1 @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,
2 @c 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
7 @chapter Target Description Macros and Functions
8 @cindex machine description macros
9 @cindex target description macros
10 @cindex macros, target description
11 @cindex @file{tm.h} macros
13 In addition to the file @file{@var{machine}.md}, a machine description
14 includes a C header file conventionally given the name
15 @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
16 The header file defines numerous macros that convey the information
17 about the target machine that does not fit into the scheme of the
18 @file{.md} file. The file @file{tm.h} should be a link to
19 @file{@var{machine}.h}. The header file @file{config.h} includes
20 @file{tm.h} and most compiler source files include @file{config.h}. The
21 source file defines a variable @code{targetm}, which is a structure
22 containing pointers to functions and data relating to the target
23 machine. @file{@var{machine}.c} should also contain their definitions,
24 if they are not defined elsewhere in GCC, and other functions called
25 through the macros defined in the @file{.h} file.
28 * Target Structure:: The @code{targetm} variable.
29 * Driver:: Controlling how the driver runs the compilation passes.
30 * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
31 * Per-Function Data:: Defining data structures for per-function information.
32 * Storage Layout:: Defining sizes and alignments of data.
33 * Type Layout:: Defining sizes and properties of basic user data types.
34 * Registers:: Naming and describing the hardware registers.
35 * Register Classes:: Defining the classes of hardware registers.
36 * Stack and Calling:: Defining which way the stack grows and by how much.
37 * Varargs:: Defining the varargs macros.
38 * Trampolines:: Code set up at run time to enter a nested function.
39 * Library Calls:: Controlling how library routines are implicitly called.
40 * Addressing Modes:: Defining addressing modes valid for memory operands.
41 * Condition Code:: Defining how insns update the condition code.
42 * Costs:: Defining relative costs of different operations.
43 * Scheduling:: Adjusting the behavior of the instruction scheduler.
44 * Sections:: Dividing storage into text, data, and other sections.
45 * PIC:: Macros for position independent code.
46 * Assembler Format:: Defining how to write insns and pseudo-ops to output.
47 * Debugging Info:: Defining the format of debugging output.
48 * Floating Point:: Handling floating point for cross-compilers.
49 * Mode Switching:: Insertion of mode-switching instructions.
50 * Target Attributes:: Defining target-specific uses of @code{__attribute__}.
51 * MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
52 * PCH Target:: Validity checking for precompiled headers.
53 * C++ ABI:: Controlling C++ ABI changes.
54 * Misc:: Everything else.
57 @node Target Structure
58 @section The Global @code{targetm} Variable
60 @cindex target functions
62 @deftypevar {struct gcc_target} targetm
63 The target @file{.c} file must define the global @code{targetm} variable
64 which contains pointers to functions and data relating to the target
65 machine. The variable is declared in @file{target.h};
66 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
67 used to initialize the variable, and macros for the default initializers
68 for elements of the structure. The @file{.c} file should override those
69 macros for which the default definition is inappropriate. For example:
72 #include "target-def.h"
74 /* @r{Initialize the GCC target structure.} */
76 #undef TARGET_COMP_TYPE_ATTRIBUTES
77 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
79 struct gcc_target targetm = TARGET_INITIALIZER;
83 Where a macro should be defined in the @file{.c} file in this manner to
84 form part of the @code{targetm} structure, it is documented below as a
85 ``Target Hook'' with a prototype. Many macros will change in future
86 from being defined in the @file{.h} file to being part of the
87 @code{targetm} structure.
90 @section Controlling the Compilation Driver, @file{gcc}
92 @cindex controlling the compilation driver
94 @c prevent bad page break with this line
95 You can control the compilation driver.
97 @defmac SWITCH_TAKES_ARG (@var{char})
98 A C expression which determines whether the option @option{-@var{char}}
99 takes arguments. The value should be the number of arguments that
100 option takes--zero, for many options.
102 By default, this macro is defined as
103 @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options
104 properly. You need not define @code{SWITCH_TAKES_ARG} unless you
105 wish to add additional options which take arguments. Any redefinition
106 should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for
110 @defmac WORD_SWITCH_TAKES_ARG (@var{name})
111 A C expression which determines whether the option @option{-@var{name}}
112 takes arguments. The value should be the number of arguments that
113 option takes--zero, for many options. This macro rather than
114 @code{SWITCH_TAKES_ARG} is used for multi-character option names.
116 By default, this macro is defined as
117 @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options
118 properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you
119 wish to add additional options which take arguments. Any redefinition
120 should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for
124 @defmac SWITCH_CURTAILS_COMPILATION (@var{char})
125 A C expression which determines whether the option @option{-@var{char}}
126 stops compilation before the generation of an executable. The value is
127 boolean, nonzero if the option does stop an executable from being
128 generated, zero otherwise.
130 By default, this macro is defined as
131 @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard
132 options properly. You need not define
133 @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional
134 options which affect the generation of an executable. Any redefinition
135 should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check
136 for additional options.
139 @defmac SWITCHES_NEED_SPACES
140 A string-valued C expression which enumerates the options for which
141 the linker needs a space between the option and its argument.
143 If this macro is not defined, the default value is @code{""}.
146 @defmac TARGET_OPTION_TRANSLATE_TABLE
147 If defined, a list of pairs of strings, the first of which is a
148 potential command line target to the @file{gcc} driver program, and the
149 second of which is a space-separated (tabs and other whitespace are not
150 supported) list of options with which to replace the first option. The
151 target defining this list is responsible for assuring that the results
152 are valid. Replacement options may not be the @code{--opt} style, they
153 must be the @code{-opt} style. It is the intention of this macro to
154 provide a mechanism for substitution that affects the multilibs chosen,
155 such as one option that enables many options, some of which select
156 multilibs. Example nonsensical definition, where @option{-malt-abi},
157 @option{-EB}, and @option{-mspoo} cause different multilibs to be chosen:
160 #define TARGET_OPTION_TRANSLATE_TABLE \
161 @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \
162 @{ "-compat", "-EB -malign=4 -mspoo" @}
166 @defmac DRIVER_SELF_SPECS
167 A list of specs for the driver itself. It should be a suitable
168 initializer for an array of strings, with no surrounding braces.
170 The driver applies these specs to its own command line between loading
171 default @file{specs} files (but not command-line specified ones) and
172 choosing the multilib directory or running any subcommands. It
173 applies them in the order given, so each spec can depend on the
174 options added by earlier ones. It is also possible to remove options
175 using @samp{%<@var{option}} in the usual way.
177 This macro can be useful when a port has several interdependent target
178 options. It provides a way of standardizing the command line so
179 that the other specs are easier to write.
181 Do not define this macro if it does not need to do anything.
184 @defmac OPTION_DEFAULT_SPECS
185 A list of specs used to support configure-time default options (i.e.@:
186 @option{--with} options) in the driver. It should be a suitable initializer
187 for an array of structures, each containing two strings, without the
188 outermost pair of surrounding braces.
190 The first item in the pair is the name of the default. This must match
191 the code in @file{config.gcc} for the target. The second item is a spec
192 to apply if a default with this name was specified. The string
193 @samp{%(VALUE)} in the spec will be replaced by the value of the default
194 everywhere it occurs.
196 The driver will apply these specs to its own command line between loading
197 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
198 the same mechanism as @code{DRIVER_SELF_SPECS}.
200 Do not define this macro if it does not need to do anything.
204 A C string constant that tells the GCC driver program options to
205 pass to CPP@. It can also specify how to translate options you
206 give to GCC into options for GCC to pass to the CPP@.
208 Do not define this macro if it does not need to do anything.
211 @defmac CPLUSPLUS_CPP_SPEC
212 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
213 than C@. If you do not define this macro, then the value of
214 @code{CPP_SPEC} (if any) will be used instead.
218 A C string constant that tells the GCC driver program options to
219 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
221 It can also specify how to translate options you give to GCC into options
222 for GCC to pass to front ends.
224 Do not define this macro if it does not need to do anything.
228 A C string constant that tells the GCC driver program options to
229 pass to @code{cc1plus}. It can also specify how to translate options you
230 give to GCC into options for GCC to pass to the @code{cc1plus}.
232 Do not define this macro if it does not need to do anything.
233 Note that everything defined in CC1_SPEC is already passed to
234 @code{cc1plus} so there is no need to duplicate the contents of
235 CC1_SPEC in CC1PLUS_SPEC@.
239 A C string constant that tells the GCC driver program options to
240 pass to the assembler. It can also specify how to translate options
241 you give to GCC into options for GCC to pass to the assembler.
242 See the file @file{sun3.h} for an example of this.
244 Do not define this macro if it does not need to do anything.
247 @defmac ASM_FINAL_SPEC
248 A C string constant that tells the GCC driver program how to
249 run any programs which cleanup after the normal assembler.
250 Normally, this is not needed. See the file @file{mips.h} for
253 Do not define this macro if it does not need to do anything.
256 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
257 Define this macro, with no value, if the driver should give the assembler
258 an argument consisting of a single dash, @option{-}, to instruct it to
259 read from its standard input (which will be a pipe connected to the
260 output of the compiler proper). This argument is given after any
261 @option{-o} option specifying the name of the output file.
263 If you do not define this macro, the assembler is assumed to read its
264 standard input if given no non-option arguments. If your assembler
265 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
266 see @file{mips.h} for instance.
270 A C string constant that tells the GCC driver program options to
271 pass to the linker. It can also specify how to translate options you
272 give to GCC into options for GCC to pass to the linker.
274 Do not define this macro if it does not need to do anything.
278 Another C string constant used much like @code{LINK_SPEC}. The difference
279 between the two is that @code{LIB_SPEC} is used at the end of the
280 command given to the linker.
282 If this macro is not defined, a default is provided that
283 loads the standard C library from the usual place. See @file{gcc.c}.
287 Another C string constant that tells the GCC driver program
288 how and when to place a reference to @file{libgcc.a} into the
289 linker command line. This constant is placed both before and after
290 the value of @code{LIB_SPEC}.
292 If this macro is not defined, the GCC driver provides a default that
293 passes the string @option{-lgcc} to the linker.
296 @defmac REAL_LIBGCC_SPEC
297 By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
298 @code{LIBGCC_SPEC} is not directly used by the driver program but is
299 instead modified to refer to different versions of @file{libgcc.a}
300 depending on the values of the command line flags @option{-static},
301 @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
302 targets where these modifications are inappropriate, define
303 @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
304 driver how to place a reference to @file{libgcc} on the link command
305 line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
308 @defmac USE_LD_AS_NEEDED
309 A macro that controls the modifications to @code{LIBGCC_SPEC}
310 mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
311 generated that uses --as-needed and the shared libgcc in place of the
312 static exception handler library, when linking without any of
313 @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
317 If defined, this C string constant is added to @code{LINK_SPEC}.
318 When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
319 the modifications to @code{LIBGCC_SPEC} mentioned in
320 @code{REAL_LIBGCC_SPEC}.
323 @defmac STARTFILE_SPEC
324 Another C string constant used much like @code{LINK_SPEC}. The
325 difference between the two is that @code{STARTFILE_SPEC} is used at
326 the very beginning of the command given to the linker.
328 If this macro is not defined, a default is provided that loads the
329 standard C startup file from the usual place. See @file{gcc.c}.
333 Another C string constant used much like @code{LINK_SPEC}. The
334 difference between the two is that @code{ENDFILE_SPEC} is used at
335 the very end of the command given to the linker.
337 Do not define this macro if it does not need to do anything.
340 @defmac THREAD_MODEL_SPEC
341 GCC @code{-v} will print the thread model GCC was configured to use.
342 However, this doesn't work on platforms that are multilibbed on thread
343 models, such as AIX 4.3. On such platforms, define
344 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
345 blanks that names one of the recognized thread models. @code{%*}, the
346 default value of this macro, will expand to the value of
347 @code{thread_file} set in @file{config.gcc}.
350 @defmac SYSROOT_SUFFIX_SPEC
351 Define this macro to add a suffix to the target sysroot when GCC is
352 configured with a sysroot. This will cause GCC to search for usr/lib,
353 et al, within sysroot+suffix.
356 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
357 Define this macro to add a headers_suffix to the target sysroot when
358 GCC is configured with a sysroot. This will cause GCC to pass the
359 updated sysroot+headers_suffix to CPP, causing it to search for
360 usr/include, et al, within sysroot+headers_suffix.
364 Define this macro to provide additional specifications to put in the
365 @file{specs} file that can be used in various specifications like
368 The definition should be an initializer for an array of structures,
369 containing a string constant, that defines the specification name, and a
370 string constant that provides the specification.
372 Do not define this macro if it does not need to do anything.
374 @code{EXTRA_SPECS} is useful when an architecture contains several
375 related targets, which have various @code{@dots{}_SPECS} which are similar
376 to each other, and the maintainer would like one central place to keep
379 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
380 define either @code{_CALL_SYSV} when the System V calling sequence is
381 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
384 The @file{config/rs6000/rs6000.h} target file defines:
387 #define EXTRA_SPECS \
388 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
390 #define CPP_SYS_DEFAULT ""
393 The @file{config/rs6000/sysv.h} target file defines:
397 "%@{posix: -D_POSIX_SOURCE @} \
398 %@{mcall-sysv: -D_CALL_SYSV @} \
399 %@{!mcall-sysv: %(cpp_sysv_default) @} \
400 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
402 #undef CPP_SYSV_DEFAULT
403 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
406 while the @file{config/rs6000/eabiaix.h} target file defines
407 @code{CPP_SYSV_DEFAULT} as:
410 #undef CPP_SYSV_DEFAULT
411 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
415 @defmac LINK_LIBGCC_SPECIAL_1
416 Define this macro if the driver program should find the library
417 @file{libgcc.a}. If you do not define this macro, the driver program will pass
418 the argument @option{-lgcc} to tell the linker to do the search.
421 @defmac LINK_GCC_C_SEQUENCE_SPEC
422 The sequence in which libgcc and libc are specified to the linker.
423 By default this is @code{%G %L %G}.
426 @defmac LINK_COMMAND_SPEC
427 A C string constant giving the complete command line need to execute the
428 linker. When you do this, you will need to update your port each time a
429 change is made to the link command line within @file{gcc.c}. Therefore,
430 define this macro only if you need to completely redefine the command
431 line for invoking the linker and there is no other way to accomplish
432 the effect you need. Overriding this macro may be avoidable by overriding
433 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
436 @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
437 A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
438 directories from linking commands. Do not give it a nonzero value if
439 removing duplicate search directories changes the linker's semantics.
442 @defmac MULTILIB_DEFAULTS
443 Define this macro as a C expression for the initializer of an array of
444 string to tell the driver program which options are defaults for this
445 target and thus do not need to be handled specially when using
446 @code{MULTILIB_OPTIONS}.
448 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
449 the target makefile fragment or if none of the options listed in
450 @code{MULTILIB_OPTIONS} are set by default.
451 @xref{Target Fragment}.
454 @defmac RELATIVE_PREFIX_NOT_LINKDIR
455 Define this macro to tell @command{gcc} that it should only translate
456 a @option{-B} prefix into a @option{-L} linker option if the prefix
457 indicates an absolute file name.
460 @defmac MD_EXEC_PREFIX
461 If defined, this macro is an additional prefix to try after
462 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
463 when the @option{-b} option is used, or the compiler is built as a cross
464 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
465 to the list of directories used to find the assembler in @file{configure.in}.
468 @defmac STANDARD_STARTFILE_PREFIX
469 Define this macro as a C string constant if you wish to override the
470 standard choice of @code{libdir} as the default prefix to
471 try when searching for startup files such as @file{crt0.o}.
472 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
473 is built as a cross compiler.
476 @defmac STANDARD_STARTFILE_PREFIX_1
477 Define this macro as a C string constant if you wish to override the
478 standard choice of @code{/lib} as a prefix to try after the default prefix
479 when searching for startup files such as @file{crt0.o}.
480 @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
481 is built as a cross compiler.
484 @defmac STANDARD_STARTFILE_PREFIX_2
485 Define this macro as a C string constant if you wish to override the
486 standard choice of @code{/lib} as yet another prefix to try after the
487 default prefix when searching for startup files such as @file{crt0.o}.
488 @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
489 is built as a cross compiler.
492 @defmac MD_STARTFILE_PREFIX
493 If defined, this macro supplies an additional prefix to try after the
494 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
495 @option{-b} option is used, or when the compiler is built as a cross
499 @defmac MD_STARTFILE_PREFIX_1
500 If defined, this macro supplies yet another prefix to try after the
501 standard prefixes. It is not searched when the @option{-b} option is
502 used, or when the compiler is built as a cross compiler.
505 @defmac INIT_ENVIRONMENT
506 Define this macro as a C string constant if you wish to set environment
507 variables for programs called by the driver, such as the assembler and
508 loader. The driver passes the value of this macro to @code{putenv} to
509 initialize the necessary environment variables.
512 @defmac LOCAL_INCLUDE_DIR
513 Define this macro as a C string constant if you wish to override the
514 standard choice of @file{/usr/local/include} as the default prefix to
515 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
516 comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
518 Cross compilers do not search either @file{/usr/local/include} or its
522 @defmac MODIFY_TARGET_NAME
523 Define this macro if you wish to define command-line switches that
524 modify the default target name.
526 For each switch, you can include a string to be appended to the first
527 part of the configuration name or a string to be deleted from the
528 configuration name, if present. The definition should be an initializer
529 for an array of structures. Each array element should have three
530 elements: the switch name (a string constant, including the initial
531 dash), one of the enumeration codes @code{ADD} or @code{DELETE} to
532 indicate whether the string should be inserted or deleted, and the string
533 to be inserted or deleted (a string constant).
535 For example, on a machine where @samp{64} at the end of the
536 configuration name denotes a 64-bit target and you want the @option{-32}
537 and @option{-64} switches to select between 32- and 64-bit targets, you would
541 #define MODIFY_TARGET_NAME \
542 @{ @{ "-32", DELETE, "64"@}, \
543 @{"-64", ADD, "64"@}@}
547 @defmac SYSTEM_INCLUDE_DIR
548 Define this macro as a C string constant if you wish to specify a
549 system-specific directory to search for header files before the standard
550 directory. @code{SYSTEM_INCLUDE_DIR} comes before
551 @code{STANDARD_INCLUDE_DIR} in the search order.
553 Cross compilers do not use this macro and do not search the directory
557 @defmac STANDARD_INCLUDE_DIR
558 Define this macro as a C string constant if you wish to override the
559 standard choice of @file{/usr/include} as the default prefix to
560 try when searching for header files.
562 Cross compilers ignore this macro and do not search either
563 @file{/usr/include} or its replacement.
566 @defmac STANDARD_INCLUDE_COMPONENT
567 The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
568 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
569 If you do not define this macro, no component is used.
572 @defmac INCLUDE_DEFAULTS
573 Define this macro if you wish to override the entire default search path
574 for include files. For a native compiler, the default search path
575 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
576 @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
577 @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
578 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
579 and specify private search areas for GCC@. The directory
580 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
582 The definition should be an initializer for an array of structures.
583 Each array element should have four elements: the directory name (a
584 string constant), the component name (also a string constant), a flag
585 for C++-only directories,
586 and a flag showing that the includes in the directory don't need to be
587 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
588 the array with a null element.
590 The component name denotes what GNU package the include file is part of,
591 if any, in all uppercase letters. For example, it might be @samp{GCC}
592 or @samp{BINUTILS}. If the package is part of a vendor-supplied
593 operating system, code the component name as @samp{0}.
595 For example, here is the definition used for VAX/VMS:
598 #define INCLUDE_DEFAULTS \
600 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
601 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
602 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
609 Here is the order of prefixes tried for exec files:
613 Any prefixes specified by the user with @option{-B}.
616 The environment variable @code{GCC_EXEC_PREFIX}, if any.
619 The directories specified by the environment variable @code{COMPILER_PATH}.
622 The macro @code{STANDARD_EXEC_PREFIX}.
625 @file{/usr/lib/gcc/}.
628 The macro @code{MD_EXEC_PREFIX}, if any.
631 Here is the order of prefixes tried for startfiles:
635 Any prefixes specified by the user with @option{-B}.
638 The environment variable @code{GCC_EXEC_PREFIX}, if any.
641 The directories specified by the environment variable @code{LIBRARY_PATH}
642 (or port-specific name; native only, cross compilers do not use this).
645 The macro @code{STANDARD_EXEC_PREFIX}.
648 @file{/usr/lib/gcc/}.
651 The macro @code{MD_EXEC_PREFIX}, if any.
654 The macro @code{MD_STARTFILE_PREFIX}, if any.
657 The macro @code{STANDARD_STARTFILE_PREFIX}.
666 @node Run-time Target
667 @section Run-time Target Specification
668 @cindex run-time target specification
669 @cindex predefined macros
670 @cindex target specifications
672 @c prevent bad page break with this line
673 Here are run-time target specifications.
675 @defmac TARGET_CPU_CPP_BUILTINS ()
676 This function-like macro expands to a block of code that defines
677 built-in preprocessor macros and assertions for the target cpu, using
678 the functions @code{builtin_define}, @code{builtin_define_std} and
679 @code{builtin_assert}. When the front end
680 calls this macro it provides a trailing semicolon, and since it has
681 finished command line option processing your code can use those
684 @code{builtin_assert} takes a string in the form you pass to the
685 command-line option @option{-A}, such as @code{cpu=mips}, and creates
686 the assertion. @code{builtin_define} takes a string in the form
687 accepted by option @option{-D} and unconditionally defines the macro.
689 @code{builtin_define_std} takes a string representing the name of an
690 object-like macro. If it doesn't lie in the user's namespace,
691 @code{builtin_define_std} defines it unconditionally. Otherwise, it
692 defines a version with two leading underscores, and another version
693 with two leading and trailing underscores, and defines the original
694 only if an ISO standard was not requested on the command line. For
695 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
696 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
697 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
698 defines only @code{_ABI64}.
700 You can also test for the C dialect being compiled. The variable
701 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
702 or @code{clk_objective_c}. Note that if we are preprocessing
703 assembler, this variable will be @code{clk_c} but the function-like
704 macro @code{preprocessing_asm_p()} will return true, so you might want
705 to check for that first. If you need to check for strict ANSI, the
706 variable @code{flag_iso} can be used. The function-like macro
707 @code{preprocessing_trad_p()} can be used to check for traditional
711 @defmac TARGET_OS_CPP_BUILTINS ()
712 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
713 and is used for the target operating system instead.
716 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
717 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
718 and is used for the target object format. @file{elfos.h} uses this
719 macro to define @code{__ELF__}, so you probably do not need to define
723 @deftypevar {extern int} target_flags
724 This variable is declared in @file{options.h}, which is included before
725 any target-specific headers.
728 @deftypevar {Target Hook} int TARGET_DEFAULT_TARGET_FLAGS
729 This variable specifies the initial value of @code{target_flags}.
730 Its default setting is 0.
733 @cindex optional hardware or system features
734 @cindex features, optional, in system conventions
736 @deftypefn {Target Hook} bool TARGET_HANDLE_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value})
737 This hook is called whenever the user specifies one of the
738 target-specific options described by the @file{.opt} definition files
739 (@pxref{Options}). It has the opportunity to do some option-specific
740 processing and should return true if the option is valid. The default
741 definition does nothing but return true.
743 @var{code} specifies the @code{OPT_@var{name}} enumeration value
744 associated with the selected option; @var{name} is just a rendering of
745 the option name in which non-alphanumeric characters are replaced by
746 underscores. @var{arg} specifies the string argument and is null if
747 no argument was given. If the option is flagged as a @code{UInteger}
748 (@pxref{Option properties}), @var{value} is the numeric value of the
749 argument. Otherwise @var{value} is 1 if the positive form of the
750 option was used and 0 if the ``no-'' form was.
753 @defmac TARGET_VERSION
754 This macro is a C statement to print on @code{stderr} a string
755 describing the particular machine description choice. Every machine
756 description should define @code{TARGET_VERSION}. For example:
760 #define TARGET_VERSION \
761 fprintf (stderr, " (68k, Motorola syntax)");
763 #define TARGET_VERSION \
764 fprintf (stderr, " (68k, MIT syntax)");
769 @defmac OVERRIDE_OPTIONS
770 Sometimes certain combinations of command options do not make sense on
771 a particular target machine. You can define a macro
772 @code{OVERRIDE_OPTIONS} to take account of this. This macro, if
773 defined, is executed once just after all the command options have been
776 Don't use this macro to turn on various extra optimizations for
777 @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for.
780 @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size})
781 Some machines may desire to change what optimizations are performed for
782 various optimization levels. This macro, if defined, is executed once
783 just after the optimization level is determined and before the remainder
784 of the command options have been parsed. Values set in this macro are
785 used as the default values for the other command line options.
787 @var{level} is the optimization level specified; 2 if @option{-O2} is
788 specified, 1 if @option{-O} is specified, and 0 if neither is specified.
790 @var{size} is nonzero if @option{-Os} is specified and zero otherwise.
792 You should not use this macro to change options that are not
793 machine-specific. These should uniformly selected by the same
794 optimization level on all supported machines. Use this macro to enable
795 machine-specific optimizations.
797 @strong{Do not examine @code{write_symbols} in
798 this macro!} The debugging options are not supposed to alter the
802 @defmac CAN_DEBUG_WITHOUT_FP
803 Define this macro if debugging can be performed even without a frame
804 pointer. If this macro is defined, GCC will turn on the
805 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
808 @node Per-Function Data
809 @section Defining data structures for per-function information.
810 @cindex per-function data
811 @cindex data structures
813 If the target needs to store information on a per-function basis, GCC
814 provides a macro and a couple of variables to allow this. Note, just
815 using statics to store the information is a bad idea, since GCC supports
816 nested functions, so you can be halfway through encoding one function
817 when another one comes along.
819 GCC defines a data structure called @code{struct function} which
820 contains all of the data specific to an individual function. This
821 structure contains a field called @code{machine} whose type is
822 @code{struct machine_function *}, which can be used by targets to point
823 to their own specific data.
825 If a target needs per-function specific data it should define the type
826 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
827 This macro should be used to initialize the function pointer
828 @code{init_machine_status}. This pointer is explained below.
830 One typical use of per-function, target specific data is to create an
831 RTX to hold the register containing the function's return address. This
832 RTX can then be used to implement the @code{__builtin_return_address}
833 function, for level 0.
835 Note---earlier implementations of GCC used a single data area to hold
836 all of the per-function information. Thus when processing of a nested
837 function began the old per-function data had to be pushed onto a
838 stack, and when the processing was finished, it had to be popped off the
839 stack. GCC used to provide function pointers called
840 @code{save_machine_status} and @code{restore_machine_status} to handle
841 the saving and restoring of the target specific information. Since the
842 single data area approach is no longer used, these pointers are no
845 @defmac INIT_EXPANDERS
846 Macro called to initialize any target specific information. This macro
847 is called once per function, before generation of any RTL has begun.
848 The intention of this macro is to allow the initialization of the
849 function pointer @code{init_machine_status}.
852 @deftypevar {void (*)(struct function *)} init_machine_status
853 If this function pointer is non-@code{NULL} it will be called once per
854 function, before function compilation starts, in order to allow the
855 target to perform any target specific initialization of the
856 @code{struct function} structure. It is intended that this would be
857 used to initialize the @code{machine} of that structure.
859 @code{struct machine_function} structures are expected to be freed by GC@.
860 Generally, any memory that they reference must be allocated by using
861 @code{ggc_alloc}, including the structure itself.
865 @section Storage Layout
866 @cindex storage layout
868 Note that the definitions of the macros in this table which are sizes or
869 alignments measured in bits do not need to be constant. They can be C
870 expressions that refer to static variables, such as the @code{target_flags}.
871 @xref{Run-time Target}.
873 @defmac BITS_BIG_ENDIAN
874 Define this macro to have the value 1 if the most significant bit in a
875 byte has the lowest number; otherwise define it to have the value zero.
876 This means that bit-field instructions count from the most significant
877 bit. If the machine has no bit-field instructions, then this must still
878 be defined, but it doesn't matter which value it is defined to. This
879 macro need not be a constant.
881 This macro does not affect the way structure fields are packed into
882 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
885 @defmac BYTES_BIG_ENDIAN
886 Define this macro to have the value 1 if the most significant byte in a
887 word has the lowest number. This macro need not be a constant.
890 @defmac WORDS_BIG_ENDIAN
891 Define this macro to have the value 1 if, in a multiword object, the
892 most significant word has the lowest number. This applies to both
893 memory locations and registers; GCC fundamentally assumes that the
894 order of words in memory is the same as the order in registers. This
895 macro need not be a constant.
898 @defmac LIBGCC2_WORDS_BIG_ENDIAN
899 Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a
900 constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
901 used only when compiling @file{libgcc2.c}. Typically the value will be set
902 based on preprocessor defines.
905 @defmac FLOAT_WORDS_BIG_ENDIAN
906 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
907 @code{TFmode} floating point numbers are stored in memory with the word
908 containing the sign bit at the lowest address; otherwise define it to
909 have the value 0. This macro need not be a constant.
911 You need not define this macro if the ordering is the same as for
915 @defmac BITS_PER_UNIT
916 Define this macro to be the number of bits in an addressable storage
917 unit (byte). If you do not define this macro the default is 8.
920 @defmac BITS_PER_WORD
921 Number of bits in a word. If you do not define this macro, the default
922 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
925 @defmac MAX_BITS_PER_WORD
926 Maximum number of bits in a word. If this is undefined, the default is
927 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
928 largest value that @code{BITS_PER_WORD} can have at run-time.
931 @defmac UNITS_PER_WORD
932 Number of storage units in a word; normally the size of a general-purpose
933 register, a power of two from 1 or 8.
936 @defmac MIN_UNITS_PER_WORD
937 Minimum number of units in a word. If this is undefined, the default is
938 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
939 smallest value that @code{UNITS_PER_WORD} can have at run-time.
942 @defmac UNITS_PER_SIMD_WORD
943 Number of units in the vectors that the vectorizer can produce.
944 The default is equal to @code{UNITS_PER_WORD}, because the vectorizer
945 can do some transformations even in absence of specialized @acronym{SIMD}
950 Width of a pointer, in bits. You must specify a value no wider than the
951 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
952 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
953 a value the default is @code{BITS_PER_WORD}.
956 @defmac POINTERS_EXTEND_UNSIGNED
957 A C expression whose value is greater than zero if pointers that need to be
958 extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to
959 be zero-extended and zero if they are to be sign-extended. If the value
960 is less then zero then there must be an "ptr_extend" instruction that
961 extends a pointer from @code{POINTER_SIZE} to @code{Pmode}.
963 You need not define this macro if the @code{POINTER_SIZE} is equal
964 to the width of @code{Pmode}.
967 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
968 A macro to update @var{m} and @var{unsignedp} when an object whose type
969 is @var{type} and which has the specified mode and signedness is to be
970 stored in a register. This macro is only called when @var{type} is a
973 On most RISC machines, which only have operations that operate on a full
974 register, define this macro to set @var{m} to @code{word_mode} if
975 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
976 cases, only integer modes should be widened because wider-precision
977 floating-point operations are usually more expensive than their narrower
980 For most machines, the macro definition does not change @var{unsignedp}.
981 However, some machines, have instructions that preferentially handle
982 either signed or unsigned quantities of certain modes. For example, on
983 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
984 sign-extend the result to 64 bits. On such machines, set
985 @var{unsignedp} according to which kind of extension is more efficient.
987 Do not define this macro if it would never modify @var{m}.
990 @defmac PROMOTE_FUNCTION_MODE
991 Like @code{PROMOTE_MODE}, but is applied to outgoing function arguments or
992 function return values, as specified by @code{TARGET_PROMOTE_FUNCTION_ARGS}
993 and @code{TARGET_PROMOTE_FUNCTION_RETURN}, respectively.
995 The default is @code{PROMOTE_MODE}.
998 @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_ARGS (tree @var{fntype})
999 This target hook should return @code{true} if the promotion described by
1000 @code{PROMOTE_FUNCTION_MODE} should be done for outgoing function
1004 @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_RETURN (tree @var{fntype})
1005 This target hook should return @code{true} if the promotion described by
1006 @code{PROMOTE_FUNCTION_MODE} should be done for the return value of
1009 If this target hook returns @code{true}, @code{FUNCTION_VALUE} must
1010 perform the same promotions done by @code{PROMOTE_FUNCTION_MODE}.
1013 @defmac PARM_BOUNDARY
1014 Normal alignment required for function parameters on the stack, in
1015 bits. All stack parameters receive at least this much alignment
1016 regardless of data type. On most machines, this is the same as the
1020 @defmac STACK_BOUNDARY
1021 Define this macro to the minimum alignment enforced by hardware for the
1022 stack pointer on this machine. The definition is a C expression for the
1023 desired alignment (measured in bits). This value is used as a default
1024 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
1025 this should be the same as @code{PARM_BOUNDARY}.
1028 @defmac PREFERRED_STACK_BOUNDARY
1029 Define this macro if you wish to preserve a certain alignment for the
1030 stack pointer, greater than what the hardware enforces. The definition
1031 is a C expression for the desired alignment (measured in bits). This
1032 macro must evaluate to a value equal to or larger than
1033 @code{STACK_BOUNDARY}.
1036 @defmac FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
1037 A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is
1038 not guaranteed by the runtime and we should emit code to align the stack
1039 at the beginning of @code{main}.
1041 @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY}
1042 If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned
1043 to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies
1044 a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may
1045 be momentarily unaligned while pushing arguments.
1048 @defmac FUNCTION_BOUNDARY
1049 Alignment required for a function entry point, in bits.
1052 @defmac BIGGEST_ALIGNMENT
1053 Biggest alignment that any data type can require on this machine, in bits.
1056 @defmac MINIMUM_ATOMIC_ALIGNMENT
1057 If defined, the smallest alignment, in bits, that can be given to an
1058 object that can be referenced in one operation, without disturbing any
1059 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1060 on machines that don't have byte or half-word store operations.
1063 @defmac BIGGEST_FIELD_ALIGNMENT
1064 Biggest alignment that any structure or union field can require on this
1065 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1066 structure and union fields only, unless the field alignment has been set
1067 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1070 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1071 An expression for the alignment of a structure field @var{field} if the
1072 alignment computed in the usual way (including applying of
1073 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1074 alignment) is @var{computed}. It overrides alignment only if the
1075 field alignment has not been set by the
1076 @code{__attribute__ ((aligned (@var{n})))} construct.
1079 @defmac MAX_OFILE_ALIGNMENT
1080 Biggest alignment supported by the object file format of this machine.
1081 Use this macro to limit the alignment which can be specified using the
1082 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1083 the default value is @code{BIGGEST_ALIGNMENT}.
1086 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1087 If defined, a C expression to compute the alignment for a variable in
1088 the static store. @var{type} is the data type, and @var{basic-align} is
1089 the alignment that the object would ordinarily have. The value of this
1090 macro is used instead of that alignment to align the object.
1092 If this macro is not defined, then @var{basic-align} is used.
1095 One use of this macro is to increase alignment of medium-size data to
1096 make it all fit in fewer cache lines. Another is to cause character
1097 arrays to be word-aligned so that @code{strcpy} calls that copy
1098 constants to character arrays can be done inline.
1101 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1102 If defined, a C expression to compute the alignment given to a constant
1103 that is being placed in memory. @var{constant} is the constant and
1104 @var{basic-align} is the alignment that the object would ordinarily
1105 have. The value of this macro is used instead of that alignment to
1108 If this macro is not defined, then @var{basic-align} is used.
1110 The typical use of this macro is to increase alignment for string
1111 constants to be word aligned so that @code{strcpy} calls that copy
1112 constants can be done inline.
1115 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1116 If defined, a C expression to compute the alignment for a variable in
1117 the local store. @var{type} is the data type, and @var{basic-align} is
1118 the alignment that the object would ordinarily have. The value of this
1119 macro is used instead of that alignment to align the object.
1121 If this macro is not defined, then @var{basic-align} is used.
1123 One use of this macro is to increase alignment of medium-size data to
1124 make it all fit in fewer cache lines.
1127 @defmac EMPTY_FIELD_BOUNDARY
1128 Alignment in bits to be given to a structure bit-field that follows an
1129 empty field such as @code{int : 0;}.
1131 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1134 @defmac STRUCTURE_SIZE_BOUNDARY
1135 Number of bits which any structure or union's size must be a multiple of.
1136 Each structure or union's size is rounded up to a multiple of this.
1138 If you do not define this macro, the default is the same as
1139 @code{BITS_PER_UNIT}.
1142 @defmac STRICT_ALIGNMENT
1143 Define this macro to be the value 1 if instructions will fail to work
1144 if given data not on the nominal alignment. If instructions will merely
1145 go slower in that case, define this macro as 0.
1148 @defmac PCC_BITFIELD_TYPE_MATTERS
1149 Define this if you wish to imitate the way many other C compilers handle
1150 alignment of bit-fields and the structures that contain them.
1152 The behavior is that the type written for a named bit-field (@code{int},
1153 @code{short}, or other integer type) imposes an alignment for the entire
1154 structure, as if the structure really did contain an ordinary field of
1155 that type. In addition, the bit-field is placed within the structure so
1156 that it would fit within such a field, not crossing a boundary for it.
1158 Thus, on most machines, a named bit-field whose type is written as
1159 @code{int} would not cross a four-byte boundary, and would force
1160 four-byte alignment for the whole structure. (The alignment used may
1161 not be four bytes; it is controlled by the other alignment parameters.)
1163 An unnamed bit-field will not affect the alignment of the containing
1166 If the macro is defined, its definition should be a C expression;
1167 a nonzero value for the expression enables this behavior.
1169 Note that if this macro is not defined, or its value is zero, some
1170 bit-fields may cross more than one alignment boundary. The compiler can
1171 support such references if there are @samp{insv}, @samp{extv}, and
1172 @samp{extzv} insns that can directly reference memory.
1174 The other known way of making bit-fields work is to define
1175 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1176 Then every structure can be accessed with fullwords.
1178 Unless the machine has bit-field instructions or you define
1179 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1180 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1182 If your aim is to make GCC use the same conventions for laying out
1183 bit-fields as are used by another compiler, here is how to investigate
1184 what the other compiler does. Compile and run this program:
1203 printf ("Size of foo1 is %d\n",
1204 sizeof (struct foo1));
1205 printf ("Size of foo2 is %d\n",
1206 sizeof (struct foo2));
1211 If this prints 2 and 5, then the compiler's behavior is what you would
1212 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1215 @defmac BITFIELD_NBYTES_LIMITED
1216 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1217 to aligning a bit-field within the structure.
1220 @deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELDS (void)
1221 When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
1222 whether unnamed bitfields affect the alignment of the containing
1223 structure. The hook should return true if the structure should inherit
1224 the alignment requirements of an unnamed bitfield's type.
1227 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1228 Return 1 if a structure or array containing @var{field} should be accessed using
1231 If @var{field} is the only field in the structure, @var{mode} is its
1232 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1233 case where structures of one field would require the structure's mode to
1234 retain the field's mode.
1236 Normally, this is not needed. See the file @file{c4x.h} for an example
1237 of how to use this macro to prevent a structure having a floating point
1238 field from being accessed in an integer mode.
1241 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1242 Define this macro as an expression for the alignment of a type (given
1243 by @var{type} as a tree node) if the alignment computed in the usual
1244 way is @var{computed} and the alignment explicitly specified was
1247 The default is to use @var{specified} if it is larger; otherwise, use
1248 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1251 @defmac MAX_FIXED_MODE_SIZE
1252 An integer expression for the size in bits of the largest integer
1253 machine mode that should actually be used. All integer machine modes of
1254 this size or smaller can be used for structures and unions with the
1255 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1256 (DImode)} is assumed.
1259 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1260 If defined, an expression of type @code{enum machine_mode} that
1261 specifies the mode of the save area operand of a
1262 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1263 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1264 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1265 having its mode specified.
