Target Description Macros and Functions
***************************************

In addition to the file MACHINE.md, a machine description includes a C header file conventionally given the name MACHINE.h and a C source file named 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 .md file.  The file tm.h should be a link to MACHINE.h.  The header file config.h includes tm.h and most compiler source files include config.h.  The source file defines a variable targetm, which is a structure containing pointers to functions and data relating to the target machine.  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 .h file.

The Global targetm Variable
===========================

 -- Variable: struct gcc_target targetm
     The target .c file must define the global targetm variable which contains pointers to functions and data relating to the target machine.  The variable is declared in target.h; target-def.h defines the macro TARGET_INITIALIZER which is used to initialize the variable, and macros for the default initializers for elements of the structure.  The .c file should override those macros for which the default definition is inappropriate.  For example:

          #include "target.h"
          #include "target-def.h"

          /* Initialize the GCC target structure.  */

          #undef TARGET_COMP_TYPE_ATTRIBUTES
          #define TARGET_COMP_TYPE_ATTRIBUTES MACHINE_comp_type_attributes

          struct gcc_target targetm = TARGET_INITIALIZER;

Where a macro should be defined in the .c file in this manner to form part of the targetm structure, it is documented below as a ``Target Hook'' with a prototype.  Many macros will change in future from being defined in the .h file to being part of the targetm structure.

Similarly, there is a targetcm variable for hooks that are specific to front ends for C-family languages, documented as ``C Target Hook''.  This is declared in c-family/c-target.h, the initializer TARGETCM_INITIALIZER in c-family/c-target-def.h.  If targets initialize targetcm themselves, they should set target_has_targetcm=yes in config.gcc; otherwise a default definition is used.

Similarly, there is a targetm_common variable for hooks that are shared between the compiler driver and the compilers proper, documented as ``Common Target Hook''.  This is declared in common/common-target.h, the initializer TARGETM_COMMON_INITIALIZER in common/common-target-def.h.  If targets initialize targetm_common themselves, they should set target_has_targetm_common=yes in config.gcc; otherwise a default definition is used.

Similarly, there is a targetdm variable for hooks that are specific to the D language front end, documented as ``D Target Hook''. This is declared in d/d-target.h, the initializer TARGETDM_INITIALIZER in d/d-target-def.h.  If targets initialize targetdm themselves, they should set target_has_targetdm=yes in config.gcc; otherwise a default definition is used.

Controlling the Compilation Driver, gcc
=======================================

You can control the compilation driver.

 -- Macro: 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 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 %<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.

 -- Macro: OPTION_DEFAULT_SPECS
     A list of specs used to support configure-time default options (i.e. --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 config.gcc for the target.  The second item is a spec to apply if a default with this name was specified.  The string %(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 specs files and processing DRIVER_SELF_SPECS, using the same mechanism as DRIVER_SELF_SPECS.

     Do not define this macro if it does not need to do anything.

 -- Macro: 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.

 -- Macro: CPLUSPLUS_CPP_SPEC
     This macro is just like CPP_SPEC, but is used for C++, rather than C.  If you do not define this macro, then the value of CPP_SPEC (if any) will be used instead.

 -- Macro: CC1_SPEC
     A C string constant that tells the GCC driver program options to pass to cc1, cc1plus, 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.

 -- Macro: CC1PLUS_SPEC
     A C string constant that tells the GCC driver program options to pass to cc1plus.  It can also specify how to translate options you give to GCC into options for GCC to pass to the 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 cc1plus so there is no need to duplicate the contents of CC1_SPEC in CC1PLUS_SPEC.

 -- Macro: 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 sun3.h for an example of this.

     Do not define this macro if it does not need to do anything.

 -- Macro: 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 mips.h for an example of this.

     Do not define this macro if it does not need to do anything.

 -- Macro: 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, -, 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 -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 %{pipe:%e} construct; see mips.h for instance.

 -- Macro: 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.

 -- Macro: LIB_SPEC
     Another C string constant used much like LINK_SPEC.  The difference between the two is that 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 gcc.c.

 -- Macro: LIBGCC_SPEC
     Another C string constant that tells the GCC driver program how and when to place a reference to libgcc.a into the linker command line.  This constant is placed both before and after the value of LIB_SPEC.

     If this macro is not defined, the GCC driver provides a default that passes the string -lgcc to the linker.

 -- Macro: REAL_LIBGCC_SPEC
     By default, if ENABLE_SHARED_LIBGCC is defined, the LIBGCC_SPEC is not directly used by the driver program but is instead modified to refer to different versions of libgcc.a depending on the values of the command line flags -static, -shared, -static-libgcc, and -shared-libgcc.  On targets where these modifications are inappropriate, define REAL_LIBGCC_SPEC instead.  REAL_LIBGCC_SPEC tells the driver how to place a reference to libgcc on the link command line, but, unlike LIBGCC_SPEC, it is used unmodified.

 -- Macro: USE_LD_AS_NEEDED
     A macro that controls the modifications to LIBGCC_SPEC mentioned in REAL_LIBGCC_SPEC.  If nonzero, a spec will be generated that uses --as-needed or equivalent options and the shared libgcc in place of the static exception handler library, when linking without any of -static, -static-libgcc, or -shared-libgcc.

 -- Macro: LINK_EH_SPEC
     If defined, this C string constant is added to LINK_SPEC. When USE_LD_AS_NEEDED is zero or undefined, it also affects the modifications to LIBGCC_SPEC mentioned in REAL_LIBGCC_SPEC.

 -- Macro: STARTFILE_SPEC
     Another C string constant used much like LINK_SPEC.  The difference between the two is that 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 gcc.c.

 -- Macro: ENDFILE_SPEC
     Another C string constant used much like LINK_SPEC.  The difference between the two is that 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.

 -- Macro: THREAD_MODEL_SPEC
     GCC -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 THREAD_MODEL_SPEC such that it evaluates to a string without blanks that names one of the recognized thread models.  %*, the default value of this macro, will expand to the value of thread_file set in config.gcc.

 -- Macro: 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.

 -- Macro: 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.

 -- Macro: EXTRA_SPECS
     Define this macro to provide additional specifications to put in the specs file that can be used in various specifications like 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.

     EXTRA_SPECS is useful when an architecture contains several related targets, which have various ..._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 EXTRA_SPECS to define either _CALL_SYSV when the System V calling sequence is used or _CALL_AIX when the older AIX-based calling sequence is used.

     The config/rs6000/rs6000.h target file defines:

          #define EXTRA_SPECS \
            { "cpp_sysv_default", CPP_SYSV_DEFAULT },

          #define CPP_SYS_DEFAULT ""

     The config/rs6000/sysv.h target file defines:

          #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"

     while the config/rs6000/eabiaix.h target file defines CPP_SYSV_DEFAULT as:

          #undef CPP_SYSV_DEFAULT
          #define CPP_SYSV_DEFAULT "-D_CALL_AIX"

 -- Macro: LINK_LIBGCC_SPECIAL_1
     Define this macro if the driver program should find the library libgcc.a.  If you do not define this macro, the driver program will pass the argument -lgcc to tell the linker to do the search.

 -- Macro: LINK_GCC_C_SEQUENCE_SPEC
     The sequence in which libgcc and libc are specified to the linker. By default this is %G %L %G.

 -- Macro: POST_LINK_SPEC
     Define this macro to add additional steps to be executed after linker. The default value of this macro is empty string.

 -- Macro: 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 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 LINK_GCC_C_SEQUENCE_SPEC instead.

TARGET_ALWAYS_STRIP_DOTDOT

 -- Macro: 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 MULTILIB_OPTIONS.

     Do not define this macro if MULTILIB_OPTIONS is not defined in the target makefile fragment or if none of the options listed in MULTILIB_OPTIONS are set by default. See Target Fragment.

 -- Macro: RELATIVE_PREFIX_NOT_LINKDIR
     Define this macro to tell gcc that it should only translate a -B prefix into a -L linker option if the prefix indicates an absolute file name.

 -- Macro: MD_EXEC_PREFIX
     If defined, this macro is an additional prefix to try after STANDARD_EXEC_PREFIX.  MD_EXEC_PREFIX is not searched when the compiler is built as a cross compiler.  If you define MD_EXEC_PREFIX, then be sure to add it to the list of directories used to find the assembler in configure.ac.

 -- Macro: STANDARD_STARTFILE_PREFIX
     Define this macro as a C string constant if you wish to override the standard choice of libdir as the default prefix to try when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX is not searched when the compiler is built as a cross compiler.

 -- Macro: STANDARD_STARTFILE_PREFIX_1
     Define this macro as a C string constant if you wish to override the standard choice of /lib as a prefix to try after the default prefix when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX_1 is not searched when the compiler is built as a cross compiler.

 -- Macro: STANDARD_STARTFILE_PREFIX_2
     Define this macro as a C string constant if you wish to override the standard choice of /lib as yet another prefix to try after the default prefix when searching for startup files such as crt0.o. STANDARD_STARTFILE_PREFIX_2 is not searched when the compiler is built as a cross compiler.

 -- Macro: MD_STARTFILE_PREFIX
     If defined, this macro supplies an additional prefix to try after the standard prefixes.  MD_EXEC_PREFIX is not searched when the compiler is built as a cross compiler.

 -- Macro: MD_STARTFILE_PREFIX_1
     If defined, this macro supplies yet another prefix to try after the standard prefixes.  It is not searched when the compiler is built as a cross compiler.

 -- Macro: 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 putenv to initialize the necessary environment variables.

 -- Macro: LOCAL_INCLUDE_DIR
     Define this macro as a C string constant if you wish to override the standard choice of /usr/local/include as the default prefix to try when searching for local header files.  LOCAL_INCLUDE_DIR comes before NATIVE_SYSTEM_HEADER_DIR (set in config.gcc, normally /usr/include) in the search order.

     Cross compilers do not search either /usr/local/include or its replacement.

 -- Macro: NATIVE_SYSTEM_HEADER_COMPONENT
     The ``component'' corresponding to NATIVE_SYSTEM_HEADER_DIR. See INCLUDE_DEFAULTS, below, for the description of components. If you do not define this macro, no component is used.

 -- Macro: 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 GCC_INCLUDE_DIR, LOCAL_INCLUDE_DIR, GPLUSPLUS_INCLUDE_DIR, and NATIVE_SYSTEM_HEADER_DIR.  In addition, GPLUSPLUS_INCLUDE_DIR and GCC_INCLUDE_DIR are defined automatically by Makefile, and specify private search areas for GCC.  The directory 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 extern 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 GCC or BINUTILS.  If the package is part of a vendor-supplied operating system, code the component name as 0.

     For example, here is the definition used for VAX/VMS:

          #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}                         \
          }

Here is the order of prefixes tried for exec files:

 1. Any prefixes specified by the user with -B.

 2. The environment variable GCC_EXEC_PREFIX or, if GCC_EXEC_PREFIX is not set and the compiler has not been installed in the configure-time PREFIX, the location in which the compiler has actually been installed.

 3. The directories specified by the environment variable COMPILER_PATH.

 4. The macro STANDARD_EXEC_PREFIX, if the compiler has been installed in the configured-time PREFIX.

 5. The location /usr/libexec/gcc/, but only if this is a native compiler.

 6. The location /usr/lib/gcc/, but only if this is a native compiler.

 7. The macro MD_EXEC_PREFIX, if defined, but only if this is a native compiler.

Here is the order of prefixes tried for startfiles:

 1. Any prefixes specified by the user with -B.

 2. The environment variable GCC_EXEC_PREFIX or its automatically determined value based on the installed toolchain location.

 3. The directories specified by the environment variable LIBRARY_PATH (or port-specific name; native only, cross compilers do not use this).

 4. The macro STANDARD_EXEC_PREFIX, but only if the toolchain is installed in the configured PREFIX or this is a native compiler.

 5. The location /usr/lib/gcc/, but only if this is a native compiler.

 6. The macro MD_EXEC_PREFIX, if defined, but only if this is a native compiler.

 7. The macro MD_STARTFILE_PREFIX, if defined, but only if this is a native compiler, or we have a target system root.

 8. The macro MD_STARTFILE_PREFIX_1, if defined, but only if this is a native compiler, or we have a target system root.

 9. The macro STANDARD_STARTFILE_PREFIX, with any sysroot modifications. If this path is relative it will be prefixed by GCC_EXEC_PREFIX and the machine suffix or STANDARD_EXEC_PREFIX and the machine suffix.

 10. The macro STANDARD_STARTFILE_PREFIX_1, but only if this is a native compiler, or we have a target system root. The default for this macro is /lib/.

 11. The macro STANDARD_STARTFILE_PREFIX_2, but only if this is a native compiler, or we have a target system root. The default for this macro is /usr/lib/.

Run-time Target Specification
=============================

Here are run-time target specifications.

 -- Macro: 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 builtin_define, builtin_define_std and 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.

     builtin_assert takes a string in the form you pass to the command-line option -A, such as cpu=mips, and creates the assertion.  builtin_define takes a string in the form accepted by option -D and unconditionally defines the macro.

     builtin_define_std takes a string representing the name of an object-like macro.  If it doesn't lie in the user's namespace, 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 unix defines __unix, __unix__ and possibly unix; passing _mips defines __mips, __mips__ and possibly _mips, and passing _ABI64 defines only _ABI64.

     You can also test for the C dialect being compiled.  The variable c_language is set to one of clk_c, clk_cplusplus or clk_objective_c.  Note that if we are preprocessing assembler, this variable will be clk_c but the function-like macro 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 flag_iso can be used.  The function-like macro preprocessing_trad_p() can be used to check for traditional preprocessing.

 -- Macro: TARGET_OS_CPP_BUILTINS ()
     Similarly to TARGET_CPU_CPP_BUILTINS but this macro is optional and is used for the target operating system instead.

 -- Macro: TARGET_OBJFMT_CPP_BUILTINS ()
     Similarly to TARGET_CPU_CPP_BUILTINS but this macro is optional and is used for the target object format.  elfos.h uses this macro to define __ELF__, so you probably do not need to define it yourself.

