| @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001, |
| @c 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. |
| @c This is part of the GCC manual. |
| @c For copying conditions, see the file gcc.texi. |
| |
| @node Target Macros |
| @chapter Target Description Macros and Functions |
| @cindex machine description macros |
| @cindex target description macros |
| @cindex macros, target description |
| @cindex @file{tm.h} macros |
| |
| In addition to the file @file{@var{machine}.md}, a machine description |
| includes a C header file conventionally given the name |
| @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. |
| The header file defines numerous macros that convey the information |
| about the target machine that does not fit into the scheme of the |
| @file{.md} file. The file @file{tm.h} should be a link to |
| @file{@var{machine}.h}. The header file @file{config.h} includes |
| @file{tm.h} and most compiler source files include @file{config.h}. The |
| source file defines a variable @code{targetm}, which is a structure |
| containing pointers to functions and data relating to the target |
| machine. @file{@var{machine}.c} should also contain their definitions, |
| if they are not defined elsewhere in GCC, and other functions called |
| through the macros defined in the @file{.h} file. |
| |
| @menu |
| * Target Structure:: The @code{targetm} variable. |
| * Driver:: Controlling how the driver runs the compilation passes. |
| * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. |
| * Per-Function Data:: Defining data structures for per-function information. |
| * Storage Layout:: Defining sizes and alignments of data. |
| * Type Layout:: Defining sizes and properties of basic user data types. |
| * Registers:: Naming and describing the hardware registers. |
| * Register Classes:: Defining the classes of hardware registers. |
| * Old Constraints:: The old way to define machine-specific constraints. |
| * Stack and Calling:: Defining which way the stack grows and by how much. |
| * Varargs:: Defining the varargs macros. |
| * Trampolines:: Code set up at run time to enter a nested function. |
| * Library Calls:: Controlling how library routines are implicitly called. |
| * Addressing Modes:: Defining addressing modes valid for memory operands. |
| * Anchored Addresses:: Defining how @option{-fsection-anchors} should work. |
| * Condition Code:: Defining how insns update the condition code. |
| * Costs:: Defining relative costs of different operations. |
| * Scheduling:: Adjusting the behavior of the instruction scheduler. |
| * Sections:: Dividing storage into text, data, and other sections. |
| * PIC:: Macros for position independent code. |
| * Assembler Format:: Defining how to write insns and pseudo-ops to output. |
| * Debugging Info:: Defining the format of debugging output. |
| * Floating Point:: Handling floating point for cross-compilers. |
| * Mode Switching:: Insertion of mode-switching instructions. |
| * Target Attributes:: Defining target-specific uses of @code{__attribute__}. |
| * MIPS Coprocessors:: MIPS coprocessor support and how to customize it. |
| * PCH Target:: Validity checking for precompiled headers. |
| * C++ ABI:: Controlling C++ ABI changes. |
| * Misc:: Everything else. |
| @end menu |
| |
| @node Target Structure |
| @section The Global @code{targetm} Variable |
| @cindex target hooks |
| @cindex target functions |
| |
| @deftypevar {struct gcc_target} targetm |
| The target @file{.c} file must define the global @code{targetm} variable |
| which contains pointers to functions and data relating to the target |
| machine. The variable is declared in @file{target.h}; |
| @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is |
| used to initialize the variable, and macros for the default initializers |
| for elements of the structure. The @file{.c} file should override those |
| macros for which the default definition is inappropriate. For example: |
| @smallexample |
| #include "target.h" |
| #include "target-def.h" |
| |
| /* @r{Initialize the GCC target structure.} */ |
| |
| #undef TARGET_COMP_TYPE_ATTRIBUTES |
| #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes |
| |
| struct gcc_target targetm = TARGET_INITIALIZER; |
| @end smallexample |
| @end deftypevar |
| |
| Where a macro should be defined in the @file{.c} file in this manner to |
| form part of the @code{targetm} structure, it is documented below as a |
| ``Target Hook'' with a prototype. Many macros will change in future |
| from being defined in the @file{.h} file to being part of the |
| @code{targetm} structure. |
| |
| @node Driver |
| @section Controlling the Compilation Driver, @file{gcc} |
| @cindex driver |
| @cindex controlling the compilation driver |
| |
| @c prevent bad page break with this line |
| You can control the compilation driver. |
| |
| @defmac SWITCH_TAKES_ARG (@var{char}) |
| A C expression which determines whether the option @option{-@var{char}} |
| takes arguments. The value should be the number of arguments that |
| option takes--zero, for many options. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options |
| properly. You need not define @code{SWITCH_TAKES_ARG} unless you |
| wish to add additional options which take arguments. Any redefinition |
| should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for |
| additional options. |
| @end defmac |
| |
| @defmac WORD_SWITCH_TAKES_ARG (@var{name}) |
| A C expression which determines whether the option @option{-@var{name}} |
| takes arguments. The value should be the number of arguments that |
| option takes--zero, for many options. This macro rather than |
| @code{SWITCH_TAKES_ARG} is used for multi-character option names. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options |
| properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you |
| wish to add additional options which take arguments. Any redefinition |
| should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for |
| additional options. |
| @end defmac |
| |
| @defmac SWITCH_CURTAILS_COMPILATION (@var{char}) |
| A C expression which determines whether the option @option{-@var{char}} |
| stops compilation before the generation of an executable. The value is |
| boolean, nonzero if the option does stop an executable from being |
| generated, zero otherwise. |
| |
| By default, this macro is defined as |
| @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard |
| options properly. You need not define |
| @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional |
| options which affect the generation of an executable. Any redefinition |
| should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check |
| for additional options. |
| @end defmac |
| |
| @defmac SWITCHES_NEED_SPACES |
| A string-valued C expression which enumerates the options for which |
| the linker needs a space between the option and its argument. |
| |
| If this macro is not defined, the default value is @code{""}. |
| @end defmac |
| |
| @defmac TARGET_OPTION_TRANSLATE_TABLE |
| If defined, a list of pairs of strings, the first of which is a |
| potential command line target to the @file{gcc} driver program, and the |
| second of which is a space-separated (tabs and other whitespace are not |
| supported) list of options with which to replace the first option. The |
| target defining this list is responsible for assuring that the results |
| are valid. Replacement options may not be the @code{--opt} style, they |
| must be the @code{-opt} style. It is the intention of this macro to |
| provide a mechanism for substitution that affects the multilibs chosen, |
| such as one option that enables many options, some of which select |
| multilibs. Example nonsensical definition, where @option{-malt-abi}, |
| @option{-EB}, and @option{-mspoo} cause different multilibs to be chosen: |
| |
| @smallexample |
| #define TARGET_OPTION_TRANSLATE_TABLE \ |
| @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \ |
| @{ "-compat", "-EB -malign=4 -mspoo" @} |
| @end smallexample |
| @end defmac |
| |
| @defmac DRIVER_SELF_SPECS |
| A list of specs for the driver itself. It should be a suitable |
| initializer for an array of strings, with no surrounding braces. |
| |
| The driver applies these specs to its own command line between loading |
| default @file{specs} files (but not command-line specified ones) and |
| choosing the multilib directory or running any subcommands. It |
| applies them in the order given, so each spec can depend on the |
| options added by earlier ones. It is also possible to remove options |
| using @samp{%<@var{option}} in the usual way. |
| |
| This macro can be useful when a port has several interdependent target |
| options. It provides a way of standardizing the command line so |
| that the other specs are easier to write. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac OPTION_DEFAULT_SPECS |
| A list of specs used to support configure-time default options (i.e.@: |
| @option{--with} options) in the driver. It should be a suitable initializer |
| for an array of structures, each containing two strings, without the |
| outermost pair of surrounding braces. |
| |
| The first item in the pair is the name of the default. This must match |
| the code in @file{config.gcc} for the target. The second item is a spec |
| to apply if a default with this name was specified. The string |
| @samp{%(VALUE)} in the spec will be replaced by the value of the default |
| everywhere it occurs. |
| |
| The driver will apply these specs to its own command line between loading |
| default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using |
| the same mechanism as @code{DRIVER_SELF_SPECS}. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac CPP_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to CPP@. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the CPP@. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac CPLUSPLUS_CPP_SPEC |
| This macro is just like @code{CPP_SPEC}, but is used for C++, rather |
| than C@. If you do not define this macro, then the value of |
| @code{CPP_SPEC} (if any) will be used instead. |
| @end defmac |
| |
| @defmac CC1_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language |
| front ends. |
| It can also specify how to translate options you give to GCC into options |
| for GCC to pass to front ends. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac CC1PLUS_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to @code{cc1plus}. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the @code{cc1plus}. |
| |
| Do not define this macro if it does not need to do anything. |
| Note that everything defined in CC1_SPEC is already passed to |
| @code{cc1plus} so there is no need to duplicate the contents of |
| CC1_SPEC in CC1PLUS_SPEC@. |
| @end defmac |
| |
| @defmac ASM_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to the assembler. It can also specify how to translate options |
| you give to GCC into options for GCC to pass to the assembler. |
| See the file @file{sun3.h} for an example of this. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac ASM_FINAL_SPEC |
| A C string constant that tells the GCC driver program how to |
| run any programs which cleanup after the normal assembler. |
| Normally, this is not needed. See the file @file{mips.h} for |
| an example of this. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT |
| Define this macro, with no value, if the driver should give the assembler |
| an argument consisting of a single dash, @option{-}, to instruct it to |
| read from its standard input (which will be a pipe connected to the |
| output of the compiler proper). This argument is given after any |
| @option{-o} option specifying the name of the output file. |
| |
| If you do not define this macro, the assembler is assumed to read its |
| standard input if given no non-option arguments. If your assembler |
| cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct; |
| see @file{mips.h} for instance. |
| @end defmac |
| |
| @defmac LINK_SPEC |
| A C string constant that tells the GCC driver program options to |
| pass to the linker. It can also specify how to translate options you |
| give to GCC into options for GCC to pass to the linker. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac LIB_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The difference |
| between the two is that @code{LIB_SPEC} is used at the end of the |
| command given to the linker. |
| |
| If this macro is not defined, a default is provided that |
| loads the standard C library from the usual place. See @file{gcc.c}. |
| @end defmac |
| |
| @defmac LIBGCC_SPEC |
| Another C string constant that tells the GCC driver program |
| how and when to place a reference to @file{libgcc.a} into the |
| linker command line. This constant is placed both before and after |
| the value of @code{LIB_SPEC}. |
| |
| If this macro is not defined, the GCC driver provides a default that |
| passes the string @option{-lgcc} to the linker. |
| @end defmac |
| |
| @defmac REAL_LIBGCC_SPEC |
| By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the |
| @code{LIBGCC_SPEC} is not directly used by the driver program but is |
| instead modified to refer to different versions of @file{libgcc.a} |
| depending on the values of the command line flags @option{-static}, |
| @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On |
| targets where these modifications are inappropriate, define |
| @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the |
| driver how to place a reference to @file{libgcc} on the link command |
| line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified. |
| @end defmac |
| |
| @defmac USE_LD_AS_NEEDED |
| A macro that controls the modifications to @code{LIBGCC_SPEC} |
| mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be |
| generated that uses --as-needed and the shared libgcc in place of the |
| static exception handler library, when linking without any of |
| @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}. |
| @end defmac |
| |
| @defmac LINK_EH_SPEC |
| If defined, this C string constant is added to @code{LINK_SPEC}. |
| When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects |
| the modifications to @code{LIBGCC_SPEC} mentioned in |
| @code{REAL_LIBGCC_SPEC}. |
| @end defmac |
| |
| @defmac STARTFILE_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The |
| difference between the two is that @code{STARTFILE_SPEC} is used at |
| the very beginning of the command given to the linker. |
| |
| If this macro is not defined, a default is provided that loads the |
| standard C startup file from the usual place. See @file{gcc.c}. |
| @end defmac |
| |
| @defmac ENDFILE_SPEC |
| Another C string constant used much like @code{LINK_SPEC}. The |
| difference between the two is that @code{ENDFILE_SPEC} is used at |
| the very end of the command given to the linker. |
| |
| Do not define this macro if it does not need to do anything. |
| @end defmac |
| |
| @defmac THREAD_MODEL_SPEC |
| GCC @code{-v} will print the thread model GCC was configured to use. |
| However, this doesn't work on platforms that are multilibbed on thread |
| models, such as AIX 4.3. On such platforms, define |
| @code{THREAD_MODEL_SPEC} such that it evaluates to a string without |
| blanks that names one of the recognized thread models. @code{%*}, the |
| default value of this macro, will expand to the value of |
| @code{thread_file} set in @file{config.gcc}. |
| @end defmac |
| |
| @defmac SYSROOT_SUFFIX_SPEC |
| Define this macro to add a suffix to the target sysroot when GCC is |
| configured with a sysroot. This will cause GCC to search for usr/lib, |
| et al, within sysroot+suffix. |
| @end defmac |
| |
| @defmac SYSROOT_HEADERS_SUFFIX_SPEC |
| Define this macro to add a headers_suffix to the target sysroot when |
| GCC is configured with a sysroot. This will cause GCC to pass the |
| updated sysroot+headers_suffix to CPP, causing it to search for |
| usr/include, et al, within sysroot+headers_suffix. |
| @end defmac |
| |
| @defmac EXTRA_SPECS |
| Define this macro to provide additional specifications to put in the |
| @file{specs} file that can be used in various specifications like |
| @code{CC1_SPEC}. |
| |
| The definition should be an initializer for an array of structures, |
| containing a string constant, that defines the specification name, and a |
| string constant that provides the specification. |
| |
| Do not define this macro if it does not need to do anything. |
| |
| @code{EXTRA_SPECS} is useful when an architecture contains several |
| related targets, which have various @code{@dots{}_SPECS} which are similar |
| to each other, and the maintainer would like one central place to keep |
| these definitions. |
| |
| For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to |
| define either @code{_CALL_SYSV} when the System V calling sequence is |
| used or @code{_CALL_AIX} when the older AIX-based calling sequence is |
| used. |
| |
| The @file{config/rs6000/rs6000.h} target file defines: |
| |
| @smallexample |
| #define EXTRA_SPECS \ |
| @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, |
| |
| #define CPP_SYS_DEFAULT "" |
| @end smallexample |
| |
| The @file{config/rs6000/sysv.h} target file defines: |
| @smallexample |
| #undef CPP_SPEC |
| #define CPP_SPEC \ |
| "%@{posix: -D_POSIX_SOURCE @} \ |
| %@{mcall-sysv: -D_CALL_SYSV @} \ |
| %@{!mcall-sysv: %(cpp_sysv_default) @} \ |
| %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" |
| |
| #undef CPP_SYSV_DEFAULT |
| #define CPP_SYSV_DEFAULT "-D_CALL_SYSV" |
| @end smallexample |
| |
| while the @file{config/rs6000/eabiaix.h} target file defines |
| @code{CPP_SYSV_DEFAULT} as: |
| |
| @smallexample |
| #undef CPP_SYSV_DEFAULT |
| #define CPP_SYSV_DEFAULT "-D_CALL_AIX" |
| @end smallexample |
| @end defmac |
| |
| @defmac LINK_LIBGCC_SPECIAL_1 |
| Define this macro if the driver program should find the library |
| @file{libgcc.a}. If you do not define this macro, the driver program will pass |
| the argument @option{-lgcc} to tell the linker to do the search. |
| @end defmac |
| |
| @defmac LINK_GCC_C_SEQUENCE_SPEC |
| The sequence in which libgcc and libc are specified to the linker. |
| By default this is @code{%G %L %G}. |
| @end defmac |
| |
| @defmac LINK_COMMAND_SPEC |
| A C string constant giving the complete command line need to execute the |
| linker. When you do this, you will need to update your port each time a |
| change is made to the link command line within @file{gcc.c}. Therefore, |
| define this macro only if you need to completely redefine the command |
| line for invoking the linker and there is no other way to accomplish |
| the effect you need. Overriding this macro may be avoidable by overriding |
| @code{LINK_GCC_C_SEQUENCE_SPEC} instead. |
| @end defmac |
| |
| @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES |
| A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search |
| directories from linking commands. Do not give it a nonzero value if |
| removing duplicate search directories changes the linker's semantics. |
| @end defmac |
| |
| @defmac MULTILIB_DEFAULTS |
| Define this macro as a C expression for the initializer of an array of |
| string to tell the driver program which options are defaults for this |
| target and thus do not need to be handled specially when using |
| @code{MULTILIB_OPTIONS}. |
| |
| Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in |
| the target makefile fragment or if none of the options listed in |
| @code{MULTILIB_OPTIONS} are set by default. |
| @xref{Target Fragment}. |
| @end defmac |
| |
| @defmac RELATIVE_PREFIX_NOT_LINKDIR |
| Define this macro to tell @command{gcc} that it should only translate |
| a @option{-B} prefix into a @option{-L} linker option if the prefix |
| indicates an absolute file name. |
| @end defmac |
| |
| @defmac MD_EXEC_PREFIX |
| If defined, this macro is an additional prefix to try after |
| @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched |
| when the @option{-b} option is used, or the compiler is built as a cross |
| compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it |
| to the list of directories used to find the assembler in @file{configure.in}. |
| @end defmac |
| |
| @defmac STANDARD_STARTFILE_PREFIX |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @code{libdir} as the default prefix to |
| try when searching for startup files such as @file{crt0.o}. |
| @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler |
| is built as a cross compiler. |
| @end defmac |
| |
| @defmac STANDARD_STARTFILE_PREFIX_1 |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @code{/lib} as a prefix to try after the default prefix |
| when searching for startup files such as @file{crt0.o}. |
| @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler |
| is built as a cross compiler. |
| @end defmac |
| |
| @defmac STANDARD_STARTFILE_PREFIX_2 |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @code{/lib} as yet another prefix to try after the |
| default prefix when searching for startup files such as @file{crt0.o}. |
| @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler |
| is built as a cross compiler. |
| @end defmac |
| |
| @defmac MD_STARTFILE_PREFIX |
| If defined, this macro supplies an additional prefix to try after the |
| standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the |
| @option{-b} option is used, or when the compiler is built as a cross |
| compiler. |
| @end defmac |
| |
| @defmac MD_STARTFILE_PREFIX_1 |
| If defined, this macro supplies yet another prefix to try after the |
| standard prefixes. It is not searched when the @option{-b} option is |
| used, or when the compiler is built as a cross compiler. |
| @end defmac |
| |
| @defmac INIT_ENVIRONMENT |
| Define this macro as a C string constant if you wish to set environment |
| variables for programs called by the driver, such as the assembler and |
| loader. The driver passes the value of this macro to @code{putenv} to |
| initialize the necessary environment variables. |
| @end defmac |
| |
| @defmac LOCAL_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/local/include} as the default prefix to |
| try when searching for local header files. @code{LOCAL_INCLUDE_DIR} |
| comes before @code{SYSTEM_INCLUDE_DIR} in the search order. |
| |
| Cross compilers do not search either @file{/usr/local/include} or its |
| replacement. |
| @end defmac |
| |
| @defmac MODIFY_TARGET_NAME |
| Define this macro if you wish to define command-line switches that |
| modify the default target name. |
| |
| For each switch, you can include a string to be appended to the first |
| part of the configuration name or a string to be deleted from the |
| configuration name, if present. The definition should be an initializer |
| for an array of structures. Each array element should have three |
| elements: the switch name (a string constant, including the initial |
| dash), one of the enumeration codes @code{ADD} or @code{DELETE} to |
| indicate whether the string should be inserted or deleted, and the string |
| to be inserted or deleted (a string constant). |
| |
| For example, on a machine where @samp{64} at the end of the |
| configuration name denotes a 64-bit target and you want the @option{-32} |
| and @option{-64} switches to select between 32- and 64-bit targets, you would |
| code |
| |
| @smallexample |
| #define MODIFY_TARGET_NAME \ |
| @{ @{ "-32", DELETE, "64"@}, \ |
| @{"-64", ADD, "64"@}@} |
| @end smallexample |
| @end defmac |
| |
| @defmac SYSTEM_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to specify a |
| system-specific directory to search for header files before the standard |
| directory. @code{SYSTEM_INCLUDE_DIR} comes before |
| @code{STANDARD_INCLUDE_DIR} in the search order. |
| |
| Cross compilers do not use this macro and do not search the directory |
| specified. |
| @end defmac |
| |
| @defmac STANDARD_INCLUDE_DIR |
| Define this macro as a C string constant if you wish to override the |
| standard choice of @file{/usr/include} as the default prefix to |
| try when searching for header files. |
| |
| Cross compilers ignore this macro and do not search either |
| @file{/usr/include} or its replacement. |
| @end defmac |
| |
| @defmac STANDARD_INCLUDE_COMPONENT |
| The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}. |
| See @code{INCLUDE_DEFAULTS}, below, for the description of components. |
| If you do not define this macro, no component is used. |
| @end defmac |
| |
| @defmac INCLUDE_DEFAULTS |
| Define this macro if you wish to override the entire default search path |
| for include files. For a native compiler, the default search path |
| usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, |
| @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and |
| @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} |
| and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, |
| and specify private search areas for GCC@. The directory |
| @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. |
| |
| The definition should be an initializer for an array of structures. |
| Each array element should have four elements: the directory name (a |
| string constant), the component name (also a string constant), a flag |
| for C++-only directories, |
| and a flag showing that the includes in the directory don't need to be |
| wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of |
| the array with a null element. |
| |
| The component name denotes what GNU package the include file is part of, |
| if any, in all uppercase letters. For example, it might be @samp{GCC} |
| or @samp{BINUTILS}. If the package is part of a vendor-supplied |
| operating system, code the component name as @samp{0}. |
| |
| For example, here is the definition used for VAX/VMS: |
| |
| @smallexample |
| #define INCLUDE_DEFAULTS \ |
| @{ \ |
| @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ |
| @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ |
| @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ |
| @{ ".", 0, 0, 0@}, \ |
| @{ 0, 0, 0, 0@} \ |
| @} |
| @end smallexample |
| @end defmac |
| |
| Here is the order of prefixes tried for exec files: |
| |
| @enumerate |
| @item |
| Any prefixes specified by the user with @option{-B}. |
| |
| @item |
| The environment variable @code{GCC_EXEC_PREFIX}, if any. |
| |
| @item |
| The directories specified by the environment variable @code{COMPILER_PATH}. |
| |
| @item |
| The macro @code{STANDARD_EXEC_PREFIX}. |
| |
| @item |
| @file{/usr/lib/gcc/}. |
| |
| @item |
| The macro @code{MD_EXEC_PREFIX}, if any. |
| @end enumerate |
| |
| Here is the order of prefixes tried for startfiles: |
| |
| @enumerate |
| @item |
| Any prefixes specified by the user with @option{-B}. |
| |
| @item |
| The environment variable @code{GCC_EXEC_PREFIX}, if any. |
| |
| @item |
| The directories specified by the environment variable @code{LIBRARY_PATH} |
| (or port-specific name; native only, cross compilers do not use this). |
| |
| @item |
| The macro @code{STANDARD_EXEC_PREFIX}. |
| |
| @item |
| @file{/usr/lib/gcc/}. |
| |
| @item |
| The macro @code{MD_EXEC_PREFIX}, if any. |
| |
| @item |
| The macro @code{MD_STARTFILE_PREFIX}, if any. |
| |
| @item |
| The macro @code{STANDARD_STARTFILE_PREFIX}. |
| |
| @item |
| @file{/lib/}. |
| |
| @item |
| @file{/usr/lib/}. |
| @end enumerate |
| |
| @node Run-time Target |
| @section Run-time Target Specification |
| @cindex run-time target specification |
| @cindex predefined macros |
| @cindex target specifications |
| |
| @c prevent bad page break with this line |
| Here are run-time target specifications. |
| |
| @defmac TARGET_CPU_CPP_BUILTINS () |
| This function-like macro expands to a block of code that defines |
| built-in preprocessor macros and assertions for the target cpu, using |
| the functions @code{builtin_define}, @code{builtin_define_std} and |
| @code{builtin_assert}. When the front end |
| calls this macro it provides a trailing semicolon, and since it has |
| finished command line option processing your code can use those |
| results freely. |
| |
| @code{builtin_assert} takes a string in the form you pass to the |
| command-line option @option{-A}, such as @code{cpu=mips}, and creates |
| the assertion. @code{builtin_define} takes a string in the form |
| accepted by option @option{-D} and unconditionally defines the macro. |
| |
| @code{builtin_define_std} takes a string representing the name of an |
| object-like macro. If it doesn't lie in the user's namespace, |
| @code{builtin_define_std} defines it unconditionally. Otherwise, it |
| defines a version with two leading underscores, and another version |
| with two leading and trailing underscores, and defines the original |
| only if an ISO standard was not requested on the command line. For |
| example, passing @code{unix} defines @code{__unix}, @code{__unix__} |
| and possibly @code{unix}; passing @code{_mips} defines @code{__mips}, |
| @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64} |
| defines only @code{_ABI64}. |
| |
| You can also test for the C dialect being compiled. The variable |
| @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus} |
| or @code{clk_objective_c}. Note that if we are preprocessing |
| assembler, this variable will be @code{clk_c} but the function-like |
| macro @code{preprocessing_asm_p()} will return true, so you might want |
| to check for that first. If you need to check for strict ANSI, the |
| variable @code{flag_iso} can be used. The function-like macro |
| @code{preprocessing_trad_p()} can be used to check for traditional |
| preprocessing. |
| @end defmac |
| |
| @defmac TARGET_OS_CPP_BUILTINS () |
| Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional |
| and is used for the target operating system instead. |
| @end defmac |
| |
| @defmac TARGET_OBJFMT_CPP_BUILTINS () |
| Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional |
| and is used for the target object format. @file{elfos.h} uses this |
| macro to define @code{__ELF__}, so you probably do not need to define |
| it yourself. |
| @end defmac |
| |
| @deftypevar {extern int} target_flags |
| This variable is declared in @file{options.h}, which is included before |
| any target-specific headers. |
| @end deftypevar |
| |
| @deftypevar {Target Hook} int TARGET_DEFAULT_TARGET_FLAGS |
| This variable specifies the initial value of @code{target_flags}. |
| Its default setting is 0. |
| @end deftypevar |
| |
| @cindex optional hardware or system features |
| @cindex features, optional, in system conventions |
| |
| @deftypefn {Target Hook} bool TARGET_HANDLE_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value}) |
| This hook is called whenever the user specifies one of the |
| target-specific options described by the @file{.opt} definition files |
| (@pxref{Options}). It has the opportunity to do some option-specific |
| processing and should return true if the option is valid. The default |
| definition does nothing but return true. |
| |
| @var{code} specifies the @code{OPT_@var{name}} enumeration value |
| associated with the selected option; @var{name} is just a rendering of |
| the option name in which non-alphanumeric characters are replaced by |
| underscores. @var{arg} specifies the string argument and is null if |
| no argument was given. If the option is flagged as a @code{UInteger} |
| (@pxref{Option properties}), @var{value} is the numeric value of the |
| argument. Otherwise @var{value} is 1 if the positive form of the |
| option was used and 0 if the ``no-'' form was. |
| @end deftypefn |
| |
| @defmac TARGET_VERSION |
| This macro is a C statement to print on @code{stderr} a string |
| describing the particular machine description choice. Every machine |
| description should define @code{TARGET_VERSION}. For example: |
| |
| @smallexample |
| #ifdef MOTOROLA |
| #define TARGET_VERSION \ |
| fprintf (stderr, " (68k, Motorola syntax)"); |
| #else |
| #define TARGET_VERSION \ |
| fprintf (stderr, " (68k, MIT syntax)"); |
| #endif |
| @end smallexample |
| @end defmac |
| |
| @defmac OVERRIDE_OPTIONS |
| Sometimes certain combinations of command options do not make sense on |
| a particular target machine. You can define a macro |
| @code{OVERRIDE_OPTIONS} to take account of this. This macro, if |
| defined, is executed once just after all the command options have been |
| parsed. |
| |
| Don't use this macro to turn on various extra optimizations for |
| @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for. |
| @end defmac |
| |
| @defmac C_COMMON_OVERRIDE_OPTIONS |
| This is similar to @code{OVERRIDE_OPTIONS} but is only used in the C |
| language frontends (C, Objective-C, C++, Objective-C++) and so can be |
| used to alter option flag variables which only exist in those |
| frontends. |
| @end defmac |
| |
| @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size}) |
| Some machines may desire to change what optimizations are performed for |
| various optimization levels. This macro, if defined, is executed once |
| just after the optimization level is determined and before the remainder |
| of the command options have been parsed. Values set in this macro are |
| used as the default values for the other command line options. |
| |
| @var{level} is the optimization level specified; 2 if @option{-O2} is |
| specified, 1 if @option{-O} is specified, and 0 if neither is specified. |
| |
| @var{size} is nonzero if @option{-Os} is specified and zero otherwise. |
| |
| You should not use this macro to change options that are not |
| machine-specific. These should uniformly selected by the same |
| optimization level on all supported machines. Use this macro to enable |
| machine-specific optimizations. |
| |
| @strong{Do not examine @code{write_symbols} in |
| this macro!} The debugging options are not supposed to alter the |
| generated code. |
| @end defmac |
| |
| @defmac CAN_DEBUG_WITHOUT_FP |
| Define this macro if debugging can be performed even without a frame |
| pointer. If this macro is defined, GCC will turn on the |
| @option{-fomit-frame-pointer} option whenever @option{-O} is specified. |
| @end defmac |
| |
| @node Per-Function Data |
| @section Defining data structures for per-function information. |
| @cindex per-function data |
| @cindex data structures |
| |
| If the target needs to store information on a per-function basis, GCC |
| provides a macro and a couple of variables to allow this. Note, just |
| using statics to store the information is a bad idea, since GCC supports |
| nested functions, so you can be halfway through encoding one function |
| when another one comes along. |
| |
| GCC defines a data structure called @code{struct function} which |
| contains all of the data specific to an individual function. This |
| structure contains a field called @code{machine} whose type is |
| @code{struct machine_function *}, which can be used by targets to point |
| to their own specific data. |
| |
| If a target needs per-function specific data it should define the type |
| @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}. |
| This macro should be used to initialize the function pointer |
| @code{init_machine_status}. This pointer is explained below. |
| |
| One typical use of per-function, target specific data is to create an |
| RTX to hold the register containing the function's return address. This |
| RTX can then be used to implement the @code{__builtin_return_address} |
| function, for level 0. |
| |
| Note---earlier implementations of GCC used a single data area to hold |
| all of the per-function information. Thus when processing of a nested |
| function began the old per-function data had to be pushed onto a |
| stack, and when the processing was finished, it had to be popped off the |
| stack. GCC used to provide function pointers called |
| @code{save_machine_status} and @code{restore_machine_status} to handle |
| the saving and restoring of the target specific information. Since the |
| single data area approach is no longer used, these pointers are no |
| longer supported. |
| |
| @defmac INIT_EXPANDERS |
| Macro called to initialize any target specific information. This macro |
| is called once per function, before generation of any RTL has begun. |
| The intention of this macro is to allow the initialization of the |
| function pointer @code{init_machine_status}. |
| @end defmac |
| |
| @deftypevar {void (*)(struct function *)} init_machine_status |
| If this function pointer is non-@code{NULL} it will be called once per |
| function, before function compilation starts, in order to allow the |
| target to perform any target specific initialization of the |
| @code{struct function} structure. It is intended that this would be |
| used to initialize the @code{machine} of that structure. |
| |
| @code{struct machine_function} structures are expected to be freed by GC@. |
| Generally, any memory that they reference must be allocated by using |
| @code{ggc_alloc}, including the structure itself. |
| @end deftypevar |
| |
| @node Storage Layout |
| @section Storage Layout |
| @cindex storage layout |
| |
| Note that the definitions of the macros in this table which are sizes or |
| alignments measured in bits do not need to be constant. They can be C |
| expressions that refer to static variables, such as the @code{target_flags}. |
| @xref{Run-time Target}. |
| |
| @defmac BITS_BIG_ENDIAN |
| Define this macro to have the value 1 if the most significant bit in a |
| byte has the lowest number; otherwise define it to have the value zero. |
| This means that bit-field instructions count from the most significant |
| bit. If the machine has no bit-field instructions, then this must still |
| be defined, but it doesn't matter which value it is defined to. This |
| macro need not be a constant. |
| |
| This macro does not affect the way structure fields are packed into |
| bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. |
| @end defmac |
| |
| @defmac BYTES_BIG_ENDIAN |
| Define this macro to have the value 1 if the most significant byte in a |
| word has the lowest number. This macro need not be a constant. |
| @end defmac |
| |
| @defmac WORDS_BIG_ENDIAN |
| Define this macro to have the value 1 if, in a multiword object, the |
| most significant word has the lowest number. This applies to both |
| memory locations and registers; GCC fundamentally assumes that the |
| order of words in memory is the same as the order in registers. This |
| macro need not be a constant. |
| @end defmac |
| |
| @defmac LIBGCC2_WORDS_BIG_ENDIAN |
| Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a |
| constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be |
| used only when compiling @file{libgcc2.c}. Typically the value will be set |
| based on preprocessor defines. |
| @end defmac |
| |
| @defmac FLOAT_WORDS_BIG_ENDIAN |
| Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or |
| @code{TFmode} floating point numbers are stored in memory with the word |
| containing the sign bit at the lowest address; otherwise define it to |
| have the value 0. This macro need not be a constant. |
| |
| You need not define this macro if the ordering is the same as for |
| multi-word integers. |
| @end defmac |
| |
| @defmac BITS_PER_UNIT |
| Define this macro to be the number of bits in an addressable storage |
| unit (byte). If you do not define this macro the default is 8. |
| @end defmac |
| |
| @defmac BITS_PER_WORD |
| Number of bits in a word. If you do not define this macro, the default |
| is @code{BITS_PER_UNIT * UNITS_PER_WORD}. |
| @end defmac |
| |
| @defmac MAX_BITS_PER_WORD |
| Maximum number of bits in a word. If this is undefined, the default is |
| @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the |
| largest value that @code{BITS_PER_WORD} can have at run-time. |
| @end defmac |
| |
| @defmac UNITS_PER_WORD |
| Number of storage units in a word; normally the size of a general-purpose |
| register, a power of two from 1 or 8. |
| @end defmac |
| |
| @defmac MIN_UNITS_PER_WORD |
| Minimum number of units in a word. If this is undefined, the default is |
| @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the |
| smallest value that @code{UNITS_PER_WORD} can have at run-time. |
| @end defmac |
| |
| @defmac UNITS_PER_SIMD_WORD |
| Number of units in the vectors that the vectorizer can produce. |
| The default is equal to @code{UNITS_PER_WORD}, because the vectorizer |
| can do some transformations even in absence of specialized @acronym{SIMD} |
| hardware. |
| @end defmac |
| |
| @defmac POINTER_SIZE |
| Width of a pointer, in bits. You must specify a value no wider than the |
| width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, |
| you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify |
| a value the default is @code{BITS_PER_WORD}. |
| @end defmac |
| |
| @defmac POINTERS_EXTEND_UNSIGNED |
| A C expression whose value is greater than zero if pointers that need to be |
| extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to |
| be zero-extended and zero if they are to be sign-extended. If the value |
| is less then zero then there must be an "ptr_extend" instruction that |
| extends a pointer from @code{POINTER_SIZE} to @code{Pmode}. |
| |
| You need not define this macro if the @code{POINTER_SIZE} is equal |
| to the width of @code{Pmode}. |
| @end defmac |
| |
| @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) |
| A macro to update @var{m} and @var{unsignedp} when an object whose type |
| is @var{type} and which has the specified mode and signedness is to be |
| stored in a register. This macro is only called when @var{type} is a |
| scalar type. |
| |
| On most RISC machines, which only have operations that operate on a full |
| register, define this macro to set @var{m} to @code{word_mode} if |
| @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most |
| cases, only integer modes should be widened because wider-precision |
| floating-point operations are usually more expensive than their narrower |
| counterparts. |
| |
| For most machines, the macro definition does not change @var{unsignedp}. |
| However, some machines, have instructions that preferentially handle |
| either signed or unsigned quantities of certain modes. For example, on |
| the DEC Alpha, 32-bit loads from memory and 32-bit add instructions |
| sign-extend the result to 64 bits. On such machines, set |
| @var{unsignedp} according to which kind of extension is more efficient. |
| |
| Do not define this macro if it would never modify @var{m}. |
| @end defmac |
| |
| @defmac PROMOTE_FUNCTION_MODE |
| Like @code{PROMOTE_MODE}, but is applied to outgoing function arguments or |
| function return values, as specified by @code{TARGET_PROMOTE_FUNCTION_ARGS} |
| and @code{TARGET_PROMOTE_FUNCTION_RETURN}, respectively. |
| |
| The default is @code{PROMOTE_MODE}. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_ARGS (tree @var{fntype}) |
| This target hook should return @code{true} if the promotion described by |
| @code{PROMOTE_FUNCTION_MODE} should be done for outgoing function |
| arguments. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_RETURN (tree @var{fntype}) |
| This target hook should return @code{true} if the promotion described by |
| @code{PROMOTE_FUNCTION_MODE} should be done for the return value of |
| functions. |
| |
| If this target hook returns @code{true}, @code{TARGET_FUNCTION_VALUE} |
| must perform the same promotions done by @code{PROMOTE_FUNCTION_MODE}. |
| @end deftypefn |
| |
| @defmac PARM_BOUNDARY |
| Normal alignment required for function parameters on the stack, in |
| bits. All stack parameters receive at least this much alignment |
| regardless of data type. On most machines, this is the same as the |
| size of an integer. |
| @end defmac |
| |
| @defmac STACK_BOUNDARY |
| Define this macro to the minimum alignment enforced by hardware for the |
| stack pointer on this machine. The definition is a C expression for the |
| desired alignment (measured in bits). This value is used as a default |
| if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, |
| this should be the same as @code{PARM_BOUNDARY}. |
| @end defmac |
| |
| @defmac PREFERRED_STACK_BOUNDARY |
| Define this macro if you wish to preserve a certain alignment for the |
| stack pointer, greater than what the hardware enforces. The definition |
| is a C expression for the desired alignment (measured in bits). This |
| macro must evaluate to a value equal to or larger than |
| @code{STACK_BOUNDARY}. |
| @end defmac |
| |
| @defmac FUNCTION_BOUNDARY |
| Alignment required for a function entry point, in bits. |
| @end defmac |
| |
| @defmac BIGGEST_ALIGNMENT |
| Biggest alignment that any data type can require on this machine, in bits. |
| @end defmac |
| |
| @c APPLE LOCAL begin 5946347 ms_struct support |
| @defmac BIGGEST_MS_STRUCT_ALIGNMENT |
| Define this macro if the target supports Microsoft structure alignment |
| (@code{TARGET_MS_BITFIELD_LAYOUT_P}) and the target definition of |
| BIGGEST_ALIGNMENT is smaller than is needed for ms_struct records. It should |
| defined as the largest field alignment required by the target for Microsoft |
| aligned structure fields. |
| |
| By default, @code{BIGGEST_MS_STRUCT_ALIGNMENT} is defined to be equivalent to |
| @code{BIGGEST_ALIGNMENT}. |
| @end defmac |
| |
| @defmac TARGET_FIELD_MS_STRUCT_ALIGN |
| Define this macro if the target supports Microsoft structure alignment |
| (@code{TARGET_MS_BITFIELD_LAYOUT_P}) and the standard type alignment |
| of non-aggregate types is not sufficient for the MS structure alignment rules. |
| |
| The @code{TARGET_FIELD_MS_STRUCT_ALIGN} macro should return the alignment required |
| for the field passed as its argument. |
| |
| By default, the type alignment of the field will be used, i.e., |
| @code{TYPE_ALIGN (TREE_TYPE (FIELD))}. |
| @end defmac |
| @c APPLE LOCAL end 5946347 ms_struct support |
| |
| @defmac MINIMUM_ATOMIC_ALIGNMENT |
| If defined, the smallest alignment, in bits, that can be given to an |
| object that can be referenced in one operation, without disturbing any |
| nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger |
| on machines that don't have byte or half-word store operations. |
| @end defmac |
| |
| @defmac BIGGEST_FIELD_ALIGNMENT |
| Biggest alignment that any structure or union field can require on this |
| machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for |
| structure and union fields only, unless the field alignment has been set |
| by the @code{__attribute__ ((aligned (@var{n})))} construct. |
| @end defmac |
| |
| @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed}) |
| An expression for the alignment of a structure field @var{field} if the |
| alignment computed in the usual way (including applying of |
| @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the |
| alignment) is @var{computed}. It overrides alignment only if the |
| field alignment has not been set by the |
| @code{__attribute__ ((aligned (@var{n})))} construct. |
| @end defmac |
| |
| @defmac MAX_OFILE_ALIGNMENT |
| Biggest alignment supported by the object file format of this machine. |
| Use this macro to limit the alignment which can be specified using the |
| @code{__attribute__ ((aligned (@var{n})))} construct. If not defined, |
| the default value is @code{BIGGEST_ALIGNMENT}. |
| @end defmac |
| |
| @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align}) |
| If defined, a C expression to compute the alignment for a variable in |
| the static store. @var{type} is the data type, and @var{basic-align} is |
| the alignment that the object would ordinarily have. The value of this |
| macro is used instead of that alignment to align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| @findex strcpy |
| One use of this macro is to increase alignment of medium-size data to |
| make it all fit in fewer cache lines. Another is to cause character |
| arrays to be word-aligned so that @code{strcpy} calls that copy |
| constants to character arrays can be done inline. |
| @end defmac |
| |
| @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align}) |
| If defined, a C expression to compute the alignment given to a constant |
| that is being placed in memory. @var{constant} is the constant and |
| @var{basic-align} is the alignment that the object would ordinarily |
| have. The value of this macro is used instead of that alignment to |
| align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| The typical use of this macro is to increase alignment for string |
| constants to be word aligned so that @code{strcpy} calls that copy |
| constants can be done inline. |
| @end defmac |
| |
| @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) |
| If defined, a C expression to compute the alignment for a variable in |
| the local store. @var{type} is the data type, and @var{basic-align} is |
| the alignment that the object would ordinarily have. The value of this |
| macro is used instead of that alignment to align the object. |
| |
| If this macro is not defined, then @var{basic-align} is used. |
| |
| One use of this macro is to increase alignment of medium-size data to |
| make it all fit in fewer cache lines. |
| @end defmac |
| |
| @defmac EMPTY_FIELD_BOUNDARY |
| Alignment in bits to be given to a structure bit-field that follows an |
| empty field such as @code{int : 0;}. |
| |
| If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro. |
| @end defmac |
| |
| @defmac STRUCTURE_SIZE_BOUNDARY |
| Number of bits which any structure or union's size must be a multiple of. |
| Each structure or union's size is rounded up to a multiple of this. |
| |
| If you do not define this macro, the default is the same as |
| @code{BITS_PER_UNIT}. |
| @end defmac |
| |
| @defmac STRICT_ALIGNMENT |
| Define this macro to be the value 1 if instructions will fail to work |
| if given data not on the nominal alignment. If instructions will merely |
| go slower in that case, define this macro as 0. |
| @end defmac |
| |
| @defmac PCC_BITFIELD_TYPE_MATTERS |
| Define this if you wish to imitate the way many other C compilers handle |
| alignment of bit-fields and the structures that contain them. |
| |
| The behavior is that the type written for a named bit-field (@code{int}, |
| @code{short}, or other integer type) imposes an alignment for the entire |
| structure, as if the structure really did contain an ordinary field of |
| that type. In addition, the bit-field is placed within the structure so |
| that it would fit within such a field, not crossing a boundary for it. |
| |
| Thus, on most machines, a named bit-field whose type is written as |
| @code{int} would not cross a four-byte boundary, and would force |
| four-byte alignment for the whole structure. (The alignment used may |
| not be four bytes; it is controlled by the other alignment parameters.) |
| |
| An unnamed bit-field will not affect the alignment of the containing |
| structure. |
| |
| If the macro is defined, its definition should be a C expression; |
| a nonzero value for the expression enables this behavior. |
| |
| Note that if this macro is not defined, or its value is zero, some |
| bit-fields may cross more than one alignment boundary. The compiler can |
| support such references if there are @samp{insv}, @samp{extv}, and |
| @samp{extzv} insns that can directly reference memory. |
| |
| The other known way of making bit-fields work is to define |
| @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. |
| Then every structure can be accessed with fullwords. |
| |
| Unless the machine has bit-field instructions or you define |
| @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define |
| @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. |
| |
| If your aim is to make GCC use the same conventions for laying out |
| bit-fields as are used by another compiler, here is how to investigate |
| what the other compiler does. Compile and run this program: |
| |
| @smallexample |
| struct foo1 |
| @{ |
| char x; |
| char :0; |
| char y; |
| @}; |
| |
| struct foo2 |
| @{ |
| char x; |
| int :0; |
| char y; |
| @}; |
| |
| main () |
| @{ |
| printf ("Size of foo1 is %d\n", |
| sizeof (struct foo1)); |
| printf ("Size of foo2 is %d\n", |
| sizeof (struct foo2)); |
| exit (0); |
| @} |
| @end smallexample |
| |
| If this prints 2 and 5, then the compiler's behavior is what you would |
| get from @code{PCC_BITFIELD_TYPE_MATTERS}. |
| @end defmac |
| |
| @defmac BITFIELD_NBYTES_LIMITED |
| Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited |
| to aligning a bit-field within the structure. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELDS (void) |
| When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine |
| whether unnamed bitfields affect the alignment of the containing |
| structure. The hook should return true if the structure should inherit |
| the alignment requirements of an unnamed bitfield's type. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELDS (void) |
| This target hook should return @code{true} if accesses to volatile bitfields |
| should use the narrowest mode possible. It should return @code{false} if |
| these accesses should use the bitfield container type. |
| |
| The default is @code{!TARGET_STRICT_ALIGN}. |
| @end deftypefn |
| |
| @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode}) |
| Return 1 if a structure or array containing @var{field} should be accessed using |
| @code{BLKMODE}. |
| |
| If @var{field} is the only field in the structure, @var{mode} is its |
| mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the |
| case where structures of one field would require the structure's mode to |
| retain the field's mode. |
| |
| Normally, this is not needed. See the file @file{c4x.h} for an example |
| of how to use this macro to prevent a structure having a floating point |
| field from being accessed in an integer mode. |
| @end defmac |
| |
| @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) |
| Define this macro as an expression for the alignment of a type (given |
| by @var{type} as a tree node) if the alignment computed in the usual |
| way is @var{computed} and the alignment explicitly specified was |
| @var{specified}. |
| |
| The default is to use @var{specified} if it is larger; otherwise, use |
| the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} |
| @end defmac |
| |
| @defmac MAX_FIXED_MODE_SIZE |
| An integer expression for the size in bits of the largest integer |
| machine mode that should actually be used. All integer machine modes of |
| this size or smaller can be used for structures and unions with the |
| appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE |
| (DImode)} is assumed. |
| @end defmac |
| |
| @defmac STACK_SAVEAREA_MODE (@var{save_level}) |
| If defined, an expression of type @code{enum machine_mode} that |
| specifies the mode of the save area operand of a |
| @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). |
| @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or |
| @code{SAVE_NONLOCAL} and selects which of the three named patterns is |
| having its mode specified. |
| |
| You need not define this macro if it always returns @code{Pmode}. You |
| would most commonly define this macro if the |
| @code{save_stack_@var{level}} patterns need to support both a 32- and a |
| 64-bit mode. |
| @end defmac |
| |
| @defmac STACK_SIZE_MODE |
| If defined, an expression of type @code{enum machine_mode} that |
| specifies the mode of the size increment operand of an |
| @code{allocate_stack} named pattern (@pxref{Standard Names}). |
| |
| You need not define this macro if it always returns @code{word_mode}. |
| You would most commonly define this macro if the @code{allocate_stack} |
| pattern needs to support both a 32- and a 64-bit mode. |
| @end defmac |
| |
| @defmac TARGET_FLOAT_FORMAT |
| A code distinguishing the floating point format of the target machine. |
| There are four defined values: |
| |
| @ftable @code |
| @item IEEE_FLOAT_FORMAT |
| This code indicates IEEE floating point. It is the default; there is no |
| need to define @code{TARGET_FLOAT_FORMAT} when the format is IEEE@. |
| |
| @item VAX_FLOAT_FORMAT |
| This code indicates the ``F float'' (for @code{float}) and ``D float'' |
| or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@. |
| |
| @item IBM_FLOAT_FORMAT |
| This code indicates the format used on the IBM System/370. |
| |
| @item C4X_FLOAT_FORMAT |
| This code indicates the format used on the TMS320C3x/C4x. |
| @end ftable |
| |
| If your target uses a floating point format other than these, you must |
| define a new @var{name}_FLOAT_FORMAT code for it, and add support for |
| it to @file{real.c}. |
| |
| The ordering of the component words of floating point values stored in |
| memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}. |
| @end defmac |
| |
| @defmac MODE_HAS_NANS (@var{mode}) |
| When defined, this macro should be true if @var{mode} has a NaN |
| representation. The compiler assumes that NaNs are not equal to |
| anything (including themselves) and that addition, subtraction, |
| multiplication and division all return NaNs when one operand is |
| NaN@. |
| |
| By default, this macro is true if @var{mode} is a floating-point |
| mode and the target floating-point format is IEEE@. |
| @end defmac |
| |
| @defmac MODE_HAS_INFINITIES (@var{mode}) |
| This macro should be true if @var{mode} can represent infinity. At |
| present, the compiler uses this macro to decide whether @samp{x - x} |
| is always defined. By default, the macro is true when @var{mode} |