1267 You need not define this macro if it always returns @code{Pmode}. You
1268 would most commonly define this macro if the
1269 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1273 @defmac STACK_SIZE_MODE
1274 If defined, an expression of type @code{enum machine_mode} that
1275 specifies the mode of the size increment operand of an
1276 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1278 You need not define this macro if it always returns @code{word_mode}.
1279 You would most commonly define this macro if the @code{allocate_stack}
1280 pattern needs to support both a 32- and a 64-bit mode.
1283 @defmac TARGET_FLOAT_FORMAT
1284 A code distinguishing the floating point format of the target machine.
1285 There are four defined values:
1288 @item IEEE_FLOAT_FORMAT
1289 This code indicates IEEE floating point. It is the default; there is no
1290 need to define @code{TARGET_FLOAT_FORMAT} when the format is IEEE@.
1292 @item VAX_FLOAT_FORMAT
1293 This code indicates the ``F float'' (for @code{float}) and ``D float''
1294 or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@.
1296 @item IBM_FLOAT_FORMAT
1297 This code indicates the format used on the IBM System/370.
1299 @item C4X_FLOAT_FORMAT
1300 This code indicates the format used on the TMS320C3x/C4x.
1303 If your target uses a floating point format other than these, you must
1304 define a new @var{name}_FLOAT_FORMAT code for it, and add support for
1305 it to @file{real.c}.
1307 The ordering of the component words of floating point values stored in
1308 memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}.
1311 @defmac MODE_HAS_NANS (@var{mode})
1312 When defined, this macro should be true if @var{mode} has a NaN
1313 representation. The compiler assumes that NaNs are not equal to
1314 anything (including themselves) and that addition, subtraction,
1315 multiplication and division all return NaNs when one operand is
1318 By default, this macro is true if @var{mode} is a floating-point
1319 mode and the target floating-point format is IEEE@.
1322 @defmac MODE_HAS_INFINITIES (@var{mode})
1323 This macro should be true if @var{mode} can represent infinity. At
1324 present, the compiler uses this macro to decide whether @samp{x - x}
1325 is always defined. By default, the macro is true when @var{mode}
1326 is a floating-point mode and the target format is IEEE@.
1329 @defmac MODE_HAS_SIGNED_ZEROS (@var{mode})
1330 True if @var{mode} distinguishes between positive and negative zero.
1331 The rules are expected to follow the IEEE standard:
1335 @samp{x + x} has the same sign as @samp{x}.
1338 If the sum of two values with opposite sign is zero, the result is
1339 positive for all rounding modes expect towards @minus{}infinity, for
1340 which it is negative.
1343 The sign of a product or quotient is negative when exactly one
1344 of the operands is negative.
1347 The default definition is true if @var{mode} is a floating-point
1348 mode and the target format is IEEE@.
1351 @defmac MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode})
1352 If defined, this macro should be true for @var{mode} if it has at
1353 least one rounding mode in which @samp{x} and @samp{-x} can be
1354 rounded to numbers of different magnitude. Two such modes are
1355 towards @minus{}infinity and towards +infinity.
1357 The default definition of this macro is true if @var{mode} is
1358 a floating-point mode and the target format is IEEE@.
1361 @defmac ROUND_TOWARDS_ZERO
1362 If defined, this macro should be true if the prevailing rounding
1363 mode is towards zero. A true value has the following effects:
1367 @code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes.
1370 @file{libgcc.a}'s floating-point emulator will round towards zero
1371 rather than towards nearest.
1374 The compiler's floating-point emulator will round towards zero after
1375 doing arithmetic, and when converting from the internal float format to
1379 The macro does not affect the parsing of string literals. When the
1380 primary rounding mode is towards zero, library functions like
1381 @code{strtod} might still round towards nearest, and the compiler's
1382 parser should behave like the target's @code{strtod} where possible.
1384 Not defining this macro is equivalent to returning zero.
1387 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1388 This macro should return true if floats with @var{size}
1389 bits do not have a NaN or infinity representation, but use the largest
1390 exponent for normal numbers instead.
1392 Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS}
1393 and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes.
1394 It also affects the way @file{libgcc.a} and @file{real.c} emulate
1395 floating-point arithmetic.
1397 The default definition of this macro returns false for all sizes.
1400 @deftypefn {Target Hook} bool TARGET_VECTOR_OPAQUE_P (tree @var{type})
1401 This target hook should return @code{true} a vector is opaque. That
1402 is, if no cast is needed when copying a vector value of type
1403 @var{type} into another vector lvalue of the same size. Vector opaque
1404 types cannot be initialized. The default is that there are no such
1408 @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type})
1409 This target hook returns @code{true} if bit-fields in the given
1410 @var{record_type} are to be laid out following the rules of Microsoft
1411 Visual C/C++, namely: (i) a bit-field won't share the same storage
1412 unit with the previous bit-field if their underlying types have
1413 different sizes, and the bit-field will be aligned to the highest
1414 alignment of the underlying types of itself and of the previous
1415 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1416 the whole enclosing structure, even if it is unnamed; except that
1417 (iii) a zero-sized bit-field will be disregarded unless it follows
1418 another bit-field of nonzero size. If this hook returns @code{true},
1419 other macros that control bit-field layout are ignored.
1421 When a bit-field is inserted into a packed record, the whole size
1422 of the underlying type is used by one or more same-size adjacent
1423 bit-fields (that is, if its long:3, 32 bits is used in the record,
1424 and any additional adjacent long bit-fields are packed into the same
1425 chunk of 32 bits. However, if the size changes, a new field of that
1426 size is allocated). In an unpacked record, this is the same as using
1427 alignment, but not equivalent when packing.
1429 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1430 the latter will take precedence. If @samp{__attribute__((packed))} is
1431 used on a single field when MS bit-fields are in use, it will take
1432 precedence for that field, but the alignment of the rest of the structure
1433 may affect its placement.
1436 @deftypefn {Target Hook} {const char *} TARGET_MANGLE_FUNDAMENTAL_TYPE (tree @var{type})
1437 If your target defines any fundamental types, define this hook to
1438 return the appropriate encoding for these types as part of a C++
1439 mangled name. The @var{type} argument is the tree structure
1440 representing the type to be mangled. The hook may be applied to trees
1441 which are not target-specific fundamental types; it should return
1442 @code{NULL} for all such types, as well as arguments it does not
1443 recognize. If the return value is not @code{NULL}, it must point to
1444 a statically-allocated string constant.
1446 Target-specific fundamental types might be new fundamental types or
1447 qualified versions of ordinary fundamental types. Encode new
1448 fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
1449 is the name used for the type in source code, and @var{n} is the
1450 length of @var{name} in decimal. Encode qualified versions of
1451 ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
1452 @var{name} is the name used for the type qualifier in source code,
1453 @var{n} is the length of @var{name} as above, and @var{code} is the
1454 code used to represent the unqualified version of this type. (See
1455 @code{write_builtin_type} in @file{cp/mangle.c} for the list of
1456 codes.) In both cases the spaces are for clarity; do not include any
1457 spaces in your string.
1459 The default version of this hook always returns @code{NULL}, which is
1460 appropriate for a target that does not define any new fundamental
1465 @section Layout of Source Language Data Types
1467 These macros define the sizes and other characteristics of the standard
1468 basic data types used in programs being compiled. Unlike the macros in
1469 the previous section, these apply to specific features of C and related
1470 languages, rather than to fundamental aspects of storage layout.
1472 @defmac INT_TYPE_SIZE
1473 A C expression for the size in bits of the type @code{int} on the
1474 target machine. If you don't define this, the default is one word.
1477 @defmac SHORT_TYPE_SIZE
1478 A C expression for the size in bits of the type @code{short} on the
1479 target machine. If you don't define this, the default is half a word.
1480 (If this would be less than one storage unit, it is rounded up to one
1484 @defmac LONG_TYPE_SIZE
1485 A C expression for the size in bits of the type @code{long} on the
1486 target machine. If you don't define this, the default is one word.
1489 @defmac ADA_LONG_TYPE_SIZE
1490 On some machines, the size used for the Ada equivalent of the type
1491 @code{long} by a native Ada compiler differs from that used by C@. In
1492 that situation, define this macro to be a C expression to be used for
1493 the size of that type. If you don't define this, the default is the
1494 value of @code{LONG_TYPE_SIZE}.
1497 @defmac LONG_LONG_TYPE_SIZE
1498 A C expression for the size in bits of the type @code{long long} on the
1499 target machine. If you don't define this, the default is two
1500 words. If you want to support GNU Ada on your machine, the value of this
1501 macro must be at least 64.
1504 @defmac CHAR_TYPE_SIZE
1505 A C expression for the size in bits of the type @code{char} on the
1506 target machine. If you don't define this, the default is
1507 @code{BITS_PER_UNIT}.
1510 @defmac BOOL_TYPE_SIZE
1511 A C expression for the size in bits of the C++ type @code{bool} and
1512 C99 type @code{_Bool} on the target machine. If you don't define
1513 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1516 @defmac FLOAT_TYPE_SIZE
1517 A C expression for the size in bits of the type @code{float} on the
1518 target machine. If you don't define this, the default is one word.
1521 @defmac DOUBLE_TYPE_SIZE
1522 A C expression for the size in bits of the type @code{double} on the
1523 target machine. If you don't define this, the default is two
1527 @defmac LONG_DOUBLE_TYPE_SIZE
1528 A C expression for the size in bits of the type @code{long double} on
1529 the target machine. If you don't define this, the default is two
1533 @defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE
1534 Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or
1535 if you want routines in @file{libgcc2.a} for a size other than
1536 @code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the
1537 default is @code{LONG_DOUBLE_TYPE_SIZE}.
1540 @defmac LIBGCC2_HAS_DF_MODE
1541 Define this macro if neither @code{LIBGCC2_DOUBLE_TYPE_SIZE} nor
1542 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is
1543 @code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a}
1544 anyway. If you don't define this and either @code{LIBGCC2_DOUBLE_TYPE_SIZE}
1545 or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1,
1549 @defmac LIBGCC2_HAS_XF_MODE
1550 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1551 @code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a}
1552 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1553 is 80 then the default is 1, otherwise it is 0.
1556 @defmac LIBGCC2_HAS_TF_MODE
1557 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1558 @code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a}
1559 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1560 is 128 then the default is 1, otherwise it is 0.
1563 @defmac TARGET_FLT_EVAL_METHOD
1564 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1565 assuming, if applicable, that the floating-point control word is in its
1566 default state. If you do not define this macro the value of
1567 @code{FLT_EVAL_METHOD} will be zero.
1570 @defmac WIDEST_HARDWARE_FP_SIZE
1571 A C expression for the size in bits of the widest floating-point format
1572 supported by the hardware. If you define this macro, you must specify a
1573 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1574 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1578 @defmac DEFAULT_SIGNED_CHAR
1579 An expression whose value is 1 or 0, according to whether the type
1580 @code{char} should be signed or unsigned by default. The user can
1581 always override this default with the options @option{-fsigned-char}
1582 and @option{-funsigned-char}.
1585 @deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void)
1586 This target hook should return true if the compiler should give an
1587 @code{enum} type only as many bytes as it takes to represent the range
1588 of possible values of that type. It should return false if all
1589 @code{enum} types should be allocated like @code{int}.
1591 The default is to return false.
1595 A C expression for a string describing the name of the data type to use
1596 for size values. The typedef name @code{size_t} is defined using the
1597 contents of the string.
1599 The string can contain more than one keyword. If so, separate them with
1600 spaces, and write first any length keyword, then @code{unsigned} if
1601 appropriate, and finally @code{int}. The string must exactly match one
1602 of the data type names defined in the function
1603 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1604 omit @code{int} or change the order---that would cause the compiler to
1607 If you don't define this macro, the default is @code{"long unsigned
1611 @defmac PTRDIFF_TYPE
1612 A C expression for a string describing the name of the data type to use
1613 for the result of subtracting two pointers. The typedef name
1614 @code{ptrdiff_t} is defined using the contents of the string. See
1615 @code{SIZE_TYPE} above for more information.
1617 If you don't define this macro, the default is @code{"long int"}.
1621 A C expression for a string describing the name of the data type to use
1622 for wide characters. The typedef name @code{wchar_t} is defined using
1623 the contents of the string. See @code{SIZE_TYPE} above for more
1626 If you don't define this macro, the default is @code{"int"}.
1629 @defmac WCHAR_TYPE_SIZE
1630 A C expression for the size in bits of the data type for wide
1631 characters. This is used in @code{cpp}, which cannot make use of
1636 A C expression for a string describing the name of the data type to
1637 use for wide characters passed to @code{printf} and returned from
1638 @code{getwc}. The typedef name @code{wint_t} is defined using the
1639 contents of the string. See @code{SIZE_TYPE} above for more
1642 If you don't define this macro, the default is @code{"unsigned int"}.
1646 A C expression for a string describing the name of the data type that
1647 can represent any value of any standard or extended signed integer type.
1648 The typedef name @code{intmax_t} is defined using the contents of the
1649 string. See @code{SIZE_TYPE} above for more information.
1651 If you don't define this macro, the default is the first of
1652 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1653 much precision as @code{long long int}.
1656 @defmac UINTMAX_TYPE
1657 A C expression for a string describing the name of the data type that
1658 can represent any value of any standard or extended unsigned integer
1659 type. The typedef name @code{uintmax_t} is defined using the contents
1660 of the string. See @code{SIZE_TYPE} above for more information.
1662 If you don't define this macro, the default is the first of
1663 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1664 unsigned int"} that has as much precision as @code{long long unsigned
1668 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1669 The C++ compiler represents a pointer-to-member-function with a struct
1676 ptrdiff_t vtable_index;
1683 The C++ compiler must use one bit to indicate whether the function that
1684 will be called through a pointer-to-member-function is virtual.
1685 Normally, we assume that the low-order bit of a function pointer must
1686 always be zero. Then, by ensuring that the vtable_index is odd, we can
1687 distinguish which variant of the union is in use. But, on some
1688 platforms function pointers can be odd, and so this doesn't work. In
1689 that case, we use the low-order bit of the @code{delta} field, and shift
1690 the remainder of the @code{delta} field to the left.
1692 GCC will automatically make the right selection about where to store
1693 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1694 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1695 set such that functions always start at even addresses, but the lowest
1696 bit of pointers to functions indicate whether the function at that
1697 address is in ARM or Thumb mode. If this is the case of your
1698 architecture, you should define this macro to
1699 @code{ptrmemfunc_vbit_in_delta}.
1701 In general, you should not have to define this macro. On architectures
1702 in which function addresses are always even, according to
1703 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1704 @code{ptrmemfunc_vbit_in_pfn}.
1707 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1708 Normally, the C++ compiler uses function pointers in vtables. This
1709 macro allows the target to change to use ``function descriptors''
1710 instead. Function descriptors are found on targets for whom a
1711 function pointer is actually a small data structure. Normally the
1712 data structure consists of the actual code address plus a data
1713 pointer to which the function's data is relative.
1715 If vtables are used, the value of this macro should be the number
1716 of words that the function descriptor occupies.
1719 @defmac TARGET_VTABLE_ENTRY_ALIGN
1720 By default, the vtable entries are void pointers, the so the alignment
1721 is the same as pointer alignment. The value of this macro specifies
1722 the alignment of the vtable entry in bits. It should be defined only
1723 when special alignment is necessary. */
1726 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1727 There are a few non-descriptor entries in the vtable at offsets below
1728 zero. If these entries must be padded (say, to preserve the alignment
1729 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1730 of words in each data entry.
1734 @section Register Usage
1735 @cindex register usage
1737 This section explains how to describe what registers the target machine
1738 has, and how (in general) they can be used.
1740 The description of which registers a specific instruction can use is
1741 done with register classes; see @ref{Register Classes}. For information
1742 on using registers to access a stack frame, see @ref{Frame Registers}.
1743 For passing values in registers, see @ref{Register Arguments}.
1744 For returning values in registers, see @ref{Scalar Return}.
1747 * Register Basics:: Number and kinds of registers.
1748 * Allocation Order:: Order in which registers are allocated.
1749 * Values in Registers:: What kinds of values each reg can hold.
1750 * Leaf Functions:: Renumbering registers for leaf functions.
1751 * Stack Registers:: Handling a register stack such as 80387.
1754 @node Register Basics
1755 @subsection Basic Characteristics of Registers
1757 @c prevent bad page break with this line
1758 Registers have various characteristics.
1760 @defmac FIRST_PSEUDO_REGISTER
1761 Number of hardware registers known to the compiler. They receive
1762 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1763 pseudo register's number really is assigned the number
1764 @code{FIRST_PSEUDO_REGISTER}.
1767 @defmac FIXED_REGISTERS
1768 @cindex fixed register
1769 An initializer that says which registers are used for fixed purposes
1770 all throughout the compiled code and are therefore not available for
1771 general allocation. These would include the stack pointer, the frame
1772 pointer (except on machines where that can be used as a general
1773 register when no frame pointer is needed), the program counter on
1774 machines where that is considered one of the addressable registers,
1775 and any other numbered register with a standard use.
1777 This information is expressed as a sequence of numbers, separated by
1778 commas and surrounded by braces. The @var{n}th number is 1 if
1779 register @var{n} is fixed, 0 otherwise.
1781 The table initialized from this macro, and the table initialized by
1782 the following one, may be overridden at run time either automatically,
1783 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1784 the user with the command options @option{-ffixed-@var{reg}},
1785 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1788 @defmac CALL_USED_REGISTERS
1789 @cindex call-used register
1790 @cindex call-clobbered register
1791 @cindex call-saved register
1792 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1793 clobbered (in general) by function calls as well as for fixed
1794 registers. This macro therefore identifies the registers that are not
1795 available for general allocation of values that must live across
1798 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1799 automatically saves it on function entry and restores it on function
1800 exit, if the register is used within the function.
1803 @defmac CALL_REALLY_USED_REGISTERS
1804 @cindex call-used register
1805 @cindex call-clobbered register
1806 @cindex call-saved register
1807 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1808 that the entire set of @code{FIXED_REGISTERS} be included.
1809 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1810 This macro is optional. If not specified, it defaults to the value
1811 of @code{CALL_USED_REGISTERS}.
1814 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1815 @cindex call-used register
1816 @cindex call-clobbered register
1817 @cindex call-saved register
1818 A C expression that is nonzero if it is not permissible to store a
1819 value of mode @var{mode} in hard register number @var{regno} across a
1820 call without some part of it being clobbered. For most machines this
1821 macro need not be defined. It is only required for machines that do not
1822 preserve the entire contents of a register across a call.
1826 @findex call_used_regs
1829 @findex reg_class_contents
1830 @defmac CONDITIONAL_REGISTER_USAGE
1831 Zero or more C statements that may conditionally modify five variables
1832 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
1833 @code{reg_names}, and @code{reg_class_contents}, to take into account
1834 any dependence of these register sets on target flags. The first three
1835 of these are of type @code{char []} (interpreted as Boolean vectors).
1836 @code{global_regs} is a @code{const char *[]}, and
1837 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
1838 called, @code{fixed_regs}, @code{call_used_regs},
1839 @code{reg_class_contents}, and @code{reg_names} have been initialized
1840 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
1841 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
1842 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
1843 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
1844 command options have been applied.
1846 You need not define this macro if it has no work to do.
1848 @cindex disabling certain registers
1849 @cindex controlling register usage
1850 If the usage of an entire class of registers depends on the target
1851 flags, you may indicate this to GCC by using this macro to modify
1852 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
1853 registers in the classes which should not be used by GCC@. Also define
1854 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
1855 to return @code{NO_REGS} if it
1856 is called with a letter for a class that shouldn't be used.
1858 (However, if this class is not included in @code{GENERAL_REGS} and all
1859 of the insn patterns whose constraints permit this class are
1860 controlled by target switches, then GCC will automatically avoid using
1861 these registers when the target switches are opposed to them.)
1864 @defmac INCOMING_REGNO (@var{out})
1865 Define this macro if the target machine has register windows. This C
1866 expression returns the register number as seen by the called function
1867 corresponding to the register number @var{out} as seen by the calling
1868 function. Return @var{out} if register number @var{out} is not an
1872 @defmac OUTGOING_REGNO (@var{in})
1873 Define this macro if the target machine has register windows. This C
1874 expression returns the register number as seen by the calling function
1875 corresponding to the register number @var{in} as seen by the called
1876 function. Return @var{in} if register number @var{in} is not an inbound
1880 @defmac LOCAL_REGNO (@var{regno})
1881 Define this macro if the target machine has register windows. This C
1882 expression returns true if the register is call-saved but is in the
1883 register window. Unlike most call-saved registers, such registers
1884 need not be explicitly restored on function exit or during non-local
1889 If the program counter has a register number, define this as that
1890 register number. Otherwise, do not define it.
1893 @node Allocation Order
1894 @subsection Order of Allocation of Registers
1895 @cindex order of register allocation
1896 @cindex register allocation order
1898 @c prevent bad page break with this line
1899 Registers are allocated in order.
1901 @defmac REG_ALLOC_ORDER
1902 If defined, an initializer for a vector of integers, containing the
1903 numbers of hard registers in the order in which GCC should prefer
1904 to use them (from most preferred to least).
1906 If this macro is not defined, registers are used lowest numbered first
1907 (all else being equal).
1909 One use of this macro is on machines where the highest numbered
1910 registers must always be saved and the save-multiple-registers
1911 instruction supports only sequences of consecutive registers. On such
1912 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
1913 the highest numbered allocable register first.
1916 @defmac ORDER_REGS_FOR_LOCAL_ALLOC
1917 A C statement (sans semicolon) to choose the order in which to allocate
1918 hard registers for pseudo-registers local to a basic block.
1920 Store the desired register order in the array @code{reg_alloc_order}.
1921 Element 0 should be the register to allocate first; element 1, the next
1922 register; and so on.
1924 The macro body should not assume anything about the contents of
1925 @code{reg_alloc_order} before execution of the macro.
1927 On most machines, it is not necessary to define this macro.
1930 @node Values in Registers
1931 @subsection How Values Fit in Registers
1933 This section discusses the macros that describe which kinds of values
1934 (specifically, which machine modes) each register can hold, and how many
1935 consecutive registers are needed for a given mode.
1937 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
1938 A C expression for the number of consecutive hard registers, starting
1939 at register number @var{regno}, required to hold a value of mode
1942 On a machine where all registers are exactly one word, a suitable
1943 definition of this macro is
1946 #define HARD_REGNO_NREGS(REGNO, MODE) \
1947 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
1952 @defmac REGMODE_NATURAL_SIZE (@var{mode})
1953 Define this macro if the natural size of registers that hold values
1954 of mode @var{mode} is not the word size. It is a C expression that
1955 should give the natural size in bytes for the specified mode. It is
1956 used by the register allocator to try to optimize its results. This
1957 happens for example on SPARC 64-bit where the natural size of
1958 floating-point registers is still 32-bit.
1961 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
1962 A C expression that is nonzero if it is permissible to store a value
1963 of mode @var{mode} in hard register number @var{regno} (or in several
1964 registers starting with that one). For a machine where all registers
1965 are equivalent, a suitable definition is
1968 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
1971 You need not include code to check for the numbers of fixed registers,
1972 because the allocation mechanism considers them to be always occupied.
1974 @cindex register pairs
1975 On some machines, double-precision values must be kept in even/odd
1976 register pairs. You can implement that by defining this macro to reject
1977 odd register numbers for such modes.
1979 The minimum requirement for a mode to be OK in a register is that the
1980 @samp{mov@var{mode}} instruction pattern support moves between the
1981 register and other hard register in the same class and that moving a
1982 value into the register and back out not alter it.
1984 Since the same instruction used to move @code{word_mode} will work for
1985 all narrower integer modes, it is not necessary on any machine for
1986 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
1987 you define patterns @samp{movhi}, etc., to take advantage of this. This
1988 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
1989 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
1992 Many machines have special registers for floating point arithmetic.
1993 Often people assume that floating point machine modes are allowed only
1994 in floating point registers. This is not true. Any registers that
1995 can hold integers can safely @emph{hold} a floating point machine
1996 mode, whether or not floating arithmetic can be done on it in those
1997 registers. Integer move instructions can be used to move the values.
1999 On some machines, though, the converse is true: fixed-point machine
2000 modes may not go in floating registers. This is true if the floating
2001 registers normalize any value stored in them, because storing a
2002 non-floating value there would garble it. In this case,
2003 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2004 floating registers. But if the floating registers do not automatically
2005 normalize, if you can store any bit pattern in one and retrieve it
2006 unchanged without a trap, then any machine mode may go in a floating
2007 register, so you can define this macro to say so.
2009 The primary significance of special floating registers is rather that
2010 they are the registers acceptable in floating point arithmetic
2011 instructions. However, this is of no concern to
2012 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2013 constraints for those instructions.
2015 On some machines, the floating registers are especially slow to access,
2016 so that it is better to store a value in a stack frame than in such a
2017 register if floating point arithmetic is not being done. As long as the
2018 floating registers are not in class @code{GENERAL_REGS}, they will not
2019 be used unless some pattern's constraint asks for one.
2022 @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
2023 A C expression that is nonzero if it is OK to rename a hard register
2024 @var{from} to another hard register @var{to}.
2026 One common use of this macro is to prevent renaming of a register to
2027 another register that is not saved by a prologue in an interrupt
2030 The default is always nonzero.
2033 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2034 A C expression that is nonzero if a value of mode
2035 @var{mode1} is accessible in mode @var{mode2} without copying.
2037 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2038 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2039 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2040 should be nonzero. If they differ for any @var{r}, you should define
2041 this macro to return zero unless some other mechanism ensures the
2042 accessibility of the value in a narrower mode.
2044 You should define this macro to return nonzero in as many cases as
2045 possible since doing so will allow GCC to perform better register
2049 @defmac AVOID_CCMODE_COPIES
2050 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2051 registers. You should only define this macro if support for copying to/from
2052 @code{CCmode} is incomplete.
2055 @node Leaf Functions
2056 @subsection Handling Leaf Functions
2058 @cindex leaf functions
2059 @cindex functions, leaf
2060 On some machines, a leaf function (i.e., one which makes no calls) can run
2061 more efficiently if it does not make its own register window. Often this
2062 means it is required to receive its arguments in the registers where they
2063 are passed by the caller, instead of the registers where they would
2066 The special treatment for leaf functions generally applies only when
2067 other conditions are met; for example, often they may use only those
2068 registers for its own variables and temporaries. We use the term ``leaf
2069 function'' to mean a function that is suitable for this special
2070 handling, so that functions with no calls are not necessarily ``leaf
2073 GCC assigns register numbers before it knows whether the function is
2074 suitable for leaf function treatment. So it needs to renumber the
2075 registers in order to output a leaf function. The following macros
2078 @defmac LEAF_REGISTERS
2079 Name of a char vector, indexed by hard register number, which
2080 contains 1 for a register that is allowable in a candidate for leaf
2083 If leaf function treatment involves renumbering the registers, then the
2084 registers marked here should be the ones before renumbering---those that
2085 GCC would ordinarily allocate. The registers which will actually be
2086 used in the assembler code, after renumbering, should not be marked with 1
2089 Define this macro only if the target machine offers a way to optimize
2090 the treatment of leaf functions.
2093 @defmac LEAF_REG_REMAP (@var{regno})
2094 A C expression whose value is the register number to which @var{regno}
2095 should be renumbered, when a function is treated as a leaf function.
2097 If @var{regno} is a register number which should not appear in a leaf
2098 function before renumbering, then the expression should yield @minus{}1, which
2099 will cause the compiler to abort.
2101 Define this macro only if the target machine offers a way to optimize the
2102 treatment of leaf functions, and registers need to be renumbered to do
2106 @findex current_function_is_leaf
2107 @findex current_function_uses_only_leaf_regs
2108 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2109 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2110 specially. They can test the C variable @code{current_function_is_leaf}
2111 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2112 set prior to local register allocation and is valid for the remaining
2113 compiler passes. They can also test the C variable
2114 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2115 functions which only use leaf registers.
2116 @code{current_function_uses_only_leaf_regs} is valid after all passes
2117 that modify the instructions have been run and is only useful if
2118 @code{LEAF_REGISTERS} is defined.
2119 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2120 @c of the next paragraph?! --mew 2feb93
2122 @node Stack Registers
2123 @subsection Registers That Form a Stack
2125 There are special features to handle computers where some of the
2126 ``registers'' form a stack. Stack registers are normally written by
2127 pushing onto the stack, and are numbered relative to the top of the
2130 Currently, GCC can only handle one group of stack-like registers, and
2131 they must be consecutively numbered. Furthermore, the existing
2132 support for stack-like registers is specific to the 80387 floating
2133 point coprocessor. If you have a new architecture that uses
2134 stack-like registers, you will need to do substantial work on
2135 @file{reg-stack.c} and write your machine description to cooperate
2136 with it, as well as defining these macros.
2139 Define this if the machine has any stack-like registers.
2142 @defmac FIRST_STACK_REG
2143 The number of the first stack-like register. This one is the top
2147 @defmac LAST_STACK_REG
2148 The number of the last stack-like register. This one is the bottom of
2152 @node Register Classes
2153 @section Register Classes
2154 @cindex register class definitions
2155 @cindex class definitions, register
2157 On many machines, the numbered registers are not all equivalent.
2158 For example, certain registers may not be allowed for indexed addressing;
2159 certain registers may not be allowed in some instructions. These machine
2160 restrictions are described to the compiler using @dfn{register classes}.
2162 You define a number of register classes, giving each one a name and saying
2163 which of the registers belong to it. Then you can specify register classes
2164 that are allowed as operands to particular instruction patterns.
2168 In general, each register will belong to several classes. In fact, one
2169 class must be named @code{ALL_REGS} and contain all the registers. Another
2170 class must be named @code{NO_REGS} and contain no registers. Often the
2171 union of two classes will be another class; however, this is not required.
2173 @findex GENERAL_REGS
2174 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2175 terribly special about the name, but the operand constraint letters
2176 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2177 the same as @code{ALL_REGS}, just define it as a macro which expands
2180 Order the classes so that if class @var{x} is contained in class @var{y}
2181 then @var{x} has a lower class number than @var{y}.
2183 The way classes other than @code{GENERAL_REGS} are specified in operand
2184 constraints is through machine-dependent operand constraint letters.
2185 You can define such letters to correspond to various classes, then use
2186 them in operand constraints.
2188 You should define a class for the union of two classes whenever some
2189 instruction allows both classes. For example, if an instruction allows
2190 either a floating point (coprocessor) register or a general register for a
2191 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2192 which includes both of them. Otherwise you will get suboptimal code.
2194 You must also specify certain redundant information about the register
2195 classes: for each class, which classes contain it and which ones are
2196 contained in it; for each pair of classes, the largest class contained
2199 When a value occupying several consecutive registers is expected in a
2200 certain class, all the registers used must belong to that class.
2201 Therefore, register classes cannot be used to enforce a requirement for
2202 a register pair to start with an even-numbered register. The way to
2203 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2205 Register classes used for input-operands of bitwise-and or shift
2206 instructions have a special requirement: each such class must have, for
2207 each fixed-point machine mode, a subclass whose registers can transfer that
2208 mode to or from memory. For example, on some machines, the operations for
2209 single-byte values (@code{QImode}) are limited to certain registers. When
2210 this is so, each register class that is used in a bitwise-and or shift
2211 instruction must have a subclass consisting of registers from which
2212 single-byte values can be loaded or stored. This is so that
2213 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2215 @deftp {Data type} {enum reg_class}
2216 An enumerated type that must be defined with all the register class names
2217 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
2218 must be the last register class, followed by one more enumerated value,
2219 @code{LIM_REG_CLASSES}, which is not a register class but rather
2220 tells how many classes there are.
2222 Each register class has a number, which is the value of casting
2223 the class name to type @code{int}. The number serves as an index
2224 in many of the tables described below.
2227 @defmac N_REG_CLASSES
2228 The number of distinct register classes, defined as follows:
2231 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2235 @defmac REG_CLASS_NAMES
2236 An initializer containing the names of the register classes as C string
2237 constants. These names are used in writing some of the debugging dumps.
2240 @defmac REG_CLASS_CONTENTS
2241 An initializer containing the contents of the register classes, as integers
2242 which are bit masks. The @var{n}th integer specifies the contents of class
2243 @var{n}. The way the integer @var{mask} is interpreted is that
2244 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2246 When the machine has more than 32 registers, an integer does not suffice.
2247 Then the integers are replaced by sub-initializers, braced groupings containing
2248 several integers. Each sub-initializer must be suitable as an initializer
2249 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2250 In this situation, the first integer in each sub-initializer corresponds to
2251 registers 0 through 31, the second integer to registers 32 through 63, and
2255 @defmac REGNO_REG_CLASS (@var{regno})
2256 A C expression whose value is a register class containing hard register
2257 @var{regno}. In general there is more than one such class; choose a class
2258 which is @dfn{minimal}, meaning that no smaller class also contains the
2262 @defmac BASE_REG_CLASS
2263 A macro whose definition is the name of the class to which a valid
2264 base register must belong. A base register is one used in an address
2265 which is the register value plus a displacement.
2268 @defmac MODE_BASE_REG_CLASS (@var{mode})
2269 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2270 the selection of a base register in a mode dependent manner. If
2271 @var{mode} is VOIDmode then it should return the same value as
2272 @code{BASE_REG_CLASS}.
2275 @defmac MODE_BASE_REG_REG_CLASS (@var{mode})
2276 A C expression whose value is the register class to which a valid
2277 base register must belong in order to be used in a base plus index
2278 register address. You should define this macro if base plus index
2279 addresses have different requirements than other base register uses.
2282 @defmac INDEX_REG_CLASS
2283 A macro whose definition is the name of the class to which a valid
2284 index register must belong. An index register is one used in an
2285 address where its value is either multiplied by a scale factor or
2286 added to another register (as well as added to a displacement).
2289 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2290 For the constraint at the start of @var{str}, which starts with the letter
2291 @var{c}, return the length. This allows you to have register class /
2292 constant / extra constraints that are longer than a single letter;
2293 you don't need to define this macro if you can do with single-letter
2294 constraints only. The definition of this macro should use
2295 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2296 to handle specially.
2297 There are some sanity checks in genoutput.c that check the constraint lengths
2298 for the md file, so you can also use this macro to help you while you are
2299 transitioning from a byzantine single-letter-constraint scheme: when you
2300 return a negative length for a constraint you want to re-use, genoutput
2301 will complain about every instance where it is used in the md file.
2304 @defmac REG_CLASS_FROM_LETTER (@var{char})
2305 A C expression which defines the machine-dependent operand constraint
2306 letters for register classes. If @var{char} is such a letter, the
2307 value should be the register class corresponding to it. Otherwise,
2308 the value should be @code{NO_REGS}. The register letter @samp{r},
2309 corresponding to class @code{GENERAL_REGS}, will not be passed
2310 to this macro; you do not need to handle it.
2313 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2314 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2315 passed in @var{str}, so that you can use suffixes to distinguish between
2319 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2320 A C expression which is nonzero if register number @var{num} is
2321 suitable for use as a base register in operand addresses. It may be
2322 either a suitable hard register or a pseudo register that has been
2323 allocated such a hard register.
2326 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2327 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2328 that expression may examine the mode of the memory reference in
2329 @var{mode}. You should define this macro if the mode of the memory
2330 reference affects whether a register may be used as a base register. If
2331 you define this macro, the compiler will use it instead of
2332 @code{REGNO_OK_FOR_BASE_P}.
2335 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
2336 A C expression which is nonzero if register number @var{num} is suitable for
2337 use as a base register in base plus index operand addresses, accessing
2338 memory in mode @var{mode}. It may be either a suitable hard register or a
2339 pseudo register that has been allocated such a hard register. You should
2340 define this macro if base plus index addresses have different requirements
2341 than other base register uses.
2344 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2345 A C expression which is nonzero if register number @var{num} is
2346 suitable for use as an index register in operand addresses. It may be
2347 either a suitable hard register or a pseudo register that has been
2348 allocated such a hard register.
2350 The difference between an index register and a base register is that
2351 the index register may be scaled. If an address involves the sum of
2352 two registers, neither one of them scaled, then either one may be
2353 labeled the ``base'' and the other the ``index''; but whichever
2354 labeling is used must fit the machine's constraints of which registers
2355 may serve in each capacity. The compiler will try both labelings,
2356 looking for one that is valid, and will reload one or both registers
2357 only if neither labeling works.
2360 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2361 A C expression that places additional restrictions on the register class
2362 to use when it is necessary to copy value @var{x} into a register in class
2363 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2364 another, smaller class. On many machines, the following definition is
2368 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2371 Sometimes returning a more restrictive class makes better code. For
2372 example, on the 68000, when @var{x} is an integer constant that is in range
2373 for a @samp{moveq} instruction, the value of this macro is always
2374 @code{DATA_REGS} as long as @var{class} includes the data registers.
2375 Requiring a data register guarantees that a @samp{moveq} will be used.
2377 One case where @code{PREFERRED_RELOAD_CLASS} must not return
2378 @var{class} is if @var{x} is a legitimate constant which cannot be
2379 loaded into some register class. By returning @code{NO_REGS} you can
2380 force @var{x} into a memory location. For example, rs6000 can load
2381 immediate values into general-purpose registers, but does not have an
2382 instruction for loading an immediate value into a floating-point
2383 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2384 @var{x} is a floating-point constant. If the constant can't be loaded
2385 into any kind of register, code generation will be better if
2386 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2387 of using @code{PREFERRED_RELOAD_CLASS}.
2390 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2391 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2392 input reloads. If you don't define this macro, the default is to use
2393 @var{class}, unchanged.
2396 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2397 A C expression that places additional restrictions on the register class
2398 to use when it is necessary to be able to hold a value of mode
2399 @var{mode} in a reload register for which class @var{class} would
2402 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2403 there are certain modes that simply can't go in certain reload classes.
2405 The value is a register class; perhaps @var{class}, or perhaps another,
2408 Don't define this macro unless the target machine has limitations which
2409 require the macro to do something nontrivial.
2412 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2413 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2414 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2415 Many machines have some registers that cannot be copied directly to or
2416 from memory or even from other types of registers. An example is the
2417 @samp{MQ} register, which on most machines, can only be copied to or
2418 from general registers, but not memory. Some machines allow copying all
2419 registers to and from memory, but require a scratch register for stores
2420 to some memory locations (e.g., those with symbolic address on the RT,
2421 and those with certain symbolic address on the SPARC when compiling
2422 PIC)@. In some cases, both an intermediate and a scratch register are
2425 You should define these macros to indicate to the reload phase that it may
2426 need to allocate at least one register for a reload in addition to the
2427 register to contain the data. Specifically, if copying @var{x} to a
2428 register @var{class} in @var{mode} requires an intermediate register,
2429 you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2430 largest register class all of whose registers can be used as
2431 intermediate registers or scratch registers.
2433 If copying a register @var{class} in @var{mode} to @var{x} requires an
2434 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2435 should be defined to return the largest register class required. If the
2436 requirements for input and output reloads are the same, the macro
2437 @code{SECONDARY_RELOAD_CLASS} should be used instead of defining both
2440 The values returned by these macros are often @code{GENERAL_REGS}.
2441 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2442 can be directly copied to or from a register of @var{class} in
2443 @var{mode} without requiring a scratch register. Do not define this
2444 macro if it would always return @code{NO_REGS}.
2446 If a scratch register is required (either with or without an
2447 intermediate register), you should define patterns for
2448 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2449 (@pxref{Standard Names}. These patterns, which will normally be
2450 implemented with a @code{define_expand}, should be similar to the
2451 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2454 Define constraints for the reload register and scratch register that
2455 contain a single register class. If the original reload register (whose
2456 class is @var{class}) can meet the constraint given in the pattern, the
2457 value returned by these macros is used for the class of the scratch
2458 register. Otherwise, two additional reload registers are required.
2459 Their classes are obtained from the constraints in the insn pattern.
2461 @var{x} might be a pseudo-register or a @code{subreg} of a
2462 pseudo-register, which could either be in a hard register or in memory.
2463 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2464 in memory and the hard register number if it is in a register.