 -- Variable: extern int target_flags
     This variable is declared in options.h, which is included before any target-specific headers.

TARGET_DEFAULT_TARGET_FLAGS
This variable specifies the initial value of target_flags. Its default setting is 0.

TARGET_HANDLE_OPTION
This hook is called whenever the user specifies one of the target-specific options described by the .opt definition files (see 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.

DECODED specifies the option and its arguments.  OPTS and OPTS_SET are the gcc_options structures to be used for storing option state, and LOC is the location at which the option was passed (UNKNOWN_LOCATION except for options passed via attributes).

TARGET_HANDLE_C_OPTION
This target hook is called whenever the user specifies one of the target-specific C language family options described by the .opt definition files(see Options).  It has the opportunity to do some option-specific processing and should return true if the option is valid.  The arguments are like for TARGET_HANDLE_OPTION.  The default definition does nothing but return false.

In general, you should use TARGET_HANDLE_OPTION to handle options.  However, if processing an option requires routines that are only available in the C (and related language) front ends, then you should use TARGET_HANDLE_C_OPTION instead.

TARGET_OBJC_CONSTRUCT_STRING_OBJECT

TARGET_OBJC_DECLARE_UNRESOLVED_CLASS_REFERENCE

TARGET_OBJC_DECLARE_CLASS_DEFINITION

TARGET_STRING_OBJECT_REF_TYPE_P

TARGET_CHECK_STRING_OBJECT_FORMAT_ARG

TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE

 -- Macro: C_COMMON_OVERRIDE_OPTIONS
     This is similar to the TARGET_OPTION_OVERRIDE hook 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.

TARGET_OPTION_OPTIMIZATION_TABLE
Some machines may desire to change what optimizations are performed for various optimization levels.   This variable, if defined, describes options to enable at particular sets of optimization levels.  These options are processed once just after the optimization level is determined and before the remainder of the command options have been parsed, so may be overridden by other options passed explicitly.

This processing is run once at program startup and when the optimization options are changed via #pragma GCC optimize or by using the optimize attribute.

TARGET_OPTION_INIT_STRUCT

 -- Macro: SWITCHABLE_TARGET
     Some targets need to switch between substantially different subtargets during compilation.  For example, the MIPS target has one subtarget for the traditional MIPS architecture and another for MIPS16.  Source code can switch between these two subarchitectures using the mips16 and nomips16 attributes.

     Such subtargets can differ in things like the set of available registers, the set of available instructions, the costs of various operations, and so on.  GCC caches a lot of this type of information in global variables, and recomputing them for each subtarget takes a significant amount of time.  The compiler therefore provides a facility for maintaining several versions of the global variables and quickly switching between them; see target-globals.h for details.

     Define this macro to 1 if your target needs this facility.  The default is 0.

TARGET_FLOAT_EXCEPTIONS_ROUNDING_SUPPORTED_P

Defining data structures for per-function information.
======================================================

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 struct function which contains all of the data specific to an individual function.  This structure contains a field called machine whose type is 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 struct machine_function and also the macro INIT_EXPANDERS. This macro should be used to initialize the function pointer 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 __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 save_machine_status and 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.

 -- Macro: 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 init_machine_status.

 -- Variable: void (*)(struct function *) init_machine_status
     If this function pointer is non-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 struct function structure.  It is intended that this would be used to initialize the machine of that structure.

     struct machine_function structures are expected to be freed by GC. Generally, any memory that they reference must be allocated by using GC allocation, including the structure itself.

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 target_flags. See Run-time Target.

 -- Macro: 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 BYTES_BIG_ENDIAN.

 -- Macro: 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.

 -- Macro: 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; see REG_WORDS_BIG_ENDIAN if the order of words in memory is not the same as the order in registers.  This macro need not be a constant.

 -- Macro: REG_WORDS_BIG_ENDIAN
     On some machines, the order of words in a multiword object differs between registers in memory.  In such a situation, define this macro to describe the order of words in a register.  The macro WORDS_BIG_ENDIAN controls the order of words in memory.

 -- Macro: FLOAT_WORDS_BIG_ENDIAN
     Define this macro to have the value 1 if DFmode, XFmode or 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.

 -- Macro: BITS_PER_WORD
     Number of bits in a word.  If you do not define this macro, the default is BITS_PER_UNIT * UNITS_PER_WORD.

 -- Macro: MAX_BITS_PER_WORD
     Maximum number of bits in a word.  If this is undefined, the default is BITS_PER_WORD.  Otherwise, it is the constant value that is the largest value that BITS_PER_WORD can have at run-time.

 -- Macro: 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.

 -- Macro: MIN_UNITS_PER_WORD
     Minimum number of units in a word.  If this is undefined, the default is UNITS_PER_WORD.  Otherwise, it is the constant value that is the smallest value that UNITS_PER_WORD can have at run-time.

 -- Macro: POINTER_SIZE
     Width of a pointer, in bits.  You must specify a value no wider than the width of Pmode.  If it is not equal to the width of Pmode, you must define POINTERS_EXTEND_UNSIGNED.  If you do not specify a value the default is BITS_PER_WORD.

 -- Macro: POINTERS_EXTEND_UNSIGNED
     A C expression that determines how pointers should be extended from ptr_mode to either Pmode or word_mode.  It is greater than zero if pointers should be zero-extended, zero if they should be sign-extended, and negative if some other sort of conversion is needed.  In the last case, the extension is done by the target's ptr_extend instruction.

     You need not define this macro if the ptr_mode, Pmode and word_mode are all the same width.

 -- Macro: PROMOTE_MODE (M, UNSIGNEDP, TYPE)
     A macro to update M and UNSIGNEDP when an object whose type is TYPE and which has the specified mode and signedness is to be stored in a register.  This macro is only called when TYPE is a scalar type.

     On most RISC machines, which only have operations that operate on a full register, define this macro to set M to word_mode if M is an integer mode narrower than 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 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 UNSIGNEDP according to which kind of extension is more efficient.

     Do not define this macro if it would never modify M.

TARGET_C_EXCESS_PRECISION

TARGET_PROMOTE_FUNCTION_MODE

 -- Macro: 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.

 -- Macro: 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 PREFERRED_STACK_BOUNDARY is not defined.  On most machines, this should be the same as PARM_BOUNDARY.

 -- Macro: 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 STACK_BOUNDARY.

 -- Macro: INCOMING_STACK_BOUNDARY
     Define this macro if the incoming stack boundary may be different from PREFERRED_STACK_BOUNDARY.  This macro must evaluate to a value equal to or larger than STACK_BOUNDARY.

 -- Macro: FUNCTION_BOUNDARY
     Alignment required for a function entry point, in bits.

 -- Macro: BIGGEST_ALIGNMENT
     Biggest alignment that any data type can require on this machine, in bits.  Note that this is not the biggest alignment that is supported, just the biggest alignment that, when violated, may cause a fault.

TARGET_ABSOLUTE_BIGGEST_ALIGNMENT

 -- Macro: MALLOC_ABI_ALIGNMENT
     Alignment, in bits, a C conformant malloc implementation has to provide.  If not defined, the default value is BITS_PER_WORD.

 -- Macro: ATTRIBUTE_ALIGNED_VALUE
     Alignment used by the __attribute__ ((aligned)) construct.  If not defined, the default value is BIGGEST_ALIGNMENT.

 -- Macro: 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 BITS_PER_UNIT, but may be larger on machines that don't have byte or half-word store operations.

 -- Macro: BIGGEST_FIELD_ALIGNMENT
     Biggest alignment that any structure or union field can require on this machine, in bits.  If defined, this overrides BIGGEST_ALIGNMENT for structure and union fields only, unless the field alignment has been set by the __attribute__ ((aligned (N))) construct.

 -- Macro: ADJUST_FIELD_ALIGN (FIELD, TYPE, COMPUTED)
     An expression for the alignment of a structure field FIELD of type TYPE if the alignment computed in the usual way (including applying of BIGGEST_ALIGNMENT and BIGGEST_FIELD_ALIGNMENT to the alignment) is COMPUTED.  It overrides alignment only if the field alignment has not been set by the __attribute__ ((aligned (N))) construct.  Note that FIELD may be NULL_TREE in case we just query for the minimum alignment of a field of type TYPE in structure context.

 -- Macro: MAX_STACK_ALIGNMENT
     Biggest stack alignment guaranteed by the backend.  Use this macro to specify the maximum alignment of a variable on stack.

     If not defined, the default value is STACK_BOUNDARY.

 -- Macro: 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 __attribute__ ((aligned (N))) construct for functions and objects with static storage duration.  The alignment of automatic objects may exceed the object file format maximum up to the maximum supported by GCC.  If not defined, the default value is BIGGEST_ALIGNMENT.

     On systems that use ELF, the default (in config/elfos.h) is the largest supported 32-bit ELF section alignment representable on a 32-bit host e.g. (((uint64_t) 1 << 28) * 8). On 32-bit ELF the largest supported section alignment in bits is (0x80000000 * 8), but this is not representable on 32-bit hosts.

TARGET_LOWER_LOCAL_DECL_ALIGNMENT

TARGET_STATIC_RTX_ALIGNMENT

 -- Macro: DATA_ALIGNMENT (TYPE, BASIC-ALIGN)
     If defined, a C expression to compute the alignment for a variable in the static store.  TYPE is the data type, and 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 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.  Another is to cause character arrays to be word-aligned so that strcpy calls that copy constants to character arrays can be done inline.

 -- Macro: DATA_ABI_ALIGNMENT (TYPE, BASIC-ALIGN)
     Similar to DATA_ALIGNMENT, but for the cases where the ABI mandates some alignment increase, instead of optimization only purposes.  E.g. AMD x86-64 psABI says that variables with array type larger than 15 bytes must be aligned to 16 byte boundaries.

     If this macro is not defined, then BASIC-ALIGN is used.

TARGET_CONSTANT_ALIGNMENT

 -- Macro: LOCAL_ALIGNMENT (TYPE, BASIC-ALIGN)
     If defined, a C expression to compute the alignment for a variable in the local store.  TYPE is the data type, and 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 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.

     If the value of this macro has a type, it should be an unsigned type.

TARGET_VECTOR_ALIGNMENT

 -- Macro: STACK_SLOT_ALIGNMENT (TYPE, MODE, BASIC-ALIGN)
     If defined, a C expression to compute the alignment for stack slot. TYPE is the data type, MODE is the widest mode available, and BASIC-ALIGN is the alignment that the slot would ordinarily have.  The value of this macro is used instead of that alignment to align the slot.

     If this macro is not defined, then BASIC-ALIGN is used when TYPE is NULL.  Otherwise, LOCAL_ALIGNMENT will be used.

     This macro is to set alignment of stack slot to the maximum alignment of all possible modes which the slot may have.

     If the value of this macro has a type, it should be an unsigned type.

 -- Macro: LOCAL_DECL_ALIGNMENT (DECL)
     If defined, a C expression to compute the alignment for a local variable DECL.

     If this macro is not defined, then LOCAL_ALIGNMENT (TREE_TYPE (DECL), DECL_ALIGN (DECL)) is used.

     One use of this macro is to increase alignment of medium-size data to make it all fit in fewer cache lines.

     If the value of this macro has a type, it should be an unsigned type.

 -- Macro: MINIMUM_ALIGNMENT (EXP, MODE, ALIGN)
     If defined, a C expression to compute the minimum required alignment for dynamic stack realignment purposes for EXP (a type or decl), MODE, assuming normal alignment ALIGN.

     If this macro is not defined, then ALIGN will be used.

 -- Macro: EMPTY_FIELD_BOUNDARY
     Alignment in bits to be given to a structure bit-field that follows an empty field such as int : 0;.

     If PCC_BITFIELD_TYPE_MATTERS is true, it overrides this macro.

 -- Macro: 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 BITS_PER_UNIT.

 -- Macro: 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.

 -- Macro: 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 (int, 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 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 insv, extv, and extzv insns that can directly reference memory.

     The other known way of making bit-fields work is to define STRUCTURE_SIZE_BOUNDARY as large as BIGGEST_ALIGNMENT. Then every structure can be accessed with fullwords.

     Unless the machine has bit-field instructions or you define STRUCTURE_SIZE_BOUNDARY that way, you must define 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:

          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);
          }

     If this prints 2 and 5, then the compiler's behavior is what you would get from PCC_BITFIELD_TYPE_MATTERS.

 -- Macro: BITFIELD_NBYTES_LIMITED
     Like PCC_BITFIELD_TYPE_MATTERS except that its effect is limited to aligning a bit-field within the structure.

TARGET_ALIGN_ANON_BITFIELD

TARGET_NARROW_VOLATILE_BITFIELD

TARGET_MEMBER_TYPE_FORCES_BLK

 -- Macro: ROUND_TYPE_ALIGN (TYPE, COMPUTED, SPECIFIED)
     Define this macro as an expression for the alignment of a type (given by TYPE as a tree node) if the alignment computed in the usual way is COMPUTED and the alignment explicitly specified was SPECIFIED.

     The default is to use SPECIFIED if it is larger; otherwise, use the smaller of COMPUTED and BIGGEST_ALIGNMENT

 -- Macro: 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, GET_MODE_BITSIZE (DImode) is assumed.

 -- Macro: STACK_SAVEAREA_MODE (SAVE_LEVEL)
     If defined, an expression of type machine_mode that specifies the mode of the save area operand of a save_stack_LEVEL named pattern (see Standard Names). SAVE_LEVEL is one of SAVE_BLOCK, SAVE_FUNCTION, or 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 Pmode.  You would most commonly define this macro if the save_stack_LEVEL patterns need to support both a 32- and a 64-bit mode.

 -- Macro: STACK_SIZE_MODE
     If defined, an expression of type machine_mode that specifies the mode of the size increment operand of an allocate_stack named pattern (see Standard Names).