| is a floating-point mode and the target format is IEEE@. |
| @end defmac |
| |
| @defmac MODE_HAS_SIGNED_ZEROS (@var{mode}) |
| True if @var{mode} distinguishes between positive and negative zero. |
| The rules are expected to follow the IEEE standard: |
| |
| @itemize @bullet |
| @item |
| @samp{x + x} has the same sign as @samp{x}. |
| |
| @item |
| If the sum of two values with opposite sign is zero, the result is |
| positive for all rounding modes expect towards @minus{}infinity, for |
| which it is negative. |
| |
| @item |
| The sign of a product or quotient is negative when exactly one |
| of the operands is negative. |
| @end itemize |
| |
| The default definition is true if @var{mode} is a floating-point |
| mode and the target format is IEEE@. |
| @end defmac |
| |
| @defmac MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode}) |
| If defined, this macro should be true for @var{mode} if it has at |
| least one rounding mode in which @samp{x} and @samp{-x} can be |
| rounded to numbers of different magnitude. Two such modes are |
| towards @minus{}infinity and towards +infinity. |
| |
| The default definition of this macro is true if @var{mode} is |
| a floating-point mode and the target format is IEEE@. |
| @end defmac |
| |
| @defmac ROUND_TOWARDS_ZERO |
| If defined, this macro should be true if the prevailing rounding |
| mode is towards zero. A true value has the following effects: |
| |
| @itemize @bullet |
| @item |
| @code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes. |
| |
| @item |
| @file{libgcc.a}'s floating-point emulator will round towards zero |
| rather than towards nearest. |
| |
| @item |
| The compiler's floating-point emulator will round towards zero after |
| doing arithmetic, and when converting from the internal float format to |
| the target format. |
| @end itemize |
| |
| The macro does not affect the parsing of string literals. When the |
| primary rounding mode is towards zero, library functions like |
| @code{strtod} might still round towards nearest, and the compiler's |
| parser should behave like the target's @code{strtod} where possible. |
| |
| Not defining this macro is equivalent to returning zero. |
| @end defmac |
| |
| @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size}) |
| This macro should return true if floats with @var{size} |
| bits do not have a NaN or infinity representation, but use the largest |
| exponent for normal numbers instead. |
| |
| Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS} |
| and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes. |
| It also affects the way @file{libgcc.a} and @file{real.c} emulate |
| floating-point arithmetic. |
| |
| The default definition of this macro returns false for all sizes. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_VECTOR_OPAQUE_P (tree @var{type}) |
| This target hook should return @code{true} a vector is opaque. That |
| is, if no cast is needed when copying a vector value of type |
| @var{type} into another vector lvalue of the same size. Vector opaque |
| types cannot be initialized. The default is that there are no such |
| types. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type}) |
| This target hook returns @code{true} if bit-fields in the given |
| @var{record_type} are to be laid out following the rules of Microsoft |
| Visual C/C++, namely: (i) a bit-field won't share the same storage |
| unit with the previous bit-field if their underlying types have |
| different sizes, and the bit-field will be aligned to the highest |
| alignment of the underlying types of itself and of the previous |
| bit-field; (ii) a zero-sized bit-field will affect the alignment of |
| the whole enclosing structure, even if it is unnamed; except that |
| (iii) a zero-sized bit-field will be disregarded unless it follows |
| another bit-field of nonzero size. If this hook returns @code{true}, |
| other macros that control bit-field layout are ignored. |
| |
| When a bit-field is inserted into a packed record, the whole size |
| of the underlying type is used by one or more same-size adjacent |
| bit-fields (that is, if its long:3, 32 bits is used in the record, |
| and any additional adjacent long bit-fields are packed into the same |
| chunk of 32 bits. However, if the size changes, a new field of that |
| size is allocated). In an unpacked record, this is the same as using |
| alignment, but not equivalent when packing. |
| |
| If both MS bit-fields and @samp{__attribute__((packed))} are used, |
| the latter will take precedence. If @samp{__attribute__((packed))} is |
| used on a single field when MS bit-fields are in use, it will take |
| precedence for that field, but the alignment of the rest of the structure |
| may affect its placement. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {bool} TARGET_DECIMAL_FLOAT_SUPPORTED_P (void) |
| Returns true if the target supports decimal floating point. |
| @end deftypefn |
| |
| @c APPLE LOCAL begin mangle_type 7105099 |
| @deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (tree @var{type}) |
| If your target defines any fundamental types, or any types your target |
| uses should be mangled differently from the default, define this hook |
| to return the appropriate encoding for these types as part of a C++ |
| mangled name. The @var{type} argument is the tree structure representing |
| the type to be mangled. The hook may be applied to trees which are |
| not target-specific fundamental types; it should return @code{NULL} |
| for all such types, as well as arguments it does not recognize. If the |
| return value is not @code{NULL}, it must point to a statically-allocated |
| string constant. |
| @c APPLE LOCAL end mangle_type 7105099 |
| |
| Target-specific fundamental types might be new fundamental types or |
| qualified versions of ordinary fundamental types. Encode new |
| fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name} |
| is the name used for the type in source code, and @var{n} is the |
| length of @var{name} in decimal. Encode qualified versions of |
| ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where |
| @var{name} is the name used for the type qualifier in source code, |
| @var{n} is the length of @var{name} as above, and @var{code} is the |
| code used to represent the unqualified version of this type. (See |
| @code{write_builtin_type} in @file{cp/mangle.c} for the list of |
| codes.) In both cases the spaces are for clarity; do not include any |
| spaces in your string. |
| |
| @c APPLE LOCAL begin mangle_type 7105099 |
| This hook is applied to types prior to typedef resolution. If the mangled |
| name for a particular type depends only on that type's main variant, you |
| can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT} |
| before mangling. |
| @c APPLE LOCAL end mangle_type 7105099 |
| |
| The default version of this hook always returns @code{NULL}, which is |
| appropriate for a target that does not define any new fundamental |
| types. |
| @end deftypefn |
| |
| @node Type Layout |
| @section Layout of Source Language Data Types |
| |
| These macros define the sizes and other characteristics of the standard |
| basic data types used in programs being compiled. Unlike the macros in |
| the previous section, these apply to specific features of C and related |
| languages, rather than to fundamental aspects of storage layout. |
| |
| @defmac INT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{int} on the |
| target machine. If you don't define this, the default is one word. |
| @end defmac |
| |
| @defmac SHORT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{short} on the |
| target machine. If you don't define this, the default is half a word. |
| (If this would be less than one storage unit, it is rounded up to one |
| unit.) |
| @end defmac |
| |
| @defmac LONG_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long} on the |
| target machine. If you don't define this, the default is one word. |
| @end defmac |
| |
| @defmac ADA_LONG_TYPE_SIZE |
| On some machines, the size used for the Ada equivalent of the type |
| @code{long} by a native Ada compiler differs from that used by C@. In |
| that situation, define this macro to be a C expression to be used for |
| the size of that type. If you don't define this, the default is the |
| value of @code{LONG_TYPE_SIZE}. |
| @end defmac |
| |
| @defmac LONG_LONG_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long long} on the |
| target machine. If you don't define this, the default is two |
| words. If you want to support GNU Ada on your machine, the value of this |
| macro must be at least 64. |
| @end defmac |
| |
| @defmac CHAR_TYPE_SIZE |
| A C expression for the size in bits of the type @code{char} on the |
| target machine. If you don't define this, the default is |
| @code{BITS_PER_UNIT}. |
| @end defmac |
| |
| @defmac BOOL_TYPE_SIZE |
| A C expression for the size in bits of the C++ type @code{bool} and |
| C99 type @code{_Bool} on the target machine. If you don't define |
| this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}. |
| @end defmac |
| |
| @defmac FLOAT_TYPE_SIZE |
| A C expression for the size in bits of the type @code{float} on the |
| target machine. If you don't define this, the default is one word. |
| @end defmac |
| |
| @defmac DOUBLE_TYPE_SIZE |
| A C expression for the size in bits of the type @code{double} on the |
| target machine. If you don't define this, the default is two |
| words. |
| @end defmac |
| |
| @defmac LONG_DOUBLE_TYPE_SIZE |
| A C expression for the size in bits of the type @code{long double} on |
| the target machine. If you don't define this, the default is two |
| words. |
| @end defmac |
| |
| @defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE |
| Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or |
| if you want routines in @file{libgcc2.a} for a size other than |
| @code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the |
| default is @code{LONG_DOUBLE_TYPE_SIZE}. |
| @end defmac |
| |
| @defmac LIBGCC2_HAS_DF_MODE |
| Define this macro if neither @code{LIBGCC2_DOUBLE_TYPE_SIZE} nor |
| @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is |
| @code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a} |
| anyway. If you don't define this and either @code{LIBGCC2_DOUBLE_TYPE_SIZE} |
| or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1, |
| otherwise it is 0. |
| @end defmac |
| |
| @defmac LIBGCC2_HAS_XF_MODE |
| Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not |
| @code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a} |
| anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} |
| is 80 then the default is 1, otherwise it is 0. |
| @end defmac |
| |
| @defmac LIBGCC2_HAS_TF_MODE |
| Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not |
| @code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a} |
| anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} |
| is 128 then the default is 1, otherwise it is 0. |
| @end defmac |
| |
| @defmac SF_SIZE |
| @defmacx DF_SIZE |
| @defmacx XF_SIZE |
| @defmacx TF_SIZE |
| Define these macros to be the size in bits of the mantissa of |
| @code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values, |
| if the defaults in @file{libgcc2.h} are inappropriate. By default, |
| @code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG} |
| for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or |
| @code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether |
| @code{LIBGCC2_DOUBLE_TYPE_SIZE} or |
| @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64. |
| @end defmac |
| |
| @defmac TARGET_FLT_EVAL_METHOD |
| A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h}, |
| assuming, if applicable, that the floating-point control word is in its |
| default state. If you do not define this macro the value of |
| @code{FLT_EVAL_METHOD} will be zero. |
| @end defmac |
| |
| @defmac WIDEST_HARDWARE_FP_SIZE |
| A C expression for the size in bits of the widest floating-point format |
| supported by the hardware. If you define this macro, you must specify a |
| value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. |
| If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} |
| is the default. |
| @end defmac |
| |
| @defmac DEFAULT_SIGNED_CHAR |
| An expression whose value is 1 or 0, according to whether the type |
| @code{char} should be signed or unsigned by default. The user can |
| always override this default with the options @option{-fsigned-char} |
| and @option{-funsigned-char}. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void) |
| This target hook should return true if the compiler should give an |
| @code{enum} type only as many bytes as it takes to represent the range |
| of possible values of that type. It should return false if all |
| @code{enum} types should be allocated like @code{int}. |
| |
| The default is to return false. |
| @end deftypefn |
| |
| @defmac SIZE_TYPE |
| A C expression for a string describing the name of the data type to use |
| for size values. The typedef name @code{size_t} is defined using the |
| contents of the string. |
| |
| The string can contain more than one keyword. If so, separate them with |
| spaces, and write first any length keyword, then @code{unsigned} if |
| appropriate, and finally @code{int}. The string must exactly match one |
| of the data type names defined in the function |
| @code{init_decl_processing} in the file @file{c-decl.c}. You may not |
| omit @code{int} or change the order---that would cause the compiler to |
| crash on startup. |
| |
| If you don't define this macro, the default is @code{"long unsigned |
| int"}. |
| @end defmac |
| |
| @defmac PTRDIFF_TYPE |
| A C expression for a string describing the name of the data type to use |
| for the result of subtracting two pointers. The typedef name |
| @code{ptrdiff_t} is defined using the contents of the string. See |
| @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is @code{"long int"}. |
| @end defmac |
| |
| @defmac WCHAR_TYPE |
| A C expression for a string describing the name of the data type to use |
| for wide characters. The typedef name @code{wchar_t} is defined using |
| the contents of the string. See @code{SIZE_TYPE} above for more |
| information. |
| |
| If you don't define this macro, the default is @code{"int"}. |
| @end defmac |
| |
| @defmac WCHAR_TYPE_SIZE |
| A C expression for the size in bits of the data type for wide |
| characters. This is used in @code{cpp}, which cannot make use of |
| @code{WCHAR_TYPE}. |
| @end defmac |
| |
| @defmac WINT_TYPE |
| A C expression for a string describing the name of the data type to |
| use for wide characters passed to @code{printf} and returned from |
| @code{getwc}. The typedef name @code{wint_t} is defined using the |
| contents of the string. See @code{SIZE_TYPE} above for more |
| information. |
| |
| If you don't define this macro, the default is @code{"unsigned int"}. |
| @end defmac |
| |
| @defmac INTMAX_TYPE |
| A C expression for a string describing the name of the data type that |
| can represent any value of any standard or extended signed integer type. |
| The typedef name @code{intmax_t} is defined using the contents of the |
| string. See @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is the first of |
| @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as |
| much precision as @code{long long int}. |
| @end defmac |
| |
| @defmac UINTMAX_TYPE |
| A C expression for a string describing the name of the data type that |
| can represent any value of any standard or extended unsigned integer |
| type. The typedef name @code{uintmax_t} is defined using the contents |
| of the string. See @code{SIZE_TYPE} above for more information. |
| |
| If you don't define this macro, the default is the first of |
| @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long |
| unsigned int"} that has as much precision as @code{long long unsigned |
| int}. |
| @end defmac |
| |
| @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION |
| The C++ compiler represents a pointer-to-member-function with a struct |
| that looks like: |
| |
| @smallexample |
| struct @{ |
| union @{ |
| void (*fn)(); |
| ptrdiff_t vtable_index; |
| @}; |
| ptrdiff_t delta; |
| @}; |
| @end smallexample |
| |
| @noindent |
| The C++ compiler must use one bit to indicate whether the function that |
| will be called through a pointer-to-member-function is virtual. |
| Normally, we assume that the low-order bit of a function pointer must |
| always be zero. Then, by ensuring that the vtable_index is odd, we can |
| distinguish which variant of the union is in use. But, on some |
| platforms function pointers can be odd, and so this doesn't work. In |
| that case, we use the low-order bit of the @code{delta} field, and shift |
| the remainder of the @code{delta} field to the left. |
| |
| GCC will automatically make the right selection about where to store |
| this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. |
| However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} |
| set such that functions always start at even addresses, but the lowest |
| bit of pointers to functions indicate whether the function at that |
| address is in ARM or Thumb mode. If this is the case of your |
| architecture, you should define this macro to |
| @code{ptrmemfunc_vbit_in_delta}. |
| |
| In general, you should not have to define this macro. On architectures |
| in which function addresses are always even, according to |
| @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to |
| @code{ptrmemfunc_vbit_in_pfn}. |
| @end defmac |
| |
| @defmac TARGET_VTABLE_USES_DESCRIPTORS |
| Normally, the C++ compiler uses function pointers in vtables. This |
| macro allows the target to change to use ``function descriptors'' |
| instead. Function descriptors are found on targets for whom a |
| function pointer is actually a small data structure. Normally the |
| data structure consists of the actual code address plus a data |
| pointer to which the function's data is relative. |
| |
| If vtables are used, the value of this macro should be the number |
| of words that the function descriptor occupies. |
| @end defmac |
| |
| @defmac TARGET_VTABLE_ENTRY_ALIGN |
| By default, the vtable entries are void pointers, the so the alignment |
| is the same as pointer alignment. The value of this macro specifies |
| the alignment of the vtable entry in bits. It should be defined only |
| when special alignment is necessary. */ |
| @end defmac |
| |
| @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE |
| There are a few non-descriptor entries in the vtable at offsets below |
| zero. If these entries must be padded (say, to preserve the alignment |
| specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number |
| of words in each data entry. |
| @end defmac |
| |
| @node Registers |
| @section Register Usage |
| @cindex register usage |
| |
| This section explains how to describe what registers the target machine |
| has, and how (in general) they can be used. |
| |
| The description of which registers a specific instruction can use is |
| done with register classes; see @ref{Register Classes}. For information |
| on using registers to access a stack frame, see @ref{Frame Registers}. |
| For passing values in registers, see @ref{Register Arguments}. |
| For returning values in registers, see @ref{Scalar Return}. |
| |
| @menu |
| * Register Basics:: Number and kinds of registers. |
| * Allocation Order:: Order in which registers are allocated. |
| * Values in Registers:: What kinds of values each reg can hold. |
| * Leaf Functions:: Renumbering registers for leaf functions. |
| * Stack Registers:: Handling a register stack such as 80387. |
| @end menu |
| |
| @node Register Basics |
| @subsection Basic Characteristics of Registers |
| |
| @c prevent bad page break with this line |
| Registers have various characteristics. |
| |
| @defmac FIRST_PSEUDO_REGISTER |
| Number of hardware registers known to the compiler. They receive |
| numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first |
| pseudo register's number really is assigned the number |
| @code{FIRST_PSEUDO_REGISTER}. |
| @end defmac |
| |
| @defmac FIXED_REGISTERS |
| @cindex fixed register |
| An initializer that says which registers are used for fixed purposes |
| all throughout the compiled code and are therefore not available for |
| general allocation. These would include the stack pointer, the frame |
| pointer (except on machines where that can be used as a general |
| register when no frame pointer is needed), the program counter on |
| machines where that is considered one of the addressable registers, |
| and any other numbered register with a standard use. |
| |
| This information is expressed as a sequence of numbers, separated by |
| commas and surrounded by braces. The @var{n}th number is 1 if |
| register @var{n} is fixed, 0 otherwise. |
| |
| The table initialized from this macro, and the table initialized by |
| the following one, may be overridden at run time either automatically, |
| by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by |
| the user with the command options @option{-ffixed-@var{reg}}, |
| @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. |
| @end defmac |
| |
| @defmac CALL_USED_REGISTERS |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| Like @code{FIXED_REGISTERS} but has 1 for each register that is |
| clobbered (in general) by function calls as well as for fixed |
| registers. This macro therefore identifies the registers that are not |
| available for general allocation of values that must live across |
| function calls. |
| |
| If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler |
| automatically saves it on function entry and restores it on function |
| exit, if the register is used within the function. |
| @end defmac |
| |
| @defmac CALL_REALLY_USED_REGISTERS |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| Like @code{CALL_USED_REGISTERS} except this macro doesn't require |
| that the entire set of @code{FIXED_REGISTERS} be included. |
| (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). |
| This macro is optional. If not specified, it defaults to the value |
| of @code{CALL_USED_REGISTERS}. |
| @end defmac |
| |
| @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode}) |
| @cindex call-used register |
| @cindex call-clobbered register |
| @cindex call-saved register |
| A C expression that is nonzero if it is not permissible to store a |
| value of mode @var{mode} in hard register number @var{regno} across a |
| call without some part of it being clobbered. For most machines this |
| macro need not be defined. It is only required for machines that do not |
| preserve the entire contents of a register across a call. |
| @end defmac |
| |
| @findex fixed_regs |
| @findex call_used_regs |
| @findex global_regs |
| @findex reg_names |
| @findex reg_class_contents |
| @defmac CONDITIONAL_REGISTER_USAGE |
| Zero or more C statements that may conditionally modify five variables |
| @code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, |
| @code{reg_names}, and @code{reg_class_contents}, to take into account |
| any dependence of these register sets on target flags. The first three |
| of these are of type @code{char []} (interpreted as Boolean vectors). |
| @code{global_regs} is a @code{const char *[]}, and |
| @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is |
| called, @code{fixed_regs}, @code{call_used_regs}, |
| @code{reg_class_contents}, and @code{reg_names} have been initialized |
| from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, |
| @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. |
| @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, |
| @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} |
| command options have been applied. |
| |
| You need not define this macro if it has no work to do. |
| |
| @cindex disabling certain registers |
| @cindex controlling register usage |
| If the usage of an entire class of registers depends on the target |
| flags, you may indicate this to GCC by using this macro to modify |
| @code{fixed_regs} and @code{call_used_regs} to 1 for each of the |
| registers in the classes which should not be used by GCC@. Also define |
| the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT} |
| to return @code{NO_REGS} if it |
| is called with a letter for a class that shouldn't be used. |
| |
| (However, if this class is not included in @code{GENERAL_REGS} and all |
| of the insn patterns whose constraints permit this class are |
| controlled by target switches, then GCC will automatically avoid using |
| these registers when the target switches are opposed to them.) |
| @end defmac |
| |
| @defmac INCOMING_REGNO (@var{out}) |
| Define this macro if the target machine has register windows. This C |
| expression returns the register number as seen by the called function |
| corresponding to the register number @var{out} as seen by the calling |
| function. Return @var{out} if register number @var{out} is not an |
| outbound register. |
| @end defmac |
| |
| @defmac OUTGOING_REGNO (@var{in}) |
| Define this macro if the target machine has register windows. This C |
| expression returns the register number as seen by the calling function |
| corresponding to the register number @var{in} as seen by the called |
| function. Return @var{in} if register number @var{in} is not an inbound |
| register. |
| @end defmac |
| |
| @defmac LOCAL_REGNO (@var{regno}) |
| Define this macro if the target machine has register windows. This C |
| expression returns true if the register is call-saved but is in the |
| register window. Unlike most call-saved registers, such registers |
| need not be explicitly restored on function exit or during non-local |
| gotos. |
| @end defmac |
| |
| @defmac PC_REGNUM |
| If the program counter has a register number, define this as that |
| register number. Otherwise, do not define it. |
| @end defmac |
| |
| @node Allocation Order |
| @subsection Order of Allocation of Registers |
| @cindex order of register allocation |
| @cindex register allocation order |
| |
| @c prevent bad page break with this line |
| Registers are allocated in order. |
| |
| @defmac REG_ALLOC_ORDER |
| If defined, an initializer for a vector of integers, containing the |
| numbers of hard registers in the order in which GCC should prefer |
| to use them (from most preferred to least). |
| |
| If this macro is not defined, registers are used lowest numbered first |
| (all else being equal). |
| |
| One use of this macro is on machines where the highest numbered |
| registers must always be saved and the save-multiple-registers |
| instruction supports only sequences of consecutive registers. On such |
| machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists |
| the highest numbered allocable register first. |
| @end defmac |
| |
| @defmac ORDER_REGS_FOR_LOCAL_ALLOC |
| A C statement (sans semicolon) to choose the order in which to allocate |
| hard registers for pseudo-registers local to a basic block. |
| |
| Store the desired register order in the array @code{reg_alloc_order}. |
| Element 0 should be the register to allocate first; element 1, the next |
| register; and so on. |
| |
| The macro body should not assume anything about the contents of |
| @code{reg_alloc_order} before execution of the macro. |
| |
| On most machines, it is not necessary to define this macro. |
| @end defmac |
| |
| @node Values in Registers |
| @subsection How Values Fit in Registers |
| |
| This section discusses the macros that describe which kinds of values |
| (specifically, which machine modes) each register can hold, and how many |
| consecutive registers are needed for a given mode. |
| |
| @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode}) |
| A C expression for the number of consecutive hard registers, starting |
| at register number @var{regno}, required to hold a value of mode |
| @var{mode}. |
| |
| On a machine where all registers are exactly one word, a suitable |
| definition of this macro is |
| |
| @smallexample |
| #define HARD_REGNO_NREGS(REGNO, MODE) \ |
| ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ |
| / UNITS_PER_WORD) |
| @end smallexample |
| @end defmac |
| |
| @defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode}) |
| A C expression that is nonzero if a value of mode @var{mode}, stored |
| in memory, ends with padding that causes it to take up more space than |
| in registers starting at register number @var{regno} (as determined by |
| multiplying GCC's notion of the size of the register when containing |
| this mode by the number of registers returned by |
| @code{HARD_REGNO_NREGS}). By default this is zero. |
| |
| For example, if a floating-point value is stored in three 32-bit |
| registers but takes up 128 bits in memory, then this would be |
| nonzero. |
| |
| This macros only needs to be defined if there are cases where |
| @code{subreg_regno_offset} and @code{subreg_offset_representable_p} |
| would otherwise wrongly determine that a @code{subreg} can be |
| represented by an offset to the register number, when in fact such a |
| @code{subreg} would contain some of the padding not stored in |
| registers and so not be representable. |
| @end defmac |
| |
| @defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode}) |
| For values of @var{regno} and @var{mode} for which |
| @code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression |
| returning the greater number of registers required to hold the value |
| including any padding. In the example above, the value would be four. |
| @end defmac |
| |
| @defmac REGMODE_NATURAL_SIZE (@var{mode}) |
| Define this macro if the natural size of registers that hold values |
| of mode @var{mode} is not the word size. It is a C expression that |
| should give the natural size in bytes for the specified mode. It is |
| used by the register allocator to try to optimize its results. This |
| happens for example on SPARC 64-bit where the natural size of |
| floating-point registers is still 32-bit. |
| @end defmac |
| |
| @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) |
| A C expression that is nonzero if it is permissible to store a value |
| of mode @var{mode} in hard register number @var{regno} (or in several |
| registers starting with that one). For a machine where all registers |
| are equivalent, a suitable definition is |
| |
| @smallexample |
| #define HARD_REGNO_MODE_OK(REGNO, MODE) 1 |
| @end smallexample |
| |
| You need not include code to check for the numbers of fixed registers, |
| because the allocation mechanism considers them to be always occupied. |
| |
| @cindex register pairs |
| On some machines, double-precision values must be kept in even/odd |
| register pairs. You can implement that by defining this macro to reject |
| odd register numbers for such modes. |
| |
| The minimum requirement for a mode to be OK in a register is that the |
| @samp{mov@var{mode}} instruction pattern support moves between the |
| register and other hard register in the same class and that moving a |
| value into the register and back out not alter it. |
| |
| Since the same instruction used to move @code{word_mode} will work for |
| all narrower integer modes, it is not necessary on any machine for |
| @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided |
| you define patterns @samp{movhi}, etc., to take advantage of this. This |
| is useful because of the interaction between @code{HARD_REGNO_MODE_OK} |
| and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes |
| to be tieable. |
| |
| Many machines have special registers for floating point arithmetic. |
| Often people assume that floating point machine modes are allowed only |
| in floating point registers. This is not true. Any registers that |
| can hold integers can safely @emph{hold} a floating point machine |
| mode, whether or not floating arithmetic can be done on it in those |
| registers. Integer move instructions can be used to move the values. |
| |
| On some machines, though, the converse is true: fixed-point machine |
| modes may not go in floating registers. This is true if the floating |
| registers normalize any value stored in them, because storing a |
| non-floating value there would garble it. In this case, |
| @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in |
| floating registers. But if the floating registers do not automatically |
| normalize, if you can store any bit pattern in one and retrieve it |
| unchanged without a trap, then any machine mode may go in a floating |
| register, so you can define this macro to say so. |
| |
| The primary significance of special floating registers is rather that |
| they are the registers acceptable in floating point arithmetic |
| instructions. However, this is of no concern to |
| @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper |
| constraints for those instructions. |
| |
| On some machines, the floating registers are especially slow to access, |
| so that it is better to store a value in a stack frame than in such a |
| register if floating point arithmetic is not being done. As long as the |
| floating registers are not in class @code{GENERAL_REGS}, they will not |
| be used unless some pattern's constraint asks for one. |
| @end defmac |
| |
| @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to}) |
| A C expression that is nonzero if it is OK to rename a hard register |
| @var{from} to another hard register @var{to}. |
| |
| One common use of this macro is to prevent renaming of a register to |
| another register that is not saved by a prologue in an interrupt |
| handler. |
| |
| The default is always nonzero. |
| @end defmac |
| |
| @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2}) |
| A C expression that is nonzero if a value of mode |
| @var{mode1} is accessible in mode @var{mode2} without copying. |
| |
| If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and |
| @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for |
| any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} |
| should be nonzero. If they differ for any @var{r}, you should define |
| this macro to return zero unless some other mechanism ensures the |
| accessibility of the value in a narrower mode. |
| |
| You should define this macro to return nonzero in as many cases as |
| possible since doing so will allow GCC to perform better register |
| allocation. |
| @end defmac |
| |
| @defmac AVOID_CCMODE_COPIES |
| Define this macro if the compiler should avoid copies to/from @code{CCmode} |
| registers. You should only define this macro if support for copying to/from |
| @code{CCmode} is incomplete. |
| @end defmac |
| |
| @node Leaf Functions |
| @subsection Handling Leaf Functions |
| |
| @cindex leaf functions |
| @cindex functions, leaf |
| On some machines, a leaf function (i.e., one which makes no calls) can run |
| more efficiently if it does not make its own register window. Often this |
| means it is required to receive its arguments in the registers where they |
| are passed by the caller, instead of the registers where they would |
| normally arrive. |
| |
| The special treatment for leaf functions generally applies only when |
| other conditions are met; for example, often they may use only those |
| registers for its own variables and temporaries. We use the term ``leaf |
| function'' to mean a function that is suitable for this special |
| handling, so that functions with no calls are not necessarily ``leaf |
| functions''. |
| |
| GCC assigns register numbers before it knows whether the function is |
| suitable for leaf function treatment. So it needs to renumber the |
| registers in order to output a leaf function. The following macros |
| accomplish this. |
| |
| @defmac LEAF_REGISTERS |
| Name of a char vector, indexed by hard register number, which |
| contains 1 for a register that is allowable in a candidate for leaf |
| function treatment. |
| |
| If leaf function treatment involves renumbering the registers, then the |
| registers marked here should be the ones before renumbering---those that |
| GCC would ordinarily allocate. The registers which will actually be |
| used in the assembler code, after renumbering, should not be marked with 1 |
| in this vector. |
| |
| Define this macro only if the target machine offers a way to optimize |
| the treatment of leaf functions. |
| @end defmac |
| |
| @defmac LEAF_REG_REMAP (@var{regno}) |
| A C expression whose value is the register number to which @var{regno} |
| should be renumbered, when a function is treated as a leaf function. |
| |
| If @var{regno} is a register number which should not appear in a leaf |
| function before renumbering, then the expression should yield @minus{}1, which |
| will cause the compiler to abort. |
| |
| Define this macro only if the target machine offers a way to optimize the |
| treatment of leaf functions, and registers need to be renumbered to do |
| this. |
| @end defmac |
| |
| @findex current_function_is_leaf |
| @findex current_function_uses_only_leaf_regs |
| @code{TARGET_ASM_FUNCTION_PROLOGUE} and |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions |
| specially. They can test the C variable @code{current_function_is_leaf} |
| which is nonzero for leaf functions. @code{current_function_is_leaf} is |
| set prior to local register allocation and is valid for the remaining |
| compiler passes. They can also test the C variable |
| @code{current_function_uses_only_leaf_regs} which is nonzero for leaf |
| functions which only use leaf registers. |
| @code{current_function_uses_only_leaf_regs} is valid after all passes |
| that modify the instructions have been run and is only useful if |
| @code{LEAF_REGISTERS} is defined. |
| @c changed this to fix overfull. ALSO: why the "it" at the beginning |
| @c of the next paragraph?! --mew 2feb93 |
| |
| @node Stack Registers |
| @subsection Registers That Form a Stack |
| |
| There are special features to handle computers where some of the |
| ``registers'' form a stack. Stack registers are normally written by |
| pushing onto the stack, and are numbered relative to the top of the |
| stack. |
| |
| Currently, GCC can only handle one group of stack-like registers, and |
| they must be consecutively numbered. Furthermore, the existing |
| support for stack-like registers is specific to the 80387 floating |
| point coprocessor. If you have a new architecture that uses |
| stack-like registers, you will need to do substantial work on |
| @file{reg-stack.c} and write your machine description to cooperate |
| with it, as well as defining these macros. |
| |
| @defmac STACK_REGS |
| Define this if the machine has any stack-like registers. |
| @end defmac |
| |
| @defmac FIRST_STACK_REG |
| The number of the first stack-like register. This one is the top |
| of the stack. |
| @end defmac |
| |
| @defmac LAST_STACK_REG |
| The number of the last stack-like register. This one is the bottom of |
| the stack. |
| @end defmac |
| |
| @node Register Classes |
| @section Register Classes |
| @cindex register class definitions |
| @cindex class definitions, register |
| |
| On many machines, the numbered registers are not all equivalent. |
| For example, certain registers may not be allowed for indexed addressing; |
| certain registers may not be allowed in some instructions. These machine |
| restrictions are described to the compiler using @dfn{register classes}. |
| |
| You define a number of register classes, giving each one a name and saying |
| which of the registers belong to it. Then you can specify register classes |
| that are allowed as operands to particular instruction patterns. |
| |
| @findex ALL_REGS |
| @findex NO_REGS |
| In general, each register will belong to several classes. In fact, one |
| class must be named @code{ALL_REGS} and contain all the registers. Another |
| class must be named @code{NO_REGS} and contain no registers. Often the |
| union of two classes will be another class; however, this is not required. |
| |
| @findex GENERAL_REGS |
| One of the classes must be named @code{GENERAL_REGS}. There is nothing |
| terribly special about the name, but the operand constraint letters |
| @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is |
| the same as @code{ALL_REGS}, just define it as a macro which expands |
| to @code{ALL_REGS}. |
| |
| Order the classes so that if class @var{x} is contained in class @var{y} |
| then @var{x} has a lower class number than @var{y}. |
| |
| The way classes other than @code{GENERAL_REGS} are specified in operand |
| constraints is through machine-dependent operand constraint letters. |
| You can define such letters to correspond to various classes, then use |
| them in operand constraints. |
| |
| You should define a class for the union of two classes whenever some |
| instruction allows both classes. For example, if an instruction allows |
| either a floating point (coprocessor) register or a general register for a |
| certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} |
| which includes both of them. Otherwise you will get suboptimal code. |
| |
| You must also specify certain redundant information about the register |
| classes: for each class, which classes contain it and which ones are |
| contained in it; for each pair of classes, the largest class contained |
| in their union. |
| |
| When a value occupying several consecutive registers is expected in a |
| certain class, all the registers used must belong to that class. |
| Therefore, register classes cannot be used to enforce a requirement for |
| a register pair to start with an even-numbered register. The way to |
| specify this requirement is with @code{HARD_REGNO_MODE_OK}. |
| |
| Register classes used for input-operands of bitwise-and or shift |
| instructions have a special requirement: each such class must have, for |
| each fixed-point machine mode, a subclass whose registers can transfer that |
| mode to or from memory. For example, on some machines, the operations for |
| single-byte values (@code{QImode}) are limited to certain registers. When |
| this is so, each register class that is used in a bitwise-and or shift |
| instruction must have a subclass consisting of registers from which |
| single-byte values can be loaded or stored. This is so that |
| @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. |
| |
| @deftp {Data type} {enum reg_class} |
| An enumerated type that must be defined with all the register class names |
| as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS} |
| must be the last register class, followed by one more enumerated value, |
| @code{LIM_REG_CLASSES}, which is not a register class but rather |
| tells how many classes there are. |
| |
| Each register class has a number, which is the value of casting |
| the class name to type @code{int}. The number serves as an index |
| in many of the tables described below. |
| @end deftp |
| |
| @defmac N_REG_CLASSES |
| The number of distinct register classes, defined as follows: |
| |
| @smallexample |
| #define N_REG_CLASSES (int) LIM_REG_CLASSES |
| @end smallexample |
| @end defmac |
| |
| @defmac REG_CLASS_NAMES |
| An initializer containing the names of the register classes as C string |
| constants. These names are used in writing some of the debugging dumps. |
| @end defmac |
| |
| @defmac REG_CLASS_CONTENTS |
| An initializer containing the contents of the register classes, as integers |
| which are bit masks. The @var{n}th integer specifies the contents of class |
| @var{n}. The way the integer @var{mask} is interpreted is that |
| register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. |
| |
| When the machine has more than 32 registers, an integer does not suffice. |
| Then the integers are replaced by sub-initializers, braced groupings containing |
| several integers. Each sub-initializer must be suitable as an initializer |
| for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. |
| In this situation, the first integer in each sub-initializer corresponds to |
| registers 0 through 31, the second integer to registers 32 through 63, and |
| so on. |
| @end defmac |
| |
| @defmac REGNO_REG_CLASS (@var{regno}) |
| A C expression whose value is a register class containing hard register |
| @var{regno}. In general there is more than one such class; choose a class |
| which is @dfn{minimal}, meaning that no smaller class also contains the |
| register. |
| @end defmac |
| |
| @defmac BASE_REG_CLASS |
| A macro whose definition is the name of the class to which a valid |
| base register must belong. A base register is one used in an address |
| which is the register value plus a displacement. |
| @end defmac |
| |
| @defmac MODE_BASE_REG_CLASS (@var{mode}) |
| This is a variation of the @code{BASE_REG_CLASS} macro which allows |
| the selection of a base register in a mode dependent manner. If |
| @var{mode} is VOIDmode then it should return the same value as |
| @code{BASE_REG_CLASS}. |
| @end defmac |
| |
| @defmac MODE_BASE_REG_REG_CLASS (@var{mode}) |
| A C expression whose value is the register class to which a valid |
| base register must belong in order to be used in a base plus index |
| register address. You should define this macro if base plus index |
| addresses have different requirements than other base register uses. |
| @end defmac |
| |
| @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code}) |
| A C expression whose value is the register class to which a valid |
| base register must belong. @var{outer_code} and @var{index_code} define the |
| context in which the base register occurs. @var{outer_code} is the code of |
| the immediately enclosing expression (@code{MEM} for the top level of an |
| address, @code{ADDRESS} for something that occurs in an |
| @code{address_operand}). @var{index_code} is the code of the corresponding |
| index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise. |
| @end defmac |
| |
| @defmac INDEX_REG_CLASS |
| A macro whose definition is the name of the class to which a valid |
| index register must belong. An index register is one used in an |
| address where its value is either multiplied by a scale factor or |
| added to another register (as well as added to a displacement). |
| @end defmac |
| |
| @defmac REGNO_OK_FOR_BASE_P (@var{num}) |
| A C expression which is nonzero if register number @var{num} is |
| suitable for use as a base register in operand addresses. It may be |
| either a suitable hard register or a pseudo register that has been |
| allocated such a hard register. |
| @end defmac |
| |
| @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) |
| A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that |
| that expression may examine the mode of the memory reference in |
| @var{mode}. You should define this macro if the mode of the memory |
| reference affects whether a register may be used as a base register. If |
| you define this macro, the compiler will use it instead of |
| @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for addresses |
| that appear outside a @code{MEM}, i.e. as an @code{address_operand}. |
| |
| @end defmac |
| |
| @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode}) |
| A C expression which is nonzero if register number @var{num} is suitable for |
| use as a base register in base plus index operand addresses, accessing |
| memory in mode @var{mode}. It may be either a suitable hard register or a |
| pseudo register that has been allocated such a hard register. You should |
| define this macro if base plus index addresses have different requirements |
| than other base register uses. |
| |
| Use of this macro is deprecated; please use the more general |
| @code{REGNO_MODE_CODE_OK_FOR_BASE_P}. |
| @end defmac |
| |
| @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code}) |
| A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except that |
| that expression may examine the context in which the register appears in the |
| memory reference. @var{outer_code} is the code of the immediately enclosing |
| expression (@code{MEM} if at the top level of the address, @code{ADDRESS} for |
| something that occurs in an @code{address_operand}). @var{index_code} is the |
| code of the corresponding index expression if @var{outer_code} is @code{PLUS}; |
| @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses |
| that appear outside a @code{MEM}, i.e. as an @code{address_operand}. |
| @end defmac |
| |
| @defmac REGNO_OK_FOR_INDEX_P (@var{num}) |
| A C expression which is nonzero if register number @var{num} is |
| suitable for use as an index register in operand addresses. It may be |
| either a suitable hard register or a pseudo register that has been |
| allocated such a hard register. |
| |
| The difference between an index register and a base register is that |
| the index register may be scaled. If an address involves the sum of |
| two registers, neither one of them scaled, then either one may be |
| labeled the ``base'' and the other the ``index''; but whichever |
| labeling is used must fit the machine's constraints of which registers |
| may serve in each capacity. The compiler will try both labelings, |
| looking for one that is valid, and will reload one or both registers |
| only if neither labeling works. |
| @end defmac |
| |
| @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) |
| A C expression that places additional restrictions on the register class |
| to use when it is necessary to copy value @var{x} into a register in class |
| @var{class}. The value is a register class; perhaps @var{class}, or perhaps |
| another, smaller class. On many machines, the following definition is |
| safe: |
| |
| @smallexample |
| #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS |
| @end smallexample |
| |
| Sometimes returning a more restrictive class makes better code. For |
| example, on the 68000, when @var{x} is an integer constant that is in range |
| for a @samp{moveq} instruction, the value of this macro is always |
| @code{DATA_REGS} as long as @var{class} includes the data registers. |
| Requiring a data register guarantees that a @samp{moveq} will be used. |
| |
| One case where @code{PREFERRED_RELOAD_CLASS} must not return |
| @var{class} is if @var{x} is a legitimate constant which cannot be |
| loaded into some register class. By returning @code{NO_REGS} you can |
| force @var{x} into a memory location. For example, rs6000 can load |
| immediate values into general-purpose registers, but does not have an |
| instruction for loading an immediate value into a floating-point |
| register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when |
| @var{x} is a floating-point constant. If the constant can't be loaded |
| into any kind of register, code generation will be better if |
| @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead |
| of using @code{PREFERRED_RELOAD_CLASS}. |
| |
| If an insn has pseudos in it after register allocation, reload will go |
| through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS} |
| to find the best one. Returning @code{NO_REGS}, in this case, makes |
| reload add a @code{!} in front of the constraint: the x86 back-end uses |
| this feature to discourage usage of 387 registers when math is done in |
| the SSE registers (and vice versa). |
| @end defmac |
| |
| @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) |
| Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of |
| input reloads. If you don't define this macro, the default is to use |
| @var{class}, unchanged. |
| |
| You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage |
| reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}. |
| @end defmac |
| |
| @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) |
| A C expression that places additional restrictions on the register class |
| to use when it is necessary to be able to hold a value of mode |
| @var{mode} in a reload register for which class @var{class} would |
| ordinarily be used. |
| |
| Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when |
| there are certain modes that simply can't go in certain reload classes. |
| |
| The value is a register class; perhaps @var{class}, or perhaps another, |
| smaller class. |
| |
| Don't define this macro unless the target machine has limitations which |
| require the macro to do something nontrivial. |
| @end defmac |
| |
| @deftypefn {Target Hook} enum reg_class TARGET_SECONDARY_RELOAD (bool @var{in_p}, rtx @var{x}, enum reg_class @var{reload_class}, enum machine_mode @var{reload_mode}, secondary_reload_info *@var{sri}) |
| Many machines have some registers that cannot be copied directly to or |
| from memory or even from other types of registers. An example is the |
| @samp{MQ} register, which on most machines, can only be copied to or |
| from general registers, but not memory. Below, we shall be using the |
| term 'intermediate register' when a move operation cannot be performed |
| directly, but has to be done by copying the source into the intermediate |
| register first, and then copying the intermediate register to the |
| destination. An intermediate register always has the same mode as |
| source and destination. Since it holds the actual value being copied, |
| reload might apply optimizations to re-use an intermediate register |
| and eliding the copy from the source when it can determine that the |
| intermediate register still holds the required value. |
| |
| Another kind of secondary reload is required on some machines which |
| allow copying all registers to and from memory, but require a scratch |
| register for stores to some memory locations (e.g., those with symbolic |
| address on the RT, and those with certain symbolic address on the SPARC |
| when compiling PIC)@. Scratch registers need not have the same mode |
| as the value being copied, and usually hold a different value that |
| that being copied. Special patterns in the md file are needed to |
| describe how the copy is performed with the help of the scratch register; |
| these patterns also describe the number, register class(es) and mode(s) |
| of the scratch register(s). |
| |
| In some cases, both an intermediate and a scratch register are required. |
| |
| For input reloads, this target hook is called with nonzero @var{in_p}, |
| and @var{x} is an rtx that needs to be copied to a register in of class |
| @var{reload_class} in @var{reload_mode}. For output reloads, this target |
| hook is called with zero @var{in_p}, and a register of class @var{reload_mode} |
| needs to be copied to rtx @var{x} in @var{reload_mode}. |
| |
| If copying a register of @var{reload_class} from/to @var{x} requires |
| an intermediate register, the hook @code{secondary_reload} should |
| return the register class required for this intermediate register. |
| If no intermediate register is required, it should return NO_REGS. |
| If more than one intermediate register is required, describe the one |
| that is closest in the copy chain to the reload register. |
| |
| If scratch registers are needed, you also have to describe how to |
| perform the copy from/to the reload register to/from this |
| closest intermediate register. Or if no intermediate register is |
| required, but still a scratch register is needed, describe the |
| copy from/to the reload register to/from the reload operand @var{x}. |
| |
| You do this by setting @code{sri->icode} to the instruction code of a pattern |
| in the md file which performs the move. Operands 0 and 1 are the output |
| and input of this copy, respectively. Operands from operand 2 onward are |
| for scratch operands. These scratch operands must have a mode, and a |
| single-register-class |
| @c [later: or memory] |
| output constraint. |
| |
| When an intermediate register is used, the @code{secondary_reload} |
| hook will be called again to determine how to copy the intermediate |
| register to/from the reload operand @var{x}, so your hook must also |
| have code to handle the register class of the intermediate operand. |
| |
| @c [For later: maybe we'll allow multi-alternative reload patterns - |
| @c the port maintainer could name a mov<mode> pattern that has clobbers - |
| @c and match the constraints of input and output to determine the required |
| @c alternative. A restriction would be that constraints used to match |
| @c against reloads registers would have to be written as register class |
| @c constraints, or we need a new target macro / hook that tells us if an |
| @c arbitrary constraint can match an unknown register of a given class. |
| @c Such a macro / hook would also be useful in other places.] |
| |
| |
| @var{x} might be a pseudo-register or a @code{subreg} of a |
| pseudo-register, which could either be in a hard register or in memory. |
| Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is |
| in memory and the hard register number if it is in a register. |
| |
| Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are |
| currently not supported. For the time being, you will have to continue |
| to use @code{SECONDARY_MEMORY_NEEDED} for that purpose. |
| |
| @code{copy_cost} also uses this target hook to find out how values are |
| copied. If you want it to include some extra cost for the need to allocate |
| (a) scratch register(s), set @code{sri->extra_cost} to the additional cost. |
| Or if two dependent moves are supposed to have a lower cost than the sum |
| of the individual moves due to expected fortuitous scheduling and/or special |
| forwarding logic, you can set @code{sri->extra_cost} to a negative amount. |