2466 These macros should not be used in the case where a particular class of
2467 registers can only be copied to memory and not to another class of
2468 registers. In that case, secondary reload registers are not needed and
2469 would not be helpful. Instead, a stack location must be used to perform
2470 the copy and the @code{mov@var{m}} pattern should use memory as an
2471 intermediate storage. This case often occurs between floating-point and
2475 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2476 Certain machines have the property that some registers cannot be copied
2477 to some other registers without using memory. Define this macro on
2478 those machines to be a C expression that is nonzero if objects of mode
2479 @var{m} in registers of @var{class1} can only be copied to registers of
2480 class @var{class2} by storing a register of @var{class1} into memory
2481 and loading that memory location into a register of @var{class2}.
2483 Do not define this macro if its value would always be zero.
2486 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2487 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2488 allocates a stack slot for a memory location needed for register copies.
2489 If this macro is defined, the compiler instead uses the memory location
2490 defined by this macro.
2492 Do not define this macro if you do not define
2493 @code{SECONDARY_MEMORY_NEEDED}.
2496 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2497 When the compiler needs a secondary memory location to copy between two
2498 registers of mode @var{mode}, it normally allocates sufficient memory to
2499 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2500 load operations in a mode that many bits wide and whose class is the
2501 same as that of @var{mode}.
2503 This is right thing to do on most machines because it ensures that all
2504 bits of the register are copied and prevents accesses to the registers
2505 in a narrower mode, which some machines prohibit for floating-point
2508 However, this default behavior is not correct on some machines, such as
2509 the DEC Alpha, that store short integers in floating-point registers
2510 differently than in integer registers. On those machines, the default
2511 widening will not work correctly and you must define this macro to
2512 suppress that widening in some cases. See the file @file{alpha.h} for
2515 Do not define this macro if you do not define
2516 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2517 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2520 @defmac SMALL_REGISTER_CLASSES
2521 On some machines, it is risky to let hard registers live across arbitrary
2522 insns. Typically, these machines have instructions that require values
2523 to be in specific registers (like an accumulator), and reload will fail
2524 if the required hard register is used for another purpose across such an
2527 Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero
2528 value on these machines. When this macro has a nonzero value, the
2529 compiler will try to minimize the lifetime of hard registers.
2531 It is always safe to define this macro with a nonzero value, but if you
2532 unnecessarily define it, you will reduce the amount of optimizations
2533 that can be performed in some cases. If you do not define this macro
2534 with a nonzero value when it is required, the compiler will run out of
2535 spill registers and print a fatal error message. For most machines, you
2536 should not define this macro at all.
2539 @defmac CLASS_LIKELY_SPILLED_P (@var{class})
2540 A C expression whose value is nonzero if pseudos that have been assigned
2541 to registers of class @var{class} would likely be spilled because
2542 registers of @var{class} are needed for spill registers.
2544 The default value of this macro returns 1 if @var{class} has exactly one
2545 register and zero otherwise. On most machines, this default should be
2546 used. Only define this macro to some other expression if pseudos
2547 allocated by @file{local-alloc.c} end up in memory because their hard
2548 registers were needed for spill registers. If this macro returns nonzero
2549 for those classes, those pseudos will only be allocated by
2550 @file{global.c}, which knows how to reallocate the pseudo to another
2551 register. If there would not be another register available for
2552 reallocation, you should not change the definition of this macro since
2553 the only effect of such a definition would be to slow down register
2557 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2558 A C expression for the maximum number of consecutive registers
2559 of class @var{class} needed to hold a value of mode @var{mode}.
2561 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2562 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2563 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2564 @var{mode})} for all @var{regno} values in the class @var{class}.
2566 This macro helps control the handling of multiple-word values
2570 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2571 If defined, a C expression that returns nonzero for a @var{class} for which
2572 a change from mode @var{from} to mode @var{to} is invalid.
2574 For the example, loading 32-bit integer or floating-point objects into
2575 floating-point registers on the Alpha extends them to 64 bits.
2576 Therefore loading a 64-bit object and then storing it as a 32-bit object
2577 does not store the low-order 32 bits, as would be the case for a normal
2578 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2582 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2583 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2584 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2588 Three other special macros describe which operands fit which constraint
2591 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2592 A C expression that defines the machine-dependent operand constraint
2593 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2594 particular ranges of integer values. If @var{c} is one of those
2595 letters, the expression should check that @var{value}, an integer, is in
2596 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2597 not one of those letters, the value should be 0 regardless of
2601 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2602 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2603 string passed in @var{str}, so that you can use suffixes to distinguish
2604 between different variants.
2607 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
2608 A C expression that defines the machine-dependent operand constraint
2609 letters that specify particular ranges of @code{const_double} values
2610 (@samp{G} or @samp{H}).
2612 If @var{c} is one of those letters, the expression should check that
2613 @var{value}, an RTX of code @code{const_double}, is in the appropriate
2614 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
2615 letters, the value should be 0 regardless of @var{value}.
2617 @code{const_double} is used for all floating-point constants and for
2618 @code{DImode} fixed-point constants. A given letter can accept either
2619 or both kinds of values. It can use @code{GET_MODE} to distinguish
2620 between these kinds.
2623 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2624 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
2625 string passed in @var{str}, so that you can use suffixes to distinguish
2626 between different variants.
2629 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
2630 A C expression that defines the optional machine-dependent constraint
2631 letters that can be used to segregate specific types of operands, usually
2632 memory references, for the target machine. Any letter that is not
2633 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
2634 @code{REG_CLASS_FROM_CONSTRAINT}
2635 may be used. Normally this macro will not be defined.
2637 If it is required for a particular target machine, it should return 1
2638 if @var{value} corresponds to the operand type represented by the
2639 constraint letter @var{c}. If @var{c} is not defined as an extra
2640 constraint, the value returned should be 0 regardless of @var{value}.
2642 For example, on the ROMP, load instructions cannot have their output
2643 in r0 if the memory reference contains a symbolic address. Constraint
2644 letter @samp{Q} is defined as representing a memory address that does
2645 @emph{not} contain a symbolic address. An alternative is specified with
2646 a @samp{Q} constraint on the input and @samp{r} on the output. The next
2647 alternative specifies @samp{m} on the input and a register class that
2648 does not include r0 on the output.
2651 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
2652 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
2653 in @var{str}, so that you can use suffixes to distinguish between different
2657 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
2658 A C expression that defines the optional machine-dependent constraint
2659 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
2660 be treated like memory constraints by the reload pass.
2662 It should return 1 if the operand type represented by the constraint
2663 at the start of @var{str}, the first letter of which is the letter @var{c},
2664 comprises a subset of all memory references including
2665 all those whose address is simply a base register. This allows the reload
2666 pass to reload an operand, if it does not directly correspond to the operand
2667 type of @var{c}, by copying its address into a base register.
2669 For example, on the S/390, some instructions do not accept arbitrary
2670 memory references, but only those that do not make use of an index
2671 register. The constraint letter @samp{Q} is defined via
2672 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
2673 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
2674 a @samp{Q} constraint can handle any memory operand, because the
2675 reload pass knows it can be reloaded by copying the memory address
2676 into a base register if required. This is analogous to the way
2677 a @samp{o} constraint can handle any memory operand.
2680 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
2681 A C expression that defines the optional machine-dependent constraint
2682 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
2683 @code{EXTRA_CONSTRAINT_STR}, that should
2684 be treated like address constraints by the reload pass.
2686 It should return 1 if the operand type represented by the constraint
2687 at the start of @var{str}, which starts with the letter @var{c}, comprises
2688 a subset of all memory addresses including
2689 all those that consist of just a base register. This allows the reload
2690 pass to reload an operand, if it does not directly correspond to the operand
2691 type of @var{str}, by copying it into a base register.
2693 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
2694 be used with the @code{address_operand} predicate. It is treated
2695 analogously to the @samp{p} constraint.
2698 @node Stack and Calling
2699 @section Stack Layout and Calling Conventions
2700 @cindex calling conventions
2702 @c prevent bad page break with this line
2703 This describes the stack layout and calling conventions.
2707 * Exception Handling::
2712 * Register Arguments::
2714 * Aggregate Return::
2719 * Stack Smashing Protection::
2723 @subsection Basic Stack Layout
2724 @cindex stack frame layout
2725 @cindex frame layout
2727 @c prevent bad page break with this line
2728 Here is the basic stack layout.
2730 @defmac STACK_GROWS_DOWNWARD
2731 Define this macro if pushing a word onto the stack moves the stack
2732 pointer to a smaller address.
2734 When we say, ``define this macro if @dots{}'', it means that the
2735 compiler checks this macro only with @code{#ifdef} so the precise
2736 definition used does not matter.
2739 @defmac STACK_PUSH_CODE
2740 This macro defines the operation used when something is pushed
2741 on the stack. In RTL, a push operation will be
2742 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
2744 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
2745 and @code{POST_INC}. Which of these is correct depends on
2746 the stack direction and on whether the stack pointer points
2747 to the last item on the stack or whether it points to the
2748 space for the next item on the stack.
2750 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
2751 defined, which is almost always right, and @code{PRE_INC} otherwise,
2752 which is often wrong.
2755 @defmac FRAME_GROWS_DOWNWARD
2756 Define this macro to non-zero value if the addresses of local variable slots
2757 are at negative offsets from the frame pointer.
2760 @defmac ARGS_GROW_DOWNWARD
2761 Define this macro if successive arguments to a function occupy decreasing
2762 addresses on the stack.
2765 @defmac STARTING_FRAME_OFFSET
2766 Offset from the frame pointer to the first local variable slot to be allocated.
2768 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
2769 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
2770 Otherwise, it is found by adding the length of the first slot to the
2771 value @code{STARTING_FRAME_OFFSET}.
2772 @c i'm not sure if the above is still correct.. had to change it to get
2773 @c rid of an overfull. --mew 2feb93
2776 @defmac STACK_ALIGNMENT_NEEDED
2777 Define to zero to disable final alignment of the stack during reload.
2778 The nonzero default for this macro is suitable for most ports.
2780 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
2781 is a register save block following the local block that doesn't require
2782 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
2783 stack alignment and do it in the backend.
2786 @defmac STACK_POINTER_OFFSET
2787 Offset from the stack pointer register to the first location at which
2788 outgoing arguments are placed. If not specified, the default value of
2789 zero is used. This is the proper value for most machines.
2791 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2792 the first location at which outgoing arguments are placed.
2795 @defmac FIRST_PARM_OFFSET (@var{fundecl})
2796 Offset from the argument pointer register to the first argument's
2797 address. On some machines it may depend on the data type of the
2800 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2801 the first argument's address.
2804 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
2805 Offset from the stack pointer register to an item dynamically allocated
2806 on the stack, e.g., by @code{alloca}.
2808 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
2809 length of the outgoing arguments. The default is correct for most
2810 machines. See @file{function.c} for details.
2813 @defmac INITIAL_FRAME_ADDRESS_RTX
2814 A C expression whose value is RTL representing the address of the initial
2815 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
2816 @code{DYNAMIC_CHAIN_ADDRESS}.
2817 If you don't define this macro, the default is to return
2818 @code{hard_frame_pointer_rtx}.
2819 This default is usually correct unless @code{-fomit-frame-pointer} is in
2821 Define this macro in order to make @code{__builtin_frame_address (0)} and
2822 @code{__builtin_return_address (0)} work even in absence of a hard frame pointer.
2825 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
2826 A C expression whose value is RTL representing the address in a stack
2827 frame where the pointer to the caller's frame is stored. Assume that
2828 @var{frameaddr} is an RTL expression for the address of the stack frame
2831 If you don't define this macro, the default is to return the value
2832 of @var{frameaddr}---that is, the stack frame address is also the
2833 address of the stack word that points to the previous frame.
2836 @defmac SETUP_FRAME_ADDRESSES
2837 If defined, a C expression that produces the machine-specific code to
2838 setup the stack so that arbitrary frames can be accessed. For example,
2839 on the SPARC, we must flush all of the register windows to the stack
2840 before we can access arbitrary stack frames. You will seldom need to
2844 @deftypefn {Target Hook} bool TARGET_BUILTIN_SETJMP_FRAME_VALUE ()
2845 This target hook should return an rtx that is used to store
2846 the address of the current frame into the built in @code{setjmp} buffer.
2847 The default value, @code{virtual_stack_vars_rtx}, is correct for most
2848 machines. One reason you may need to define this target hook is if
2849 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
2852 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
2853 A C expression whose value is RTL representing the value of the return
2854 address for the frame @var{count} steps up from the current frame, after
2855 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
2856 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
2857 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
2859 The value of the expression must always be the correct address when
2860 @var{count} is zero, but may be @code{NULL_RTX} if there is not way to
2861 determine the return address of other frames.
2864 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
2865 Define this if the return address of a particular stack frame is accessed
2866 from the frame pointer of the previous stack frame.
2869 @defmac INCOMING_RETURN_ADDR_RTX
2870 A C expression whose value is RTL representing the location of the
2871 incoming return address at the beginning of any function, before the
2872 prologue. This RTL is either a @code{REG}, indicating that the return
2873 value is saved in @samp{REG}, or a @code{MEM} representing a location in
2876 You only need to define this macro if you want to support call frame
2877 debugging information like that provided by DWARF 2.
2879 If this RTL is a @code{REG}, you should also define
2880 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
2883 @defmac DWARF_ALT_FRAME_RETURN_COLUMN
2884 A C expression whose value is an integer giving a DWARF 2 column
2885 number that may be used as an alternate return column. This should
2886 be defined only if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
2887 general register, but an alternate column needs to be used for
2891 @defmac DWARF_ZERO_REG
2892 A C expression whose value is an integer giving a DWARF 2 register
2893 number that is considered to always have the value zero. This should
2894 only be defined if the target has an architected zero register, and
2895 someone decided it was a good idea to use that register number to
2896 terminate the stack backtrace. New ports should avoid this.
2899 @deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index})
2900 This target hook allows the backend to emit frame-related insns that
2901 contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
2902 info engine will invoke it on insns of the form
2904 (set (reg) (unspec [...] UNSPEC_INDEX))
2908 (set (reg) (unspec_volatile [...] UNSPECV_INDEX)).
2910 to let the backend emit the call frame instructions. @var{label} is
2911 the CFI label attached to the insn, @var{pattern} is the pattern of
2912 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
2915 @defmac INCOMING_FRAME_SP_OFFSET
2916 A C expression whose value is an integer giving the offset, in bytes,
2917 from the value of the stack pointer register to the top of the stack
2918 frame at the beginning of any function, before the prologue. The top of
2919 the frame is defined to be the value of the stack pointer in the
2920 previous frame, just before the call instruction.
2922 You only need to define this macro if you want to support call frame
2923 debugging information like that provided by DWARF 2.
2926 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
2927 A C expression whose value is an integer giving the offset, in bytes,
2928 from the argument pointer to the canonical frame address (cfa). The
2929 final value should coincide with that calculated by
2930 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
2931 during virtual register instantiation.
2933 The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)},
2934 which is correct for most machines; in general, the arguments are found
2935 immediately before the stack frame. Note that this is not the case on
2936 some targets that save registers into the caller's frame, such as SPARC
2937 and rs6000, and so such targets need to define this macro.
2939 You only need to define this macro if the default is incorrect, and you
2940 want to support call frame debugging information like that provided by
2944 @node Exception Handling
2945 @subsection Exception Handling Support
2946 @cindex exception handling
2948 @defmac EH_RETURN_DATA_REGNO (@var{N})
2949 A C expression whose value is the @var{N}th register number used for
2950 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
2951 @var{N} registers are usable.
2953 The exception handling library routines communicate with the exception
2954 handlers via a set of agreed upon registers. Ideally these registers
2955 should be call-clobbered; it is possible to use call-saved registers,
2956 but may negatively impact code size. The target must support at least
2957 2 data registers, but should define 4 if there are enough free registers.
2959 You must define this macro if you want to support call frame exception
2960 handling like that provided by DWARF 2.
2963 @defmac EH_RETURN_STACKADJ_RTX
2964 A C expression whose value is RTL representing a location in which
2965 to store a stack adjustment to be applied before function return.
2966 This is used to unwind the stack to an exception handler's call frame.
2967 It will be assigned zero on code paths that return normally.
2969 Typically this is a call-clobbered hard register that is otherwise
2970 untouched by the epilogue, but could also be a stack slot.
2972 Do not define this macro if the stack pointer is saved and restored
2973 by the regular prolog and epilog code in the call frame itself; in
2974 this case, the exception handling library routines will update the
2975 stack location to be restored in place. Otherwise, you must define
2976 this macro if you want to support call frame exception handling like
2977 that provided by DWARF 2.
2980 @defmac EH_RETURN_HANDLER_RTX
2981 A C expression whose value is RTL representing a location in which
2982 to store the address of an exception handler to which we should
2983 return. It will not be assigned on code paths that return normally.
2985 Typically this is the location in the call frame at which the normal
2986 return address is stored. For targets that return by popping an
2987 address off the stack, this might be a memory address just below
2988 the @emph{target} call frame rather than inside the current call
2989 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
2990 been assigned, so it may be used to calculate the location of the
2993 Some targets have more complex requirements than storing to an
2994 address calculable during initial code generation. In that case
2995 the @code{eh_return} instruction pattern should be used instead.
2997 If you want to support call frame exception handling, you must
2998 define either this macro or the @code{eh_return} instruction pattern.
3001 @defmac RETURN_ADDR_OFFSET
3002 If defined, an integer-valued C expression for which rtl will be generated
3003 to add it to the exception handler address before it is searched in the
3004 exception handling tables, and to subtract it again from the address before
3005 using it to return to the exception handler.
3008 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3009 This macro chooses the encoding of pointers embedded in the exception
3010 handling sections. If at all possible, this should be defined such
3011 that the exception handling section will not require dynamic relocations,
3012 and so may be read-only.
3014 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3015 @var{global} is true if the symbol may be affected by dynamic relocations.
3016 The macro should return a combination of the @code{DW_EH_PE_*} defines
3017 as found in @file{dwarf2.h}.
3019 If this macro is not defined, pointers will not be encoded but
3020 represented directly.
3023 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3024 This macro allows the target to emit whatever special magic is required
3025 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3026 Generic code takes care of pc-relative and indirect encodings; this must
3027 be defined if the target uses text-relative or data-relative encodings.
3029 This is a C statement that branches to @var{done} if the format was
3030 handled. @var{encoding} is the format chosen, @var{size} is the number
3031 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3035 @defmac MD_UNWIND_SUPPORT
3036 A string specifying a file to be #include'd in unwind-dw2.c. The file
3037 so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}.
3040 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
3041 This macro allows the target to add cpu and operating system specific
3042 code to the call-frame unwinder for use when there is no unwind data
3043 available. The most common reason to implement this macro is to unwind
3044 through signal frames.
3046 This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c}
3047 and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3048 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3049 for the address of the code being executed and @code{context->cfa} for
3050 the stack pointer value. If the frame can be decoded, the register save
3051 addresses should be updated in @var{fs} and the macro should evaluate to
3052 @code{_URC_NO_REASON}. If the frame cannot be decoded, the macro should
3053 evaluate to @code{_URC_END_OF_STACK}.
3055 For proper signal handling in Java this macro is accompanied by
3056 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3059 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
3060 This macro allows the target to add operating system specific code to the
3061 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
3062 usually used for signal or interrupt frames.
3064 This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}.
3065 @var{context} is an @code{_Unwind_Context};
3066 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
3067 for the abi and context in the @code{.unwabi} directive. If the
3068 @code{.unwabi} directive can be handled, the register save addresses should
3069 be updated in @var{fs}.
3072 @defmac TARGET_USES_WEAK_UNWIND_INFO
3073 A C expression that evaluates to true if the target requires unwind
3074 info to be given comdat linkage. Define it to be @code{1} if comdat
3075 linkage is necessary. The default is @code{0}.
3078 @node Stack Checking
3079 @subsection Specifying How Stack Checking is Done
3081 GCC will check that stack references are within the boundaries of
3082 the stack, if the @option{-fstack-check} is specified, in one of three ways:
3086 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3087 will assume that you have arranged for stack checking to be done at
3088 appropriate places in the configuration files, e.g., in
3089 @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special
3093 If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern
3094 called @code{check_stack} in your @file{md} file, GCC will call that
3095 pattern with one argument which is the address to compare the stack
3096 value against. You must arrange for this pattern to report an error if
3097 the stack pointer is out of range.
3100 If neither of the above are true, GCC will generate code to periodically
3101 ``probe'' the stack pointer using the values of the macros defined below.
3104 Normally, you will use the default values of these macros, so GCC
3105 will use the third approach.
3107 @defmac STACK_CHECK_BUILTIN
3108 A nonzero value if stack checking is done by the configuration files in a
3109 machine-dependent manner. You should define this macro if stack checking
3110 is require by the ABI of your machine or if you would like to have to stack
3111 checking in some more efficient way than GCC's portable approach.
3112 The default value of this macro is zero.
3115 @defmac STACK_CHECK_PROBE_INTERVAL
3116 An integer representing the interval at which GCC must generate stack
3117 probe instructions. You will normally define this macro to be no larger
3118 than the size of the ``guard pages'' at the end of a stack area. The
3119 default value of 4096 is suitable for most systems.
3122 @defmac STACK_CHECK_PROBE_LOAD
3123 A integer which is nonzero if GCC should perform the stack probe
3124 as a load instruction and zero if GCC should use a store instruction.
3125 The default is zero, which is the most efficient choice on most systems.
3128 @defmac STACK_CHECK_PROTECT
3129 The number of bytes of stack needed to recover from a stack overflow,
3130 for languages where such a recovery is supported. The default value of
3131 75 words should be adequate for most machines.
3134 @defmac STACK_CHECK_MAX_FRAME_SIZE
3135 The maximum size of a stack frame, in bytes. GCC will generate probe
3136 instructions in non-leaf functions to ensure at least this many bytes of
3137 stack are available. If a stack frame is larger than this size, stack
3138 checking will not be reliable and GCC will issue a warning. The
3139 default is chosen so that GCC only generates one instruction on most
3140 systems. You should normally not change the default value of this macro.
3143 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3144 GCC uses this value to generate the above warning message. It
3145 represents the amount of fixed frame used by a function, not including
3146 space for any callee-saved registers, temporaries and user variables.
3147 You need only specify an upper bound for this amount and will normally
3148 use the default of four words.
3151 @defmac STACK_CHECK_MAX_VAR_SIZE
3152 The maximum size, in bytes, of an object that GCC will place in the
3153 fixed area of the stack frame when the user specifies
3154 @option{-fstack-check}.
3155 GCC computed the default from the values of the above macros and you will
3156 normally not need to override that default.
3160 @node Frame Registers
3161 @subsection Registers That Address the Stack Frame
3163 @c prevent bad page break with this line
3164 This discusses registers that address the stack frame.
3166 @defmac STACK_POINTER_REGNUM
3167 The register number of the stack pointer register, which must also be a
3168 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3169 the hardware determines which register this is.
3172 @defmac FRAME_POINTER_REGNUM
3173 The register number of the frame pointer register, which is used to
3174 access automatic variables in the stack frame. On some machines, the
3175 hardware determines which register this is. On other machines, you can
3176 choose any register you wish for this purpose.
3179 @defmac HARD_FRAME_POINTER_REGNUM
3180 On some machines the offset between the frame pointer and starting
3181 offset of the automatic variables is not known until after register
3182 allocation has been done (for example, because the saved registers are
3183 between these two locations). On those machines, define
3184 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3185 be used internally until the offset is known, and define
3186 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3187 used for the frame pointer.
3189 You should define this macro only in the very rare circumstances when it
3190 is not possible to calculate the offset between the frame pointer and
3191 the automatic variables until after register allocation has been
3192 completed. When this macro is defined, you must also indicate in your
3193 definition of @code{ELIMINABLE_REGS} how to eliminate
3194 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3195 or @code{STACK_POINTER_REGNUM}.
3197 Do not define this macro if it would be the same as
3198 @code{FRAME_POINTER_REGNUM}.
3201 @defmac ARG_POINTER_REGNUM
3202 The register number of the arg pointer register, which is used to access
3203 the function's argument list. On some machines, this is the same as the
3204 frame pointer register. On some machines, the hardware determines which
3205 register this is. On other machines, you can choose any register you
3206 wish for this purpose. If this is not the same register as the frame
3207 pointer register, then you must mark it as a fixed register according to
3208 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3209 (@pxref{Elimination}).
3212 @defmac RETURN_ADDRESS_POINTER_REGNUM
3213 The register number of the return address pointer register, which is used to
3214 access the current function's return address from the stack. On some
3215 machines, the return address is not at a fixed offset from the frame
3216 pointer or stack pointer or argument pointer. This register can be defined
3217 to point to the return address on the stack, and then be converted by
3218 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3220 Do not define this macro unless there is no other way to get the return
3221 address from the stack.
3224 @defmac STATIC_CHAIN_REGNUM
3225 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3226 Register numbers used for passing a function's static chain pointer. If
3227 register windows are used, the register number as seen by the called
3228 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3229 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3230 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3233 The static chain register need not be a fixed register.
3235 If the static chain is passed in memory, these macros should not be
3236 defined; instead, the next two macros should be defined.
3239 @defmac STATIC_CHAIN
3240 @defmacx STATIC_CHAIN_INCOMING
3241 If the static chain is passed in memory, these macros provide rtx giving
3242 @code{mem} expressions that denote where they are stored.
3243 @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations
3244 as seen by the calling and called functions, respectively. Often the former
3245 will be at an offset from the stack pointer and the latter at an offset from
3248 @findex stack_pointer_rtx
3249 @findex frame_pointer_rtx
3250 @findex arg_pointer_rtx
3251 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3252 @code{arg_pointer_rtx} will have been initialized prior to the use of these
3253 macros and should be used to refer to those items.
3255 If the static chain is passed in a register, the two previous macros should
3259 @defmac DWARF_FRAME_REGISTERS
3260 This macro specifies the maximum number of hard registers that can be
3261 saved in a call frame. This is used to size data structures used in
3262 DWARF2 exception handling.
3264 Prior to GCC 3.0, this macro was needed in order to establish a stable
3265 exception handling ABI in the face of adding new hard registers for ISA
3266 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3267 in the number of hard registers. Nevertheless, this macro can still be
3268 used to reduce the runtime memory requirements of the exception handling
3269 routines, which can be substantial if the ISA contains a lot of
3270 registers that are not call-saved.
3272 If this macro is not defined, it defaults to
3273 @code{FIRST_PSEUDO_REGISTER}.
3276 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3278 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3279 for backward compatibility in pre GCC 3.0 compiled code.
3281 If this macro is not defined, it defaults to
3282 @code{DWARF_FRAME_REGISTERS}.
3285 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3287 Define this macro if the target's representation for dwarf registers
3288 is different than the internal representation for unwind column.
3289 Given a dwarf register, this macro should return the internal unwind
3290 column number to use instead.
3292 See the PowerPC's SPE target for an example.
3295 @defmac DWARF_FRAME_REGNUM (@var{regno})
3297 Define this macro if the target's representation for dwarf registers
3298 used in .eh_frame or .debug_frame is different from that used in other
3299 debug info sections. Given a GCC hard register number, this macro
3300 should return the .eh_frame register number. The default is
3301 @code{DBX_REGISTER_NUMBER (@var{regno})}.
3305 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
3307 Define this macro to map register numbers held in the call frame info
3308 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
3309 should be output in .debug_frame (@code{@var{for_eh}} is zero) and
3310 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to
3311 return @code{@var{regno}}.
3316 @subsection Eliminating Frame Pointer and Arg Pointer
3318 @c prevent bad page break with this line
3319 This is about eliminating the frame pointer and arg pointer.
3321 @defmac FRAME_POINTER_REQUIRED
3322 A C expression which is nonzero if a function must have and use a frame
3323 pointer. This expression is evaluated in the reload pass. If its value is
3324 nonzero the function will have a frame pointer.
3326 The expression can in principle examine the current function and decide
3327 according to the facts, but on most machines the constant 0 or the
3328 constant 1 suffices. Use 0 when the machine allows code to be generated
3329 with no frame pointer, and doing so saves some time or space. Use 1
3330 when there is no possible advantage to avoiding a frame pointer.
3332 In certain cases, the compiler does not know how to produce valid code
3333 without a frame pointer. The compiler recognizes those cases and
3334 automatically gives the function a frame pointer regardless of what
3335 @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about
3338 In a function that does not require a frame pointer, the frame pointer
3339 register can be allocated for ordinary usage, unless you mark it as a
3340 fixed register. See @code{FIXED_REGISTERS} for more information.
3343 @findex get_frame_size
3344 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3345 A C statement to store in the variable @var{depth-var} the difference
3346 between the frame pointer and the stack pointer values immediately after
3347 the function prologue. The value would be computed from information
3348 such as the result of @code{get_frame_size ()} and the tables of
3349 registers @code{regs_ever_live} and @code{call_used_regs}.
3351 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3352 need not be defined. Otherwise, it must be defined even if
3353 @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that
3354 case, you may set @var{depth-var} to anything.
3357 @defmac ELIMINABLE_REGS
3358 If defined, this macro specifies a table of register pairs used to
3359 eliminate unneeded registers that point into the stack frame. If it is not
3360 defined, the only elimination attempted by the compiler is to replace
3361 references to the frame pointer with references to the stack pointer.
3363 The definition of this macro is a list of structure initializations, each
3364 of which specifies an original and replacement register.
3366 On some machines, the position of the argument pointer is not known until
3367 the compilation is completed. In such a case, a separate hard register
3368 must be used for the argument pointer. This register can be eliminated by
3369 replacing it with either the frame pointer or the argument pointer,
3370 depending on whether or not the frame pointer has been eliminated.
3372 In this case, you might specify:
3374 #define ELIMINABLE_REGS \
3375 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3376 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3377 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3380 Note that the elimination of the argument pointer with the stack pointer is
3381 specified first since that is the preferred elimination.
3384 @defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg})
3385 A C expression that returns nonzero if the compiler is allowed to try
3386 to replace register number @var{from-reg} with register number
3387 @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS}
3388 is defined, and will usually be the constant 1, since most of the cases
3389 preventing register elimination are things that the compiler already
3393 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3394 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3395 specifies the initial difference between the specified pair of
3396 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3400 @node Stack Arguments
3401 @subsection Passing Function Arguments on the Stack
3402 @cindex arguments on stack
3403 @cindex stack arguments
3405 The macros in this section control how arguments are passed
3406 on the stack. See the following section for other macros that
3407 control passing certain arguments in registers.
3409 @deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (tree @var{fntype})
3410 This target hook returns @code{true} if an argument declared in a
3411 prototype as an integral type smaller than @code{int} should actually be
3412 passed as an @code{int}. In addition to avoiding errors in certain
3413 cases of mismatch, it also makes for better code on certain machines.
3414 The default is to not promote prototypes.
3418 A C expression. If nonzero, push insns will be used to pass
3420 If the target machine does not have a push instruction, set it to zero.
3421 That directs GCC to use an alternate strategy: to
3422 allocate the entire argument block and then store the arguments into
3423 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3426 @defmac PUSH_ARGS_REVERSED
3427 A C expression. If nonzero, function arguments will be evaluated from
3428 last to first, rather than from first to last. If this macro is not
3429 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3430 and args grow in opposite directions, and 0 otherwise.
3433 @defmac PUSH_ROUNDING (@var{npushed})
3434 A C expression that is the number of bytes actually pushed onto the
3435 stack when an instruction attempts to push @var{npushed} bytes.
3437 On some machines, the definition
3440 #define PUSH_ROUNDING(BYTES) (BYTES)
3444 will suffice. But on other machines, instructions that appear
3445 to push one byte actually push two bytes in an attempt to maintain
3446 alignment. Then the definition should be
3449 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3453 @findex current_function_outgoing_args_size
3454 @defmac ACCUMULATE_OUTGOING_ARGS
3455 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3456 will be computed and placed into the variable
3457 @code{current_function_outgoing_args_size}. No space will be pushed
3458 onto the stack for each call; instead, the function prologue should
3459 increase the stack frame size by this amount.
3461 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3465 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3466 Define this macro if functions should assume that stack space has been
3467 allocated for arguments even when their values are passed in
3470 The value of this macro is the size, in bytes, of the area reserved for
3471 arguments passed in registers for the function represented by @var{fndecl},
3472 which can be zero if GCC is calling a library function.
3474 This space can be allocated by the caller, or be a part of the
3475 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3478 @c above is overfull. not sure what to do. --mew 5feb93 did
3479 @c something, not sure if it looks good. --mew 10feb93
3481 @defmac OUTGOING_REG_PARM_STACK_SPACE
3482 Define this if it is the responsibility of the caller to allocate the area
3483 reserved for arguments passed in registers.
3485 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3486 whether the space for these arguments counts in the value of
3487 @code{current_function_outgoing_args_size}.
3490 @defmac STACK_PARMS_IN_REG_PARM_AREA
3491 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3492 stack parameters don't skip the area specified by it.
3493 @c i changed this, makes more sens and it should have taken care of the
3494 @c overfull.. not as specific, tho. --mew 5feb93
3496 Normally, when a parameter is not passed in registers, it is placed on the
3497 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3498 suppresses this behavior and causes the parameter to be passed on the
3499 stack in its natural location.
3502 @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size})
3503 A C expression that should indicate the number of bytes of its own
3504 arguments that a function pops on returning, or 0 if the
3505 function pops no arguments and the caller must therefore pop them all
3506 after the function returns.
3508 @var{fundecl} is a C variable whose value is a tree node that describes
3509 the function in question. Normally it is a node of type
3510 @code{FUNCTION_DECL} that describes the declaration of the function.
3511 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3513 @var{funtype} is a C variable whose value is a tree node that
3514 describes the function in question. Normally it is a node of type
3515 @code{FUNCTION_TYPE} that describes the data type of the function.
3516 From this it is possible to obtain the data types of the value and
3517 arguments (if known).
3519 When a call to a library function is being considered, @var{fundecl}
3520 will contain an identifier node for the library function. Thus, if
3521 you need to distinguish among various library functions, you can do so
3522 by their names. Note that ``library function'' in this context means
3523 a function used to perform arithmetic, whose name is known specially
3524 in the compiler and was not mentioned in the C code being compiled.
3526 @var{stack-size} is the number of bytes of arguments passed on the
3527 stack. If a variable number of bytes is passed, it is zero, and
3528 argument popping will always be the responsibility of the calling function.
3530 On the VAX, all functions always pop their arguments, so the definition
3531 of this macro is @var{stack-size}. On the 68000, using the standard
3532 calling convention, no functions pop their arguments, so the value of
3533 the macro is always 0 in this case. But an alternative calling
3534 convention is available in which functions that take a fixed number of
3535 arguments pop them but other functions (such as @code{printf}) pop
3536 nothing (the caller pops all). When this convention is in use,
3537 @var{funtype} is examined to determine whether a function takes a fixed
3538 number of arguments.
3541 @defmac CALL_POPS_ARGS (@var{cum})
3542 A C expression that should indicate the number of bytes a call sequence
3543 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3544 when compiling a function call.
3546 @var{cum} is the variable in which all arguments to the called function
3547 have been accumulated.
3549 On certain architectures, such as the SH5, a call trampoline is used
3550 that pops certain registers off the stack, depending on the arguments
3551 that have been passed to the function. Since this is a property of the
3552 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3556 @node Register Arguments
3557 @subsection Passing Arguments in Registers
3558 @cindex arguments in registers
3559 @cindex registers arguments
3561 This section describes the macros which let you control how various
3562 types of arguments are passed in registers or how they are arranged in
3565 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3566 A C expression that controls whether a function argument is passed
3567 in a register, and which register.
3569 The arguments are @var{cum}, which summarizes all the previous
3570 arguments; @var{mode}, the machine mode of the argument; @var{type},
3571 the data type of the argument as a tree node or 0 if that is not known
3572 (which happens for C support library functions); and @var{named},
3573 which is 1 for an ordinary argument and 0 for nameless arguments that
3574 correspond to @samp{@dots{}} in the called function's prototype.
3575 @var{type} can be an incomplete type if a syntax error has previously
3578 The value of the expression is usually either a @code{reg} RTX for the
3579 hard register in which to pass the argument, or zero to pass the
3580 argument on the stack.
3582 For machines like the VAX and 68000, where normally all arguments are
3583 pushed, zero suffices as a definition.
3585 The value of the expression can also be a @code{parallel} RTX@. This is
3586 used when an argument is passed in multiple locations. The mode of the
3587 @code{parallel} should be the mode of the entire argument. The
3588 @code{parallel} holds any number of @code{expr_list} pairs; each one
3589 describes where part of the argument is passed. In each
3590 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
3591 register in which to pass this part of the argument, and the mode of the
3592 register RTX indicates how large this part of the argument is. The
3593 second operand of the @code{expr_list} is a @code{const_int} which gives
3594 the offset in bytes into the entire argument of where this part starts.
3595 As a special exception the first @code{expr_list} in the @code{parallel}
3596 RTX may have a first operand of zero. This indicates that the entire
3597 argument is also stored on the stack.
3599 The last time this macro is called, it is called with @code{MODE ==
3600 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
3601 pattern as operands 2 and 3 respectively.
3603 @cindex @file{stdarg.h} and register arguments
3604 The usual way to make the ISO library @file{stdarg.h} work on a machine
3605 where some arguments are usually passed in registers, is to cause
3606 nameless arguments to be passed on the stack instead. This is done
3607 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
3609 @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
3610 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
3611 You may use the hook @code{targetm.calls.must_pass_in_stack}
3612 in the definition of this macro to determine if this argument is of a
3613 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
3614 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
3615 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
3616 defined, the argument will be computed in the stack and then loaded into
3620 @deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (enum machine_mode @var{mode}, tree @var{type})
3621 This target hook should return @code{true} if we should not pass @var{type}
3622 solely in registers. The file @file{expr.h} defines a
3623 definition that is usually appropriate, refer to @file{expr.h} for additional
3627 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3628 Define this macro if the target machine has ``register windows'', so
3629 that the register in which a function sees an arguments is not
3630 necessarily the same as the one in which the caller passed the
3633 For such machines, @code{FUNCTION_ARG} computes the register in which
3634 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
3635 be defined in a similar fashion to tell the function being called
3636 where the arguments will arrive.
3638 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
3639 serves both purposes.
3642 @deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
3643 This target hook returns the number of bytes at the beginning of an
3644 argument that must be put in registers. The value must be zero for
3645 arguments that are passed entirely in registers or that are entirely
3646 pushed on the stack.
3648 On some machines, certain arguments must be passed partially in
3649 registers and partially in memory. On these machines, typically the
3650 first few words of arguments are passed in registers, and the rest
3651 on the stack. If a multi-word argument (a @code{double} or a
3652 structure) crosses that boundary, its first few words must be passed
3653 in registers and the rest must be pushed. This macro tells the
3654 compiler when this occurs, and how many bytes should go in registers.
3656 @code{FUNCTION_ARG} for these arguments should return the first
3657 register to be used by the caller for this argument; likewise
3658 @code{FUNCTION_INCOMING_ARG}, for the called function.
3661 @deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
3662 This target hook should return @code{true} if an argument at the
3663 position indicated by @var{cum} should be passed by reference. This
3664 predicate is queried after target independent reasons for being
3665 passed by reference, such as @code{TREE_ADDRESSABLE (type)}.
3667 If the hook returns true, a copy of that argument is made in memory and a
3668 pointer to the argument is passed instead of the argument itself.
3669 The pointer is passed in whatever way is appropriate for passing a pointer
3673 @deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named})
3674 The function argument described by the parameters to this hook is
3675 known to be passed by reference. The hook should return true if the
3676 function argument should be copied by the callee instead of copied
3679 For any argument for which the hook returns true, if it can be
3680 determined that the argument is not modified, then a copy need
3683 The default version of this hook always returns false.
3686 @defmac CUMULATIVE_ARGS
3687 A C type for declaring a variable that is used as the first argument of
3688 @code{FUNCTION_ARG} and other related values. For some target machines,
3689 the type @code{int} suffices and can hold the number of bytes of
3692 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
3693 arguments that have been passed on the stack. The compiler has other
3694 variables to keep track of that. For target machines on which all
3695 arguments are passed on the stack, there is no need to store anything in
3696 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
3697 should not be empty, so use @code{int}.