     You need not define this macro if it always returns word_mode. You would most commonly define this macro if the allocate_stack pattern needs to support both a 32- and a 64-bit mode.

TARGET_LIBGCC_CMP_RETURN_MODE

TARGET_LIBGCC_SHIFT_COUNT_MODE

TARGET_UNWIND_WORD_MODE

TARGET_MS_BITFIELD_LAYOUT_P

TARGET_DECIMAL_FLOAT_SUPPORTED_P

TARGET_FIXED_POINT_SUPPORTED_P

TARGET_EXPAND_TO_RTL_HOOK

TARGET_INSTANTIATE_DECLS

TARGET_MANGLE_TYPE

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.

 -- Macro: INT_TYPE_SIZE
     A C expression for the size in bits of the type int on the target machine.  If you don't define this, the default is one word.

 -- Macro: SHORT_TYPE_SIZE
     A C expression for the size in bits of the type 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.)

 -- Macro: LONG_TYPE_SIZE
     A C expression for the size in bits of the type long on the target machine.  If you don't define this, the default is one word.

 -- Macro: ADA_LONG_TYPE_SIZE
     On some machines, the size used for the Ada equivalent of the type 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 LONG_TYPE_SIZE.

 -- Macro: LONG_LONG_TYPE_SIZE
     A C expression for the size in bits of the type 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.

 -- Macro: CHAR_TYPE_SIZE
     A C expression for the size in bits of the type char on the target machine.  If you don't define this, the default is BITS_PER_UNIT.

 -- Macro: BOOL_TYPE_SIZE
     A C expression for the size in bits of the C++ type bool and C99 type _Bool on the target machine.  If you don't define this, and you probably shouldn't, the default is CHAR_TYPE_SIZE.

 -- Macro: FLOAT_TYPE_SIZE
     A C expression for the size in bits of the type float on the target machine.  If you don't define this, the default is one word.

 -- Macro: DOUBLE_TYPE_SIZE
     A C expression for the size in bits of the type double on the target machine.  If you don't define this, the default is two words.

 -- Macro: LONG_DOUBLE_TYPE_SIZE
     A C expression for the size in bits of the type long double on the target machine.  If you don't define this, the default is two words.

 -- Macro: SHORT_FRACT_TYPE_SIZE
     A C expression for the size in bits of the type short _Fract on the target machine.  If you don't define this, the default is BITS_PER_UNIT.

 -- Macro: FRACT_TYPE_SIZE
     A C expression for the size in bits of the type _Fract on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 2.

 -- Macro: LONG_FRACT_TYPE_SIZE
     A C expression for the size in bits of the type long _Fract on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 4.

 -- Macro: LONG_LONG_FRACT_TYPE_SIZE
     A C expression for the size in bits of the type long long _Fract on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 8.

 -- Macro: SHORT_ACCUM_TYPE_SIZE
     A C expression for the size in bits of the type short _Accum on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 2.

 -- Macro: ACCUM_TYPE_SIZE
     A C expression for the size in bits of the type _Accum on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 4.

 -- Macro: LONG_ACCUM_TYPE_SIZE
     A C expression for the size in bits of the type long _Accum on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 8.

 -- Macro: LONG_LONG_ACCUM_TYPE_SIZE
     A C expression for the size in bits of the type long long _Accum on the target machine.  If you don't define this, the default is BITS_PER_UNIT * 16.

 -- Macro: LIBGCC2_GNU_PREFIX
     This macro corresponds to the TARGET_LIBFUNC_GNU_PREFIX target hook and should be defined if that hook is overriden to be true.  It causes function names in libgcc to be changed to use a __gnu_ prefix for their name rather than the default __.  A port which uses this macro should also arrange to use t-gnu-prefix in the libgcc config.host.

 -- Macro: 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 LONG_DOUBLE_TYPE_SIZE. If you do not define this macro, the value of LONG_DOUBLE_TYPE_SIZE is the default.

 -- Macro: DEFAULT_SIGNED_CHAR
     An expression whose value is 1 or 0, according to whether the type char should be signed or unsigned by default.  The user can always override this default with the options -fsigned-char and -funsigned-char.

TARGET_DEFAULT_SHORT_ENUMS

 -- Macro: SIZE_TYPE
     A C expression for a string describing the name of the data type to use for size values.  The typedef name 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 unsigned if appropriate, and finally int.  The string must exactly match one of the data type names defined in the function c_common_nodes_and_builtins in the file c-family/c-common.c. You may not omit int or change the order---that would cause the compiler to crash on startup.

     If you don't define this macro, the default is "long unsigned int".

 -- Macro: SIZETYPE
     GCC defines internal types (sizetype, ssizetype, bitsizetype and sbitsizetype) for expressions dealing with size.  This macro is a C expression for a string describing the name of the data type from which the precision of sizetype is extracted.

     The string has the same restrictions as SIZE_TYPE string.

     If you don't define this macro, the default is SIZE_TYPE.

 -- Macro: 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 ptrdiff_t is defined using the contents of the string.  See SIZE_TYPE above for more information.

     If you don't define this macro, the default is "long int".

 -- Macro: WCHAR_TYPE
     A C expression for a string describing the name of the data type to use for wide characters.  The typedef name wchar_t is defined using the contents of the string.  See SIZE_TYPE above for more information.

     If you don't define this macro, the default is "int".

 -- Macro: WCHAR_TYPE_SIZE
     A C expression for the size in bits of the data type for wide characters.  This is used in cpp, which cannot make use of WCHAR_TYPE.

 -- Macro: WINT_TYPE
     A C expression for a string describing the name of the data type to use for wide characters passed to printf and returned from getwc.  The typedef name wint_t is defined using the contents of the string.  See SIZE_TYPE above for more information.

     If you don't define this macro, the default is "unsigned int".

 -- Macro: 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 intmax_t is defined using the contents of the string.  See SIZE_TYPE above for more information.

     If you don't define this macro, the default is the first of "int", "long int", or "long long int" that has as much precision as long long int.

 -- Macro: 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 uintmax_t is defined using the contents of the string.  See SIZE_TYPE above for more information.

     If you don't define this macro, the default is the first of "unsigned int", "long unsigned int", or "long long unsigned int" that has as much precision as long long unsigned int.

 -- Macro: SIG_ATOMIC_TYPE
 -- Macro: INT8_TYPE
 -- Macro: INT16_TYPE
 -- Macro: INT32_TYPE
 -- Macro: INT64_TYPE
 -- Macro: UINT8_TYPE
 -- Macro: UINT16_TYPE
 -- Macro: UINT32_TYPE
 -- Macro: UINT64_TYPE
 -- Macro: INT_LEAST8_TYPE
 -- Macro: INT_LEAST16_TYPE
 -- Macro: INT_LEAST32_TYPE
 -- Macro: INT_LEAST64_TYPE
 -- Macro: UINT_LEAST8_TYPE
 -- Macro: UINT_LEAST16_TYPE
 -- Macro: UINT_LEAST32_TYPE
 -- Macro: UINT_LEAST64_TYPE
 -- Macro: INT_FAST8_TYPE
 -- Macro: INT_FAST16_TYPE
 -- Macro: INT_FAST32_TYPE
 -- Macro: INT_FAST64_TYPE
 -- Macro: UINT_FAST8_TYPE
 -- Macro: UINT_FAST16_TYPE
 -- Macro: UINT_FAST32_TYPE
 -- Macro: UINT_FAST64_TYPE
 -- Macro: INTPTR_TYPE
 -- Macro: UINTPTR_TYPE
     C expressions for the standard types sig_atomic_t, int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t, uint64_t, int_least8_t, int_least16_t, int_least32_t, int_least64_t, uint_least8_t, uint_least16_t, uint_least32_t, uint_least64_t, int_fast8_t, int_fast16_t, int_fast32_t, int_fast64_t, uint_fast8_t, uint_fast16_t, uint_fast32_t, uint_fast64_t, intptr_t, and uintptr_t.  See SIZE_TYPE above for more information.

     If any of these macros evaluates to a null pointer, the corresponding type is not supported; if GCC is configured to provide <stdint.h> in such a case, the header provided may not conform to C99, depending on the type in question.  The defaults for all of these macros are null pointers.

 -- Macro: TARGET_PTRMEMFUNC_VBIT_LOCATION
     The C++ compiler represents a pointer-to-member-function with a struct that looks like:

            struct {
              union {
                void (*fn)();
                ptrdiff_t vtable_index;
              };
              ptrdiff_t delta;
            };

     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 delta field, and shift the remainder of the delta field to the left.

     GCC will automatically make the right selection about where to store this bit using the FUNCTION_BOUNDARY setting for your platform. However, some platforms such as ARM/Thumb have 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 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 FUNCTION_BOUNDARY, GCC will automatically define this macro to ptrmemfunc_vbit_in_pfn.

 -- Macro: 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.

 -- Macro: 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. */

 -- Macro: 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 TARGET_VTABLE_ENTRY_ALIGN), set this to the number of words in each data entry.

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 Register Classes.  For information on using registers to access a stack frame, see Frame Registers. For passing values in registers, see Register Arguments. For returning values in registers, see Scalar Return.

Basic Characteristics of Registers
----------------------------------

Registers have various characteristics.

 -- Macro: FIRST_PSEUDO_REGISTER
     Number of hardware registers known to the compiler.  They receive numbers 0 through FIRST_PSEUDO_REGISTER-1; thus, the first pseudo register's number really is assigned the number FIRST_PSEUDO_REGISTER.

 -- Macro: FIXED_REGISTERS
     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 Nth number is 1 if register 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 CONDITIONAL_REGISTER_USAGE, or by the user with the command options -ffixed-REG, -fcall-used-REG and -fcall-saved-REG.

 -- Macro: CALL_USED_REGISTERS
     Like 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 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.

     Exactly one of CALL_USED_REGISTERS and CALL_REALLY_USED_REGISTERS must be defined.  Modern ports should define CALL_REALLY_USED_REGISTERS.

 -- Macro: CALL_REALLY_USED_REGISTERS
     Like CALL_USED_REGISTERS except this macro doesn't require that the entire set of FIXED_REGISTERS be included. (CALL_USED_REGISTERS must be a superset of FIXED_REGISTERS).

     Exactly one of CALL_USED_REGISTERS and CALL_REALLY_USED_REGISTERS must be defined.  Modern ports should define CALL_REALLY_USED_REGISTERS.

TARGET_FNTYPE_ABI

TARGET_INSN_CALLEE_ABI

TARGET_HARD_REGNO_CALL_PART_CLOBBERED

TARGET_GET_MULTILIB_ABI_NAME

TARGET_CONDITIONAL_REGISTER_USAGE

 -- Macro: INCOMING_REGNO (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 OUT as seen by the calling function.  Return OUT if register number OUT is not an outbound register.

 -- Macro: OUTGOING_REGNO (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 IN as seen by the called function.  Return IN if register number IN is not an inbound register.

 -- Macro: LOCAL_REGNO (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.

 -- Macro: PC_REGNUM
     If the program counter has a register number, define this as that register number.  Otherwise, do not define it.

Order of Allocation of Registers
--------------------------------

Registers are allocated in order.

 -- Macro: 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 REG_ALLOC_ORDER to be an initializer that lists the highest numbered allocable register first.

 -- Macro: ADJUST_REG_ALLOC_ORDER
     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 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 reg_alloc_order before execution of the macro.

     On most machines, it is not necessary to define this macro.

 -- Macro: HONOR_REG_ALLOC_ORDER
     Normally, IRA tries to estimate the costs for saving a register in the prologue and restoring it in the epilogue.  This discourages it from using call-saved registers.  If a machine wants to ensure that IRA allocates registers in the order given by REG_ALLOC_ORDER even if some call-saved registers appear earlier than call-used ones, then define this macro as a C expression to nonzero. Default is 0.

 -- Macro: IRA_HARD_REGNO_ADD_COST_MULTIPLIER (REGNO)
     In some case register allocation order is not enough for the Integrated Register Allocator (IRA) to generate a good code. If this macro is defined, it should return a floating point value based on REGNO.  The cost of using REGNO for a pseudo will be increased by approximately the pseudo's usage frequency times the value returned by this macro.  Not defining this macro is equivalent to having it always return 0.0.

     On most machines, it is not necessary to define this macro.

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.

TARGET_HARD_REGNO_NREGS

 -- Macro: HARD_REGNO_NREGS_HAS_PADDING (REGNO, MODE)
     A C expression that is nonzero if a value of mode MODE, stored in memory, ends with padding that causes it to take up more space than in registers starting at register number 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 TARGET_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 subreg_get_info would otherwise wrongly determine that a subreg can be represented by an offset to the register number, when in fact such a subreg would contain some of the padding not stored in registers and so not be representable.

 -- Macro: HARD_REGNO_NREGS_WITH_PADDING (REGNO, MODE)
     For values of REGNO and MODE for which 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.

 -- Macro: REGMODE_NATURAL_SIZE (MODE)
     Define this macro if the natural size of registers that hold values of mode 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.

TARGET_HARD_REGNO_MODE_OK

 -- Macro: HARD_REGNO_RENAME_OK (FROM, TO)
     A C expression that is nonzero if it is OK to rename a hard register FROM to another hard register 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.

TARGET_MODES_TIEABLE_P

TARGET_HARD_REGNO_SCRATCH_OK

 -- Macro: AVOID_CCMODE_COPIES
     Define this macro if the compiler should avoid copies to/from CCmode registers.  You should only define this macro if support for copying to/from CCmode is incomplete.

Handling Leaf Functions
-----------------------

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.

 -- Macro: 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.

 -- Macro: LEAF_REG_REMAP (REGNO)
     A C expression whose value is the register number to which REGNO should be renumbered, when a function is treated as a leaf function.

     If REGNO is a register number which should not appear in a leaf function before renumbering, then the expression should yield -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.