| @end deftypefn |
| |
| @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) |
| These macros are obsolete, new ports should use the target hook |
| @code{TARGET_SECONDARY_RELOAD} instead. |
| |
| These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD} |
| target hook. Older ports still define these macros to indicate to the |
| reload phase that it may |
| need to allocate at least one register for a reload in addition to the |
| register to contain the data. Specifically, if copying @var{x} to a |
| register @var{class} in @var{mode} requires an intermediate register, |
| you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the |
| largest register class all of whose registers can be used as |
| intermediate registers or scratch registers. |
| |
| If copying a register @var{class} in @var{mode} to @var{x} requires an |
| intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} |
| was supposed to be defined be defined to return the largest register |
| class required. If the |
| requirements for input and output reloads were the same, the macro |
| @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both |
| macros identically. |
| |
| The values returned by these macros are often @code{GENERAL_REGS}. |
| Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} |
| can be directly copied to or from a register of @var{class} in |
| @var{mode} without requiring a scratch register. Do not define this |
| macro if it would always return @code{NO_REGS}. |
| |
| If a scratch register is required (either with or without an |
| intermediate register), you were supposed to define patterns for |
| @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required |
| (@pxref{Standard Names}. These patterns, which were normally |
| implemented with a @code{define_expand}, should be similar to the |
| @samp{mov@var{m}} patterns, except that operand 2 is the scratch |
| register. |
| |
| These patterns need constraints for the reload register and scratch |
| register that |
| contain a single register class. If the original reload register (whose |
| class is @var{class}) can meet the constraint given in the pattern, the |
| value returned by these macros is used for the class of the scratch |
| register. Otherwise, two additional reload registers are required. |
| Their classes are obtained from the constraints in the insn pattern. |
| |
| @var{x} might be a pseudo-register or a @code{subreg} of a |
| pseudo-register, which could either be in a hard register or in memory. |
| Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is |
| in memory and the hard register number if it is in a register. |
| |
| These macros should not be used in the case where a particular class of |
| registers can only be copied to memory and not to another class of |
| registers. In that case, secondary reload registers are not needed and |
| would not be helpful. Instead, a stack location must be used to perform |
| the copy and the @code{mov@var{m}} pattern should use memory as an |
| intermediate storage. This case often occurs between floating-point and |
| general registers. |
| @end defmac |
| |
| @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) |
| Certain machines have the property that some registers cannot be copied |
| to some other registers without using memory. Define this macro on |
| those machines to be a C expression that is nonzero if objects of mode |
| @var{m} in registers of @var{class1} can only be copied to registers of |
| class @var{class2} by storing a register of @var{class1} into memory |
| and loading that memory location into a register of @var{class2}. |
| |
| Do not define this macro if its value would always be zero. |
| @end defmac |
| |
| @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) |
| Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler |
| allocates a stack slot for a memory location needed for register copies. |
| If this macro is defined, the compiler instead uses the memory location |
| defined by this macro. |
| |
| Do not define this macro if you do not define |
| @code{SECONDARY_MEMORY_NEEDED}. |
| @end defmac |
| |
| @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) |
| When the compiler needs a secondary memory location to copy between two |
| registers of mode @var{mode}, it normally allocates sufficient memory to |
| hold a quantity of @code{BITS_PER_WORD} bits and performs the store and |
| load operations in a mode that many bits wide and whose class is the |
| same as that of @var{mode}. |
| |
| This is right thing to do on most machines because it ensures that all |
| bits of the register are copied and prevents accesses to the registers |
| in a narrower mode, which some machines prohibit for floating-point |
| registers. |
| |
| However, this default behavior is not correct on some machines, such as |
| the DEC Alpha, that store short integers in floating-point registers |
| differently than in integer registers. On those machines, the default |
| widening will not work correctly and you must define this macro to |
| suppress that widening in some cases. See the file @file{alpha.h} for |
| details. |
| |
| Do not define this macro if you do not define |
| @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that |
| is @code{BITS_PER_WORD} bits wide is correct for your machine. |
| @end defmac |
| |
| @defmac SMALL_REGISTER_CLASSES |
| On some machines, it is risky to let hard registers live across arbitrary |
| insns. Typically, these machines have instructions that require values |
| to be in specific registers (like an accumulator), and reload will fail |
| if the required hard register is used for another purpose across such an |
| insn. |
| |
| Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero |
| value on these machines. When this macro has a nonzero value, the |
| compiler will try to minimize the lifetime of hard registers. |
| |
| It is always safe to define this macro with a nonzero value, but if you |
| unnecessarily define it, you will reduce the amount of optimizations |
| that can be performed in some cases. If you do not define this macro |
| with a nonzero value when it is required, the compiler will run out of |
| spill registers and print a fatal error message. For most machines, you |
| should not define this macro at all. |
| @end defmac |
| |
| @defmac CLASS_LIKELY_SPILLED_P (@var{class}) |
| A C expression whose value is nonzero if pseudos that have been assigned |
| to registers of class @var{class} would likely be spilled because |
| registers of @var{class} are needed for spill registers. |
| |
| The default value of this macro returns 1 if @var{class} has exactly one |
| register and zero otherwise. On most machines, this default should be |
| used. Only define this macro to some other expression if pseudos |
| allocated by @file{local-alloc.c} end up in memory because their hard |
| registers were needed for spill registers. If this macro returns nonzero |
| for those classes, those pseudos will only be allocated by |
| @file{global.c}, which knows how to reallocate the pseudo to another |
| register. If there would not be another register available for |
| reallocation, you should not change the definition of this macro since |
| the only effect of such a definition would be to slow down register |
| allocation. |
| @end defmac |
| |
| @defmac CLASS_MAX_NREGS (@var{class}, @var{mode}) |
| A C expression for the maximum number of consecutive registers |
| of class @var{class} needed to hold a value of mode @var{mode}. |
| |
| This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, |
| the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} |
| should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, |
| @var{mode})} for all @var{regno} values in the class @var{class}. |
| |
| This macro helps control the handling of multiple-word values |
| in the reload pass. |
| @end defmac |
| |
| @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class}) |
| If defined, a C expression that returns nonzero for a @var{class} for which |
| a change from mode @var{from} to mode @var{to} is invalid. |
| |
| For the example, loading 32-bit integer or floating-point objects into |
| floating-point registers on the Alpha extends them to 64 bits. |
| Therefore loading a 64-bit object and then storing it as a 32-bit object |
| does not store the low-order 32 bits, as would be the case for a normal |
| register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS} |
| as below: |
| |
| @smallexample |
| #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \ |
| (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \ |
| ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0) |
| @end smallexample |
| @end defmac |
| |
| @node Old Constraints |
| @section Obsolete Macros for Defining Constraints |
| @cindex defining constraints, obsolete method |
| @cindex constraints, defining, obsolete method |
| |
| Machine-specific constraints can be defined with these macros instead |
| of the machine description constructs described in @ref{Define |
| Constraints}. This mechanism is obsolete. New ports should not use |
| it; old ports should convert to the new mechanism. |
| |
| @defmac CONSTRAINT_LEN (@var{char}, @var{str}) |
| For the constraint at the start of @var{str}, which starts with the letter |
| @var{c}, return the length. This allows you to have register class / |
| constant / extra constraints that are longer than a single letter; |
| you don't need to define this macro if you can do with single-letter |
| constraints only. The definition of this macro should use |
| DEFAULT_CONSTRAINT_LEN for all the characters that you don't want |
| to handle specially. |
| There are some sanity checks in genoutput.c that check the constraint lengths |
| for the md file, so you can also use this macro to help you while you are |
| transitioning from a byzantine single-letter-constraint scheme: when you |
| return a negative length for a constraint you want to re-use, genoutput |
| will complain about every instance where it is used in the md file. |
| @end defmac |
| |
| @defmac REG_CLASS_FROM_LETTER (@var{char}) |
| A C expression which defines the machine-dependent operand constraint |
| letters for register classes. If @var{char} is such a letter, the |
| value should be the register class corresponding to it. Otherwise, |
| the value should be @code{NO_REGS}. The register letter @samp{r}, |
| corresponding to class @code{GENERAL_REGS}, will not be passed |
| to this macro; you do not need to handle it. |
| @end defmac |
| |
| @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str}) |
| Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string |
| passed in @var{str}, so that you can use suffixes to distinguish between |
| different variants. |
| @end defmac |
| |
| @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) |
| A C expression that defines the machine-dependent operand constraint |
| letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify |
| particular ranges of integer values. If @var{c} is one of those |
| letters, the expression should check that @var{value}, an integer, is in |
| the appropriate range and return 1 if so, 0 otherwise. If @var{c} is |
| not one of those letters, the value should be 0 regardless of |
| @var{value}. |
| @end defmac |
| |
| @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) |
| Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint |
| string passed in @var{str}, so that you can use suffixes to distinguish |
| between different variants. |
| @end defmac |
| |
| @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) |
| A C expression that defines the machine-dependent operand constraint |
| letters that specify particular ranges of @code{const_double} values |
| (@samp{G} or @samp{H}). |
| |
| If @var{c} is one of those letters, the expression should check that |
| @var{value}, an RTX of code @code{const_double}, is in the appropriate |
| range and return 1 if so, 0 otherwise. If @var{c} is not one of those |
| letters, the value should be 0 regardless of @var{value}. |
| |
| @code{const_double} is used for all floating-point constants and for |
| @code{DImode} fixed-point constants. A given letter can accept either |
| or both kinds of values. It can use @code{GET_MODE} to distinguish |
| between these kinds. |
| @end defmac |
| |
| @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) |
| Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint |
| string passed in @var{str}, so that you can use suffixes to distinguish |
| between different variants. |
| @end defmac |
| |
| @defmac EXTRA_CONSTRAINT (@var{value}, @var{c}) |
| A C expression that defines the optional machine-dependent constraint |
| letters that can be used to segregate specific types of operands, usually |
| memory references, for the target machine. Any letter that is not |
| elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} / |
| @code{REG_CLASS_FROM_CONSTRAINT} |
| may be used. Normally this macro will not be defined. |
| |
| If it is required for a particular target machine, it should return 1 |
| if @var{value} corresponds to the operand type represented by the |
| constraint letter @var{c}. If @var{c} is not defined as an extra |
| constraint, the value returned should be 0 regardless of @var{value}. |
| |
| For example, on the ROMP, load instructions cannot have their output |
| in r0 if the memory reference contains a symbolic address. Constraint |
| letter @samp{Q} is defined as representing a memory address that does |
| @emph{not} contain a symbolic address. An alternative is specified with |
| a @samp{Q} constraint on the input and @samp{r} on the output. The next |
| alternative specifies @samp{m} on the input and a register class that |
| does not include r0 on the output. |
| @end defmac |
| |
| @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str}) |
| Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed |
| in @var{str}, so that you can use suffixes to distinguish between different |
| variants. |
| @end defmac |
| |
| @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str}) |
| A C expression that defines the optional machine-dependent constraint |
| letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should |
| be treated like memory constraints by the reload pass. |
| |
| It should return 1 if the operand type represented by the constraint |
| at the start of @var{str}, the first letter of which is the letter @var{c}, |
| comprises a subset of all memory references including |
| all those whose address is simply a base register. This allows the reload |
| pass to reload an operand, if it does not directly correspond to the operand |
| type of @var{c}, by copying its address into a base register. |
| |
| For example, on the S/390, some instructions do not accept arbitrary |
| memory references, but only those that do not make use of an index |
| register. The constraint letter @samp{Q} is defined via |
| @code{EXTRA_CONSTRAINT} as representing a memory address of this type. |
| If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT}, |
| a @samp{Q} constraint can handle any memory operand, because the |
| reload pass knows it can be reloaded by copying the memory address |
| into a base register if required. This is analogous to the way |
| a @samp{o} constraint can handle any memory operand. |
| @end defmac |
| |
| @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str}) |
| A C expression that defines the optional machine-dependent constraint |
| letters, amongst those accepted by @code{EXTRA_CONSTRAINT} / |
| @code{EXTRA_CONSTRAINT_STR}, that should |
| be treated like address constraints by the reload pass. |
| |
| It should return 1 if the operand type represented by the constraint |
| at the start of @var{str}, which starts with the letter @var{c}, comprises |
| a subset of all memory addresses including |
| all those that consist of just a base register. This allows the reload |
| pass to reload an operand, if it does not directly correspond to the operand |
| type of @var{str}, by copying it into a base register. |
| |
| Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only |
| be used with the @code{address_operand} predicate. It is treated |
| analogously to the @samp{p} constraint. |
| @end defmac |
| |
| @node Stack and Calling |
| @section Stack Layout and Calling Conventions |
| @cindex calling conventions |
| |
| @c prevent bad page break with this line |
| This describes the stack layout and calling conventions. |
| |
| @menu |
| * Frame Layout:: |
| * Exception Handling:: |
| * Stack Checking:: |
| * Frame Registers:: |
| * Elimination:: |
| * Stack Arguments:: |
| * Register Arguments:: |
| * Scalar Return:: |
| * Aggregate Return:: |
| * Caller Saves:: |
| * Function Entry:: |
| * Profiling:: |
| * Tail Calls:: |
| * Stack Smashing Protection:: |
| @end menu |
| |
| @node Frame Layout |
| @subsection Basic Stack Layout |
| @cindex stack frame layout |
| @cindex frame layout |
| |
| @c prevent bad page break with this line |
| Here is the basic stack layout. |
| |
| @defmac STACK_GROWS_DOWNWARD |
| Define this macro if pushing a word onto the stack moves the stack |
| pointer to a smaller address. |
| |
| When we say, ``define this macro if @dots{}'', it means that the |
| compiler checks this macro only with @code{#ifdef} so the precise |
| definition used does not matter. |
| @end defmac |
| |
| @defmac STACK_PUSH_CODE |
| This macro defines the operation used when something is pushed |
| on the stack. In RTL, a push operation will be |
| @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} |
| |
| The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, |
| and @code{POST_INC}. Which of these is correct depends on |
| the stack direction and on whether the stack pointer points |
| to the last item on the stack or whether it points to the |
| space for the next item on the stack. |
| |
| The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is |
| defined, which is almost always right, and @code{PRE_INC} otherwise, |
| which is often wrong. |
| @end defmac |
| |
| @defmac FRAME_GROWS_DOWNWARD |
| Define this macro to nonzero value if the addresses of local variable slots |
| are at negative offsets from the frame pointer. |
| @end defmac |
| |
| @defmac ARGS_GROW_DOWNWARD |
| Define this macro if successive arguments to a function occupy decreasing |
| addresses on the stack. |
| @end defmac |
| |
| @defmac STARTING_FRAME_OFFSET |
| Offset from the frame pointer to the first local variable slot to be allocated. |
| |
| If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by |
| subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. |
| Otherwise, it is found by adding the length of the first slot to the |
| value @code{STARTING_FRAME_OFFSET}. |
| @c i'm not sure if the above is still correct.. had to change it to get |
| @c rid of an overfull. --mew 2feb93 |
| @end defmac |
| |
| @defmac STACK_ALIGNMENT_NEEDED |
| Define to zero to disable final alignment of the stack during reload. |
| The nonzero default for this macro is suitable for most ports. |
| |
| On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there |
| is a register save block following the local block that doesn't require |
| alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable |
| stack alignment and do it in the backend. |
| @end defmac |
| |
| @defmac STACK_POINTER_OFFSET |
| Offset from the stack pointer register to the first location at which |
| outgoing arguments are placed. If not specified, the default value of |
| zero is used. This is the proper value for most machines. |
| |
| If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above |
| the first location at which outgoing arguments are placed. |
| @end defmac |
| |
| @defmac FIRST_PARM_OFFSET (@var{fundecl}) |
| Offset from the argument pointer register to the first argument's |
| address. On some machines it may depend on the data type of the |
| function. |
| |
| If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above |
| the first argument's address. |
| @end defmac |
| |
| @defmac STACK_DYNAMIC_OFFSET (@var{fundecl}) |
| Offset from the stack pointer register to an item dynamically allocated |
| on the stack, e.g., by @code{alloca}. |
| |
| The default value for this macro is @code{STACK_POINTER_OFFSET} plus the |
| length of the outgoing arguments. The default is correct for most |
| machines. See @file{function.c} for details. |
| @end defmac |
| |
| @defmac INITIAL_FRAME_ADDRESS_RTX |
| A C expression whose value is RTL representing the address of the initial |
| stack frame. This address is passed to @code{RETURN_ADDR_RTX} and |
| @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable |
| default value will be used. Define this macro in order to make frame pointer |
| elimination work in the presence of @code{__builtin_frame_address (count)} and |
| @code{__builtin_return_address (count)} for @code{count} not equal to zero. |
| @end defmac |
| |
| @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) |
| A C expression whose value is RTL representing the address in a stack |
| frame where the pointer to the caller's frame is stored. Assume that |
| @var{frameaddr} is an RTL expression for the address of the stack frame |
| itself. |
| |
| If you don't define this macro, the default is to return the value |
| of @var{frameaddr}---that is, the stack frame address is also the |
| address of the stack word that points to the previous frame. |
| @end defmac |
| |
| @defmac SETUP_FRAME_ADDRESSES |
| If defined, a C expression that produces the machine-specific code to |
| setup the stack so that arbitrary frames can be accessed. For example, |
| on the SPARC, we must flush all of the register windows to the stack |
| before we can access arbitrary stack frames. You will seldom need to |
| define this macro. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_BUILTIN_SETJMP_FRAME_VALUE () |
| This target hook should return an rtx that is used to store |
| the address of the current frame into the built in @code{setjmp} buffer. |
| The default value, @code{virtual_stack_vars_rtx}, is correct for most |
| machines. One reason you may need to define this target hook is if |
| @code{hard_frame_pointer_rtx} is the appropriate value on your machine. |
| @end deftypefn |
| |
| @defmac FRAME_ADDR_RTX (@var{frameaddr}) |
| A C expression whose value is RTL representing the value of the frame |
| address for the current frame. @var{frameaddr} is the frame pointer |
| of the current frame. This is used for __builtin_frame_address. |
| You need only define this macro if the frame address is not the same |
| as the frame pointer. Most machines do not need to define it. |
| @end defmac |
| |
| @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) |
| A C expression whose value is RTL representing the value of the return |
| address for the frame @var{count} steps up from the current frame, after |
| the prologue. @var{frameaddr} is the frame pointer of the @var{count} |
| frame, or the frame pointer of the @var{count} @minus{} 1 frame if |
| @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. |
| |
| The value of the expression must always be the correct address when |
| @var{count} is zero, but may be @code{NULL_RTX} if there is not way to |
| determine the return address of other frames. |
| @end defmac |
| |
| @defmac RETURN_ADDR_IN_PREVIOUS_FRAME |
| Define this if the return address of a particular stack frame is accessed |
| from the frame pointer of the previous stack frame. |
| @end defmac |
| |
| @defmac INCOMING_RETURN_ADDR_RTX |
| A C expression whose value is RTL representing the location of the |
| incoming return address at the beginning of any function, before the |
| prologue. This RTL is either a @code{REG}, indicating that the return |
| value is saved in @samp{REG}, or a @code{MEM} representing a location in |
| the stack. |
| |
| You only need to define this macro if you want to support call frame |
| debugging information like that provided by DWARF 2. |
| |
| If this RTL is a @code{REG}, you should also define |
| @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. |
| @end defmac |
| |
| @defmac DWARF_ALT_FRAME_RETURN_COLUMN |
| A C expression whose value is an integer giving a DWARF 2 column |
| number that may be used as an alternate return column. This should |
| be defined only if @code{DWARF_FRAME_RETURN_COLUMN} is set to a |
| general register, but an alternate column needs to be used for |
| signal frames. |
| @end defmac |
| |
| @defmac DWARF_ZERO_REG |
| A C expression whose value is an integer giving a DWARF 2 register |
| number that is considered to always have the value zero. This should |
| only be defined if the target has an architected zero register, and |
| someone decided it was a good idea to use that register number to |
| terminate the stack backtrace. New ports should avoid this. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index}) |
| This target hook allows the backend to emit frame-related insns that |
| contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging |
| info engine will invoke it on insns of the form |
| @smallexample |
| (set (reg) (unspec [...] UNSPEC_INDEX)) |
| @end smallexample |
| and |
| @smallexample |
| (set (reg) (unspec_volatile [...] UNSPECV_INDEX)). |
| @end smallexample |
| to let the backend emit the call frame instructions. @var{label} is |
| the CFI label attached to the insn, @var{pattern} is the pattern of |
| the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}. |
| @end deftypefn |
| |
| @defmac INCOMING_FRAME_SP_OFFSET |
| A C expression whose value is an integer giving the offset, in bytes, |
| from the value of the stack pointer register to the top of the stack |
| frame at the beginning of any function, before the prologue. The top of |
| the frame is defined to be the value of the stack pointer in the |
| previous frame, just before the call instruction. |
| |
| You only need to define this macro if you want to support call frame |
| debugging information like that provided by DWARF 2. |
| @end defmac |
| |
| @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl}) |
| A C expression whose value is an integer giving the offset, in bytes, |
| from the argument pointer to the canonical frame address (cfa). The |
| final value should coincide with that calculated by |
| @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable |
| during virtual register instantiation. |
| |
| The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)}, |
| which is correct for most machines; in general, the arguments are found |
| immediately before the stack frame. Note that this is not the case on |
| some targets that save registers into the caller's frame, such as SPARC |
| and rs6000, and so such targets need to define this macro. |
| |
| You only need to define this macro if the default is incorrect, and you |
| want to support call frame debugging information like that provided by |
| DWARF 2. |
| @end defmac |
| |
| @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl}) |
| If defined, a C expression whose value is an integer giving the offset |
| in bytes from the frame pointer to the canonical frame address (cfa). |
| The final value should coincide with that calculated by |
| @code{INCOMING_FRAME_SP_OFFSET}. |
| |
| Normally the CFA is calculated as an offset from the argument pointer, |
| via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is |
| variable due to the ABI, this may not be possible. If this macro is |
| defined, it implies that the virtual register instantiation should be |
| based on the frame pointer instead of the argument pointer. Only one |
| of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET} |
| should be defined. |
| @end defmac |
| |
| @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl}) |
| If defined, a C expression whose value is an integer giving the offset |
| in bytes from the canonical frame address (cfa) to the frame base used |
| in DWARF 2 debug information. The default is zero. A different value |
| may reduce the size of debug information on some ports. |
| @end defmac |
| |
| @node Exception Handling |
| @subsection Exception Handling Support |
| @cindex exception handling |
| |
| @defmac EH_RETURN_DATA_REGNO (@var{N}) |
| A C expression whose value is the @var{N}th register number used for |
| data by exception handlers, or @code{INVALID_REGNUM} if fewer than |
| @var{N} registers are usable. |
| |
| The exception handling library routines communicate with the exception |
| handlers via a set of agreed upon registers. Ideally these registers |
| should be call-clobbered; it is possible to use call-saved registers, |
| but may negatively impact code size. The target must support at least |
| 2 data registers, but should define 4 if there are enough free registers. |
| |
| You must define this macro if you want to support call frame exception |
| handling like that provided by DWARF 2. |
| @end defmac |
| |
| @defmac EH_RETURN_STACKADJ_RTX |
| A C expression whose value is RTL representing a location in which |
| to store a stack adjustment to be applied before function return. |
| This is used to unwind the stack to an exception handler's call frame. |
| It will be assigned zero on code paths that return normally. |
| |
| Typically this is a call-clobbered hard register that is otherwise |
| untouched by the epilogue, but could also be a stack slot. |
| |
| Do not define this macro if the stack pointer is saved and restored |
| by the regular prolog and epilog code in the call frame itself; in |
| this case, the exception handling library routines will update the |
| stack location to be restored in place. Otherwise, you must define |
| this macro if you want to support call frame exception handling like |
| that provided by DWARF 2. |
| @end defmac |
| |
| @defmac EH_RETURN_HANDLER_RTX |
| A C expression whose value is RTL representing a location in which |
| to store the address of an exception handler to which we should |
| return. It will not be assigned on code paths that return normally. |
| |
| Typically this is the location in the call frame at which the normal |
| return address is stored. For targets that return by popping an |
| address off the stack, this might be a memory address just below |
| the @emph{target} call frame rather than inside the current call |
| frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already |
| been assigned, so it may be used to calculate the location of the |
| target call frame. |
| |
| Some targets have more complex requirements than storing to an |
| address calculable during initial code generation. In that case |
| the @code{eh_return} instruction pattern should be used instead. |
| |
| If you want to support call frame exception handling, you must |
| define either this macro or the @code{eh_return} instruction pattern. |
| @end defmac |
| |
| @defmac RETURN_ADDR_OFFSET |
| If defined, an integer-valued C expression for which rtl will be generated |
| to add it to the exception handler address before it is searched in the |
| exception handling tables, and to subtract it again from the address before |
| using it to return to the exception handler. |
| @end defmac |
| |
| @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global}) |
| This macro chooses the encoding of pointers embedded in the exception |
| handling sections. If at all possible, this should be defined such |
| that the exception handling section will not require dynamic relocations, |
| and so may be read-only. |
| |
| @var{code} is 0 for data, 1 for code labels, 2 for function pointers. |
| @var{global} is true if the symbol may be affected by dynamic relocations. |
| The macro should return a combination of the @code{DW_EH_PE_*} defines |
| as found in @file{dwarf2.h}. |
| |
| If this macro is not defined, pointers will not be encoded but |
| represented directly. |
| @end defmac |
| |
| @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) |
| This macro allows the target to emit whatever special magic is required |
| to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. |
| Generic code takes care of pc-relative and indirect encodings; this must |
| be defined if the target uses text-relative or data-relative encodings. |
| |
| This is a C statement that branches to @var{done} if the format was |
| handled. @var{encoding} is the format chosen, @var{size} is the number |
| of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} |
| to be emitted. |
| @end defmac |
| |
| @defmac MD_UNWIND_SUPPORT |
| A string specifying a file to be #include'd in unwind-dw2.c. The file |
| so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}. |
| @end defmac |
| |
| @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}) |
| This macro allows the target to add cpu and operating system specific |
| code to the call-frame unwinder for use when there is no unwind data |
| available. The most common reason to implement this macro is to unwind |
| through signal frames. |
| |
| This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c} |
| and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; |
| @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} |
| for the address of the code being executed and @code{context->cfa} for |
| the stack pointer value. If the frame can be decoded, the register save |
| addresses should be updated in @var{fs} and the macro should evaluate to |
| @code{_URC_NO_REASON}. If the frame cannot be decoded, the macro should |
| evaluate to @code{_URC_END_OF_STACK}. |
| |
| For proper signal handling in Java this macro is accompanied by |
| @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers. |
| @end defmac |
| |
| @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs}) |
| This macro allows the target to add operating system specific code to the |
| call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive, |
| usually used for signal or interrupt frames. |
| |
| This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}. |
| @var{context} is an @code{_Unwind_Context}; |
| @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi} |
| for the abi and context in the @code{.unwabi} directive. If the |
| @code{.unwabi} directive can be handled, the register save addresses should |
| be updated in @var{fs}. |
| @end defmac |
| |
| @defmac TARGET_USES_WEAK_UNWIND_INFO |
| A C expression that evaluates to true if the target requires unwind |
| info to be given comdat linkage. Define it to be @code{1} if comdat |
| linkage is necessary. The default is @code{0}. |
| @end defmac |
| |
| @node Stack Checking |
| @subsection Specifying How Stack Checking is Done |
| |
| GCC will check that stack references are within the boundaries of |
| the stack, if the @option{-fstack-check} is specified, in one of three ways: |
| |
| @enumerate |
| @item |
| If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC |
| will assume that you have arranged for stack checking to be done at |
| appropriate places in the configuration files, e.g., in |
| @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special |
| processing. |
| |
| @item |
| If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern |
| called @code{check_stack} in your @file{md} file, GCC will call that |
| pattern with one argument which is the address to compare the stack |
| value against. You must arrange for this pattern to report an error if |
| the stack pointer is out of range. |
| |
| @item |
| If neither of the above are true, GCC will generate code to periodically |
| ``probe'' the stack pointer using the values of the macros defined below. |
| @end enumerate |
| |
| Normally, you will use the default values of these macros, so GCC |
| will use the third approach. |
| |
| @defmac STACK_CHECK_BUILTIN |
| A nonzero value if stack checking is done by the configuration files in a |
| machine-dependent manner. You should define this macro if stack checking |
| is require by the ABI of your machine or if you would like to have to stack |
| checking in some more efficient way than GCC's portable approach. |
| The default value of this macro is zero. |
| @end defmac |
| |
| @defmac STACK_CHECK_PROBE_INTERVAL |
| An integer representing the interval at which GCC must generate stack |
| probe instructions. You will normally define this macro to be no larger |
| than the size of the ``guard pages'' at the end of a stack area. The |
| default value of 4096 is suitable for most systems. |
| @end defmac |
| |
| @defmac STACK_CHECK_PROBE_LOAD |
| A integer which is nonzero if GCC should perform the stack probe |
| as a load instruction and zero if GCC should use a store instruction. |
| The default is zero, which is the most efficient choice on most systems. |
| @end defmac |
| |
| @defmac STACK_CHECK_PROTECT |
| The number of bytes of stack needed to recover from a stack overflow, |
| for languages where such a recovery is supported. The default value of |
| 75 words should be adequate for most machines. |
| @end defmac |
| |
| @defmac STACK_CHECK_MAX_FRAME_SIZE |
| The maximum size of a stack frame, in bytes. GCC will generate probe |
| instructions in non-leaf functions to ensure at least this many bytes of |
| stack are available. If a stack frame is larger than this size, stack |
| checking will not be reliable and GCC will issue a warning. The |
| default is chosen so that GCC only generates one instruction on most |
| systems. You should normally not change the default value of this macro. |
| @end defmac |
| |
| @defmac STACK_CHECK_FIXED_FRAME_SIZE |
| GCC uses this value to generate the above warning message. It |
| represents the amount of fixed frame used by a function, not including |
| space for any callee-saved registers, temporaries and user variables. |
| You need only specify an upper bound for this amount and will normally |
| use the default of four words. |
| @end defmac |
| |
| @defmac STACK_CHECK_MAX_VAR_SIZE |
| The maximum size, in bytes, of an object that GCC will place in the |
| fixed area of the stack frame when the user specifies |
| @option{-fstack-check}. |
| GCC computed the default from the values of the above macros and you will |
| normally not need to override that default. |
| @end defmac |
| |
| @need 2000 |
| @node Frame Registers |
| @subsection Registers That Address the Stack Frame |
| |
| @c prevent bad page break with this line |
| This discusses registers that address the stack frame. |
| |
| @defmac STACK_POINTER_REGNUM |
| The register number of the stack pointer register, which must also be a |
| fixed register according to @code{FIXED_REGISTERS}. On most machines, |
| the hardware determines which register this is. |
| @end defmac |
| |
| @defmac FRAME_POINTER_REGNUM |
| The register number of the frame pointer register, which is used to |
| access automatic variables in the stack frame. On some machines, the |
| hardware determines which register this is. On other machines, you can |
| choose any register you wish for this purpose. |
| @end defmac |
| |
| @defmac HARD_FRAME_POINTER_REGNUM |
| On some machines the offset between the frame pointer and starting |
| offset of the automatic variables is not known until after register |
| allocation has been done (for example, because the saved registers are |
| between these two locations). On those machines, define |
| @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to |
| be used internally until the offset is known, and define |
| @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number |
| used for the frame pointer. |
| |
| You should define this macro only in the very rare circumstances when it |
| is not possible to calculate the offset between the frame pointer and |
| the automatic variables until after register allocation has been |
| completed. When this macro is defined, you must also indicate in your |
| definition of @code{ELIMINABLE_REGS} how to eliminate |
| @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} |
| or @code{STACK_POINTER_REGNUM}. |
| |
| Do not define this macro if it would be the same as |
| @code{FRAME_POINTER_REGNUM}. |
| @end defmac |
| |
| @defmac ARG_POINTER_REGNUM |
| The register number of the arg pointer register, which is used to access |
| the function's argument list. On some machines, this is the same as the |
| frame pointer register. On some machines, the hardware determines which |
| register this is. On other machines, you can choose any register you |
| wish for this purpose. If this is not the same register as the frame |
| pointer register, then you must mark it as a fixed register according to |
| @code{FIXED_REGISTERS}, or arrange to be able to eliminate it |
| (@pxref{Elimination}). |
| @end defmac |
| |
| @defmac RETURN_ADDRESS_POINTER_REGNUM |
| The register number of the return address pointer register, which is used to |
| access the current function's return address from the stack. On some |
| machines, the return address is not at a fixed offset from the frame |
| pointer or stack pointer or argument pointer. This register can be defined |
| to point to the return address on the stack, and then be converted by |
| @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. |
| |
| Do not define this macro unless there is no other way to get the return |
| address from the stack. |
| @end defmac |
| |
| @defmac STATIC_CHAIN_REGNUM |
| @defmacx STATIC_CHAIN_INCOMING_REGNUM |
| Register numbers used for passing a function's static chain pointer. If |
| register windows are used, the register number as seen by the called |
| function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register |
| number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If |
| these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need |
| not be defined. |
| |
| The static chain register need not be a fixed register. |
| |
| If the static chain is passed in memory, these macros should not be |
| defined; instead, the next two macros should be defined. |
| @end defmac |
| |
| @defmac STATIC_CHAIN |
| @defmacx STATIC_CHAIN_INCOMING |
| If the static chain is passed in memory, these macros provide rtx giving |
| @code{mem} expressions that denote where they are stored. |
| @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations |
| as seen by the calling and called functions, respectively. Often the former |
| will be at an offset from the stack pointer and the latter at an offset from |
| the frame pointer. |
| |
| @findex stack_pointer_rtx |
| @findex frame_pointer_rtx |
| @findex arg_pointer_rtx |
| The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and |
| @code{arg_pointer_rtx} will have been initialized prior to the use of these |
| macros and should be used to refer to those items. |
| |
| If the static chain is passed in a register, the two previous macros should |
| be defined instead. |
| @end defmac |
| |
| @defmac DWARF_FRAME_REGISTERS |
| This macro specifies the maximum number of hard registers that can be |
| saved in a call frame. This is used to size data structures used in |
| DWARF2 exception handling. |
| |
| Prior to GCC 3.0, this macro was needed in order to establish a stable |
| exception handling ABI in the face of adding new hard registers for ISA |
| extensions. In GCC 3.0 and later, the EH ABI is insulated from changes |
| in the number of hard registers. Nevertheless, this macro can still be |
| used to reduce the runtime memory requirements of the exception handling |
| routines, which can be substantial if the ISA contains a lot of |
| registers that are not call-saved. |
| |
| If this macro is not defined, it defaults to |
| @code{FIRST_PSEUDO_REGISTER}. |
| @end defmac |
| |
| @defmac PRE_GCC3_DWARF_FRAME_REGISTERS |
| |
| This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided |
| for backward compatibility in pre GCC 3.0 compiled code. |
| |
| If this macro is not defined, it defaults to |
| @code{DWARF_FRAME_REGISTERS}. |
| @end defmac |
| |
| @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno}) |
| |
| Define this macro if the target's representation for dwarf registers |
| is different than the internal representation for unwind column. |
| Given a dwarf register, this macro should return the internal unwind |
| column number to use instead. |
| |
| See the PowerPC's SPE target for an example. |
| @end defmac |
| |
| @defmac DWARF_FRAME_REGNUM (@var{regno}) |
| |
| Define this macro if the target's representation for dwarf registers |
| used in .eh_frame or .debug_frame is different from that used in other |
| debug info sections. Given a GCC hard register number, this macro |
| should return the .eh_frame register number. The default is |
| @code{DBX_REGISTER_NUMBER (@var{regno})}. |
| |
| @end defmac |
| |
| @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh}) |
| |
| Define this macro to map register numbers held in the call frame info |
| that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that |
| should be output in .debug_frame (@code{@var{for_eh}} is zero) and |
| .eh_frame (@code{@var{for_eh}} is nonzero). The default is to |
| return @code{@var{regno}}. |
| |
| @end defmac |
| |
| @node Elimination |
| @subsection Eliminating Frame Pointer and Arg Pointer |
| |
| @c prevent bad page break with this line |
| This is about eliminating the frame pointer and arg pointer. |
| |
| @defmac FRAME_POINTER_REQUIRED |
| A C expression which is nonzero if a function must have and use a frame |
| pointer. This expression is evaluated in the reload pass. If its value is |
| nonzero the function will have a frame pointer. |
| |
| The expression can in principle examine the current function and decide |
| according to the facts, but on most machines the constant 0 or the |
| constant 1 suffices. Use 0 when the machine allows code to be generated |
| with no frame pointer, and doing so saves some time or space. Use 1 |
| when there is no possible advantage to avoiding a frame pointer. |
| |
| In certain cases, the compiler does not know how to produce valid code |
| without a frame pointer. The compiler recognizes those cases and |
| automatically gives the function a frame pointer regardless of what |
| @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about |
| them. |
| |
| In a function that does not require a frame pointer, the frame pointer |
| register can be allocated for ordinary usage, unless you mark it as a |
| fixed register. See @code{FIXED_REGISTERS} for more information. |
| @end defmac |
| |
| @findex get_frame_size |
| @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) |
| A C statement to store in the variable @var{depth-var} the difference |
| between the frame pointer and the stack pointer values immediately after |
| the function prologue. The value would be computed from information |
| such as the result of @code{get_frame_size ()} and the tables of |
| registers @code{regs_ever_live} and @code{call_used_regs}. |
| |
| If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and |
| need not be defined. Otherwise, it must be defined even if |
| @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that |
| case, you may set @var{depth-var} to anything. |
| @end defmac |
| |
| @defmac ELIMINABLE_REGS |
| If defined, this macro specifies a table of register pairs used to |
| eliminate unneeded registers that point into the stack frame. If it is not |
| defined, the only elimination attempted by the compiler is to replace |
| references to the frame pointer with references to the stack pointer. |
| |
| The definition of this macro is a list of structure initializations, each |
| of which specifies an original and replacement register. |
| |
| On some machines, the position of the argument pointer is not known until |
| the compilation is completed. In such a case, a separate hard register |
| must be used for the argument pointer. This register can be eliminated by |
| replacing it with either the frame pointer or the argument pointer, |
| depending on whether or not the frame pointer has been eliminated. |
| |
| In this case, you might specify: |
| @smallexample |
| #define ELIMINABLE_REGS \ |
| @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ |
| @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ |
| @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} |
| @end smallexample |
| |
| Note that the elimination of the argument pointer with the stack pointer is |
| specified first since that is the preferred elimination. |
| @end defmac |
| |
| @defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg}) |
| A C expression that returns nonzero if the compiler is allowed to try |
| to replace register number @var{from-reg} with register number |
| @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS} |
| is defined, and will usually be the constant 1, since most of the cases |
| preventing register elimination are things that the compiler already |
| knows about. |
| @end defmac |
| |
| @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) |
| This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It |
| specifies the initial difference between the specified pair of |
| registers. This macro must be defined if @code{ELIMINABLE_REGS} is |
| defined. |
| @end defmac |
| |
| @node Stack Arguments |
| @subsection Passing Function Arguments on the Stack |
| @cindex arguments on stack |
| @cindex stack arguments |
| |
| The macros in this section control how arguments are passed |
| on the stack. See the following section for other macros that |
| control passing certain arguments in registers. |
| |
| @deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (tree @var{fntype}) |
| This target hook returns @code{true} if an argument declared in a |
| prototype as an integral type smaller than @code{int} should actually be |
| passed as an @code{int}. In addition to avoiding errors in certain |
| cases of mismatch, it also makes for better code on certain machines. |
| The default is to not promote prototypes. |
| @end deftypefn |
| |
| @defmac PUSH_ARGS |
| A C expression. If nonzero, push insns will be used to pass |
| outgoing arguments. |
| If the target machine does not have a push instruction, set it to zero. |
| That directs GCC to use an alternate strategy: to |
| allocate the entire argument block and then store the arguments into |
| it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. |
| @end defmac |
| |
| @defmac PUSH_ARGS_REVERSED |
| A C expression. If nonzero, function arguments will be evaluated from |
| last to first, rather than from first to last. If this macro is not |
| defined, it defaults to @code{PUSH_ARGS} on targets where the stack |
| and args grow in opposite directions, and 0 otherwise. |
| @end defmac |
| |
| @defmac PUSH_ROUNDING (@var{npushed}) |
| A C expression that is the number of bytes actually pushed onto the |
| stack when an instruction attempts to push @var{npushed} bytes. |
| |
| On some machines, the definition |
| |
| @smallexample |
| #define PUSH_ROUNDING(BYTES) (BYTES) |
| @end smallexample |
| |
| @noindent |
| will suffice. But on other machines, instructions that appear |
| to push one byte actually push two bytes in an attempt to maintain |
| alignment. Then the definition should be |
| |
| @smallexample |
| #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) |
| @end smallexample |
| @end defmac |
| |
| @findex current_function_outgoing_args_size |
| @defmac ACCUMULATE_OUTGOING_ARGS |
| A C expression. If nonzero, the maximum amount of space required for outgoing arguments |
| will be computed and placed into the variable |
| @code{current_function_outgoing_args_size}. No space will be pushed |
| onto the stack for each call; instead, the function prologue should |
| increase the stack frame size by this amount. |
| |
| Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} |
| is not proper. |
| @end defmac |
| |
| @defmac REG_PARM_STACK_SPACE (@var{fndecl}) |
| Define this macro if functions should assume that stack space has been |
| allocated for arguments even when their values are passed in |
| registers. |
| |
| The value of this macro is the size, in bytes, of the area reserved for |
| arguments passed in registers for the function represented by @var{fndecl}, |
| which can be zero if GCC is calling a library function. |
| |
| This space can be allocated by the caller, or be a part of the |
| machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says |
| which. |
| @end defmac |
| @c above is overfull. not sure what to do. --mew 5feb93 did |
| @c something, not sure if it looks good. --mew 10feb93 |
| |
| @defmac OUTGOING_REG_PARM_STACK_SPACE |
| Define this if it is the responsibility of the caller to allocate the area |
| reserved for arguments passed in registers. |
| |
| If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls |
| whether the space for these arguments counts in the value of |
| @code{current_function_outgoing_args_size}. |
| @end defmac |
| |
| @defmac STACK_PARMS_IN_REG_PARM_AREA |
| Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the |
| stack parameters don't skip the area specified by it. |
| @c i changed this, makes more sens and it should have taken care of the |
| @c overfull.. not as specific, tho. --mew 5feb93 |
| |
| Normally, when a parameter is not passed in registers, it is placed on the |
| stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro |
| suppresses this behavior and causes the parameter to be passed on the |
| stack in its natural location. |
| @end defmac |
| |
| @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size}) |
| A C expression that should indicate the number of bytes of its own |
| arguments that a function pops on returning, or 0 if the |
| function pops no arguments and the caller must therefore pop them all |
| after the function returns. |
| |
| @var{fundecl} is a C variable whose value is a tree node that describes |
| the function in question. Normally it is a node of type |
| @code{FUNCTION_DECL} that describes the declaration of the function. |
| From this you can obtain the @code{DECL_ATTRIBUTES} of the function. |
| |
| @var{funtype} is a C variable whose value is a tree node that |
| describes the function in question. Normally it is a node of type |
| @code{FUNCTION_TYPE} that describes the data type of the function. |
| From this it is possible to obtain the data types of the value and |
| arguments (if known). |
| |
| When a call to a library function is being considered, @var{fundecl} |
| will contain an identifier node for the library function. Thus, if |
| you need to distinguish among various library functions, you can do so |
| by their names. Note that ``library function'' in this context means |
| a function used to perform arithmetic, whose name is known specially |
| in the compiler and was not mentioned in the C code being compiled. |
| |
| @var{stack-size} is the number of bytes of arguments passed on the |
| stack. If a variable number of bytes is passed, it is zero, and |
| argument popping will always be the responsibility of the calling function. |
| |
| On the VAX, all functions always pop their arguments, so the definition |
| of this macro is @var{stack-size}. On the 68000, using the standard |
| calling convention, no functions pop their arguments, so the value of |
| the macro is always 0 in this case. But an alternative calling |
| convention is available in which functions that take a fixed number of |
| arguments pop them but other functions (such as @code{printf}) pop |
| nothing (the caller pops all). When this convention is in use, |
| @var{funtype} is examined to determine whether a function takes a fixed |
| number of arguments. |
| @end defmac |
| |
| @defmac CALL_POPS_ARGS (@var{cum}) |
| A C expression that should indicate the number of bytes a call sequence |
| pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} |
| when compiling a function call. |
| |
| @var{cum} is the variable in which all arguments to the called function |
| have been accumulated. |
| |
| On certain architectures, such as the SH5, a call trampoline is used |
| that pops certain registers off the stack, depending on the arguments |
| that have been passed to the function. Since this is a property of the |
| call site, not of the called function, @code{RETURN_POPS_ARGS} is not |
| appropriate. |
| @end defmac |
| |
| @node Register Arguments |
| @subsection Passing Arguments in Registers |
| @cindex arguments in registers |
| @cindex registers arguments |
| |
| This section describes the macros which let you control how various |
| types of arguments are passed in registers or how they are arranged in |
| the stack. |
| |
| @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C expression that controls whether a function argument is passed |
| in a register, and which register. |
| |
| The arguments are @var{cum}, which summarizes all the previous |
| arguments; @var{mode}, the machine mode of the argument; @var{type}, |
| the data type of the argument as a tree node or 0 if that is not known |
| (which happens for C support library functions); and @var{named}, |
| which is 1 for an ordinary argument and 0 for nameless arguments that |
| correspond to @samp{@dots{}} in the called function's prototype. |
| @var{type} can be an incomplete type if a syntax error has previously |
| occurred. |
| |
| The value of the expression is usually either a @code{reg} RTX for the |
| hard register in which to pass the argument, or zero to pass the |
| argument on the stack. |
| |
| For machines like the VAX and 68000, where normally all arguments are |
| pushed, zero suffices as a definition. |
| |