3700 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
3701 A C statement (sans semicolon) for initializing the variable
3702 @var{cum} for the state at the beginning of the argument list. The
3703 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
3704 is the tree node for the data type of the function which will receive
3705 the args, or 0 if the args are to a compiler support library function.
3706 For direct calls that are not libcalls, @var{fndecl} contain the
3707 declaration node of the function. @var{fndecl} is also set when
3708 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
3709 being compiled. @var{n_named_args} is set to the number of named
3710 arguments, including a structure return address if it is passed as a
3711 parameter, when making a call. When processing incoming arguments,
3712 @var{n_named_args} is set to @minus{}1.
3714 When processing a call to a compiler support library function,
3715 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
3716 contains the name of the function, as a string. @var{libname} is 0 when
3717 an ordinary C function call is being processed. Thus, each time this
3718 macro is called, either @var{libname} or @var{fntype} is nonzero, but
3719 never both of them at once.
3722 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
3723 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
3724 it gets a @code{MODE} argument instead of @var{fntype}, that would be
3725 @code{NULL}. @var{indirect} would always be zero, too. If this macro
3726 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
3727 0)} is used instead.
3730 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
3731 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
3732 finding the arguments for the function being compiled. If this macro is
3733 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
3735 The value passed for @var{libname} is always 0, since library routines
3736 with special calling conventions are never compiled with GCC@. The
3737 argument @var{libname} exists for symmetry with
3738 @code{INIT_CUMULATIVE_ARGS}.
3739 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
3740 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
3743 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
3744 A C statement (sans semicolon) to update the summarizer variable
3745 @var{cum} to advance past an argument in the argument list. The
3746 values @var{mode}, @var{type} and @var{named} describe that argument.
3747 Once this is done, the variable @var{cum} is suitable for analyzing
3748 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
3750 This macro need not do anything if the argument in question was passed
3751 on the stack. The compiler knows how to track the amount of stack space
3752 used for arguments without any special help.
3755 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
3756 If defined, a C expression which determines whether, and in which direction,
3757 to pad out an argument with extra space. The value should be of type
3758 @code{enum direction}: either @code{upward} to pad above the argument,
3759 @code{downward} to pad below, or @code{none} to inhibit padding.
3761 The @emph{amount} of padding is always just enough to reach the next
3762 multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control
3765 This macro has a default definition which is right for most systems.
3766 For little-endian machines, the default is to pad upward. For
3767 big-endian machines, the default is to pad downward for an argument of
3768 constant size shorter than an @code{int}, and upward otherwise.
3771 @defmac PAD_VARARGS_DOWN
3772 If defined, a C expression which determines whether the default
3773 implementation of va_arg will attempt to pad down before reading the
3774 next argument, if that argument is smaller than its aligned space as
3775 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
3776 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
3779 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
3780 Specify padding for the last element of a block move between registers and
3781 memory. @var{first} is nonzero if this is the only element. Defining this
3782 macro allows better control of register function parameters on big-endian
3783 machines, without using @code{PARALLEL} rtl. In particular,
3784 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
3785 registers, as there is no longer a "wrong" part of a register; For example,
3786 a three byte aggregate may be passed in the high part of a register if so
3790 @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type})
3791 If defined, a C expression that gives the alignment boundary, in bits,
3792 of an argument with the specified mode and type. If it is not defined,
3793 @code{PARM_BOUNDARY} is used for all arguments.
3796 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
3797 A C expression that is nonzero if @var{regno} is the number of a hard
3798 register in which function arguments are sometimes passed. This does
3799 @emph{not} include implicit arguments such as the static chain and
3800 the structure-value address. On many machines, no registers can be
3801 used for this purpose since all function arguments are pushed on the
3805 @deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (tree @var{type})
3806 This hook should return true if parameter of type @var{type} are passed
3807 as two scalar parameters. By default, GCC will attempt to pack complex
3808 arguments into the target's word size. Some ABIs require complex arguments
3809 to be split and treated as their individual components. For example, on
3810 AIX64, complex floats should be passed in a pair of floating point
3811 registers, even though a complex float would fit in one 64-bit floating
3814 The default value of this hook is @code{NULL}, which is treated as always
3818 @deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void)
3819 This hook returns a type node for @code{va_list} for the target.
3820 The default version of the hook returns @code{void*}.
3823 @deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, tree *@var{pre_p}, tree *@var{post_p})
3824 This hook performs target-specific gimplification of
3825 @code{VA_ARG_EXPR}. The first two parameters correspond to the
3826 arguments to @code{va_arg}; the latter two are as in
3827 @code{gimplify.c:gimplify_expr}.
3830 @deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (enum machine_mode @var{mode})
3831 Define this to return nonzero if the port can handle pointers
3832 with machine mode @var{mode}. The default version of this
3833 hook returns true for both @code{ptr_mode} and @code{Pmode}.
3836 @deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
3837 Define this to return nonzero if the port is prepared to handle
3838 insns involving scalar mode @var{mode}. For a scalar mode to be
3839 considered supported, all the basic arithmetic and comparisons
3842 The default version of this hook returns true for any mode
3843 required to handle the basic C types (as defined by the port).
3844 Included here are the double-word arithmetic supported by the
3845 code in @file{optabs.c}.
3848 @deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (enum machine_mode @var{mode})
3849 Define this to return nonzero if the port is prepared to handle
3850 insns involving vector mode @var{mode}. At the very least, it
3851 must have move patterns for this mode.
3855 @subsection How Scalar Function Values Are Returned
3856 @cindex return values in registers
3857 @cindex values, returned by functions
3858 @cindex scalars, returned as values
3860 This section discusses the macros that control returning scalars as
3861 values---values that can fit in registers.
3863 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
3864 A C expression to create an RTX representing the place where a
3865 function returns a value of data type @var{valtype}. @var{valtype} is
3866 a tree node representing a data type. Write @code{TYPE_MODE
3867 (@var{valtype})} to get the machine mode used to represent that type.
3868 On many machines, only the mode is relevant. (Actually, on most
3869 machines, scalar values are returned in the same place regardless of
3872 The value of the expression is usually a @code{reg} RTX for the hard
3873 register where the return value is stored. The value can also be a
3874 @code{parallel} RTX, if the return value is in multiple places. See
3875 @code{FUNCTION_ARG} for an explanation of the @code{parallel} form.
3877 If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply the same
3878 promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a
3881 If the precise function being called is known, @var{func} is a tree
3882 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3883 pointer. This makes it possible to use a different value-returning
3884 convention for specific functions when all their calls are
3887 @code{FUNCTION_VALUE} is not used for return vales with aggregate data
3888 types, because these are returned in another way. See
3889 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
3892 @defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func})
3893 Define this macro if the target machine has ``register windows''
3894 so that the register in which a function returns its value is not
3895 the same as the one in which the caller sees the value.
3897 For such machines, @code{FUNCTION_VALUE} computes the register in which
3898 the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be
3899 defined in a similar fashion to tell the function where to put the
3902 If @code{FUNCTION_OUTGOING_VALUE} is not defined,
3903 @code{FUNCTION_VALUE} serves both purposes.
3905 @code{FUNCTION_OUTGOING_VALUE} is not used for return vales with
3906 aggregate data types, because these are returned in another way. See
3907 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
3910 @defmac LIBCALL_VALUE (@var{mode})
3911 A C expression to create an RTX representing the place where a library
3912 function returns a value of mode @var{mode}. If the precise function
3913 being called is known, @var{func} is a tree node
3914 (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3915 pointer. This makes it possible to use a different value-returning
3916 convention for specific functions when all their calls are
3919 Note that ``library function'' in this context means a compiler
3920 support routine, used to perform arithmetic, whose name is known
3921 specially by the compiler and was not mentioned in the C code being
3924 The definition of @code{LIBRARY_VALUE} need not be concerned aggregate
3925 data types, because none of the library functions returns such types.
3928 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
3929 A C expression that is nonzero if @var{regno} is the number of a hard
3930 register in which the values of called function may come back.
3932 A register whose use for returning values is limited to serving as the
3933 second of a pair (for a value of type @code{double}, say) need not be
3934 recognized by this macro. So for most machines, this definition
3938 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
3941 If the machine has register windows, so that the caller and the called
3942 function use different registers for the return value, this macro
3943 should recognize only the caller's register numbers.
3946 @defmac APPLY_RESULT_SIZE
3947 Define this macro if @samp{untyped_call} and @samp{untyped_return}
3948 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
3949 saving and restoring an arbitrary return value.
3952 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (tree @var{type})
3953 This hook should return true if values of type @var{type} are returned
3954 at the most significant end of a register (in other words, if they are
3955 padded at the least significant end). You can assume that @var{type}
3956 is returned in a register; the caller is required to check this.
3958 Note that the register provided by @code{FUNCTION_VALUE} must be able
3959 to hold the complete return value. For example, if a 1-, 2- or 3-byte
3960 structure is returned at the most significant end of a 4-byte register,
3961 @code{FUNCTION_VALUE} should provide an @code{SImode} rtx.
3964 @node Aggregate Return
3965 @subsection How Large Values Are Returned
3966 @cindex aggregates as return values
3967 @cindex large return values
3968 @cindex returning aggregate values
3969 @cindex structure value address
3971 When a function value's mode is @code{BLKmode} (and in some other
3972 cases), the value is not returned according to @code{FUNCTION_VALUE}
3973 (@pxref{Scalar Return}). Instead, the caller passes the address of a
3974 block of memory in which the value should be stored. This address
3975 is called the @dfn{structure value address}.
3977 This section describes how to control returning structure values in
3980 @deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (tree @var{type}, tree @var{fntype})
3981 This target hook should return a nonzero value to say to return the
3982 function value in memory, just as large structures are always returned.
3983 Here @var{type} will be the data type of the value, and @var{fntype}
3984 will be the type of the function doing the returning, or @code{NULL} for
3987 Note that values of mode @code{BLKmode} must be explicitly handled
3988 by this function. Also, the option @option{-fpcc-struct-return}
3989 takes effect regardless of this macro. On most systems, it is
3990 possible to leave the hook undefined; this causes a default
3991 definition to be used, whose value is the constant 1 for @code{BLKmode}
3992 values, and 0 otherwise.
3994 Do not use this hook to indicate that structures and unions should always
3995 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
3999 @defmac DEFAULT_PCC_STRUCT_RETURN
4000 Define this macro to be 1 if all structure and union return values must be
4001 in memory. Since this results in slower code, this should be defined
4002 only if needed for compatibility with other compilers or with an ABI@.
4003 If you define this macro to be 0, then the conventions used for structure
4004 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
4007 If not defined, this defaults to the value 1.
4010 @deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming})
4011 This target hook should return the location of the structure value
4012 address (normally a @code{mem} or @code{reg}), or 0 if the address is
4013 passed as an ``invisible'' first argument. Note that @var{fndecl} may
4014 be @code{NULL}, for libcalls. You do not need to define this target
4015 hook if the address is always passed as an ``invisible'' first
4018 On some architectures the place where the structure value address
4019 is found by the called function is not the same place that the
4020 caller put it. This can be due to register windows, or it could
4021 be because the function prologue moves it to a different place.
4022 @var{incoming} is @code{true} when the location is needed in
4023 the context of the called function, and @code{false} in the context of
4026 If @var{incoming} is @code{true} and the address is to be found on the
4027 stack, return a @code{mem} which refers to the frame pointer.
4030 @defmac PCC_STATIC_STRUCT_RETURN
4031 Define this macro if the usual system convention on the target machine
4032 for returning structures and unions is for the called function to return
4033 the address of a static variable containing the value.
4035 Do not define this if the usual system convention is for the caller to
4036 pass an address to the subroutine.
4038 This macro has effect in @option{-fpcc-struct-return} mode, but it does
4039 nothing when you use @option{-freg-struct-return} mode.
4043 @subsection Caller-Saves Register Allocation
4045 If you enable it, GCC can save registers around function calls. This
4046 makes it possible to use call-clobbered registers to hold variables that
4047 must live across calls.
4049 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
4050 A C expression to determine whether it is worthwhile to consider placing
4051 a pseudo-register in a call-clobbered hard register and saving and
4052 restoring it around each function call. The expression should be 1 when
4053 this is worth doing, and 0 otherwise.
4055 If you don't define this macro, a default is used which is good on most
4056 machines: @code{4 * @var{calls} < @var{refs}}.
4059 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
4060 A C expression specifying which mode is required for saving @var{nregs}
4061 of a pseudo-register in call-clobbered hard register @var{regno}. If
4062 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4063 returned. For most machines this macro need not be defined since GCC
4064 will select the smallest suitable mode.
4067 @node Function Entry
4068 @subsection Function Entry and Exit
4069 @cindex function entry and exit
4073 This section describes the macros that output function entry
4074 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4076 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4077 If defined, a function that outputs the assembler code for entry to a
4078 function. The prologue is responsible for setting up the stack frame,
4079 initializing the frame pointer register, saving registers that must be
4080 saved, and allocating @var{size} additional bytes of storage for the
4081 local variables. @var{size} is an integer. @var{file} is a stdio
4082 stream to which the assembler code should be output.
4084 The label for the beginning of the function need not be output by this
4085 macro. That has already been done when the macro is run.
4087 @findex regs_ever_live
4088 To determine which registers to save, the macro can refer to the array
4089 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4090 @var{r} is used anywhere within the function. This implies the function
4091 prologue should save register @var{r}, provided it is not one of the
4092 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4093 @code{regs_ever_live}.)
4095 On machines that have ``register windows'', the function entry code does
4096 not save on the stack the registers that are in the windows, even if
4097 they are supposed to be preserved by function calls; instead it takes
4098 appropriate steps to ``push'' the register stack, if any non-call-used
4099 registers are used in the function.
4101 @findex frame_pointer_needed
4102 On machines where functions may or may not have frame-pointers, the
4103 function entry code must vary accordingly; it must set up the frame
4104 pointer if one is wanted, and not otherwise. To determine whether a
4105 frame pointer is in wanted, the macro can refer to the variable
4106 @code{frame_pointer_needed}. The variable's value will be 1 at run
4107 time in a function that needs a frame pointer. @xref{Elimination}.
4109 The function entry code is responsible for allocating any stack space
4110 required for the function. This stack space consists of the regions
4111 listed below. In most cases, these regions are allocated in the
4112 order listed, with the last listed region closest to the top of the
4113 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4114 the highest address if it is not defined). You can use a different order
4115 for a machine if doing so is more convenient or required for
4116 compatibility reasons. Except in cases where required by standard
4117 or by a debugger, there is no reason why the stack layout used by GCC
4118 need agree with that used by other compilers for a machine.
4121 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
4122 If defined, a function that outputs assembler code at the end of a
4123 prologue. This should be used when the function prologue is being
4124 emitted as RTL, and you have some extra assembler that needs to be
4125 emitted. @xref{prologue instruction pattern}.
4128 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
4129 If defined, a function that outputs assembler code at the start of an
4130 epilogue. This should be used when the function epilogue is being
4131 emitted as RTL, and you have some extra assembler that needs to be
4132 emitted. @xref{epilogue instruction pattern}.
4135 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4136 If defined, a function that outputs the assembler code for exit from a
4137 function. The epilogue is responsible for restoring the saved
4138 registers and stack pointer to their values when the function was
4139 called, and returning control to the caller. This macro takes the
4140 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4141 registers to restore are determined from @code{regs_ever_live} and
4142 @code{CALL_USED_REGISTERS} in the same way.
4144 On some machines, there is a single instruction that does all the work
4145 of returning from the function. On these machines, give that
4146 instruction the name @samp{return} and do not define the macro
4147 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4149 Do not define a pattern named @samp{return} if you want the
4150 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4151 switches to control whether return instructions or epilogues are used,
4152 define a @samp{return} pattern with a validity condition that tests the
4153 target switches appropriately. If the @samp{return} pattern's validity
4154 condition is false, epilogues will be used.
4156 On machines where functions may or may not have frame-pointers, the
4157 function exit code must vary accordingly. Sometimes the code for these
4158 two cases is completely different. To determine whether a frame pointer
4159 is wanted, the macro can refer to the variable
4160 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4161 a function that needs a frame pointer.
4163 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4164 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4165 The C variable @code{current_function_is_leaf} is nonzero for such a
4166 function. @xref{Leaf Functions}.
4168 On some machines, some functions pop their arguments on exit while
4169 others leave that for the caller to do. For example, the 68020 when
4170 given @option{-mrtd} pops arguments in functions that take a fixed
4171 number of arguments.
4173 @findex current_function_pops_args
4174 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4175 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4176 needs to know what was decided. The variable that is called
4177 @code{current_function_pops_args} is the number of bytes of its
4178 arguments that a function should pop. @xref{Scalar Return}.
4179 @c what is the "its arguments" in the above sentence referring to, pray
4180 @c tell? --mew 5feb93
4185 @findex current_function_pretend_args_size
4186 A region of @code{current_function_pretend_args_size} bytes of
4187 uninitialized space just underneath the first argument arriving on the
4188 stack. (This may not be at the very start of the allocated stack region
4189 if the calling sequence has pushed anything else since pushing the stack
4190 arguments. But usually, on such machines, nothing else has been pushed
4191 yet, because the function prologue itself does all the pushing.) This
4192 region is used on machines where an argument may be passed partly in
4193 registers and partly in memory, and, in some cases to support the
4194 features in @code{<stdarg.h>}.
4197 An area of memory used to save certain registers used by the function.
4198 The size of this area, which may also include space for such things as
4199 the return address and pointers to previous stack frames, is
4200 machine-specific and usually depends on which registers have been used
4201 in the function. Machines with register windows often do not require
4205 A region of at least @var{size} bytes, possibly rounded up to an allocation
4206 boundary, to contain the local variables of the function. On some machines,
4207 this region and the save area may occur in the opposite order, with the
4208 save area closer to the top of the stack.
4211 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4212 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4213 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4214 argument lists of the function. @xref{Stack Arguments}.
4217 @defmac EXIT_IGNORE_STACK
4218 Define this macro as a C expression that is nonzero if the return
4219 instruction or the function epilogue ignores the value of the stack
4220 pointer; in other words, if it is safe to delete an instruction to
4221 adjust the stack pointer before a return from the function. The
4224 Note that this macro's value is relevant only for functions for which
4225 frame pointers are maintained. It is never safe to delete a final
4226 stack adjustment in a function that has no frame pointer, and the
4227 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4230 @defmac EPILOGUE_USES (@var{regno})
4231 Define this macro as a C expression that is nonzero for registers that are
4232 used by the epilogue or the @samp{return} pattern. The stack and frame
4233 pointer registers are already be assumed to be used as needed.
4236 @defmac EH_USES (@var{regno})
4237 Define this macro as a C expression that is nonzero for registers that are
4238 used by the exception handling mechanism, and so should be considered live
4239 on entry to an exception edge.
4242 @defmac DELAY_SLOTS_FOR_EPILOGUE
4243 Define this macro if the function epilogue contains delay slots to which
4244 instructions from the rest of the function can be ``moved''. The
4245 definition should be a C expression whose value is an integer
4246 representing the number of delay slots there.
4249 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4250 A C expression that returns 1 if @var{insn} can be placed in delay
4251 slot number @var{n} of the epilogue.
4253 The argument @var{n} is an integer which identifies the delay slot now
4254 being considered (since different slots may have different rules of
4255 eligibility). It is never negative and is always less than the number
4256 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4257 If you reject a particular insn for a given delay slot, in principle, it
4258 may be reconsidered for a subsequent delay slot. Also, other insns may
4259 (at least in principle) be considered for the so far unfilled delay
4262 @findex current_function_epilogue_delay_list
4263 @findex final_scan_insn
4264 The insns accepted to fill the epilogue delay slots are put in an RTL
4265 list made with @code{insn_list} objects, stored in the variable
4266 @code{current_function_epilogue_delay_list}. The insn for the first
4267 delay slot comes first in the list. Your definition of the macro
4268 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4269 outputting the insns in this list, usually by calling
4270 @code{final_scan_insn}.
4272 You need not define this macro if you did not define
4273 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4276 @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})
4277 A function that outputs the assembler code for a thunk
4278 function, used to implement C++ virtual function calls with multiple
4279 inheritance. The thunk acts as a wrapper around a virtual function,
4280 adjusting the implicit object parameter before handing control off to
4283 First, emit code to add the integer @var{delta} to the location that
4284 contains the incoming first argument. Assume that this argument
4285 contains a pointer, and is the one used to pass the @code{this} pointer
4286 in C++. This is the incoming argument @emph{before} the function prologue,
4287 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4288 all other incoming arguments.
4290 Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
4291 made after adding @code{delta}. In particular, if @var{p} is the
4292 adjusted pointer, the following adjustment should be made:
4295 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4298 After the additions, emit code to jump to @var{function}, which is a
4299 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4300 not touch the return address. Hence returning from @var{FUNCTION} will
4301 return to whoever called the current @samp{thunk}.
4303 The effect must be as if @var{function} had been called directly with
4304 the adjusted first argument. This macro is responsible for emitting all
4305 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4306 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4308 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4309 have already been extracted from it.) It might possibly be useful on
4310 some targets, but probably not.
4312 If you do not define this macro, the target-independent code in the C++
4313 front end will generate a less efficient heavyweight thunk that calls
4314 @var{function} instead of jumping to it. The generic approach does
4315 not support varargs.
4318 @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})
4319 A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
4320 to output the assembler code for the thunk function specified by the
4321 arguments it is passed, and false otherwise. In the latter case, the
4322 generic approach will be used by the C++ front end, with the limitations
4327 @subsection Generating Code for Profiling
4328 @cindex profiling, code generation
4330 These macros will help you generate code for profiling.
4332 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4333 A C statement or compound statement to output to @var{file} some
4334 assembler code to call the profiling subroutine @code{mcount}.
4337 The details of how @code{mcount} expects to be called are determined by
4338 your operating system environment, not by GCC@. To figure them out,
4339 compile a small program for profiling using the system's installed C
4340 compiler and look at the assembler code that results.
4342 Older implementations of @code{mcount} expect the address of a counter
4343 variable to be loaded into some register. The name of this variable is
4344 @samp{LP} followed by the number @var{labelno}, so you would generate
4345 the name using @samp{LP%d} in a @code{fprintf}.
4348 @defmac PROFILE_HOOK
4349 A C statement or compound statement to output to @var{file} some assembly
4350 code to call the profiling subroutine @code{mcount} even the target does
4351 not support profiling.
4354 @defmac NO_PROFILE_COUNTERS
4355 Define this macro if the @code{mcount} subroutine on your system does
4356 not need a counter variable allocated for each function. This is true
4357 for almost all modern implementations. If you define this macro, you
4358 must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}.
4361 @defmac PROFILE_BEFORE_PROLOGUE
4362 Define this macro if the code for function profiling should come before
4363 the function prologue. Normally, the profiling code comes after.
4367 @subsection Permitting tail calls
4370 @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
4371 True if it is ok to do sibling call optimization for the specified
4372 call expression @var{exp}. @var{decl} will be the called function,
4373 or @code{NULL} if this is an indirect call.
4375 It is not uncommon for limitations of calling conventions to prevent
4376 tail calls to functions outside the current unit of translation, or
4377 during PIC compilation. The hook is used to enforce these restrictions,
4378 as the @code{sibcall} md pattern can not fail, or fall over to a
4379 ``normal'' call. The criteria for successful sibling call optimization
4380 may vary greatly between different architectures.
4383 @node Stack Smashing Protection
4384 @subsection Stack smashing protection
4385 @cindex stack smashing protection
4387 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void)
4388 This hook returns a @code{DECL} node for the external variable to use
4389 for the stack protection guard. This variable is initialized by the
4390 runtime to some random value and is used to initialize the guard value
4391 that is placed at the top of the local stack frame. The type of this
4392 variable must be @code{ptr_type_node}.
4394 The default version of this hook creates a variable called
4395 @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
4398 @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void)
4399 This hook returns a tree expression that alerts the runtime that the
4400 stack protect guard variable has been modified. This expression should
4401 involve a call to a @code{noreturn} function.
4403 The default version of this hook invokes a function called
4404 @samp{__stack_chk_fail}, taking no arguments. This function is
4405 normally defined in @file{libgcc2.c}.
4409 @section Implementing the Varargs Macros
4410 @cindex varargs implementation
4412 GCC comes with an implementation of @code{<varargs.h>} and
4413 @code{<stdarg.h>} that work without change on machines that pass arguments
4414 on the stack. Other machines require their own implementations of
4415 varargs, and the two machine independent header files must have
4416 conditionals to include it.
4418 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4419 the calling convention for @code{va_start}. The traditional
4420 implementation takes just one argument, which is the variable in which
4421 to store the argument pointer. The ISO implementation of
4422 @code{va_start} takes an additional second argument. The user is
4423 supposed to write the last named argument of the function here.
4425 However, @code{va_start} should not use this argument. The way to find
4426 the end of the named arguments is with the built-in functions described
4429 @defmac __builtin_saveregs ()
4430 Use this built-in function to save the argument registers in memory so
4431 that the varargs mechanism can access them. Both ISO and traditional
4432 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
4433 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
4435 On some machines, @code{__builtin_saveregs} is open-coded under the
4436 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
4437 other machines, it calls a routine written in assembler language,
4438 found in @file{libgcc2.c}.
4440 Code generated for the call to @code{__builtin_saveregs} appears at the
4441 beginning of the function, as opposed to where the call to
4442 @code{__builtin_saveregs} is written, regardless of what the code is.
4443 This is because the registers must be saved before the function starts
4444 to use them for its own purposes.
4445 @c i rewrote the first sentence above to fix an overfull hbox. --mew
4449 @defmac __builtin_args_info (@var{category})
4450 Use this built-in function to find the first anonymous arguments in
4453 In general, a machine may have several categories of registers used for
4454 arguments, each for a particular category of data types. (For example,
4455 on some machines, floating-point registers are used for floating-point
4456 arguments while other arguments are passed in the general registers.)
4457 To make non-varargs functions use the proper calling convention, you
4458 have defined the @code{CUMULATIVE_ARGS} data type to record how many
4459 registers in each category have been used so far
4461 @code{__builtin_args_info} accesses the same data structure of type
4462 @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished
4463 with it, with @var{category} specifying which word to access. Thus, the
4464 value indicates the first unused register in a given category.
4466 Normally, you would use @code{__builtin_args_info} in the implementation
4467 of @code{va_start}, accessing each category just once and storing the
4468 value in the @code{va_list} object. This is because @code{va_list} will
4469 have to update the values, and there is no way to alter the
4470 values accessed by @code{__builtin_args_info}.
4473 @defmac __builtin_next_arg (@var{lastarg})
4474 This is the equivalent of @code{__builtin_args_info}, for stack
4475 arguments. It returns the address of the first anonymous stack
4476 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
4477 returns the address of the location above the first anonymous stack
4478 argument. Use it in @code{va_start} to initialize the pointer for
4479 fetching arguments from the stack. Also use it in @code{va_start} to
4480 verify that the second parameter @var{lastarg} is the last named argument
4481 of the current function.
4484 @defmac __builtin_classify_type (@var{object})
4485 Since each machine has its own conventions for which data types are
4486 passed in which kind of register, your implementation of @code{va_arg}
4487 has to embody these conventions. The easiest way to categorize the
4488 specified data type is to use @code{__builtin_classify_type} together
4489 with @code{sizeof} and @code{__alignof__}.
4491 @code{__builtin_classify_type} ignores the value of @var{object},
4492 considering only its data type. It returns an integer describing what
4493 kind of type that is---integer, floating, pointer, structure, and so on.
4495 The file @file{typeclass.h} defines an enumeration that you can use to
4496 interpret the values of @code{__builtin_classify_type}.
4499 These machine description macros help implement varargs:
4501 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void)
4502 If defined, this hook produces the machine-specific code for a call to
4503 @code{__builtin_saveregs}. This code will be moved to the very
4504 beginning of the function, before any parameter access are made. The
4505 return value of this function should be an RTX that contains the value
4506 to use as the return of @code{__builtin_saveregs}.
4509 @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})
4510 This target hook offers an alternative to using
4511 @code{__builtin_saveregs} and defining the hook
4512 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
4513 register arguments into the stack so that all the arguments appear to
4514 have been passed consecutively on the stack. Once this is done, you can
4515 use the standard implementation of varargs that works for machines that
4516 pass all their arguments on the stack.
4518 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
4519 structure, containing the values that are obtained after processing the
4520 named arguments. The arguments @var{mode} and @var{type} describe the
4521 last named argument---its machine mode and its data type as a tree node.
4523 The target hook should do two things: first, push onto the stack all the
4524 argument registers @emph{not} used for the named arguments, and second,
4525 store the size of the data thus pushed into the @code{int}-valued
4526 variable pointed to by @var{pretend_args_size}. The value that you
4527 store here will serve as additional offset for setting up the stack
4530 Because you must generate code to push the anonymous arguments at
4531 compile time without knowing their data types,
4532 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
4533 have just a single category of argument register and use it uniformly
4536 If the argument @var{second_time} is nonzero, it means that the
4537 arguments of the function are being analyzed for the second time. This
4538 happens for an inline function, which is not actually compiled until the
4539 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
4540 not generate any instructions in this case.
4543 @deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca})
4544 Define this hook to return @code{true} if the location where a function
4545 argument is passed depends on whether or not it is a named argument.
4547 This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
4548 is set for varargs and stdarg functions. If this hook returns
4549 @code{true}, the @var{named} argument is always true for named
4550 arguments, and false for unnamed arguments. If it returns @code{false},
4551 but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
4552 then all arguments are treated as named. Otherwise, all named arguments
4553 except the last are treated as named.
4555 You need not define this hook if it always returns zero.
4558 @deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED
4559 If you need to conditionally change ABIs so that one works with
4560 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
4561 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
4562 defined, then define this hook to return @code{true} if
4563 @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
4564 Otherwise, you should not define this hook.
4568 @section Trampolines for Nested Functions
4569 @cindex trampolines for nested functions
4570 @cindex nested functions, trampolines for
4572 A @dfn{trampoline} is a small piece of code that is created at run time
4573 when the address of a nested function is taken. It normally resides on
4574 the stack, in the stack frame of the containing function. These macros
4575 tell GCC how to generate code to allocate and initialize a
4578 The instructions in the trampoline must do two things: load a constant
4579 address into the static chain register, and jump to the real address of
4580 the nested function. On CISC machines such as the m68k, this requires
4581 two instructions, a move immediate and a jump. Then the two addresses
4582 exist in the trampoline as word-long immediate operands. On RISC
4583 machines, it is often necessary to load each address into a register in
4584 two parts. Then pieces of each address form separate immediate
4587 The code generated to initialize the trampoline must store the variable
4588 parts---the static chain value and the function address---into the
4589 immediate operands of the instructions. On a CISC machine, this is
4590 simply a matter of copying each address to a memory reference at the
4591 proper offset from the start of the trampoline. On a RISC machine, it
4592 may be necessary to take out pieces of the address and store them
4595 @defmac TRAMPOLINE_TEMPLATE (@var{file})
4596 A C statement to output, on the stream @var{file}, assembler code for a
4597 block of data that contains the constant parts of a trampoline. This
4598 code should not include a label---the label is taken care of
4601 If you do not define this macro, it means no template is needed
4602 for the target. Do not define this macro on systems where the block move
4603 code to copy the trampoline into place would be larger than the code
4604 to generate it on the spot.
4607 @defmac TRAMPOLINE_SECTION
4608 The name of a subroutine to switch to the section in which the
4609 trampoline template is to be placed (@pxref{Sections}). The default is
4610 a value of @samp{readonly_data_section}, which places the trampoline in
4611 the section containing read-only data.
4614 @defmac TRAMPOLINE_SIZE
4615 A C expression for the size in bytes of the trampoline, as an integer.
4618 @defmac TRAMPOLINE_ALIGNMENT
4619 Alignment required for trampolines, in bits.
4621 If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT}
4622 is used for aligning trampolines.
4625 @defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain})
4626 A C statement to initialize the variable parts of a trampoline.
4627 @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is
4628 an RTX for the address of the nested function; @var{static_chain} is an
4629 RTX for the static chain value that should be passed to the function
4633 @defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr})
4634 A C statement that should perform any machine-specific adjustment in
4635 the address of the trampoline. Its argument contains the address that
4636 was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be
4637 used for a function call should be different from the address in which
4638 the template was stored, the different address should be assigned to
4639 @var{addr}. If this macro is not defined, @var{addr} will be used for
4642 @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines
4643 @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines
4644 If this macro is not defined, by default the trampoline is allocated as
4645 a stack slot. This default is right for most machines. The exceptions
4646 are machines where it is impossible to execute instructions in the stack
4647 area. On such machines, you may have to implement a separate stack,
4648 using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE}
4649 and @code{TARGET_ASM_FUNCTION_EPILOGUE}.
4651 @var{fp} points to a data structure, a @code{struct function}, which
4652 describes the compilation status of the immediate containing function of
4653 the function which the trampoline is for. The stack slot for the
4654 trampoline is in the stack frame of this containing function. Other
4655 allocation strategies probably must do something analogous with this
4659 Implementing trampolines is difficult on many machines because they have
4660 separate instruction and data caches. Writing into a stack location
4661 fails to clear the memory in the instruction cache, so when the program
4662 jumps to that location, it executes the old contents.
4664 Here are two possible solutions. One is to clear the relevant parts of
4665 the instruction cache whenever a trampoline is set up. The other is to
4666 make all trampolines identical, by having them jump to a standard
4667 subroutine. The former technique makes trampoline execution faster; the
4668 latter makes initialization faster.
4670 To clear the instruction cache when a trampoline is initialized, define
4671 the following macro.
4673 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
4674 If defined, expands to a C expression clearing the @emph{instruction
4675 cache} in the specified interval. The definition of this macro would
4676 typically be a series of @code{asm} statements. Both @var{beg} and
4677 @var{end} are both pointer expressions.
4680 The operating system may also require the stack to be made executable
4681 before calling the trampoline. To implement this requirement, define
4682 the following macro.
4684 @defmac ENABLE_EXECUTE_STACK
4685 Define this macro if certain operations must be performed before executing
4686 code located on the stack. The macro should expand to a series of C
4687 file-scope constructs (e.g.@: functions) and provide a unique entry point
4688 named @code{__enable_execute_stack}. The target is responsible for
4689 emitting calls to the entry point in the code, for example from the
4690 @code{INITIALIZE_TRAMPOLINE} macro.
4693 To use a standard subroutine, define the following macro. In addition,
4694 you must make sure that the instructions in a trampoline fill an entire
4695 cache line with identical instructions, or else ensure that the
4696 beginning of the trampoline code is always aligned at the same point in
4697 its cache line. Look in @file{m68k.h} as a guide.
4699 @defmac TRANSFER_FROM_TRAMPOLINE
4700 Define this macro if trampolines need a special subroutine to do their
4701 work. The macro should expand to a series of @code{asm} statements
4702 which will be compiled with GCC@. They go in a library function named
4703 @code{__transfer_from_trampoline}.
4705 If you need to avoid executing the ordinary prologue code of a compiled
4706 C function when you jump to the subroutine, you can do so by placing a
4707 special label of your own in the assembler code. Use one @code{asm}
4708 statement to generate an assembler label, and another to make the label
4709 global. Then trampolines can use that label to jump directly to your
4710 special assembler code.
4714 @section Implicit Calls to Library Routines
4715 @cindex library subroutine names
4716 @cindex @file{libgcc.a}
4718 @c prevent bad page break with this line
4719 Here is an explanation of implicit calls to library routines.
4721 @defmac DECLARE_LIBRARY_RENAMES
4722 This macro, if defined, should expand to a piece of C code that will get
4723 expanded when compiling functions for libgcc.a. It can be used to
4724 provide alternate names for GCC's internal library functions if there
4725 are ABI-mandated names that the compiler should provide.
4728 @findex init_one_libfunc
4729 @findex set_optab_libfunc
4730 @deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void)
4731 This hook should declare additional library routines or rename
4732 existing ones, using the functions @code{set_optab_libfunc} and
4733 @code{init_one_libfunc} defined in @file{optabs.c}.
4734 @code{init_optabs} calls this macro after initializing all the normal
4737 The default is to do nothing. Most ports don't need to define this hook.
4740 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
4741 This macro should return @code{true} if the library routine that
4742 implements the floating point comparison operator @var{comparison} in
4743 mode @var{mode} will return a boolean, and @var{false} if it will
4746 GCC's own floating point libraries return tristates from the
4747 comparison operators, so the default returns false always. Most ports
4748 don't need to define this macro.
4751 @defmac TARGET_LIB_INT_CMP_BIASED
4752 This macro should evaluate to @code{true} if the integer comparison
4753 functions (like @code{__cmpdi2}) return 0 to indicate that the first
4754 operand is smaller than the second, 1 to indicate that they are equal,
4755 and 2 to indicate that the first operand is greater than the second.
4756 If this macro evaluates to @code{false} the comparison functions return
4757 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
4758 in @file{libgcc.a}, you do not need to define this macro.
4761 @cindex US Software GOFAST, floating point emulation library
4762 @cindex floating point emulation library, US Software GOFAST
4763 @cindex GOFAST, floating point emulation library
4764 @findex gofast_maybe_init_libfuncs
4765 @defmac US_SOFTWARE_GOFAST
4766 Define this macro if your system C library uses the US Software GOFAST
4767 library to provide floating point emulation.
4769 In addition to defining this macro, your architecture must set
4770 @code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or
4771 else call that function from its version of that hook. It is defined
4772 in @file{config/gofast.h}, which must be included by your
4773 architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for
4776 If this macro is defined, the
4777 @code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return
4778 false for @code{SFmode} and @code{DFmode} comparisons.
4781 @cindex @code{EDOM}, implicit usage
4784 The value of @code{EDOM} on the target machine, as a C integer constant
4785 expression. If you don't define this macro, GCC does not attempt to
4786 deposit the value of @code{EDOM} into @code{errno} directly. Look in
4787 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
4790 If you do not define @code{TARGET_EDOM}, then compiled code reports
4791 domain errors by calling the library function and letting it report the
4792 error. If mathematical functions on your system use @code{matherr} when
4793 there is an error, then you should leave @code{TARGET_EDOM} undefined so
4794 that @code{matherr} is used normally.
4797 @cindex @code{errno}, implicit usage
4798 @defmac GEN_ERRNO_RTX
4799 Define this macro as a C expression to create an rtl expression that
4800 refers to the global ``variable'' @code{errno}. (On certain systems,
4801 @code{errno} may not actually be a variable.) If you don't define this
4802 macro, a reasonable default is used.
4805 @cindex C99 math functions, implicit usage
4806 @defmac TARGET_C99_FUNCTIONS
4807 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
4808 @code{sinf} and similarly for other functions defined by C99 standard. The
4809 default is nonzero that should be proper value for most modern systems, however
4810 number of existing systems lacks support for these functions in the runtime so
4811 they needs this macro to be redefined to 0.
4814 @defmac NEXT_OBJC_RUNTIME
4815 Define this macro to generate code for Objective-C message sending using
4816 the calling convention of the NeXT system. This calling convention
4817 involves passing the object, the selector and the method arguments all
4818 at once to the method-lookup library function.
4820 The default calling convention passes just the object and the selector
4821 to the lookup function, which returns a pointer to the method.
4824 @node Addressing Modes
4825 @section Addressing Modes
4826 @cindex addressing modes
4828 @c prevent bad page break with this line
4829 This is about addressing modes.
4831 @defmac HAVE_PRE_INCREMENT
4832 @defmacx HAVE_PRE_DECREMENT
4833 @defmacx HAVE_POST_INCREMENT
4834 @defmacx HAVE_POST_DECREMENT
4835 A C expression that is nonzero if the machine supports pre-increment,
4836 pre-decrement, post-increment, or post-decrement addressing respectively.