TARGET_ASM_FUNCTION_PROLOGUE and TARGET_ASM_FUNCTION_EPILOGUE must usually treat leaf functions specially.  They can test the C variable current_function_is_leaf which is nonzero for leaf functions.  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 current_function_uses_only_leaf_regs which is nonzero for leaf functions which only use leaf registers. current_function_uses_only_leaf_regs is valid after all passes that modify the instructions have been run and is only useful if LEAF_REGISTERS is defined.

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 reg-stack.c and write your machine description to cooperate with it, as well as defining these macros.

 -- Macro: STACK_REGS
     Define this if the machine has any stack-like registers.

 -- Macro: STACK_REG_COVER_CLASS
     This is a cover class containing the stack registers.  Define this if the machine has any stack-like registers.

 -- Macro: FIRST_STACK_REG
     The number of the first stack-like register.  This one is the top of the stack.

 -- Macro: LAST_STACK_REG
     The number of the last stack-like register.  This one is the bottom of the stack.

Register Classes
================

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 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.

In general, each register will belong to several classes.  In fact, one class must be named ALL_REGS and contain all the registers.  Another class must be named NO_REGS and contain no registers.  Often the union of two classes will be another class; however, this is not required.

One of the classes must be named GENERAL_REGS.  There is nothing terribly special about the name, but the operand constraint letters r and g specify this class.  If GENERAL_REGS is the same as ALL_REGS, just define it as a macro which expands to ALL_REGS.

Order the classes so that if class X is contained in class Y then X has a lower class number than Y.

The way classes other than 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 must define the narrowest register classes for allocatable registers, so that each class either has no subclasses, or that for some mode, the move cost between registers within the class is cheaper than moving a register in the class to or from memory (see Costs).

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 FLOAT_OR_GENERAL_REGS which includes both of them.  Otherwise you will get suboptimal code, or even internal compiler errors when reload cannot find a register in the class computed via reg_class_subunion.

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 TARGET_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 (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 PREFERRED_RELOAD_CLASS can always have a possible value to return.

 -- Data type: enum reg_class
     An enumerated type that must be defined with all the register class names as enumerated values.  NO_REGS must be first.  ALL_REGS must be the last register class, followed by one more enumerated value, 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 int.  The number serves as an index in many of the tables described below.

 -- Macro: N_REG_CLASSES
     The number of distinct register classes, defined as follows:

          #define N_REG_CLASSES (int) LIM_REG_CLASSES

 -- Macro: 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.

 -- Macro: REG_CLASS_CONTENTS
     An initializer containing the contents of the register classes, as integers which are bit masks.  The Nth integer specifies the contents of class N.  The way the integer MASK is interpreted is that register R is in the class if MASK & (1 << 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 HARD_REG_SET which is defined in 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.

 -- Macro: REGNO_REG_CLASS (REGNO)
     A C expression whose value is a register class containing hard register REGNO.  In general there is more than one such class; choose a class which is minimal, meaning that no smaller class also contains the register.

 -- Macro: 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.

 -- Macro: MODE_BASE_REG_CLASS (MODE)
     This is a variation of the BASE_REG_CLASS macro which allows the selection of a base register in a mode dependent manner.  If MODE is VOIDmode then it should return the same value as BASE_REG_CLASS.

 -- Macro: MODE_BASE_REG_REG_CLASS (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.

 -- Macro: MODE_CODE_BASE_REG_CLASS (MODE, ADDRESS_SPACE, OUTER_CODE, INDEX_CODE)
     A C expression whose value is the register class to which a valid base register for a memory reference in mode MODE to address space ADDRESS_SPACE must belong.  OUTER_CODE and INDEX_CODE define the context in which the base register occurs.  OUTER_CODE is the code of the immediately enclosing expression (MEM for the top level of an address, ADDRESS for something that occurs in an address_operand).  INDEX_CODE is the code of the corresponding index expression if OUTER_CODE is PLUS; SCRATCH otherwise.

 -- Macro: 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).

 -- Macro: REGNO_OK_FOR_BASE_P (NUM)
     A C expression which is nonzero if register number NUM is suitable for use as a base register in operand addresses.

 -- Macro: REGNO_MODE_OK_FOR_BASE_P (NUM, MODE)
     A C expression that is just like REGNO_OK_FOR_BASE_P, except that that expression may examine the mode of the memory reference in 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 REGNO_OK_FOR_BASE_P.  The mode may be VOIDmode for addresses that appear outside a MEM, i.e., as an address_operand.

 -- Macro: REGNO_MODE_OK_FOR_REG_BASE_P (NUM, MODE)
     A C expression which is nonzero if register number NUM is suitable for use as a base register in base plus index operand addresses, accessing memory in mode 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 REGNO_MODE_CODE_OK_FOR_BASE_P.

 -- Macro: REGNO_MODE_CODE_OK_FOR_BASE_P (NUM, MODE, ADDRESS_SPACE, OUTER_CODE, INDEX_CODE)
     A C expression which is nonzero if register number NUM is suitable for use as a base register in operand addresses, accessing memory in mode MODE in address space ADDRESS_SPACE. This is similar to REGNO_MODE_OK_FOR_BASE_P, except that that expression may examine the context in which the register appears in the memory reference.  OUTER_CODE is the code of the immediately enclosing expression (MEM if at the top level of the address, ADDRESS for something that occurs in an address_operand).  INDEX_CODE is the code of the corresponding index expression if OUTER_CODE is PLUS; SCRATCH otherwise.  The mode may be VOIDmode for addresses that appear outside a MEM, i.e., as an address_operand.

 -- Macro: REGNO_OK_FOR_INDEX_P (NUM)
     A C expression which is nonzero if register number 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.

TARGET_PREFERRED_RENAME_CLASS

TARGET_PREFERRED_RELOAD_CLASS

 -- Macro: PREFERRED_RELOAD_CLASS (X, CLASS)
     A C expression that places additional restrictions on the register class to use when it is necessary to copy value X into a register in class CLASS.  The value is a register class; perhaps CLASS, or perhaps another, smaller class.  On many machines, the following definition is safe:

          #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS

     Sometimes returning a more restrictive class makes better code.  For example, on the 68000, when X is an integer constant that is in range for a moveq instruction, the value of this macro is always DATA_REGS as long as CLASS includes the data registers. Requiring a data register guarantees that a moveq will be used.

     One case where PREFERRED_RELOAD_CLASS must not return CLASS is if X is a legitimate constant which cannot be loaded into some register class.  By returning NO_REGS you can force 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 PREFERRED_RELOAD_CLASS returns NO_REGS when X is a floating-point constant.  If the constant cannot be loaded into any kind of register, code generation will be better if TARGET_LEGITIMATE_CONSTANT_P makes the constant illegitimate instead of using TARGET_PREFERRED_RELOAD_CLASS.

     If an insn has pseudos in it after register allocation, reload will go through the alternatives and call repeatedly PREFERRED_RELOAD_CLASS to find the best one.  Returning NO_REGS, in this case, makes reload add a ! 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).

TARGET_PREFERRED_OUTPUT_RELOAD_CLASS

 -- Macro: LIMIT_RELOAD_CLASS (MODE, 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 MODE in a reload register for which class CLASS would ordinarily be used.

     Unlike PREFERRED_RELOAD_CLASS, this macro should be used when there are certain modes that simply cannot go in certain reload classes.

     The value is a register class; perhaps 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.

TARGET_SECONDARY_RELOAD

 -- Macro: SECONDARY_RELOAD_CLASS (CLASS, MODE, X)
 -- Macro: SECONDARY_INPUT_RELOAD_CLASS (CLASS, MODE, X)
 -- Macro: SECONDARY_OUTPUT_RELOAD_CLASS (CLASS, MODE, X)
     These macros are obsolete, new ports should use the target hook TARGET_SECONDARY_RELOAD instead.

     These are obsolete macros, replaced by the 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 X to a register CLASS in MODE requires an intermediate register, you were supposed to define 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 CLASS in MODE to X requires an intermediate or scratch register, 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 SECONDARY_RELOAD_CLASS should have been used instead of defining both macros identically.

     The values returned by these macros are often GENERAL_REGS. Return NO_REGS if no spare register is needed; i.e., if X can be directly copied to or from a register of CLASS in MODE without requiring a scratch register.  Do not define this macro if it would always return NO_REGS.

     If a scratch register is required (either with or without an intermediate register), you were supposed to define patterns for reload_inM or reload_outM, as required (see Standard Names.  These patterns, which were normally implemented with a define_expand, should be similar to the movM 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 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.

     X might be a pseudo-register or a subreg of a pseudo-register, which could either be in a hard register or in memory. Use true_regnum to find out; it will return -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 movM pattern should use memory as an intermediate storage.  This case often occurs between floating-point and general registers.

TARGET_SECONDARY_MEMORY_NEEDED

 -- Macro: SECONDARY_MEMORY_NEEDED_RTX (MODE)
     Normally when TARGET_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 TARGET_SECONDARY_MEMORY_NEEDED.

TARGET_SECONDARY_MEMORY_NEEDED_MODE

TARGET_SELECT_EARLY_REMAT_MODES

TARGET_CLASS_LIKELY_SPILLED_P

TARGET_CLASS_MAX_NREGS

 -- Macro: CLASS_MAX_NREGS (CLASS, MODE)
     A C expression for the maximum number of consecutive registers of class CLASS needed to hold a value of mode MODE.

     This is closely related to the macro TARGET_HARD_REGNO_NREGS.  In fact, the value of the macro CLASS_MAX_NREGS (CLASS, MODE) should be the maximum value of TARGET_HARD_REGNO_NREGS (REGNO, MODE) for all REGNO values in the class CLASS.

     This macro helps control the handling of multiple-word values in the reload pass.

TARGET_CAN_CHANGE_MODE_CLASS

TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS

TARGET_LRA_P

TARGET_REGISTER_PRIORITY

TARGET_REGISTER_USAGE_LEVELING_P

TARGET_DIFFERENT_ADDR_DISPLACEMENT_P

TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P

TARGET_LEGITIMIZE_ADDRESS_DISPLACEMENT

TARGET_SPILL_CLASS

TARGET_ADDITIONAL_ALLOCNO_CLASS_P

TARGET_CSTORE_MODE

TARGET_COMPUTE_PRESSURE_CLASSES

Stack Layout and Calling Conventions
====================================

This describes the stack layout and calling conventions.

Basic Stack Layout
------------------

Here is the basic stack layout.

 -- Macro: STACK_GROWS_DOWNWARD
     Define this macro to be true if pushing a word onto the stack moves the stack pointer to a smaller address, and false otherwise.

 -- Macro: STACK_PUSH_CODE
     This macro defines the operation used when something is pushed on the stack.  In RTL, a push operation will be (set (mem (STACK_PUSH_CODE (reg sp))) ...)

     The choices are PRE_DEC, POST_DEC, PRE_INC, and 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 PRE_DEC when STACK_GROWS_DOWNWARD is true, which is almost always right, and PRE_INC otherwise, which is often wrong.

 -- Macro: FRAME_GROWS_DOWNWARD
     Define this macro to nonzero value if the addresses of local variable slots are at negative offsets from the frame pointer.

 -- Macro: ARGS_GROW_DOWNWARD
     Define this macro if successive arguments to a function occupy decreasing addresses on the stack.

TARGET_STARTING_FRAME_OFFSET

 -- Macro: 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 TARGET_STARTING_FRAME_OFFSET is nonzero or where there is a register save block following the local block that doesn't require alignment to STACK_BOUNDARY, it may be beneficial to disable stack alignment and do it in the backend.

 -- Macro: 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 ARGS_GROW_DOWNWARD, this is the offset to the location above the first location at which outgoing arguments are placed.

 -- Macro: FIRST_PARM_OFFSET (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 ARGS_GROW_DOWNWARD, this is the offset to the location above the first argument's address.

 -- Macro: STACK_DYNAMIC_OFFSET (FUNDECL)
     Offset from the stack pointer register to an item dynamically allocated on the stack, e.g., by alloca.

     The default value for this macro is STACK_POINTER_OFFSET plus the length of the outgoing arguments.  The default is correct for most machines.  See function.c for details.

 -- Macro: INITIAL_FRAME_ADDRESS_RTX
     A C expression whose value is RTL representing the address of the initial stack frame. This address is passed to RETURN_ADDR_RTX and 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 __builtin_frame_address (count) and __builtin_return_address (count) for count not equal to zero.

 -- Macro: DYNAMIC_CHAIN_ADDRESS (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 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 FRAMEADDR---that is, the stack frame address is also the address of the stack word that points to the previous frame.

 -- Macro: SETUP_FRAME_ADDRESSES
     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.  The default is to do nothing.

TARGET_BUILTIN_SETJMP_FRAME_VALUE

 -- Macro: FRAME_ADDR_RTX (FRAMEADDR)
     A C expression whose value is RTL representing the value of the frame address for the current frame.  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.

 -- Macro: RETURN_ADDR_RTX (COUNT, FRAMEADDR)
     A C expression whose value is RTL representing the value of the return address for the frame COUNT steps up from the current frame, after the prologue.  FRAMEADDR is the frame pointer of the COUNT frame, or the frame pointer of the COUNT - 1 frame if RETURN_ADDR_IN_PREVIOUS_FRAME is nonzero.

     The value of the expression must always be the correct address when COUNT is zero, but may be NULL_RTX if there is no way to determine the return address of other frames.

 -- Macro: RETURN_ADDR_IN_PREVIOUS_FRAME
     Define this macro to nonzero value if the return address of a particular stack frame is accessed from the frame pointer of the previous stack frame.  The zero default for this macro is suitable for most ports.

 -- Macro: 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 REG, indicating that the return value is saved in REG, or a 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 REG, you should also define DWARF_FRAME_RETURN_COLUMN to DWARF_FRAME_REGNUM (REGNO).

 -- Macro: 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 alternative return column.  The column must not correspond to any gcc hard register (that is, it must not be in the range of DWARF_FRAME_REGNUM).

     This macro can be useful if DWARF_FRAME_RETURN_COLUMN is set to a general register, but an alternative column needs to be used for signal frames.  Some targets have also used different frame return columns over time.