| The value of the expression can also be a @code{parallel} RTX@. This is |
| used when an argument is passed in multiple locations. The mode of the |
| @code{parallel} should be the mode of the entire argument. The |
| @code{parallel} holds any number of @code{expr_list} pairs; each one |
| describes where part of the argument is passed. In each |
| @code{expr_list} the first operand must be a @code{reg} RTX for the hard |
| register in which to pass this part of the argument, and the mode of the |
| register RTX indicates how large this part of the argument is. The |
| second operand of the @code{expr_list} is a @code{const_int} which gives |
| the offset in bytes into the entire argument of where this part starts. |
| As a special exception the first @code{expr_list} in the @code{parallel} |
| RTX may have a first operand of zero. This indicates that the entire |
| argument is also stored on the stack. |
| |
| The last time this macro is called, it is called with @code{MODE == |
| VOIDmode}, and its result is passed to the @code{call} or @code{call_value} |
| pattern as operands 2 and 3 respectively. |
| |
| @cindex @file{stdarg.h} and register arguments |
| The usual way to make the ISO library @file{stdarg.h} work on a machine |
| where some arguments are usually passed in registers, is to cause |
| nameless arguments to be passed on the stack instead. This is done |
| by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. |
| |
| @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} |
| @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} |
| You may use the hook @code{targetm.calls.must_pass_in_stack} |
| in the definition of this macro to determine if this argument is of a |
| type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} |
| is not defined and @code{FUNCTION_ARG} returns nonzero for such an |
| argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is |
| defined, the argument will be computed in the stack and then loaded into |
| a register. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (enum machine_mode @var{mode}, tree @var{type}) |
| This target hook should return @code{true} if we should not pass @var{type} |
| solely in registers. The file @file{expr.h} defines a |
| definition that is usually appropriate, refer to @file{expr.h} for additional |
| documentation. |
| @end deftypefn |
| |
| @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| Define this macro if the target machine has ``register windows'', so |
| that the register in which a function sees an arguments is not |
| necessarily the same as the one in which the caller passed the |
| argument. |
| |
| For such machines, @code{FUNCTION_ARG} computes the register in which |
| the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should |
| be defined in a similar fashion to tell the function being called |
| where the arguments will arrive. |
| |
| If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} |
| serves both purposes. |
| @end defmac |
| |
| @deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) |
| This target hook returns the number of bytes at the beginning of an |
| argument that must be put in registers. The value must be zero for |
| arguments that are passed entirely in registers or that are entirely |
| pushed on the stack. |
| |
| On some machines, certain arguments must be passed partially in |
| registers and partially in memory. On these machines, typically the |
| first few words of arguments are passed in registers, and the rest |
| on the stack. If a multi-word argument (a @code{double} or a |
| structure) crosses that boundary, its first few words must be passed |
| in registers and the rest must be pushed. This macro tells the |
| compiler when this occurs, and how many bytes should go in registers. |
| |
| @code{FUNCTION_ARG} for these arguments should return the first |
| register to be used by the caller for this argument; likewise |
| @code{FUNCTION_INCOMING_ARG}, for the called function. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) |
| This target hook should return @code{true} if an argument at the |
| position indicated by @var{cum} should be passed by reference. This |
| predicate is queried after target independent reasons for being |
| passed by reference, such as @code{TREE_ADDRESSABLE (type)}. |
| |
| If the hook returns true, a copy of that argument is made in memory and a |
| pointer to the argument is passed instead of the argument itself. |
| The pointer is passed in whatever way is appropriate for passing a pointer |
| to that type. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) |
| The function argument described by the parameters to this hook is |
| known to be passed by reference. The hook should return true if the |
| function argument should be copied by the callee instead of copied |
| by the caller. |
| |
| For any argument for which the hook returns true, if it can be |
| determined that the argument is not modified, then a copy need |
| not be generated. |
| |
| The default version of this hook always returns false. |
| @end deftypefn |
| |
| @defmac CUMULATIVE_ARGS |
| A C type for declaring a variable that is used as the first argument of |
| @code{FUNCTION_ARG} and other related values. For some target machines, |
| the type @code{int} suffices and can hold the number of bytes of |
| argument so far. |
| |
| There is no need to record in @code{CUMULATIVE_ARGS} anything about the |
| arguments that have been passed on the stack. The compiler has other |
| variables to keep track of that. For target machines on which all |
| arguments are passed on the stack, there is no need to store anything in |
| @code{CUMULATIVE_ARGS}; however, the data structure must exist and |
| should not be empty, so use @code{int}. |
| @end defmac |
| |
| @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args}) |
| A C statement (sans semicolon) for initializing the variable |
| @var{cum} for the state at the beginning of the argument list. The |
| variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} |
| is the tree node for the data type of the function which will receive |
| the args, or 0 if the args are to a compiler support library function. |
| For direct calls that are not libcalls, @var{fndecl} contain the |
| declaration node of the function. @var{fndecl} is also set when |
| @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function |
| being compiled. @var{n_named_args} is set to the number of named |
| arguments, including a structure return address if it is passed as a |
| parameter, when making a call. When processing incoming arguments, |
| @var{n_named_args} is set to @minus{}1. |
| |
| When processing a call to a compiler support library function, |
| @var{libname} identifies which one. It is a @code{symbol_ref} rtx which |
| contains the name of the function, as a string. @var{libname} is 0 when |
| an ordinary C function call is being processed. Thus, each time this |
| macro is called, either @var{libname} or @var{fntype} is nonzero, but |
| never both of them at once. |
| @end defmac |
| |
| @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) |
| Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, |
| it gets a @code{MODE} argument instead of @var{fntype}, that would be |
| @code{NULL}. @var{indirect} would always be zero, too. If this macro |
| is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, |
| 0)} is used instead. |
| @end defmac |
| |
| @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) |
| Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of |
| finding the arguments for the function being compiled. If this macro is |
| undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. |
| |
| The value passed for @var{libname} is always 0, since library routines |
| with special calling conventions are never compiled with GCC@. The |
| argument @var{libname} exists for symmetry with |
| @code{INIT_CUMULATIVE_ARGS}. |
| @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. |
| @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 |
| @end defmac |
| |
| @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) |
| A C statement (sans semicolon) to update the summarizer variable |
| @var{cum} to advance past an argument in the argument list. The |
| values @var{mode}, @var{type} and @var{named} describe that argument. |
| Once this is done, the variable @var{cum} is suitable for analyzing |
| the @emph{following} argument with @code{FUNCTION_ARG}, etc. |
| |
| This macro need not do anything if the argument in question was passed |
| on the stack. The compiler knows how to track the amount of stack space |
| used for arguments without any special help. |
| @end defmac |
| |
| @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type}) |
| If defined, a C expression which determines whether, and in which direction, |
| to pad out an argument with extra space. The value should be of type |
| @code{enum direction}: either @code{upward} to pad above the argument, |
| @code{downward} to pad below, or @code{none} to inhibit padding. |
| |
| The @emph{amount} of padding is always just enough to reach the next |
| multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control |
| it. |
| |
| This macro has a default definition which is right for most systems. |
| For little-endian machines, the default is to pad upward. For |
| big-endian machines, the default is to pad downward for an argument of |
| constant size shorter than an @code{int}, and upward otherwise. |
| @end defmac |
| |
| @defmac PAD_VARARGS_DOWN |
| If defined, a C expression which determines whether the default |
| implementation of va_arg will attempt to pad down before reading the |
| next argument, if that argument is smaller than its aligned space as |
| controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such |
| arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. |
| @end defmac |
| |
| @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first}) |
| Specify padding for the last element of a block move between registers and |
| memory. @var{first} is nonzero if this is the only element. Defining this |
| macro allows better control of register function parameters on big-endian |
| machines, without using @code{PARALLEL} rtl. In particular, |
| @code{MUST_PASS_IN_STACK} need not test padding and mode of types in |
| registers, as there is no longer a "wrong" part of a register; For example, |
| a three byte aggregate may be passed in the high part of a register if so |
| required. |
| @end defmac |
| |
| @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type}) |
| If defined, a C expression that gives the alignment boundary, in bits, |
| of an argument with the specified mode and type. If it is not defined, |
| @code{PARM_BOUNDARY} is used for all arguments. |
| @end defmac |
| |
| @defmac FUNCTION_ARG_REGNO_P (@var{regno}) |
| A C expression that is nonzero if @var{regno} is the number of a hard |
| register in which function arguments are sometimes passed. This does |
| @emph{not} include implicit arguments such as the static chain and |
| the structure-value address. On many machines, no registers can be |
| used for this purpose since all function arguments are pushed on the |
| stack. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (tree @var{type}) |
| This hook should return true if parameter of type @var{type} are passed |
| as two scalar parameters. By default, GCC will attempt to pack complex |
| arguments into the target's word size. Some ABIs require complex arguments |
| to be split and treated as their individual components. For example, on |
| AIX64, complex floats should be passed in a pair of floating point |
| registers, even though a complex float would fit in one 64-bit floating |
| point register. |
| |
| The default value of this hook is @code{NULL}, which is treated as always |
| false. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void) |
| This hook returns a type node for @code{va_list} for the target. |
| The default version of the hook returns @code{void*}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, tree *@var{pre_p}, tree *@var{post_p}) |
| This hook performs target-specific gimplification of |
| @code{VA_ARG_EXPR}. The first two parameters correspond to the |
| arguments to @code{va_arg}; the latter two are as in |
| @code{gimplify.c:gimplify_expr}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (enum machine_mode @var{mode}) |
| Define this to return nonzero if the port can handle pointers |
| with machine mode @var{mode}. The default version of this |
| hook returns true for both @code{ptr_mode} and @code{Pmode}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (enum machine_mode @var{mode}) |
| Define this to return nonzero if the port is prepared to handle |
| insns involving scalar mode @var{mode}. For a scalar mode to be |
| considered supported, all the basic arithmetic and comparisons |
| must work. |
| |
| The default version of this hook returns true for any mode |
| required to handle the basic C types (as defined by the port). |
| Included here are the double-word arithmetic supported by the |
| code in @file{optabs.c}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (enum machine_mode @var{mode}) |
| Define this to return nonzero if the port is prepared to handle |
| insns involving vector mode @var{mode}. At the very least, it |
| must have move patterns for this mode. |
| @end deftypefn |
| |
| @node Scalar Return |
| @subsection How Scalar Function Values Are Returned |
| @cindex return values in registers |
| @cindex values, returned by functions |
| @cindex scalars, returned as values |
| |
| This section discusses the macros that control returning scalars as |
| values---values that can fit in registers. |
| |
| @deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (tree @var{ret_type}, tree @var{fn_decl_or_type}, bool @var{outgoing}) |
| |
| Define this to return an RTX representing the place where a function |
| returns or receives a value of data type @var{ret_type}, a tree node |
| node representing a data type. @var{fn_decl_or_type} is a tree node |
| representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a |
| function being called. If @var{outgoing} is false, the hook should |
| compute the register in which the caller will see the return value. |
| Otherwise, the hook should return an RTX representing the place where |
| a function returns a value. |
| |
| On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant. |
| (Actually, on most machines, scalar values are returned in the same |
| place regardless of mode.) The value of the expression is usually a |
| @code{reg} RTX for the hard register where the return value is stored. |
| The value can also be a @code{parallel} RTX, if the return value is in |
| multiple places. See @code{FUNCTION_ARG} for an explanation of the |
| @code{parallel} form. |
| |
| If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply |
| the same promotion rules specified in @code{PROMOTE_MODE} if |
| @var{valtype} is a scalar type. |
| |
| If the precise function being called is known, @var{func} is a tree |
| node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null |
| pointer. This makes it possible to use a different value-returning |
| convention for specific functions when all their calls are |
| known. |
| |
| Some target machines have ``register windows'' so that the register in |
| which a function returns its value is not the same as the one in which |
| the caller sees the value. For such machines, you should return |
| different RTX depending on @var{outgoing}. |
| |
| @code{TARGET_FUNCTION_VALUE} is not used for return values with |
| aggregate data types, because these are returned in another way. See |
| @code{TARGET_STRUCT_VALUE_RTX} and related macros, below. |
| @end deftypefn |
| |
| @defmac FUNCTION_VALUE (@var{valtype}, @var{func}) |
| This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for |
| a new target instead. |
| @end defmac |
| |
| @defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func}) |
| This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for |
| a new target instead. |
| @end defmac |
| |
| @defmac LIBCALL_VALUE (@var{mode}) |
| A C expression to create an RTX representing the place where a library |
| function returns a value of mode @var{mode}. If the precise function |
| being called is known, @var{func} is a tree node |
| (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null |
| pointer. This makes it possible to use a different value-returning |
| convention for specific functions when all their calls are |
| known. |
| |
| Note that ``library function'' in this context means a compiler |
| support routine, used to perform arithmetic, whose name is known |
| specially by the compiler and was not mentioned in the C code being |
| compiled. |
| |
| The definition of @code{LIBRARY_VALUE} need not be concerned aggregate |
| data types, because none of the library functions returns such types. |
| @end defmac |
| |
| @defmac FUNCTION_VALUE_REGNO_P (@var{regno}) |
| A C expression that is nonzero if @var{regno} is the number of a hard |
| register in which the values of called function may come back. |
| |
| A register whose use for returning values is limited to serving as the |
| second of a pair (for a value of type @code{double}, say) need not be |
| recognized by this macro. So for most machines, this definition |
| suffices: |
| |
| @smallexample |
| #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) |
| @end smallexample |
| |
| If the machine has register windows, so that the caller and the called |
| function use different registers for the return value, this macro |
| should recognize only the caller's register numbers. |
| @end defmac |
| |
| @defmac APPLY_RESULT_SIZE |
| Define this macro if @samp{untyped_call} and @samp{untyped_return} |
| need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for |
| saving and restoring an arbitrary return value. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (tree @var{type}) |
| This hook should return true if values of type @var{type} are returned |
| at the most significant end of a register (in other words, if they are |
| padded at the least significant end). You can assume that @var{type} |
| is returned in a register; the caller is required to check this. |
| |
| Note that the register provided by @code{TARGET_FUNCTION_VALUE} must |
| be able to hold the complete return value. For example, if a 1-, 2- |
| or 3-byte structure is returned at the most significant end of a |
| 4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an |
| @code{SImode} rtx. |
| @end deftypefn |
| |
| @node Aggregate Return |
| @subsection How Large Values Are Returned |
| @cindex aggregates as return values |
| @cindex large return values |
| @cindex returning aggregate values |
| @cindex structure value address |
| |
| When a function value's mode is @code{BLKmode} (and in some other |
| cases), the value is not returned according to |
| @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the |
| caller passes the address of a block of memory in which the value |
| should be stored. This address is called the @dfn{structure value |
| address}. |
| |
| This section describes how to control returning structure values in |
| memory. |
| |
| @deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (tree @var{type}, tree @var{fntype}) |
| This target hook should return a nonzero value to say to return the |
| function value in memory, just as large structures are always returned. |
| Here @var{type} will be the data type of the value, and @var{fntype} |
| will be the type of the function doing the returning, or @code{NULL} for |
| libcalls. |
| |
| Note that values of mode @code{BLKmode} must be explicitly handled |
| by this function. Also, the option @option{-fpcc-struct-return} |
| takes effect regardless of this macro. On most systems, it is |
| possible to leave the hook undefined; this causes a default |
| definition to be used, whose value is the constant 1 for @code{BLKmode} |
| values, and 0 otherwise. |
| |
| Do not use this hook to indicate that structures and unions should always |
| be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} |
| to indicate this. |
| @end deftypefn |
| |
| @defmac DEFAULT_PCC_STRUCT_RETURN |
| Define this macro to be 1 if all structure and union return values must be |
| in memory. Since this results in slower code, this should be defined |
| only if needed for compatibility with other compilers or with an ABI@. |
| If you define this macro to be 0, then the conventions used for structure |
| and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY} |
| target hook. |
| |
| If not defined, this defaults to the value 1. |
| @end defmac |
| |
| @deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming}) |
| This target hook should return the location of the structure value |
| address (normally a @code{mem} or @code{reg}), or 0 if the address is |
| passed as an ``invisible'' first argument. Note that @var{fndecl} may |
| be @code{NULL}, for libcalls. You do not need to define this target |
| hook if the address is always passed as an ``invisible'' first |
| argument. |
| |
| On some architectures the place where the structure value address |
| is found by the called function is not the same place that the |
| caller put it. This can be due to register windows, or it could |
| be because the function prologue moves it to a different place. |
| @var{incoming} is @code{1} or @code{2} when the location is needed in |
| the context of the called function, and @code{0} in the context of |
| the caller. |
| |
| If @var{incoming} is nonzero and the address is to be found on the |
| stack, return a @code{mem} which refers to the frame pointer. If |
| @var{incoming} is @code{2}, the result is being used to fetch the |
| structure value address at the beginning of a function. If you need |
| to emit adjusting code, you should do it at this point. |
| @end deftypefn |
| |
| @defmac PCC_STATIC_STRUCT_RETURN |
| Define this macro if the usual system convention on the target machine |
| for returning structures and unions is for the called function to return |
| the address of a static variable containing the value. |
| |
| Do not define this if the usual system convention is for the caller to |
| pass an address to the subroutine. |
| |
| This macro has effect in @option{-fpcc-struct-return} mode, but it does |
| nothing when you use @option{-freg-struct-return} mode. |
| @end defmac |
| |
| @node Caller Saves |
| @subsection Caller-Saves Register Allocation |
| |
| If you enable it, GCC can save registers around function calls. This |
| makes it possible to use call-clobbered registers to hold variables that |
| must live across calls. |
| |
| @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) |
| A C expression to determine whether it is worthwhile to consider placing |
| a pseudo-register in a call-clobbered hard register and saving and |
| restoring it around each function call. The expression should be 1 when |
| this is worth doing, and 0 otherwise. |
| |
| If you don't define this macro, a default is used which is good on most |
| machines: @code{4 * @var{calls} < @var{refs}}. |
| @end defmac |
| |
| @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) |
| A C expression specifying which mode is required for saving @var{nregs} |
| of a pseudo-register in call-clobbered hard register @var{regno}. If |
| @var{regno} is unsuitable for caller save, @code{VOIDmode} should be |
| returned. For most machines this macro need not be defined since GCC |
| will select the smallest suitable mode. |
| @end defmac |
| |
| @node Function Entry |
| @subsection Function Entry and Exit |
| @cindex function entry and exit |
| @cindex prologue |
| @cindex epilogue |
| |
| This section describes the macros that output function entry |
| (@dfn{prologue}) and exit (@dfn{epilogue}) code. |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) |
| If defined, a function that outputs the assembler code for entry to a |
| function. The prologue is responsible for setting up the stack frame, |
| initializing the frame pointer register, saving registers that must be |
| saved, and allocating @var{size} additional bytes of storage for the |
| local variables. @var{size} is an integer. @var{file} is a stdio |
| stream to which the assembler code should be output. |
| |
| The label for the beginning of the function need not be output by this |
| macro. That has already been done when the macro is run. |
| |
| @findex regs_ever_live |
| To determine which registers to save, the macro can refer to the array |
| @code{regs_ever_live}: element @var{r} is nonzero if hard register |
| @var{r} is used anywhere within the function. This implies the function |
| prologue should save register @var{r}, provided it is not one of the |
| call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use |
| @code{regs_ever_live}.) |
| |
| On machines that have ``register windows'', the function entry code does |
| not save on the stack the registers that are in the windows, even if |
| they are supposed to be preserved by function calls; instead it takes |
| appropriate steps to ``push'' the register stack, if any non-call-used |
| registers are used in the function. |
| |
| @findex frame_pointer_needed |
| On machines where functions may or may not have frame-pointers, the |
| function entry code must vary accordingly; it must set up the frame |
| pointer if one is wanted, and not otherwise. To determine whether a |
| frame pointer is in wanted, the macro can refer to the variable |
| @code{frame_pointer_needed}. The variable's value will be 1 at run |
| time in a function that needs a frame pointer. @xref{Elimination}. |
| |
| The function entry code is responsible for allocating any stack space |
| required for the function. This stack space consists of the regions |
| listed below. In most cases, these regions are allocated in the |
| order listed, with the last listed region closest to the top of the |
| stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and |
| the highest address if it is not defined). You can use a different order |
| for a machine if doing so is more convenient or required for |
| compatibility reasons. Except in cases where required by standard |
| or by a debugger, there is no reason why the stack layout used by GCC |
| need agree with that used by other compilers for a machine. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) |
| If defined, a function that outputs assembler code at the end of a |
| prologue. This should be used when the function prologue is being |
| emitted as RTL, and you have some extra assembler that needs to be |
| emitted. @xref{prologue instruction pattern}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) |
| If defined, a function that outputs assembler code at the start of an |
| epilogue. This should be used when the function epilogue is being |
| emitted as RTL, and you have some extra assembler that needs to be |
| emitted. @xref{epilogue instruction pattern}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) |
| If defined, a function that outputs the assembler code for exit from a |
| function. The epilogue is responsible for restoring the saved |
| registers and stack pointer to their values when the function was |
| called, and returning control to the caller. This macro takes the |
| same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the |
| registers to restore are determined from @code{regs_ever_live} and |
| @code{CALL_USED_REGISTERS} in the same way. |
| |
| On some machines, there is a single instruction that does all the work |
| of returning from the function. On these machines, give that |
| instruction the name @samp{return} and do not define the macro |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} at all. |
| |
| Do not define a pattern named @samp{return} if you want the |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target |
| switches to control whether return instructions or epilogues are used, |
| define a @samp{return} pattern with a validity condition that tests the |
| target switches appropriately. If the @samp{return} pattern's validity |
| condition is false, epilogues will be used. |
| |
| On machines where functions may or may not have frame-pointers, the |
| function exit code must vary accordingly. Sometimes the code for these |
| two cases is completely different. To determine whether a frame pointer |
| is wanted, the macro can refer to the variable |
| @code{frame_pointer_needed}. The variable's value will be 1 when compiling |
| a function that needs a frame pointer. |
| |
| Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. |
| The C variable @code{current_function_is_leaf} is nonzero for such a |
| function. @xref{Leaf Functions}. |
| |
| On some machines, some functions pop their arguments on exit while |
| others leave that for the caller to do. For example, the 68020 when |
| given @option{-mrtd} pops arguments in functions that take a fixed |
| number of arguments. |
| |
| @findex current_function_pops_args |
| Your definition of the macro @code{RETURN_POPS_ARGS} decides which |
| functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} |
| needs to know what was decided. The variable that is called |
| @code{current_function_pops_args} is the number of bytes of its |
| arguments that a function should pop. @xref{Scalar Return}. |
| @c what is the "its arguments" in the above sentence referring to, pray |
| @c tell? --mew 5feb93 |
| @end deftypefn |
| |
| @itemize @bullet |
| @item |
| @findex current_function_pretend_args_size |
| A region of @code{current_function_pretend_args_size} bytes of |
| uninitialized space just underneath the first argument arriving on the |
| stack. (This may not be at the very start of the allocated stack region |
| if the calling sequence has pushed anything else since pushing the stack |
| arguments. But usually, on such machines, nothing else has been pushed |
| yet, because the function prologue itself does all the pushing.) This |
| region is used on machines where an argument may be passed partly in |
| registers and partly in memory, and, in some cases to support the |
| features in @code{<stdarg.h>}. |
| |
| @item |
| An area of memory used to save certain registers used by the function. |
| The size of this area, which may also include space for such things as |
| the return address and pointers to previous stack frames, is |
| machine-specific and usually depends on which registers have been used |
| in the function. Machines with register windows often do not require |
| a save area. |
| |
| @item |
| A region of at least @var{size} bytes, possibly rounded up to an allocation |
| boundary, to contain the local variables of the function. On some machines, |
| this region and the save area may occur in the opposite order, with the |
| save area closer to the top of the stack. |
| |
| @item |
| @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames |
| Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of |
| @code{current_function_outgoing_args_size} bytes to be used for outgoing |
| argument lists of the function. @xref{Stack Arguments}. |
| @end itemize |
| |
| @defmac EXIT_IGNORE_STACK |
| Define this macro as a C expression that is nonzero if the return |
| instruction or the function epilogue ignores the value of the stack |
| pointer; in other words, if it is safe to delete an instruction to |
| adjust the stack pointer before a return from the function. The |
| default is 0. |
| |
| Note that this macro's value is relevant only for functions for which |
| frame pointers are maintained. It is never safe to delete a final |
| stack adjustment in a function that has no frame pointer, and the |
| compiler knows this regardless of @code{EXIT_IGNORE_STACK}. |
| @end defmac |
| |
| @defmac EPILOGUE_USES (@var{regno}) |
| Define this macro as a C expression that is nonzero for registers that are |
| used by the epilogue or the @samp{return} pattern. The stack and frame |
| pointer registers are already assumed to be used as needed. |
| @end defmac |
| |
| @defmac EH_USES (@var{regno}) |
| Define this macro as a C expression that is nonzero for registers that are |
| used by the exception handling mechanism, and so should be considered live |
| on entry to an exception edge. |
| @end defmac |
| |
| @defmac DELAY_SLOTS_FOR_EPILOGUE |
| Define this macro if the function epilogue contains delay slots to which |
| instructions from the rest of the function can be ``moved''. The |
| definition should be a C expression whose value is an integer |
| representing the number of delay slots there. |
| @end defmac |
| |
| @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) |
| A C expression that returns 1 if @var{insn} can be placed in delay |
| slot number @var{n} of the epilogue. |
| |
| The argument @var{n} is an integer which identifies the delay slot now |
| being considered (since different slots may have different rules of |
| eligibility). It is never negative and is always less than the number |
| of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). |
| If you reject a particular insn for a given delay slot, in principle, it |
| may be reconsidered for a subsequent delay slot. Also, other insns may |
| (at least in principle) be considered for the so far unfilled delay |
| slot. |
| |
| @findex current_function_epilogue_delay_list |
| @findex final_scan_insn |
| The insns accepted to fill the epilogue delay slots are put in an RTL |
| list made with @code{insn_list} objects, stored in the variable |
| @code{current_function_epilogue_delay_list}. The insn for the first |
| delay slot comes first in the list. Your definition of the macro |
| @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by |
| outputting the insns in this list, usually by calling |
| @code{final_scan_insn}. |
| |
| You need not define this macro if you did not define |
| @code{DELAY_SLOTS_FOR_EPILOGUE}. |
| @end defmac |
| |
| @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}) |
| A function that outputs the assembler code for a thunk |
| function, used to implement C++ virtual function calls with multiple |
| inheritance. The thunk acts as a wrapper around a virtual function, |
| adjusting the implicit object parameter before handing control off to |
| the real function. |
| |
| First, emit code to add the integer @var{delta} to the location that |
| contains the incoming first argument. Assume that this argument |
| contains a pointer, and is the one used to pass the @code{this} pointer |
| in C++. This is the incoming argument @emph{before} the function prologue, |
| e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of |
| all other incoming arguments. |
| |
| Then, if @var{vcall_offset} is nonzero, an additional adjustment should be |
| made after adding @code{delta}. In particular, if @var{p} is the |
| adjusted pointer, the following adjustment should be made: |
| |
| @smallexample |
| p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)] |
| @end smallexample |
| |
| After the additions, emit code to jump to @var{function}, which is a |
| @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does |
| not touch the return address. Hence returning from @var{FUNCTION} will |
| return to whoever called the current @samp{thunk}. |
| |
| The effect must be as if @var{function} had been called directly with |
| the adjusted first argument. This macro is responsible for emitting all |
| of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} |
| and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. |
| |
| The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} |
| have already been extracted from it.) It might possibly be useful on |
| some targets, but probably not. |
| |
| If you do not define this macro, the target-independent code in the C++ |
| front end will generate a less efficient heavyweight thunk that calls |
| @var{function} instead of jumping to it. The generic approach does |
| not support varargs. |
| @end deftypefn |
| |
| @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}) |
| A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able |
| to output the assembler code for the thunk function specified by the |
| arguments it is passed, and false otherwise. In the latter case, the |
| generic approach will be used by the C++ front end, with the limitations |
| previously exposed. |
| @end deftypefn |
| |
| @node Profiling |
| @subsection Generating Code for Profiling |
| @cindex profiling, code generation |
| |
| These macros will help you generate code for profiling. |
| |
| @defmac FUNCTION_PROFILER (@var{file}, @var{labelno}) |
| A C statement or compound statement to output to @var{file} some |
| assembler code to call the profiling subroutine @code{mcount}. |
| |
| @findex mcount |
| The details of how @code{mcount} expects to be called are determined by |
| your operating system environment, not by GCC@. To figure them out, |
| compile a small program for profiling using the system's installed C |
| compiler and look at the assembler code that results. |
| |
| Older implementations of @code{mcount} expect the address of a counter |
| variable to be loaded into some register. The name of this variable is |
| @samp{LP} followed by the number @var{labelno}, so you would generate |
| the name using @samp{LP%d} in a @code{fprintf}. |
| @end defmac |
| |
| @defmac PROFILE_HOOK |
| A C statement or compound statement to output to @var{file} some assembly |
| code to call the profiling subroutine @code{mcount} even the target does |
| not support profiling. |
| @end defmac |
| |
| @defmac NO_PROFILE_COUNTERS |
| Define this macro to be an expression with a nonzero value if the |
| @code{mcount} subroutine on your system does not need a counter variable |
| allocated for each function. This is true for almost all modern |
| implementations. If you define this macro, you must not use the |
| @var{labelno} argument to @code{FUNCTION_PROFILER}. |
| @end defmac |
| |
| @defmac PROFILE_BEFORE_PROLOGUE |
| Define this macro if the code for function profiling should come before |
| the function prologue. Normally, the profiling code comes after. |
| @end defmac |
| |
| @node Tail Calls |
| @subsection Permitting tail calls |
| @cindex tail calls |
| |
| @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp}) |
| True if it is ok to do sibling call optimization for the specified |
| call expression @var{exp}. @var{decl} will be the called function, |
| or @code{NULL} if this is an indirect call. |
| |
| It is not uncommon for limitations of calling conventions to prevent |
| tail calls to functions outside the current unit of translation, or |
| during PIC compilation. The hook is used to enforce these restrictions, |
| as the @code{sibcall} md pattern can not fail, or fall over to a |
| ``normal'' call. The criteria for successful sibling call optimization |
| may vary greatly between different architectures. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap *@var{regs}) |
| Add any hard registers to @var{regs} that are live on entry to the |
| function. This hook only needs to be defined to provide registers that |
| cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved |
| registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM, |
| TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES, |
| FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM. |
| @end deftypefn |
| |
| @node Stack Smashing Protection |
| @subsection Stack smashing protection |
| @cindex stack smashing protection |
| |
| @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void) |
| This hook returns a @code{DECL} node for the external variable to use |
| for the stack protection guard. This variable is initialized by the |
| runtime to some random value and is used to initialize the guard value |
| that is placed at the top of the local stack frame. The type of this |
| variable must be @code{ptr_type_node}. |
| |
| The default version of this hook creates a variable called |
| @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void) |
| This hook returns a tree expression that alerts the runtime that the |
| stack protect guard variable has been modified. This expression should |
| involve a call to a @code{noreturn} function. |
| |
| The default version of this hook invokes a function called |
| @samp{__stack_chk_fail}, taking no arguments. This function is |
| normally defined in @file{libgcc2.c}. |
| @end deftypefn |
| |
| @node Varargs |
| @section Implementing the Varargs Macros |
| @cindex varargs implementation |
| |
| GCC comes with an implementation of @code{<varargs.h>} and |
| @code{<stdarg.h>} that work without change on machines that pass arguments |
| on the stack. Other machines require their own implementations of |
| varargs, and the two machine independent header files must have |
| conditionals to include it. |
| |
| ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in |
| the calling convention for @code{va_start}. The traditional |
| implementation takes just one argument, which is the variable in which |
| to store the argument pointer. The ISO implementation of |
| @code{va_start} takes an additional second argument. The user is |
| supposed to write the last named argument of the function here. |
| |
| However, @code{va_start} should not use this argument. The way to find |
| the end of the named arguments is with the built-in functions described |
| below. |
| |
| @defmac __builtin_saveregs () |
| Use this built-in function to save the argument registers in memory so |
| that the varargs mechanism can access them. Both ISO and traditional |
| versions of @code{va_start} must use @code{__builtin_saveregs}, unless |
| you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead. |
| |
| On some machines, @code{__builtin_saveregs} is open-coded under the |
| control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On |
| other machines, it calls a routine written in assembler language, |
| found in @file{libgcc2.c}. |
| |
| Code generated for the call to @code{__builtin_saveregs} appears at the |
| beginning of the function, as opposed to where the call to |
| @code{__builtin_saveregs} is written, regardless of what the code is. |
| This is because the registers must be saved before the function starts |
| to use them for its own purposes. |
| @c i rewrote the first sentence above to fix an overfull hbox. --mew |
| @c 10feb93 |
| @end defmac |
| |
| @defmac __builtin_args_info (@var{category}) |
| Use this built-in function to find the first anonymous arguments in |
| registers. |
| |
| In general, a machine may have several categories of registers used for |
| arguments, each for a particular category of data types. (For example, |
| on some machines, floating-point registers are used for floating-point |
| arguments while other arguments are passed in the general registers.) |
| To make non-varargs functions use the proper calling convention, you |
| have defined the @code{CUMULATIVE_ARGS} data type to record how many |
| registers in each category have been used so far |
| |
| @code{__builtin_args_info} accesses the same data structure of type |
| @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished |
| with it, with @var{category} specifying which word to access. Thus, the |
| value indicates the first unused register in a given category. |
| |
| Normally, you would use @code{__builtin_args_info} in the implementation |
| of @code{va_start}, accessing each category just once and storing the |
| value in the @code{va_list} object. This is because @code{va_list} will |
| have to update the values, and there is no way to alter the |
| values accessed by @code{__builtin_args_info}. |
| @end defmac |
| |
| @defmac __builtin_next_arg (@var{lastarg}) |
| This is the equivalent of @code{__builtin_args_info}, for stack |
| arguments. It returns the address of the first anonymous stack |
| argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it |
| returns the address of the location above the first anonymous stack |
| argument. Use it in @code{va_start} to initialize the pointer for |
| fetching arguments from the stack. Also use it in @code{va_start} to |
| verify that the second parameter @var{lastarg} is the last named argument |
| of the current function. |
| @end defmac |
| |
| @defmac __builtin_classify_type (@var{object}) |
| Since each machine has its own conventions for which data types are |
| passed in which kind of register, your implementation of @code{va_arg} |
| has to embody these conventions. The easiest way to categorize the |
| specified data type is to use @code{__builtin_classify_type} together |
| with @code{sizeof} and @code{__alignof__}. |
| |
| @code{__builtin_classify_type} ignores the value of @var{object}, |
| considering only its data type. It returns an integer describing what |
| kind of type that is---integer, floating, pointer, structure, and so on. |
| |
| The file @file{typeclass.h} defines an enumeration that you can use to |
| interpret the values of @code{__builtin_classify_type}. |
| @end defmac |
| |
| These machine description macros help implement varargs: |
| |
| @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void) |
| If defined, this hook produces the machine-specific code for a call to |
| @code{__builtin_saveregs}. This code will be moved to the very |
| beginning of the function, before any parameter access are made. The |
| return value of this function should be an RTX that contains the value |
| to use as the return of @code{__builtin_saveregs}. |
| @end deftypefn |
| |
| @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}) |
| This target hook offers an alternative to using |
| @code{__builtin_saveregs} and defining the hook |
| @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous |
| register arguments into the stack so that all the arguments appear to |
| have been passed consecutively on the stack. Once this is done, you can |
| use the standard implementation of varargs that works for machines that |
| pass all their arguments on the stack. |
| |
| The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data |
| structure, containing the values that are obtained after processing the |
| named arguments. The arguments @var{mode} and @var{type} describe the |
| last named argument---its machine mode and its data type as a tree node. |
| |
| The target hook should do two things: first, push onto the stack all the |
| argument registers @emph{not} used for the named arguments, and second, |
| store the size of the data thus pushed into the @code{int}-valued |
| variable pointed to by @var{pretend_args_size}. The value that you |
| store here will serve as additional offset for setting up the stack |
| frame. |
| |
| Because you must generate code to push the anonymous arguments at |
| compile time without knowing their data types, |
| @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that |
| have just a single category of argument register and use it uniformly |
| for all data types. |
| |
| If the argument @var{second_time} is nonzero, it means that the |
| arguments of the function are being analyzed for the second time. This |
| happens for an inline function, which is not actually compiled until the |
| end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should |
| not generate any instructions in this case. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca}) |
| Define this hook to return @code{true} if the location where a function |
| argument is passed depends on whether or not it is a named argument. |
| |
| This hook controls how the @var{named} argument to @code{FUNCTION_ARG} |
| is set for varargs and stdarg functions. If this hook returns |
| @code{true}, the @var{named} argument is always true for named |
| arguments, and false for unnamed arguments. If it returns @code{false}, |
| but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true}, |
| then all arguments are treated as named. Otherwise, all named arguments |
| except the last are treated as named. |
| |
| You need not define this hook if it always returns zero. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED |
| If you need to conditionally change ABIs so that one works with |
| @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither |
| @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was |
| defined, then define this hook to return @code{true} if |
| @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise. |
| Otherwise, you should not define this hook. |
| @end deftypefn |
| |
| @node Trampolines |
| @section Trampolines for Nested Functions |
| @cindex trampolines for nested functions |
| @cindex nested functions, trampolines for |
| |
| A @dfn{trampoline} is a small piece of code that is created at run time |
| when the address of a nested function is taken. It normally resides on |
| the stack, in the stack frame of the containing function. These macros |
| tell GCC how to generate code to allocate and initialize a |
| trampoline. |
| |
| The instructions in the trampoline must do two things: load a constant |
| address into the static chain register, and jump to the real address of |
| the nested function. On CISC machines such as the m68k, this requires |
| two instructions, a move immediate and a jump. Then the two addresses |
| exist in the trampoline as word-long immediate operands. On RISC |
| machines, it is often necessary to load each address into a register in |
| two parts. Then pieces of each address form separate immediate |
| operands. |
| |
| The code generated to initialize the trampoline must store the variable |
| parts---the static chain value and the function address---into the |
| immediate operands of the instructions. On a CISC machine, this is |
| simply a matter of copying each address to a memory reference at the |
| proper offset from the start of the trampoline. On a RISC machine, it |
| may be necessary to take out pieces of the address and store them |
| separately. |
| |
| @defmac TRAMPOLINE_TEMPLATE (@var{file}) |
| A C statement to output, on the stream @var{file}, assembler code for a |
| block of data that contains the constant parts of a trampoline. This |
| code should not include a label---the label is taken care of |
| automatically. |
| |
| If you do not define this macro, it means no template is needed |
| for the target. Do not define this macro on systems where the block move |
| code to copy the trampoline into place would be larger than the code |
| to generate it on the spot. |
| @end defmac |
| |
| @defmac TRAMPOLINE_SECTION |
| Return the section into which the trampoline template is to be placed |
| (@pxref{Sections}). The default value is @code{readonly_data_section}. |
| @end defmac |
| |
| @defmac TRAMPOLINE_SIZE |
| A C expression for the size in bytes of the trampoline, as an integer. |
| @end defmac |
| |
| @defmac TRAMPOLINE_ALIGNMENT |
| Alignment required for trampolines, in bits. |
| |
| If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT} |
| is used for aligning trampolines. |
| @end defmac |
| |
| @defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain}) |
| A C statement to initialize the variable parts of a trampoline. |
| @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is |
| an RTX for the address of the nested function; @var{static_chain} is an |
| RTX for the static chain value that should be passed to the function |
| when it is called. |
| @end defmac |
| |
| @defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr}) |
| A C statement that should perform any machine-specific adjustment in |
| the address of the trampoline. Its argument contains the address that |
| was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be |
| used for a function call should be different from the address in which |
| the template was stored, the different address should be assigned to |
| @var{addr}. If this macro is not defined, @var{addr} will be used for |
| function calls. |
| |
| @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines |
| @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines |
| If this macro is not defined, by default the trampoline is allocated as |
| a stack slot. This default is right for most machines. The exceptions |
| are machines where it is impossible to execute instructions in the stack |
| area. On such machines, you may have to implement a separate stack, |
| using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE} |
| and @code{TARGET_ASM_FUNCTION_EPILOGUE}. |
| |
| @var{fp} points to a data structure, a @code{struct function}, which |
| describes the compilation status of the immediate containing function of |
| the function which the trampoline is for. The stack slot for the |
| trampoline is in the stack frame of this containing function. Other |
| allocation strategies probably must do something analogous with this |
| information. |
| @end defmac |
| |
| Implementing trampolines is difficult on many machines because they have |
| separate instruction and data caches. Writing into a stack location |
| fails to clear the memory in the instruction cache, so when the program |
| jumps to that location, it executes the old contents. |
| |
| Here are two possible solutions. One is to clear the relevant parts of |
| the instruction cache whenever a trampoline is set up. The other is to |
| make all trampolines identical, by having them jump to a standard |
| subroutine. The former technique makes trampoline execution faster; the |
| latter makes initialization faster. |
| |
| To clear the instruction cache when a trampoline is initialized, define |
| the following macro. |
| |
| @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end}) |
| If defined, expands to a C expression clearing the @emph{instruction |
| cache} in the specified interval. The definition of this macro would |
| typically be a series of @code{asm} statements. Both @var{beg} and |
| @var{end} are both pointer expressions. |
| @end defmac |
| |
| The operating system may also require the stack to be made executable |
| before calling the trampoline. To implement this requirement, define |
| the following macro. |
| |
| @defmac ENABLE_EXECUTE_STACK |
| Define this macro if certain operations must be performed before executing |
| code located on the stack. The macro should expand to a series of C |
| file-scope constructs (e.g.@: functions) and provide a unique entry point |
| named @code{__enable_execute_stack}. The target is responsible for |
| emitting calls to the entry point in the code, for example from the |
| @code{INITIALIZE_TRAMPOLINE} macro. |
| @end defmac |
| |
| To use a standard subroutine, define the following macro. In addition, |
| you must make sure that the instructions in a trampoline fill an entire |
| cache line with identical instructions, or else ensure that the |
| beginning of the trampoline code is always aligned at the same point in |
| its cache line. Look in @file{m68k.h} as a guide. |
| |
| @defmac TRANSFER_FROM_TRAMPOLINE |
| Define this macro if trampolines need a special subroutine to do their |
| work. The macro should expand to a series of @code{asm} statements |
| which will be compiled with GCC@. They go in a library function named |
| @code{__transfer_from_trampoline}. |
| |
| If you need to avoid executing the ordinary prologue code of a compiled |
| C function when you jump to the subroutine, you can do so by placing a |
| special label of your own in the assembler code. Use one @code{asm} |
| statement to generate an assembler label, and another to make the label |
| global. Then trampolines can use that label to jump directly to your |
| special assembler code. |
| @end defmac |
| |
| @node Library Calls |
| @section Implicit Calls to Library Routines |
| @cindex library subroutine names |
| @cindex @file{libgcc.a} |
| |
| @c prevent bad page break with this line |
| Here is an explanation of implicit calls to library routines. |
| |
| @defmac DECLARE_LIBRARY_RENAMES |
| This macro, if defined, should expand to a piece of C code that will get |
| expanded when compiling functions for libgcc.a. It can be used to |
| provide alternate names for GCC's internal library functions if there |
| are ABI-mandated names that the compiler should provide. |
| @end defmac |
| |
| @findex init_one_libfunc |
| @findex set_optab_libfunc |
| @deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void) |
| This hook should declare additional library routines or rename |
| existing ones, using the functions @code{set_optab_libfunc} and |
| @code{init_one_libfunc} defined in @file{optabs.c}. |
| @code{init_optabs} calls this macro after initializing all the normal |
| library routines. |
| |
| The default is to do nothing. Most ports don't need to define this hook. |
| @end deftypefn |
| |
| @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) |
| This macro should return @code{true} if the library routine that |
| implements the floating point comparison operator @var{comparison} in |
| mode @var{mode} will return a boolean, and @var{false} if it will |
| return a tristate. |
| |
| GCC's own floating point libraries return tristates from the |
| comparison operators, so the default returns false always. Most ports |
| don't need to define this macro. |
| @end defmac |
| |
| @defmac TARGET_LIB_INT_CMP_BIASED |
| This macro should evaluate to @code{true} if the integer comparison |
| functions (like @code{__cmpdi2}) return 0 to indicate that the first |
| operand is smaller than the second, 1 to indicate that they are equal, |
