguments should be allocated to stack slots. Normally, GCC allocates
10878 stacks slots for arguments when not optimizing in order to make
10879 debugging easier. However, when a function is declared with
10880 @code{__attribute__((naked))}, there is no stack frame, and the compiler
10881 cannot safely move arguments from the registers in which they are passed
10882 to the stack. Therefore, this hook should return true in general, but
10883 false for naked functions. The default implementation always returns true.
10887 @deftypevr {Target Hook} {unsigned HOST_WIDE_INT} TARGET_CONST_ANCHOR
10888 On some architectures it can take multiple instructions to synthesize
10889 a constant. If there is another constant already in a register that
10890 is close enough in value then it is preferable that the new constant
10891 is computed from this register using immediate addition or
10892 substraction. We accomplish this through CSE. Besides the value of
10893 the constant we also add a lower and an upper constant anchor to the
10894 available expressions. These are then queried when encountering new
10895 constants. The anchors are computed by rounding the constant up and
10896 down to a multiple of the value of @code{TARGET_CONST_ANCHOR}.
10897 @code{TARGET_CONST_ANCHOR} should be the maximum positive value
10898 accepted by immediate-add plus one. We currently assume that the
10899 value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on
10900 MIPS, where add-immediate takes a 16-bit signed value,
10901 @code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value
10902 is zero, which disables this optimization. @end deftypevr