 -- Macro: 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.

TARGET_DWARF_HANDLE_FRAME_UNSPEC

TARGET_DWARF_POLY_INDETERMINATE_VALUE

 -- Macro: 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.

 -- Macro: DEFAULT_INCOMING_FRAME_SP_OFFSET
     Like INCOMING_FRAME_SP_OFFSET, but must be the same for all functions of the same ABI, and when using GAS .cfi_* directives must also agree with the default CFI GAS emits.  Define this macro only if INCOMING_FRAME_SP_OFFSET can have different values between different functions of the same ABI or when INCOMING_FRAME_SP_OFFSET does not agree with GAS default CFI.

 -- Macro: ARG_POINTER_CFA_OFFSET (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 INCOMING_FRAME_SP_OFFSET.  Which is unfortunately not usable during virtual register instantiation.

     The default value for this macro is FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size, 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.

 -- Macro: FRAME_POINTER_CFA_OFFSET (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 INCOMING_FRAME_SP_OFFSET.

     Normally the CFA is calculated as an offset from the argument pointer, via 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 FRAME_POINTER_CFA_OFFSET and ARG_POINTER_CFA_OFFSET should be defined.

 -- Macro: CFA_FRAME_BASE_OFFSET (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.

Exception Handling Support
--------------------------

 -- Macro: EH_RETURN_DATA_REGNO (N)
     A C expression whose value is the Nth register number used for data by exception handlers, or INVALID_REGNUM if fewer than 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.

 -- Macro: 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.

 -- Macro: 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 target call frame rather than inside the current call frame.  If defined, 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 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 eh_return instruction pattern.

 -- Macro: 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.

 -- Macro: ASM_PREFERRED_EH_DATA_FORMAT (CODE, 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.

     CODE is 0 for data, 1 for code labels, 2 for function pointers. GLOBAL is true if the symbol may be affected by dynamic relocations. The macro should return a combination of the DW_EH_PE_* defines as found in dwarf2.h.

     If this macro is not defined, pointers will not be encoded but represented directly.

 -- Macro: ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (FILE, ENCODING, SIZE, ADDR, DONE)
     This macro allows the target to emit whatever special magic is required to represent the encoding chosen by 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 DONE if the format was handled.  ENCODING is the format chosen, SIZE is the number of bytes that the format occupies, ADDR is the SYMBOL_REF to be emitted.

 -- Macro: MD_FALLBACK_FRAME_STATE_FOR (CONTEXT, 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 uw_frame_state_for in unwind-dw2.c, unwind-dw2-xtensa.c and unwind-ia64.c.  CONTEXT is an _Unwind_Context; FS is an _Unwind_FrameState.  Examine context->ra for the address of the code being executed and context->cfa for the stack pointer value.  If the frame can be decoded, the register save addresses should be updated in FS and the macro should evaluate to _URC_NO_REASON.  If the frame cannot be decoded, the macro should evaluate to _URC_END_OF_STACK.

     For proper signal handling in Java this macro is accompanied by MAKE_THROW_FRAME, defined in libjava/include/*-signal.h headers.

 -- Macro: MD_HANDLE_UNWABI (CONTEXT, FS)
     This macro allows the target to add operating system specific code to the call-frame unwinder to handle the IA-64 .unwabi unwinding directive, usually used for signal or interrupt frames.

     This macro is called from uw_update_context in libgcc's unwind-ia64.c.  CONTEXT is an _Unwind_Context; FS is an _Unwind_FrameState.  Examine fs->unwabi for the abi and context in the .unwabi directive.  If the .unwabi directive can be handled, the register save addresses should be updated in FS.

 -- Macro: 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 1 if comdat linkage is necessary.  The default is 0.

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:

 1. If the value of the STACK_CHECK_BUILTIN macro is nonzero, GCC will assume that you have arranged for full stack checking to be done at appropriate places in the configuration files.  GCC will not do other special processing.

 2. If STACK_CHECK_BUILTIN is zero and the value of the STACK_CHECK_STATIC_BUILTIN macro is nonzero, GCC will assume that you have arranged for static stack checking (checking of the static stack frame of functions) to be done at appropriate places in the configuration files.  GCC will only emit code to do dynamic stack checking (checking on dynamic stack allocations) using the third approach below.

 3. 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.

If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined, GCC will change its allocation strategy for large objects if the option -fstack-check is specified: they will always be allocated dynamically if their size exceeds STACK_CHECK_MAX_VAR_SIZE bytes.

 -- Macro: 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 required by the ABI of your machine or if you would like to do stack checking in some more efficient way than the generic approach.  The default value of this macro is zero.

 -- Macro: STACK_CHECK_STATIC_BUILTIN
     A nonzero value if static stack checking is done by the configuration files in a machine-dependent manner.  You should define this macro if you would like to do static stack checking in some more efficient way than the generic approach.  The default value of this macro is zero.

 -- Macro: STACK_CHECK_PROBE_INTERVAL_EXP
     An integer specifying the interval at which GCC must generate stack probe instructions, defined as 2 raised to this integer.  You will normally define this macro so that the interval be no larger than the size of the ``guard pages'' at the end of a stack area.  The default value of 12 (4096-byte interval) is suitable for most systems.

 -- Macro: STACK_CHECK_MOVING_SP
     An integer which is nonzero if GCC should move the stack pointer page by page when doing probes.  This can be necessary on systems where the stack pointer contains the bottom address of the memory area accessible to the executing thread at any point in time.  In this situation an alternate signal stack is required in order to be able to recover from a stack overflow.  The default value of this macro is zero.

 -- Macro: 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 4KB/8KB with the setjmp/longjmp-based exception handling mechanism and 8KB/12KB with other exception handling mechanisms should be adequate for most architectures and operating systems.

The following macros are relevant only if neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether in the opposite case.

 -- Macro: 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.

 -- Macro: 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.

 -- Macro: 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 -fstack-check. GCC computed the default from the values of the above macros and you will normally not need to override that default.

TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE

Registers That Address the Stack Frame
--------------------------------------

This discusses registers that address the stack frame.

 -- Macro: STACK_POINTER_REGNUM
     The register number of the stack pointer register, which must also be a fixed register according to FIXED_REGISTERS.  On most machines, the hardware determines which register this is.

 -- Macro: 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.

 -- Macro: 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 FRAME_POINTER_REGNUM the number of a special, fixed register to be used internally until the offset is known, and define 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 ELIMINABLE_REGS how to eliminate FRAME_POINTER_REGNUM into either HARD_FRAME_POINTER_REGNUM or STACK_POINTER_REGNUM.

     Do not define this macro if it would be the same as FRAME_POINTER_REGNUM.

 -- Macro: 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 FIXED_REGISTERS, or arrange to be able to eliminate it (see Elimination).

 -- Macro: HARD_FRAME_POINTER_IS_FRAME_POINTER
     Define this to a preprocessor constant that is nonzero if hard_frame_pointer_rtx and frame_pointer_rtx should be the same.  The default definition is (HARD_FRAME_POINTER_REGNUM == FRAME_POINTER_REGNUM); you only need to define this macro if that definition is not suitable for use in preprocessor conditionals.

 -- Macro: HARD_FRAME_POINTER_IS_ARG_POINTER
     Define this to a preprocessor constant that is nonzero if hard_frame_pointer_rtx and arg_pointer_rtx should be the same.  The default definition is (HARD_FRAME_POINTER_REGNUM == ARG_POINTER_REGNUM); you only need to define this macro if that definition is not suitable for use in preprocessor conditionals.

 -- Macro: 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 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.

 -- Macro: STATIC_CHAIN_REGNUM
 -- Macro: 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 STATIC_CHAIN_INCOMING_REGNUM, while the register number as seen by the calling function is STATIC_CHAIN_REGNUM.  If these registers are the same, 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 TARGET_STATIC_CHAIN hook should be used.

TARGET_STATIC_CHAIN

 -- Macro: 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 FIRST_PSEUDO_REGISTER.

 -- Macro: PRE_GCC3_DWARF_FRAME_REGISTERS

     This macro is similar to 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 DWARF_FRAME_REGISTERS.

 -- Macro: DWARF_REG_TO_UNWIND_COLUMN (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.

 -- Macro: DWARF_FRAME_REGNUM (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 DBX_REGISTER_NUMBER (REGNO).

 -- Macro: DWARF2_FRAME_REG_OUT (REGNO, FOR_EH)

     Define this macro to map register numbers held in the call frame info that GCC has collected using DWARF_FRAME_REGNUM to those that should be output in .debug_frame (FOR_EH is zero) and .eh_frame (FOR_EH is nonzero).  The default is to return REGNO.

 -- Macro: REG_VALUE_IN_UNWIND_CONTEXT

     Define this macro if the target stores register values as _Unwind_Word type in unwind context.  It should be defined if target register size is larger than the size of void *.  The default is to store register values as void * type.

 -- Macro: ASSUME_EXTENDED_UNWIND_CONTEXT

     Define this macro to be 1 if the target always uses extended unwind context with version, args_size and by_value fields.  If it is undefined, it will be defined to 1 when REG_VALUE_IN_UNWIND_CONTEXT is defined and 0 otherwise.

 -- Macro: DWARF_LAZY_REGISTER_VALUE (REGNO, VALUE)
     Define this macro if the target has pseudo DWARF registers whose values need to be computed lazily on demand by the unwinder (such as when referenced in a CFA expression).  The macro returns true if REGNO is such a register and stores its value in *VALUE if so.

Eliminating Frame Pointer and Arg Pointer
-----------------------------------------

This is about eliminating the frame pointer and arg pointer.

TARGET_FRAME_POINTER_REQUIRED

 -- Macro: ELIMINABLE_REGS
     This macro specifies a table of register pairs used to eliminate unneeded registers that point into the stack frame.

     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:

          #define ELIMINABLE_REGS  \
          {{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \
           {ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \
           {FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}}

     Note that the elimination of the argument pointer with the stack pointer is specified first since that is the preferred elimination.

TARGET_CAN_ELIMINATE

 -- Macro: INITIAL_ELIMINATION_OFFSET (FROM-REG, TO-REG, OFFSET-VAR)
     This macro returns the initial difference between the specified pair of registers.  The value would be computed from information such as the result of get_frame_size () and the tables of registers df_regs_ever_live_p and call_used_regs.

TARGET_COMPUTE_FRAME_LAYOUT

Passing Function Arguments on the Stack
---------------------------------------

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.

TARGET_PROMOTE_PROTOTYPES

 -- Macro: 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 PUSH_ARGS is nonzero, PUSH_ROUNDING must be defined too.

 -- Macro: 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 PUSH_ARGS on targets where the stack and args grow in opposite directions, and 0 otherwise.

 -- Macro: PUSH_ROUNDING (NPUSHED)
     A C expression that is the number of bytes actually pushed onto the stack when an instruction attempts to push NPUSHED bytes.

     On some machines, the definition

          #define PUSH_ROUNDING(BYTES) (BYTES)

     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

          #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)

     If the value of this macro has a type, it should be an unsigned type.

 -- Macro: ACCUMULATE_OUTGOING_ARGS
     A C expression.  If nonzero, the maximum amount of space required for outgoing arguments will be computed and placed into crtl->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 PUSH_ARGS and ACCUMULATE_OUTGOING_ARGS is not proper.

 -- Macro: REG_PARM_STACK_SPACE (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 FNDECL, which can be zero if GCC is calling a library function. The argument FNDECL can be the FUNCTION_DECL, or the type itself of the function.

     This space can be allocated by the caller, or be a part of the machine-dependent stack frame: OUTGOING_REG_PARM_STACK_SPACE says which.

 -- Macro: INCOMING_REG_PARM_STACK_SPACE (FNDECL)
     Like REG_PARM_STACK_SPACE, but for incoming register arguments. Define this macro if space guaranteed when compiling a function body is different to space required when making a call, a situation that can arise with K&R style function definitions.

 -- Macro: OUTGOING_REG_PARM_STACK_SPACE (FNTYPE)
     Define this to a nonzero value if it is the responsibility of the caller to allocate the area reserved for arguments passed in registers when calling a function of FNTYPE.  FNTYPE may be NULL if the function called is a library function.

     If ACCUMULATE_OUTGOING_ARGS is defined, this macro controls whether the space for these arguments counts in the value of crtl->outgoing_args_size.

 -- Macro: STACK_PARMS_IN_REG_PARM_AREA
     Define this macro if REG_PARM_STACK_SPACE is defined, but the stack parameters don't skip the area specified by it.

     Normally, when a parameter is not passed in registers, it is placed on the stack beyond the 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.

TARGET_RETURN_POPS_ARGS

 -- Macro: CALL_POPS_ARGS (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 RETURN_POPS_ARGS when compiling a function call.

     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, RETURN_POPS_ARGS is not appropriate.

Passing Arguments in Registers
------------------------------

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.

TARGET_FUNCTION_ARG

TARGET_MUST_PASS_IN_STACK

TARGET_FUNCTION_INCOMING_ARG

TARGET_USE_PSEUDO_PIC_REG

TARGET_INIT_PIC_REG

TARGET_ARG_PARTIAL_BYTES

TARGET_PASS_BY_REFERENCE

TARGET_CALLEE_COPIES

 -- Macro: CUMULATIVE_ARGS
     A C type for declaring a variable that is used as the first argument of TARGET_FUNCTION_ARG and other related values.  For some target machines, the type int suffices and can hold the number of bytes of argument so far.

     There is no need to record in 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 CUMULATIVE_ARGS; however, the data structure must exist and should not be empty, so use int.

 -- Macro: OVERRIDE_ABI_FORMAT (FNDECL)
     If defined, this macro is called before generating any code for a function, but after the CFUN descriptor for the function has been created.  The back end may use this macro to update CFUN to reflect an ABI other than that which would normally be used by default. If the compiler is generating code for a compiler-generated function, FNDECL may be NULL.