| and 2 to indicate that the first operand is greater than the second. |
| If this macro evaluates to @code{false} the comparison functions return |
| @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines |
| in @file{libgcc.a}, you do not need to define this macro. |
| @end defmac |
| |
| @cindex US Software GOFAST, floating point emulation library |
| @cindex floating point emulation library, US Software GOFAST |
| @cindex GOFAST, floating point emulation library |
| @findex gofast_maybe_init_libfuncs |
| @defmac US_SOFTWARE_GOFAST |
| Define this macro if your system C library uses the US Software GOFAST |
| library to provide floating point emulation. |
| |
| In addition to defining this macro, your architecture must set |
| @code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or |
| else call that function from its version of that hook. It is defined |
| in @file{config/gofast.h}, which must be included by your |
| architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for |
| an example. |
| |
| If this macro is defined, the |
| @code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return |
| false for @code{SFmode} and @code{DFmode} comparisons. |
| @end defmac |
| |
| @cindex @code{EDOM}, implicit usage |
| @findex matherr |
| @defmac TARGET_EDOM |
| The value of @code{EDOM} on the target machine, as a C integer constant |
| expression. If you don't define this macro, GCC does not attempt to |
| deposit the value of @code{EDOM} into @code{errno} directly. Look in |
| @file{/usr/include/errno.h} to find the value of @code{EDOM} on your |
| system. |
| |
| If you do not define @code{TARGET_EDOM}, then compiled code reports |
| domain errors by calling the library function and letting it report the |
| error. If mathematical functions on your system use @code{matherr} when |
| there is an error, then you should leave @code{TARGET_EDOM} undefined so |
| that @code{matherr} is used normally. |
| @end defmac |
| |
| @cindex @code{errno}, implicit usage |
| @defmac GEN_ERRNO_RTX |
| Define this macro as a C expression to create an rtl expression that |
| refers to the global ``variable'' @code{errno}. (On certain systems, |
| @code{errno} may not actually be a variable.) If you don't define this |
| macro, a reasonable default is used. |
| @end defmac |
| |
| @cindex C99 math functions, implicit usage |
| @defmac TARGET_C99_FUNCTIONS |
| When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into |
| @code{sinf} and similarly for other functions defined by C99 standard. The |
| default is nonzero that should be proper value for most modern systems, however |
| number of existing systems lacks support for these functions in the runtime so |
| they needs this macro to be redefined to 0. |
| @end defmac |
| |
| @defmac NEXT_OBJC_RUNTIME |
| Define this macro to generate code for Objective-C message sending using |
| the calling convention of the NeXT system. This calling convention |
| involves passing the object, the selector and the method arguments all |
| at once to the method-lookup library function. |
| |
| The default calling convention passes just the object and the selector |
| to the lookup function, which returns a pointer to the method. |
| @end defmac |
| |
| @node Addressing Modes |
| @section Addressing Modes |
| @cindex addressing modes |
| |
| @c prevent bad page break with this line |
| This is about addressing modes. |
| |
| @defmac HAVE_PRE_INCREMENT |
| @defmacx HAVE_PRE_DECREMENT |
| @defmacx HAVE_POST_INCREMENT |
| @defmacx HAVE_POST_DECREMENT |
| A C expression that is nonzero if the machine supports pre-increment, |
| pre-decrement, post-increment, or post-decrement addressing respectively. |
| @end defmac |
| |
| @defmac HAVE_PRE_MODIFY_DISP |
| @defmacx HAVE_POST_MODIFY_DISP |
| A C expression that is nonzero if the machine supports pre- or |
| post-address side-effect generation involving constants other than |
| the size of the memory operand. |
| @end defmac |
| |
| @defmac HAVE_PRE_MODIFY_REG |
| @defmacx HAVE_POST_MODIFY_REG |
| A C expression that is nonzero if the machine supports pre- or |
| post-address side-effect generation involving a register displacement. |
| @end defmac |
| |
| @defmac CONSTANT_ADDRESS_P (@var{x}) |
| A C expression that is 1 if the RTX @var{x} is a constant which |
| is a valid address. On most machines, this can be defined as |
| @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive |
| in which constant addresses are supported. |
| @end defmac |
| |
| @defmac CONSTANT_P (@var{x}) |
| @code{CONSTANT_P}, which is defined by target-independent code, |
| accepts integer-values expressions whose values are not explicitly |
| known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} |
| expressions and @code{const} arithmetic expressions, in addition to |
| @code{const_int} and @code{const_double} expressions. |
| @end defmac |
| |
| @defmac MAX_REGS_PER_ADDRESS |
| A number, the maximum number of registers that can appear in a valid |
| memory address. Note that it is up to you to specify a value equal to |
| the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever |
| accept. |
| @end defmac |
| |
| @defmac GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) |
| A C compound statement with a conditional @code{goto @var{label};} |
| executed if @var{x} (an RTX) is a legitimate memory address on the |
| target machine for a memory operand of mode @var{mode}. |
| |
| It usually pays to define several simpler macros to serve as |
| subroutines for this one. Otherwise it may be too complicated to |
| understand. |
| |
| This macro must exist in two variants: a strict variant and a |
| non-strict one. The strict variant is used in the reload pass. It |
| must be defined so that any pseudo-register that has not been |
| allocated a hard register is considered a memory reference. In |
| contexts where some kind of register is required, a pseudo-register |
| with no hard register must be rejected. |
| |
| The non-strict variant is used in other passes. It must be defined to |
| accept all pseudo-registers in every context where some kind of |
| register is required. |
| |
| @findex REG_OK_STRICT |
| Compiler source files that want to use the strict variant of this |
| macro define the macro @code{REG_OK_STRICT}. You should use an |
| @code{#ifdef REG_OK_STRICT} conditional to define the strict variant |
| in that case and the non-strict variant otherwise. |
| |
| Subroutines to check for acceptable registers for various purposes (one |
| for base registers, one for index registers, and so on) are typically |
| among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}. |
| Then only these subroutine macros need have two variants; the higher |
| levels of macros may be the same whether strict or not. |
| |
| Normally, constant addresses which are the sum of a @code{symbol_ref} |
| and an integer are stored inside a @code{const} RTX to mark them as |
| constant. Therefore, there is no need to recognize such sums |
| specifically as legitimate addresses. Normally you would simply |
| recognize any @code{const} as legitimate. |
| |
| Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant |
| sums that are not marked with @code{const}. It assumes that a naked |
| @code{plus} indicates indexing. If so, then you @emph{must} reject such |
| naked constant sums as illegitimate addresses, so that none of them will |
| be given to @code{PRINT_OPERAND_ADDRESS}. |
| |
| @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation |
| On some machines, whether a symbolic address is legitimate depends on |
| the section that the address refers to. On these machines, define the |
| target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information |
| into the @code{symbol_ref}, and then check for it here. When you see a |
| @code{const}, you will have to look inside it to find the |
| @code{symbol_ref} in order to determine the section. @xref{Assembler |
| Format}. |
| @end defmac |
| |
| @defmac FIND_BASE_TERM (@var{x}) |
| A C expression to determine the base term of address @var{x}. |
| This macro is used in only one place: `find_base_term' in alias.c. |
| |
| It is always safe for this macro to not be defined. It exists so |
| that alias analysis can understand machine-dependent addresses. |
| |
| The typical use of this macro is to handle addresses containing |
| a label_ref or symbol_ref within an UNSPEC@. |
| @end defmac |
| |
| @defmac LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win}) |
| A C compound statement that attempts to replace @var{x} with a valid |
| memory address for an operand of mode @var{mode}. @var{win} will be a |
| C statement label elsewhere in the code; the macro definition may use |
| |
| @smallexample |
| GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win}); |
| @end smallexample |
| |
| @noindent |
| to avoid further processing if the address has become legitimate. |
| |
| @findex break_out_memory_refs |
| @var{x} will always be the result of a call to @code{break_out_memory_refs}, |
| and @var{oldx} will be the operand that was given to that function to produce |
| @var{x}. |
| |
| The code generated by this macro should not alter the substructure of |
| @var{x}. If it transforms @var{x} into a more legitimate form, it |
| should assign @var{x} (which will always be a C variable) a new value. |
| |
| It is not necessary for this macro to come up with a legitimate |
| address. The compiler has standard ways of doing so in all cases. In |
| fact, it is safe to omit this macro. But often a |
| machine-dependent strategy can generate better code. |
| @end defmac |
| |
| @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) |
| A C compound statement that attempts to replace @var{x}, which is an address |
| that needs reloading, with a valid memory address for an operand of mode |
| @var{mode}. @var{win} will be a C statement label elsewhere in the code. |
| It is not necessary to define this macro, but it might be useful for |
| performance reasons. |
| |
| For example, on the i386, it is sometimes possible to use a single |
| reload register instead of two by reloading a sum of two pseudo |
| registers into a register. On the other hand, for number of RISC |
| processors offsets are limited so that often an intermediate address |
| needs to be generated in order to address a stack slot. By defining |
| @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses |
| generated for adjacent some stack slots can be made identical, and thus |
| be shared. |
| |
| @emph{Note}: This macro should be used with caution. It is necessary |
| to know something of how reload works in order to effectively use this, |
| and it is quite easy to produce macros that build in too much knowledge |
| of reload internals. |
| |
| @emph{Note}: This macro must be able to reload an address created by a |
| previous invocation of this macro. If it fails to handle such addresses |
| then the compiler may generate incorrect code or abort. |
| |
| @findex push_reload |
| The macro definition should use @code{push_reload} to indicate parts that |
| need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually |
| suitable to be passed unaltered to @code{push_reload}. |
| |
| The code generated by this macro must not alter the substructure of |
| @var{x}. If it transforms @var{x} into a more legitimate form, it |
| should assign @var{x} (which will always be a C variable) a new value. |
| This also applies to parts that you change indirectly by calling |
| @code{push_reload}. |
| |
| @findex strict_memory_address_p |
| The macro definition may use @code{strict_memory_address_p} to test if |
| the address has become legitimate. |
| |
| @findex copy_rtx |
| If you want to change only a part of @var{x}, one standard way of doing |
| this is to use @code{copy_rtx}. Note, however, that is unshares only a |
| single level of rtl. Thus, if the part to be changed is not at the |
| top level, you'll need to replace first the top level. |
| It is not necessary for this macro to come up with a legitimate |
| address; but often a machine-dependent strategy can generate better code. |
| @end defmac |
| |
| @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) |
| A C statement or compound statement with a conditional @code{goto |
| @var{label};} executed if memory address @var{x} (an RTX) can have |
| different meanings depending on the machine mode of the memory |
| reference it is used for or if the address is valid for some modes |
| but not others. |
| |
| Autoincrement and autodecrement addresses typically have mode-dependent |
| effects because the amount of the increment or decrement is the size |
| of the operand being addressed. Some machines have other mode-dependent |
| addresses. Many RISC machines have no mode-dependent addresses. |
| |
| You may assume that @var{addr} is a valid address for the machine. |
| @end defmac |
| |
| @defmac LEGITIMATE_CONSTANT_P (@var{x}) |
| A C expression that is nonzero if @var{x} is a legitimate constant for |
| an immediate operand on the target machine. You can assume that |
| @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, |
| @samp{1} is a suitable definition for this macro on machines where |
| anything @code{CONSTANT_P} is valid. |
| @end defmac |
| |
| @deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x}) |
| This hook is used to undo the possibly obfuscating effects of the |
| @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target |
| macros. Some backend implementations of these macros wrap symbol |
| references inside an @code{UNSPEC} rtx to represent PIC or similar |
| addressing modes. This target hook allows GCC's optimizers to understand |
| the semantics of these opaque @code{UNSPEC}s by converting them back |
| into their original form. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (rtx @var{x}) |
| This hook should return true if @var{x} is of a form that cannot (or |
| should not) be spilled to the constant pool. The default version of |
| this hook returns false. |
| |
| The primary reason to define this hook is to prevent reload from |
| deciding that a non-legitimate constant would be better reloaded |
| from the constant pool instead of spilling and reloading a register |
| holding the constant. This restriction is often true of addresses |
| of TLS symbols for various targets. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (enum machine_mode @var{mode}, rtx @var{x}) |
| This hook should return true if pool entries for constant @var{x} can |
| be placed in an @code{object_block} structure. @var{mode} is the mode |
| of @var{x}. |
| |
| The default version returns false for all constants. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void) |
| This hook should return the DECL of a function @var{f} that given an |
| address @var{addr} as an argument returns a mask @var{m} that can be |
| used to extract from two vectors the relevant data that resides in |
| @var{addr} in case @var{addr} is not properly aligned. |
| |
| The autovectrizer, when vectorizing a load operation from an address |
| @var{addr} that may be unaligned, will generate two vector loads from |
| the two aligned addresses around @var{addr}. It then generates a |
| @code{REALIGN_LOAD} operation to extract the relevant data from the |
| two loaded vectors. The first two arguments to @code{REALIGN_LOAD}, |
| @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and |
| the third argument, @var{OFF}, defines how the data will be extracted |
| from these two vectors: if @var{OFF} is 0, then the returned vector is |
| @var{v2}; otherwise, the returned vector is composed from the last |
| @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first |
| @var{OFF} elements of @var{v2}. |
| |
| If this hook is defined, the autovectorizer will generate a call |
| to @var{f} (using the DECL tree that this hook returns) and will |
| use the return value of @var{f} as the argument @var{OFF} to |
| @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f} |
| should comply with the semantics expected by @code{REALIGN_LOAD} |
| described above. |
| If this hook is not defined, then @var{addr} will be used as |
| the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low |
| log2(@var{VS})-1 bits of @var{addr} will be considered. |
| @end deftypefn |
| |
| @node Anchored Addresses |
| @section Anchored Addresses |
| @cindex anchored addresses |
| @cindex @option{-fsection-anchors} |
| |
| GCC usually addresses every static object as a separate entity. |
| For example, if we have: |
| |
| @smallexample |
| static int a, b, c; |
| int foo (void) @{ return a + b + c; @} |
| @end smallexample |
| |
| the code for @code{foo} will usually calculate three separate symbolic |
| addresses: those of @code{a}, @code{b} and @code{c}. On some targets, |
| it would be better to calculate just one symbolic address and access |
| the three variables relative to it. The equivalent pseudocode would |
| be something like: |
| |
| @smallexample |
| int foo (void) |
| @{ |
| register int *xr = &x; |
| return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; |
| @} |
| @end smallexample |
| |
| (which isn't valid C). We refer to shared addresses like @code{x} as |
| ``section anchors''. Their use is controlled by @option{-fsection-anchors}. |
| |
| The hooks below describe the target properties that GCC needs to know |
| in order to make effective use of section anchors. It won't use |
| section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET} |
| or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value. |
| |
| @deftypevar {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET |
| The minimum offset that should be applied to a section anchor. |
| On most targets, it should be the smallest offset that can be |
| applied to a base register while still giving a legitimate address |
| for every mode. The default value is 0. |
| @end deftypevar |
| |
| @deftypevar {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET |
| Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive) |
| offset that should be applied to section anchors. The default |
| value is 0. |
| @end deftypevar |
| |
| @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x}) |
| Write the assembly code to define section anchor @var{x}, which is a |
| @code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true. |
| The hook is called with the assembly output position set to the beginning |
| of @code{SYMBOL_REF_BLOCK (@var{x})}. |
| |
| If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses |
| it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}. |
| If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition |
| is @code{NULL}, which disables the use of section anchors altogether. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (rtx @var{x}) |
| Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF} |
| @var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and |
| @samp{!SYMBOL_REF_ANCHOR_P (@var{x})}. |
| |
| The default version is correct for most targets, but you might need to |
| intercept this hook to handle things like target-specific attributes |
| or target-specific sections. |
| @end deftypefn |
| |
| @node Condition Code |
| @section Condition Code Status |
| @cindex condition code status |
| |
| @c prevent bad page break with this line |
| This describes the condition code status. |
| |
| @findex cc_status |
| The file @file{conditions.h} defines a variable @code{cc_status} to |
| describe how the condition code was computed (in case the interpretation of |
| the condition code depends on the instruction that it was set by). This |
| variable contains the RTL expressions on which the condition code is |
| currently based, and several standard flags. |
| |
| Sometimes additional machine-specific flags must be defined in the machine |
| description header file. It can also add additional machine-specific |
| information by defining @code{CC_STATUS_MDEP}. |
| |
| @defmac CC_STATUS_MDEP |
| C code for a data type which is used for declaring the @code{mdep} |
| component of @code{cc_status}. It defaults to @code{int}. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| @end defmac |
| |
| @defmac CC_STATUS_MDEP_INIT |
| A C expression to initialize the @code{mdep} field to ``empty''. |
| The default definition does nothing, since most machines don't use |
| the field anyway. If you want to use the field, you should probably |
| define this macro to initialize it. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| @end defmac |
| |
| @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn}) |
| A C compound statement to set the components of @code{cc_status} |
| appropriately for an insn @var{insn} whose body is @var{exp}. It is |
| this macro's responsibility to recognize insns that set the condition |
| code as a byproduct of other activity as well as those that explicitly |
| set @code{(cc0)}. |
| |
| This macro is not used on machines that do not use @code{cc0}. |
| |
| If there are insns that do not set the condition code but do alter |
| other machine registers, this macro must check to see whether they |
| invalidate the expressions that the condition code is recorded as |
| reflecting. For example, on the 68000, insns that store in address |
| registers do not set the condition code, which means that usually |
| @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such |
| insns. But suppose that the previous insn set the condition code |
| based on location @samp{a4@@(102)} and the current insn stores a new |
| value in @samp{a4}. Although the condition code is not changed by |
| this, it will no longer be true that it reflects the contents of |
| @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter |
| @code{cc_status} in this case to say that nothing is known about the |
| condition code value. |
| |
| The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal |
| with the results of peephole optimization: insns whose patterns are |
| @code{parallel} RTXs containing various @code{reg}, @code{mem} or |
| constants which are just the operands. The RTL structure of these |
| insns is not sufficient to indicate what the insns actually do. What |
| @code{NOTICE_UPDATE_CC} should do when it sees one is just to run |
| @code{CC_STATUS_INIT}. |
| |
| A possible definition of @code{NOTICE_UPDATE_CC} is to call a function |
| that looks at an attribute (@pxref{Insn Attributes}) named, for example, |
| @samp{cc}. This avoids having detailed information about patterns in |
| two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. |
| @end defmac |
| |
| @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) |
| Returns a mode from class @code{MODE_CC} to be used when comparison |
| operation code @var{op} is applied to rtx @var{x} and @var{y}. For |
| example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see |
| @pxref{Jump Patterns} for a description of the reason for this |
| definition) |
| |
| @smallexample |
| #define SELECT_CC_MODE(OP,X,Y) \ |
| (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ |
| ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ |
| : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ |
| || GET_CODE (X) == NEG) \ |
| ? CC_NOOVmode : CCmode)) |
| @end smallexample |
| |
| You should define this macro if and only if you define extra CC modes |
| in @file{@var{machine}-modes.def}. |
| @end defmac |
| |
| @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) |
| On some machines not all possible comparisons are defined, but you can |
| convert an invalid comparison into a valid one. For example, the Alpha |
| does not have a @code{GT} comparison, but you can use an @code{LT} |
| comparison instead and swap the order of the operands. |
| |
| On such machines, define this macro to be a C statement to do any |
| required conversions. @var{code} is the initial comparison code |
| and @var{op0} and @var{op1} are the left and right operands of the |
| comparison, respectively. You should modify @var{code}, @var{op0}, and |
| @var{op1} as required. |
| |
| GCC will not assume that the comparison resulting from this macro is |
| valid but will see if the resulting insn matches a pattern in the |
| @file{md} file. |
| |
| You need not define this macro if it would never change the comparison |
| code or operands. |
| @end defmac |
| |
| @defmac REVERSIBLE_CC_MODE (@var{mode}) |
| A C expression whose value is one if it is always safe to reverse a |
| comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} |
| can ever return @var{mode} for a floating-point inequality comparison, |
| then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. |
| |
| You need not define this macro if it would always returns zero or if the |
| floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. |
| For example, here is the definition used on the SPARC, where floating-point |
| inequality comparisons are always given @code{CCFPEmode}: |
| |
| @smallexample |
| #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) |
| @end smallexample |
| @end defmac |
| |
| @defmac REVERSE_CONDITION (@var{code}, @var{mode}) |
| A C expression whose value is reversed condition code of the @var{code} for |
| comparison done in CC_MODE @var{mode}. The macro is used only in case |
| @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case |
| machine has some non-standard way how to reverse certain conditionals. For |
| instance in case all floating point conditions are non-trapping, compiler may |
| freely convert unordered compares to ordered one. Then definition may look |
| like: |
| |
| @smallexample |
| #define REVERSE_CONDITION(CODE, MODE) \ |
| ((MODE) != CCFPmode ? reverse_condition (CODE) \ |
| : reverse_condition_maybe_unordered (CODE)) |
| @end smallexample |
| @end defmac |
| |
| @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2}) |
| A C expression that returns true if the conditional execution predicate |
| @var{op1}, a comparison operation, is the inverse of @var{op2} and vice |
| versa. Define this to return 0 if the target has conditional execution |
| predicates that cannot be reversed safely. There is no need to validate |
| that the arguments of op1 and op2 are the same, this is done separately. |
| If no expansion is specified, this macro is defined as follows: |
| |
| @smallexample |
| #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ |
| (GET_CODE ((x)) == reversed_comparison_code ((y), NULL)) |
| @end smallexample |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *, unsigned int *) |
| On targets which do not use @code{(cc0)}, and which use a hard |
| register rather than a pseudo-register to hold condition codes, the |
| regular CSE passes are often not able to identify cases in which the |
| hard register is set to a common value. Use this hook to enable a |
| small pass which optimizes such cases. This hook should return true |
| to enable this pass, and it should set the integers to which its |
| arguments point to the hard register numbers used for condition codes. |
| When there is only one such register, as is true on most systems, the |
| integer pointed to by the second argument should be set to |
| @code{INVALID_REGNUM}. |
| |
| The default version of this hook returns false. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} enum machine_mode TARGET_CC_MODES_COMPATIBLE (enum machine_mode, enum machine_mode) |
| On targets which use multiple condition code modes in class |
| @code{MODE_CC}, it is sometimes the case that a comparison can be |
| validly done in more than one mode. On such a system, define this |
| target hook to take two mode arguments and to return a mode in which |
| both comparisons may be validly done. If there is no such mode, |
| return @code{VOIDmode}. |
| |
| The default version of this hook checks whether the modes are the |
| same. If they are, it returns that mode. If they are different, it |
| returns @code{VOIDmode}. |
| @end deftypefn |
| |
| @node Costs |
| @section Describing Relative Costs of Operations |
| @cindex costs of instructions |
| @cindex relative costs |
| @cindex speed of instructions |
| |
| These macros let you describe the relative speed of various operations |
| on the target machine. |
| |
| @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) |
| A C expression for the cost of moving data of mode @var{mode} from a |
| register in class @var{from} to one in class @var{to}. The classes are |
| expressed using the enumeration values such as @code{GENERAL_REGS}. A |
| value of 2 is the default; other values are interpreted relative to |
| that. |
| |
| It is not required that the cost always equal 2 when @var{from} is the |
| same as @var{to}; on some machines it is expensive to move between |
| registers if they are not general registers. |
| |
| If reload sees an insn consisting of a single @code{set} between two |
| hard registers, and if @code{REGISTER_MOVE_COST} applied to their |
| classes returns a value of 2, reload does not check to ensure that the |
| constraints of the insn are met. Setting a cost of other than 2 will |
| allow reload to verify that the constraints are met. You should do this |
| if the @samp{mov@var{m}} pattern's constraints do not allow such copying. |
| @end defmac |
| |
| @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) |
| A C expression for the cost of moving data of mode @var{mode} between a |
| register of class @var{class} and memory; @var{in} is zero if the value |
| is to be written to memory, nonzero if it is to be read in. This cost |
| is relative to those in @code{REGISTER_MOVE_COST}. If moving between |
| registers and memory is more expensive than between two registers, you |
| should define this macro to express the relative cost. |
| |
| If you do not define this macro, GCC uses a default cost of 4 plus |
| the cost of copying via a secondary reload register, if one is |
| needed. If your machine requires a secondary reload register to copy |
| between memory and a register of @var{class} but the reload mechanism is |
| more complex than copying via an intermediate, define this macro to |
| reflect the actual cost of the move. |
| |
| GCC defines the function @code{memory_move_secondary_cost} if |
| secondary reloads are needed. It computes the costs due to copying via |
| a secondary register. If your machine copies from memory using a |
| secondary register in the conventional way but the default base value of |
| 4 is not correct for your machine, define this macro to add some other |
| value to the result of that function. The arguments to that function |
| are the same as to this macro. |
| @end defmac |
| |
| @defmac BRANCH_COST |
| A C expression for the cost of a branch instruction. A value of 1 is |
| the default; other values are interpreted relative to that. |
| @end defmac |
| |
| Here are additional macros which do not specify precise relative costs, |
| but only that certain actions are more expensive than GCC would |
| ordinarily expect. |
| |
| @defmac SLOW_BYTE_ACCESS |
| Define this macro as a C expression which is nonzero if accessing less |
| than a word of memory (i.e.@: a @code{char} or a @code{short}) is no |
| faster than accessing a word of memory, i.e., if such access |
| require more than one instruction or if there is no difference in cost |
| between byte and (aligned) word loads. |
| |
| When this macro is not defined, the compiler will access a field by |
| finding the smallest containing object; when it is defined, a fullword |
| load will be used if alignment permits. Unless bytes accesses are |
| faster than word accesses, using word accesses is preferable since it |
| may eliminate subsequent memory access if subsequent accesses occur to |
| other fields in the same word of the structure, but to different bytes. |
| @end defmac |
| |
| @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) |
| Define this macro to be the value 1 if memory accesses described by the |
| @var{mode} and @var{alignment} parameters have a cost many times greater |
| than aligned accesses, for example if they are emulated in a trap |
| handler. |
| |
| When this macro is nonzero, the compiler will act as if |
| @code{STRICT_ALIGNMENT} were nonzero when generating code for block |
| moves. This can cause significantly more instructions to be produced. |
| Therefore, do not set this macro nonzero if unaligned accesses only add a |
| cycle or two to the time for a memory access. |
| |
| If the value of this macro is always zero, it need not be defined. If |
| this macro is defined, it should produce a nonzero value when |
| @code{STRICT_ALIGNMENT} is nonzero. |
| @end defmac |
| |
| @defmac MOVE_RATIO |
| The threshold of number of scalar memory-to-memory move insns, @emph{below} |
| which a sequence of insns should be generated instead of a |
| string move insn or a library call. Increasing the value will always |
| make code faster, but eventually incurs high cost in increased code size. |
| |
| Note that on machines where the corresponding move insn is a |
| @code{define_expand} that emits a sequence of insns, this macro counts |
| the number of such sequences. |
| |
| If you don't define this, a reasonable default is used. |
| @end defmac |
| |
| @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment}) |
| A C expression used to determine whether @code{move_by_pieces} will be used to |
| copy a chunk of memory, or whether some other block move mechanism |
| will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less |
| than @code{MOVE_RATIO}. |
| @end defmac |
| |
| @defmac MOVE_MAX_PIECES |
| A C expression used by @code{move_by_pieces} to determine the largest unit |
| a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. |
| @end defmac |
| |
| @defmac CLEAR_RATIO |
| The threshold of number of scalar move insns, @emph{below} which a sequence |
| of insns should be generated to clear memory instead of a string clear insn |
| or a library call. Increasing the value will always make code faster, but |
| eventually incurs high cost in increased code size. |
| |
| If you don't define this, a reasonable default is used. |
| @end defmac |
| |
| @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment}) |
| A C expression used to determine whether @code{clear_by_pieces} will be used |
| to clear a chunk of memory, or whether some other block clear mechanism |
| will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less |
| than @code{CLEAR_RATIO}. |
| @end defmac |
| |
| @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment}) |
| A C expression used to determine whether @code{store_by_pieces} will be |
| used to set a chunk of memory to a constant value, or whether some other |
| mechanism will be used. Used by @code{__builtin_memset} when storing |
| values other than constant zero and by @code{__builtin_strcpy} when |
| when called with a constant source string. |
| Defaults to 1 if @code{move_by_pieces_ninsns} returns less |
| than @code{MOVE_RATIO}. |
| @end defmac |
| |
| @defmac USE_LOAD_POST_INCREMENT (@var{mode}) |
| A C expression used to determine whether a load postincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_INCREMENT}. |
| @end defmac |
| |
| @defmac USE_LOAD_POST_DECREMENT (@var{mode}) |
| A C expression used to determine whether a load postdecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_DECREMENT}. |
| @end defmac |
| |
| @defmac USE_LOAD_PRE_INCREMENT (@var{mode}) |
| A C expression used to determine whether a load preincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_INCREMENT}. |
| @end defmac |
| |
| @defmac USE_LOAD_PRE_DECREMENT (@var{mode}) |
| A C expression used to determine whether a load predecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_DECREMENT}. |
| @end defmac |
| |
| @defmac USE_STORE_POST_INCREMENT (@var{mode}) |
| A C expression used to determine whether a store postincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_INCREMENT}. |
| @end defmac |
| |
| @defmac USE_STORE_POST_DECREMENT (@var{mode}) |
| A C expression used to determine whether a store postdecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_POST_DECREMENT}. |
| @end defmac |
| |
| @defmac USE_STORE_PRE_INCREMENT (@var{mode}) |
| This macro is used to determine whether a store preincrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_INCREMENT}. |
| @end defmac |
| |
| @defmac USE_STORE_PRE_DECREMENT (@var{mode}) |
| This macro is used to determine whether a store predecrement is a good |
| thing to use for a given mode. Defaults to the value of |
| @code{HAVE_PRE_DECREMENT}. |
| @end defmac |
| |
| @defmac NO_FUNCTION_CSE |
| Define this macro if it is as good or better to call a constant |
| function address than to call an address kept in a register. |
| @end defmac |
| |
| @defmac RANGE_TEST_NON_SHORT_CIRCUIT |
| Define this macro if a non-short-circuit operation produced by |
| @samp{fold_range_test ()} is optimal. This macro defaults to true if |
| @code{BRANCH_COST} is greater than or equal to the value 2. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total}) |
| This target hook describes the relative costs of RTL expressions. |
| |
| The cost may depend on the precise form of the expression, which is |
| available for examination in @var{x}, and the rtx code of the expression |
| in which it is contained, found in @var{outer_code}. @var{code} is the |
| expression code---redundant, since it can be obtained with |
| @code{GET_CODE (@var{x})}. |
| |
| In implementing this hook, you can use the construct |
| @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast |
| instructions. |
| |
| On entry to the hook, @code{*@var{total}} contains a default estimate |
| for the cost of the expression. The hook should modify this value as |
| necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)} |
| for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus |
| operations, and @code{COSTS_N_INSNS (1)} for all other operations. |
| |
| When optimizing for code size, i.e.@: when @code{optimize_size} is |
| nonzero, this target hook should be used to estimate the relative |
| size cost of an expression, again relative to @code{COSTS_N_INSNS}. |
| |
| The hook returns true when all subexpressions of @var{x} have been |
| processed, and false when @code{rtx_cost} should recurse. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address}) |
| This hook computes the cost of an addressing mode that contains |
| @var{address}. If not defined, the cost is computed from |
| the @var{address} expression and the @code{TARGET_RTX_COST} hook. |
| |
| For most CISC machines, the default cost is a good approximation of the |
| true cost of the addressing mode. However, on RISC machines, all |
| instructions normally have the same length and execution time. Hence |
| all addresses will have equal costs. |
| |
| In cases where more than one form of an address is known, the form with |
| the lowest cost will be used. If multiple forms have the same, lowest, |
| cost, the one that is the most complex will be used. |
| |
| For example, suppose an address that is equal to the sum of a register |
| and a constant is used twice in the same basic block. When this macro |
| is not defined, the address will be computed in a register and memory |
| references will be indirect through that register. On machines where |
| the cost of the addressing mode containing the sum is no higher than |
| that of a simple indirect reference, this will produce an additional |
| instruction and possibly require an additional register. Proper |
| specification of this macro eliminates this overhead for such machines. |
| |
| This hook is never called with an invalid address. |
| |
| On machines where an address involving more than one register is as |
| cheap as an address computation involving only one register, defining |
| @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to |
| be live over a region of code where only one would have been if |
| @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect |
| should be considered in the definition of this macro. Equivalent costs |
| should probably only be given to addresses with different numbers of |
| registers on machines with lots of registers. |
| @end deftypefn |
| |
| @node Scheduling |
| @section Adjusting the Instruction Scheduler |
| |
| The instruction scheduler may need a fair amount of machine-specific |
| adjustment in order to produce good code. GCC provides several target |
| hooks for this purpose. It is usually enough to define just a few of |
| them: try the first ones in this list first. |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) |
| This hook returns the maximum number of instructions that can ever |
| issue at the same time on the target machine. The default is one. |
| Although the insn scheduler can define itself the possibility of issue |
| an insn on the same cycle, the value can serve as an additional |
| constraint to issue insns on the same simulated processor cycle (see |
| hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}). |
| This value must be constant over the entire compilation. If you need |
| it to vary depending on what the instructions are, you must use |
| @samp{TARGET_SCHED_VARIABLE_ISSUE}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more}) |
| This hook is executed by the scheduler after it has scheduled an insn |
| from the ready list. It should return the number of insns which can |
| still be issued in the current cycle. The default is |
| @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and |
| @code{USE}, which normally are not counted against the issue rate. |
| You should define this hook if some insns take more machine resources |
| than others, so that fewer insns can follow them in the same cycle. |
| @var{file} is either a null pointer, or a stdio stream to write any |
| debug output to. @var{verbose} is the verbose level provided by |
| @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that |
| was scheduled. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost}) |
| This function corrects the value of @var{cost} based on the |
| relationship between @var{insn} and @var{dep_insn} through the |
| dependence @var{link}. It should return the new value. The default |
| is to make no adjustment to @var{cost}. This can be used for example |
| to specify to the scheduler using the traditional pipeline description |
| that an output- or anti-dependence does not incur the same cost as a |
| data-dependence. If the scheduler using the automaton based pipeline |
| description, the cost of anti-dependence is zero and the cost of |
| output-dependence is maximum of one and the difference of latency |
| times of the first and the second insns. If these values are not |
| acceptable, you could use the hook to modify them too. See also |
| @pxref{Processor pipeline description}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority}) |
| This hook adjusts the integer scheduling priority @var{priority} of |
| @var{insn}. It should return the new priority. Increase the priority to |
| execute @var{insn} earlier, reduce the priority to execute @var{insn} |
| later. Do not define this hook if you do not need to adjust the |
| scheduling priorities of insns. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock}) |
| This hook is executed by the scheduler after it has scheduled the ready |
| list, to allow the machine description to reorder it (for example to |
| combine two small instructions together on @samp{VLIW} machines). |
| @var{file} is either a null pointer, or a stdio stream to write any |
| debug output to. @var{verbose} is the verbose level provided by |
| @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready |
| list of instructions that are ready to be scheduled. @var{n_readyp} is |
| a pointer to the number of elements in the ready list. The scheduler |
| reads the ready list in reverse order, starting with |
| @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock} |
| is the timer tick of the scheduler. You may modify the ready list and |
| the number of ready insns. The return value is the number of insns that |
| can issue this cycle; normally this is just @code{issue_rate}. See also |
| @samp{TARGET_SCHED_REORDER2}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock}) |
| Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That |
| function is called whenever the scheduler starts a new cycle. This one |
| is called once per iteration over a cycle, immediately after |
| @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and |
| return the number of insns to be scheduled in the same cycle. Defining |
| this hook can be useful if there are frequent situations where |
| scheduling one insn causes other insns to become ready in the same |
| cycle. These other insns can then be taken into account properly. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail}) |
| This hook is called after evaluation forward dependencies of insns in |
| chain given by two parameter values (@var{head} and @var{tail} |
| correspondingly) but before insns scheduling of the insn chain. For |
| example, it can be used for better insn classification if it requires |
| analysis of dependencies. This hook can use backward and forward |
| dependencies of the insn scheduler because they are already |
| calculated. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) |
| This hook is executed by the scheduler at the beginning of each block of |
| instructions that are to be scheduled. @var{file} is either a null |
| pointer, or a stdio stream to write any debug output to. @var{verbose} |
| is the verbose level provided by @option{-fsched-verbose-@var{n}}. |
| @var{max_ready} is the maximum number of insns in the current scheduling |
| region that can be live at the same time. This can be used to allocate |
| scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) |
| This hook is executed by the scheduler at the end of each block of |
| instructions that are to be scheduled. It can be used to perform |
| cleanup of any actions done by the other scheduling hooks. @var{file} |
| is either a null pointer, or a stdio stream to write any debug output |
| to. @var{verbose} is the verbose level provided by |
| @option{-fsched-verbose-@var{n}}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid}) |
| This hook is executed by the scheduler after function level initializations. |
| @var{file} is either a null pointer, or a stdio stream to write any debug output to. |
| @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. |
| @var{old_max_uid} is the maximum insn uid when scheduling begins. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose}) |
| This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}. |
| @var{file} is either a null pointer, or a stdio stream to write any debug output to. |
| @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void) |
| The hook returns an RTL insn. The automaton state used in the |
| pipeline hazard recognizer is changed as if the insn were scheduled |
| when the new simulated processor cycle starts. Usage of the hook may |
| simplify the automaton pipeline description for some @acronym{VLIW} |
| processors. If the hook is defined, it is used only for the automaton |
| based pipeline description. The default is not to change the state |
| when the new simulated processor cycle starts. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void) |
| The hook can be used to initialize data used by the previous hook. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void) |
| The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used |
| to changed the state as if the insn were scheduled when the new |
| simulated processor cycle finishes. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void) |
| The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but |
| used to initialize data used by the previous hook. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void) |
| This hook controls better choosing an insn from the ready insn queue |
| for the @acronym{DFA}-based insn scheduler. Usually the scheduler |
| chooses the first insn from the queue. If the hook returns a positive |
| value, an additional scheduler code tries all permutations of |
| @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()} |
| subsequent ready insns to choose an insn whose issue will result in |
| maximal number of issued insns on the same cycle. For the |
| @acronym{VLIW} processor, the code could actually solve the problem of |
| packing simple insns into the @acronym{VLIW} insn. Of course, if the |
| rules of @acronym{VLIW} packing are described in the automaton. |
| |
| This code also could be used for superscalar @acronym{RISC} |
| processors. Let us consider a superscalar @acronym{RISC} processor |
| with 3 pipelines. Some insns can be executed in pipelines @var{A} or |
| @var{B}, some insns can be executed only in pipelines @var{B} or |
| @var{C}, and one insn can be executed in pipeline @var{B}. The |
| processor may issue the 1st insn into @var{A} and the 2nd one into |
| @var{B}. In this case, the 3rd insn will wait for freeing @var{B} |
| until the next cycle. If the scheduler issues the 3rd insn the first, |
| the processor could issue all 3 insns per cycle. |
| |
| Actually this code demonstrates advantages of the automaton based |
| pipeline hazard recognizer. We try quickly and easy many insn |
| schedules to choose the best one. |
| |
| The default is no multipass scheduling. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx) |
| |
| This hook controls what insns from the ready insn queue will be |
| considered for the multipass insn scheduling. If the hook returns |
| zero for insn passed as the parameter, the insn will be not chosen to |
| be issued. |
| |
| The default is that any ready insns can be chosen to be issued. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *) |
| |
| This hook is called by the insn scheduler before issuing insn passed |
| as the third parameter on given cycle. If the hook returns nonzero, |
| the insn is not issued on given processors cycle. Instead of that, |
| the processor cycle is advanced. If the value passed through the last |
| parameter is zero, the insn ready queue is not sorted on the new cycle |
| start as usually. The first parameter passes file for debugging |
| output. The second one passes the scheduler verbose level of the |
| debugging output. The forth and the fifth parameter values are |
| correspondingly processor cycle on which the previous insn has been |
| issued and the current processor cycle. |
| @end deftypefn |
| |
| @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}) |
| This hook is used to define which dependences are considered costly by |
| the target, so costly that it is not advisable to schedule the insns that |
| are involved in the dependence too close to one another. The parameters |
| to this hook are as follows: The second parameter @var{insn2} is dependent |
| upon the first parameter @var{insn1}. The dependence between @var{insn1} |
| and @var{insn2} is represented by the third parameter @var{dep_link}. The |
| fourth parameter @var{cost} is the cost of the dependence, and the fifth |
| parameter @var{distance} is the distance in cycles between the two insns. |
| The hook returns @code{true} if considering the distance between the two |
| insns the dependence between them is considered costly by the target, |
| and @code{false} otherwise. |
| |
| Defining this hook can be useful in multiple-issue out-of-order machines, |
| where (a) it's practically hopeless to predict the actual data/resource |
| delays, however: (b) there's a better chance to predict the actual grouping |
| that will be formed, and (c) correctly emulating the grouping can be very |
| important. In such targets one may want to allow issuing dependent insns |
| closer to one another---i.e., closer than the dependence distance; however, |
| not in cases of "costly dependences", which this hooks allows to define. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST_2 (rtx @var{insn}, int @var{dep_type}, rtx @var{dep_insn}, int @var{cost}) |
| This hook is a modified version of @samp{TARGET_SCHED_ADJUST_COST}. Instead |
| of passing dependence as a second parameter, it passes a type of that |
| dependence. This is useful to calculate cost of dependence between insns |
| not having the corresponding link. If @samp{TARGET_SCHED_ADJUST_COST_2} is |
| defined it is used instead of @samp{TARGET_SCHED_ADJUST_COST}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void) |
| This hook is called by the insn scheduler after emitting a new instruction to |
| the instruction stream. The hook notifies a target backend to extend its |
| per instruction data structures. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx @var{insn}, int @var{request}, rtx *@var{new_pat}) |
| This hook is called by the insn scheduler when @var{insn} has only |
| speculative dependencies and therefore can be scheduled speculatively. |
| The hook is used to check if the pattern of @var{insn} has a speculative |
| version and, in case of successful check, to generate that speculative |
| pattern. The hook should return 1, if the instruction has a speculative form, |
| or -1, if it doesn't. @var{request} describes the type of requested |
| speculation. If the return value equals 1 then @var{new_pat} is assigned |
| the generated speculative pattern. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_NEEDS_BLOCK_P (rtx @var{insn}) |
| This hook is called by the insn scheduler during generation of recovery code |
| for @var{insn}. It should return nonzero, if the corresponding check |
| instruction should branch to recovery code, or zero otherwise. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} rtx TARGET_SCHED_GEN_CHECK (rtx @var{insn}, rtx @var{label}, int @var{mutate_p}) |
| This hook is called by the insn scheduler to generate a pattern for recovery |
| check instruction. If @var{mutate_p} is zero, then @var{insn} is a |
| speculative instruction for which the check should be generated. |
| @var{label} is either a label of a basic block, where recovery code should |
| be emitted, or a null pointer, when requested check doesn't branch to |
| recovery code (a simple check). If @var{mutate_p} is nonzero, then |
| a pattern for a branchy check corresponding to a simple check denoted by |
| @var{insn} should be generated. In this case @var{label} can't be null. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC (rtx @var{insn}) |
| This hook is used as a workaround for |
| @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being |
| called on the first instruction of the ready list. The hook is used to |
| discard speculative instruction that stand first in the ready list from |
| being scheduled on the current cycle. For non-speculative instructions, |
| the hook should always return nonzero. For example, in the ia64 backend |
| the hook is used to cancel data speculative insns when the ALAT table |
| is nearly full. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (unsigned int *@var{flags}, spec_info_t @var{spec_info}) |
| This hook is used by the insn scheduler to find out what features should be |
| enabled/used. @var{flags} initially may have either the SCHED_RGN or SCHED_EBB |
| bit set. This denotes the scheduler pass for which the data should be |
| provided. The target backend should modify @var{flags} by modifying |
| the bits corresponding to the following features: USE_DEPS_LIST, USE_GLAT, |
| DETACH_LIFE_INFO, and DO_SPECULATION. For the DO_SPECULATION feature |
| an additional structure @var{spec_info} should be filled by the target. |
| The structure describes speculation types that can be used in the scheduler. |
| @end deftypefn |
| |
| @node Sections |
| @section Dividing the Output into Sections (Texts, Data, @dots{}) |
| @c the above section title is WAY too long. maybe cut the part between |
| @c the (...)? --mew 10feb93 |
| |
| An object file is divided into sections containing different types of |
| data. In the most common case, there are three sections: the @dfn{text |
| section}, which holds instructions and read-only data; the @dfn{data |
| section}, which holds initialized writable data; and the @dfn{bss |
| section}, which holds uninitialized data. Some systems have other kinds |
| of sections. |
| |
| @file{varasm.c} provides several well-known sections, such as |
| @code{text_section}, @code{data_section} and @code{bss_section}. |
| The normal way of controlling a @code{@var{foo}_section} variable |
| is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro, |
| as described below. The macros are only read once, when @file{varasm.c} |
| initializes itself, so their values must be run-time constants. |
| They may however depend on command-line flags. |
| |
| @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make |
| use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them |
| to be string literals. |
| |
| Some assemblers require a different string to be written every time a |
| section is selected. If your assembler falls into this category, you |
| should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use |
| @code{get_unnamed_section} to set up the sections. |
| |
| You must always create a @code{text_section}, either by defining |
| @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section} |
| in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of |
| @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not |
| create a distinct @code{readonly_data_section}, the default is to |
| reuse @code{text_section}. |
| |