4839 @defmac HAVE_PRE_MODIFY_DISP
4840 @defmacx HAVE_POST_MODIFY_DISP
4841 A C expression that is nonzero if the machine supports pre- or
4842 post-address side-effect generation involving constants other than
4843 the size of the memory operand.
4846 @defmac HAVE_PRE_MODIFY_REG
4847 @defmacx HAVE_POST_MODIFY_REG
4848 A C expression that is nonzero if the machine supports pre- or
4849 post-address side-effect generation involving a register displacement.
4852 @defmac CONSTANT_ADDRESS_P (@var{x})
4853 A C expression that is 1 if the RTX @var{x} is a constant which
4854 is a valid address. On most machines, this can be defined as
4855 @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive
4856 in which constant addresses are supported.
4859 @defmac CONSTANT_P (@var{x})
4860 @code{CONSTANT_P}, which is defined by target-independent code,
4861 accepts integer-values expressions whose values are not explicitly
4862 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
4863 expressions and @code{const} arithmetic expressions, in addition to
4864 @code{const_int} and @code{const_double} expressions.
4867 @defmac MAX_REGS_PER_ADDRESS
4868 A number, the maximum number of registers that can appear in a valid
4869 memory address. Note that it is up to you to specify a value equal to
4870 the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever
4874 @defmac GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
4875 A C compound statement with a conditional @code{goto @var{label};}
4876 executed if @var{x} (an RTX) is a legitimate memory address on the
4877 target machine for a memory operand of mode @var{mode}.
4879 It usually pays to define several simpler macros to serve as
4880 subroutines for this one. Otherwise it may be too complicated to
4883 This macro must exist in two variants: a strict variant and a
4884 non-strict one. The strict variant is used in the reload pass. It
4885 must be defined so that any pseudo-register that has not been
4886 allocated a hard register is considered a memory reference. In
4887 contexts where some kind of register is required, a pseudo-register
4888 with no hard register must be rejected.
4890 The non-strict variant is used in other passes. It must be defined to
4891 accept all pseudo-registers in every context where some kind of
4892 register is required.
4894 @findex REG_OK_STRICT
4895 Compiler source files that want to use the strict variant of this
4896 macro define the macro @code{REG_OK_STRICT}. You should use an
4897 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant
4898 in that case and the non-strict variant otherwise.
4900 Subroutines to check for acceptable registers for various purposes (one
4901 for base registers, one for index registers, and so on) are typically
4902 among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}.
4903 Then only these subroutine macros need have two variants; the higher
4904 levels of macros may be the same whether strict or not.
4906 Normally, constant addresses which are the sum of a @code{symbol_ref}
4907 and an integer are stored inside a @code{const} RTX to mark them as
4908 constant. Therefore, there is no need to recognize such sums
4909 specifically as legitimate addresses. Normally you would simply
4910 recognize any @code{const} as legitimate.
4912 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
4913 sums that are not marked with @code{const}. It assumes that a naked
4914 @code{plus} indicates indexing. If so, then you @emph{must} reject such
4915 naked constant sums as illegitimate addresses, so that none of them will
4916 be given to @code{PRINT_OPERAND_ADDRESS}.
4918 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
4919 On some machines, whether a symbolic address is legitimate depends on
4920 the section that the address refers to. On these machines, define the
4921 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
4922 into the @code{symbol_ref}, and then check for it here. When you see a
4923 @code{const}, you will have to look inside it to find the
4924 @code{symbol_ref} in order to determine the section. @xref{Assembler
4928 @defmac REG_OK_FOR_BASE_P (@var{x})
4929 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4930 RTX) is valid for use as a base register. For hard registers, it
4931 should always accept those which the hardware permits and reject the
4932 others. Whether the macro accepts or rejects pseudo registers must be
4933 controlled by @code{REG_OK_STRICT} as described above. This usually
4934 requires two variant definitions, of which @code{REG_OK_STRICT}
4935 controls the one actually used.
4938 @defmac REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode})
4939 A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that
4940 that expression may examine the mode of the memory reference in
4941 @var{mode}. You should define this macro if the mode of the memory
4942 reference affects whether a register may be used as a base register. If
4943 you define this macro, the compiler will use it instead of
4944 @code{REG_OK_FOR_BASE_P}.
4947 @defmac REG_MODE_OK_FOR_REG_BASE_P (@var{x}, @var{mode})
4948 A C expression which is nonzero if @var{x} (assumed to be a @code{reg} RTX)
4949 is suitable for use as a base register in base plus index operand addresses,
4950 accessing memory in mode @var{mode}. It may be either a suitable hard
4951 register or a pseudo register that has been allocated such a hard register.
4952 You should define this macro if base plus index addresses have different
4953 requirements than other base register uses.
4956 @defmac REG_OK_FOR_INDEX_P (@var{x})
4957 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4958 RTX) is valid for use as an index register.
4960 The difference between an index register and a base register is that
4961 the index register may be scaled. If an address involves the sum of
4962 two registers, neither one of them scaled, then either one may be
4963 labeled the ``base'' and the other the ``index''; but whichever
4964 labeling is used must fit the machine's constraints of which registers
4965 may serve in each capacity. The compiler will try both labelings,
4966 looking for one that is valid, and will reload one or both registers
4967 only if neither labeling works.
4970 @defmac FIND_BASE_TERM (@var{x})
4971 A C expression to determine the base term of address @var{x}.
4972 This macro is used in only one place: `find_base_term' in alias.c.
4974 It is always safe for this macro to not be defined. It exists so
4975 that alias analysis can understand machine-dependent addresses.
4977 The typical use of this macro is to handle addresses containing
4978 a label_ref or symbol_ref within an UNSPEC@.
4981 @defmac LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win})
4982 A C compound statement that attempts to replace @var{x} with a valid
4983 memory address for an operand of mode @var{mode}. @var{win} will be a
4984 C statement label elsewhere in the code; the macro definition may use
4987 GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win});
4991 to avoid further processing if the address has become legitimate.
4993 @findex break_out_memory_refs
4994 @var{x} will always be the result of a call to @code{break_out_memory_refs},
4995 and @var{oldx} will be the operand that was given to that function to produce
4998 The code generated by this macro should not alter the substructure of
4999 @var{x}. If it transforms @var{x} into a more legitimate form, it
5000 should assign @var{x} (which will always be a C variable) a new value.
5002 It is not necessary for this macro to come up with a legitimate
5003 address. The compiler has standard ways of doing so in all cases. In
5004 fact, it is safe to omit this macro. But often a
5005 machine-dependent strategy can generate better code.
5008 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
5009 A C compound statement that attempts to replace @var{x}, which is an address
5010 that needs reloading, with a valid memory address for an operand of mode
5011 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
5012 It is not necessary to define this macro, but it might be useful for
5013 performance reasons.
5015 For example, on the i386, it is sometimes possible to use a single
5016 reload register instead of two by reloading a sum of two pseudo
5017 registers into a register. On the other hand, for number of RISC
5018 processors offsets are limited so that often an intermediate address
5019 needs to be generated in order to address a stack slot. By defining
5020 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
5021 generated for adjacent some stack slots can be made identical, and thus
5024 @emph{Note}: This macro should be used with caution. It is necessary
5025 to know something of how reload works in order to effectively use this,
5026 and it is quite easy to produce macros that build in too much knowledge
5027 of reload internals.
5029 @emph{Note}: This macro must be able to reload an address created by a
5030 previous invocation of this macro. If it fails to handle such addresses
5031 then the compiler may generate incorrect code or abort.
5034 The macro definition should use @code{push_reload} to indicate parts that
5035 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
5036 suitable to be passed unaltered to @code{push_reload}.
5038 The code generated by this macro must not alter the substructure of
5039 @var{x}. If it transforms @var{x} into a more legitimate form, it
5040 should assign @var{x} (which will always be a C variable) a new value.
5041 This also applies to parts that you change indirectly by calling
5044 @findex strict_memory_address_p
5045 The macro definition may use @code{strict_memory_address_p} to test if
5046 the address has become legitimate.
5049 If you want to change only a part of @var{x}, one standard way of doing
5050 this is to use @code{copy_rtx}. Note, however, that is unshares only a
5051 single level of rtl. Thus, if the part to be changed is not at the
5052 top level, you'll need to replace first the top level.
5053 It is not necessary for this macro to come up with a legitimate
5054 address; but often a machine-dependent strategy can generate better code.
5057 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
5058 A C statement or compound statement with a conditional @code{goto
5059 @var{label};} executed if memory address @var{x} (an RTX) can have
5060 different meanings depending on the machine mode of the memory
5061 reference it is used for or if the address is valid for some modes
5064 Autoincrement and autodecrement addresses typically have mode-dependent
5065 effects because the amount of the increment or decrement is the size
5066 of the operand being addressed. Some machines have other mode-dependent
5067 addresses. Many RISC machines have no mode-dependent addresses.
5069 You may assume that @var{addr} is a valid address for the machine.
5072 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5073 A C expression that is nonzero if @var{x} is a legitimate constant for
5074 an immediate operand on the target machine. You can assume that
5075 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5076 @samp{1} is a suitable definition for this macro on machines where
5077 anything @code{CONSTANT_P} is valid.
5080 @deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x})
5081 This hook is used to undo the possibly obfuscating effects of the
5082 @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
5083 macros. Some backend implementations of these macros wrap symbol
5084 references inside an @code{UNSPEC} rtx to represent PIC or similar
5085 addressing modes. This target hook allows GCC's optimizers to understand
5086 the semantics of these opaque @code{UNSPEC}s by converting them back
5087 into their original form.
5090 @deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (rtx @var{x})
5091 This hook should return true if @var{x} is of a form that cannot (or
5092 should not) be spilled to the constant pool. The default version of
5093 this hook returns false.
5095 The primary reason to define this hook is to prevent reload from
5096 deciding that a non-legitimate constant would be better reloaded
5097 from the constant pool instead of spilling and reloading a register
5098 holding the constant. This restriction is often true of addresses
5099 of TLS symbols for various targets.
5102 @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void)
5103 This hook should return the DECL of a function @var{f} that given an
5104 address @var{addr} as an argument returns a mask @var{m} that can be
5105 used to extract from two vectors the relevant data that resides in
5106 @var{addr} in case @var{addr} is not properly aligned.
5108 The autovectrizer, when vectorizing a load operation from an address
5109 @var{addr} that may be unaligned, will generate two vector loads from
5110 the two aligned addresses around @var{addr}. It then generates a
5111 @code{REALIGN_LOAD} operation to extract the relevant data from the
5112 two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
5113 @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
5114 the third argument, @var{OFF}, defines how the data will be extracted
5115 from these two vectors: if @var{OFF} is 0, then the returned vector is
5116 @var{v2}; otherwise, the returned vector is composed from the last
5117 @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
5118 @var{OFF} elements of @var{v2}.
5120 If this hook is defined, the autovectorizer will generate a call
5121 to @var{f} (using the DECL tree that this hook returns) and will
5122 use the return value of @var{f} as the argument @var{OFF} to
5123 @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
5124 should comply with the semantics expected by @code{REALIGN_LOAD}
5126 If this hook is not defined, then @var{addr} will be used as
5127 the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
5128 log2(@var{VS})-1 bits of @var{addr} will be considered.
5131 @node Condition Code
5132 @section Condition Code Status
5133 @cindex condition code status
5135 @c prevent bad page break with this line
5136 This describes the condition code status.
5139 The file @file{conditions.h} defines a variable @code{cc_status} to
5140 describe how the condition code was computed (in case the interpretation of
5141 the condition code depends on the instruction that it was set by). This
5142 variable contains the RTL expressions on which the condition code is
5143 currently based, and several standard flags.
5145 Sometimes additional machine-specific flags must be defined in the machine
5146 description header file. It can also add additional machine-specific
5147 information by defining @code{CC_STATUS_MDEP}.
5149 @defmac CC_STATUS_MDEP
5150 C code for a data type which is used for declaring the @code{mdep}
5151 component of @code{cc_status}. It defaults to @code{int}.
5153 This macro is not used on machines that do not use @code{cc0}.
5156 @defmac CC_STATUS_MDEP_INIT
5157 A C expression to initialize the @code{mdep} field to ``empty''.
5158 The default definition does nothing, since most machines don't use
5159 the field anyway. If you want to use the field, you should probably
5160 define this macro to initialize it.
5162 This macro is not used on machines that do not use @code{cc0}.
5165 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5166 A C compound statement to set the components of @code{cc_status}
5167 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5168 this macro's responsibility to recognize insns that set the condition
5169 code as a byproduct of other activity as well as those that explicitly
5172 This macro is not used on machines that do not use @code{cc0}.
5174 If there are insns that do not set the condition code but do alter
5175 other machine registers, this macro must check to see whether they
5176 invalidate the expressions that the condition code is recorded as
5177 reflecting. For example, on the 68000, insns that store in address
5178 registers do not set the condition code, which means that usually
5179 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5180 insns. But suppose that the previous insn set the condition code
5181 based on location @samp{a4@@(102)} and the current insn stores a new
5182 value in @samp{a4}. Although the condition code is not changed by
5183 this, it will no longer be true that it reflects the contents of
5184 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5185 @code{cc_status} in this case to say that nothing is known about the
5186 condition code value.
5188 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5189 with the results of peephole optimization: insns whose patterns are
5190 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5191 constants which are just the operands. The RTL structure of these
5192 insns is not sufficient to indicate what the insns actually do. What
5193 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5194 @code{CC_STATUS_INIT}.
5196 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5197 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5198 @samp{cc}. This avoids having detailed information about patterns in
5199 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5202 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5203 Returns a mode from class @code{MODE_CC} to be used when comparison
5204 operation code @var{op} is applied to rtx @var{x} and @var{y}. For
5205 example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see
5206 @pxref{Jump Patterns} for a description of the reason for this
5210 #define SELECT_CC_MODE(OP,X,Y) \
5211 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
5212 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
5213 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
5214 || GET_CODE (X) == NEG) \
5215 ? CC_NOOVmode : CCmode))
5218 You should define this macro if and only if you define extra CC modes
5219 in @file{@var{machine}-modes.def}.
5222 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
5223 On some machines not all possible comparisons are defined, but you can
5224 convert an invalid comparison into a valid one. For example, the Alpha
5225 does not have a @code{GT} comparison, but you can use an @code{LT}
5226 comparison instead and swap the order of the operands.
5228 On such machines, define this macro to be a C statement to do any
5229 required conversions. @var{code} is the initial comparison code
5230 and @var{op0} and @var{op1} are the left and right operands of the
5231 comparison, respectively. You should modify @var{code}, @var{op0}, and
5232 @var{op1} as required.
5234 GCC will not assume that the comparison resulting from this macro is
5235 valid but will see if the resulting insn matches a pattern in the
5238 You need not define this macro if it would never change the comparison
5242 @defmac REVERSIBLE_CC_MODE (@var{mode})
5243 A C expression whose value is one if it is always safe to reverse a
5244 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
5245 can ever return @var{mode} for a floating-point inequality comparison,
5246 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
5248 You need not define this macro if it would always returns zero or if the
5249 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
5250 For example, here is the definition used on the SPARC, where floating-point
5251 inequality comparisons are always given @code{CCFPEmode}:
5254 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
5258 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
5259 A C expression whose value is reversed condition code of the @var{code} for
5260 comparison done in CC_MODE @var{mode}. The macro is used only in case
5261 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
5262 machine has some non-standard way how to reverse certain conditionals. For
5263 instance in case all floating point conditions are non-trapping, compiler may
5264 freely convert unordered compares to ordered one. Then definition may look
5268 #define REVERSE_CONDITION(CODE, MODE) \
5269 ((MODE) != CCFPmode ? reverse_condition (CODE) \
5270 : reverse_condition_maybe_unordered (CODE))
5274 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2})
5275 A C expression that returns true if the conditional execution predicate
5276 @var{op1}, a comparison operation, is the inverse of @var{op2} and vice
5277 versa. Define this to return 0 if the target has conditional execution
5278 predicates that cannot be reversed safely. There is no need to validate
5279 that the arguments of op1 and op2 are the same, this is done separately.
5280 If no expansion is specified, this macro is defined as follows:
5283 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
5284 (GET_CODE ((x)) == reversed_comparison_code ((y), NULL))
5288 @deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *, unsigned int *)
5289 On targets which do not use @code{(cc0)}, and which use a hard
5290 register rather than a pseudo-register to hold condition codes, the
5291 regular CSE passes are often not able to identify cases in which the
5292 hard register is set to a common value. Use this hook to enable a
5293 small pass which optimizes such cases. This hook should return true
5294 to enable this pass, and it should set the integers to which its
5295 arguments point to the hard register numbers used for condition codes.
5296 When there is only one such register, as is true on most systems, the
5297 integer pointed to by the second argument should be set to
5298 @code{INVALID_REGNUM}.
5300 The default version of this hook returns false.
5303 @deftypefn {Target Hook} enum machine_mode TARGET_CC_MODES_COMPATIBLE (enum machine_mode, enum machine_mode)
5304 On targets which use multiple condition code modes in class
5305 @code{MODE_CC}, it is sometimes the case that a comparison can be
5306 validly done in more than one mode. On such a system, define this
5307 target hook to take two mode arguments and to return a mode in which
5308 both comparisons may be validly done. If there is no such mode,
5309 return @code{VOIDmode}.
5311 The default version of this hook checks whether the modes are the
5312 same. If they are, it returns that mode. If they are different, it
5313 returns @code{VOIDmode}.
5317 @section Describing Relative Costs of Operations
5318 @cindex costs of instructions
5319 @cindex relative costs
5320 @cindex speed of instructions
5322 These macros let you describe the relative speed of various operations
5323 on the target machine.
5325 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
5326 A C expression for the cost of moving data of mode @var{mode} from a
5327 register in class @var{from} to one in class @var{to}. The classes are
5328 expressed using the enumeration values such as @code{GENERAL_REGS}. A
5329 value of 2 is the default; other values are interpreted relative to
5332 It is not required that the cost always equal 2 when @var{from} is the
5333 same as @var{to}; on some machines it is expensive to move between
5334 registers if they are not general registers.
5336 If reload sees an insn consisting of a single @code{set} between two
5337 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
5338 classes returns a value of 2, reload does not check to ensure that the
5339 constraints of the insn are met. Setting a cost of other than 2 will
5340 allow reload to verify that the constraints are met. You should do this
5341 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
5344 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
5345 A C expression for the cost of moving data of mode @var{mode} between a
5346 register of class @var{class} and memory; @var{in} is zero if the value
5347 is to be written to memory, nonzero if it is to be read in. This cost
5348 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
5349 registers and memory is more expensive than between two registers, you
5350 should define this macro to express the relative cost.
5352 If you do not define this macro, GCC uses a default cost of 4 plus
5353 the cost of copying via a secondary reload register, if one is
5354 needed. If your machine requires a secondary reload register to copy
5355 between memory and a register of @var{class} but the reload mechanism is
5356 more complex than copying via an intermediate, define this macro to
5357 reflect the actual cost of the move.
5359 GCC defines the function @code{memory_move_secondary_cost} if
5360 secondary reloads are needed. It computes the costs due to copying via
5361 a secondary register. If your machine copies from memory using a
5362 secondary register in the conventional way but the default base value of
5363 4 is not correct for your machine, define this macro to add some other
5364 value to the result of that function. The arguments to that function
5365 are the same as to this macro.
5369 A C expression for the cost of a branch instruction. A value of 1 is
5370 the default; other values are interpreted relative to that.
5373 Here are additional macros which do not specify precise relative costs,
5374 but only that certain actions are more expensive than GCC would
5377 @defmac SLOW_BYTE_ACCESS
5378 Define this macro as a C expression which is nonzero if accessing less
5379 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
5380 faster than accessing a word of memory, i.e., if such access
5381 require more than one instruction or if there is no difference in cost
5382 between byte and (aligned) word loads.
5384 When this macro is not defined, the compiler will access a field by
5385 finding the smallest containing object; when it is defined, a fullword
5386 load will be used if alignment permits. Unless bytes accesses are
5387 faster than word accesses, using word accesses is preferable since it
5388 may eliminate subsequent memory access if subsequent accesses occur to
5389 other fields in the same word of the structure, but to different bytes.
5392 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
5393 Define this macro to be the value 1 if memory accesses described by the
5394 @var{mode} and @var{alignment} parameters have a cost many times greater
5395 than aligned accesses, for example if they are emulated in a trap
5398 When this macro is nonzero, the compiler will act as if
5399 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
5400 moves. This can cause significantly more instructions to be produced.
5401 Therefore, do not set this macro nonzero if unaligned accesses only add a
5402 cycle or two to the time for a memory access.
5404 If the value of this macro is always zero, it need not be defined. If
5405 this macro is defined, it should produce a nonzero value when
5406 @code{STRICT_ALIGNMENT} is nonzero.
5410 The threshold of number of scalar memory-to-memory move insns, @emph{below}
5411 which a sequence of insns should be generated instead of a
5412 string move insn or a library call. Increasing the value will always
5413 make code faster, but eventually incurs high cost in increased code size.
5415 Note that on machines where the corresponding move insn is a
5416 @code{define_expand} that emits a sequence of insns, this macro counts
5417 the number of such sequences.
5419 If you don't define this, a reasonable default is used.
5422 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
5423 A C expression used to determine whether @code{move_by_pieces} will be used to
5424 copy a chunk of memory, or whether some other block move mechanism
5425 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5426 than @code{MOVE_RATIO}.
5429 @defmac MOVE_MAX_PIECES
5430 A C expression used by @code{move_by_pieces} to determine the largest unit
5431 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
5435 The threshold of number of scalar move insns, @emph{below} which a sequence
5436 of insns should be generated to clear memory instead of a string clear insn
5437 or a library call. Increasing the value will always make code faster, but
5438 eventually incurs high cost in increased code size.
5440 If you don't define this, a reasonable default is used.
5443 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
5444 A C expression used to determine whether @code{clear_by_pieces} will be used
5445 to clear a chunk of memory, or whether some other block clear mechanism
5446 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5447 than @code{CLEAR_RATIO}.
5450 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
5451 A C expression used to determine whether @code{store_by_pieces} will be
5452 used to set a chunk of memory to a constant value, or whether some other
5453 mechanism will be used. Used by @code{__builtin_memset} when storing
5454 values other than constant zero and by @code{__builtin_strcpy} when
5455 when called with a constant source string.
5456 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5457 than @code{MOVE_RATIO}.
5460 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
5461 A C expression used to determine whether a load postincrement is a good
5462 thing to use for a given mode. Defaults to the value of
5463 @code{HAVE_POST_INCREMENT}.
5466 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
5467 A C expression used to determine whether a load postdecrement is a good
5468 thing to use for a given mode. Defaults to the value of
5469 @code{HAVE_POST_DECREMENT}.
5472 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
5473 A C expression used to determine whether a load preincrement is a good
5474 thing to use for a given mode. Defaults to the value of
5475 @code{HAVE_PRE_INCREMENT}.
5478 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
5479 A C expression used to determine whether a load predecrement is a good
5480 thing to use for a given mode. Defaults to the value of
5481 @code{HAVE_PRE_DECREMENT}.
5484 @defmac USE_STORE_POST_INCREMENT (@var{mode})
5485 A C expression used to determine whether a store postincrement is a good
5486 thing to use for a given mode. Defaults to the value of
5487 @code{HAVE_POST_INCREMENT}.
5490 @defmac USE_STORE_POST_DECREMENT (@var{mode})
5491 A C expression used to determine whether a store postdecrement is a good
5492 thing to use for a given mode. Defaults to the value of
5493 @code{HAVE_POST_DECREMENT}.
5496 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
5497 This macro is used to determine whether a store preincrement is a good
5498 thing to use for a given mode. Defaults to the value of
5499 @code{HAVE_PRE_INCREMENT}.
5502 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
5503 This macro is used to determine whether a store predecrement is a good
5504 thing to use for a given mode. Defaults to the value of
5505 @code{HAVE_PRE_DECREMENT}.
5508 @defmac NO_FUNCTION_CSE
5509 Define this macro if it is as good or better to call a constant
5510 function address than to call an address kept in a register.
5513 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
5514 Define this macro if a non-short-circuit operation produced by
5515 @samp{fold_range_test ()} is optimal. This macro defaults to true if
5516 @code{BRANCH_COST} is greater than or equal to the value 2.
5519 @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total})
5520 This target hook describes the relative costs of RTL expressions.
5522 The cost may depend on the precise form of the expression, which is
5523 available for examination in @var{x}, and the rtx code of the expression
5524 in which it is contained, found in @var{outer_code}. @var{code} is the
5525 expression code---redundant, since it can be obtained with
5526 @code{GET_CODE (@var{x})}.
5528 In implementing this hook, you can use the construct
5529 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
5532 On entry to the hook, @code{*@var{total}} contains a default estimate
5533 for the cost of the expression. The hook should modify this value as
5534 necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
5535 for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
5536 operations, and @code{COSTS_N_INSNS (1)} for all other operations.
5538 When optimizing for code size, i.e.@: when @code{optimize_size} is
5539 nonzero, this target hook should be used to estimate the relative
5540 size cost of an expression, again relative to @code{COSTS_N_INSNS}.
5542 The hook returns true when all subexpressions of @var{x} have been
5543 processed, and false when @code{rtx_cost} should recurse.
5546 @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address})
5547 This hook computes the cost of an addressing mode that contains
5548 @var{address}. If not defined, the cost is computed from
5549 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
5551 For most CISC machines, the default cost is a good approximation of the
5552 true cost of the addressing mode. However, on RISC machines, all
5553 instructions normally have the same length and execution time. Hence
5554 all addresses will have equal costs.
5556 In cases where more than one form of an address is known, the form with
5557 the lowest cost will be used. If multiple forms have the same, lowest,
5558 cost, the one that is the most complex will be used.
5560 For example, suppose an address that is equal to the sum of a register
5561 and a constant is used twice in the same basic block. When this macro
5562 is not defined, the address will be computed in a register and memory
5563 references will be indirect through that register. On machines where
5564 the cost of the addressing mode containing the sum is no higher than
5565 that of a simple indirect reference, this will produce an additional
5566 instruction and possibly require an additional register. Proper
5567 specification of this macro eliminates this overhead for such machines.
5569 This hook is never called with an invalid address.
5571 On machines where an address involving more than one register is as
5572 cheap as an address computation involving only one register, defining
5573 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
5574 be live over a region of code where only one would have been if
5575 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
5576 should be considered in the definition of this macro. Equivalent costs
5577 should probably only be given to addresses with different numbers of
5578 registers on machines with lots of registers.
5582 @section Adjusting the Instruction Scheduler
5584 The instruction scheduler may need a fair amount of machine-specific
5585 adjustment in order to produce good code. GCC provides several target
5586 hooks for this purpose. It is usually enough to define just a few of
5587 them: try the first ones in this list first.
5589 @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
5590 This hook returns the maximum number of instructions that can ever
5591 issue at the same time on the target machine. The default is one.
5592 Although the insn scheduler can define itself the possibility of issue
5593 an insn on the same cycle, the value can serve as an additional
5594 constraint to issue insns on the same simulated processor cycle (see
5595 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
5596 This value must be constant over the entire compilation. If you need
5597 it to vary depending on what the instructions are, you must use
5598 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
5600 You could define this hook to return the value of the macro
5601 @code{MAX_DFA_ISSUE_RATE}.
5604 @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
5605 This hook is executed by the scheduler after it has scheduled an insn
5606 from the ready list. It should return the number of insns which can
5607 still be issued in the current cycle. The default is
5608 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
5609 @code{USE}, which normally are not counted against the issue rate.
5610 You should define this hook if some insns take more machine resources
5611 than others, so that fewer insns can follow them in the same cycle.
5612 @var{file} is either a null pointer, or a stdio stream to write any
5613 debug output to. @var{verbose} is the verbose level provided by
5614 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
5618 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
5619 This function corrects the value of @var{cost} based on the
5620 relationship between @var{insn} and @var{dep_insn} through the
5621 dependence @var{link}. It should return the new value. The default
5622 is to make no adjustment to @var{cost}. This can be used for example
5623 to specify to the scheduler using the traditional pipeline description
5624 that an output- or anti-dependence does not incur the same cost as a
5625 data-dependence. If the scheduler using the automaton based pipeline
5626 description, the cost of anti-dependence is zero and the cost of
5627 output-dependence is maximum of one and the difference of latency
5628 times of the first and the second insns. If these values are not
5629 acceptable, you could use the hook to modify them too. See also
5630 @pxref{Processor pipeline description}.
5633 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
5634 This hook adjusts the integer scheduling priority @var{priority} of
5635 @var{insn}. It should return the new priority. Reduce the priority to
5636 execute @var{insn} earlier, increase the priority to execute @var{insn}
5637 later. Do not define this hook if you do not need to adjust the
5638 scheduling priorities of insns.
5641 @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
5642 This hook is executed by the scheduler after it has scheduled the ready
5643 list, to allow the machine description to reorder it (for example to
5644 combine two small instructions together on @samp{VLIW} machines).
5645 @var{file} is either a null pointer, or a stdio stream to write any
5646 debug output to. @var{verbose} is the verbose level provided by
5647 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
5648 list of instructions that are ready to be scheduled. @var{n_readyp} is
5649 a pointer to the number of elements in the ready list. The scheduler
5650 reads the ready list in reverse order, starting with
5651 @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock}
5652 is the timer tick of the scheduler. You may modify the ready list and
5653 the number of ready insns. The return value is the number of insns that
5654 can issue this cycle; normally this is just @code{issue_rate}. See also
5655 @samp{TARGET_SCHED_REORDER2}.
5658 @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock})
5659 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
5660 function is called whenever the scheduler starts a new cycle. This one
5661 is called once per iteration over a cycle, immediately after
5662 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
5663 return the number of insns to be scheduled in the same cycle. Defining
5664 this hook can be useful if there are frequent situations where
5665 scheduling one insn causes other insns to become ready in the same
5666 cycle. These other insns can then be taken into account properly.
5669 @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail})
5670 This hook is called after evaluation forward dependencies of insns in
5671 chain given by two parameter values (@var{head} and @var{tail}
5672 correspondingly) but before insns scheduling of the insn chain. For
5673 example, it can be used for better insn classification if it requires
5674 analysis of dependencies. This hook can use backward and forward
5675 dependencies of the insn scheduler because they are already
5679 @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
5680 This hook is executed by the scheduler at the beginning of each block of
5681 instructions that are to be scheduled. @var{file} is either a null
5682 pointer, or a stdio stream to write any debug output to. @var{verbose}
5683 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
5684 @var{max_ready} is the maximum number of insns in the current scheduling
5685 region that can be live at the same time. This can be used to allocate
5686 scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
5689 @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
5690 This hook is executed by the scheduler at the end of each block of
5691 instructions that are to be scheduled. It can be used to perform
5692 cleanup of any actions done by the other scheduling hooks. @var{file}
5693 is either a null pointer, or a stdio stream to write any debug output
5694 to. @var{verbose} is the verbose level provided by
5695 @option{-fsched-verbose-@var{n}}.
5698 @deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid})
5699 This hook is executed by the scheduler after function level initializations.
5700 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
5701 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
5702 @var{old_max_uid} is the maximum insn uid when scheduling begins.
5705 @deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose})
5706 This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
5707 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
5708 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
5711 @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
5712 The hook returns an RTL insn. The automaton state used in the
5713 pipeline hazard recognizer is changed as if the insn were scheduled
5714 when the new simulated processor cycle starts. Usage of the hook may
5715 simplify the automaton pipeline description for some @acronym{VLIW}
5716 processors. If the hook is defined, it is used only for the automaton
5717 based pipeline description. The default is not to change the state
5718 when the new simulated processor cycle starts.
5721 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
5722 The hook can be used to initialize data used by the previous hook.
5725 @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
5726 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
5727 to changed the state as if the insn were scheduled when the new
5728 simulated processor cycle finishes.
5731 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
5732 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
5733 used to initialize data used by the previous hook.
5736 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
5737 This hook controls better choosing an insn from the ready insn queue
5738 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
5739 chooses the first insn from the queue. If the hook returns a positive
5740 value, an additional scheduler code tries all permutations of
5741 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
5742 subsequent ready insns to choose an insn whose issue will result in
5743 maximal number of issued insns on the same cycle. For the
5744 @acronym{VLIW} processor, the code could actually solve the problem of
5745 packing simple insns into the @acronym{VLIW} insn. Of course, if the
5746 rules of @acronym{VLIW} packing are described in the automaton.
5748 This code also could be used for superscalar @acronym{RISC}
5749 processors. Let us consider a superscalar @acronym{RISC} processor
5750 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
5751 @var{B}, some insns can be executed only in pipelines @var{B} or
5752 @var{C}, and one insn can be executed in pipeline @var{B}. The
5753 processor may issue the 1st insn into @var{A} and the 2nd one into
5754 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
5755 until the next cycle. If the scheduler issues the 3rd insn the first,
5756 the processor could issue all 3 insns per cycle.
5758 Actually this code demonstrates advantages of the automaton based
5759 pipeline hazard recognizer. We try quickly and easy many insn
5760 schedules to choose the best one.
5762 The default is no multipass scheduling.
5765 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx)
5767 This hook controls what insns from the ready insn queue will be
5768 considered for the multipass insn scheduling. If the hook returns
5769 zero for insn passed as the parameter, the insn will be not chosen to
5772 The default is that any ready insns can be chosen to be issued.
5775 @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *)
5777 This hook is called by the insn scheduler before issuing insn passed
5778 as the third parameter on given cycle. If the hook returns nonzero,
5779 the insn is not issued on given processors cycle. Instead of that,
5780 the processor cycle is advanced. If the value passed through the last
5781 parameter is zero, the insn ready queue is not sorted on the new cycle
5782 start as usually. The first parameter passes file for debugging
5783 output. The second one passes the scheduler verbose level of the
5784 debugging output. The forth and the fifth parameter values are
5785 correspondingly processor cycle on which the previous insn has been
5786 issued and the current processor cycle.
5789 @deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (rtx @var{insn1}, rtx @var{insn2}, rtx @var{dep_link}, int @var{dep_cost}, int @var{distance})
5790 This hook is used to define which dependences are considered costly by
5791 the target, so costly that it is not advisable to schedule the insns that
5792 are involved in the dependence too close to one another. The parameters
5793 to this hook are as follows: The second parameter @var{insn2} is dependent
5794 upon the first parameter @var{insn1}. The dependence between @var{insn1}
5795 and @var{insn2} is represented by the third parameter @var{dep_link}. The
5796 fourth parameter @var{cost} is the cost of the dependence, and the fifth
5797 parameter @var{distance} is the distance in cycles between the two insns.
5798 The hook returns @code{true} if considering the distance between the two
5799 insns the dependence between them is considered costly by the target,
5800 and @code{false} otherwise.
5802 Defining this hook can be useful in multiple-issue out-of-order machines,
5803 where (a) it's practically hopeless to predict the actual data/resource
5804 delays, however: (b) there's a better chance to predict the actual grouping
5805 that will be formed, and (c) correctly emulating the grouping can be very
5806 important. In such targets one may want to allow issuing dependent insns
5807 closer to one another---i.e., closer than the dependence distance; however,
5808 not in cases of "costly dependences", which this hooks allows to define.
5811 Macros in the following table are generated by the program
5812 @file{genattr} and can be useful for writing the hooks.
5814 @defmac MAX_DFA_ISSUE_RATE
5815 The macro definition is generated in the automaton based pipeline
5816 description interface. Its value is calculated from the automaton
5817 based pipeline description and is equal to maximal number of all insns
5818 described in constructions @samp{define_insn_reservation} which can be
5819 issued on the same processor cycle.
5823 @section Dividing the Output into Sections (Texts, Data, @dots{})
5824 @c the above section title is WAY too long. maybe cut the part between
5825 @c the (...)? --mew 10feb93
5827 An object file is divided into sections containing different types of
5828 data. In the most common case, there are three sections: the @dfn{text
5829 section}, which holds instructions and read-only data; the @dfn{data
5830 section}, which holds initialized writable data; and the @dfn{bss
5831 section}, which holds uninitialized data. Some systems have other kinds
5834 The compiler must tell the assembler when to switch sections. These
5835 macros control what commands to output to tell the assembler this. You
5836 can also define additional sections.
5838 @defmac TEXT_SECTION_ASM_OP
5839 A C expression whose value is a string, including spacing, containing the
5840 assembler operation that should precede instructions and read-only data.
5841 Normally @code{"\t.text"} is right.
5844 @defmac HOT_TEXT_SECTION_NAME
5845 If defined, a C string constant for the name of the section containing most
5846 frequently executed functions of the program. If not defined, GCC will provide
5847 a default definition if the target supports named sections.
5850 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
5851 If defined, a C string constant for the name of the section containing unlikely
5852 executed functions in the program.
5855 @defmac DATA_SECTION_ASM_OP
5856 A C expression whose value is a string, including spacing, containing the
5857 assembler operation to identify the following data as writable initialized
5858 data. Normally @code{"\t.data"} is right.
5861 @defmac READONLY_DATA_SECTION_ASM_OP
5862 A C expression whose value is a string, including spacing, containing the
5863 assembler operation to identify the following data as read-only initialized
5867 @defmac READONLY_DATA_SECTION
5868 A macro naming a function to call to switch to the proper section for
5869 read-only data. The default is to use @code{READONLY_DATA_SECTION_ASM_OP}
5870 if defined, else fall back to @code{text_section}.
5872 The most common definition will be @code{data_section}, if the target
5873 does not have a special read-only data section, and does not put data
5874 in the text section.
5877 @defmac BSS_SECTION_ASM_OP
5878 If defined, a C expression whose value is a string, including spacing,
5879 containing the assembler operation to identify the following data as
5880 uninitialized global data. If not defined, and neither
5881 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
5882 uninitialized global data will be output in the data section if
5883 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
5887 @defmac INIT_SECTION_ASM_OP
5888 If defined, a C expression whose value is a string, including spacing,
5889 containing the assembler operation to identify the following data as
5890 initialization code. If not defined, GCC will assume such a section does
5894 @defmac FINI_SECTION_ASM_OP
5895 If defined, a C expression whose value is a string, including spacing,
5896 containing the assembler operation to identify the following data as
5897 finalization code. If not defined, GCC will assume such a section does
5901 @defmac INIT_ARRAY_SECTION_ASM_OP
5902 If defined, a C expression whose value is a string, including spacing,
5903 containing the assembler operation to identify the following data as
5904 part of the @code{.init_array} (or equivalent) section. If not
5905 defined, GCC will assume such a section does not exist. Do not define
5906 both this macro and @code{INIT_SECTION_ASM_OP}.
5909 @defmac FINI_ARRAY_SECTION_ASM_OP
5910 If defined, a C expression whose value is a string, including spacing,
5911 containing the assembler operation to identify the following data as
5912 part of the @code{.fini_array} (or equivalent) section. If not
5913 defined, GCC will assume such a section does not exist. Do not define
5914 both this macro and @code{FINI_SECTION_ASM_OP}.
5917 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
5918 If defined, an ASM statement that switches to a different section
5919 via @var{section_op}, calls @var{function}, and switches back to
5920 the text section. This is used in @file{crtstuff.c} if
5921 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
5922 to initialization and finalization functions from the init and fini
5923 sections. By default, this macro uses a simple function call. Some
5924 ports need hand-crafted assembly code to avoid dependencies on
5925 registers initialized in the function prologue or to ensure that
5926 constant pools don't end up too far way in the text section.
5929 @defmac FORCE_CODE_SECTION_ALIGN
5930 If defined, an ASM statement that aligns a code section to some
5931 arbitrary boundary. This is used to force all fragments of the
5932 @code{.init} and @code{.fini} sections to have to same alignment
5933 and thus prevent the linker from having to add any padding.
5938 @defmac EXTRA_SECTIONS
5939 A list of names for sections other than the standard two, which are
5940 @code{in_text} and @code{in_data}. You need not define this macro
5941 on a system with no other sections (that GCC needs to use).