 -- Macro: INIT_CUMULATIVE_ARGS (CUM, FNTYPE, LIBNAME, FNDECL, N_NAMED_ARGS)
     A C statement (sans semicolon) for initializing the variable CUM for the state at the beginning of the argument list.  The variable has type CUMULATIVE_ARGS.  The value of 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, FNDECL contain the declaration node of the function.  FNDECL is also set when INIT_CUMULATIVE_ARGS is used to find arguments for the function being compiled.  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, N_NAMED_ARGS is set to -1.

     When processing a call to a compiler support library function, LIBNAME identifies which one.  It is a symbol_ref rtx which contains the name of the function, as a string.  LIBNAME is 0 when an ordinary C function call is being processed.  Thus, each time this macro is called, either LIBNAME or FNTYPE is nonzero, but never both of them at once.

 -- Macro: INIT_CUMULATIVE_LIBCALL_ARGS (CUM, MODE, LIBNAME)
     Like INIT_CUMULATIVE_ARGS but only used for outgoing libcalls, it gets a MODE argument instead of FNTYPE, that would be NULL.  INDIRECT would always be zero, too.  If this macro is not defined, INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, 0) is used instead.

 -- Macro: INIT_CUMULATIVE_INCOMING_ARGS (CUM, FNTYPE, LIBNAME)
     Like INIT_CUMULATIVE_ARGS but overrides it for the purposes of finding the arguments for the function being compiled.  If this macro is undefined, INIT_CUMULATIVE_ARGS is used instead.

     The value passed for LIBNAME is always 0, since library routines with special calling conventions are never compiled with GCC.  The argument LIBNAME exists for symmetry with INIT_CUMULATIVE_ARGS.

TARGET_FUNCTION_ARG_ADVANCE

TARGET_FUNCTION_ARG_OFFSET

TARGET_FUNCTION_ARG_PADDING

 -- Macro: 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 PARM_BOUNDARY.  If this macro is not defined, all such arguments are padded down if BYTES_BIG_ENDIAN is true.

 -- Macro: BLOCK_REG_PADDING (MODE, TYPE, FIRST)
     Specify padding for the last element of a block move between registers and memory.  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 PARALLEL rtl.  In particular, 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.

TARGET_FUNCTION_ARG_BOUNDARY

TARGET_FUNCTION_ARG_ROUND_BOUNDARY

 -- Macro: FUNCTION_ARG_REGNO_P (REGNO)
     A C expression that is nonzero if REGNO is the number of a hard register in which function arguments are sometimes passed.  This does 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.

TARGET_SPLIT_COMPLEX_ARG

TARGET_BUILD_BUILTIN_VA_LIST

TARGET_ENUM_VA_LIST_P

TARGET_FN_ABI_VA_LIST

TARGET_CANONICAL_VA_LIST_TYPE

TARGET_GIMPLIFY_VA_ARG_EXPR

TARGET_VALID_POINTER_MODE

TARGET_REF_MAY_ALIAS_ERRNO

TARGET_TRANSLATE_MODE_ATTRIBUTE

TARGET_SCALAR_MODE_SUPPORTED_P

TARGET_VECTOR_MODE_SUPPORTED_P

TARGET_COMPATIBLE_VECTOR_TYPES_P

TARGET_ARRAY_MODE

TARGET_ARRAY_MODE_SUPPORTED_P

TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P

TARGET_FLOATN_MODE

TARGET_FLOATN_BUILTIN_P

TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P

How Scalar Function Values Are Returned
---------------------------------------

This section discusses the macros that control returning scalars as values---values that can fit in registers.

TARGET_FUNCTION_VALUE

 -- Macro: FUNCTION_VALUE (VALTYPE, FUNC)
     This macro has been deprecated.  Use TARGET_FUNCTION_VALUE for a new target instead.

 -- Macro: LIBCALL_VALUE (MODE)
     A C expression to create an RTX representing the place where a library function returns a value of mode MODE.

     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.

TARGET_LIBCALL_VALUE

 -- Macro: FUNCTION_VALUE_REGNO_P (REGNO)
     A C expression that is nonzero if 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 double, say) need not be recognized by this macro.  So for most machines, this definition suffices:

          #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)

     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.

     This macro has been deprecated.  Use TARGET_FUNCTION_VALUE_REGNO_P for a new target instead.

TARGET_FUNCTION_VALUE_REGNO_P

 -- Macro: APPLY_RESULT_SIZE
     Define this macro if untyped_call and untyped_return need more space than is implied by FUNCTION_VALUE_REGNO_P for saving and restoring an arbitrary return value.

TARGET_OMIT_STRUCT_RETURN_REG

TARGET_RETURN_IN_MSB

How Large Values Are Returned
-----------------------------

When a function value's mode is BLKmode (and in some other cases), the value is not returned according to TARGET_FUNCTION_VALUE (see 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 structure value address.

This section describes how to control returning structure values in memory.

TARGET_RETURN_IN_MEMORY

 -- Macro: 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 TARGET_RETURN_IN_MEMORY target hook.

     If not defined, this defaults to the value 1.

TARGET_STRUCT_VALUE_RTX

 -- Macro: 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 -fpcc-struct-return mode, but it does nothing when you use -freg-struct-return mode.

TARGET_GET_RAW_RESULT_MODE

TARGET_GET_RAW_ARG_MODE

TARGET_EMPTY_RECORD_P

TARGET_WARN_PARAMETER_PASSING_ABI

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.

 -- Macro: HARD_REGNO_CALLER_SAVE_MODE (REGNO, NREGS)
     A C expression specifying which mode is required for saving NREGS of a pseudo-register in call-clobbered hard register REGNO.  If REGNO is unsuitable for caller save, VOIDmode should be returned.  For most machines this macro need not be defined since GCC will select the smallest suitable mode.

Function Entry and Exit
-----------------------

This section describes the macros that output function entry (prologue) and exit (epilogue) code.

TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY

TARGET_ASM_FUNCTION_PROLOGUE

TARGET_ASM_FUNCTION_END_PROLOGUE

TARGET_ASM_FUNCTION_BEGIN_EPILOGUE

TARGET_ASM_FUNCTION_EPILOGUE

  * A region of crtl->args.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 <stdarg.h>.

  * 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.

  * A region of at least 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.

  * Optionally, when ACCUMULATE_OUTGOING_ARGS is defined, a region of crtl->outgoing_args_size bytes to be used for outgoing argument lists of the function.  See Stack Arguments.

 -- Macro: 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 EXIT_IGNORE_STACK.

 -- Macro: EPILOGUE_USES (REGNO)
     Define this macro as a C expression that is nonzero for registers that are used by the epilogue or the return pattern.  The stack and frame pointer registers are already assumed to be used as needed.

 -- Macro: EH_USES (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.

TARGET_ASM_OUTPUT_MI_THUNK

TARGET_ASM_CAN_OUTPUT_MI_THUNK

Generating Code for Profiling
-----------------------------

These macros will help you generate code for profiling.

 -- Macro: FUNCTION_PROFILER (FILE, LABELNO)
     A C statement or compound statement to output to FILE some assembler code to call the profiling subroutine mcount.

     The details of how 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 mcount expect the address of a counter variable to be loaded into some register.  The name of this variable is LP followed by the number LABELNO, so you would generate the name using LP%d in a fprintf.

 -- Macro: PROFILE_HOOK
     A C statement or compound statement to output to FILE some assembly code to call the profiling subroutine mcount even the target does not support profiling.

 -- Macro: NO_PROFILE_COUNTERS
     Define this macro to be an expression with a nonzero value if the 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 LABELNO argument to FUNCTION_PROFILER.

 -- Macro: PROFILE_BEFORE_PROLOGUE
     Define this macro if the code for function profiling should come before the function prologue.  Normally, the profiling code comes after.

TARGET_KEEP_LEAF_WHEN_PROFILED

Permitting tail calls
---------------------

TARGET_FUNCTION_OK_FOR_SIBCALL

TARGET_EXTRA_LIVE_ON_ENTRY

TARGET_SET_UP_BY_PROLOGUE

TARGET_WARN_FUNC_RETURN

Shrink-wrapping separate components
-----------------------------------

The prologue may perform a variety of target dependent tasks such as saving callee-saved registers, saving the return address, aligning the stack, creating a stack frame, initializing the PIC register, setting up the static chain, etc.

On some targets some of these tasks may be independent of others and thus may be shrink-wrapped separately.  These independent tasks are referred to as components and are handled generically by the target independent parts of GCC.

Using the following hooks those prologue or epilogue components can be shrink-wrapped separately, so that the initialization (and possibly teardown) those components do is not done as frequently on execution paths where this would unnecessary.

What exactly those components are is up to the target code; the generic code treats them abstractly, as a bit in an sbitmap.  These sbitmaps are allocated by the shrink_wrap.get_separate_components and shrink_wrap.components_for_bb hooks, and deallocated by the generic code.

TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS

TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB

TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS

TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS

TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS

TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS

Stack smashing protection
-------------------------

TARGET_STACK_PROTECT_GUARD

TARGET_STACK_PROTECT_FAIL

TARGET_STACK_PROTECT_RUNTIME_ENABLED_P

TARGET_SUPPORTS_SPLIT_STACK

TARGET_GET_VALID_OPTION_VALUES

Miscellaneous register hooks
----------------------------

TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS

Implementing the Varargs Macros
===============================

GCC comes with an implementation of <varargs.h> and <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 <stdarg.h> differs from traditional <varargs.h> mainly in the calling convention for va_start.  The traditional implementation takes just one argument, which is the variable in which to store the argument pointer.  The ISO implementation of va_start takes an additional second argument.  The user is supposed to write the last named argument of the function here.

However, 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.

 -- Macro: __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 va_start must use __builtin_saveregs, unless you use TARGET_SETUP_INCOMING_VARARGS (see below) instead.

     On some machines, __builtin_saveregs is open-coded under the control of the target hook TARGET_EXPAND_BUILTIN_SAVEREGS.  On other machines, it calls a routine written in assembler language, found in libgcc2.c.

     Code generated for the call to __builtin_saveregs appears at the beginning of the function, as opposed to where the call to __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.

 -- Macro: __builtin_next_arg (LASTARG)
     This builtin returns the address of the first anonymous stack argument, as type void *.  If ARGS_GROW_DOWNWARD, it returns the address of the location above the first anonymous stack argument.  Use it in va_start to initialize the pointer for fetching arguments from the stack.  Also use it in va_start to verify that the second parameter LASTARG is the last named argument of the current function.

 -- Macro: __builtin_classify_type (OBJECT)
     Since each machine has its own conventions for which data types are passed in which kind of register, your implementation of va_arg has to embody these conventions.  The easiest way to categorize the specified data type is to use __builtin_classify_type together with sizeof and __alignof__.

     __builtin_classify_type ignores the value of 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 typeclass.h defines an enumeration that you can use to interpret the values of __builtin_classify_type.

These machine description macros help implement varargs:

TARGET_EXPAND_BUILTIN_SAVEREGS

TARGET_SETUP_INCOMING_VARARGS

TARGET_STRICT_ARGUMENT_NAMING

TARGET_CALL_ARGS

TARGET_END_CALL_ARGS

TARGET_PRETEND_OUTGOING_VARARGS_NAMED

TARGET_LOAD_BOUNDS_FOR_ARG

TARGET_STORE_BOUNDS_FOR_ARG

TARGET_LOAD_RETURNED_BOUNDS

TARGET_STORE_RETURNED_BOUNDS

Support for Nested Functions
============================

Taking the address of a nested function requires special compiler handling to ensure that the static chain register is loaded when the function is invoked via an indirect call.

GCC has traditionally supported nested functions by creating an executable trampoline at run time when the address of a nested function is taken.  This is a small piece of code which normally resides on the stack, in the stack frame of the containing function. The trampoline loads the static chain register and then jumps to the real address of the nested function.

The use of trampolines requires an executable stack, which is a security risk.  To avoid this problem, GCC also supports another strategy: using descriptors for nested functions.  Under this model, taking the address of a nested function results in a pointer to a non-executable function descriptor object.  Initializing the static chain from the descriptor is handled at indirect call sites.

On some targets, including HPPA and IA-64, function descriptors may be mandated by the ABI or be otherwise handled in a target-specific way by the back end in its code generation strategy for indirect calls. GCC also provides its own generic descriptor implementation to support the -fno-trampolines option.  In this case runtime detection of function descriptors at indirect call sites relies on descriptor pointers being tagged with a bit that is never set in bare function addresses.  Since GCC's generic function descriptors are not ABI-compliant, this option is typically used only on a per-language basis (notably by Ada) or when it can otherwise be applied to the whole program.

Define the following hook if your backend either implements ABI-specified descriptor support, or can use GCC's generic descriptor implementation for nested functions.

TARGET_CUSTOM_FUNCTION_DESCRIPTORS

The following macros tell GCC how to generate code to allocate and initialize an executable trampoline.  You can also use this interface if your back end needs to create ABI-specified non-executable descriptors; in this case the "trampoline" created is the descriptor containing data only.

The instructions in an executable 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.

TARGET_ASM_TRAMPOLINE_TEMPLATE

 -- Macro: TRAMPOLINE_SECTION
     Return the section into which the trampoline template is to be placed (see Sections).  The default value is readonly_data_section.

 -- Macro: TRAMPOLINE_SIZE
     A C expression for the size in bytes of the trampoline, as an integer.

 -- Macro: TRAMPOLINE_ALIGNMENT
     Alignment required for trampolines, in bits.

     If you don't define this macro, the value of FUNCTION_ALIGNMENT is used for aligning trampolines.

TARGET_TRAMPOLINE_INIT

TARGET_EMIT_CALL_BUILTIN___CLEAR_CACHE

TARGET_TRAMPOLINE_ADJUST_ADDRESS

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.

 -- Macro: CLEAR_INSN_CACHE (BEG, END)
     If defined, expands to a C expression clearing the instruction cache in the specified interval.  The definition of this macro would typically be a series of asm statements.  Both BEG and END are pointer expressions.