| All the other @file{varasm.c} sections are optional, and are null |
| if the target does not provide them. |
| |
| @defmac TEXT_SECTION_ASM_OP |
| A C expression whose value is a string, including spacing, containing the |
| assembler operation that should precede instructions and read-only data. |
| Normally @code{"\t.text"} is right. |
| @end defmac |
| |
| @defmac HOT_TEXT_SECTION_NAME |
| If defined, a C string constant for the name of the section containing most |
| frequently executed functions of the program. If not defined, GCC will provide |
| a default definition if the target supports named sections. |
| @end defmac |
| |
| @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME |
| If defined, a C string constant for the name of the section containing unlikely |
| executed functions in the program. |
| @end defmac |
| |
| @defmac DATA_SECTION_ASM_OP |
| A C expression whose value is a string, including spacing, containing the |
| assembler operation to identify the following data as writable initialized |
| data. Normally @code{"\t.data"} is right. |
| @end defmac |
| |
| @defmac SDATA_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| initialized, writable small data. |
| @end defmac |
| |
| @defmac READONLY_DATA_SECTION_ASM_OP |
| A C expression whose value is a string, including spacing, containing the |
| assembler operation to identify the following data as read-only initialized |
| data. |
| @end defmac |
| |
| @defmac BSS_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| uninitialized global data. If not defined, and neither |
| @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, |
| uninitialized global data will be output in the data section if |
| @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be |
| used. |
| @end defmac |
| |
| @defmac SBSS_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| uninitialized, writable small data. |
| @end defmac |
| |
| @defmac INIT_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| initialization code. If not defined, GCC will assume such a section does |
| not exist. This section has no corresponding @code{init_section} |
| variable; it is used entirely in runtime code. |
| @end defmac |
| |
| @defmac FINI_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| finalization code. If not defined, GCC will assume such a section does |
| not exist. This section has no corresponding @code{fini_section} |
| variable; it is used entirely in runtime code. |
| @end defmac |
| |
| @defmac INIT_ARRAY_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| part of the @code{.init_array} (or equivalent) section. If not |
| defined, GCC will assume such a section does not exist. Do not define |
| both this macro and @code{INIT_SECTION_ASM_OP}. |
| @end defmac |
| |
| @defmac FINI_ARRAY_SECTION_ASM_OP |
| If defined, a C expression whose value is a string, including spacing, |
| containing the assembler operation to identify the following data as |
| part of the @code{.fini_array} (or equivalent) section. If not |
| defined, GCC will assume such a section does not exist. Do not define |
| both this macro and @code{FINI_SECTION_ASM_OP}. |
| @end defmac |
| |
| @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) |
| If defined, an ASM statement that switches to a different section |
| via @var{section_op}, calls @var{function}, and switches back to |
| the text section. This is used in @file{crtstuff.c} if |
| @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls |
| to initialization and finalization functions from the init and fini |
| sections. By default, this macro uses a simple function call. Some |
| ports need hand-crafted assembly code to avoid dependencies on |
| registers initialized in the function prologue or to ensure that |
| constant pools don't end up too far way in the text section. |
| @end defmac |
| |
| @defmac TARGET_LIBGCC_SDATA_SECTION |
| If defined, a string which names the section into which small |
| variables defined in crtstuff and libgcc should go. This is useful |
| when the target has options for optimizing access to small data, and |
| you want the crtstuff and libgcc routines to be conservative in what |
| they expect of your application yet liberal in what your application |
| expects. For example, for targets with a @code{.sdata} section (like |
| MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't |
| require small data support from your application, but use this macro |
| to put small data into @code{.sdata} so that your application can |
| access these variables whether it uses small data or not. |
| @end defmac |
| |
| @defmac FORCE_CODE_SECTION_ALIGN |
| If defined, an ASM statement that aligns a code section to some |
| arbitrary boundary. This is used to force all fragments of the |
| @code{.init} and @code{.fini} sections to have to same alignment |
| and thus prevent the linker from having to add any padding. |
| @end defmac |
| |
| @defmac JUMP_TABLES_IN_TEXT_SECTION |
| Define this macro to be an expression with a nonzero value if jump |
| tables (for @code{tablejump} insns) should be output in the text |
| section, along with the assembler instructions. Otherwise, the |
| readonly data section is used. |
| |
| This macro is irrelevant if there is no separate readonly data section. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void) |
| Define this hook if you need to do something special to set up the |
| @file{varasm.c} sections, or if your target has some special sections |
| of its own that you need to create. |
| |
| GCC calls this hook after processing the command line, but before writing |
| any assembly code, and before calling any of the section-returning hooks |
| described below. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} TARGET_ASM_RELOC_RW_MASK (void) |
| Return a mask describing how relocations should be treated when |
| selecting sections. Bit 1 should be set if global relocations |
| should be placed in a read-write section; bit 0 should be set if |
| local relocations should be placed in a read-write section. |
| |
| The default version of this function returns 3 when @option{-fpic} |
| is in effect, and 0 otherwise. The hook is typically redefined |
| when the target cannot support (some kinds of) dynamic relocations |
| in read-only sections even in executables. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align}) |
| Return the section into which @var{exp} should be placed. You can |
| assume that @var{exp} is either a @code{VAR_DECL} node or a constant of |
| some sort. @var{reloc} indicates whether the initial value of @var{exp} |
| requires link-time relocations. Bit 0 is set when variable contains |
| local relocations only, while bit 1 is set for global relocations. |
| @var{align} is the constant alignment in bits. |
| |
| The default version of this function takes care of putting read-only |
| variables in @code{readonly_data_section}. |
| |
| See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}. |
| @end deftypefn |
| |
| @defmac USE_SELECT_SECTION_FOR_FUNCTIONS |
| Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called |
| for @code{FUNCTION_DECL}s as well as for variables and constants. |
| |
| In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the |
| function has been determined to be likely to be called, and nonzero if |
| it is unlikely to be called. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc}) |
| Build up a unique section name, expressed as a @code{STRING_CST} node, |
| and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. |
| As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether |
| the initial value of @var{exp} requires link-time relocations. |
| |
| The default version of this function appends the symbol name to the |
| ELF section name that would normally be used for the symbol. For |
| example, the function @code{foo} would be placed in @code{.text.foo}. |
| Whatever the actual target object format, this is often good enough. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl}) |
| Return the readonly data section associated with |
| @samp{DECL_SECTION_NAME (@var{decl})}. |
| The default version of this function selects @code{.gnu.linkonce.r.name} if |
| the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name} |
| if function is in @code{.text.name}, and the normal readonly-data section |
| otherwise. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align}) |
| Return the section into which a constant @var{x}, of mode @var{mode}, |
| should be placed. You can assume that @var{x} is some kind of |
| constant in RTL@. The argument @var{mode} is redundant except in the |
| case of a @code{const_int} rtx. @var{align} is the constant alignment |
| in bits. |
| |
| The default version of this function takes care of putting symbolic |
| constants in @code{flag_pic} mode in @code{data_section} and everything |
| else in @code{readonly_data_section}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p}) |
| Define this hook if references to a symbol or a constant must be |
| treated differently depending on something about the variable or |
| function named by the symbol (such as what section it is in). |
| |
| The hook is executed immediately after rtl has been created for |
| @var{decl}, which may be a variable or function declaration or |
| an entry in the constant pool. In either case, @var{rtl} is the |
| rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})} |
| in this hook; that field may not have been initialized yet. |
| |
| In the case of a constant, it is safe to assume that the rtl is |
| a @code{mem} whose address is a @code{symbol_ref}. Most decls |
| will also have this form, but that is not guaranteed. Global |
| register variables, for instance, will have a @code{reg} for their |
| rtl. (Normally the right thing to do with such unusual rtl is |
| leave it alone.) |
| |
| The @var{new_decl_p} argument will be true if this is the first time |
| that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will |
| be false for subsequent invocations, which will happen for duplicate |
| declarations. Whether or not anything must be done for the duplicate |
| declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}. |
| @var{new_decl_p} is always true when the hook is called for a constant. |
| |
| @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO} |
| The usual thing for this hook to do is to record flags in the |
| @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}. |
| Historically, the name string was modified if it was necessary to |
| encode more than one bit of information, but this practice is now |
| discouraged; use @code{SYMBOL_REF_FLAGS}. |
| |
| The default definition of this hook, @code{default_encode_section_info} |
| in @file{varasm.c}, sets a number of commonly-useful bits in |
| @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need |
| before overriding it. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name) |
| Decode @var{name} and return the real name part, sans |
| the characters that @code{TARGET_ENCODE_SECTION_INFO} |
| may have added. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp}) |
| Returns true if @var{exp} should be placed into a ``small data'' section. |
| The default version of this hook always returns false. |
| @end deftypefn |
| |
| @deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION |
| Contains the value true if the target places read-only |
| ``small data'' into a separate section. The default value is false. |
| @end deftypevar |
| |
| @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp}) |
| Returns true if @var{exp} names an object for which name resolution |
| rules must resolve to the current ``module'' (dynamic shared library |
| or executable image). |
| |
| The default version of this hook implements the name resolution rules |
| for ELF, which has a looser model of global name binding than other |
| currently supported object file formats. |
| @end deftypefn |
| |
| @deftypevar {Target Hook} bool TARGET_HAVE_TLS |
| Contains the value true if the target supports thread-local storage. |
| The default value is false. |
| @end deftypevar |
| |
| |
| @node PIC |
| @section Position Independent Code |
| @cindex position independent code |
| @cindex PIC |
| |
| This section describes macros that help implement generation of position |
| independent code. Simply defining these macros is not enough to |
| generate valid PIC; you must also add support to the macros |
| @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as |
| well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of |
| @samp{movsi} to do something appropriate when the source operand |
| contains a symbolic address. You may also need to alter the handling of |
| switch statements so that they use relative addresses. |
| @c i rearranged the order of the macros above to try to force one of |
| @c them to the next line, to eliminate an overfull hbox. --mew 10feb93 |
| |
| @defmac PIC_OFFSET_TABLE_REGNUM |
| The register number of the register used to address a table of static |
| data addresses in memory. In some cases this register is defined by a |
| processor's ``application binary interface'' (ABI)@. When this macro |
| is defined, RTL is generated for this register once, as with the stack |
| pointer and frame pointer registers. If this macro is not defined, it |
| is up to the machine-dependent files to allocate such a register (if |
| necessary). Note that this register must be fixed when in use (e.g.@: |
| when @code{flag_pic} is true). |
| @end defmac |
| |
| @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED |
| Define this macro if the register defined by |
| @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define |
| this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. |
| @end defmac |
| |
| @defmac LEGITIMATE_PIC_OPERAND_P (@var{x}) |
| A C expression that is nonzero if @var{x} is a legitimate immediate |
| operand on the target machine when generating position independent code. |
| You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not |
| check this. You can also assume @var{flag_pic} is true, so you need not |
| check it either. You need not define this macro if all constants |
| (including @code{SYMBOL_REF}) can be immediate operands when generating |
| position independent code. |
| @end defmac |
| |
| @node Assembler Format |
| @section Defining the Output Assembler Language |
| |
| This section describes macros whose principal purpose is to describe how |
| to write instructions in assembler language---rather than what the |
| instructions do. |
| |
| @menu |
| * File Framework:: Structural information for the assembler file. |
| * Data Output:: Output of constants (numbers, strings, addresses). |
| * Uninitialized Data:: Output of uninitialized variables. |
| * Label Output:: Output and generation of labels. |
| * Initialization:: General principles of initialization |
| and termination routines. |
| * Macros for Initialization:: |
| Specific macros that control the handling of |
| initialization and termination routines. |
| * Instruction Output:: Output of actual instructions. |
| * Dispatch Tables:: Output of jump tables. |
| * Exception Region Output:: Output of exception region code. |
| * Alignment Output:: Pseudo ops for alignment and skipping data. |
| @end menu |
| |
| @node File Framework |
| @subsection The Overall Framework of an Assembler File |
| @cindex assembler format |
| @cindex output of assembler code |
| |
| @c prevent bad page break with this line |
| This describes the overall framework of an assembly file. |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FILE_START () |
| @findex default_file_start |
| Output to @code{asm_out_file} any text which the assembler expects to |
| find at the beginning of a file. The default behavior is controlled |
| by two flags, documented below. Unless your target's assembler is |
| quite unusual, if you override the default, you should call |
| @code{default_file_start} at some point in your target hook. This |
| lets other target files rely on these variables. |
| @end deftypefn |
| |
| @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF |
| If this flag is true, the text of the macro @code{ASM_APP_OFF} will be |
| printed as the very first line in the assembly file, unless |
| @option{-fverbose-asm} is in effect. (If that macro has been defined |
| to the empty string, this variable has no effect.) With the normal |
| definition of @code{ASM_APP_OFF}, the effect is to notify the GNU |
| assembler that it need not bother stripping comments or extra |
| whitespace from its input. This allows it to work a bit faster. |
| |
| The default is false. You should not set it to true unless you have |
| verified that your port does not generate any extra whitespace or |
| comments that will cause GAS to issue errors in NO_APP mode. |
| @end deftypevr |
| |
| @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE |
| If this flag is true, @code{output_file_directive} will be called |
| for the primary source file, immediately after printing |
| @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect |
| this to be done. The default is false. |
| @end deftypevr |
| |
| @deftypefn {Target Hook} void TARGET_ASM_FILE_END () |
| Output to @code{asm_out_file} any text which the assembler expects |
| to find at the end of a file. The default is to output nothing. |
| @end deftypefn |
| |
| @deftypefun void file_end_indicate_exec_stack () |
| Some systems use a common convention, the @samp{.note.GNU-stack} |
| special section, to indicate whether or not an object file relies on |
| the stack being executable. If your system uses this convention, you |
| should define @code{TARGET_ASM_FILE_END} to this function. If you |
| need to do other things in that hook, have your hook function call |
| this function. |
| @end deftypefun |
| |
| @defmac ASM_COMMENT_START |
| A C string constant describing how to begin a comment in the target |
| assembler language. The compiler assumes that the comment will end at |
| the end of the line. |
| @end defmac |
| |
| @defmac ASM_APP_ON |
| A C string constant for text to be output before each @code{asm} |
| statement or group of consecutive ones. Normally this is |
| @code{"#APP"}, which is a comment that has no effect on most |
| assemblers but tells the GNU assembler that it must check the lines |
| that follow for all valid assembler constructs. |
| @end defmac |
| |
| @defmac ASM_APP_OFF |
| A C string constant for text to be output after each @code{asm} |
| statement or group of consecutive ones. Normally this is |
| @code{"#NO_APP"}, which tells the GNU assembler to resume making the |
| time-saving assumptions that are valid for ordinary compiler output. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) |
| A C statement to output COFF information or DWARF debugging information |
| which indicates that filename @var{name} is the current source file to |
| the stdio stream @var{stream}. |
| |
| This macro need not be defined if the standard form of output |
| for the file format in use is appropriate. |
| @end defmac |
| |
| @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) |
| A C statement to output the string @var{string} to the stdio stream |
| @var{stream}. If you do not call the function @code{output_quoted_string} |
| in your config files, GCC will only call it to output filenames to |
| the assembler source. So you can use it to canonicalize the format |
| of the filename using this macro. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string}) |
| A C statement to output something to the assembler file to handle a |
| @samp{#ident} directive containing the text @var{string}. If this |
| macro is not defined, nothing is output for a @samp{#ident} directive. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align}) |
| Output assembly directives to switch to section @var{name}. The section |
| should have attributes as specified by @var{flags}, which is a bit mask |
| of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align} |
| is nonzero, it contains an alignment in bytes to be used for the section, |
| otherwise some target default should be used. Only targets that must |
| specify an alignment within the section directive need pay attention to |
| @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS |
| This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. |
| @end deftypefn |
| |
| @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} |
| @deftypefn {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS |
| This flag is true if we can create zeroed data by switching to a BSS |
| section and then using @code{ASM_OUTPUT_SKIP} to allocate the space. |
| This is true on most ELF targets. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) |
| Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} |
| based on a variable or function decl, a section name, and whether or not the |
| declaration's initializer may contain runtime relocations. @var{decl} may be |
| null, in which case read-write data should be assumed. |
| |
| The default version of this function handles choosing code vs data, |
| read-only vs read-write data, and @code{flag_pic}. You should only |
| need to override this if your target has special flags that might be |
| set via @code{__attribute__}. |
| @end deftypefn |
| |
| @need 2000 |
| @node Data Output |
| @subsection Output of Data |
| |
| |
| @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP |
| These hooks specify assembly directives for creating certain kinds |
| of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a |
| byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an |
| aligned two-byte object, and so on. Any of the hooks may be |
| @code{NULL}, indicating that no suitable directive is available. |
| |
| The compiler will print these strings at the start of a new line, |
| followed immediately by the object's initial value. In most cases, |
| the string should contain a tab, a pseudo-op, and then another tab. |
| @end deftypevr |
| |
| @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) |
| The @code{assemble_integer} function uses this hook to output an |
| integer object. @var{x} is the object's value, @var{size} is its size |
| in bytes and @var{aligned_p} indicates whether it is aligned. The |
| function should return @code{true} if it was able to output the |
| object. If it returns false, @code{assemble_integer} will try to |
| split the object into smaller parts. |
| |
| The default implementation of this hook will use the |
| @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} |
| when the relevant string is @code{NULL}. |
| @end deftypefn |
| |
| @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) |
| A C statement to recognize @var{rtx} patterns that |
| @code{output_addr_const} can't deal with, and output assembly code to |
| @var{stream} corresponding to the pattern @var{x}. This may be used to |
| allow machine-dependent @code{UNSPEC}s to appear within constants. |
| |
| If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must |
| @code{goto fail}, so that a standard error message is printed. If it |
| prints an error message itself, by calling, for example, |
| @code{output_operand_lossage}, it may just complete normally. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| instruction to assemble a string constant containing the @var{len} |
| bytes at @var{ptr}. @var{ptr} will be a C expression of type |
| @code{char *} and @var{len} a C expression of type @code{int}. |
| |
| If the assembler has a @code{.ascii} pseudo-op as found in the |
| Berkeley Unix assembler, do not define the macro |
| @code{ASM_OUTPUT_ASCII}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) |
| A C statement to output word @var{n} of a function descriptor for |
| @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} |
| is defined, and is otherwise unused. |
| @end defmac |
| |
| @defmac CONSTANT_POOL_BEFORE_FUNCTION |
| You may define this macro as a C expression. You should define the |
| expression to have a nonzero value if GCC should output the constant |
| pool for a function before the code for the function, or a zero value if |
| GCC should output the constant pool after the function. If you do |
| not define this macro, the usual case, GCC will output the constant |
| pool before the function. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) |
| A C statement to output assembler commands to define the start of the |
| constant pool for a function. @var{funname} is a string giving |
| the name of the function. Should the return type of the function |
| be required, it can be obtained via @var{fundecl}. @var{size} |
| is the size, in bytes, of the constant pool that will be written |
| immediately after this call. |
| |
| If no constant-pool prefix is required, the usual case, this macro need |
| not be defined. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) |
| A C statement (with or without semicolon) to output a constant in the |
| constant pool, if it needs special treatment. (This macro need not do |
| anything for RTL expressions that can be output normally.) |
| |
| The argument @var{file} is the standard I/O stream to output the |
| assembler code on. @var{x} is the RTL expression for the constant to |
| output, and @var{mode} is the machine mode (in case @var{x} is a |
| @samp{const_int}). @var{align} is the required alignment for the value |
| @var{x}; you should output an assembler directive to force this much |
| alignment. |
| |
| The argument @var{labelno} is a number to use in an internal label for |
| the address of this pool entry. The definition of this macro is |
| responsible for outputting the label definition at the proper place. |
| Here is how to do this: |
| |
| @smallexample |
| @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno}); |
| @end smallexample |
| |
| When you output a pool entry specially, you should end with a |
| @code{goto} to the label @var{jumpto}. This will prevent the same pool |
| entry from being output a second time in the usual manner. |
| |
| You need not define this macro if it would do nothing. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) |
| A C statement to output assembler commands to at the end of the constant |
| pool for a function. @var{funname} is a string giving the name of the |
| function. Should the return type of the function be required, you can |
| obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the |
| constant pool that GCC wrote immediately before this call. |
| |
| If no constant-pool epilogue is required, the usual case, you need not |
| define this macro. |
| @end defmac |
| |
| @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}) |
| Define this macro as a C expression which is nonzero if @var{C} is |
| used as a logical line separator by the assembler. |
| |
| If you do not define this macro, the default is that only |
| the character @samp{;} is treated as a logical line separator. |
| @end defmac |
| |
| @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN |
| @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN |
| These target hooks are C string constants, describing the syntax in the |
| assembler for grouping arithmetic expressions. If not overridden, they |
| default to normal parentheses, which is correct for most assemblers. |
| @end deftypevr |
| |
| These macros are provided by @file{real.h} for writing the definitions |
| of @code{ASM_OUTPUT_DOUBLE} and the like: |
| |
| @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) |
| @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) |
| @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) |
| @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l}) |
| @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l}) |
| @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l}) |
| These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the |
| target's floating point representation, and store its bit pattern in |
| the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and |
| @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a |
| simple @code{long int}. For the others, it should be an array of |
| @code{long int}. The number of elements in this array is determined |
| by the size of the desired target floating point data type: 32 bits of |
| it go in each @code{long int} array element. Each array element holds |
| 32 bits of the result, even if @code{long int} is wider than 32 bits |
| on the host machine. |
| |
| The array element values are designed so that you can print them out |
| using @code{fprintf} in the order they should appear in the target |
| machine's memory. |
| @end defmac |
| |
| @node Uninitialized Data |
| @subsection Output of Uninitialized Variables |
| |
| Each of the macros in this section is used to do the whole job of |
| outputting a single uninitialized variable. |
| |
| @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a common-label named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. |
| |
| This macro controls how the assembler definitions of uninitialized |
| common global variables are output. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the |
| variable to be output, if there is one, or @code{NULL_TREE} if there |
| is no corresponding variable. If you define this macro, GCC will use it |
| in place of both @code{ASM_OUTPUT_COMMON} and |
| @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see |
| the variable's decl in order to chose what to output. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of uninitialized global @var{decl} named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Try to use function @code{asm_output_bss} defined in @file{varasm.c} when |
| defining this macro. If unable, use the expression |
| @code{assemble_name (@var{stream}, @var{name})} to output the name itself; |
| before and after that, output the additional assembler syntax for defining |
| the name, and a newline. |
| |
| There are two ways of handling global BSS. One is to define either |
| this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}. |
| The other is to have @code{TARGET_ASM_SELECT_SECTION} return a |
| switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). |
| You do not need to do both. |
| |
| Some languages do not have @code{common} data, and require a |
| non-common form of global BSS in order to handle uninitialized globals |
| efficiently. C++ is one example of this. However, if the target does |
| not support global BSS, the front end may choose to make globals |
| common in order to save space in the object file. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| |
| Try to use function @code{asm_output_aligned_bss} defined in file |
| @file{varasm.c} when defining this macro. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a local-common-label named |
| @var{name} whose size is @var{size} bytes. The variable @var{rounded} |
| is the size rounded up to whatever alignment the caller wants. |
| |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. |
| |
| This macro controls how the assembler definitions of uninitialized |
| static variables are output. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a |
| separate, explicit argument. If you define this macro, it is used in |
| place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in |
| handling the required alignment of the variable. The alignment is specified |
| as the number of bits. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) |
| Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the |
| variable to be output, if there is one, or @code{NULL_TREE} if there |
| is no corresponding variable. If you define this macro, GCC will use it |
| in place of both @code{ASM_OUTPUT_DECL} and |
| @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see |
| the variable's decl in order to chose what to output. |
| @end defmac |
| |
| @node Label Output |
| @subsection Output and Generation of Labels |
| |
| @c prevent bad page break with this line |
| This is about outputting labels. |
| |
| @findex assemble_name |
| @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} the assembler definition of a label named @var{name}. |
| Use the expression @code{assemble_name (@var{stream}, @var{name})} to |
| output the name itself; before and after that, output the additional |
| assembler syntax for defining the name, and a newline. A default |
| definition of this macro is provided which is correct for most systems. |
| @end defmac |
| |
| @findex assemble_name_raw |
| @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name}) |
| Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known |
| to refer to a compiler-generated label. The default definition uses |
| @code{assemble_name_raw}, which is like @code{assemble_name} except |
| that it is more efficient. |
| @end defmac |
| |
| @defmac SIZE_ASM_OP |
| A C string containing the appropriate assembler directive to specify the |
| size of a symbol, without any arguments. On systems that use ELF, the |
| default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other |
| systems, the default is not to define this macro. |
| |
| Define this macro only if it is correct to use the default definitions |
| of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} |
| for your system. If you need your own custom definitions of those |
| macros, or if you do not need explicit symbol sizes at all, do not |
| define this macro. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} a directive telling the assembler that the size of the |
| symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. |
| If you define @code{SIZE_ASM_OP}, a default definition of this macro is |
| provided. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} a directive telling the assembler to calculate the size of |
| the symbol @var{name} by subtracting its address from the current |
| address. |
| |
| If you define @code{SIZE_ASM_OP}, a default definition of this macro is |
| provided. The default assumes that the assembler recognizes a special |
| @samp{.} symbol as referring to the current address, and can calculate |
| the difference between this and another symbol. If your assembler does |
| not recognize @samp{.} or cannot do calculations with it, you will need |
| to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. |
| @end defmac |
| |
| @defmac TYPE_ASM_OP |
| A C string containing the appropriate assembler directive to specify the |
| type of a symbol, without any arguments. On systems that use ELF, the |
| default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other |
| systems, the default is not to define this macro. |
| |
| Define this macro only if it is correct to use the default definition of |
| @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own |
| custom definition of this macro, or if you do not need explicit symbol |
| types at all, do not define this macro. |
| @end defmac |
| |
| @defmac TYPE_OPERAND_FMT |
| A C string which specifies (using @code{printf} syntax) the format of |
| the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the |
| default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, |
| the default is not to define this macro. |
| |
| Define this macro only if it is correct to use the default definition of |
| @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own |
| custom definition of this macro, or if you do not need explicit symbol |
| types at all, do not define this macro. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} a directive telling the assembler that the type of the |
| symbol @var{name} is @var{type}. @var{type} is a C string; currently, |
| that string is always either @samp{"function"} or @samp{"object"}, but |
| you should not count on this. |
| |
| If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default |
| definition of this macro is provided. |
| @end defmac |
| |
| @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name @var{name} of a |
| function which is being defined. This macro is responsible for |
| outputting the label definition (perhaps using |
| @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the |
| @code{FUNCTION_DECL} tree node representing the function. |
| |
| If this macro is not defined, then the function name is defined in the |
| usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). |
| |
| You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition |
| of this macro. |
| @end defmac |
| |
| @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the size of a function |
| which is being defined. The argument @var{name} is the name of the |
| function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node |
| representing the function. |
| |
| If this macro is not defined, then the function size is not defined. |
| |
| You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition |
| of this macro. |
| @end defmac |
| |
| @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name @var{name} of an |
| initialized variable which is being defined. This macro must output the |
| label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument |
| @var{decl} is the @code{VAR_DECL} tree node representing the variable. |
| |
| If this macro is not defined, then the variable name is defined in the |
| usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). |
| |
| You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or |
| @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. |
| @end defmac |
| |
| @defmac ASM_DECLARE_CONSTANT_NAME (@var{stream}, @var{name}, @var{exp}, @var{size}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name @var{name} of a |
| constant which is being defined. This macro is responsible for |
| outputting the label definition (perhaps using |
| @code{ASM_OUTPUT_LABEL}). The argument @var{exp} is the |
| value of the constant, and @var{size} is the size of the constant |
| in bytes. @var{name} will be an internal label. |
| |
| If this macro is not defined, then the @var{name} is defined in the |
| usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). |
| |
| You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition |
| of this macro. |
| @end defmac |
| |
| @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for claiming a register @var{regno} |
| for a global variable @var{decl} with name @var{name}. |
| |
| If you don't define this macro, that is equivalent to defining it to do |
| nothing. |
| @end defmac |
| |
| @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) |
| A C statement (sans semicolon) to finish up declaring a variable name |
| once the compiler has processed its initializer fully and thus has had a |
| chance to determine the size of an array when controlled by an |
| initializer. This is used on systems where it's necessary to declare |
| something about the size of the object. |
| |
| If you don't define this macro, that is equivalent to defining it to do |
| nothing. |
| |
| You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or |
| @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name}) |
| This target hook is a function to output to the stdio stream |
| @var{stream} some commands that will make the label @var{name} global; |
| that is, available for reference from other files. |
| |
| The default implementation relies on a proper definition of |
| @code{GLOBAL_ASM_OP}. |
| @end deftypefn |
| |
| @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} some commands that will make the label @var{name} weak; |
| that is, available for reference from other files but only used if |
| no other definition is available. Use the expression |
| @code{assemble_name (@var{stream}, @var{name})} to output the name |
| itself; before and after that, output the additional assembler syntax |
| for making that name weak, and a newline. |
| |
| If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not |
| support weak symbols and you should not define the @code{SUPPORTS_WEAK} |
| macro. |
| @end defmac |
| |
| @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) |
| Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and |
| @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function |
| or variable decl. If @var{value} is not @code{NULL}, this C statement |
| should output to the stdio stream @var{stream} assembler code which |
| defines (equates) the weak symbol @var{name} to have the value |
| @var{value}. If @var{value} is @code{NULL}, it should output commands |
| to make @var{name} weak. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value}) |
| Outputs a directive that enables @var{name} to be used to refer to |
| symbol @var{value} with weak-symbol semantics. @code{decl} is the |
| declaration of @code{name}. |
| @end defmac |
| |
| @defmac SUPPORTS_WEAK |
| A C expression which evaluates to true if the target supports weak symbols. |
| |
| If you don't define this macro, @file{defaults.h} provides a default |
| definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} |
| is defined, the default definition is @samp{1}; otherwise, it is |
| @samp{0}. Define this macro if you want to control weak symbol support |
| with a compiler flag such as @option{-melf}. |
| @end defmac |
| |
| @defmac MAKE_DECL_ONE_ONLY (@var{decl}) |
| A C statement (sans semicolon) to mark @var{decl} to be emitted as a |
| public symbol such that extra copies in multiple translation units will |
| be discarded by the linker. Define this macro if your object file |
| format provides support for this concept, such as the @samp{COMDAT} |
| section flags in the Microsoft Windows PE/COFF format, and this support |
| requires changes to @var{decl}, such as putting it in a separate section. |
| @end defmac |
| |
| @defmac SUPPORTS_ONE_ONLY |
| A C expression which evaluates to true if the target supports one-only |
| semantics. |
| |
| If you don't define this macro, @file{varasm.c} provides a default |
| definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default |
| definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if |
| you want to control one-only symbol support with a compiler flag, or if |
| setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to |
| be emitted as one-only. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility}) |
| This target hook is a function to output to @var{asm_out_file} some |
| commands that will make the symbol(s) associated with @var{decl} have |
| hidden, protected or internal visibility as specified by @var{visibility}. |
| @end deftypefn |
| |
| @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC |
| A C expression that evaluates to true if the target's linker expects |
| that weak symbols do not appear in a static archive's table of contents. |
| The default is @code{0}. |
| |
| Leaving weak symbols out of an archive's table of contents means that, |
| if a symbol will only have a definition in one translation unit and |
| will have undefined references from other translation units, that |
| symbol should not be weak. Defining this macro to be nonzero will |
| thus have the effect that certain symbols that would normally be weak |
| (explicit template instantiations, and vtables for polymorphic classes |
| with noninline key methods) will instead be nonweak. |
| |
| The C++ ABI requires this macro to be zero. Define this macro for |
| targets where full C++ ABI compliance is impossible and where linker |
| restrictions require weak symbols to be left out of a static archive's |
| table of contents. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} any text necessary for declaring the name of an external |
| symbol named @var{name} which is referenced in this compilation but |
| not defined. The value of @var{decl} is the tree node for the |
| declaration. |
| |
| This macro need not be defined if it does not need to output anything. |
| The GNU assembler and most Unix assemblers don't require anything. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref}) |
| This target hook is a function to output to @var{asm_out_file} an assembler |
| pseudo-op to declare a library function name external. The name of the |
| library function is given by @var{symref}, which is a @code{symbol_ref}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (tree @var{decl}) |
| This target hook is a function to output to @var{asm_out_file} an assembler |
| directive to annotate used symbol. Darwin target use .no_dead_code_strip |
| directive. |
| @end deftypefn |
| |
| @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} a reference in assembler syntax to a label named |
| @var{name}. This should add @samp{_} to the front of the name, if that |
| is customary on your operating system, as it is in most Berkeley Unix |
| systems. This macro is used in @code{assemble_name}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) |
| A C statement (sans semicolon) to output a reference to |
| @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} |
| will be used to output the name of the symbol. This macro may be used |
| to modify the way a symbol is referenced depending on information |
| encoded by @code{TARGET_ENCODE_SECTION_INFO}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) |
| A C statement (sans semicolon) to output a reference to @var{buf}, the |
| result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, |
| @code{assemble_name} will be used to output the name of the symbol. |
| This macro is not used by @code{output_asm_label}, or the @code{%l} |
| specifier that calls it; the intention is that this macro should be set |
| when it is necessary to output a label differently when its address is |
| being taken. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno}) |
| A function to output to the stdio stream @var{stream} a label whose |
| name is made from the string @var{prefix} and the number @var{labelno}. |
| |
| It is absolutely essential that these labels be distinct from the labels |
| used for user-level functions and variables. Otherwise, certain programs |
| will have name conflicts with internal labels. |
| |
| It is desirable to exclude internal labels from the symbol table of the |
| object file. Most assemblers have a naming convention for labels that |
| should be excluded; on many systems, the letter @samp{L} at the |
| beginning of a label has this effect. You should find out what |
| convention your system uses, and follow it. |
| |
| The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}. |
| @end deftypefn |
| |
| @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) |
| A C statement to output to the stdio stream @var{stream} a debug info |
| label whose name is made from the string @var{prefix} and the number |
| @var{num}. This is useful for VLIW targets, where debug info labels |
| may need to be treated differently than branch target labels. On some |
| systems, branch target labels must be at the beginning of instruction |
| bundles, but debug info labels can occur in the middle of instruction |
| bundles. |
| |
| If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be |
| used. |
| @end defmac |
| |
| @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) |
| A C statement to store into the string @var{string} a label whose name |
| is made from the string @var{prefix} and the number @var{num}. |
| |
| This string, when output subsequently by @code{assemble_name}, should |
| produce the output that @code{(*targetm.asm_out.internal_label)} would produce |
| with the same @var{prefix} and @var{num}. |
| |
| If the string begins with @samp{*}, then @code{assemble_name} will |
| output the rest of the string unchanged. It is often convenient for |
| @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the |
| string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets |
| to output the string, and may change it. (Of course, |
| @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so |
| you should know what it does on your machine.) |
| @end defmac |
| |
| @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) |
| A C expression to assign to @var{outvar} (which is a variable of type |
| @code{char *}) a newly allocated string made from the string |
| @var{name} and the number @var{number}, with some suitable punctuation |
| added. Use @code{alloca} to get space for the string. |
| |
| The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to |
| produce an assembler label for an internal static variable whose name is |
| @var{name}. Therefore, the string must be such as to result in valid |
| assembler code. The argument @var{number} is different each time this |
| macro is executed; it prevents conflicts between similarly-named |
| internal static variables in different scopes. |
| |
| Ideally this string should not be a valid C identifier, to prevent any |
| conflict with the user's own symbols. Most assemblers allow periods |
| or percent signs in assembler symbols; putting at least one of these |
| between the name and the number will suffice. |
| |
| If this macro is not defined, a default definition will be provided |
| which is correct for most systems. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the symbol @var{name} to have the value @var{value}. |
| |
| @findex SET_ASM_OP |
| If @code{SET_ASM_OP} is defined, a default definition is provided which is |
| correct for most systems. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the symbol whose tree node is @var{decl_of_name} |
| to have the value of the tree node @var{decl_of_value}. This macro will |
| be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if |
| the tree nodes are available. |
| |
| @findex SET_ASM_OP |
| If @code{SET_ASM_OP} is defined, a default definition is provided which is |
| correct for most systems. |
| @end defmac |
| |
| @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value}) |
| A C statement that evaluates to true if the assembler code which defines |
| (equates) the symbol whose tree node is @var{decl_of_name} to have the value |
| of the tree node @var{decl_of_value} should be emitted near the end of the |
| current compilation unit. The default is to not defer output of defines. |
| This macro affects defines output by @samp{ASM_OUTPUT_DEF} and |
| @samp{ASM_OUTPUT_DEF_FROM_DECLS}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) |
| A C statement to output to the stdio stream @var{stream} assembler code |
| which defines (equates) the weak symbol @var{name} to have the value |
| @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as |
| an undefined weak symbol. |
| |
| Define this macro if the target only supports weak aliases; define |
| @code{ASM_OUTPUT_DEF} instead if possible. |
| @end defmac |
| |
| @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) |
| Define this macro to override the default assembler names used for |
| Objective-C methods. |
| |
| The default name is a unique method number followed by the name of the |
| class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of |
| the category is also included in the assembler name (e.g.@: |
| @samp{_1_Foo_Bar}). |
| |
| These names are safe on most systems, but make debugging difficult since |
| the method's selector is not present in the name. Therefore, particular |
| systems define other ways of computing names. |
| |
| @var{buf} is an expression of type @code{char *} which gives you a |
| buffer in which to store the name; its length is as long as |
| @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus |
| 50 characters extra. |
| |
| The argument @var{is_inst} specifies whether the method is an instance |
| method or a class method; @var{class_name} is the name of the class; |
| @var{cat_name} is the name of the category (or @code{NULL} if the method is not |
| in a category); and @var{sel_name} is the name of the selector. |
| |
| On systems where the assembler can handle quoted names, you can use this |
| macro to provide more human-readable names. |
| @end defmac |
| |
| @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} commands to declare that the label @var{name} is an |
| Objective-C class reference. This is only needed for targets whose |
| linkers have special support for NeXT-style runtimes. |
| @end defmac |
| |
| @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) |
| A C statement (sans semicolon) to output to the stdio stream |
| @var{stream} commands to declare that the label @var{name} is an |
| unresolved Objective-C class reference. This is only needed for targets |
| whose linkers have special support for NeXT-style runtimes. |
| @end defmac |
| |
| @node Initialization |
| @subsection How Initialization Functions Are Handled |
| @cindex initialization routines |
| @cindex termination routines |
| @cindex constructors, output of |
| @cindex destructors, output of |
| |
| The compiled code for certain languages includes @dfn{constructors} |
| (also called @dfn{initialization routines})---functions to initialize |
| data in the program when the program is started. These functions need |
| to be called before the program is ``started''---that is to say, before |
| @code{main} is called. |
| |
| Compiling some languages generates @dfn{destructors} (also called |
| @dfn{termination routines}) that should be called when the program |
| terminates. |
| |
| To make the initialization and termination functions work, the compiler |
| must output something in the assembler code to cause those functions to |
| be called at the appropriate time. When you port the compiler to a new |
| system, you need to specify how to do this. |
| |
| There are two major ways that GCC currently supports the execution of |
| initialization and termination functions. Each way has two variants. |
| Much of the structure is common to all four variations. |
| |
| @findex __CTOR_LIST__ |
| @findex __DTOR_LIST__ |
| The linker must build two lists of these functions---a list of |
| initialization functions, called @code{__CTOR_LIST__}, and a list of |
| termination functions, called @code{__DTOR_LIST__}. |
| |
| Each list always begins with an ignored function pointer (which may hold |
| 0, @minus{}1, or a count of the function pointers after it, depending on |
| the environment). This is followed by a series of zero or more function |
| pointers to constructors (or destructors), followed by a function |
| pointer containing zero. |
| |
| Depending on the operating system and its executable file format, either |
| @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup |
| time and exit time. Constructors are called in reverse order of the |
| list; destructors in forward order. |
| |
| The best way to handle static constructors works only for object file |
| formats which provide arbitrarily-named sections. A section is set |
| aside for a list of constructors, and another for a list of destructors. |
| Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each |
| object file that defines an initialization function also puts a word in |
| the constructor section to point to that function. The linker |
| accumulates all these words into one contiguous @samp{.ctors} section. |
| Termination functions are handled similarly. |
| |
| This method will be chosen as the default by @file{target-def.h} if |
| @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not |
| support arbitrary sections, but does support special designated |
| constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} |
| and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. |
| |
| When arbitrary sections are available, there are two variants, depending |
| upon how the code in @file{crtstuff.c} is called. On systems that |
| support a @dfn{.init} section which is executed at program startup, |
| parts of @file{crtstuff.c} are compiled into that section. The |
| program is linked by the @command{gcc} driver like this: |
| |
| @smallexample |
| ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o |
| @end smallexample |
| |
| The prologue of a function (@code{__init}) appears in the @code{.init} |
| section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise |
| for the function @code{__fini} in the @dfn{.fini} section. Normally these |
| files are provided by the operating system or by the GNU C library, but |
| are provided by GCC for a few targets. |
| |
| The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) |
| compiled from @file{crtstuff.c}. They contain, among other things, code |
| fragments within the @code{.init} and @code{.fini} sections that branch |
| to routines in the @code{.text} section. The linker will pull all parts |
| of a section together, which results in a complete @code{__init} function |
| that invokes the routines we need at startup. |
| |
| To use this variant, you must define the @code{INIT_SECTION_ASM_OP} |
| macro properly. |
| |
| If no init section is available, when GCC compiles any function called |
| @code{main} (or more accurately, any function designated as a program |
| entry point by the language front end calling @code{expand_main_function}), |
| it inserts a procedure call to @code{__main} as the first executable code |
| after the function prologue. The @code{__main} function is defined |
| in @file{libgcc2.c} and runs the global constructors. |
| |
| In file formats that don't support arbitrary sections, there are again |
| two variants. In the simplest variant, the GNU linker (GNU @code{ld}) |
| and an `a.out' format must be used. In this case, |
| @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} |
| entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, |
| and with the address of the void function containing the initialization |