5944 @findex text_section
5945 @findex data_section
5946 @defmac EXTRA_SECTION_FUNCTIONS
5947 One or more functions to be defined in @file{varasm.c}. These
5948 functions should do jobs analogous to those of @code{text_section} and
5949 @code{data_section}, for your additional sections. Do not define this
5950 macro if you do not define @code{EXTRA_SECTIONS}.
5953 @defmac JUMP_TABLES_IN_TEXT_SECTION
5954 Define this macro to be an expression with a nonzero value if jump
5955 tables (for @code{tablejump} insns) should be output in the text
5956 section, along with the assembler instructions. Otherwise, the
5957 readonly data section is used.
5959 This macro is irrelevant if there is no separate readonly data section.
5962 @deftypefn {Target Hook} void TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
5963 Switches to the appropriate section for output of @var{exp}. You can
5964 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
5965 some sort. @var{reloc} indicates whether the initial value of @var{exp}
5966 requires link-time relocations. Bit 0 is set when variable contains
5967 local relocations only, while bit 1 is set for global relocations.
5968 Select the section by calling @code{data_section} or one of the
5969 alternatives for other sections. @var{align} is the constant alignment
5972 The default version of this function takes care of putting read-only
5973 variables in @code{readonly_data_section}.
5975 See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
5978 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS
5979 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
5980 for @code{FUNCTION_DECL}s as well as for variables and constants.
5982 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
5983 function has been determined to be likely to be called, and nonzero if
5984 it is unlikely to be called.
5987 @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
5988 Build up a unique section name, expressed as a @code{STRING_CST} node,
5989 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
5990 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
5991 the initial value of @var{exp} requires link-time relocations.
5993 The default version of this function appends the symbol name to the
5994 ELF section name that would normally be used for the symbol. For
5995 example, the function @code{foo} would be placed in @code{.text.foo}.
5996 Whatever the actual target object format, this is often good enough.
5999 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl})
6000 Switches to a readonly data section associated with
6001 @samp{DECL_SECTION_NAME (@var{decl})}.
6002 The default version of this function switches to @code{.gnu.linkonce.r.name}
6003 section if function's section is @code{.gnu.linkonce.t.name}, to
6004 @code{.rodata.name} if function is in @code{.text.name} section
6005 and otherwise switches to the normal readonly data section.
6008 @deftypefn {Target Hook} void TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
6009 Switches to the appropriate section for output of constant pool entry
6010 @var{x} in @var{mode}. You can assume that @var{x} is some kind of
6011 constant in RTL@. The argument @var{mode} is redundant except in the
6012 case of a @code{const_int} rtx. Select the section by calling
6013 @code{readonly_data_section} or one of the alternatives for other
6014 sections. @var{align} is the constant alignment in bits.
6016 The default version of this function takes care of putting symbolic
6017 constants in @code{flag_pic} mode in @code{data_section} and everything
6018 else in @code{readonly_data_section}.
6021 @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
6022 Define this hook if references to a symbol or a constant must be
6023 treated differently depending on something about the variable or
6024 function named by the symbol (such as what section it is in).
6026 The hook is executed immediately after rtl has been created for
6027 @var{decl}, which may be a variable or function declaration or
6028 an entry in the constant pool. In either case, @var{rtl} is the
6029 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
6030 in this hook; that field may not have been initialized yet.
6032 In the case of a constant, it is safe to assume that the rtl is
6033 a @code{mem} whose address is a @code{symbol_ref}. Most decls
6034 will also have this form, but that is not guaranteed. Global
6035 register variables, for instance, will have a @code{reg} for their
6036 rtl. (Normally the right thing to do with such unusual rtl is
6039 The @var{new_decl_p} argument will be true if this is the first time
6040 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
6041 be false for subsequent invocations, which will happen for duplicate
6042 declarations. Whether or not anything must be done for the duplicate
6043 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
6044 @var{new_decl_p} is always true when the hook is called for a constant.
6046 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
6047 The usual thing for this hook to do is to record flags in the
6048 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
6049 Historically, the name string was modified if it was necessary to
6050 encode more than one bit of information, but this practice is now
6051 discouraged; use @code{SYMBOL_REF_FLAGS}.
6053 The default definition of this hook, @code{default_encode_section_info}
6054 in @file{varasm.c}, sets a number of commonly-useful bits in
6055 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
6056 before overriding it.
6059 @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name)
6060 Decode @var{name} and return the real name part, sans
6061 the characters that @code{TARGET_ENCODE_SECTION_INFO}
6065 @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp})
6066 Returns true if @var{exp} should be placed into a ``small data'' section.
6067 The default version of this hook always returns false.
6070 @deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
6071 Contains the value true if the target places read-only
6072 ``small data'' into a separate section. The default value is false.
6075 @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp})
6076 Returns true if @var{exp} names an object for which name resolution
6077 rules must resolve to the current ``module'' (dynamic shared library
6078 or executable image).
6080 The default version of this hook implements the name resolution rules
6081 for ELF, which has a looser model of global name binding than other
6082 currently supported object file formats.
6085 @deftypevar {Target Hook} bool TARGET_HAVE_TLS
6086 Contains the value true if the target supports thread-local storage.
6087 The default value is false.
6092 @section Position Independent Code
6093 @cindex position independent code
6096 This section describes macros that help implement generation of position
6097 independent code. Simply defining these macros is not enough to
6098 generate valid PIC; you must also add support to the macros
6099 @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as
6100 well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of
6101 @samp{movsi} to do something appropriate when the source operand
6102 contains a symbolic address. You may also need to alter the handling of
6103 switch statements so that they use relative addresses.
6104 @c i rearranged the order of the macros above to try to force one of
6105 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
6107 @defmac PIC_OFFSET_TABLE_REGNUM
6108 The register number of the register used to address a table of static
6109 data addresses in memory. In some cases this register is defined by a
6110 processor's ``application binary interface'' (ABI)@. When this macro
6111 is defined, RTL is generated for this register once, as with the stack
6112 pointer and frame pointer registers. If this macro is not defined, it
6113 is up to the machine-dependent files to allocate such a register (if
6114 necessary). Note that this register must be fixed when in use (e.g.@:
6115 when @code{flag_pic} is true).
6118 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
6119 Define this macro if the register defined by
6120 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define
6121 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
6124 @defmac FINALIZE_PIC
6125 By generating position-independent code, when two different programs (A
6126 and B) share a common library (libC.a), the text of the library can be
6127 shared whether or not the library is linked at the same address for both
6128 programs. In some of these environments, position-independent code
6129 requires not only the use of different addressing modes, but also
6130 special code to enable the use of these addressing modes.
6132 The @code{FINALIZE_PIC} macro serves as a hook to emit these special
6133 codes once the function is being compiled into assembly code, but not
6134 before. (It is not done before, because in the case of compiling an
6135 inline function, it would lead to multiple PIC prologues being
6136 included in functions which used inline functions and were compiled to
6140 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
6141 A C expression that is nonzero if @var{x} is a legitimate immediate
6142 operand on the target machine when generating position independent code.
6143 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
6144 check this. You can also assume @var{flag_pic} is true, so you need not
6145 check it either. You need not define this macro if all constants
6146 (including @code{SYMBOL_REF}) can be immediate operands when generating
6147 position independent code.
6150 @node Assembler Format
6151 @section Defining the Output Assembler Language
6153 This section describes macros whose principal purpose is to describe how
6154 to write instructions in assembler language---rather than what the
6158 * File Framework:: Structural information for the assembler file.
6159 * Data Output:: Output of constants (numbers, strings, addresses).
6160 * Uninitialized Data:: Output of uninitialized variables.
6161 * Label Output:: Output and generation of labels.
6162 * Initialization:: General principles of initialization
6163 and termination routines.
6164 * Macros for Initialization::
6165 Specific macros that control the handling of
6166 initialization and termination routines.
6167 * Instruction Output:: Output of actual instructions.
6168 * Dispatch Tables:: Output of jump tables.
6169 * Exception Region Output:: Output of exception region code.
6170 * Alignment Output:: Pseudo ops for alignment and skipping data.
6173 @node File Framework
6174 @subsection The Overall Framework of an Assembler File
6175 @cindex assembler format
6176 @cindex output of assembler code
6178 @c prevent bad page break with this line
6179 This describes the overall framework of an assembly file.
6181 @deftypefn {Target Hook} void TARGET_ASM_FILE_START ()
6182 @findex default_file_start
6183 Output to @code{asm_out_file} any text which the assembler expects to
6184 find at the beginning of a file. The default behavior is controlled
6185 by two flags, documented below. Unless your target's assembler is
6186 quite unusual, if you override the default, you should call
6187 @code{default_file_start} at some point in your target hook. This
6188 lets other target files rely on these variables.
6191 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
6192 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
6193 printed as the very first line in the assembly file, unless
6194 @option{-fverbose-asm} is in effect. (If that macro has been defined
6195 to the empty string, this variable has no effect.) With the normal
6196 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
6197 assembler that it need not bother stripping comments or extra
6198 whitespace from its input. This allows it to work a bit faster.
6200 The default is false. You should not set it to true unless you have
6201 verified that your port does not generate any extra whitespace or
6202 comments that will cause GAS to issue errors in NO_APP mode.
6205 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
6206 If this flag is true, @code{output_file_directive} will be called
6207 for the primary source file, immediately after printing
6208 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
6209 this to be done. The default is false.
6212 @deftypefn {Target Hook} void TARGET_ASM_FILE_END ()
6213 Output to @code{asm_out_file} any text which the assembler expects
6214 to find at the end of a file. The default is to output nothing.
6217 @deftypefun void file_end_indicate_exec_stack ()
6218 Some systems use a common convention, the @samp{.note.GNU-stack}
6219 special section, to indicate whether or not an object file relies on
6220 the stack being executable. If your system uses this convention, you
6221 should define @code{TARGET_ASM_FILE_END} to this function. If you
6222 need to do other things in that hook, have your hook function call
6226 @defmac ASM_COMMENT_START
6227 A C string constant describing how to begin a comment in the target
6228 assembler language. The compiler assumes that the comment will end at
6229 the end of the line.
6233 A C string constant for text to be output before each @code{asm}
6234 statement or group of consecutive ones. Normally this is
6235 @code{"#APP"}, which is a comment that has no effect on most
6236 assemblers but tells the GNU assembler that it must check the lines
6237 that follow for all valid assembler constructs.
6241 A C string constant for text to be output after each @code{asm}
6242 statement or group of consecutive ones. Normally this is
6243 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
6244 time-saving assumptions that are valid for ordinary compiler output.
6247 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
6248 A C statement to output COFF information or DWARF debugging information
6249 which indicates that filename @var{name} is the current source file to
6250 the stdio stream @var{stream}.
6252 This macro need not be defined if the standard form of output
6253 for the file format in use is appropriate.
6256 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
6257 A C statement to output the string @var{string} to the stdio stream
6258 @var{stream}. If you do not call the function @code{output_quoted_string}
6259 in your config files, GCC will only call it to output filenames to
6260 the assembler source. So you can use it to canonicalize the format
6261 of the filename using this macro.
6264 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
6265 A C statement to output something to the assembler file to handle a
6266 @samp{#ident} directive containing the text @var{string}. If this
6267 macro is not defined, nothing is output for a @samp{#ident} directive.
6270 @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align})
6271 Output assembly directives to switch to section @var{name}. The section
6272 should have attributes as specified by @var{flags}, which is a bit mask
6273 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align}
6274 is nonzero, it contains an alignment in bytes to be used for the section,
6275 otherwise some target default should be used. Only targets that must
6276 specify an alignment within the section directive need pay attention to
6277 @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}.
6280 @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
6281 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
6284 @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
6285 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
6286 based on a variable or function decl, a section name, and whether or not the
6287 declaration's initializer may contain runtime relocations. @var{decl} may be
6288 null, in which case read-write data should be assumed.
6290 The default version if this function handles choosing code vs data,
6291 read-only vs read-write data, and @code{flag_pic}. You should only
6292 need to override this if your target has special flags that might be
6293 set via @code{__attribute__}.
6298 @subsection Output of Data
6301 @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
6302 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
6303 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
6304 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
6305 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
6306 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
6307 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
6308 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
6309 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
6310 These hooks specify assembly directives for creating certain kinds
6311 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
6312 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
6313 aligned two-byte object, and so on. Any of the hooks may be
6314 @code{NULL}, indicating that no suitable directive is available.
6316 The compiler will print these strings at the start of a new line,
6317 followed immediately by the object's initial value. In most cases,
6318 the string should contain a tab, a pseudo-op, and then another tab.
6321 @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
6322 The @code{assemble_integer} function uses this hook to output an
6323 integer object. @var{x} is the object's value, @var{size} is its size
6324 in bytes and @var{aligned_p} indicates whether it is aligned. The
6325 function should return @code{true} if it was able to output the
6326 object. If it returns false, @code{assemble_integer} will try to
6327 split the object into smaller parts.
6329 The default implementation of this hook will use the
6330 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
6331 when the relevant string is @code{NULL}.
6334 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
6335 A C statement to recognize @var{rtx} patterns that
6336 @code{output_addr_const} can't deal with, and output assembly code to
6337 @var{stream} corresponding to the pattern @var{x}. This may be used to
6338 allow machine-dependent @code{UNSPEC}s to appear within constants.
6340 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
6341 @code{goto fail}, so that a standard error message is printed. If it
6342 prints an error message itself, by calling, for example,
6343 @code{output_operand_lossage}, it may just complete normally.
6346 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
6347 A C statement to output to the stdio stream @var{stream} an assembler
6348 instruction to assemble a string constant containing the @var{len}
6349 bytes at @var{ptr}. @var{ptr} will be a C expression of type
6350 @code{char *} and @var{len} a C expression of type @code{int}.
6352 If the assembler has a @code{.ascii} pseudo-op as found in the
6353 Berkeley Unix assembler, do not define the macro
6354 @code{ASM_OUTPUT_ASCII}.
6357 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
6358 A C statement to output word @var{n} of a function descriptor for
6359 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
6360 is defined, and is otherwise unused.
6363 @defmac CONSTANT_POOL_BEFORE_FUNCTION
6364 You may define this macro as a C expression. You should define the
6365 expression to have a nonzero value if GCC should output the constant
6366 pool for a function before the code for the function, or a zero value if
6367 GCC should output the constant pool after the function. If you do
6368 not define this macro, the usual case, GCC will output the constant
6369 pool before the function.
6372 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
6373 A C statement to output assembler commands to define the start of the
6374 constant pool for a function. @var{funname} is a string giving
6375 the name of the function. Should the return type of the function
6376 be required, it can be obtained via @var{fundecl}. @var{size}
6377 is the size, in bytes, of the constant pool that will be written
6378 immediately after this call.
6380 If no constant-pool prefix is required, the usual case, this macro need
6384 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
6385 A C statement (with or without semicolon) to output a constant in the
6386 constant pool, if it needs special treatment. (This macro need not do
6387 anything for RTL expressions that can be output normally.)
6389 The argument @var{file} is the standard I/O stream to output the
6390 assembler code on. @var{x} is the RTL expression for the constant to
6391 output, and @var{mode} is the machine mode (in case @var{x} is a
6392 @samp{const_int}). @var{align} is the required alignment for the value
6393 @var{x}; you should output an assembler directive to force this much
6396 The argument @var{labelno} is a number to use in an internal label for
6397 the address of this pool entry. The definition of this macro is
6398 responsible for outputting the label definition at the proper place.
6399 Here is how to do this:
6402 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
6405 When you output a pool entry specially, you should end with a
6406 @code{goto} to the label @var{jumpto}. This will prevent the same pool
6407 entry from being output a second time in the usual manner.
6409 You need not define this macro if it would do nothing.
6412 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
6413 A C statement to output assembler commands to at the end of the constant
6414 pool for a function. @var{funname} is a string giving the name of the
6415 function. Should the return type of the function be required, you can
6416 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
6417 constant pool that GCC wrote immediately before this call.
6419 If no constant-pool epilogue is required, the usual case, you need not
6423 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C})
6424 Define this macro as a C expression which is nonzero if @var{C} is
6425 used as a logical line separator by the assembler.
6427 If you do not define this macro, the default is that only
6428 the character @samp{;} is treated as a logical line separator.
6431 @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
6432 @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
6433 These target hooks are C string constants, describing the syntax in the
6434 assembler for grouping arithmetic expressions. If not overridden, they
6435 default to normal parentheses, which is correct for most assemblers.
6438 These macros are provided by @file{real.h} for writing the definitions
6439 of @code{ASM_OUTPUT_DOUBLE} and the like:
6441 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
6442 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
6443 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
6444 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's
6445 floating point representation, and store its bit pattern in the variable
6446 @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE}, this variable should
6447 be a simple @code{long int}. For the others, it should be an array of
6448 @code{long int}. The number of elements in this array is determined by
6449 the size of the desired target floating point data type: 32 bits of it
6450 go in each @code{long int} array element. Each array element holds 32
6451 bits of the result, even if @code{long int} is wider than 32 bits on the
6454 The array element values are designed so that you can print them out
6455 using @code{fprintf} in the order they should appear in the target
6459 @node Uninitialized Data
6460 @subsection Output of Uninitialized Variables
6462 Each of the macros in this section is used to do the whole job of
6463 outputting a single uninitialized variable.
6465 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6466 A C statement (sans semicolon) to output to the stdio stream
6467 @var{stream} the assembler definition of a common-label named
6468 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6469 is the size rounded up to whatever alignment the caller wants.
6471 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6472 output the name itself; before and after that, output the additional
6473 assembler syntax for defining the name, and a newline.
6475 This macro controls how the assembler definitions of uninitialized
6476 common global variables are output.
6479 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
6480 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
6481 separate, explicit argument. If you define this macro, it is used in
6482 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
6483 handling the required alignment of the variable. The alignment is specified
6484 as the number of bits.
6487 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6488 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
6489 variable to be output, if there is one, or @code{NULL_TREE} if there
6490 is no corresponding variable. If you define this macro, GCC will use it
6491 in place of both @code{ASM_OUTPUT_COMMON} and
6492 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
6493 the variable's decl in order to chose what to output.
6496 @defmac ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6497 If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it
6498 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON}
6502 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6503 A C statement (sans semicolon) to output to the stdio stream
6504 @var{stream} the assembler definition of uninitialized global @var{decl} named
6505 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6506 is the size rounded up to whatever alignment the caller wants.
6508 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
6509 defining this macro. If unable, use the expression
6510 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
6511 before and after that, output the additional assembler syntax for defining
6512 the name, and a newline.
6514 This macro controls how the assembler definitions of uninitialized global
6515 variables are output. This macro exists to properly support languages like
6516 C++ which do not have @code{common} data. However, this macro currently
6517 is not defined for all targets. If this macro and
6518 @code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON}
6519 or @code{ASM_OUTPUT_ALIGNED_COMMON} or
6520 @code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used.
6523 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6524 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
6525 separate, explicit argument. If you define this macro, it is used in
6526 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
6527 handling the required alignment of the variable. The alignment is specified
6528 as the number of bits.
6530 Try to use function @code{asm_output_aligned_bss} defined in file
6531 @file{varasm.c} when defining this macro.
6534 @defmac ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6535 If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it
6536 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS}
6540 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6541 A C statement (sans semicolon) to output to the stdio stream
6542 @var{stream} the assembler definition of a local-common-label named
6543 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6544 is the size rounded up to whatever alignment the caller wants.
6546 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6547 output the name itself; before and after that, output the additional
6548 assembler syntax for defining the name, and a newline.
6550 This macro controls how the assembler definitions of uninitialized
6551 static variables are output.
6554 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
6555 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
6556 separate, explicit argument. If you define this macro, it is used in
6557 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
6558 handling the required alignment of the variable. The alignment is specified
6559 as the number of bits.
6562 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6563 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
6564 variable to be output, if there is one, or @code{NULL_TREE} if there
6565 is no corresponding variable. If you define this macro, GCC will use it
6566 in place of both @code{ASM_OUTPUT_DECL} and
6567 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
6568 the variable's decl in order to chose what to output.
6571 @defmac ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6572 If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it
6573 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL}
6578 @subsection Output and Generation of Labels
6580 @c prevent bad page break with this line
6581 This is about outputting labels.
6583 @findex assemble_name
6584 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
6585 A C statement (sans semicolon) to output to the stdio stream
6586 @var{stream} the assembler definition of a label named @var{name}.
6587 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6588 output the name itself; before and after that, output the additional
6589 assembler syntax for defining the name, and a newline. A default
6590 definition of this macro is provided which is correct for most systems.
6593 @findex assemble_name_raw
6594 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
6595 Identical to @code{ASM_OUTPUT_lABEL}, except that @var{name} is known
6596 to refer to a compiler-generated label. The default definition uses
6597 @code{assemble_name_raw}, which is like @code{assemble_name} except
6598 that it is more efficient.
6602 A C string containing the appropriate assembler directive to specify the
6603 size of a symbol, without any arguments. On systems that use ELF, the
6604 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
6605 systems, the default is not to define this macro.
6607 Define this macro only if it is correct to use the default definitions
6608 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
6609 for your system. If you need your own custom definitions of those
6610 macros, or if you do not need explicit symbol sizes at all, do not
6614 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
6615 A C statement (sans semicolon) to output to the stdio stream
6616 @var{stream} a directive telling the assembler that the size of the
6617 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
6618 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6622 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
6623 A C statement (sans semicolon) to output to the stdio stream
6624 @var{stream} a directive telling the assembler to calculate the size of
6625 the symbol @var{name} by subtracting its address from the current
6628 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6629 provided. The default assumes that the assembler recognizes a special
6630 @samp{.} symbol as referring to the current address, and can calculate
6631 the difference between this and another symbol. If your assembler does
6632 not recognize @samp{.} or cannot do calculations with it, you will need
6633 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
6637 A C string containing the appropriate assembler directive to specify the
6638 type of a symbol, without any arguments. On systems that use ELF, the
6639 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
6640 systems, the default is not to define this macro.
6642 Define this macro only if it is correct to use the default definition of
6643 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6644 custom definition of this macro, or if you do not need explicit symbol
6645 types at all, do not define this macro.
6648 @defmac TYPE_OPERAND_FMT
6649 A C string which specifies (using @code{printf} syntax) the format of
6650 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
6651 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
6652 the default is not to define this macro.
6654 Define this macro only if it is correct to use the default definition of
6655 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6656 custom definition of this macro, or if you do not need explicit symbol
6657 types at all, do not define this macro.
6660 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
6661 A C statement (sans semicolon) to output to the stdio stream
6662 @var{stream} a directive telling the assembler that the type of the
6663 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
6664 that string is always either @samp{"function"} or @samp{"object"}, but
6665 you should not count on this.
6667 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
6668 definition of this macro is provided.
6671 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
6672 A C statement (sans semicolon) to output to the stdio stream
6673 @var{stream} any text necessary for declaring the name @var{name} of a
6674 function which is being defined. This macro is responsible for
6675 outputting the label definition (perhaps using
6676 @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the
6677 @code{FUNCTION_DECL} tree node representing the function.
6679 If this macro is not defined, then the function name is defined in the
6680 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6682 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
6686 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
6687 A C statement (sans semicolon) to output to the stdio stream
6688 @var{stream} any text necessary for declaring the size of a function
6689 which is being defined. The argument @var{name} is the name of the
6690 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
6691 representing the function.
6693 If this macro is not defined, then the function size is not defined.
6695 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
6699 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
6700 A C statement (sans semicolon) to output to the stdio stream
6701 @var{stream} any text necessary for declaring the name @var{name} of an
6702 initialized variable which is being defined. This macro must output the
6703 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
6704 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
6706 If this macro is not defined, then the variable name is defined in the
6707 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6709 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
6710 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
6713 @defmac ASM_DECLARE_CONSTANT_NAME (@var{stream}, @var{name}, @var{exp}, @var{size})
6714 A C statement (sans semicolon) to output to the stdio stream
6715 @var{stream} any text necessary for declaring the name @var{name} of a
6716 constant which is being defined. This macro is responsible for
6717 outputting the label definition (perhaps using
6718 @code{ASM_OUTPUT_LABEL}). The argument @var{exp} is the
6719 value of the constant, and @var{size} is the size of the constant
6720 in bytes. @var{name} will be an internal label.
6722 If this macro is not defined, then the @var{name} is defined in the
6723 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6725 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
6729 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
6730 A C statement (sans semicolon) to output to the stdio stream
6731 @var{stream} any text necessary for claiming a register @var{regno}
6732 for a global variable @var{decl} with name @var{name}.
6734 If you don't define this macro, that is equivalent to defining it to do
6738 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
6739 A C statement (sans semicolon) to finish up declaring a variable name
6740 once the compiler has processed its initializer fully and thus has had a
6741 chance to determine the size of an array when controlled by an
6742 initializer. This is used on systems where it's necessary to declare
6743 something about the size of the object.
6745 If you don't define this macro, that is equivalent to defining it to do
6748 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
6749 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
6752 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
6753 This target hook is a function to output to the stdio stream
6754 @var{stream} some commands that will make the label @var{name} global;
6755 that is, available for reference from other files.
6757 The default implementation relies on a proper definition of
6758 @code{GLOBAL_ASM_OP}.
6761 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
6762 A C statement (sans semicolon) to output to the stdio stream
6763 @var{stream} some commands that will make the label @var{name} weak;
6764 that is, available for reference from other files but only used if
6765 no other definition is available. Use the expression
6766 @code{assemble_name (@var{stream}, @var{name})} to output the name
6767 itself; before and after that, output the additional assembler syntax
6768 for making that name weak, and a newline.
6770 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
6771 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
6775 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
6776 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
6777 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
6778 or variable decl. If @var{value} is not @code{NULL}, this C statement
6779 should output to the stdio stream @var{stream} assembler code which
6780 defines (equates) the weak symbol @var{name} to have the value
6781 @var{value}. If @var{value} is @code{NULL}, it should output commands
6782 to make @var{name} weak.
6785 @defmac SUPPORTS_WEAK
6786 A C expression which evaluates to true if the target supports weak symbols.
6788 If you don't define this macro, @file{defaults.h} provides a default
6789 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
6790 is defined, the default definition is @samp{1}; otherwise, it is
6791 @samp{0}. Define this macro if you want to control weak symbol support
6792 with a compiler flag such as @option{-melf}.
6795 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
6796 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
6797 public symbol such that extra copies in multiple translation units will
6798 be discarded by the linker. Define this macro if your object file
6799 format provides support for this concept, such as the @samp{COMDAT}
6800 section flags in the Microsoft Windows PE/COFF format, and this support
6801 requires changes to @var{decl}, such as putting it in a separate section.
6804 @defmac SUPPORTS_ONE_ONLY
6805 A C expression which evaluates to true if the target supports one-only
6808 If you don't define this macro, @file{varasm.c} provides a default
6809 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
6810 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
6811 you want to control one-only symbol support with a compiler flag, or if
6812 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
6813 be emitted as one-only.
6816 @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility})
6817 This target hook is a function to output to @var{asm_out_file} some
6818 commands that will make the symbol(s) associated with @var{decl} have
6819 hidden, protected or internal visibility as specified by @var{visibility}.
6822 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
6823 A C expression that evaluates to true if the target's linker expects
6824 that weak symbols do not appear in a static archive's table of contents.
6825 The default is @code{0}.
6827 Leaving weak symbols out of an archive's table of contents means that,
6828 if a symbol will only have a definition in one translation unit and
6829 will have undefined references from other translation units, that
6830 symbol should not be weak. Defining this macro to be nonzero will
6831 thus have the effect that certain symbols that would normally be weak
6832 (explicit template instantiations, and vtables for polymorphic classes
6833 with noninline key methods) will instead be nonweak.
6835 The C++ ABI requires this macro to be zero. Define this macro for
6836 targets where full C++ ABI compliance is impossible and where linker
6837 restrictions require weak symbols to be left out of a static archive's
6841 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
6842 A C statement (sans semicolon) to output to the stdio stream
6843 @var{stream} any text necessary for declaring the name of an external
6844 symbol named @var{name} which is referenced in this compilation but
6845 not defined. The value of @var{decl} is the tree node for the
6848 This macro need not be defined if it does not need to output anything.
6849 The GNU assembler and most Unix assemblers don't require anything.
6852 @deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref})
6853 This target hook is a function to output to @var{asm_out_file} an assembler
6854 pseudo-op to declare a library function name external. The name of the
6855 library function is given by @var{symref}, which is a @code{symbol_ref}.
6858 @deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (tree @var{decl})
6859 This target hook is a function to output to @var{asm_out_file} an assembler
6860 directive to annotate used symbol. Darwin target use .no_dead_code_strip
6864 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
6865 A C statement (sans semicolon) to output to the stdio stream
6866 @var{stream} a reference in assembler syntax to a label named
6867 @var{name}. This should add @samp{_} to the front of the name, if that
6868 is customary on your operating system, as it is in most Berkeley Unix
6869 systems. This macro is used in @code{assemble_name}.
6872 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
6873 A C statement (sans semicolon) to output a reference to
6874 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
6875 will be used to output the name of the symbol. This macro may be used
6876 to modify the way a symbol is referenced depending on information
6877 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
6880 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
6881 A C statement (sans semicolon) to output a reference to @var{buf}, the
6882 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
6883 @code{assemble_name} will be used to output the name of the symbol.
6884 This macro is not used by @code{output_asm_label}, or the @code{%l}
6885 specifier that calls it; the intention is that this macro should be set
6886 when it is necessary to output a label differently when its address is
6890 @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
6891 A function to output to the stdio stream @var{stream} a label whose
6892 name is made from the string @var{prefix} and the number @var{labelno}.
6894 It is absolutely essential that these labels be distinct from the labels
6895 used for user-level functions and variables. Otherwise, certain programs
6896 will have name conflicts with internal labels.
6898 It is desirable to exclude internal labels from the symbol table of the
6899 object file. Most assemblers have a naming convention for labels that
6900 should be excluded; on many systems, the letter @samp{L} at the
6901 beginning of a label has this effect. You should find out what
6902 convention your system uses, and follow it.
6904 The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
6907 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
6908 A C statement to output to the stdio stream @var{stream} a debug info
6909 label whose name is made from the string @var{prefix} and the number
6910 @var{num}. This is useful for VLIW targets, where debug info labels
6911 may need to be treated differently than branch target labels. On some
6912 systems, branch target labels must be at the beginning of instruction
6913 bundles, but debug info labels can occur in the middle of instruction
6916 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
6920 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
6921 A C statement to store into the string @var{string} a label whose name
6922 is made from the string @var{prefix} and the number @var{num}.
6924 This string, when output subsequently by @code{assemble_name}, should
6925 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
6926 with the same @var{prefix} and @var{num}.
6928 If the string begins with @samp{*}, then @code{assemble_name} will
6929 output the rest of the string unchanged. It is often convenient for
6930 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
6931 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
6932 to output the string, and may change it. (Of course,
6933 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
6934 you should know what it does on your machine.)
6937 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
6938 A C expression to assign to @var{outvar} (which is a variable of type
6939 @code{char *}) a newly allocated string made from the string
6940 @var{name} and the number @var{number}, with some suitable punctuation
6941 added. Use @code{alloca} to get space for the string.
6943 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
6944 produce an assembler label for an internal static variable whose name is
6945 @var{name}. Therefore, the string must be such as to result in valid
6946 assembler code. The argument @var{number} is different each time this
6947 macro is executed; it prevents conflicts between similarly-named
6948 internal static variables in different scopes.
6950 Ideally this string should not be a valid C identifier, to prevent any
6951 conflict with the user's own symbols. Most assemblers allow periods
6952 or percent signs in assembler symbols; putting at least one of these
6953 between the name and the number will suffice.
6955 If this macro is not defined, a default definition will be provided
6956 which is correct for most systems.
6959 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
6960 A C statement to output to the stdio stream @var{stream} assembler code
6961 which defines (equates) the symbol @var{name} to have the value @var{value}.
6964 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6965 correct for most systems.
6968 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
6969 A C statement to output to the stdio stream @var{stream} assembler code
6970 which defines (equates) the symbol whose tree node is @var{decl_of_name}
6971 to have the value of the tree node @var{decl_of_value}. This macro will
6972 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
6973 the tree nodes are available.
6976 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6977 correct for most systems.
6980 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
6981 A C statement that evaluates to true if the assembler code which defines
6982 (equates) the symbol whose tree node is @var{decl_of_name} to have the value
6983 of the tree node @var{decl_of_value} should be emitted near the end of the
6984 current compilation unit. The default is to not defer output of defines.
6985 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
6986 @samp{ASM_OUTPUT_DEF_FROM_DECLS}.
6989 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
6990 A C statement to output to the stdio stream @var{stream} assembler code
6991 which defines (equates) the weak symbol @var{name} to have the value
6992 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
6993 an undefined weak symbol.
6995 Define this macro if the target only supports weak aliases; define
6996 @code{ASM_OUTPUT_DEF} instead if possible.
6999 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
7000 Define this macro to override the default assembler names used for
7001 Objective-C methods.
7003 The default name is a unique method number followed by the name of the
7004 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
7005 the category is also included in the assembler name (e.g.@:
7008 These names are safe on most systems, but make debugging difficult since
7009 the method's selector is not present in the name. Therefore, particular
7010 systems define other ways of computing names.
7012 @var{buf} is an expression of type @code{char *} which gives you a
7013 buffer in which to store the name; its length is as long as
7014 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
7015 50 characters extra.
7017 The argument @var{is_inst} specifies whether the method is an instance
7018 method or a class method; @var{class_name} is the name of the class;
7019 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
7020 in a category); and @var{sel_name} is the name of the selector.
7022 On systems where the assembler can handle quoted names, you can use this
7023 macro to provide more human-readable names.
7026 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
7027 A C statement (sans semicolon) to output to the stdio stream
7028 @var{stream} commands to declare that the label @var{name} is an
7029 Objective-C class reference. This is only needed for targets whose
7030 linkers have special support for NeXT-style runtimes.
7033 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
7034 A C statement (sans semicolon) to output to the stdio stream
7035 @var{stream} commands to declare that the label @var{name} is an
7036 unresolved Objective-C class reference. This is only needed for targets
7037 whose linkers have special support for NeXT-style runtimes.
7040 @node Initialization
7041 @subsection How Initialization Functions Are Handled
7042 @cindex initialization routines
7043 @cindex termination routines
7044 @cindex constructors, output of
7045 @cindex destructors, output of
7047 The compiled code for certain languages includes @dfn{constructors}
7048 (also called @dfn{initialization routines})---functions to initialize
7049 data in the program when the program is started. These functions need
7050 to be called before the program is ``started''---that is to say, before
7051 @code{main} is called.
7053 Compiling some languages generates @dfn{destructors} (also called
7054 @dfn{termination routines}) that should be called when the program
7057 To make the initialization and termination functions work, the compiler
7058 must output something in the assembler code to cause those functions to
7059 be called at the appropriate time. When you port the compiler to a new
7060 system, you need to specify how to do this.
7062 There are two major ways that GCC currently supports the execution of
7063 initialization and termination functions. Each way has two variants.
7064 Much of the structure is common to all four variations.
7066 @findex __CTOR_LIST__
7067 @findex __DTOR_LIST__
7068 The linker must build two lists of these functions---a list of
7069 initialization functions, called @code{__CTOR_LIST__}, and a list of
7070 termination functions, called @code{__DTOR_LIST__}.
7072 Each list always begins with an ignored function pointer (which may hold
7073 0, @minus{}1, or a count of the function pointers after it, depending on
7074 the environment). This is followed by a series of zero or more function
7075 pointers to constructors (or destructors), followed by a function
7076 pointer containing zero.
7078 Depending on the operating system and its executable file format, either
7079 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
7080 time and exit time. Constructors are called in reverse order of the
7081 list; destructors in forward order.
7083 The best way to handle static constructors works only for object file
7084 formats which provide arbitrarily-named sections. A section is set
7085 aside for a list of constructors, and another for a list of destructors.
7086 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
7087 object file that defines an initialization function also puts a word in
7088 the constructor section to point to that function. The linker
7089 accumulates all these words into one contiguous @samp{.ctors} section.
7090 Termination functions are handled similarly.
7092 This method will be chosen as the default by @file{target-def.h} if
7093 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
7094 support arbitrary sections, but does support special designated
7095 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
7096 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
7098 When arbitrary sections are available, there are two variants, depending
7099 upon how the code in @file{crtstuff.c} is called. On systems that
7100 support a @dfn{.init} section which is executed at program startup,
7101 parts of @file{crtstuff.c} are compiled into that section. The
7102 program is linked by the @command{gcc} driver like this:
7105 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
7108 The prologue of a function (@code{__init}) appears in the @code{.init}
7109 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
7110 for the function @code{__fini} in the @dfn{.fini} section. Normally these
7111 files are provided by the operating system or by the GNU C library, but
7112 are provided by GCC for a few targets.
7114 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
7115 compiled from @file{crtstuff.c}. They contain, among other things, code
7116 fragments within the @code{.init} and @code{.fini} sections that branch
7117 to routines in the @code{.text} section. The linker will pull all parts
7118 of a section together, which results in a complete @code{__init} function
7119 that invokes the routines we need at startup.
7121 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
7124 If no init section is available, when GCC compiles any function called
7125 @code{main} (or more accurately, any function designated as a program
7126 entry point by the language front end calling @code{expand_main_function}),
7127 it inserts a procedure call to @code{__main} as the first executable code
7128 after the function prologue. The @code{__main} function is defined
7129 in @file{libgcc2.c} and runs the global constructors.
7131 In file formats that don't support arbitrary sections, there are again
7132 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
7133 and an `a.out' format must be used. In this case,
7134 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
7135 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
7136 and with the address of the void function containing the initialization
7137 code as its value. The GNU linker recognizes this as a request to add
7138 the value to a @dfn{set}; the values are accumulated, and are eventually
7139 placed in the executable as a vector in the format described above, with
7140 a leading (ignored) count and a trailing zero element.
7141 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
7142 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
7143 the compilation of @code{main} to call @code{__main} as above, starting
7144 the initialization process.
7146 The last variant uses neither arbitrary sections nor the GNU linker.
7147 This is preferable when you want to do dynamic linking and when using
7148 file formats which the GNU linker does not support, such as `ECOFF'@. In
7149 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
7150 termination functions are recognized simply by their names. This requires
7151 an extra program in the linkage step, called @command{collect2}. This program
7152 pretends to be the linker, for use with GCC; it does its job by running
7153 the ordinary linker, but also arranges to include the vectors of
7154 initialization and termination functions. These functions are called
7155 via @code{__main} as described above. In order to use this method,
7156 @code{use_collect2} must be defined in the target in @file{config.gcc}.
7159 The following section describes the specific macros that control and
7160 customize the handling of initialization and termination functions.
7163 @node Macros for Initialization
7164 @subsection Macros Controlling Initialization Routines
7166 Here are the macros that control how the compiler handles initialization
7167 and termination functions:
7169 @defmac INIT_SECTION_ASM_OP
7170 If defined, a C string constant, including spacing, for the assembler
7171 operation to identify the following data as initialization code. If not
7172 defined, GCC will assume such a section does not exist. When you are
7173 using special sections for initialization and termination functions, this
7174 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
7175 run the initialization functions.
7178 @defmac HAS_INIT_SECTION
7179 If defined, @code{main} will not call @code{__main} as described above.
7180 This macro should be defined for systems that control start-up code
7181 on a symbol-by-symbol basis, such as OSF/1, and should not
7182 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
7185 @defmac LD_INIT_SWITCH
7186 If defined, a C string constant for a switch that tells the linker that
7187 the following symbol is an initialization routine.
7190 @defmac LD_FINI_SWITCH
7191 If defined, a C string constant for a switch that tells the linker that
7192 the following symbol is a finalization routine.
7195 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
7196 If defined, a C statement that will write a function that can be
7197 automatically called when a shared library is loaded. The function
7198 should call @var{func}, which takes no arguments. If not defined, and
7199 the object format requires an explicit initialization function, then a
7200 function called @code{_GLOBAL__DI} will be generated.