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 m68k.h as a guide.

 -- Macro: TRANSFER_FROM_TRAMPOLINE
     Define this macro if trampolines need a special subroutine to do their work.  The macro should expand to a series of asm statements which will be compiled with GCC.  They go in a library function named __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 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.

Implicit Calls to Library Routines
==================================

Here is an explanation of implicit calls to library routines.

 -- Macro: 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.

TARGET_INIT_LIBFUNCS

TARGET_LIBFUNC_GNU_PREFIX

 -- Macro: FLOAT_LIB_COMPARE_RETURNS_BOOL (MODE, COMPARISON)
     This macro should return true if the library routine that implements the floating point comparison operator COMPARISON in mode MODE will return a boolean, and 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.

 -- Macro: TARGET_LIB_INT_CMP_BIASED
     This macro should evaluate to true if the integer comparison functions (like __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 false the comparison functions return -1, 0, and 1 instead of 0, 1, and 2.  If the target uses the routines in libgcc.a, you do not need to define this macro.

 -- Macro: TARGET_HAS_NO_HW_DIVIDE
     This macro should be defined if the target has no hardware divide instructions.  If this macro is defined, GCC will use an algorithm which make use of simple logical and arithmetic operations for 64-bit division.  If the macro is not defined, GCC will use an algorithm which make use of a 64-bit by 32-bit divide primitive.

 -- Macro: TARGET_EDOM
     The value of 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 EDOM into errno directly.  Look in /usr/include/errno.h to find the value of EDOM on your system.

     If you do not define 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 matherr when there is an error, then you should leave TARGET_EDOM undefined so that matherr is used normally.

 -- Macro: GEN_ERRNO_RTX
     Define this macro as a C expression to create an rtl expression that refers to the global ``variable'' errno.  (On certain systems, errno may not actually be a variable.)  If you don't define this macro, a reasonable default is used.

TARGET_LIBC_HAS_FUNCTION

TARGET_LIBC_HAS_FAST_FUNCTION

 -- Macro: NEXT_OBJC_RUNTIME
     Set this macro to 1 to use the "NeXT" Objective-C message sending conventions by default.  This calling convention involves passing the object, the selector and the method arguments all at once to the method-lookup library function. This is the usual setting when targeting Darwin/Mac OS X systems, which have the NeXT runtime installed.

     If the macro is set to 0, the "GNU" Objective-C message sending convention will be used by default.  This convention passes just the object and the selector to the method-lookup function, which returns a pointer to the method.

     In either case, it remains possible to select code-generation for the alternate scheme, by means of compiler command line switches.

Addressing Modes
================

This is about addressing modes.

 -- Macro: HAVE_PRE_INCREMENT
 -- Macro: HAVE_PRE_DECREMENT
 -- Macro: HAVE_POST_INCREMENT
 -- Macro: HAVE_POST_DECREMENT
     A C expression that is nonzero if the machine supports pre-increment, pre-decrement, post-increment, or post-decrement addressing respectively.

 -- Macro: HAVE_PRE_MODIFY_DISP
 -- Macro: 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.

 -- Macro: HAVE_PRE_MODIFY_REG
 -- Macro: 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.

 -- Macro: CONSTANT_ADDRESS_P (X)
     A C expression that is 1 if the RTX X is a constant which is a valid address.  On most machines the default definition of (CONSTANT_P (X) && GET_CODE (X) != CONST_DOUBLE) is acceptable, but a few machines are more restrictive as to which constant addresses are supported.

 -- Macro: CONSTANT_P (X)
     CONSTANT_P, which is defined by target-independent code, accepts integer-values expressions whose values are not explicitly known, such as symbol_ref, label_ref, and high expressions and const arithmetic expressions, in addition to const_int and const_double expressions.

 -- Macro: 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 TARGET_LEGITIMATE_ADDRESS_P would ever accept.

TARGET_LEGITIMATE_ADDRESS_P

 -- Macro: TARGET_MEM_CONSTRAINT
     A single character to be used instead of the default 'm' character for general memory addresses.  This defines the constraint letter which matches the memory addresses accepted by TARGET_LEGITIMATE_ADDRESS_P.  Define this macro if you want to support new address formats in your back end without changing the semantics of the 'm' constraint.  This is necessary in order to preserve functionality of inline assembly constructs using the 'm' constraint.

 -- Macro: FIND_BASE_TERM (X)
     A C expression to determine the base term of address X, or to provide a simplified version of X from which alias.c can easily find the base term.  This macro is used in only two places: find_base_value and 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.

TARGET_LEGITIMIZE_ADDRESS

 -- Macro: LEGITIMIZE_RELOAD_ADDRESS (X, MODE, OPNUM, TYPE, IND_LEVELS, WIN)
     A C compound statement that attempts to replace X, which is an address that needs reloading, with a valid memory address for an operand of mode MODE.  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 LEGITIMIZE_RELOAD_ADDRESS appropriately, the intermediate addresses generated for adjacent some stack slots can be made identical, and thus be shared.

     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.

     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.

     The macro definition should use push_reload to indicate parts that need reloading; OPNUM, TYPE and IND_LEVELS are usually suitable to be passed unaltered to push_reload.

     The code generated by this macro must not alter the substructure of X.  If it transforms X into a more legitimate form, it should assign X (which will always be a C variable) a new value. This also applies to parts that you change indirectly by calling push_reload.

     The macro definition may use strict_memory_address_p to test if the address has become legitimate.

     If you want to change only a part of X, one standard way of doing this is to use copy_rtx.  Note, however, that it 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.

TARGET_MODE_DEPENDENT_ADDRESS_P

TARGET_LEGITIMATE_CONSTANT_P

TARGET_PRECOMPUTE_TLS_P

TARGET_DELEGITIMIZE_ADDRESS

TARGET_CONST_NOT_OK_FOR_DEBUG_P

TARGET_CANNOT_FORCE_CONST_MEM

TARGET_USE_BLOCKS_FOR_CONSTANT_P

TARGET_USE_BLOCKS_FOR_DECL_P

TARGET_BUILTIN_RECIPROCAL

TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD

TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST

TARGET_VECTORIZE_PREFERRED_VECTOR_ALIGNMENT

TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE

TARGET_VECTORIZE_VEC_PERM_CONST

TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION

TARGET_VECTORIZE_BUILTIN_MD_VECTORIZED_FUNCTION

TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT

TARGET_VECTORIZE_PREFERRED_SIMD_MODE

TARGET_VECTORIZE_SPLIT_REDUCTION

TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_MODES

TARGET_VECTORIZE_RELATED_MODE

TARGET_VECTORIZE_GET_MASK_MODE

TARGET_VECTORIZE_EMPTY_MASK_IS_EXPENSIVE

TARGET_VECTORIZE_INIT_COST

TARGET_VECTORIZE_ADD_STMT_COST

TARGET_VECTORIZE_FINISH_COST

TARGET_VECTORIZE_DESTROY_COST_DATA

TARGET_VECTORIZE_BUILTIN_GATHER

TARGET_VECTORIZE_BUILTIN_SCATTER

TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN

TARGET_SIMD_CLONE_ADJUST

TARGET_SIMD_CLONE_USABLE

TARGET_SIMT_VF

TARGET_OMP_DEVICE_KIND_ARCH_ISA

TARGET_GOACC_VALIDATE_DIMS

TARGET_GOACC_DIM_LIMIT

TARGET_GOACC_FORK_JOIN

TARGET_GOACC_REDUCTION

TARGET_PREFERRED_ELSE_VALUE

Anchored Addresses
==================

GCC usually addresses every static object as a separate entity. For example, if we have:

     static int a, b, c;
     int foo (void) { return a + b + c; }

the code for foo will usually calculate three separate symbolic addresses: those of a, b and 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:

     int foo (void)
     {
       register int *xr = &x;
       return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
     }

(which isn't valid C).  We refer to shared addresses like x as ``section anchors''.  Their use is controlled by -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 TARGET_MIN_ANCHOR_OFFSET or TARGET_MAX_ANCHOR_OFFSET is set to a nonzero value.

TARGET_MIN_ANCHOR_OFFSET

TARGET_MAX_ANCHOR_OFFSET

TARGET_ASM_OUTPUT_ANCHOR

TARGET_USE_ANCHORS_FOR_SYMBOL_P

Condition Code Status
=====================

The macros in this section can be split in two families, according to the two ways of representing condition codes in GCC.

The first representation is the so called (cc0) representation (see Jump Patterns), where all instructions can have an implicit clobber of the condition codes.  The second is the condition code register representation, which provides better schedulability for architectures that do have a condition code register, but on which most instructions do not affect it.  The latter category includes most RISC machines.

The implicit clobbering poses a strong restriction on the placement of the definition and use of the condition code.  In the past the definition and use were always adjacent.  However, recent changes to support trapping arithmatic may result in the definition and user being in different blocks. Thus, there may be a NOTE_INSN_BASIC_BLOCK between them.  Additionally, the definition may be the source of exception handling edges.

These restrictions can prevent important optimizations on some machines.  For example, on the IBM RS/6000, there is a delay for taken branches unless the condition code register is set three instructions earlier than the conditional branch.  The instruction scheduler cannot perform this optimization if it is not permitted to separate the definition and use of the condition code register.

For this reason, it is possible and suggested to use a register to represent the condition code for new ports.  If there is a specific condition code register in the machine, use a hard register.  If the condition code or comparison result can be placed in any general register, or if there are multiple condition registers, use a pseudo register. Registers used to store the condition code value will usually have a mode that is in class MODE_CC.

Alternatively, you can use BImode if the comparison operator is specified already in the compare instruction.  In this case, you are not interested in most macros in this section.

Representation of condition codes using (cc0)
---------------------------------------------

The file conditions.h defines a variable 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 CC_STATUS_MDEP.

 -- Macro: CC_STATUS_MDEP
     C code for a data type which is used for declaring the mdep component of cc_status.  It defaults to int.

     This macro is not used on machines that do not use cc0.

 -- Macro: CC_STATUS_MDEP_INIT
     A C expression to initialize the 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 cc0.

 -- Macro: NOTICE_UPDATE_CC (EXP, INSN)
     A C compound statement to set the components of cc_status appropriately for an insn INSN whose body is 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 (cc0).

     This macro is not used on machines that do not use 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 NOTICE_UPDATE_CC can leave cc_status unaltered for such insns.  But suppose that the previous insn set the condition code based on location a4@(102) and the current insn stores a new value in a4.  Although the condition code is not changed by this, it will no longer be true that it reflects the contents of a4@(102).  Therefore, NOTICE_UPDATE_CC must alter cc_status in this case to say that nothing is known about the condition code value.

     The definition of NOTICE_UPDATE_CC must be prepared to deal with the results of peephole optimization: insns whose patterns are parallel RTXs containing various reg, 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 NOTICE_UPDATE_CC should do when it sees one is just to run CC_STATUS_INIT.

     A possible definition of NOTICE_UPDATE_CC is to call a function that looks at an attribute (see Insn Attributes) named, for example, cc.  This avoids having detailed information about patterns in two places, the md file and in NOTICE_UPDATE_CC.

Representation of condition codes using registers
-------------------------------------------------

 -- Macro: SELECT_CC_MODE (OP, X, Y)
     On many machines, the condition code may be produced by other instructions than compares, for example the branch can use directly the condition code set by a subtract instruction.  However, on some machines when the condition code is set this way some bits (such as the overflow bit) are not set in the same way as a test instruction, so that a different branch instruction must be used for some conditional branches.  When this happens, use the machine mode of the condition code register to record different formats of the condition code register.  Modes can also be used to record which compare instruction (e.g. a signed or an unsigned comparison) produced the condition codes.

     If other modes than CCmode are required, add them to MACHINE-modes.def and define SELECT_CC_MODE to choose a mode given an operand of a compare.  This is needed because the modes have to be chosen not only during RTL generation but also, for example, by instruction combination.  The result of SELECT_CC_MODE should be consistent with the mode used in the patterns; for example to support the case of the add on the SPARC discussed above, we have the pattern

          (define_insn ""
            [(set (reg:CCNZ 0)
                  (compare:CCNZ
                    (plus:SI (match_operand:SI 0 "register_operand" "%r")
                             (match_operand:SI 1 "arith_operand" "rI"))
                    (const_int 0)))]
            ""
            "...")

     together with a SELECT_CC_MODE that returns CCNZmode for comparisons whose argument is a plus:

          #define SELECT_CC_MODE(OP,X,Y) \
            (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT           \
             ? ((OP == LT || OP == LE || OP == GT || OP == GE)     \
                ? CCFPEmode : CCFPmode)                            \
             : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS     \
                 || GET_CODE (X) == NEG || GET_CODE (x) == ASHIFT) \
                ? CCNZmode : CCmode))

     Another reason to use modes is to retain information on which operands were used by the comparison; see REVERSIBLE_CC_MODE later in this section.

     You should define this macro if and only if you define extra CC modes in MACHINE-modes.def.

TARGET_CANONICALIZE_COMPARISON

 -- Macro: REVERSIBLE_CC_MODE (MODE)
     A C expression whose value is one if it is always safe to reverse a comparison whose mode is MODE.  If SELECT_CC_MODE can ever return MODE for a floating-point inequality comparison, then REVERSIBLE_CC_MODE (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 IEEE_FLOAT_FORMAT. For example, here is the definition used on the SPARC, where floating-point inequality comparisons are given either CCFPEmode or CCFPmode:

          #define REVERSIBLE_CC_MODE(MODE) \
             ((MODE) != CCFPEmode && (MODE) != CCFPmode)

 -- Macro: REVERSE_CONDITION (CODE, MODE)
     A C expression whose value is reversed condition code of the CODE for comparison done in CC_MODE MODE.  The macro is used only in case REVERSIBLE_CC_MODE (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 ones.  Then definition may look like:

          #define REVERSE_CONDITION(CODE, MODE) \
             ((MODE) != CCFPmode ? reverse_condition (CODE) \
              : reverse_condition_maybe_unordered (CODE))

TARGET_FIXED_CONDITION_CODE_REGS

TARGET_CC_MODES_COMPATIBLE

TARGET_FLAGS_REGNUM

Describing Relative Costs of Operations
=======================================

These macros let you describe the relative speed of various operations on the target machine.