| code as its value. The GNU linker recognizes this as a request to add |
| the value to a @dfn{set}; the values are accumulated, and are eventually |
| placed in the executable as a vector in the format described above, with |
| a leading (ignored) count and a trailing zero element. |
| @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init |
| section is available, the absence of @code{INIT_SECTION_ASM_OP} causes |
| the compilation of @code{main} to call @code{__main} as above, starting |
| the initialization process. |
| |
| The last variant uses neither arbitrary sections nor the GNU linker. |
| This is preferable when you want to do dynamic linking and when using |
| file formats which the GNU linker does not support, such as `ECOFF'@. In |
| this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and |
| termination functions are recognized simply by their names. This requires |
| an extra program in the linkage step, called @command{collect2}. This program |
| pretends to be the linker, for use with GCC; it does its job by running |
| the ordinary linker, but also arranges to include the vectors of |
| initialization and termination functions. These functions are called |
| via @code{__main} as described above. In order to use this method, |
| @code{use_collect2} must be defined in the target in @file{config.gcc}. |
| |
| @ifinfo |
| The following section describes the specific macros that control and |
| customize the handling of initialization and termination functions. |
| @end ifinfo |
| |
| @node Macros for Initialization |
| @subsection Macros Controlling Initialization Routines |
| |
| Here are the macros that control how the compiler handles initialization |
| and termination functions: |
| |
| @defmac INIT_SECTION_ASM_OP |
| If defined, a C string constant, including spacing, for the assembler |
| operation to identify the following data as initialization code. If not |
| defined, GCC will assume such a section does not exist. When you are |
| using special sections for initialization and termination functions, this |
| macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to |
| run the initialization functions. |
| @end defmac |
| |
| @defmac HAS_INIT_SECTION |
| If defined, @code{main} will not call @code{__main} as described above. |
| This macro should be defined for systems that control start-up code |
| on a symbol-by-symbol basis, such as OSF/1, and should not |
| be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. |
| @end defmac |
| |
| @defmac LD_INIT_SWITCH |
| If defined, a C string constant for a switch that tells the linker that |
| the following symbol is an initialization routine. |
| @end defmac |
| |
| @defmac LD_FINI_SWITCH |
| If defined, a C string constant for a switch that tells the linker that |
| the following symbol is a finalization routine. |
| @end defmac |
| |
| @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) |
| If defined, a C statement that will write a function that can be |
| automatically called when a shared library is loaded. The function |
| should call @var{func}, which takes no arguments. If not defined, and |
| the object format requires an explicit initialization function, then a |
| function called @code{_GLOBAL__DI} will be generated. |
| |
| This function and the following one are used by collect2 when linking a |
| shared library that needs constructors or destructors, or has DWARF2 |
| exception tables embedded in the code. |
| @end defmac |
| |
| @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) |
| If defined, a C statement that will write a function that can be |
| automatically called when a shared library is unloaded. The function |
| should call @var{func}, which takes no arguments. If not defined, and |
| the object format requires an explicit finalization function, then a |
| function called @code{_GLOBAL__DD} will be generated. |
| @end defmac |
| |
| @defmac INVOKE__main |
| If defined, @code{main} will call @code{__main} despite the presence of |
| @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems |
| where the init section is not actually run automatically, but is still |
| useful for collecting the lists of constructors and destructors. |
| @end defmac |
| |
| @defmac SUPPORTS_INIT_PRIORITY |
| If nonzero, the C++ @code{init_priority} attribute is supported and the |
| compiler should emit instructions to control the order of initialization |
| of objects. If zero, the compiler will issue an error message upon |
| encountering an @code{init_priority} attribute. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS |
| This value is true if the target supports some ``native'' method of |
| collecting constructors and destructors to be run at startup and exit. |
| It is false if we must use @command{collect2}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) |
| If defined, a function that outputs assembler code to arrange to call |
| the function referenced by @var{symbol} at initialization time. |
| |
| Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking |
| no arguments and with no return value. If the target supports initialization |
| priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; |
| otherwise it must be @code{DEFAULT_INIT_PRIORITY}. |
| |
| If this macro is not defined by the target, a suitable default will |
| be chosen if (1) the target supports arbitrary section names, (2) the |
| target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} |
| is not defined. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) |
| This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination |
| functions rather than initialization functions. |
| @end deftypefn |
| |
| If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine |
| generated for the generated object file will have static linkage. |
| |
| If your system uses @command{collect2} as the means of processing |
| constructors, then that program normally uses @command{nm} to scan |
| an object file for constructor functions to be called. |
| |
| On certain kinds of systems, you can define this macro to make |
| @command{collect2} work faster (and, in some cases, make it work at all): |
| |
| @defmac OBJECT_FORMAT_COFF |
| Define this macro if the system uses COFF (Common Object File Format) |
| object files, so that @command{collect2} can assume this format and scan |
| object files directly for dynamic constructor/destructor functions. |
| |
| This macro is effective only in a native compiler; @command{collect2} as |
| part of a cross compiler always uses @command{nm} for the target machine. |
| @end defmac |
| |
| @defmac REAL_NM_FILE_NAME |
| Define this macro as a C string constant containing the file name to use |
| to execute @command{nm}. The default is to search the path normally for |
| @command{nm}. |
| |
| If your system supports shared libraries and has a program to list the |
| dynamic dependencies of a given library or executable, you can define |
| these macros to enable support for running initialization and |
| termination functions in shared libraries: |
| @end defmac |
| |
| @defmac LDD_SUFFIX |
| Define this macro to a C string constant containing the name of the program |
| which lists dynamic dependencies, like @command{"ldd"} under SunOS 4. |
| @end defmac |
| |
| @defmac PARSE_LDD_OUTPUT (@var{ptr}) |
| Define this macro to be C code that extracts filenames from the output |
| of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable |
| of type @code{char *} that points to the beginning of a line of output |
| from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the |
| code must advance @var{ptr} to the beginning of the filename on that |
| line. Otherwise, it must set @var{ptr} to @code{NULL}. |
| @end defmac |
| |
| @node Instruction Output |
| @subsection Output of Assembler Instructions |
| |
| @c prevent bad page break with this line |
| This describes assembler instruction output. |
| |
| @defmac REGISTER_NAMES |
| A C initializer containing the assembler's names for the machine |
| registers, each one as a C string constant. This is what translates |
| register numbers in the compiler into assembler language. |
| @end defmac |
| |
| @defmac ADDITIONAL_REGISTER_NAMES |
| If defined, a C initializer for an array of structures containing a name |
| and a register number. This macro defines additional names for hard |
| registers, thus allowing the @code{asm} option in declarations to refer |
| to registers using alternate names. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) |
| Define this macro if you are using an unusual assembler that |
| requires different names for the machine instructions. |
| |
| The definition is a C statement or statements which output an |
| assembler instruction opcode to the stdio stream @var{stream}. The |
| macro-operand @var{ptr} is a variable of type @code{char *} which |
| points to the opcode name in its ``internal'' form---the form that is |
| written in the machine description. The definition should output the |
| opcode name to @var{stream}, performing any translation you desire, and |
| increment the variable @var{ptr} to point at the end of the opcode |
| so that it will not be output twice. |
| |
| In fact, your macro definition may process less than the entire opcode |
| name, or more than the opcode name; but if you want to process text |
| that includes @samp{%}-sequences to substitute operands, you must take |
| care of the substitution yourself. Just be sure to increment |
| @var{ptr} over whatever text should not be output normally. |
| |
| @findex recog_data.operand |
| If you need to look at the operand values, they can be found as the |
| elements of @code{recog_data.operand}. |
| |
| If the macro definition does nothing, the instruction is output |
| in the usual way. |
| @end defmac |
| |
| @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) |
| If defined, a C statement to be executed just prior to the output of |
| assembler code for @var{insn}, to modify the extracted operands so |
| they will be output differently. |
| |
| Here the argument @var{opvec} is the vector containing the operands |
| extracted from @var{insn}, and @var{noperands} is the number of |
| elements of the vector which contain meaningful data for this insn. |
| The contents of this vector are what will be used to convert the insn |
| template into assembler code, so you can change the assembler output |
| by changing the contents of the vector. |
| |
| This macro is useful when various assembler syntaxes share a single |
| file of instruction patterns; by defining this macro differently, you |
| can cause a large class of instructions to be output differently (such |
| as with rearranged operands). Naturally, variations in assembler |
| syntax affecting individual insn patterns ought to be handled by |
| writing conditional output routines in those patterns. |
| |
| If this macro is not defined, it is equivalent to a null statement. |
| @end defmac |
| |
| @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) |
| A C compound statement to output to stdio stream @var{stream} the |
| assembler syntax for an instruction operand @var{x}. @var{x} is an |
| RTL expression. |
| |
| @var{code} is a value that can be used to specify one of several ways |
| of printing the operand. It is used when identical operands must be |
| printed differently depending on the context. @var{code} comes from |
| the @samp{%} specification that was used to request printing of the |
| operand. If the specification was just @samp{%@var{digit}} then |
| @var{code} is 0; if the specification was @samp{%@var{ltr} |
| @var{digit}} then @var{code} is the ASCII code for @var{ltr}. |
| |
| @findex reg_names |
| If @var{x} is a register, this macro should print the register's name. |
| The names can be found in an array @code{reg_names} whose type is |
| @code{char *[]}. @code{reg_names} is initialized from |
| @code{REGISTER_NAMES}. |
| |
| When the machine description has a specification @samp{%@var{punct}} |
| (a @samp{%} followed by a punctuation character), this macro is called |
| with a null pointer for @var{x} and the punctuation character for |
| @var{code}. |
| @end defmac |
| |
| @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code}) |
| A C expression which evaluates to true if @var{code} is a valid |
| punctuation character for use in the @code{PRINT_OPERAND} macro. If |
| @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no |
| punctuation characters (except for the standard one, @samp{%}) are used |
| in this way. |
| @end defmac |
| |
| @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) |
| A C compound statement to output to stdio stream @var{stream} the |
| assembler syntax for an instruction operand that is a memory reference |
| whose address is @var{x}. @var{x} is an RTL expression. |
| |
| @cindex @code{TARGET_ENCODE_SECTION_INFO} usage |
| On some machines, the syntax for a symbolic address depends on the |
| section that the address refers to. On these machines, define the hook |
| @code{TARGET_ENCODE_SECTION_INFO} to store the information into the |
| @code{symbol_ref}, and then check for it here. @xref{Assembler |
| Format}. |
| @end defmac |
| |
| @findex dbr_sequence_length |
| @defmac DBR_OUTPUT_SEQEND (@var{file}) |
| A C statement, to be executed after all slot-filler instructions have |
| been output. If necessary, call @code{dbr_sequence_length} to |
| determine the number of slots filled in a sequence (zero if not |
| currently outputting a sequence), to decide how many no-ops to output, |
| or whatever. |
| |
| Don't define this macro if it has nothing to do, but it is helpful in |
| reading assembly output if the extent of the delay sequence is made |
| explicit (e.g.@: with white space). |
| @end defmac |
| |
| @findex final_sequence |
| Note that output routines for instructions with delay slots must be |
| prepared to deal with not being output as part of a sequence |
| (i.e.@: when the scheduling pass is not run, or when no slot fillers could be |
| found.) The variable @code{final_sequence} is null when not |
| processing a sequence, otherwise it contains the @code{sequence} rtx |
| being output. |
| |
| @findex asm_fprintf |
| @defmac REGISTER_PREFIX |
| @defmacx LOCAL_LABEL_PREFIX |
| @defmacx USER_LABEL_PREFIX |
| @defmacx IMMEDIATE_PREFIX |
| If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, |
| @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see |
| @file{final.c}). These are useful when a single @file{md} file must |
| support multiple assembler formats. In that case, the various @file{tm.h} |
| files can define these macros differently. |
| @end defmac |
| |
| @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format}) |
| If defined this macro should expand to a series of @code{case} |
| statements which will be parsed inside the @code{switch} statement of |
| the @code{asm_fprintf} function. This allows targets to define extra |
| printf formats which may useful when generating their assembler |
| statements. Note that uppercase letters are reserved for future |
| generic extensions to asm_fprintf, and so are not available to target |
| specific code. The output file is given by the parameter @var{file}. |
| The varargs input pointer is @var{argptr} and the rest of the format |
| string, starting the character after the one that is being switched |
| upon, is pointed to by @var{format}. |
| @end defmac |
| |
| @defmac ASSEMBLER_DIALECT |
| If your target supports multiple dialects of assembler language (such as |
| different opcodes), define this macro as a C expression that gives the |
| numeric index of the assembler language dialect to use, with zero as the |
| first variant. |
| |
| If this macro is defined, you may use constructs of the form |
| @smallexample |
| @samp{@{option0|option1|option2@dots{}@}} |
| @end smallexample |
| @noindent |
| in the output templates of patterns (@pxref{Output Template}) or in the |
| first argument of @code{asm_fprintf}. This construct outputs |
| @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of |
| @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters |
| within these strings retain their usual meaning. If there are fewer |
| alternatives within the braces than the value of |
| @code{ASSEMBLER_DIALECT}, the construct outputs nothing. |
| |
| If you do not define this macro, the characters @samp{@{}, @samp{|} and |
| @samp{@}} do not have any special meaning when used in templates or |
| operands to @code{asm_fprintf}. |
| |
| Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, |
| @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express |
| the variations in assembler language syntax with that mechanism. Define |
| @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax |
| if the syntax variant are larger and involve such things as different |
| opcodes or operand order. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) |
| A C expression to output to @var{stream} some assembler code |
| which will push hard register number @var{regno} onto the stack. |
| The code need not be optimal, since this macro is used only when |
| profiling. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) |
| A C expression to output to @var{stream} some assembler code |
| which will pop hard register number @var{regno} off of the stack. |
| The code need not be optimal, since this macro is used only when |
| profiling. |
| @end defmac |
| |
| @node Dispatch Tables |
| @subsection Output of Dispatch Tables |
| |
| @c prevent bad page break with this line |
| This concerns dispatch tables. |
| |
| @cindex dispatch table |
| @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| pseudo-instruction to generate a difference between two labels. |
| @var{value} and @var{rel} are the numbers of two internal labels. The |
| definitions of these labels are output using |
| @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same |
| way here. For example, |
| |
| @smallexample |
| fprintf (@var{stream}, "\t.word L%d-L%d\n", |
| @var{value}, @var{rel}) |
| @end smallexample |
| |
| You must provide this macro on machines where the addresses in a |
| dispatch table are relative to the table's own address. If defined, GCC |
| will also use this macro on all machines when producing PIC@. |
| @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the |
| mode and flags can be read. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) |
| This macro should be provided on machines where the addresses |
| in a dispatch table are absolute. |
| |
| The definition should be a C statement to output to the stdio stream |
| @var{stream} an assembler pseudo-instruction to generate a reference to |
| a label. @var{value} is the number of an internal label whose |
| definition is output using @code{(*targetm.asm_out.internal_label)}. |
| For example, |
| |
| @smallexample |
| fprintf (@var{stream}, "\t.word L%d\n", @var{value}) |
| @end smallexample |
| @end defmac |
| |
| @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) |
| Define this if the label before a jump-table needs to be output |
| specially. The first three arguments are the same as for |
| @code{(*targetm.asm_out.internal_label)}; the fourth argument is the |
| jump-table which follows (a @code{jump_insn} containing an |
| @code{addr_vec} or @code{addr_diff_vec}). |
| |
| This feature is used on system V to output a @code{swbeg} statement |
| for the table. |
| |
| If this macro is not defined, these labels are output with |
| @code{(*targetm.asm_out.internal_label)}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) |
| Define this if something special must be output at the end of a |
| jump-table. The definition should be a C statement to be executed |
| after the assembler code for the table is written. It should write |
| the appropriate code to stdio stream @var{stream}. The argument |
| @var{table} is the jump-table insn, and @var{num} is the label-number |
| of the preceding label. |
| |
| If this macro is not defined, nothing special is output at the end of |
| the jump-table. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (@var{stream}, @var{decl}, @var{for_eh}, @var{empty}) |
| This target hook emits a label at the beginning of each FDE@. It |
| should be defined on targets where FDEs need special labels, and it |
| should write the appropriate label, for the FDE associated with the |
| function declaration @var{decl}, to the stdio stream @var{stream}. |
| The third argument, @var{for_eh}, is a boolean: true if this is for an |
| exception table. The fourth argument, @var{empty}, is a boolean: |
| true if this is a placeholder label for an omitted FDE@. |
| |
| The default is that FDEs are not given nonlocal labels. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (@var{stream}) |
| This target hook emits a label at the beginning of the exception table. |
| It should be defined on targets where it is desirable for the table |
| to be broken up according to function. |
| |
| The default is that no label is emitted. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_UNWIND_EMIT (FILE * @var{stream}, rtx @var{insn}) |
| This target hook emits and assembly directives required to unwind the |
| given instruction. This is only used when TARGET_UNWIND_INFO is set. |
| @end deftypefn |
| |
| @node Exception Region Output |
| @subsection Assembler Commands for Exception Regions |
| |
| @c prevent bad page break with this line |
| |
| This describes commands marking the start and the end of an exception |
| region. |
| |
| @defmac EH_FRAME_SECTION_NAME |
| If defined, a C string constant for the name of the section containing |
| exception handling frame unwind information. If not defined, GCC will |
| provide a default definition if the target supports named sections. |
| @file{crtstuff.c} uses this macro to switch to the appropriate section. |
| |
| You should define this symbol if your target supports DWARF 2 frame |
| unwind information and the default definition does not work. |
| @end defmac |
| |
| @defmac EH_FRAME_IN_DATA_SECTION |
| If defined, DWARF 2 frame unwind information will be placed in the |
| data section even though the target supports named sections. This |
| might be necessary, for instance, if the system linker does garbage |
| collection and sections cannot be marked as not to be collected. |
| |
| Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is |
| also defined. |
| @end defmac |
| |
| @defmac EH_TABLES_CAN_BE_READ_ONLY |
| Define this macro to 1 if your target is such that no frame unwind |
| information encoding used with non-PIC code will ever require a |
| runtime relocation, but the linker may not support merging read-only |
| and read-write sections into a single read-write section. |
| @end defmac |
| |
| @defmac MASK_RETURN_ADDR |
| An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so |
| that it does not contain any extraneous set bits in it. |
| @end defmac |
| |
| @defmac DWARF2_UNWIND_INFO |
| Define this macro to 0 if your target supports DWARF 2 frame unwind |
| information, but it does not yet work with exception handling. |
| Otherwise, if your target supports this information (if it defines |
| @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP} |
| or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1. |
| |
| If @code{TARGET_UNWIND_INFO} is defined, the target specific unwinder |
| will be used in all cases. Defining this macro will enable the generation |
| of DWARF 2 frame debugging information. |
| |
| If @code{TARGET_UNWIND_INFO} is not defined, and this macro is defined to 1, |
| the DWARF 2 unwinder will be the default exception handling mechanism; |
| otherwise, the @code{setjmp}/@code{longjmp}-based scheme will be used by |
| default. |
| @end defmac |
| |
| @defmac TARGET_UNWIND_INFO |
| Define this macro if your target has ABI specified unwind tables. Usually |
| these will be output by @code{TARGET_UNWIND_EMIT}. |
| @end defmac |
| |
| @deftypevar {Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT |
| This variable should be set to @code{true} if the target ABI requires unwinding |
| tables even when exceptions are not used. |
| @end deftypevar |
| |
| @defmac MUST_USE_SJLJ_EXCEPTIONS |
| This macro need only be defined if @code{DWARF2_UNWIND_INFO} is |
| runtime-variable. In that case, @file{except.h} cannot correctly |
| determine the corresponding definition of @code{MUST_USE_SJLJ_EXCEPTIONS}, |
| so the target must provide it directly. |
| @end defmac |
| |
| @defmac DONT_USE_BUILTIN_SETJMP |
| Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme |
| should use the @code{setjmp}/@code{longjmp} functions from the C library |
| instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery. |
| @end defmac |
| |
| @defmac DWARF_CIE_DATA_ALIGNMENT |
| This macro need only be defined if the target might save registers in the |
| function prologue at an offset to the stack pointer that is not aligned to |
| @code{UNITS_PER_WORD}. The definition should be the negative minimum |
| alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive |
| minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if |
| the target supports DWARF 2 frame unwind information. |
| @end defmac |
| |
| @deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO |
| Contains the value true if the target should add a zero word onto the |
| end of a Dwarf-2 frame info section when used for exception handling. |
| Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and |
| true otherwise. |
| @end deftypevar |
| |
| @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg}) |
| Given a register, this hook should return a parallel of registers to |
| represent where to find the register pieces. Define this hook if the |
| register and its mode are represented in Dwarf in non-contiguous |
| locations, or if the register should be represented in more than one |
| register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}. |
| If not defined, the default is to return @code{NULL_RTX}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym}) |
| This hook is used to output a reference from a frame unwinding table to |
| the type_info object identified by @var{sym}. It should return @code{true} |
| if the reference was output. Returning @code{false} will cause the |
| reference to be output using the normal Dwarf2 routines. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_ARM_EABI_UNWINDER |
| This hook should be set to @code{true} on targets that use an ARM EABI |
| based unwinding library, and @code{false} on other targets. This effects |
| the format of unwinding tables, and how the unwinder in entered after |
| running a cleanup. The default is @code{false}. |
| @end deftypefn |
| |
| @node Alignment Output |
| @subsection Assembler Commands for Alignment |
| |
| @c prevent bad page break with this line |
| This describes commands for alignment. |
| |
| @defmac JUMP_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which is |
| a common destination of jumps and has no fallthru incoming edge. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @var{align_jumps} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. |
| @end defmac |
| |
| @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which follows |
| a @code{BARRIER}. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| @end defmac |
| |
| @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP |
| The maximum number of bytes to skip when applying |
| @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if |
| @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| @end defmac |
| |
| @defmac LOOP_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}, which follows |
| a @code{NOTE_INSN_LOOP_BEG} note. |
| |
| This macro need not be defined if you don't want any special alignment |
| to be done at such a time. Most machine descriptions do not currently |
| define the macro. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @code{align_loops} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. |
| @end defmac |
| |
| @defmac LOOP_ALIGN_MAX_SKIP |
| The maximum number of bytes to skip when applying @code{LOOP_ALIGN}. |
| This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| @end defmac |
| |
| @defmac LABEL_ALIGN (@var{label}) |
| The alignment (log base 2) to put in front of @var{label}. |
| If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, |
| the maximum of the specified values is used. |
| |
| Unless it's necessary to inspect the @var{label} parameter, it is better |
| to set the variable @code{align_labels} in the target's |
| @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's |
| selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. |
| @end defmac |
| |
| @defmac LABEL_ALIGN_MAX_SKIP |
| The maximum number of bytes to skip when applying @code{LABEL_ALIGN}. |
| This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| instruction to advance the location counter by @var{nbytes} bytes. |
| Those bytes should be zero when loaded. @var{nbytes} will be a C |
| expression of type @code{int}. |
| @end defmac |
| |
| @defmac ASM_NO_SKIP_IN_TEXT |
| Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the |
| text section because it fails to put zeros in the bytes that are skipped. |
| This is true on many Unix systems, where the pseudo--op to skip bytes |
| produces no-op instructions rather than zeros when used in the text |
| section. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| command to advance the location counter to a multiple of 2 to the |
| @var{power} bytes. @var{power} will be a C expression of type @code{int}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) |
| Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used |
| for padding, if necessary. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) |
| A C statement to output to the stdio stream @var{stream} an assembler |
| command to advance the location counter to a multiple of 2 to the |
| @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to |
| satisfy the alignment request. @var{power} and @var{max_skip} will be |
| a C expression of type @code{int}. |
| @end defmac |
| |
| @need 3000 |
| @node Debugging Info |
| @section Controlling Debugging Information Format |
| |
| @c prevent bad page break with this line |
| This describes how to specify debugging information. |
| |
| @menu |
| * All Debuggers:: Macros that affect all debugging formats uniformly. |
| * DBX Options:: Macros enabling specific options in DBX format. |
| * DBX Hooks:: Hook macros for varying DBX format. |
| * File Names and DBX:: Macros controlling output of file names in DBX format. |
| * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. |
| * VMS Debug:: Macros for VMS debug format. |
| @end menu |
| |
| @node All Debuggers |
| @subsection Macros Affecting All Debugging Formats |
| |
| @c prevent bad page break with this line |
| These macros affect all debugging formats. |
| |
| @defmac DBX_REGISTER_NUMBER (@var{regno}) |
| A C expression that returns the DBX register number for the compiler |
| register number @var{regno}. In the default macro provided, the value |
| of this expression will be @var{regno} itself. But sometimes there are |
| some registers that the compiler knows about and DBX does not, or vice |
| versa. In such cases, some register may need to have one number in the |
| compiler and another for DBX@. |
| |
| If two registers have consecutive numbers inside GCC, and they can be |
| used as a pair to hold a multiword value, then they @emph{must} have |
| consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. |
| Otherwise, debuggers will be unable to access such a pair, because they |
| expect register pairs to be consecutive in their own numbering scheme. |
| |
| If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that |
| does not preserve register pairs, then what you must do instead is |
| redefine the actual register numbering scheme. |
| @end defmac |
| |
| @defmac DEBUGGER_AUTO_OFFSET (@var{x}) |
| A C expression that returns the integer offset value for an automatic |
| variable having address @var{x} (an RTL expression). The default |
| computation assumes that @var{x} is based on the frame-pointer and |
| gives the offset from the frame-pointer. This is required for targets |
| that produce debugging output for DBX or COFF-style debugging output |
| for SDB and allow the frame-pointer to be eliminated when the |
| @option{-g} options is used. |
| @end defmac |
| |
| @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) |
| A C expression that returns the integer offset value for an argument |
| having address @var{x} (an RTL expression). The nominal offset is |
| @var{offset}. |
| @end defmac |
| |
| @defmac PREFERRED_DEBUGGING_TYPE |
| A C expression that returns the type of debugging output GCC should |
| produce when the user specifies just @option{-g}. Define |
| this if you have arranged for GCC to support more than one format of |
| debugging output. Currently, the allowable values are @code{DBX_DEBUG}, |
| @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, |
| @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. |
| |
| When the user specifies @option{-ggdb}, GCC normally also uses the |
| value of this macro to select the debugging output format, but with two |
| exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the |
| value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is |
| defined, GCC uses @code{DBX_DEBUG}. |
| |
| The value of this macro only affects the default debugging output; the |
| user can always get a specific type of output by using @option{-gstabs}, |
| @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}. |
| @end defmac |
| |
| @node DBX Options |
| @subsection Specific Options for DBX Output |
| |
| @c prevent bad page break with this line |
| These are specific options for DBX output. |
| |
| @defmac DBX_DEBUGGING_INFO |
| Define this macro if GCC should produce debugging output for DBX |
| in response to the @option{-g} option. |
| @end defmac |
| |
| @defmac XCOFF_DEBUGGING_INFO |
| Define this macro if GCC should produce XCOFF format debugging output |
| in response to the @option{-g} option. This is a variant of DBX format. |
| @end defmac |
| |
| @defmac DEFAULT_GDB_EXTENSIONS |
| Define this macro to control whether GCC should by default generate |
| GDB's extended version of DBX debugging information (assuming DBX-format |
| debugging information is enabled at all). If you don't define the |
| macro, the default is 1: always generate the extended information |
| if there is any occasion to. |
| @end defmac |
| |
| @defmac DEBUG_SYMS_TEXT |
| Define this macro if all @code{.stabs} commands should be output while |
| in the text section. |
| @end defmac |
| |
| @defmac ASM_STABS_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. |
| If you don't define this macro, @code{"\t.stabs\t"} is used. This macro |
| applies only to DBX debugging information format. |
| @end defmac |
| |
| @defmac ASM_STABD_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabd\t"} to define a debugging symbol whose |
| value is the current location. If you don't define this macro, |
| @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging |
| information format. |
| @end defmac |
| |
| @defmac ASM_STABN_OP |
| A C string constant, including spacing, naming the assembler pseudo op to |
| use instead of @code{"\t.stabn\t"} to define a debugging symbol with no |
| name. If you don't define this macro, @code{"\t.stabn\t"} is used. This |
| macro applies only to DBX debugging information format. |
| @end defmac |
| |
| @defmac DBX_NO_XREFS |
| Define this macro if DBX on your system does not support the construct |
| @samp{xs@var{tagname}}. On some systems, this construct is used to |
| describe a forward reference to a structure named @var{tagname}. |
| On other systems, this construct is not supported at all. |
| @end defmac |
| |
| @defmac DBX_CONTIN_LENGTH |
| A symbol name in DBX-format debugging information is normally |
| continued (split into two separate @code{.stabs} directives) when it |
| exceeds a certain length (by default, 80 characters). On some |
| operating systems, DBX requires this splitting; on others, splitting |
| must not be done. You can inhibit splitting by defining this macro |
| with the value zero. You can override the default splitting-length by |
| defining this macro as an expression for the length you desire. |
| @end defmac |
| |
| @defmac DBX_CONTIN_CHAR |
| Normally continuation is indicated by adding a @samp{\} character to |
| the end of a @code{.stabs} string when a continuation follows. To use |
| a different character instead, define this macro as a character |
| constant for the character you want to use. Do not define this macro |
| if backslash is correct for your system. |
| @end defmac |
| |
| @defmac DBX_STATIC_STAB_DATA_SECTION |
| Define this macro if it is necessary to go to the data section before |
| outputting the @samp{.stabs} pseudo-op for a non-global static |
| variable. |
| @end defmac |
| |
| @defmac DBX_TYPE_DECL_STABS_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a typedef. The default is @code{N_LSYM}. |
| @end defmac |
| |
| @defmac DBX_STATIC_CONST_VAR_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a static variable located in the text section. DBX format does not |
| provide any ``right'' way to do this. The default is @code{N_FUN}. |
| @end defmac |
| |
| @defmac DBX_REGPARM_STABS_CODE |
| The value to use in the ``code'' field of the @code{.stabs} directive |
| for a parameter passed in registers. DBX format does not provide any |
| ``right'' way to do this. The default is @code{N_RSYM}. |
| @end defmac |
| |
| @defmac DBX_REGPARM_STABS_LETTER |
| The letter to use in DBX symbol data to identify a symbol as a parameter |
| passed in registers. DBX format does not customarily provide any way to |
| do this. The default is @code{'P'}. |
| @end defmac |
| |
| @defmac DBX_FUNCTION_FIRST |
| Define this macro if the DBX information for a function and its |
| arguments should precede the assembler code for the function. Normally, |
| in DBX format, the debugging information entirely follows the assembler |
| code. |
| @end defmac |
| |
| @defmac DBX_BLOCKS_FUNCTION_RELATIVE |
| Define this macro, with value 1, if the value of a symbol describing |
| the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be |
| relative to the start of the enclosing function. Normally, GCC uses |
| an absolute address. |
| @end defmac |
| |
| @defmac DBX_LINES_FUNCTION_RELATIVE |
| Define this macro, with value 1, if the value of a symbol indicating |
| the current line number (@code{N_SLINE}) should be relative to the |
| start of the enclosing function. Normally, GCC uses an absolute address. |
| @end defmac |
| |
| @defmac DBX_USE_BINCL |
| Define this macro if GCC should generate @code{N_BINCL} and |
| @code{N_EINCL} stabs for included header files, as on Sun systems. This |
| macro also directs GCC to output a type number as a pair of a file |
| number and a type number within the file. Normally, GCC does not |
| generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single |
| number for a type number. |
| @end defmac |
| |
| @node DBX Hooks |
| @subsection Open-Ended Hooks for DBX Format |
| |
| @c prevent bad page break with this line |
| These are hooks for DBX format. |
| |
| @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) |
| Define this macro to say how to output to @var{stream} the debugging |
| information for the start of a scope level for variable names. The |
| argument @var{name} is the name of an assembler symbol (for use with |
| @code{assemble_name}) whose value is the address where the scope begins. |
| @end defmac |
| |
| @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) |
| Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. |
| @end defmac |
| |
| @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl}) |
| Define this macro if the target machine requires special handling to |
| output an @code{N_FUN} entry for the function @var{decl}. |
| @end defmac |
| |
| @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter}) |
| A C statement to output DBX debugging information before code for line |
| number @var{line} of the current source file to the stdio stream |
| @var{stream}. @var{counter} is the number of time the macro was |
| invoked, including the current invocation; it is intended to generate |
| unique labels in the assembly output. |
| |
| This macro should not be defined if the default output is correct, or |
| if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}. |
| @end defmac |
| |
| @defmac NO_DBX_FUNCTION_END |
| Some stabs encapsulation formats (in particular ECOFF), cannot handle the |
| @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. |
| On those machines, define this macro to turn this feature off without |
| disturbing the rest of the gdb extensions. |
| @end defmac |
| |
| @defmac NO_DBX_BNSYM_ENSYM |
| Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx |
| extension construct. On those machines, define this macro to turn this |
| feature off without disturbing the rest of the gdb extensions. |
| @end defmac |
| |
| @node File Names and DBX |
| @subsection File Names in DBX Format |
| |
| @c prevent bad page break with this line |
| This describes file names in DBX format. |
| |
| @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information to the stdio stream |
| @var{stream}, which indicates that file @var{name} is the main source |
| file---the file specified as the input file for compilation. |
| This macro is called only once, at the beginning of compilation. |
| |
| This macro need not be defined if the standard form of output |
| for DBX debugging information is appropriate. |
| |
| It may be necessary to refer to a label equal to the beginning of the |
| text section. You can use @samp{assemble_name (stream, ltext_label_name)} |
| to do so. If you do this, you must also set the variable |
| @var{used_ltext_label_name} to @code{true}. |
| @end defmac |
| |
| @defmac NO_DBX_MAIN_SOURCE_DIRECTORY |
| Define this macro, with value 1, if GCC should not emit an indication |
| of the current directory for compilation and current source language at |
| the beginning of the file. |
| @end defmac |
| |
| @defmac NO_DBX_GCC_MARKER |
| Define this macro, with value 1, if GCC should not emit an indication |
| that this object file was compiled by GCC@. The default is to emit |
| an @code{N_OPT} stab at the beginning of every source file, with |
| @samp{gcc2_compiled.} for the string and value 0. |
| @end defmac |
| |
| @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) |
| A C statement to output DBX debugging information at the end of |
| compilation of the main source file @var{name}. Output should be |
| written to the stdio stream @var{stream}. |
| |
| If you don't define this macro, nothing special is output at the end |
| of compilation, which is correct for most machines. |
| @end defmac |
| |
| @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END |
| Define this macro @emph{instead of} defining |
| @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at |
| the end of compilation is a @code{N_SO} stab with an empty string, |
| whose value is the highest absolute text address in the file. |
| @end defmac |
| |
| @need 2000 |
| @node SDB and DWARF |
| @subsection Macros for SDB and DWARF Output |
| |
| @c prevent bad page break with this line |
| Here are macros for SDB and DWARF output. |
| |
| @defmac SDB_DEBUGGING_INFO |
| Define this macro if GCC should produce COFF-style debugging output |
| for SDB in response to the @option{-g} option. |
| @end defmac |
| |
| @defmac DWARF2_DEBUGGING_INFO |
| Define this macro if GCC should produce dwarf version 2 format |
| debugging output in response to the @option{-g} option. |
| |
| @deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (tree @var{function}) |
| Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to |
| be emitted for each function. Instead of an integer return the enum |
| value for the @code{DW_CC_} tag. |
| @end deftypefn |
| |
| To support optional call frame debugging information, you must also |
| define @code{INCOMING_RETURN_ADDR_RTX} and either set |
| @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the |
| prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} |
| as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. |
| @end defmac |
| |
| @defmac DWARF2_FRAME_INFO |
| Define this macro to a nonzero value if GCC should always output |
| Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO} |
| (@pxref{Exception Region Output} is nonzero, GCC will output this |
| information not matter how you define @code{DWARF2_FRAME_INFO}. |
| @end defmac |
| |
| @defmac DWARF2_ASM_LINE_DEBUG_INFO |
| Define this macro to be a nonzero value if the assembler can generate Dwarf 2 |
| line debug info sections. This will result in much more compact line number |
| tables, and hence is desirable if it works. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) |
| A C statement to issue assembly directives that create a difference |
| @var{lab1} minus @var{lab2}, using an integer of the given @var{size}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section}) |
| A C statement to issue assembly directives that create a |
| section-relative reference to the given @var{label}, using an integer of the |
| given @var{size}. The label is known to be defined in the given @var{section}. |
| @end defmac |
| |
| @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) |
| A C statement to issue assembly directives that create a self-relative |
| reference to the given @var{label}, using an integer of the given @var{size}. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{FILE}, int @var{size}, rtx @var{x}) |
| If defined, this target hook is a function which outputs a DTP-relative |
| reference to the given TLS symbol of the specified size. |
| @end deftypefn |
| |
| @defmac PUT_SDB_@dots{} |
| Define these macros to override the assembler syntax for the special |
| SDB assembler directives. See @file{sdbout.c} for a list of these |
| macros and their arguments. If the standard syntax is used, you need |
| not define them yourself. |
| @end defmac |
| |
| @defmac SDB_DELIM |
| Some assemblers do not support a semicolon as a delimiter, even between |
| SDB assembler directives. In that case, define this macro to be the |
| delimiter to use (usually @samp{\n}). It is not necessary to define |
| a new set of @code{PUT_SDB_@var{op}} macros if this is the only change |
| required. |
| @end defmac |
| |
| @defmac SDB_ALLOW_UNKNOWN_REFERENCES |
| Define this macro to allow references to unknown structure, |
| union, or enumeration tags to be emitted. Standard COFF does not |
| allow handling of unknown references, MIPS ECOFF has support for |
| it. |
| @end defmac |
| |
| @defmac SDB_ALLOW_FORWARD_REFERENCES |
| Define this macro to allow references to structure, union, or |
| enumeration tags that have not yet been seen to be handled. Some |
| assemblers choke if forward tags are used, while some require it. |
| @end defmac |
| |
| @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) |
| A C statement to output SDB debugging information before code for line |
| number @var{line} of the current source file to the stdio stream |
| @var{stream}. The default is to emit an @code{.ln} directive. |
| @end defmac |
| |
| @need 2000 |
| @node VMS Debug |
| @subsection Macros for VMS Debug Format |
| |
| @c prevent bad page break with this line |
| Here are macros for VMS debug format. |
| |
| @defmac VMS_DEBUGGING_INFO |
| Define this macro if GCC should produce debugging output for VMS |
| in response to the @option{-g} option. The default behavior for VMS |
| is to generate minimal debug info for a traceback in the absence of |
| @option{-g} unless explicitly overridden with @option{-g0}. This |
| behavior is controlled by @code{OPTIMIZATION_OPTIONS} and |
| @code{OVERRIDE_OPTIONS}. |
| @end defmac |
| |
| @node Floating Point |
| @section Cross Compilation and Floating Point |
| @cindex cross compilation and floating point |
| @cindex floating point and cross compilation |
| |
| While all modern machines use twos-complement representation for integers, |
| there are a variety of representations for floating point numbers. This |
| means that in a cross-compiler the representation of floating point numbers |
| in the compiled program may be different from that used in the machine |
| doing the compilation. |
| |
| Because different representation systems may offer different amounts of |
| range and precision, all floating point constants must be represented in |
| the target machine's format. Therefore, the cross compiler cannot |
| safely use the host machine's floating point arithmetic; it must emulate |
| the target's arithmetic. To ensure consistency, GCC always uses |
| emulation to work with floating point values, even when the host and |
| target floating point formats are identical. |
| |
| The following macros are provided by @file{real.h} for the compiler to |
| use. All parts of the compiler which generate or optimize |
| floating-point calculations must use these macros. They may evaluate |
| their operands more than once, so operands must not have side effects. |
| |
| @defmac REAL_VALUE_TYPE |
| The C data type to be used to hold a floating point value in the target |
| machine's format. Typically this is a @code{struct} containing an |
| array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque |
| quantity. |
| @end defmac |
| |
| @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) |
| Compares for equality the two values, @var{x} and @var{y}. If the target |
| floating point format supports negative zeroes and/or NaNs, |
| @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and |
| @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false. |
| @end deftypefn |
| |
| @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) |
| Tests whether @var{x} is less than @var{y}. |
| @end deftypefn |
| |
| @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) |
| Truncates @var{x} to a signed integer, rounding toward zero. |
| @end deftypefn |
| |
| @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) |
| Truncates @var{x} to an unsigned integer, rounding toward zero. If |
| @var{x} is negative, returns zero. |
| @end deftypefn |
| |
| @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode}) |
| Converts @var{string} into a floating point number in the target machine's |
| representation for mode @var{mode}. This routine can handle both |
| decimal and hexadecimal floating point constants, using the syntax |
| defined by the C language for both. |
| @end deftypefn |
| |
| @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) |
| Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. |
| @end deftypefn |
| |
| @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) |
| Determines whether @var{x} represents infinity (positive or negative). |
| @end deftypefn |
| |
| @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) |
| Determines whether @var{x} represents a ``NaN'' (not-a-number). |
| @end deftypefn |
| |
| @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}) |
| Calculates an arithmetic operation on the two floating point values |
| @var{x} and @var{y}, storing the result in @var{output} (which must be a |
| variable). |
| |
| The operation to be performed is specified by @var{code}. Only the |
| following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR}, |
| @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}. |
| |
| If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the |
| target's floating point format cannot represent infinity, it will call |
| @code{abort}. Callers should check for this situation first, using |
| @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}. |
| @end deftypefn |
| |
| @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) |
| Returns the negative of the floating point value @var{x}. |
| @end deftypefn |
| |
| @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) |
| Returns the absolute value of @var{x}. |
| @end deftypefn |
| |
| @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x}) |
| Truncates the floating point value @var{x} to fit in @var{mode}. The |
| return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an |
| appropriate bit pattern to be output asa floating constant whose |
| precision accords with mode @var{mode}. |
| @end deftypefn |
| |
| @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x}) |
| Converts a floating point value @var{x} into a double-precision integer |
| which is then stored into @var{low} and @var{high}. If the value is not |
| integral, it is truncated. |
| @end deftypefn |
| |
| @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}) |
| Converts a double-precision integer found in @var{low} and @var{high}, |
| into a floating point value which is then stored into @var{x}. The |
| value is truncated to fit in mode @var{mode}. |
| @end deftypefn |
| |
| @node Mode Switching |
| @section Mode Switching Instructions |
| @cindex mode switching |
| The following macros control mode switching optimizations: |
| |
| @defmac OPTIMIZE_MODE_SWITCHING (@var{entity}) |
| Define this macro if the port needs extra instructions inserted for mode |
| switching in an optimizing compilation. |
| |
| For an example, the SH4 can perform both single and double precision |
| floating point operations, but to perform a single precision operation, |
| the FPSCR PR bit has to be cleared, while for a double precision |
| operation, this bit has to be set. Changing the PR bit requires a general |
| purpose register as a scratch register, hence these FPSCR sets have to |
| be inserted before reload, i.e.@: you can't put this into instruction emitting |
| or @code{TARGET_MACHINE_DEPENDENT_REORG}. |
| |
| You can have multiple entities that are mode-switched, and select at run time |
| which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should |
| return nonzero for any @var{entity} that needs mode-switching. |
| If you define this macro, you also have to define |
| @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, |
| @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. |
| @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT} |
| are optional. |
| @end defmac |
| |
| @defmac NUM_MODES_FOR_MODE_SWITCHING |
| If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as |
| initializer for an array of integers. Each initializer element |
| N refers to an entity that needs mode switching, and specifies the number |
| of different modes that might need to be set for this entity. |
| The position of the initializer in the initializer---starting counting at |
| zero---determines the integer that is used to refer to the mode-switched |
| entity in question. |
| In macros that take mode arguments / yield a mode result, modes are |
| represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode |
| switch is needed / supplied. |
| @end defmac |
| |
| @defmac MODE_NEEDED (@var{entity}, @var{insn}) |
| @var{entity} is an integer specifying a mode-switched entity. If |
| @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to |
| return an integer value not larger than the corresponding element in |
| @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must |
| be switched into prior to the execution of @var{insn}. |
| @end defmac |
| |
| @defmac MODE_AFTER (@var{mode}, @var{insn}) |
| If this macro is defined, it is evaluated for every @var{insn} during |
| mode switching. It determines the mode that an insn results in (if |
| different from the incoming mode). |
| @end defmac |
| |
| @defmac MODE_ENTRY (@var{entity}) |
| If this macro is defined, it is evaluated for every @var{entity} that needs |
| mode switching. It should evaluate to an integer, which is a mode that |
| @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY} |
| is defined then @code{MODE_EXIT} must be defined. |
| @end defmac |
| |
| @defmac MODE_EXIT (@var{entity}) |
| If this macro is defined, it is evaluated for every @var{entity} that needs |
| mode switching. It should evaluate to an integer, which is a mode that |
| @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT} |
| is defined then @code{MODE_ENTRY} must be defined. |
| @end defmac |
| |
| @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) |
| This macro specifies the order in which modes for @var{entity} are processed. |
| 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the |
| lowest. The value of the macro should be an integer designating a mode |
| for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} |
| (@var{entity}, @var{n}) shall be a bijection in 0 @dots{} |
| @code{num_modes_for_mode_switching[@var{entity}] - 1}. |
| @end defmac |
| |
| @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) |
| Generate one or more insns to set @var{entity} to @var{mode}. |
| @var{hard_reg_live} is the set of hard registers live at the point where |
| the insn(s) are to be inserted. |
| @end defmac |
| |
| @node Target Attributes |
| @section Defining target-specific uses of @code{__attribute__} |
| @cindex target attributes |
| @cindex machine attributes |
| @cindex attributes, target-specific |
| |
| Target-specific attributes may be defined for functions, data and types. |
| These are described using the following target hooks; they also need to |
| be documented in @file{extend.texi}. |
| |
| @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE |
| If defined, this target hook points to an array of @samp{struct |
| attribute_spec} (defined in @file{tree.h}) specifying the machine |
| specific attributes for this target and some of the restrictions on the |
| entities to which these attributes are applied and the arguments they |
| take. |
| @end deftypevr |
| |
| @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) |
| If defined, this target hook is a function which returns zero if the attributes on |
| @var{type1} and @var{type2} are incompatible, one if they are compatible, |
| and two if they are nearly compatible (which causes a warning to be |
| generated). If this is not defined, machine-specific attributes are |
| supposed always to be compatible. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) |
| If defined, this target hook is a function which assigns default attributes to |
| newly defined @var{type}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) |
| Define this target hook if the merging of type attributes needs special |
| handling. If defined, the result is a list of the combined |
| @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed |
| that @code{comptypes} has already been called and returned 1. This |
| function may call @code{merge_attributes} to handle machine-independent |
| merging. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) |
| Define this target hook if the merging of decl attributes needs special |
| handling. If defined, the result is a list of the combined |
| @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. |
| @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of |
| when this is needed are when one attribute overrides another, or when an |
| attribute is nullified by a subsequent definition. This function may |
| call @code{merge_attributes} to handle machine-independent merging. |
| |
| @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES |
| If the only target-specific handling you require is @samp{dllimport} |
| for Microsoft Windows targets, you should define the macro |
| @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler |
| will then define a function called |
| @code{merge_dllimport_decl_attributes} which can then be defined as |
| the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also |
| add @code{handle_dll_attribute} in the attribute table for your port |
| to perform initial processing of the @samp{dllimport} and |
| @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and |
| @file{i386/i386.c}, for example. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (tree @var{decl}) |
| @var{decl} is a variable or function with @code{__attribute__((dllimport))} |
| specified. Use this hook if the target needs to add extra validation |
| checks to @code{handle_dll_attribute}. |
| @end deftypefn |
| |
| @defmac TARGET_DECLSPEC |
| Define this macro to a nonzero value if you want to treat |
| @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By |
| default, this behavior is enabled only for targets that define |
| @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation |
| of @code{__declspec} is via a built-in macro, but you should not rely |
| on this implementation detail. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) |
| Define this target hook if you want to be able to add attributes to a decl |
| when it is being created. This is normally useful for back ends which |
| wish to implement a pragma by using the attributes which correspond to |
| the pragma's effect. The @var{node} argument is the decl which is being |
| created. The @var{attr_ptr} argument is a pointer to the attribute list |
| for this decl. The list itself should not be modified, since it may be |
| shared with other decls, but attributes may be chained on the head of |
| the list and @code{*@var{attr_ptr}} modified to point to the new |
| attributes, or a copy of the list may be made if further changes are |
| needed. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl}) |
| @cindex inlining |
| This target hook returns @code{true} if it is ok to inline @var{fndecl} |
| into the current function, despite its having target-specific |
| attributes, @code{false} otherwise. By default, if a function has a |
| target specific attribute attached to it, it will not be inlined. |
| @end deftypefn |
| |
| @node MIPS Coprocessors |
| @section Defining coprocessor specifics for MIPS targets. |
| @cindex MIPS coprocessor-definition macros |
| |
| The MIPS specification allows MIPS implementations to have as many as 4 |
| coprocessors, each with as many as 32 private registers. GCC supports |
| accessing these registers and transferring values between the registers |
| and memory using asm-ized variables. For example: |
| |
| @smallexample |
| register unsigned int cp0count asm ("c0r1"); |
| unsigned int d; |
| |
| d = cp0count + 3; |
| @end smallexample |
| |
| (``c0r1'' is the default name of register 1 in coprocessor 0; alternate |
| names may be added as described below, or the default names may be |
| overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) |
| |
| Coprocessor registers are assumed to be epilogue-used; sets to them will |
| be preserved even if it does not appear that the register is used again |
| later in the function. |
| |
| Another note: according to the MIPS spec, coprocessor 1 (if present) is |
| the FPU@. One accesses COP1 registers through standard mips |
| floating-point support; they are not included in this mechanism. |
| |
| There is one macro used in defining the MIPS coprocessor interface which |
| you may want to override in subtargets; it is described below. |
| |
| @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES |
| A comma-separated list (with leading comma) of pairs describing the |
| alternate names of coprocessor registers. The format of each entry should be |
| @smallexample |
| @{ @var{alternatename}, @var{register_number}@} |
| @end smallexample |
| Default: empty. |
| @end defmac |
| |
| @node PCH Target |
| @section Parameters for Precompiled Header Validity Checking |
| @cindex parameters, precompiled headers |
| |
| @deftypefn {Target Hook} void *TARGET_GET_PCH_VALIDITY (size_t *@var{sz}) |
| This hook returns the data needed by @code{TARGET_PCH_VALID_P} and sets |
| @samp{*@var{sz}} to the size of the data in bytes. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} const char *TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz}) |
| This hook checks whether the options used to create a PCH file are |
| compatible with the current settings. It returns @code{NULL} |
| if so and a suitable error message if not. Error messages will |
| be presented to the user and must be localized using @samp{_(@var{msg})}. |
| |
| @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY} |
| when the PCH file was created and @var{sz} is the size of that data in bytes. |
| It's safe to assume that the data was created by the same version of the |
| compiler, so no format checking is needed. |
| |
| The default definition of @code{default_pch_valid_p} should be |
| suitable for most targets. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} const char *TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags}) |
| If this hook is nonnull, the default implementation of |
| @code{TARGET_PCH_VALID_P} will use it to check for compatible values |
| of @code{target_flags}. @var{pch_flags} specifies the value that |
| @code{target_flags} had when the PCH file was created. The return |
| value is the same as for @code{TARGET_PCH_VALID_P}. |
| @end deftypefn |
| |
| @node C++ ABI |
| @section C++ ABI parameters |
| @cindex parameters, c++ abi |
| |
| @deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void) |
| Define this hook to override the integer type used for guard variables. |
| These are used to implement one-time construction of static objects. The |
| default is long_long_integer_type_node. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void) |
| This hook determines how guard variables are used. It should return |
| @code{false} (the default) if first byte should be used. A return value of |
| @code{true} indicates the least significant bit should be used. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type}) |
| This hook returns the size of the cookie to use when allocating an array |
| whose elements have the indicated @var{type}. Assumes that it is already |
| known that a cookie is needed. The default is |
| @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the |
| IA64/Generic C++ ABI@. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void) |
| This hook should return @code{true} if the element size should be stored in |
| array cookies. The default is to return @code{false}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export}) |
| If defined by a backend this hook allows the decision made to export |
| class @var{type} to be overruled. Upon entry @var{import_export} |
| will contain 1 if the class is going to be exported, @minus{}1 if it is going |
| to be imported and 0 otherwise. This function should return the |
| modified value and perform any other actions necessary to support the |
| backend's targeted operating system. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void) |
| This hook should return @code{true} if constructors and destructors return |
| the address of the object created/destroyed. The default is to return |
| @code{false}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void) |
| This hook returns true if the key method for a class (i.e., the method |
| which, if defined in the current translation unit, causes the virtual |
| table to be emitted) may be an inline function. Under the standard |
| Itanium C++ ABI the key method may be an inline function so long as |
| the function is not declared inline in the class definition. Under |
| some variants of the ABI, an inline function can never be the key |
| method. The default is to return @code{true}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl}) |
| @var{decl} is a virtual table, virtual table table, typeinfo object, |
| or other similar implicit class data object that will be emitted with |
| external linkage in this translation unit. No ELF visibility has been |
| explicitly specified. If the target needs to specify a visibility |
| other than that of the containing class, use this hook to set |
| @code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void) |
| This hook returns true (the default) if virtual tables and other |
| similar implicit class data objects are always COMDAT if they have |
| external linkage. If this hook returns false, then class data for |
| classes whose virtual table will be emitted in only one translation |
| unit will not be COMDAT. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void) |
| This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI) |
| should be used to register static destructors when @option{-fuse-cxa-atexit} |
| is in effect. The default is to return false to use @code{__cxa_atexit}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type}) |
| @var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just been |
| defined. Use this hook to make adjustments to the class (eg, tweak |
| visibility or perform any other required target modifications). |
| @end deftypefn |
| |
| @c APPLE LOCAL begin mainline 4.3 2006-01-10 4871915 |
| @deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void) |
| This hook returns true (the default) if the RTTI information for |
| the basic types which is defined in the C++ runtime should always |
| be COMDAT, false if it should not be COMDAT. |
| @end deftypefn |
| |
| @c APPLE LOCAL end mainline 4.3 2006-01-10 4871915 |
| @node Misc |
| @section Miscellaneous Parameters |
| @cindex parameters, miscellaneous |
| |
| @c prevent bad page break with this line |
| Here are several miscellaneous parameters. |
| |
| @defmac HAS_LONG_COND_BRANCH |
| Define this boolean macro to indicate whether or not your architecture |
| has conditional branches that can span all of memory. It is used in |
| conjunction with an optimization that partitions hot and cold basic |
| blocks into separate sections of the executable. If this macro is |
| set to false, gcc will convert any conditional branches that attempt |
| to cross between sections into unconditional branches or indirect jumps. |
| @end defmac |
| |
| @defmac HAS_LONG_UNCOND_BRANCH |
| Define this boolean macro to indicate whether or not your architecture |
| has unconditional branches that can span all of memory. It is used in |
| conjunction with an optimization that partitions hot and cold basic |
| blocks into separate sections of the executable. If this macro is |
| set to false, gcc will convert any unconditional branches that attempt |
| to cross between sections into indirect jumps. |
| @end defmac |
| |
| @defmac CASE_VECTOR_MODE |
| An alias for a machine mode name. This is the machine mode that |
| elements of a jump-table should have. |
| @end defmac |
| |
| @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) |
| Optional: return the preferred mode for an @code{addr_diff_vec} |
| when the minimum and maximum offset are known. If you define this, |
| it enables extra code in branch shortening to deal with @code{addr_diff_vec}. |
| To make this work, you also have to define @code{INSN_ALIGN} and |
| make the alignment for @code{addr_diff_vec} explicit. |
| The @var{body} argument is provided so that the offset_unsigned and scale |
| flags can be updated. |
| @end defmac |
| |
| @defmac CASE_VECTOR_PC_RELATIVE |
| Define this macro to be a C expression to indicate when jump-tables |
| should contain relative addresses. You need not define this macro if |
| jump-tables never contain relative addresses, or jump-tables should |
| contain relative addresses only when @option{-fPIC} or @option{-fPIC} |
| is in effect. |
| @end defmac |
| |
| @defmac CASE_VALUES_THRESHOLD |
| Define this to be the smallest number of different values for which it |
| is best to use a jump-table instead of a tree of conditional branches. |
| The default is four for machines with a @code{casesi} instruction and |
| five otherwise. This is best for most machines. |
| @end defmac |
| |
| @defmac CASE_USE_BIT_TESTS |
| Define this macro to be a C expression to indicate whether C switch |
| statements may be implemented by a sequence of bit tests. This is |
| advantageous on processors that can efficiently implement left shift |
| of 1 by the number of bits held in a register, but inappropriate on |
| targets that would require a loop. By default, this macro returns |
| @code{true} if the target defines an @code{ashlsi3} pattern, and |
| @code{false} otherwise. |
| @end defmac |
| |
| @defmac WORD_REGISTER_OPERATIONS |
| Define this macro if operations between registers with integral mode |
| smaller than a word are always performed on the entire register. |
| Most RISC machines have this property and most CISC machines do not. |
| @end defmac |
| |
| @defmac LOAD_EXTEND_OP (@var{mem_mode}) |
| Define this macro to be a C expression indicating when insns that read |
| memory in @var{mem_mode}, an integral mode narrower than a word, set the |
| bits outside of @var{mem_mode} to be either the sign-extension or the |
| zero-extension of the data read. Return @code{SIGN_EXTEND} for values |
| of @var{mem_mode} for which the |
| insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and |
| @code{UNKNOWN} for other modes. |
| |
| This macro is not called with @var{mem_mode} non-integral or with a width |
| greater than or equal to @code{BITS_PER_WORD}, so you may return any |
| value in this case. Do not define this macro if it would always return |
| @code{UNKNOWN}. On machines where this macro is defined, you will normally |
| define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. |
| |
| You may return a non-@code{UNKNOWN} value even if for some hard registers |
| the sign extension is not performed, if for the @code{REGNO_REG_CLASS} |
| of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero |
| when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any |
| integral mode larger than this but not larger than @code{word_mode}. |
| |
| You must return @code{UNKNOWN} if for some hard registers that allow this |
| mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to |
| @code{word_mode}, but that they can change to another integral mode that |
| is larger then @var{mem_mode} but still smaller than @code{word_mode}. |
| @end defmac |
| |
| @defmac SHORT_IMMEDIATES_SIGN_EXTEND |
| Define this macro if loading short immediate values into registers sign |
| extends. |
| @end defmac |
| |
| @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC |
| Define this macro if the same instructions that convert a floating |
| point number to a signed fixed point number also convert validly to an |
| unsigned one. |
| @end defmac |
| |
| @deftypefn {Target Hook} int TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (enum machine_mode @var{mode}) |
| When @option{-ffast-math} is in effect, GCC tries to optimize |
| divisions by the same divisor, by turning them into multiplications by |
| the reciprocal. This target hook specifies the minimum number of divisions |
| that should be there for GCC to perform the optimization for a variable |
| of mode @var{mode}. The default implementation returns 3 if the machine |
| has an instruction for the division, and 2 if it does not. |
| @end deftypefn |
| |
| @defmac MOVE_MAX |
| The maximum number of bytes that a single instruction can move quickly |
| between memory and registers or between two memory locations. |
| @end defmac |
| |
| @defmac MAX_MOVE_MAX |
| The maximum number of bytes that a single instruction can move quickly |
| between memory and registers or between two memory locations. If this |
| is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the |
| constant value that is the largest value that @code{MOVE_MAX} can have |
| at run-time. |
| @end defmac |
| |
| @defmac SHIFT_COUNT_TRUNCATED |
| A C expression that is nonzero if on this machine the number of bits |
| actually used for the count of a shift operation is equal to the number |
| of bits needed to represent the size of the object being shifted. When |
| this macro is nonzero, the compiler will assume that it is safe to omit |
| a sign-extend, zero-extend, and certain bitwise `and' instructions that |
| truncates the count of a shift operation. On machines that have |
| instructions that act on bit-fields at variable positions, which may |
| include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} |
| also enables deletion of truncations of the values that serve as |
| arguments to bit-field instructions. |
| |
| If both types of instructions truncate the count (for shifts) and |
| position (for bit-field operations), or if no variable-position bit-field |
| instructions exist, you should define this macro. |
| |
| However, on some machines, such as the 80386 and the 680x0, truncation |
| only applies to shift operations and not the (real or pretended) |
| bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on |
| such machines. Instead, add patterns to the @file{md} file that include |
| the implied truncation of the shift instructions. |
| |
| You need not define this macro if it would always have the value of zero. |
| @end defmac |
| |
| @anchor{TARGET_SHIFT_TRUNCATION_MASK} |
| @deftypefn {Target Hook} int TARGET_SHIFT_TRUNCATION_MASK (enum machine_mode @var{mode}) |
| This function describes how the standard shift patterns for @var{mode} |
| deal with shifts by negative amounts or by more than the width of the mode. |
| @xref{shift patterns}. |
| |
| On many machines, the shift patterns will apply a mask @var{m} to the |
| shift count, meaning that a fixed-width shift of @var{x} by @var{y} is |
| equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If |
| this is true for mode @var{mode}, the function should return @var{m}, |
| otherwise it should return 0. A return value of 0 indicates that no |
| particular behavior is guaranteed. |
| |
| Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does |
| @emph{not} apply to general shift rtxes; it applies only to instructions |
| that are generated by the named shift patterns. |
| |
| The default implementation of this function returns |
| @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED} |
| and 0 otherwise. This definition is always safe, but if |
| @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns |
| nevertheless truncate the shift count, you may get better code |
| by overriding it. |
| @end deftypefn |
| |
| @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) |
| A C expression which is nonzero if on this machine it is safe to |
| ``convert'' an integer of @var{inprec} bits to one of @var{outprec} |
| bits (where @var{outprec} is smaller than @var{inprec}) by merely |
| operating on it as if it had only @var{outprec} bits. |
| |
| On many machines, this expression can be 1. |
| |
| @c rearranged this, removed the phrase "it is reported that". this was |
| @c to fix an overfull hbox. --mew 10feb93 |
| When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for |
| modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. |
| If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in |
| such cases may improve things. |
| @end defmac |
| |
| @deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (enum machine_mode @var{mode}, enum machine_mode @var{rep_mode}) |
| The representation of an integral mode can be such that the values |
| are always extended to a wider integral mode. Return |
| @code{SIGN_EXTEND} if values of @var{mode} are represented in |
| sign-extended form to @var{rep_mode}. Return @code{UNKNOWN} |
| otherwise. (Currently, none of the targets use zero-extended |
| representation this way so unlike @code{LOAD_EXTEND_OP}, |
| @code{TARGET_MODE_REP_EXTENDED} is expected to return either |
| @code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends |
| @var{mode} to @var{mode_rep} so that @var{mode_rep} is not the next |
| widest integral mode and currently we take advantage of this fact.) |
| |
| Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN} |
| value even if the extension is not performed on certain hard registers |
| as long as for the @code{REGNO_REG_CLASS} of these hard registers |
| @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero. |
| |
| Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP} |
| describe two related properties. If you define |
| @code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want |
| to define @code{LOAD_EXTEND_OP (mode)} to return the same type of |
| extension. |
| |
| In order to enforce the representation of @code{mode}, |
| @code{TRULY_NOOP_TRUNCATION} should return false when truncating to |
| @code{mode}. |
| @end deftypefn |
| |
| @defmac STORE_FLAG_VALUE |
| A C expression describing the value returned by a comparison operator |
| with an integral mode and stored by a store-flag instruction |
| (@samp{s@var{cond}}) when the condition is true. This description must |
| apply to @emph{all} the @samp{s@var{cond}} patterns and all the |
| comparison operators whose results have a @code{MODE_INT} mode. |
| |
| A value of 1 or @minus{}1 means that the instruction implementing the |
| comparison operator returns exactly 1 or @minus{}1 when the comparison is true |
| and 0 when the comparison is false. Otherwise, the value indicates |
| which bits of the result are guaranteed to be 1 when the comparison is |
| true. This value is interpreted in the mode of the comparison |
| operation, which is given by the mode of the first operand in the |
| @samp{s@var{cond}} pattern. Either the low bit or the sign bit of |
| @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by |
| the compiler. |
| |
| If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will |
| generate code that depends only on the specified bits. It can also |
| replace comparison operators with equivalent operations if they cause |
| the required bits to be set, even if the remaining bits are undefined. |
| For example, on a machine whose comparison operators return an |
| @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as |
| @samp{0x80000000}, saying that just the sign bit is relevant, the |
| expression |
| |
| @smallexample |
| (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) |
| @end smallexample |
| |
| @noindent |
| can be converted to |
| |
| @smallexample |
| (ashift:SI @var{x} (const_int @var{n})) |
| @end smallexample |
| |
| @noindent |
| where @var{n} is the appropriate shift count to move the bit being |
| tested into the sign bit. |
| |
| There is no way to describe a machine that always sets the low-order bit |
| for a true value, but does not guarantee the value of any other bits, |
| but we do not know of any machine that has such an instruction. If you |
| are trying to port GCC to such a machine, include an instruction to |
| perform a logical-and of the result with 1 in the pattern for the |
| comparison operators and let us know at @email{gcc@@gcc.gnu.org}. |
| |
| Often, a machine will have multiple instructions that obtain a value |
| from a comparison (or the condition codes). Here are rules to guide the |
| choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions |
| to be used: |
| |
| @itemize @bullet |
| @item |
| Use the shortest sequence that yields a valid definition for |
| @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to |
| ``normalize'' the value (convert it to, e.g., 1 or 0) than for the |
| comparison operators to do so because there may be opportunities to |
| combine the normalization with other operations. |
| |
| @item |
| For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being |
| slightly preferred on machines with expensive jumps and 1 preferred on |
| other machines. |
| |
| @item |
| As a second choice, choose a value of @samp{0x80000001} if instructions |
| exist that set both the sign and low-order bits but do not define the |
| others. |
| |
| @item |
| Otherwise, use a value of @samp{0x80000000}. |
| @end itemize |
| |
| Many machines can produce both the value chosen for |
| @code{STORE_FLAG_VALUE} and its negation in the same number of |
| instructions. On those machines, you should also define a pattern for |
| those cases, e.g., one matching |
| |
| @smallexample |
| (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) |
| @end smallexample |
| |
| Some machines can also perform @code{and} or @code{plus} operations on |
| condition code values with less instructions than the corresponding |
| @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those |
| machines, define the appropriate patterns. Use the names @code{incscc} |
| and @code{decscc}, respectively, for the patterns which perform |
| @code{plus} or @code{minus} operations on condition code values. See |
| @file{rs6000.md} for some examples. The GNU Superoptizer can be used to |
| find such instruction sequences on other machines. |
| |
| If this macro is not defined, the default value, 1, is used. You need |
| not define @code{STORE_FLAG_VALUE} if the machine has no store-flag |
| instructions, or if the value generated by these instructions is 1. |
| @end defmac |
| |
| @defmac FLOAT_STORE_FLAG_VALUE (@var{mode}) |
| A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is |
| returned when comparison operators with floating-point results are true. |
| Define this macro on machines that have comparison operations that return |
| floating-point values. If there are no such operations, do not define |
| this macro. |
| @end defmac |
| |
| @defmac VECTOR_STORE_FLAG_VALUE (@var{mode}) |
| A C expression that gives a rtx representing the nonzero true element |
| for vector comparisons. The returned rtx should be valid for the inner |
| mode of @var{mode} which is guaranteed to be a vector mode. Define |
| this macro on machines that have vector comparison operations that |
| return a vector result. If there are no such operations, do not define |
| this macro. Typically, this macro is defined as @code{const1_rtx} or |
| @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent |
| the compiler optimizing such vector comparison operations for the |
| given mode. |
| @end defmac |
| |
| @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) |
| @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) |
| A C expression that evaluates to true if the architecture defines a value |
| for @code{clz} or @code{ctz} with a zero operand. If so, @var{value} |
| should be set to this value. If this macro is not defined, the value of |
| @code{clz} or @code{ctz} is assumed to be undefined. |
| |
| This macro must be defined if the target's expansion for @code{ffs} |
| relies on a particular value to get correct results. Otherwise it |
| is not necessary, though it may be used to optimize some corner cases. |
| |
| Note that regardless of this macro the ``definedness'' of @code{clz} |
| and @code{ctz} at zero do @emph{not} extend to the builtin functions |
| visible to the user. Thus one may be free to adjust the value at will |
| to match the target expansion of these operations without fear of |
| breaking the API@. |
| @end defmac |
| |
| @defmac Pmode |
| An alias for the machine mode for pointers. On most machines, define |
| this to be the integer mode corresponding to the width of a hardware |
| pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. |
| On some machines you must define this to be one of the partial integer |
| modes, such as @code{PSImode}. |
| |
| The width of @code{Pmode} must be at least as large as the value of |
| @code{POINTER_SIZE}. If it is not equal, you must define the macro |
| @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended |
| to @code{Pmode}. |
| @end defmac |
| |
| @defmac FUNCTION_MODE |
| An alias for the machine mode used for memory references to functions |
| being called, in @code{call} RTL expressions. On most machines this |
| should be @code{QImode}. |
| @end defmac |
| |
| @defmac STDC_0_IN_SYSTEM_HEADERS |
| In normal operation, the preprocessor expands @code{__STDC__} to the |
| constant 1, to signify that GCC conforms to ISO Standard C@. On some |
| hosts, like Solaris, the system compiler uses a different convention, |
| where @code{__STDC__} is normally 0, but is 1 if the user specifies |
| strict conformance to the C Standard. |
| |
| Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host |
| convention when processing system header files, but when processing user |
| files @code{__STDC__} will always expand to 1. |
| @end defmac |
| |
| @defmac NO_IMPLICIT_EXTERN_C |
| Define this macro if the system header files support C++ as well as C@. |
| This macro inhibits the usual method of using system header files in |
| C++, which is to pretend that the file's contents are enclosed in |
| @samp{extern "C" @{@dots{}@}}. |
| @end defmac |
| |
| @findex #pragma |
| @findex pragma |
| @defmac REGISTER_TARGET_PRAGMAS () |
| Define this macro if you want to implement any target-specific pragmas. |
| If defined, it is a C expression which makes a series of calls to |
| @code{c_register_pragma} or @code{c_register_pragma_with_expansion} |
| for each pragma. The macro may also do any |
| setup required for the pragmas. |
| |
| The primary reason to define this macro is to provide compatibility with |
| other compilers for the same target. In general, we discourage |
| definition of target-specific pragmas for GCC@. |
| |
| If the pragma can be implemented by attributes then you should consider |
| defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. |
| |
| Preprocessor macros that appear on pragma lines are not expanded. All |
| @samp{#pragma} directives that do not match any registered pragma are |
| silently ignored, unless the user specifies @option{-Wunknown-pragmas}. |
| @end defmac |
| |
| @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) |
| @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) |
| |
| Each call to @code{c_register_pragma} or |
| @code{c_register_pragma_with_expansion} establishes one pragma. The |
| @var{callback} routine will be called when the preprocessor encounters a |
| pragma of the form |
| |
| @smallexample |
| #pragma [@var{space}] @var{name} @dots{} |
| @end smallexample |
| |
| @var{space} is the case-sensitive namespace of the pragma, or |
| @code{NULL} to put the pragma in the global namespace. The callback |
| routine receives @var{pfile} as its first argument, which can be passed |
| on to cpplib's functions if necessary. You can lex tokens after the |
| @var{name} by calling @code{pragma_lex}. Tokens that are not read by the |
| callback will be silently ignored. The end of the line is indicated by |
| a token of type @code{CPP_EOF}. Macro expansion occurs on the |
| arguments of pragmas registered with |
| @code{c_register_pragma_with_expansion} but not on the arguments of |
| pragmas registered with @code{c_register_pragma}. |
| |
| For an example use of this routine, see @file{c4x.h} and the callback |
| routines defined in @file{c4x-c.c}. |
| |
| Note that the use of @code{pragma_lex} is specific to the C and C++ |
| compilers. It will not work in the Java or Fortran compilers, or any |
| other language compilers for that matter. Thus if @code{pragma_lex} is going |
| to be called from target-specific code, it must only be done so when |
| building the C and C++ compilers. This can be done by defining the |
| variables @code{c_target_objs} and @code{cxx_target_objs} in the |
| target entry in the @file{config.gcc} file. These variables should name |
| the target-specific, language-specific object file which contains the |
| code that uses @code{pragma_lex}. Note it will also be necessary to add a |
| rule to the makefile fragment pointed to by @code{tmake_file} that shows |
| how to build this object file. |
| @end deftypefun |
| |
| @findex #pragma |
| @findex pragma |
| @defmac HANDLE_SYSV_PRAGMA |
| Define this macro (to a value of 1) if you want the System V style |
| pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name> |
| [=<value>]} to be supported by gcc. |
| |
| The pack pragma specifies the maximum alignment (in bytes) of fields |
| within a structure, in much the same way as the @samp{__aligned__} and |
| @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets |
| the behavior to the default. |
| |
| A subtlety for Microsoft Visual C/C++ style bit-field packing |
| (e.g.@: -mms-bitfields) for targets that support it: |
| When a bit-field is inserted into a packed record, the whole size |
| of the underlying type is used by one or more same-size adjacent |
| bit-fields (that is, if its long:3, 32 bits is used in the record, |
| and any additional adjacent long bit-fields are packed into the same |
| chunk of 32 bits. However, if the size changes, a new field of that |
| size is allocated). |
| |
| If both MS bit-fields and @samp{__attribute__((packed))} are used, |
| the latter will take precedence. If @samp{__attribute__((packed))} is |
| used on a single field when MS bit-fields are in use, it will take |
| precedence for that field, but the alignment of the rest of the structure |
| may affect its placement. |
| |
| The weak pragma only works if @code{SUPPORTS_WEAK} and |
| @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation |
| of specifically named weak labels, optionally with a value. |
| @end defmac |
| |
| @findex #pragma |
| @findex pragma |
| @defmac HANDLE_PRAGMA_PACK_PUSH_POP |
| Define this macro (to a value of 1) if you want to support the Win32 |
| style pragmas @samp{#pragma pack(push[,@var{n}])} and @samp{#pragma |
| pack(pop)}. The @samp{pack(push,[@var{n}])} pragma specifies the maximum |
| alignment (in bytes) of fields within a structure, in much the same way as |
| the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A |
| pack value of zero resets the behavior to the default. Successive |
| invocations of this pragma cause the previous values to be stacked, so |
| that invocations of @samp{#pragma pack(pop)} will return to the previous |
| value. |
| @end defmac |
| |
| @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION |
| Define this macro, as well as |
| @code{HANDLE_SYSV_PRAGMA}, if macros should be expanded in the |
| arguments of @samp{#pragma pack}. |
| @end defmac |
| |
| @defmac TARGET_DEFAULT_PACK_STRUCT |
| If your target requires a structure packing default other than 0 (meaning |
| the machine default), define this macro to the necessary value (in bytes). |
| This must be a value that would also be valid to use with |
| @samp{#pragma pack()} (that is, a small power of two). |
| @end defmac |
| |
| @defmac DOLLARS_IN_IDENTIFIERS |
| Define this macro to control use of the character @samp{$} in |
| identifier names for the C family of languages. 0 means @samp{$} is |
| not allowed by default; 1 means it is allowed. 1 is the default; |
| there is no need to define this macro in that case. |
| @end defmac |
| |
| @defmac NO_DOLLAR_IN_LABEL |
| Define this macro if the assembler does not accept the character |
| @samp{$} in label names. By default constructors and destructors in |
| G++ have @samp{$} in the identifiers. If this macro is defined, |
| @samp{.} is used instead. |
| @end defmac |
| |
| @defmac NO_DOT_IN_LABEL |
| Define this macro if the assembler does not accept the character |
| @samp{.} in label names. By default constructors and destructors in G++ |
| have names that use @samp{.}. If this macro is defined, these names |
| are rewritten to avoid @samp{.}. |
| @end defmac |
| |
| @defmac INSN_SETS_ARE_DELAYED (@var{insn}) |
| Define this macro as a C expression that is nonzero if it is safe for the |
| delay slot scheduler to place instructions in the delay slot of @var{insn}, |
| even if they appear to use a resource set or clobbered in @var{insn}. |
| @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that |
| every @code{call_insn} has this behavior. On machines where some @code{insn} |
| or @code{jump_insn} is really a function call and hence has this behavior, |
| you should define this macro. |
| |
| You need not define this macro if it would always return zero. |
| @end defmac |
| |
| @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn}) |
| Define this macro as a C expression that is nonzero if it is safe for the |
| delay slot scheduler to place instructions in the delay slot of @var{insn}, |
| even if they appear to set or clobber a resource referenced in @var{insn}. |
| @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where |
| some @code{insn} or @code{jump_insn} is really a function call and its operands |
| are registers whose use is actually in the subroutine it calls, you should |
| define this macro. Doing so allows the delay slot scheduler to move |
| instructions which copy arguments into the argument registers into the delay |
| slot of @var{insn}. |
| |
| You need not define this macro if it would always return zero. |
| @end defmac |
| |
| @defmac MULTIPLE_SYMBOL_SPACES |
| Define this macro as a C expression that is nonzero if, in some cases, |
| global symbols from one translation unit may not be bound to undefined |
| symbols in another translation unit without user intervention. For |
| instance, under Microsoft Windows symbols must be explicitly imported |
| from shared libraries (DLLs). |
| |
| You need not define this macro if it would always evaluate to zero. |
| @end defmac |
| |
| @deftypefn {Target Hook} tree TARGET_MD_ASM_CLOBBERS (tree @var{outputs}, tree @var{inputs}, tree @var{clobbers}) |
| This target hook should add to @var{clobbers} @code{STRING_CST} trees for |
| any hard regs the port wishes to automatically clobber for an asm. |
| It should return the result of the last @code{tree_cons} used to add a |
| clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the |
| corresponding parameters to the asm and may be inspected to avoid |
| clobbering a register that is an input or output of the asm. You can use |
| @code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test |
| for overlap with regards to asm-declared registers. |
| @end deftypefn |
| |
| @defmac MATH_LIBRARY |
| Define this macro as a C string constant for the linker argument to link |
| in the system math library, or @samp{""} if the target does not have a |
| separate math library. |
| |
| You need only define this macro if the default of @samp{"-lm"} is wrong. |
| @end defmac |
| |
| @defmac LIBRARY_PATH_ENV |
| Define this macro as a C string constant for the environment variable that |
| specifies where the linker should look for libraries. |
| |
| You need only define this macro if the default of @samp{"LIBRARY_PATH"} |
| is wrong. |
| @end defmac |
| |
| @defmac TARGET_POSIX_IO |
| Define this macro if the target supports the following POSIX@ file |
| functions, access, mkdir and file locking with fcntl / F_SETLKW@. |
| Defining @code{TARGET_POSIX_IO} will enable the test coverage code |
| to use file locking when exiting a program, which avoids race conditions |
| if the program has forked. It will also create directories at run-time |
| for cross-profiling. |
| @end defmac |
| |
| @defmac MAX_CONDITIONAL_EXECUTE |
| |
| A C expression for the maximum number of instructions to execute via |
| conditional execution instructions instead of a branch. A value of |
| @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and |
| 1 if it does use cc0. |
| @end defmac |
| |
| @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr}) |
| Used if the target needs to perform machine-dependent modifications on the |
| conditionals used for turning basic blocks into conditionally executed code. |
| @var{ce_info} points to a data structure, @code{struct ce_if_block}, which |
| contains information about the currently processed blocks. @var{true_expr} |
| and @var{false_expr} are the tests that are used for converting the |
| then-block and the else-block, respectively. Set either @var{true_expr} or |
| @var{false_expr} to a null pointer if the tests cannot be converted. |
| @end defmac |
| |
| @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) |
| Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated |
| if-statements into conditions combined by @code{and} and @code{or} operations. |
| @var{bb} contains the basic block that contains the test that is currently |
| being processed and about to be turned into a condition. |
| @end defmac |
| |
| @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn}) |
| A C expression to modify the @var{PATTERN} of an @var{INSN} that is to |
| be converted to conditional execution format. @var{ce_info} points to |
| a data structure, @code{struct ce_if_block}, which contains information |
| about the currently processed blocks. |
| @end defmac |
| |
| @defmac IFCVT_MODIFY_FINAL (@var{ce_info}) |
| A C expression to perform any final machine dependent modifications in |
| converting code to conditional execution. The involved basic blocks |
| can be found in the @code{struct ce_if_block} structure that is pointed |
| to by @var{ce_info}. |
| @end defmac |
| |
| @defmac IFCVT_MODIFY_CANCEL (@var{ce_info}) |
| A C expression to cancel any machine dependent modifications in |
| converting code to conditional execution. The involved basic blocks |
| can be found in the @code{struct ce_if_block} structure that is pointed |
| to by @var{ce_info}. |
| @end defmac |
| |
| @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info}) |
| A C expression to initialize any extra fields in a @code{struct ce_if_block} |
| structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro. |
| @end defmac |
| |
| @defmac IFCVT_EXTRA_FIELDS |
| If defined, it should expand to a set of field declarations that will be |
| added to the @code{struct ce_if_block} structure. These should be initialized |
| by the @code{IFCVT_INIT_EXTRA_FIELDS} macro. |
| @end defmac |
| |
| @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG () |
| If non-null, this hook performs a target-specific pass over the |
| instruction stream. The compiler will run it at all optimization levels, |
| just before the point at which it normally does delayed-branch scheduling. |
| |
| The exact purpose of the hook varies from target to target. Some use |
| it to do transformations that are necessary for correctness, such as |
| laying out in-function constant pools or avoiding hardware hazards. |
| Others use it as an opportunity to do some machine-dependent optimizations. |
| |
| You need not implement the hook if it has nothing to do. The default |
| definition is null. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} void TARGET_INIT_BUILTINS () |
| Define this hook if you have any machine-specific built-in functions |
| that need to be defined. It should be a function that performs the |
| necessary setup. |
| |
| Machine specific built-in functions can be useful to expand special machine |
| instructions that would otherwise not normally be generated because |
| they have no equivalent in the source language (for example, SIMD vector |
| instructions or prefetch instructions). |
| |
| To create a built-in function, call the function |
| @code{lang_hooks.builtin_function} |
| which is defined by the language front end. You can use any type nodes set |
| up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; |
| only language front ends that use those two functions will call |
| @samp{TARGET_INIT_BUILTINS}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore}) |
| |
| Expand a call to a machine specific built-in function that was set up by |
| @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the |
| function call; the result should go to @var{target} if that is |
| convenient, and have mode @var{mode} if that is convenient. |
| @var{subtarget} may be used as the target for computing one of |
| @var{exp}'s operands. @var{ignore} is nonzero if the value is to be |
| ignored. This function should return the result of the call to the |
| built-in function. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (tree @var{fndecl}, tree @var{arglist}) |
| |
| Select a replacement for a machine specific built-in function that |
| was set up by @samp{TARGET_INIT_BUILTINS}. This is done |
| @emph{before} regular type checking, and so allows the target to |
| implement a crude form of function overloading. @var{fndecl} is the |
| declaration of the built-in function. @var{arglist} is the list of |
| arguments passed to the built-in function. The result is a |
| complete expression that implements the operation, usually |
| another @code{CALL_EXPR}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, tree @var{arglist}, bool @var{ignore}) |
| |
| Fold a call to a machine specific built-in function that was set up by |
| @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the |
| built-in function. @var{arglist} is the list of arguments passed to |
| the built-in function. The result is another tree containing a |
| simplified expression for the call's result. If @var{ignore} is true |
| the value will be ignored. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} const char * TARGET_INVALID_WITHIN_DOLOOP (rtx @var{insn}) |
| |
| Take an instruction in @var{insn} and return NULL if it is valid within a |
| low-overhead loop, otherwise return a string why doloop could not be applied. |
| |
| Many targets use special registers for low-overhead looping. For any |
| instruction that clobbers these this function should return a string indicating |
| the reason why the doloop could not be applied. |
| By default, the RTL loop optimizer does not use a present doloop pattern for |
| loops containing function calls or branch on table instructions. |
| @end deftypefn |
| |
| @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2}) |
| |
| Take a branch insn in @var{branch1} and another in @var{branch2}. |
| Return true if redirecting @var{branch1} to the destination of |
| @var{branch2} is possible. |
| |
| On some targets, branches may have a limited range. Optimizing the |
| filling of delay slots can result in branches being redirected, and this |
| may in turn cause a branch offset to overflow. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (rtx @var{x}, @var{outer_code}) |
| This target hook returns @code{true} if @var{x} is considered to be commutative. |
| Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider |
| PLUS to be commutative inside a MEM. @var{outer_code} is the rtx code |
| of the enclosing rtl, if known, otherwise it is UNKNOWN. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg}) |
| |
| When the initial value of a hard register has been copied in a pseudo |
| register, it is often not necessary to actually allocate another register |
| to this pseudo register, because the original hard register or a stack slot |
| it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE} |
| is called at the start of register allocation once for each hard register |
| that had its initial value copied by using |
| @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. |
| Possible values are @code{NULL_RTX}, if you don't want |
| to do any special allocation, a @code{REG} rtx---that would typically be |
| the hard register itself, if it is known not to be clobbered---or a |
| @code{MEM}. |
| If you are returning a @code{MEM}, this is only a hint for the allocator; |
| it might decide to use another register anyways. |
| You may use @code{current_function_leaf_function} in the hook, functions |
| that use @code{REG_N_SETS}, to determine if the hard |
| register in question will not be clobbered. |
| The default value of this hook is @code{NULL}, which disables any special |
| allocation. |
| @end deftypefn |
| |
| @defmac TARGET_OBJECT_SUFFIX |
| Define this macro to be a C string representing the suffix for object |
| files on your target machine. If you do not define this macro, GCC will |
| use @samp{.o} as the suffix for object files. |
| @end defmac |
| |
| @defmac TARGET_EXECUTABLE_SUFFIX |
| Define this macro to be a C string representing the suffix to be |
| automatically added to executable files on your target machine. If you |
| do not define this macro, GCC will use the null string as the suffix for |
| executable files. |
| @end defmac |
| |
| @defmac COLLECT_EXPORT_LIST |
| If defined, @code{collect2} will scan the individual object files |
| specified on its command line and create an export list for the linker. |
| Define this macro for systems like AIX, where the linker discards |
| object files that are not referenced from @code{main} and uses export |
| lists. |
| @end defmac |
| |
| @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl}) |
| Define this macro to a C expression representing a variant of the |
| method call @var{mdecl}, if Java Native Interface (JNI) methods |
| must be invoked differently from other methods on your target. |
| For example, on 32-bit Microsoft Windows, JNI methods must be invoked using |
| the @code{stdcall} calling convention and this macro is then |
| defined as this expression: |
| |
| @smallexample |
| build_type_attribute_variant (@var{mdecl}, |
| build_tree_list |
| (get_identifier ("stdcall"), |
| NULL)) |
| @end smallexample |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void) |
| This target hook returns @code{true} past the point in which new jump |
| instructions could be created. On machines that require a register for |
| every jump such as the SHmedia ISA of SH5, this point would typically be |
| reload, so this target hook should be defined to a function such as: |
| |
| @smallexample |
| static bool |
| cannot_modify_jumps_past_reload_p () |
| @{ |
| return (reload_completed || reload_in_progress); |
| @} |
| @end smallexample |
| @end deftypefn |
| |
| @deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void) |
| This target hook returns a register class for which branch target register |
| optimizations should be applied. All registers in this class should be |
| usable interchangeably. After reload, registers in this class will be |
| re-allocated and loads will be hoisted out of loops and be subjected |
| to inter-block scheduling. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen}) |
| Branch target register optimization will by default exclude callee-saved |
| registers |
| that are not already live during the current function; if this target hook |
| returns true, they will be included. The target code must than make sure |
| that all target registers in the class returned by |
| @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are |
| saved. @var{after_prologue_epilogue_gen} indicates if prologues and |
| epilogues have already been generated. Note, even if you only return |
| true when @var{after_prologue_epilogue_gen} is false, you still are likely |
| to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET} |
| to reserve space for caller-saved target registers. |
| @end deftypefn |
| |
| @defmac POWI_MAX_MULTS |
| If defined, this macro is interpreted as a signed integer C expression |
| that specifies the maximum number of floating point multiplications |
| that should be emitted when expanding exponentiation by an integer |
| constant inline. When this value is defined, exponentiation requiring |
| more than this number of multiplications is implemented by calling the |
| system library's @code{pow}, @code{powf} or @code{powl} routines. |
| The default value places no upper bound on the multiplication count. |
| @end defmac |
| |
| @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) |
| This target hook should register any extra include files for the |
| target. The parameter @var{stdinc} indicates if normal include files |
| are present. The parameter @var{sysroot} is the system root directory. |
| The parameter @var{iprefix} is the prefix for the gcc directory. |
| @end deftypefn |
| |
| @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) |
| This target hook should register any extra include files for the |
| target before any standard headers. The parameter @var{stdinc} |
| indicates if normal include files are present. The parameter |
| @var{sysroot} is the system root directory. The parameter |
| @var{iprefix} is the prefix for the gcc directory. |
| @end deftypefn |
| |
| @deftypefn Macro void TARGET_OPTF (char *@var{path}) |
| This target hook should register special include paths for the target. |
| The parameter @var{path} is the include to register. On Darwin |
| systems, this is used for Framework includes, which have semantics |
| that are different from @option{-I}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl}) |
| This target hook returns @code{true} if it is safe to use a local alias |
| for a virtual function @var{fndecl} when constructing thunks, |
| @code{false} otherwise. By default, the hook returns @code{true} for all |
| functions, if a target supports aliases (i.e.@: defines |
| @code{ASM_OUTPUT_DEF}), @code{false} otherwise, |
| @end deftypefn |
| |
| @defmac TARGET_FORMAT_TYPES |
| If defined, this macro is the name of a global variable containing |
| target-specific format checking information for the @option{-Wformat} |
| option. The default is to have no target-specific format checks. |
| @end defmac |
| |
| @defmac TARGET_N_FORMAT_TYPES |
| If defined, this macro is the number of entries in |
| @code{TARGET_FORMAT_TYPES}. |
| @end defmac |
| |
| @deftypefn {Target Hook} bool TARGET_RELAXED_ORDERING |
| If set to @code{true}, means that the target's memory model does not |
| guarantee that loads which do not depend on one another will access |
| main memory in the order of the instruction stream; if ordering is |
| important, an explicit memory barrier must be used. This is true of |
| many recent processors which implement a policy of ``relaxed,'' |
| ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC, |
| and ia64. The default is @code{false}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} const char *TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (tree @var{typelist}, tree @var{funcdecl}, tree @var{val}) |
| If defined, this macro returns the diagnostic message when it is |
| illegal to pass argument @var{val} to function @var{funcdecl} |
| with prototype @var{typelist}. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (tree @var{fromtype}, tree @var{totype}) |
| If defined, this macro returns the diagnostic message when it is |
| invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL} |
| if validity should be determined by the front end. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, tree @var{type}) |
| If defined, this macro returns the diagnostic message when it is |
| invalid to apply operation @var{op} (where unary plus is denoted by |
| @code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL} |
| if validity should be determined by the front end. |
| @end deftypefn |
| |
| @deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, tree @var{type1}, tree @var{type2}) |
| If defined, this macro returns the diagnostic message when it is |
| invalid to apply operation @var{op} to operands of types @var{type1} |
| and @var{type2}, or @code{NULL} if validity should be determined by |
| the front end. |
| @end deftypefn |
| |
| @defmac TARGET_USE_JCR_SECTION |
| This macro determines whether to use the JCR section to register Java |
| classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both |
| SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0. |
| @end defmac |
| |
| @defmac OBJC_JBLEN |
| This macro determines the size of the objective C jump buffer for the |
| NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value. |
| @end defmac |