7202 This function and the following one are used by collect2 when linking a
7203 shared library that needs constructors or destructors, or has DWARF2
7204 exception tables embedded in the code.
7207 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
7208 If defined, a C statement that will write a function that can be
7209 automatically called when a shared library is unloaded. The function
7210 should call @var{func}, which takes no arguments. If not defined, and
7211 the object format requires an explicit finalization function, then a
7212 function called @code{_GLOBAL__DD} will be generated.
7215 @defmac INVOKE__main
7216 If defined, @code{main} will call @code{__main} despite the presence of
7217 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
7218 where the init section is not actually run automatically, but is still
7219 useful for collecting the lists of constructors and destructors.
7222 @defmac SUPPORTS_INIT_PRIORITY
7223 If nonzero, the C++ @code{init_priority} attribute is supported and the
7224 compiler should emit instructions to control the order of initialization
7225 of objects. If zero, the compiler will issue an error message upon
7226 encountering an @code{init_priority} attribute.
7229 @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS
7230 This value is true if the target supports some ``native'' method of
7231 collecting constructors and destructors to be run at startup and exit.
7232 It is false if we must use @command{collect2}.
7235 @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
7236 If defined, a function that outputs assembler code to arrange to call
7237 the function referenced by @var{symbol} at initialization time.
7239 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
7240 no arguments and with no return value. If the target supports initialization
7241 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
7242 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
7244 If this macro is not defined by the target, a suitable default will
7245 be chosen if (1) the target supports arbitrary section names, (2) the
7246 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
7250 @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
7251 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
7252 functions rather than initialization functions.
7255 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
7256 generated for the generated object file will have static linkage.
7258 If your system uses @command{collect2} as the means of processing
7259 constructors, then that program normally uses @command{nm} to scan
7260 an object file for constructor functions to be called.
7262 On certain kinds of systems, you can define this macro to make
7263 @command{collect2} work faster (and, in some cases, make it work at all):
7265 @defmac OBJECT_FORMAT_COFF
7266 Define this macro if the system uses COFF (Common Object File Format)
7267 object files, so that @command{collect2} can assume this format and scan
7268 object files directly for dynamic constructor/destructor functions.
7270 This macro is effective only in a native compiler; @command{collect2} as
7271 part of a cross compiler always uses @command{nm} for the target machine.
7274 @defmac REAL_NM_FILE_NAME
7275 Define this macro as a C string constant containing the file name to use
7276 to execute @command{nm}. The default is to search the path normally for
7279 If your system supports shared libraries and has a program to list the
7280 dynamic dependencies of a given library or executable, you can define
7281 these macros to enable support for running initialization and
7282 termination functions in shared libraries:
7286 Define this macro to a C string constant containing the name of the program
7287 which lists dynamic dependencies, like @command{"ldd"} under SunOS 4.
7290 @defmac PARSE_LDD_OUTPUT (@var{ptr})
7291 Define this macro to be C code that extracts filenames from the output
7292 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
7293 of type @code{char *} that points to the beginning of a line of output
7294 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
7295 code must advance @var{ptr} to the beginning of the filename on that
7296 line. Otherwise, it must set @var{ptr} to @code{NULL}.
7299 @node Instruction Output
7300 @subsection Output of Assembler Instructions
7302 @c prevent bad page break with this line
7303 This describes assembler instruction output.
7305 @defmac REGISTER_NAMES
7306 A C initializer containing the assembler's names for the machine
7307 registers, each one as a C string constant. This is what translates
7308 register numbers in the compiler into assembler language.
7311 @defmac ADDITIONAL_REGISTER_NAMES
7312 If defined, a C initializer for an array of structures containing a name
7313 and a register number. This macro defines additional names for hard
7314 registers, thus allowing the @code{asm} option in declarations to refer
7315 to registers using alternate names.
7318 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
7319 Define this macro if you are using an unusual assembler that
7320 requires different names for the machine instructions.
7322 The definition is a C statement or statements which output an
7323 assembler instruction opcode to the stdio stream @var{stream}. The
7324 macro-operand @var{ptr} is a variable of type @code{char *} which
7325 points to the opcode name in its ``internal'' form---the form that is
7326 written in the machine description. The definition should output the
7327 opcode name to @var{stream}, performing any translation you desire, and
7328 increment the variable @var{ptr} to point at the end of the opcode
7329 so that it will not be output twice.
7331 In fact, your macro definition may process less than the entire opcode
7332 name, or more than the opcode name; but if you want to process text
7333 that includes @samp{%}-sequences to substitute operands, you must take
7334 care of the substitution yourself. Just be sure to increment
7335 @var{ptr} over whatever text should not be output normally.
7337 @findex recog_data.operand
7338 If you need to look at the operand values, they can be found as the
7339 elements of @code{recog_data.operand}.
7341 If the macro definition does nothing, the instruction is output
7345 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
7346 If defined, a C statement to be executed just prior to the output of
7347 assembler code for @var{insn}, to modify the extracted operands so
7348 they will be output differently.
7350 Here the argument @var{opvec} is the vector containing the operands
7351 extracted from @var{insn}, and @var{noperands} is the number of
7352 elements of the vector which contain meaningful data for this insn.
7353 The contents of this vector are what will be used to convert the insn
7354 template into assembler code, so you can change the assembler output
7355 by changing the contents of the vector.
7357 This macro is useful when various assembler syntaxes share a single
7358 file of instruction patterns; by defining this macro differently, you
7359 can cause a large class of instructions to be output differently (such
7360 as with rearranged operands). Naturally, variations in assembler
7361 syntax affecting individual insn patterns ought to be handled by
7362 writing conditional output routines in those patterns.
7364 If this macro is not defined, it is equivalent to a null statement.
7367 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
7368 A C compound statement to output to stdio stream @var{stream} the
7369 assembler syntax for an instruction operand @var{x}. @var{x} is an
7372 @var{code} is a value that can be used to specify one of several ways
7373 of printing the operand. It is used when identical operands must be
7374 printed differently depending on the context. @var{code} comes from
7375 the @samp{%} specification that was used to request printing of the
7376 operand. If the specification was just @samp{%@var{digit}} then
7377 @var{code} is 0; if the specification was @samp{%@var{ltr}
7378 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
7381 If @var{x} is a register, this macro should print the register's name.
7382 The names can be found in an array @code{reg_names} whose type is
7383 @code{char *[]}. @code{reg_names} is initialized from
7384 @code{REGISTER_NAMES}.
7386 When the machine description has a specification @samp{%@var{punct}}
7387 (a @samp{%} followed by a punctuation character), this macro is called
7388 with a null pointer for @var{x} and the punctuation character for
7392 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
7393 A C expression which evaluates to true if @var{code} is a valid
7394 punctuation character for use in the @code{PRINT_OPERAND} macro. If
7395 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
7396 punctuation characters (except for the standard one, @samp{%}) are used
7400 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
7401 A C compound statement to output to stdio stream @var{stream} the
7402 assembler syntax for an instruction operand that is a memory reference
7403 whose address is @var{x}. @var{x} is an RTL expression.
7405 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
7406 On some machines, the syntax for a symbolic address depends on the
7407 section that the address refers to. On these machines, define the hook
7408 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
7409 @code{symbol_ref}, and then check for it here. @xref{Assembler
7413 @findex dbr_sequence_length
7414 @defmac DBR_OUTPUT_SEQEND (@var{file})
7415 A C statement, to be executed after all slot-filler instructions have
7416 been output. If necessary, call @code{dbr_sequence_length} to
7417 determine the number of slots filled in a sequence (zero if not
7418 currently outputting a sequence), to decide how many no-ops to output,
7421 Don't define this macro if it has nothing to do, but it is helpful in
7422 reading assembly output if the extent of the delay sequence is made
7423 explicit (e.g.@: with white space).
7426 @findex final_sequence
7427 Note that output routines for instructions with delay slots must be
7428 prepared to deal with not being output as part of a sequence
7429 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
7430 found.) The variable @code{final_sequence} is null when not
7431 processing a sequence, otherwise it contains the @code{sequence} rtx
7435 @defmac REGISTER_PREFIX
7436 @defmacx LOCAL_LABEL_PREFIX
7437 @defmacx USER_LABEL_PREFIX
7438 @defmacx IMMEDIATE_PREFIX
7439 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
7440 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
7441 @file{final.c}). These are useful when a single @file{md} file must
7442 support multiple assembler formats. In that case, the various @file{tm.h}
7443 files can define these macros differently.
7446 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
7447 If defined this macro should expand to a series of @code{case}
7448 statements which will be parsed inside the @code{switch} statement of
7449 the @code{asm_fprintf} function. This allows targets to define extra
7450 printf formats which may useful when generating their assembler
7451 statements. Note that uppercase letters are reserved for future
7452 generic extensions to asm_fprintf, and so are not available to target
7453 specific code. The output file is given by the parameter @var{file}.
7454 The varargs input pointer is @var{argptr} and the rest of the format
7455 string, starting the character after the one that is being switched
7456 upon, is pointed to by @var{format}.
7459 @defmac ASSEMBLER_DIALECT
7460 If your target supports multiple dialects of assembler language (such as
7461 different opcodes), define this macro as a C expression that gives the
7462 numeric index of the assembler language dialect to use, with zero as the
7465 If this macro is defined, you may use constructs of the form
7467 @samp{@{option0|option1|option2@dots{}@}}
7470 in the output templates of patterns (@pxref{Output Template}) or in the
7471 first argument of @code{asm_fprintf}. This construct outputs
7472 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
7473 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
7474 within these strings retain their usual meaning. If there are fewer
7475 alternatives within the braces than the value of
7476 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
7478 If you do not define this macro, the characters @samp{@{}, @samp{|} and
7479 @samp{@}} do not have any special meaning when used in templates or
7480 operands to @code{asm_fprintf}.
7482 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
7483 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
7484 the variations in assembler language syntax with that mechanism. Define
7485 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
7486 if the syntax variant are larger and involve such things as different
7487 opcodes or operand order.
7490 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
7491 A C expression to output to @var{stream} some assembler code
7492 which will push hard register number @var{regno} onto the stack.
7493 The code need not be optimal, since this macro is used only when
7497 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
7498 A C expression to output to @var{stream} some assembler code
7499 which will pop hard register number @var{regno} off of the stack.
7500 The code need not be optimal, since this macro is used only when
7504 @node Dispatch Tables
7505 @subsection Output of Dispatch Tables
7507 @c prevent bad page break with this line
7508 This concerns dispatch tables.
7510 @cindex dispatch table
7511 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
7512 A C statement to output to the stdio stream @var{stream} an assembler
7513 pseudo-instruction to generate a difference between two labels.
7514 @var{value} and @var{rel} are the numbers of two internal labels. The
7515 definitions of these labels are output using
7516 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
7517 way here. For example,
7520 fprintf (@var{stream}, "\t.word L%d-L%d\n",
7521 @var{value}, @var{rel})
7524 You must provide this macro on machines where the addresses in a
7525 dispatch table are relative to the table's own address. If defined, GCC
7526 will also use this macro on all machines when producing PIC@.
7527 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
7528 mode and flags can be read.
7531 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
7532 This macro should be provided on machines where the addresses
7533 in a dispatch table are absolute.
7535 The definition should be a C statement to output to the stdio stream
7536 @var{stream} an assembler pseudo-instruction to generate a reference to
7537 a label. @var{value} is the number of an internal label whose
7538 definition is output using @code{(*targetm.asm_out.internal_label)}.
7542 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
7546 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
7547 Define this if the label before a jump-table needs to be output
7548 specially. The first three arguments are the same as for
7549 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
7550 jump-table which follows (a @code{jump_insn} containing an
7551 @code{addr_vec} or @code{addr_diff_vec}).
7553 This feature is used on system V to output a @code{swbeg} statement
7556 If this macro is not defined, these labels are output with
7557 @code{(*targetm.asm_out.internal_label)}.
7560 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
7561 Define this if something special must be output at the end of a
7562 jump-table. The definition should be a C statement to be executed
7563 after the assembler code for the table is written. It should write
7564 the appropriate code to stdio stream @var{stream}. The argument
7565 @var{table} is the jump-table insn, and @var{num} is the label-number
7566 of the preceding label.
7568 If this macro is not defined, nothing special is output at the end of
7572 @deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (@var{stream}, @var{decl}, @var{for_eh}, @var{empty})
7573 This target hook emits a label at the beginning of each FDE@. It
7574 should be defined on targets where FDEs need special labels, and it
7575 should write the appropriate label, for the FDE associated with the
7576 function declaration @var{decl}, to the stdio stream @var{stream}.
7577 The third argument, @var{for_eh}, is a boolean: true if this is for an
7578 exception table. The fourth argument, @var{empty}, is a boolean:
7579 true if this is a placeholder label for an omitted FDE@.
7581 The default is that FDEs are not given nonlocal labels.
7584 @deftypefn {Taget Hook} void TARGET_UNWIND_EMIT (FILE * @var{stream}, rtx @var{insn})
7585 This target hook emits and assembly directives required to unwind the
7586 given instruction. This is only used when TARGET_UNWIND_INFO is set.
7589 @node Exception Region Output
7590 @subsection Assembler Commands for Exception Regions
7592 @c prevent bad page break with this line
7594 This describes commands marking the start and the end of an exception
7597 @defmac EH_FRAME_SECTION_NAME
7598 If defined, a C string constant for the name of the section containing
7599 exception handling frame unwind information. If not defined, GCC will
7600 provide a default definition if the target supports named sections.
7601 @file{crtstuff.c} uses this macro to switch to the appropriate section.
7603 You should define this symbol if your target supports DWARF 2 frame
7604 unwind information and the default definition does not work.
7607 @defmac EH_FRAME_IN_DATA_SECTION
7608 If defined, DWARF 2 frame unwind information will be placed in the
7609 data section even though the target supports named sections. This
7610 might be necessary, for instance, if the system linker does garbage
7611 collection and sections cannot be marked as not to be collected.
7613 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
7617 @defmac EH_TABLES_CAN_BE_READ_ONLY
7618 Define this macro to 1 if your target is such that no frame unwind
7619 information encoding used with non-PIC code will ever require a
7620 runtime relocation, but the linker may not support merging read-only
7621 and read-write sections into a single read-write section.
7624 @defmac MASK_RETURN_ADDR
7625 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
7626 that it does not contain any extraneous set bits in it.
7629 @defmac DWARF2_UNWIND_INFO
7630 Define this macro to 0 if your target supports DWARF 2 frame unwind
7631 information, but it does not yet work with exception handling.
7632 Otherwise, if your target supports this information (if it defines
7633 @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP}
7634 or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of
7637 If @code{TARGET_UNWIND_INFO} is defined, the target specific unwinder
7638 will be used in all cases. Defining this macro will enable the generation
7639 of DWARF 2 frame debugging information.
7641 If @code{TARGET_UNWIND_INFO} is not defined, and this macro is defined to 1,
7642 the DWARF 2 unwinder will be the default exception handling mechanism;
7643 otherwise, @code{setjmp}/@code{longjmp} will be used by default.
7646 @defmac TARGET_UNWIND_INFO
7647 Define this macro if your target has ABI specified unwind tables. Usually
7648 these will be output by @code{TARGET_UNWIND_EMIT}.
7651 @defmac MUST_USE_SJLJ_EXCEPTIONS
7652 This macro need only be defined if @code{DWARF2_UNWIND_INFO} is
7653 runtime-variable. In that case, @file{except.h} cannot correctly
7654 determine the corresponding definition of
7655 @code{MUST_USE_SJLJ_EXCEPTIONS}, so the target must provide it directly.
7658 @defmac DWARF_CIE_DATA_ALIGNMENT
7659 This macro need only be defined if the target might save registers in the
7660 function prologue at an offset to the stack pointer that is not aligned to
7661 @code{UNITS_PER_WORD}. The definition should be the negative minimum
7662 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
7663 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
7664 the target supports DWARF 2 frame unwind information.
7667 @deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION ()
7668 If defined, a function that switches to the section in which the main
7669 exception table is to be placed (@pxref{Sections}). The default is a
7670 function that switches to a section named @code{.gcc_except_table} on
7671 machines that support named sections via
7672 @code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or
7673 @option{-fPIC} is in effect, the @code{data_section}, otherwise the
7674 @code{readonly_data_section}.
7677 @deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION ()
7678 If defined, a function that switches to the section in which the DWARF 2
7679 frame unwind information to be placed (@pxref{Sections}). The default
7680 is a function that outputs a standard GAS section directive, if
7681 @code{EH_FRAME_SECTION_NAME} is defined, or else a data section
7682 directive followed by a synthetic label.
7685 @deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
7686 Contains the value true if the target should add a zero word onto the
7687 end of a Dwarf-2 frame info section when used for exception handling.
7688 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
7692 @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
7693 Given a register, this hook should return a parallel of registers to
7694 represent where to find the register pieces. Define this hook if the
7695 register and its mode are represented in Dwarf in non-contiguous
7696 locations, or if the register should be represented in more than one
7697 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
7698 If not defined, the default is to return @code{NULL_RTX}.
7701 @node Alignment Output
7702 @subsection Assembler Commands for Alignment
7704 @c prevent bad page break with this line
7705 This describes commands for alignment.
7707 @defmac JUMP_ALIGN (@var{label})
7708 The alignment (log base 2) to put in front of @var{label}, which is
7709 a common destination of jumps and has no fallthru incoming edge.
7711 This macro need not be defined if you don't want any special alignment
7712 to be done at such a time. Most machine descriptions do not currently
7715 Unless it's necessary to inspect the @var{label} parameter, it is better
7716 to set the variable @var{align_jumps} in the target's
7717 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7718 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
7721 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
7722 The alignment (log base 2) to put in front of @var{label}, which follows
7725 This macro need not be defined if you don't want any special alignment
7726 to be done at such a time. Most machine descriptions do not currently
7730 @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
7731 The maximum number of bytes to skip when applying
7732 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
7733 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7736 @defmac LOOP_ALIGN (@var{label})
7737 The alignment (log base 2) to put in front of @var{label}, which follows
7738 a @code{NOTE_INSN_LOOP_BEG} note.
7740 This macro need not be defined if you don't want any special alignment
7741 to be done at such a time. Most machine descriptions do not currently
7744 Unless it's necessary to inspect the @var{label} parameter, it is better
7745 to set the variable @code{align_loops} in the target's
7746 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7747 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
7750 @defmac LOOP_ALIGN_MAX_SKIP
7751 The maximum number of bytes to skip when applying @code{LOOP_ALIGN}.
7752 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7755 @defmac LABEL_ALIGN (@var{label})
7756 The alignment (log base 2) to put in front of @var{label}.
7757 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
7758 the maximum of the specified values is used.
7760 Unless it's necessary to inspect the @var{label} parameter, it is better
7761 to set the variable @code{align_labels} in the target's
7762 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7763 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
7766 @defmac LABEL_ALIGN_MAX_SKIP
7767 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}.
7768 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7771 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
7772 A C statement to output to the stdio stream @var{stream} an assembler
7773 instruction to advance the location counter by @var{nbytes} bytes.
7774 Those bytes should be zero when loaded. @var{nbytes} will be a C
7775 expression of type @code{int}.
7778 @defmac ASM_NO_SKIP_IN_TEXT
7779 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
7780 text section because it fails to put zeros in the bytes that are skipped.
7781 This is true on many Unix systems, where the pseudo--op to skip bytes
7782 produces no-op instructions rather than zeros when used in the text
7786 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
7787 A C statement to output to the stdio stream @var{stream} an assembler
7788 command to advance the location counter to a multiple of 2 to the
7789 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
7792 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
7793 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
7794 for padding, if necessary.
7797 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
7798 A C statement to output to the stdio stream @var{stream} an assembler
7799 command to advance the location counter to a multiple of 2 to the
7800 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
7801 satisfy the alignment request. @var{power} and @var{max_skip} will be
7802 a C expression of type @code{int}.
7806 @node Debugging Info
7807 @section Controlling Debugging Information Format
7809 @c prevent bad page break with this line
7810 This describes how to specify debugging information.
7813 * All Debuggers:: Macros that affect all debugging formats uniformly.
7814 * DBX Options:: Macros enabling specific options in DBX format.
7815 * DBX Hooks:: Hook macros for varying DBX format.
7816 * File Names and DBX:: Macros controlling output of file names in DBX format.
7817 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
7818 * VMS Debug:: Macros for VMS debug format.
7822 @subsection Macros Affecting All Debugging Formats
7824 @c prevent bad page break with this line
7825 These macros affect all debugging formats.
7827 @defmac DBX_REGISTER_NUMBER (@var{regno})
7828 A C expression that returns the DBX register number for the compiler
7829 register number @var{regno}. In the default macro provided, the value
7830 of this expression will be @var{regno} itself. But sometimes there are
7831 some registers that the compiler knows about and DBX does not, or vice
7832 versa. In such cases, some register may need to have one number in the
7833 compiler and another for DBX@.
7835 If two registers have consecutive numbers inside GCC, and they can be
7836 used as a pair to hold a multiword value, then they @emph{must} have
7837 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
7838 Otherwise, debuggers will be unable to access such a pair, because they
7839 expect register pairs to be consecutive in their own numbering scheme.
7841 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
7842 does not preserve register pairs, then what you must do instead is
7843 redefine the actual register numbering scheme.
7846 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
7847 A C expression that returns the integer offset value for an automatic
7848 variable having address @var{x} (an RTL expression). The default
7849 computation assumes that @var{x} is based on the frame-pointer and
7850 gives the offset from the frame-pointer. This is required for targets
7851 that produce debugging output for DBX or COFF-style debugging output
7852 for SDB and allow the frame-pointer to be eliminated when the
7853 @option{-g} options is used.
7856 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
7857 A C expression that returns the integer offset value for an argument
7858 having address @var{x} (an RTL expression). The nominal offset is
7862 @defmac PREFERRED_DEBUGGING_TYPE
7863 A C expression that returns the type of debugging output GCC should
7864 produce when the user specifies just @option{-g}. Define
7865 this if you have arranged for GCC to support more than one format of
7866 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
7867 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
7868 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
7870 When the user specifies @option{-ggdb}, GCC normally also uses the
7871 value of this macro to select the debugging output format, but with two
7872 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
7873 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
7874 defined, GCC uses @code{DBX_DEBUG}.
7876 The value of this macro only affects the default debugging output; the
7877 user can always get a specific type of output by using @option{-gstabs},
7878 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
7882 @subsection Specific Options for DBX Output
7884 @c prevent bad page break with this line
7885 These are specific options for DBX output.
7887 @defmac DBX_DEBUGGING_INFO
7888 Define this macro if GCC should produce debugging output for DBX
7889 in response to the @option{-g} option.
7892 @defmac XCOFF_DEBUGGING_INFO
7893 Define this macro if GCC should produce XCOFF format debugging output
7894 in response to the @option{-g} option. This is a variant of DBX format.
7897 @defmac DEFAULT_GDB_EXTENSIONS
7898 Define this macro to control whether GCC should by default generate
7899 GDB's extended version of DBX debugging information (assuming DBX-format
7900 debugging information is enabled at all). If you don't define the
7901 macro, the default is 1: always generate the extended information
7902 if there is any occasion to.
7905 @defmac DEBUG_SYMS_TEXT
7906 Define this macro if all @code{.stabs} commands should be output while
7907 in the text section.
7910 @defmac ASM_STABS_OP
7911 A C string constant, including spacing, naming the assembler pseudo op to
7912 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
7913 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
7914 applies only to DBX debugging information format.
7917 @defmac ASM_STABD_OP
7918 A C string constant, including spacing, naming the assembler pseudo op to
7919 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
7920 value is the current location. If you don't define this macro,
7921 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
7925 @defmac ASM_STABN_OP
7926 A C string constant, including spacing, naming the assembler pseudo op to
7927 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
7928 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
7929 macro applies only to DBX debugging information format.
7932 @defmac DBX_NO_XREFS
7933 Define this macro if DBX on your system does not support the construct
7934 @samp{xs@var{tagname}}. On some systems, this construct is used to
7935 describe a forward reference to a structure named @var{tagname}.
7936 On other systems, this construct is not supported at all.
7939 @defmac DBX_CONTIN_LENGTH
7940 A symbol name in DBX-format debugging information is normally
7941 continued (split into two separate @code{.stabs} directives) when it
7942 exceeds a certain length (by default, 80 characters). On some
7943 operating systems, DBX requires this splitting; on others, splitting
7944 must not be done. You can inhibit splitting by defining this macro
7945 with the value zero. You can override the default splitting-length by
7946 defining this macro as an expression for the length you desire.
7949 @defmac DBX_CONTIN_CHAR
7950 Normally continuation is indicated by adding a @samp{\} character to
7951 the end of a @code{.stabs} string when a continuation follows. To use
7952 a different character instead, define this macro as a character
7953 constant for the character you want to use. Do not define this macro
7954 if backslash is correct for your system.
7957 @defmac DBX_STATIC_STAB_DATA_SECTION
7958 Define this macro if it is necessary to go to the data section before
7959 outputting the @samp{.stabs} pseudo-op for a non-global static
7963 @defmac DBX_TYPE_DECL_STABS_CODE
7964 The value to use in the ``code'' field of the @code{.stabs} directive
7965 for a typedef. The default is @code{N_LSYM}.
7968 @defmac DBX_STATIC_CONST_VAR_CODE
7969 The value to use in the ``code'' field of the @code{.stabs} directive
7970 for a static variable located in the text section. DBX format does not
7971 provide any ``right'' way to do this. The default is @code{N_FUN}.
7974 @defmac DBX_REGPARM_STABS_CODE
7975 The value to use in the ``code'' field of the @code{.stabs} directive
7976 for a parameter passed in registers. DBX format does not provide any
7977 ``right'' way to do this. The default is @code{N_RSYM}.
7980 @defmac DBX_REGPARM_STABS_LETTER
7981 The letter to use in DBX symbol data to identify a symbol as a parameter
7982 passed in registers. DBX format does not customarily provide any way to
7983 do this. The default is @code{'P'}.
7986 @defmac DBX_FUNCTION_FIRST
7987 Define this macro if the DBX information for a function and its
7988 arguments should precede the assembler code for the function. Normally,
7989 in DBX format, the debugging information entirely follows the assembler
7993 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
7994 Define this macro, with value 1, if the value of a symbol describing
7995 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
7996 relative to the start of the enclosing function. Normally, GCC uses
7997 an absolute address.
8000 @defmac DBX_LINES_FUNCTION_RELATIVE
8001 Define this macro, with value 1, if the value of a symbol indicating
8002 the current line number (@code{N_SLINE}) should be relative to the
8003 start of the enclosing function. Normally, GCC uses an absolute address.
8006 @defmac DBX_USE_BINCL
8007 Define this macro if GCC should generate @code{N_BINCL} and
8008 @code{N_EINCL} stabs for included header files, as on Sun systems. This
8009 macro also directs GCC to output a type number as a pair of a file
8010 number and a type number within the file. Normally, GCC does not
8011 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
8012 number for a type number.
8016 @subsection Open-Ended Hooks for DBX Format
8018 @c prevent bad page break with this line
8019 These are hooks for DBX format.
8021 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
8022 Define this macro to say how to output to @var{stream} the debugging
8023 information for the start of a scope level for variable names. The
8024 argument @var{name} is the name of an assembler symbol (for use with
8025 @code{assemble_name}) whose value is the address where the scope begins.
8028 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
8029 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
8032 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
8033 Define this macro if the target machine requires special handling to
8034 output an @code{N_FUN} entry for the function @var{decl}.
8037 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
8038 A C statement to output DBX debugging information before code for line
8039 number @var{line} of the current source file to the stdio stream
8040 @var{stream}. @var{counter} is the number of time the macro was
8041 invoked, including the current invocation; it is intended to generate
8042 unique labels in the assembly output.
8044 This macro should not be defined if the default output is correct, or
8045 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
8048 @defmac NO_DBX_FUNCTION_END
8049 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
8050 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
8051 On those machines, define this macro to turn this feature off without
8052 disturbing the rest of the gdb extensions.
8055 @defmac NO_DBX_BNSYM_ENSYM
8056 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
8057 extension construct. On those machines, define this macro to turn this
8058 feature off without disturbing the rest of the gdb extensions.
8061 @node File Names and DBX
8062 @subsection File Names in DBX Format
8064 @c prevent bad page break with this line
8065 This describes file names in DBX format.
8067 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
8068 A C statement to output DBX debugging information to the stdio stream
8069 @var{stream}, which indicates that file @var{name} is the main source
8070 file---the file specified as the input file for compilation.
8071 This macro is called only once, at the beginning of compilation.
8073 This macro need not be defined if the standard form of output
8074 for DBX debugging information is appropriate.
8076 It may be necessary to refer to a label equal to the beginning of the
8077 text section. You can use @samp{assemble_name (stream, ltext_label_name)}
8078 to do so. If you do this, you must also set the variable
8079 @var{used_ltext_label_name} to @code{true}.
8082 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY
8083 Define this macro, with value 1, if GCC should not emit an indication
8084 of the current directory for compilation and current source language at
8085 the beginning of the file.
8088 @defmac NO_DBX_GCC_MARKER
8089 Define this macro, with value 1, if GCC should not emit an indication
8090 that this object file was compiled by GCC@. The default is to emit
8091 an @code{N_OPT} stab at the beginning of every source file, with
8092 @samp{gcc2_compiled.} for the string and value 0.
8095 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
8096 A C statement to output DBX debugging information at the end of
8097 compilation of the main source file @var{name}. Output should be
8098 written to the stdio stream @var{stream}.
8100 If you don't define this macro, nothing special is output at the end
8101 of compilation, which is correct for most machines.
8104 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
8105 Define this macro @emph{instead of} defining
8106 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
8107 the end of compilation is a @code{N_SO} stab with an empty string,
8108 whose value is the highest absolute text address in the file.
8113 @subsection Macros for SDB and DWARF Output
8115 @c prevent bad page break with this line
8116 Here are macros for SDB and DWARF output.
8118 @defmac SDB_DEBUGGING_INFO
8119 Define this macro if GCC should produce COFF-style debugging output
8120 for SDB in response to the @option{-g} option.
8123 @defmac DWARF2_DEBUGGING_INFO
8124 Define this macro if GCC should produce dwarf version 2 format
8125 debugging output in response to the @option{-g} option.
8127 @deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (tree @var{function})
8128 Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
8129 be emitted for each function. Instead of an integer return the enum
8130 value for the @code{DW_CC_} tag.
8133 To support optional call frame debugging information, you must also
8134 define @code{INCOMING_RETURN_ADDR_RTX} and either set
8135 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
8136 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
8137 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
8140 @defmac DWARF2_FRAME_INFO
8141 Define this macro to a nonzero value if GCC should always output
8142 Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO}
8143 (@pxref{Exception Region Output} is nonzero, GCC will output this
8144 information not matter how you define @code{DWARF2_FRAME_INFO}.
8147 @defmac DWARF2_ASM_LINE_DEBUG_INFO
8148 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
8149 line debug info sections. This will result in much more compact line number
8150 tables, and hence is desirable if it works.
8153 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
8154 A C statement to issue assembly directives that create a difference
8155 between the two given labels, using an integer of the given size.
8158 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label})
8159 A C statement to issue assembly directives that create a
8160 section-relative reference to the given label, using an integer of the
8164 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
8165 A C statement to issue assembly directives that create a self-relative
8166 reference to the given label, using an integer of the given size.
8169 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{FILE}, int @var{size}, rtx @var{x})
8170 If defined, this target hook is a function which outputs a DTP-relative
8171 reference to the given TLS symbol of the specified size.
8174 @defmac PUT_SDB_@dots{}
8175 Define these macros to override the assembler syntax for the special
8176 SDB assembler directives. See @file{sdbout.c} for a list of these
8177 macros and their arguments. If the standard syntax is used, you need
8178 not define them yourself.
8182 Some assemblers do not support a semicolon as a delimiter, even between
8183 SDB assembler directives. In that case, define this macro to be the
8184 delimiter to use (usually @samp{\n}). It is not necessary to define
8185 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
8189 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
8190 Define this macro to allow references to unknown structure,
8191 union, or enumeration tags to be emitted. Standard COFF does not
8192 allow handling of unknown references, MIPS ECOFF has support for
8196 @defmac SDB_ALLOW_FORWARD_REFERENCES
8197 Define this macro to allow references to structure, union, or
8198 enumeration tags that have not yet been seen to be handled. Some
8199 assemblers choke if forward tags are used, while some require it.
8202 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
8203 A C statement to output SDB debugging information before code for line
8204 number @var{line} of the current source file to the stdio stream
8205 @var{stream}. The default is to emit an @code{.ln} directive.
8210 @subsection Macros for VMS Debug Format
8212 @c prevent bad page break with this line
8213 Here are macros for VMS debug format.
8215 @defmac VMS_DEBUGGING_INFO
8216 Define this macro if GCC should produce debugging output for VMS
8217 in response to the @option{-g} option. The default behavior for VMS
8218 is to generate minimal debug info for a traceback in the absence of
8219 @option{-g} unless explicitly overridden with @option{-g0}. This
8220 behavior is controlled by @code{OPTIMIZATION_OPTIONS} and
8221 @code{OVERRIDE_OPTIONS}.
8224 @node Floating Point
8225 @section Cross Compilation and Floating Point
8226 @cindex cross compilation and floating point
8227 @cindex floating point and cross compilation
8229 While all modern machines use twos-complement representation for integers,
8230 there are a variety of representations for floating point numbers. This
8231 means that in a cross-compiler the representation of floating point numbers
8232 in the compiled program may be different from that used in the machine
8233 doing the compilation.
8235 Because different representation systems may offer different amounts of
8236 range and precision, all floating point constants must be represented in
8237 the target machine's format. Therefore, the cross compiler cannot
8238 safely use the host machine's floating point arithmetic; it must emulate
8239 the target's arithmetic. To ensure consistency, GCC always uses
8240 emulation to work with floating point values, even when the host and
8241 target floating point formats are identical.
8243 The following macros are provided by @file{real.h} for the compiler to
8244 use. All parts of the compiler which generate or optimize
8245 floating-point calculations must use these macros. They may evaluate
8246 their operands more than once, so operands must not have side effects.
8248 @defmac REAL_VALUE_TYPE
8249 The C data type to be used to hold a floating point value in the target
8250 machine's format. Typically this is a @code{struct} containing an
8251 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
8255 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8256 Compares for equality the two values, @var{x} and @var{y}. If the target
8257 floating point format supports negative zeroes and/or NaNs,
8258 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
8259 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
8262 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8263 Tests whether @var{x} is less than @var{y}.
8266 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
8267 Truncates @var{x} to a signed integer, rounding toward zero.
8270 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
8271 Truncates @var{x} to an unsigned integer, rounding toward zero. If
8272 @var{x} is negative, returns zero.
8275 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
8276 Converts @var{string} into a floating point number in the target machine's
8277 representation for mode @var{mode}. This routine can handle both
8278 decimal and hexadecimal floating point constants, using the syntax
8279 defined by the C language for both.
8282 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
8283 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
8286 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
8287 Determines whether @var{x} represents infinity (positive or negative).
8290 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
8291 Determines whether @var{x} represents a ``NaN'' (not-a-number).
8294 @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})
8295 Calculates an arithmetic operation on the two floating point values
8296 @var{x} and @var{y}, storing the result in @var{output} (which must be a
8299 The operation to be performed is specified by @var{code}. Only the
8300 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
8301 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
8303 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
8304 target's floating point format cannot represent infinity, it will call
8305 @code{abort}. Callers should check for this situation first, using
8306 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
8309 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
8310 Returns the negative of the floating point value @var{x}.
8313 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
8314 Returns the absolute value of @var{x}.
8317 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
8318 Truncates the floating point value @var{x} to fit in @var{mode}. The
8319 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
8320 appropriate bit pattern to be output asa floating constant whose
8321 precision accords with mode @var{mode}.
8324 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
8325 Converts a floating point value @var{x} into a double-precision integer
8326 which is then stored into @var{low} and @var{high}. If the value is not
8327 integral, it is truncated.
8330 @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})
8331 Converts a double-precision integer found in @var{low} and @var{high},
8332 into a floating point value which is then stored into @var{x}. The
8333 value is truncated to fit in mode @var{mode}.
8336 @node Mode Switching
8337 @section Mode Switching Instructions
8338 @cindex mode switching
8339 The following macros control mode switching optimizations:
8341 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
8342 Define this macro if the port needs extra instructions inserted for mode
8343 switching in an optimizing compilation.
8345 For an example, the SH4 can perform both single and double precision
8346 floating point operations, but to perform a single precision operation,
8347 the FPSCR PR bit has to be cleared, while for a double precision
8348 operation, this bit has to be set. Changing the PR bit requires a general
8349 purpose register as a scratch register, hence these FPSCR sets have to
8350 be inserted before reload, i.e.@: you can't put this into instruction emitting
8351 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
8353 You can have multiple entities that are mode-switched, and select at run time
8354 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
8355 return nonzero for any @var{entity} that needs mode-switching.
8356 If you define this macro, you also have to define
8357 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
8358 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
8359 @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT}
8363 @defmac NUM_MODES_FOR_MODE_SWITCHING
8364 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
8365 initializer for an array of integers. Each initializer element
8366 N refers to an entity that needs mode switching, and specifies the number
8367 of different modes that might need to be set for this entity.
8368 The position of the initializer in the initializer---starting counting at
8369 zero---determines the integer that is used to refer to the mode-switched
8371 In macros that take mode arguments / yield a mode result, modes are
8372 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
8373 switch is needed / supplied.
8376 @defmac MODE_NEEDED (@var{entity}, @var{insn})
8377 @var{entity} is an integer specifying a mode-switched entity. If
8378 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
8379 return an integer value not larger than the corresponding element in
8380 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
8381 be switched into prior to the execution of @var{insn}.
8384 @defmac MODE_AFTER (@var{mode}, @var{insn})
8385 If this macro is defined, it is evaluated for every @var{insn} during
8386 mode switching. It determines the mode that an insn results in (if
8387 different from the incoming mode).
8390 @defmac MODE_ENTRY (@var{entity})
8391 If this macro is defined, it is evaluated for every @var{entity} that needs
8392 mode switching. It should evaluate to an integer, which is a mode that
8393 @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY}
8394 is defined then @code{MODE_EXIT} must be defined.
8397 @defmac MODE_EXIT (@var{entity})
8398 If this macro is defined, it is evaluated for every @var{entity} that needs
8399 mode switching. It should evaluate to an integer, which is a mode that
8400 @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT}
8401 is defined then @code{MODE_ENTRY} must be defined.
8404 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
8405 This macro specifies the order in which modes for @var{entity} are processed.
8406 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
8407 lowest. The value of the macro should be an integer designating a mode
8408 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
8409 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
8410 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
8413 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
8414 Generate one or more insns to set @var{entity} to @var{mode}.
8415 @var{hard_reg_live} is the set of hard registers live at the point where
8416 the insn(s) are to be inserted.
8419 @node Target Attributes
8420 @section Defining target-specific uses of @code{__attribute__}
8421 @cindex target attributes
8422 @cindex machine attributes
8423 @cindex attributes, target-specific
8425 Target-specific attributes may be defined for functions, data and types.
8426 These are described using the following target hooks; they also need to
8427 be documented in @file{extend.texi}.
8429 @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
8430 If defined, this target hook points to an array of @samp{struct
8431 attribute_spec} (defined in @file{tree.h}) specifying the machine
8432 specific attributes for this target and some of the restrictions on the
8433 entities to which these attributes are applied and the arguments they
8437 @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8438 If defined, this target hook is a function which returns zero if the attributes on
8439 @var{type1} and @var{type2} are incompatible, one if they are compatible,
8440 and two if they are nearly compatible (which causes a warning to be
8441 generated). If this is not defined, machine-specific attributes are
8442 supposed always to be compatible.
8445 @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
8446 If defined, this target hook is a function which assigns default attributes to
8447 newly defined @var{type}.
8450 @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8451 Define this target hook if the merging of type attributes needs special
8452 handling. If defined, the result is a list of the combined
8453 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
8454 that @code{comptypes} has already been called and returned 1. This
8455 function may call @code{merge_attributes} to handle machine-independent
8459 @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
8460 Define this target hook if the merging of decl attributes needs special
8461 handling. If defined, the result is a list of the combined
8462 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
8463 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
8464 when this is needed are when one attribute overrides another, or when an
8465 attribute is nullified by a subsequent definition. This function may
8466 call @code{merge_attributes} to handle machine-independent merging.
8468 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
8469 If the only target-specific handling you require is @samp{dllimport}
8470 for Microsoft Windows targets, you should define the macro
8471 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler
8472 will then define a function called
8473 @code{merge_dllimport_decl_attributes} which can then be defined as
8474 the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also
8475 add @code{handle_dll_attribute} in the attribute table for your port
8476 to perform initial processing of the @samp{dllimport} and
8477 @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and
8478 @file{i386/i386.c}, for example.
8481 @defmac TARGET_DECLSPEC
8482 Define this macro to a nonzero value if you want to treat
8483 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
8484 default, this behavior is enabled only for targets that define
8485 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
8486 of @code{__declspec} is via a built-in macro, but you should not rely
8487 on this implementation detail.
8490 @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
8491 Define this target hook if you want to be able to add attributes to a decl
8492 when it is being created. This is normally useful for back ends which
8493 wish to implement a pragma by using the attributes which correspond to
8494 the pragma's effect. The @var{node} argument is the decl which is being
8495 created. The @var{attr_ptr} argument is a pointer to the attribute list
8496 for this decl. The list itself should not be modified, since it may be
8497 shared with other decls, but attributes may be chained on the head of
8498 the list and @code{*@var{attr_ptr}} modified to point to the new
8499 attributes, or a copy of the list may be made if further changes are
8503 @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl})
8505 This target hook returns @code{true} if it is ok to inline @var{fndecl}
8506 into the current function, despite its having target-specific
8507 attributes, @code{false} otherwise. By default, if a function has a
8508 target specific attribute attached to it, it will not be inlined.
8511 @node MIPS Coprocessors
8512 @section Defining coprocessor specifics for MIPS targets.
8513 @cindex MIPS coprocessor-definition macros
8515 The MIPS specification allows MIPS implementations to have as many as 4
8516 coprocessors, each with as many as 32 private registers. GCC supports
8517 accessing these registers and transferring values between the registers
8518 and memory using asm-ized variables. For example:
8521 register unsigned int cp0count asm ("c0r1");
8527 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
8528 names may be added as described below, or the default names may be
8529 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
8531 Coprocessor registers are assumed to be epilogue-used; sets to them will
8532 be preserved even if it does not appear that the register is used again
8533 later in the function.
8535 Another note: according to the MIPS spec, coprocessor 1 (if present) is
8536 the FPU@. One accesses COP1 registers through standard mips
8537 floating-point support; they are not included in this mechanism.
8539 There is one macro used in defining the MIPS coprocessor interface which
8540 you may want to override in subtargets; it is described below.
8542 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
8543 A comma-separated list (with leading comma) of pairs describing the
8544 alternate names of coprocessor registers. The format of each entry should be
8546 @{ @var{alternatename}, @var{register_number}@}
8552 @section Parameters for Precompiled Header Validity Checking
8553 @cindex parameters, precompiled headers
8555 @deftypefn {Target Hook} void *TARGET_GET_PCH_VALIDITY (size_t *@var{sz})
8556 This hook returns the data needed by @code{TARGET_PCH_VALID_P} and sets
8557 @samp{*@var{sz}} to the size of the data in bytes.
8560 @deftypefn {Target Hook} const char *TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz})
8561 This hook checks whether the options used to create a PCH file are
8562 compatible with the current settings. It returns @code{NULL}
8563 if so and a suitable error message if not. Error messages will
8564 be presented to the user and must be localized using @samp{_(@var{msg})}.
8566 @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
8567 when the PCH file was created and @var{sz} is the size of that data in bytes.
8568 It's safe to assume that the data was created by the same version of the
8569 compiler, so no format checking is needed.
8571 The default definition of @code{default_pch_valid_p} should be
8572 suitable for most targets.
8575 @deftypefn {Target Hook} const char *TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags})
8576 If this hook is nonnull, the default implementation of
8577 @code{TARGET_PCH_VALID_P} will use it to check for compatible values
8578 of @code{target_flags}. @var{pch_flags} specifies the value that
8579 @code{target_flags} had when the PCH file was created. The return
8580 value is the same as for @code{TARGET_PCH_VALID_P}.
8584 @section C++ ABI parameters
8585 @cindex parameters, c++ abi
8587 @deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void)
8588 Define this hook to override the integer type used for guard variables.
8589 These are used to implement one-time construction of static objects. The
8590 default is long_long_integer_type_node.
8593 @deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void)
8594 This hook determines how guard variables are used. It should return
8595 @code{false} (the default) if first byte should be used. A return value of
8596 @code{true} indicates the least significant bit should be used.
8599 @deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type})
8600 This hook returns the size of the cookie to use when allocating an array
8601 whose elements have the indicated @var{type}. Assumes that it is already
8602 known that a cookie is needed. The default is
8603 @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
8604 IA64/Generic C++ ABI@.
8607 @deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void)
8608 This hook should return @code{true} if the element size should be stored in
8609 array cookies. The default is to return @code{false}.
8612 @deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export})
8613 If defined by a backend this hook allows the decision made to export
8614 class @var{type} to be overruled. Upon entry @var{import_export}
8615 will contain 1 if the class is going to be exported, @minus{}1 if it is going
8616 to be imported and 0 otherwise. This function should return the
8617 modified value and perform any other actions necessary to support the
8618 backend's targeted operating system.
8621 @deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void)
8622 This hook should return @code{true} if constructors and destructors return
8623 the address of the object created/destroyed. The default is to return
8627 @deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void)
8628 This hook returns true if the key method for a class (i.e., the method
8629 which, if defined in the current translation unit, causes the virtual
8630 table to be emitted) may be an inline function. Under the standard
8631 Itanium C++ ABI the key method may be an inline function so long as
8632 the function is not declared inline in the class definition. Under
8633 some variants of the ABI, an inline function can never be the key
8634 method. The default is to return @code{true}.
8637 @deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl})
8638 @var{decl} is a virtual table, virtual table table, typeinfo object,
8639 or other similar implicit class data object that will be emitted with
8640 external linkage in this translation unit. No ELF visibility has been
8641 explicitly specified. If the target needs to specify a visibility
8642 other than that of the containing class, use this hook to set
8643 @code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}.
8646 @deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void)
8647 This hook returns true (the default) if virtual tables and other
8648 similar implicit class data objects are always COMDAT if they have
8649 external linkage. If this hook returns false, then class data for
8650 classes whose virtual table will be emitted in only one translation
8651 unit will not be COMDAT.
8654 @deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void)
8655 This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
8656 should be used to register static destructors when @option{-fuse-cxa-atexit}
8657 is in effect. The default is to return false to use @code{__cxa_atexit}.
8661 @section Miscellaneous Parameters
8662 @cindex parameters, miscellaneous
8664 @c prevent bad page break with this line
8665 Here are several miscellaneous parameters.
8667 @defmac PREDICATE_CODES
8668 Define this if you have defined special-purpose predicates in the file
8669 @file{@var{machine}.c}. This macro is called within an initializer of an
8670 array of structures. The first field in the structure is the name of a
8671 predicate and the second field is an array of rtl codes. For each
8672 predicate, list all rtl codes that can be in expressions matched by the
8673 predicate. The list should have a trailing comma. Here is an example
8674 of two entries in the list for a typical RISC machine:
8677 #define PREDICATE_CODES \
8678 @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \
8679 @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@},
8682 Defining this macro does not affect the generated code (however,
8683 incorrect definitions that omit an rtl code that may be matched by the
8684 predicate can cause the compiler to malfunction). Instead, it allows
8685 the table built by @file{genrecog} to be more compact and efficient,
8686 thus speeding up the compiler. The most important predicates to include
8687 in the list specified by this macro are those used in the most insn
8690 For each predicate function named in @code{PREDICATE_CODES}, a
8691 declaration will be generated in @file{insn-codes.h}.
8693 Use of this macro is deprecated; use @code{define_predicate} instead.
8694 @xref{Defining Predicates}.
8697 @defmac SPECIAL_MODE_PREDICATES
8698 Define this if you have special predicates that know special things
8699 about modes. Genrecog will warn about certain forms of
8700 @code{match_operand} without a mode; if the operand predicate is
8701 listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be
8704 Here is an example from the IA-32 port (@code{ext_register_operand}
8705 specially checks for @code{HImode} or @code{SImode} in preparation
8706 for a byte extraction from @code{%ah} etc.).
8709 #define SPECIAL_MODE_PREDICATES \
8710 "ext_register_operand",
8713 Use of this macro is deprecated; use @code{define_special_predicate}
8714 instead. @xref{Defining Predicates}.
8717 @defmac HAS_LONG_COND_BRANCH
8718 Define this boolean macro to indicate whether or not your architecture
8719 has conditional branches that can span all of memory. It is used in
8720 conjunction with an optimization that partitions hot and cold basic
8721 blocks into separate sections of the executable. If this macro is
8722 set to false, gcc will convert any conditional branches that attempt
8723 to cross between sections into unconditional branches or indirect jumps.
8726 @defmac HAS_LONG_UNCOND_BRANCH
8727 Define this boolean macro to indicate whether or not your architecture
8728 has unconditional branches that can span all of memory. It is used in
8729 conjunction with an optimization that partitions hot and cold basic
8730 blocks into separate sections of the executable. If this macro is
8731 set to false, gcc will convert any unconditional branches that attempt
8732 to cross between sections into indirect jumps.
8735 @defmac CASE_VECTOR_MODE
8736 An alias for a machine mode name. This is the machine mode that
8737 elements of a jump-table should have.
8740 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
8741 Optional: return the preferred mode for an @code{addr_diff_vec}
8742 when the minimum and maximum offset are known. If you define this,
8743 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
8744 To make this work, you also have to define @code{INSN_ALIGN} and
8745 make the alignment for @code{addr_diff_vec} explicit.
8746 The @var{body} argument is provided so that the offset_unsigned and scale
8747 flags can be updated.
8750 @defmac CASE_VECTOR_PC_RELATIVE
8751 Define this macro to be a C expression to indicate when jump-tables
8752 should contain relative addresses. You need not define this macro if
8753 jump-tables never contain relative addresses, or jump-tables should
8754 contain relative addresses only when @option{-fPIC} or @option{-fPIC}
8758 @defmac CASE_VALUES_THRESHOLD
8759 Define this to be the smallest number of different values for which it
8760 is best to use a jump-table instead of a tree of conditional branches.
8761 The default is four for machines with a @code{casesi} instruction and
8762 five otherwise. This is best for most machines.
8765 @defmac CASE_USE_BIT_TESTS
8766 Define this macro to be a C expression to indicate whether C switch
8767 statements may be implemented by a sequence of bit tests. This is
8768 advantageous on processors that can efficiently implement left shift
8769 of 1 by the number of bits held in a register, but inappropriate on
8770 targets that would require a loop. By default, this macro returns
8771 @code{true} if the target defines an @code{ashlsi3} pattern, and
8772 @code{false} otherwise.
8775 @defmac WORD_REGISTER_OPERATIONS
8776 Define this macro if operations between registers with integral mode
8777 smaller than a word are always performed on the entire register.
8778 Most RISC machines have this property and most CISC machines do not.
8781 @defmac LOAD_EXTEND_OP (@var{mem_mode})
8782 Define this macro to be a C expression indicating when insns that read
8783 memory in @var{mem_mode}, an integral mode narrower than a word, set the
8784 bits outside of @var{mem_mode} to be either the sign-extension or the
8785 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
8786 of @var{mem_mode} for which the
8787 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
8788 @code{UNKNOWN} for other modes.
8790 This macro is not called with @var{mem_mode} non-integral or with a width
8791 greater than or equal to @code{BITS_PER_WORD}, so you may return any
8792 value in this case. Do not define this macro if it would always return
8793 @code{UNKNOWN}. On machines where this macro is defined, you will normally
8794 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
8796 You may return a non-@code{UNKNOWN} value even if for some hard registers
8797 the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
8798 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
8799 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
8800 integral mode larger than this but not larger than @code{word_mode}.
8802 You must return @code{UNKNOWN} if for some hard registers that allow this
8803 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
8804 @code{word_mode}, but that they can change to another integral mode that
8805 is larger then @var{mem_mode} but still smaller than @code{word_mode}.
8808 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
8809 Define this macro if loading short immediate values into registers sign
8813 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
8814 Define this macro if the same instructions that convert a floating
8815 point number to a signed fixed point number also convert validly to an
8820 The maximum number of bytes that a single instruction can move quickly
8821 between memory and registers or between two memory locations.
8824 @defmac MAX_MOVE_MAX
8825 The maximum number of bytes that a single instruction can move quickly
8826 between memory and registers or between two memory locations. If this
8827 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
8828 constant value that is the largest value that @code{MOVE_MAX} can have
8832 @defmac SHIFT_COUNT_TRUNCATED
8833 A C expression that is nonzero if on this machine the number of bits
8834 actually used for the count of a shift operation is equal to the number
8835 of bits needed to represent the size of the object being shifted. When
8836 this macro is nonzero, the compiler will assume that it is safe to omit
8837 a sign-extend, zero-extend, and certain bitwise `and' instructions that
8838 truncates the count of a shift operation. On machines that have
8839 instructions that act on bit-fields at variable positions, which may
8840 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
8841 also enables deletion of truncations of the values that serve as
8842 arguments to bit-field instructions.
8844 If both types of instructions truncate the count (for shifts) and
8845 position (for bit-field operations), or if no variable-position bit-field
8846 instructions exist, you should define this macro.
8848 However, on some machines, such as the 80386 and the 680x0, truncation
8849 only applies to shift operations and not the (real or pretended)
8850 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
8851 such machines. Instead, add patterns to the @file{md} file that include
8852 the implied truncation of the shift instructions.
8854 You need not define this macro if it would always have the value of zero.
8857 @anchor{TARGET_SHIFT_TRUNCATION_MASK}
8858 @deftypefn {Target Hook} int TARGET_SHIFT_TRUNCATION_MASK (enum machine_mode @var{mode})
8859 This function describes how the standard shift patterns for @var{mode}
8860 deal with shifts by negative amounts or by more than the width of the mode.
8861 @xref{shift patterns}.
8863 On many machines, the shift patterns will apply a mask @var{m} to the
8864 shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
8865 equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If
8866 this is true for mode @var{mode}, the function should return @var{m},
8867 otherwise it should return 0. A return value of 0 indicates that no
8868 particular behavior is guaranteed.
8870 Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
8871 @emph{not} apply to general shift rtxes; it applies only to instructions
8872 that are generated by the named shift patterns.
8874 The default implementation of this function returns
8875 @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
8876 and 0 otherwise. This definition is always safe, but if
8877 @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
8878 nevertheless truncate the shift count, you may get better code
8882 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
8883 A C expression which is nonzero if on this machine it is safe to
8884 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
8885 bits (where @var{outprec} is smaller than @var{inprec}) by merely
8886 operating on it as if it had only @var{outprec} bits.
8888 On many machines, this expression can be 1.
8890 @c rearranged this, removed the phrase "it is reported that". this was
8891 @c to fix an overfull hbox. --mew 10feb93
8892 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
8893 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
8894 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
8895 such cases may improve things.
8898 @defmac STORE_FLAG_VALUE
8899 A C expression describing the value returned by a comparison operator
8900 with an integral mode and stored by a store-flag instruction
8901 (@samp{s@var{cond}}) when the condition is true. This description must
8902 apply to @emph{all} the @samp{s@var{cond}} patterns and all the
8903 comparison operators whose results have a @code{MODE_INT} mode.
8905 A value of 1 or @minus{}1 means that the instruction implementing the
8906 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
8907 and 0 when the comparison is false. Otherwise, the value indicates
8908 which bits of the result are guaranteed to be 1 when the comparison is
8909 true. This value is interpreted in the mode of the comparison
8910 operation, which is given by the mode of the first operand in the
8911 @samp{s@var{cond}} pattern. Either the low bit or the sign bit of
8912 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
8915 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
8916 generate code that depends only on the specified bits. It can also
8917 replace comparison operators with equivalent operations if they cause
8918 the required bits to be set, even if the remaining bits are undefined.
8919 For example, on a machine whose comparison operators return an
8920 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
8921 @samp{0x80000000}, saying that just the sign bit is relevant, the
8925 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
8932 (ashift:SI @var{x} (const_int @var{n}))
8936 where @var{n} is the appropriate shift count to move the bit being
8937 tested into the sign bit.
8939 There is no way to describe a machine that always sets the low-order bit
8940 for a true value, but does not guarantee the value of any other bits,
8941 but we do not know of any machine that has such an instruction. If you
8942 are trying to port GCC to such a machine, include an instruction to
8943 perform a logical-and of the result with 1 in the pattern for the
8944 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
8946 Often, a machine will have multiple instructions that obtain a value
8947 from a comparison (or the condition codes). Here are rules to guide the
8948 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
8953 Use the shortest sequence that yields a valid definition for
8954 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
8955 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
8956 comparison operators to do so because there may be opportunities to
8957 combine the normalization with other operations.
8960 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
8961 slightly preferred on machines with expensive jumps and 1 preferred on
8965 As a second choice, choose a value of @samp{0x80000001} if instructions
8966 exist that set both the sign and low-order bits but do not define the
8970 Otherwise, use a value of @samp{0x80000000}.
8973 Many machines can produce both the value chosen for
8974 @code{STORE_FLAG_VALUE} and its negation in the same number of
8975 instructions. On those machines, you should also define a pattern for
8976 those cases, e.g., one matching
8979 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
8982 Some machines can also perform @code{and} or @code{plus} operations on
8983 condition code values with less instructions than the corresponding
8984 @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those
8985 machines, define the appropriate patterns. Use the names @code{incscc}
8986 and @code{decscc}, respectively, for the patterns which perform
8987 @code{plus} or @code{minus} operations on condition code values. See
8988 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
8989 find such instruction sequences on other machines.
8991 If this macro is not defined, the default value, 1, is used. You need
8992 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
8993 instructions, or if the value generated by these instructions is 1.
8996 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
8997 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
8998 returned when comparison operators with floating-point results are true.
8999 Define this macro on machines that have comparison operations that return
9000 floating-point values. If there are no such operations, do not define
9004 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
9005 A C expression that gives a rtx representing the non-zero true element
9006 for vector comparisons. The returned rtx should be valid for the inner
9007 mode of @var{mode} which is guaranteed to be a vector mode. Define
9008 this macro on machines that have vector comparison operations that
9009 return a vector result. If there are no such operations, do not define
9010 this macro. Typically, this macro is defined as @code{const1_rtx} or
9011 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
9012 the compiler optimizing such vector comparison operations for the
9016 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
9017 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
9018 A C expression that evaluates to true if the architecture defines a value
9019 for @code{clz} or @code{ctz} with a zero operand. If so, @var{value}
9020 should be set to this value. If this macro is not defined, the value of
9021 @code{clz} or @code{ctz} is assumed to be undefined.
9023 This macro must be defined if the target's expansion for @code{ffs}
9024 relies on a particular value to get correct results. Otherwise it
9025 is not necessary, though it may be used to optimize some corner cases.
9027 Note that regardless of this macro the ``definedness'' of @code{clz}
9028 and @code{ctz} at zero do @emph{not} extend to the builtin functions
9029 visible to the user. Thus one may be free to adjust the value at will
9030 to match the target expansion of these operations without fear of
9035 An alias for the machine mode for pointers. On most machines, define
9036 this to be the integer mode corresponding to the width of a hardware
9037 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
9038 On some machines you must define this to be one of the partial integer
9039 modes, such as @code{PSImode}.
9041 The width of @code{Pmode} must be at least as large as the value of
9042 @code{POINTER_SIZE}. If it is not equal, you must define the macro
9043 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
9047 @defmac FUNCTION_MODE
9048 An alias for the machine mode used for memory references to functions
9049 being called, in @code{call} RTL expressions. On most machines this
9050 should be @code{QImode}.
9053 @defmac STDC_0_IN_SYSTEM_HEADERS
9054 In normal operation, the preprocessor expands @code{__STDC__} to the
9055 constant 1, to signify that GCC conforms to ISO Standard C@. On some
9056 hosts, like Solaris, the system compiler uses a different convention,
9057 where @code{__STDC__} is normally 0, but is 1 if the user specifies
9058 strict conformance to the C Standard.
9060 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
9061 convention when processing system header files, but when processing user
9062 files @code{__STDC__} will always expand to 1.
9065 @defmac NO_IMPLICIT_EXTERN_C
9066 Define this macro if the system header files support C++ as well as C@.
9067 This macro inhibits the usual method of using system header files in
9068 C++, which is to pretend that the file's contents are enclosed in
9069 @samp{extern "C" @{@dots{}@}}.
9074 @defmac REGISTER_TARGET_PRAGMAS ()
9075 Define this macro if you want to implement any target-specific pragmas.
9076 If defined, it is a C expression which makes a series of calls to
9077 @code{c_register_pragma} or @code{c_register_pragma_with_expansion}
9078 for each pragma. The macro may also do any
9079 setup required for the pragmas.
9081 The primary reason to define this macro is to provide compatibility with
9082 other compilers for the same target. In general, we discourage
9083 definition of target-specific pragmas for GCC@.
9085 If the pragma can be implemented by attributes then you should consider
9086 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
9088 Preprocessor macros that appear on pragma lines are not expanded. All
9089 @samp{#pragma} directives that do not match any registered pragma are
9090 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
9093 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
9094 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
9096 Each call to @code{c_register_pragma} or
9097 @code{c_register_pragma_with_expansion} establishes one pragma. The
9098 @var{callback} routine will be called when the preprocessor encounters a
9102 #pragma [@var{space}] @var{name} @dots{}
9105 @var{space} is the case-sensitive namespace of the pragma, or
9106 @code{NULL} to put the pragma in the global namespace. The callback
9107 routine receives @var{pfile} as its first argument, which can be passed
9108 on to cpplib's functions if necessary. You can lex tokens after the
9109 @var{name} by calling @code{c_lex}. Tokens that are not read by the
9110 callback will be silently ignored. The end of the line is indicated by
9111 a token of type @code{CPP_EOF}. Macro expansion occurs on the
9112 arguments of pragmas registered with
9113 @code{c_register_pragma_with_expansion} but not on the arguments of
9114 pragmas registered with @code{c_register_pragma}.
9116 For an example use of this routine, see @file{c4x.h} and the callback
9117 routines defined in @file{c4x-c.c}.
9119 Note that the use of @code{c_lex} is specific to the C and C++
9120 compilers. It will not work in the Java or Fortran compilers, or any
9121 other language compilers for that matter. Thus if @code{c_lex} is going
9122 to be called from target-specific code, it must only be done so when
9123 building the C and C++ compilers. This can be done by defining the
9124 variables @code{c_target_objs} and @code{cxx_target_objs} in the
9125 target entry in the @file{config.gcc} file. These variables should name
9126 the target-specific, language-specific object file which contains the
9127 code that uses @code{c_lex}. Note it will also be necessary to add a
9128 rule to the makefile fragment pointed to by @code{tmake_file} that shows
9129 how to build this object file.
9134 @defmac HANDLE_SYSV_PRAGMA
9135 Define this macro (to a value of 1) if you want the System V style
9136 pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name>
9137 [=<value>]} to be supported by gcc.
9139 The pack pragma specifies the maximum alignment (in bytes) of fields
9140 within a structure, in much the same way as the @samp{__aligned__} and
9141 @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets
9142 the behavior to the default.
9144 A subtlety for Microsoft Visual C/C++ style bit-field packing
9145 (e.g.@: -mms-bitfields) for targets that support it:
9146 When a bit-field is inserted into a packed record, the whole size
9147 of the underlying type is used by one or more same-size adjacent
9148 bit-fields (that is, if its long:3, 32 bits is used in the record,
9149 and any additional adjacent long bit-fields are packed into the same
9150 chunk of 32 bits. However, if the size changes, a new field of that
9153 If both MS bit-fields and @samp{__attribute__((packed))} are used,
9154 the latter will take precedence. If @samp{__attribute__((packed))} is
9155 used on a single field when MS bit-fields are in use, it will take
9156 precedence for that field, but the alignment of the rest of the structure
9157 may affect its placement.
9159 The weak pragma only works if @code{SUPPORTS_WEAK} and
9160 @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation
9161 of specifically named weak labels, optionally with a value.
9166 @defmac HANDLE_PRAGMA_PACK_PUSH_POP
9167 Define this macro (to a value of 1) if you want to support the Win32
9168 style pragmas @samp{#pragma pack(push[,@var{n}])} and @samp{#pragma
9169 pack(pop)}. The @samp{pack(push,[@var{n}])} pragma specifies the maximum
9170 alignment (in bytes) of fields within a structure, in much the same way as
9171 the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A
9172 pack value of zero resets the behavior to the default. Successive
9173 invocations of this pragma cause the previous values to be stacked, so
9174 that invocations of @samp{#pragma pack(pop)} will return to the previous
9178 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
9179 Define this macro, as well as
9180 @code{HANDLE_SYSV_PRAGMA}, if macros should be expanded in the
9181 arguments of @samp{#pragma pack}.
9184 @defmac TARGET_DEFAULT_PACK_STRUCT
9185 If your target requires a structure packing default other than 0 (meaning
9186 the machine default), define this macro to the necessary value (in bytes).
9187 This must be a value that would also valid to be used with
9188 @samp{#pragma pack()} (that is, a small power of two).
9191 @defmac DOLLARS_IN_IDENTIFIERS
9192 Define this macro to control use of the character @samp{$} in
9193 identifier names for the C family of languages. 0 means @samp{$} is
9194 not allowed by default; 1 means it is allowed. 1 is the default;
9195 there is no need to define this macro in that case.
9198 @defmac NO_DOLLAR_IN_LABEL
9199 Define this macro if the assembler does not accept the character
9200 @samp{$} in label names. By default constructors and destructors in
9201 G++ have @samp{$} in the identifiers. If this macro is defined,
9202 @samp{.} is used instead.
9205 @defmac NO_DOT_IN_LABEL
9206 Define this macro if the assembler does not accept the character
9207 @samp{.} in label names. By default constructors and destructors in G++
9208 have names that use @samp{.}. If this macro is defined, these names
9209 are rewritten to avoid @samp{.}.
9212 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
9213 Define this macro as a C expression that is nonzero if it is safe for the
9214 delay slot scheduler to place instructions in the delay slot of @var{insn},
9215 even if they appear to use a resource set or clobbered in @var{insn}.
9216 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
9217 every @code{call_insn} has this behavior. On machines where some @code{insn}
9218 or @code{jump_insn} is really a function call and hence has this behavior,
9219 you should define this macro.
9221 You need not define this macro if it would always return zero.
9224 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
9225 Define this macro as a C expression that is nonzero if it is safe for the
9226 delay slot scheduler to place instructions in the delay slot of @var{insn},
9227 even if they appear to set or clobber a resource referenced in @var{insn}.
9228 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
9229 some @code{insn} or @code{jump_insn} is really a function call and its operands
9230 are registers whose use is actually in the subroutine it calls, you should
9231 define this macro. Doing so allows the delay slot scheduler to move
9232 instructions which copy arguments into the argument registers into the delay
9235 You need not define this macro if it would always return zero.
9238 @defmac MULTIPLE_SYMBOL_SPACES
9239 Define this macro as a C expression that is nonzero if, in some cases,
9240 global symbols from one translation unit may not be bound to undefined
9241 symbols in another translation unit without user intervention. For
9242 instance, under Microsoft Windows symbols must be explicitly imported
9243 from shared libraries (DLLs).
9245 You need not define this macro if it would always evaluate to zero.
9248 @deftypefn {Target Hook} tree TARGET_MD_ASM_CLOBBERS (tree @var{outputs}, tree @var{inputs}, tree @var{clobbers})
9249 This target hook should add to @var{clobbers} @code{STRING_CST} trees for
9250 any hard regs the port wishes to automatically clobber for an asm.
9251 It should return the result of the last @code{tree_cons} used to add a
9252 clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the
9253 corresponding parameters to the asm and may be inspected to avoid
9254 clobbering a register that is an input or output of the asm. You can use
9255 @code{decl_overlaps_hard_reg_set_p}, declared in @file{tree.h}, to test
9256 for overlap with regards to asm-declared registers.
9259 @defmac MATH_LIBRARY
9260 Define this macro as a C string constant for the linker argument to link
9261 in the system math library, or @samp{""} if the target does not have a
9262 separate math library.
9264 You need only define this macro if the default of @samp{"-lm"} is wrong.
9267 @defmac LIBRARY_PATH_ENV
9268 Define this macro as a C string constant for the environment variable that
9269 specifies where the linker should look for libraries.
9271 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
9275 @defmac TARGET_HAS_F_SETLKW
9276 Define this macro if the target supports file locking with fcntl / F_SETLKW@.
9277 Note that this functionality is part of POSIX@.
9278 Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code
9279 to use file locking when exiting a program, which avoids race conditions
9280 if the program has forked.
9283 @defmac MAX_CONDITIONAL_EXECUTE
9285 A C expression for the maximum number of instructions to execute via
9286 conditional execution instructions instead of a branch. A value of
9287 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
9288 1 if it does use cc0.
9291 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
9292 Used if the target needs to perform machine-dependent modifications on the
9293 conditionals used for turning basic blocks into conditionally executed code.
9294 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
9295 contains information about the currently processed blocks. @var{true_expr}
9296 and @var{false_expr} are the tests that are used for converting the
9297 then-block and the else-block, respectively. Set either @var{true_expr} or
9298 @var{false_expr} to a null pointer if the tests cannot be converted.
9301 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
9302 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
9303 if-statements into conditions combined by @code{and} and @code{or} operations.
9304 @var{bb} contains the basic block that contains the test that is currently
9305 being processed and about to be turned into a condition.
9308 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
9309 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
9310 be converted to conditional execution format. @var{ce_info} points to
9311 a data structure, @code{struct ce_if_block}, which contains information
9312 about the currently processed blocks.
9315 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
9316 A C expression to perform any final machine dependent modifications in
9317 converting code to conditional execution. The involved basic blocks
9318 can be found in the @code{struct ce_if_block} structure that is pointed
9319 to by @var{ce_info}.
9322 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
9323 A C expression to cancel any machine dependent modifications in
9324 converting code to conditional execution. The involved basic blocks
9325 can be found in the @code{struct ce_if_block} structure that is pointed
9326 to by @var{ce_info}.
9329 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
9330 A C expression to initialize any extra fields in a @code{struct ce_if_block}
9331 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
9334 @defmac IFCVT_EXTRA_FIELDS
9335 If defined, it should expand to a set of field declarations that will be
9336 added to the @code{struct ce_if_block} structure. These should be initialized
9337 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
9340 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG ()
9341 If non-null, this hook performs a target-specific pass over the
9342 instruction stream. The compiler will run it at all optimization levels,
9343 just before the point at which it normally does delayed-branch scheduling.
9345 The exact purpose of the hook varies from target to target. Some use
9346 it to do transformations that are necessary for correctness, such as
9347 laying out in-function constant pools or avoiding hardware hazards.
9348 Others use it as an opportunity to do some machine-dependent optimizations.
9350 You need not implement the hook if it has nothing to do. The default
9354 @deftypefn {Target Hook} void TARGET_INIT_BUILTINS ()
9355 Define this hook if you have any machine-specific built-in functions
9356 that need to be defined. It should be a function that performs the
9359 Machine specific built-in functions can be useful to expand special machine
9360 instructions that would otherwise not normally be generated because
9361 they have no equivalent in the source language (for example, SIMD vector
9362 instructions or prefetch instructions).
9364 To create a built-in function, call the function
9365 @code{lang_hooks.builtin_function}
9366 which is defined by the language front end. You can use any type nodes set
9367 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
9368 only language front ends that use those two functions will call
9369 @samp{TARGET_INIT_BUILTINS}.
9372 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore})
9374 Expand a call to a machine specific built-in function that was set up by
9375 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
9376 function call; the result should go to @var{target} if that is
9377 convenient, and have mode @var{mode} if that is convenient.
9378 @var{subtarget} may be used as the target for computing one of
9379 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
9380 ignored. This function should return the result of the call to the
9384 @deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (tree @var{fndecl}, tree @var{arglist})
9386 Select a replacement for a machine specific built-in function that
9387 was set up by @samp{TARGET_INIT_BUILTINS}. This is done
9388 @emph{before} regular type checking, and so allows the target to
9389 implement a crude form of function overloading. @var{fndecl} is the
9390 declaration of the built-in function. @var{arglist} is the list of
9391 arguments passed to the built-in function. The result is a
9392 complete expression that implements the operation, usually
9393 another @code{CALL_EXPR}.
9396 @deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, tree @var{arglist}, bool @var{ignore})
9398 Fold a call to a machine specific built-in function that was set up by
9399 @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the
9400 built-in function. @var{arglist} is the list of arguments passed to
9401 the built-in function. The result is another tree containing a
9402 simplified expression for the call's result. If @var{ignore} is true
9403 the value will be ignored.
9406 @deftypefn {Target Hook} const char * TARGET_INVALID_WITHIN_DOLOOP (rtx @var{insn})
9408 Take an instruction in @var{insn} and return NULL if it is valid within a
9409 low-overhead loop, otherwise return a string why doloop could not be applied.
9411 Many targets use special registers for low-overhead looping. For any
9412 instruction that clobbers these this function should return a string indicating
9413 the reason why the doloop could not be applied.
9414 By default, the RTL loop optimizer does not use a present doloop pattern for
9415 loops containing function calls or branch on table instructions.
9418 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
9420 Take a branch insn in @var{branch1} and another in @var{branch2}.
9421 Return true if redirecting @var{branch1} to the destination of
9422 @var{branch2} is possible.
9424 On some targets, branches may have a limited range. Optimizing the
9425 filling of delay slots can result in branches being redirected, and this
9426 may in turn cause a branch offset to overflow.
9429 @defmac ALLOCATE_INITIAL_VALUE (@var{hard_reg})
9431 When the initial value of a hard register has been copied in a pseudo
9432 register, it is often not necessary to actually allocate another register
9433 to this pseudo register, because the original hard register or a stack slot
9434 it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if
9435 defined, is called at the start of register allocation once for each
9436 hard register that had its initial value copied by using
9437 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
9438 Possible values are @code{NULL_RTX}, if you don't want
9439 to do any special allocation, a @code{REG} rtx---that would typically be
9440 the hard register itself, if it is known not to be clobbered---or a
9442 If you are returning a @code{MEM}, this is only a hint for the allocator;
9443 it might decide to use another register anyways.
9444 You may use @code{current_function_leaf_function} in the definition of the
9445 macro, functions that use @code{REG_N_SETS}, to determine if the hard
9446 register in question will not be clobbered.
9449 @defmac TARGET_OBJECT_SUFFIX
9450 Define this macro to be a C string representing the suffix for object
9451 files on your target machine. If you do not define this macro, GCC will
9452 use @samp{.o} as the suffix for object files.
9455 @defmac TARGET_EXECUTABLE_SUFFIX
9456 Define this macro to be a C string representing the suffix to be
9457 automatically added to executable files on your target machine. If you
9458 do not define this macro, GCC will use the null string as the suffix for
9462 @defmac COLLECT_EXPORT_LIST
9463 If defined, @code{collect2} will scan the individual object files
9464 specified on its command line and create an export list for the linker.
9465 Define this macro for systems like AIX, where the linker discards
9466 object files that are not referenced from @code{main} and uses export
9470 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
9471 Define this macro to a C expression representing a variant of the
9472 method call @var{mdecl}, if Java Native Interface (JNI) methods
9473 must be invoked differently from other methods on your target.
9474 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
9475 the @code{stdcall} calling convention and this macro is then
9476 defined as this expression:
9479 build_type_attribute_variant (@var{mdecl},
9481 (get_identifier ("stdcall"),
9486 @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
9487 This target hook returns @code{true} past the point in which new jump
9488 instructions could be created. On machines that require a register for
9489 every jump such as the SHmedia ISA of SH5, this point would typically be
9490 reload, so this target hook should be defined to a function such as:
9494 cannot_modify_jumps_past_reload_p ()
9496 return (reload_completed || reload_in_progress);
9501 @deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void)
9502 This target hook returns a register class for which branch target register
9503 optimizations should be applied. All registers in this class should be
9504 usable interchangeably. After reload, registers in this class will be
9505 re-allocated and loads will be hoisted out of loops and be subjected
9506 to inter-block scheduling.
9509 @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen})
9510 Branch target register optimization will by default exclude callee-saved
9512 that are not already live during the current function; if this target hook
9513 returns true, they will be included. The target code must than make sure
9514 that all target registers in the class returned by
9515 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
9516 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
9517 epilogues have already been generated. Note, even if you only return
9518 true when @var{after_prologue_epilogue_gen} is false, you still are likely
9519 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
9520 to reserve space for caller-saved target registers.
9523 @defmac POWI_MAX_MULTS
9524 If defined, this macro is interpreted as a signed integer C expression
9525 that specifies the maximum number of floating point multiplications
9526 that should be emitted when expanding exponentiation by an integer
9527 constant inline. When this value is defined, exponentiation requiring
9528 more than this number of multiplications is implemented by calling the
9529 system library's @code{pow}, @code{powf} or @code{powl} routines.
9530 The default value places no upper bound on the multiplication count.
9533 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
9534 This target hook should register any extra include files for the
9535 target. The parameter @var{stdinc} indicates if normal include files
9536 are present. The parameter @var{sysroot} is the system root directory.
9537 The parameter @var{iprefix} is the prefix for the gcc directory.
9540 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
9541 This target hook should register any extra include files for the
9542 target before any standard headers. The parameter @var{stdinc}
9543 indicates if normal include files are present. The parameter
9544 @var{sysroot} is the system root directory. The parameter
9545 @var{iprefix} is the prefix for the gcc directory.
9548 @deftypefn Macro void TARGET_OPTF (char *@var{path})
9549 This target hook should register special include paths for the target.
9550 The parameter @var{path} is the include to register. On Darwin
9551 systems, this is used for Framework includes, which have semantics
9552 that are different from @option{-I}.
9555 @deftypefn {Target Hook} bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
9556 This target hook returns @code{true} if it is safe to use a local alias
9557 for a virtual function @var{fndecl} when constructing thunks,
9558 @code{false} otherwise. By default, the hook returns @code{true} for all
9559 functions, if a target supports aliases (i.e.@: defines
9560 @code{ASM_OUTPUT_DEF}), @code{false} otherwise,
9563 @defmac TARGET_FORMAT_TYPES
9564 If defined, this macro is the name of a global variable containing
9565 target-specific format checking information for the @option{-Wformat}
9566 option. The default is to have no target-specific format checks.
9569 @defmac TARGET_N_FORMAT_TYPES
9570 If defined, this macro is the number of entries in
9571 @code{TARGET_FORMAT_TYPES}.
9574 @deftypefn {Target Hook} bool TARGET_RELAXED_ORDERING
9575 If set to @code{true}, means that the target's memory model does not
9576 guarantee that loads which do not depend on one another will access
9577 main memory in the order of the instruction stream; if ordering is
9578 important, an explicit memory barrier must be used. This is true of
9579 many recent processors which implement a policy of ``relaxed,''
9580 ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC,
9581 and ia64. The default is @code{false}.
9584 @deftypefn {Target Hook} const char *TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (tree @var{typelist}, tree @var{funcdecl}, tree @var{val})
9585 If defined, this macro returns the diagnostic message when it is
9586 illegal to pass argument @var{val} to function @var{funcdecl}
9587 with prototype @var{typelist}.
9590 @defmac TARGET_USE_JCR_SECTION
9591 This macro determines whether to use the JCR section to register Java
9592 classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both
9593 SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0.