 -- Macro: REGISTER_MOVE_COST (MODE, FROM, TO)
     A C expression for the cost of moving data of mode MODE from a register in class FROM to one in class TO.  The classes are expressed using the enumeration values such as 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 FROM is the same as 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 set between two hard registers, and if 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 movM pattern's constraints do not allow such copying.

     These macros are obsolete, new ports should use the target hook TARGET_REGISTER_MOVE_COST instead.

TARGET_REGISTER_MOVE_COST

 -- Macro: MEMORY_MOVE_COST (MODE, CLASS, IN)
     A C expression for the cost of moving data of mode MODE between a register of class CLASS and memory; 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 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 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 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.

     These macros are obsolete, new ports should use the target hook TARGET_MEMORY_MOVE_COST instead.

TARGET_MEMORY_MOVE_COST

 -- Macro: BRANCH_COST (SPEED_P, PREDICTABLE_P)
     A C expression for the cost of a branch instruction.  A value of 1 is the default; other values are interpreted relative to that. Parameter SPEED_P is true when the branch in question should be optimized for speed.  When it is false, BRANCH_COST should return a value optimal for code size rather than performance.  PREDICTABLE_P is true for well-predicted branches. On many architectures the BRANCH_COST can be reduced then.

Here are additional macros which do not specify precise relative costs, but only that certain actions are more expensive than GCC would ordinarily expect.

 -- Macro: SLOW_BYTE_ACCESS
     Define this macro as a C expression which is nonzero if accessing less than a word of memory (i.e. a char or a 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.

TARGET_SLOW_UNALIGNED_ACCESS

 -- Macro: MOVE_RATIO (SPEED)
     The threshold of number of scalar memory-to-memory move insns, 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 define_expand that emits a sequence of insns, this macro counts the number of such sequences.

     The parameter SPEED is true if the code is currently being optimized for speed rather than size.

     If you don't define this, a reasonable default is used.

TARGET_USE_BY_PIECES_INFRASTRUCTURE_P

TARGET_COMPARE_BY_PIECES_BRANCH_RATIO

 -- Macro: MOVE_MAX_PIECES
     A C expression used by move_by_pieces to determine the largest unit a load or store used to copy memory is.  Defaults to MOVE_MAX.

 -- Macro: STORE_MAX_PIECES
     A C expression used by store_by_pieces to determine the largest unit a store used to memory is.  Defaults to MOVE_MAX_PIECES, or two times the size of HOST_WIDE_INT, whichever is smaller.

 -- Macro: COMPARE_MAX_PIECES
     A C expression used by compare_by_pieces to determine the largest unit a load or store used to compare memory is.  Defaults to MOVE_MAX_PIECES.

 -- Macro: CLEAR_RATIO (SPEED)
     The threshold of number of scalar move insns, 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.

     The parameter SPEED is true if the code is currently being optimized for speed rather than size.

     If you don't define this, a reasonable default is used.

 -- Macro: SET_RATIO (SPEED)
     The threshold of number of scalar move insns, below which a sequence of insns should be generated to set memory to a constant value, instead of a block set insn or a library call. Increasing the value will always make code faster, but eventually incurs high cost in increased code size.

     The parameter SPEED is true if the code is currently being optimized for speed rather than size.

     If you don't define this, it defaults to the value of MOVE_RATIO.

 -- Macro: USE_LOAD_POST_INCREMENT (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 HAVE_POST_INCREMENT.

 -- Macro: USE_LOAD_POST_DECREMENT (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 HAVE_POST_DECREMENT.

 -- Macro: USE_LOAD_PRE_INCREMENT (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 HAVE_PRE_INCREMENT.

 -- Macro: USE_LOAD_PRE_DECREMENT (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 HAVE_PRE_DECREMENT.

 -- Macro: USE_STORE_POST_INCREMENT (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 HAVE_POST_INCREMENT.

 -- Macro: USE_STORE_POST_DECREMENT (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 HAVE_POST_DECREMENT.

 -- Macro: USE_STORE_PRE_INCREMENT (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 HAVE_PRE_INCREMENT.

 -- Macro: USE_STORE_PRE_DECREMENT (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 HAVE_PRE_DECREMENT.

 -- Macro: NO_FUNCTION_CSE
     Define this macro to be true if it is as good or better to call a constant function address than to call an address kept in a register.

 -- Macro: LOGICAL_OP_NON_SHORT_CIRCUIT
     Define this macro if a non-short-circuit operation produced by fold_range_test () is optimal.  This macro defaults to true if BRANCH_COST is greater than or equal to the value 2.

TARGET_OPTAB_SUPPORTED_P

TARGET_RTX_COSTS

TARGET_ADDRESS_COST

TARGET_INSN_COST

TARGET_MAX_NOCE_IFCVT_SEQ_COST

TARGET_NOCE_CONVERSION_PROFITABLE_P

TARGET_NEW_ADDRESS_PROFITABLE_P

TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P

TARGET_ESTIMATED_POLY_VALUE

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.

TARGET_SCHED_ISSUE_RATE

TARGET_SCHED_VARIABLE_ISSUE

TARGET_SCHED_ADJUST_COST

TARGET_SCHED_ADJUST_PRIORITY

TARGET_SCHED_REORDER

TARGET_SCHED_REORDER2

TARGET_SCHED_MACRO_FUSION_P

TARGET_SCHED_MACRO_FUSION_PAIR_P

TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK

TARGET_SCHED_INIT

TARGET_SCHED_FINISH

TARGET_SCHED_INIT_GLOBAL

TARGET_SCHED_FINISH_GLOBAL

TARGET_SCHED_DFA_PRE_CYCLE_INSN

TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN

TARGET_SCHED_DFA_POST_CYCLE_INSN

TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN

TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE

TARGET_SCHED_DFA_POST_ADVANCE_CYCLE

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT

TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI

TARGET_SCHED_DFA_NEW_CYCLE

TARGET_SCHED_IS_COSTLY_DEPENDENCE

TARGET_SCHED_H_I_D_EXTENDED

TARGET_SCHED_ALLOC_SCHED_CONTEXT

TARGET_SCHED_INIT_SCHED_CONTEXT

TARGET_SCHED_SET_SCHED_CONTEXT

TARGET_SCHED_CLEAR_SCHED_CONTEXT

TARGET_SCHED_FREE_SCHED_CONTEXT

TARGET_SCHED_SPECULATE_INSN

TARGET_SCHED_NEEDS_BLOCK_P

TARGET_SCHED_GEN_SPEC_CHECK

TARGET_SCHED_SET_SCHED_FLAGS

TARGET_SCHED_CAN_SPECULATE_INSN

TARGET_SCHED_SMS_RES_MII

TARGET_SCHED_DISPATCH

TARGET_SCHED_DISPATCH_DO

TARGET_SCHED_EXPOSED_PIPELINE

TARGET_SCHED_REASSOCIATION_WIDTH

TARGET_SCHED_FUSION_PRIORITY

TARGET_EXPAND_DIVMOD_LIBFUNC

Dividing the Output into Sections (Texts, Data, ...)
====================================================

An object file is divided into sections containing different types of data.  In the most common case, there are three sections: the text section, which holds instructions and read-only data; the data section, which holds initialized writable data; and the bss section, which holds uninitialized data.  Some systems have other kinds of sections.

varasm.c provides several well-known sections, such as text_section, data_section and bss_section. The normal way of controlling a FOO_section variable is to define the associated FOO_SECTION_ASM_OP macro, as described below.  The macros are only read once, when varasm.c initializes itself, so their values must be run-time constants. They may however depend on command-line flags.

Note: Some run-time files, such crtstuff.c, also make use of the 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 TARGET_ASM_INIT_SECTIONS hook and use get_unnamed_section to set up the sections.

You must always create a text_section, either by defining TEXT_SECTION_ASM_OP or by initializing text_section in TARGET_ASM_INIT_SECTIONS.  The same is true of data_section and DATA_SECTION_ASM_OP.  If you do not create a distinct readonly_data_section, the default is to reuse text_section.

All the other varasm.c sections are optional, and are null if the target does not provide them.

 -- Macro: 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 "\t.text" is right.

 -- Macro: 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.

 -- Macro: UNLIKELY_EXECUTED_TEXT_SECTION_NAME
     If defined, a C string constant for the name of the section containing unlikely executed functions in the program.

 -- Macro: 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 "\t.data" is right.

 -- Macro: 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.

 -- Macro: 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.

 -- Macro: 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 ASM_OUTPUT_ALIGNED_BSS not defined, uninitialized global data will be output in the data section if -fno-common is passed, otherwise ASM_OUTPUT_COMMON will be used.

 -- Macro: 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.

 -- Macro: TLS_COMMON_ASM_OP
     If defined, a C expression whose value is a string containing the assembler operation to identify the following data as thread-local common data.  The default is ".tls_common".

 -- Macro: TLS_SECTION_ASM_FLAG
     If defined, a C expression whose value is a character constant containing the flag used to mark a section as a TLS section.  The default is 'T'.

 -- Macro: 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 init_section variable; it is used entirely in runtime code.

 -- Macro: 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 fini_section variable; it is used entirely in runtime code.

 -- Macro: 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 .init_array (or equivalent) section.  If not defined, GCC will assume such a section does not exist.  Do not define both this macro and INIT_SECTION_ASM_OP.

 -- Macro: 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 .fini_array (or equivalent) section.  If not defined, GCC will assume such a section does not exist.  Do not define both this macro and FINI_SECTION_ASM_OP.

 -- Macro: MACH_DEP_SECTION_ASM_FLAG
     If defined, a C expression whose value is a character constant containing the flag used to mark a machine-dependent section.  This corresponds to the SECTION_MACH_DEP section flag.

 -- Macro: CRT_CALL_STATIC_FUNCTION (SECTION_OP, FUNCTION)
     If defined, an ASM statement that switches to a different section via SECTION_OP, calls FUNCTION, and switches back to the text section.  This is used in crtstuff.c if INIT_SECTION_ASM_OP or 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.

 -- Macro: 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 .sdata section (like MIPS), you could compile crtstuff with -G 0 so that it doesn't require small data support from your application, but use this macro to put small data into .sdata so that your application can access these variables whether it uses small data or not.

 -- Macro: 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 .init and .fini sections to have to same alignment and thus prevent the linker from having to add any padding.

 -- Macro: JUMP_TABLES_IN_TEXT_SECTION
     Define this macro to be an expression with a nonzero value if jump tables (for 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.

TARGET_ASM_INIT_SECTIONS

TARGET_ASM_RELOC_RW_MASK

TARGET_ASM_GENERATE_PIC_ADDR_DIFF_VEC

TARGET_ASM_SELECT_SECTION

 -- Macro: USE_SELECT_SECTION_FOR_FUNCTIONS
     Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called for FUNCTION_DECLs as well as for variables and constants.

     In the case of a FUNCTION_DECL, 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.

TARGET_ASM_UNIQUE_SECTION

TARGET_ASM_FUNCTION_RODATA_SECTION

TARGET_ASM_MERGEABLE_RODATA_PREFIX

TARGET_ASM_TM_CLONE_TABLE_SECTION

TARGET_ASM_SELECT_RTX_SECTION

TARGET_MANGLE_DECL_ASSEMBLER_NAME

TARGET_ENCODE_SECTION_INFO

TARGET_STRIP_NAME_ENCODING

TARGET_IN_SMALL_DATA_P

TARGET_HAVE_SRODATA_SECTION

TARGET_PROFILE_BEFORE_PROLOGUE

TARGET_BINDS_LOCAL_P

TARGET_HAVE_TLS

Position Independent Code
=========================

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 hook TARGET_LEGITIMATE_ADDRESS_P and to the macro PRINT_OPERAND_ADDRESS, as well as LEGITIMIZE_ADDRESS.  You must modify the definition of 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.

 -- Macro: 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 flag_pic is true).

 -- Macro: PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
     A C expression that is nonzero if the register defined by PIC_OFFSET_TABLE_REGNUM is clobbered by calls.  If not defined, the default is zero.  Do not define this macro if PIC_OFFSET_TABLE_REGNUM is not defined.

 -- Macro: LEGITIMATE_PIC_OPERAND_P (X)
     A C expression that is nonzero if X is a legitimate immediate operand on the target machine when generating position independent code. You can assume that X satisfies CONSTANT_P, so you need not check this.  You can also assume FLAG_PIC is true, so you need not check it either.  You need not define this macro if all constants (including SYMBOL_REF) can be immediate operands when generating position independent code.

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.

The Overall Framework of an Assembler File
------------------------------------------

This describes the overall framework of an assembly file.

TARGET_ASM_FILE_START

TARGET_ASM_FILE_START_APP_OFF

TARGET_ASM_FILE_START_FILE_DIRECTIVE

TARGET_ASM_FILE_END

 -- Function: void file_end_indicate_exec_stack ()
     Some systems use a common convention, the .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 TARGET_ASM_FILE_END to this function.  If you need to do other things in that hook, have your hook function call this function.

TARGET_ASM_LTO_START

TARGET_ASM_LTO_END

TARGET_ASM_CODE_END

 -- Macro: 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.

 -- Macro: ASM_APP_ON
     A C string constant for text to be output before each asm statement or group of consecutive ones.  Normally this is "#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.

 -- Macro: ASM_APP_OFF
     A C string constant for text to be output after each asm statement or group of consecutive ones.  Normally this is "#NO_APP", which tells the GNU assembler to resume making the time-saving assumptions that are valid for ordinary compiler output.

 -- Macro: ASM_OUTPUT_SOURCE_FILENAME (STREAM, NAME)
     A C statement to output COFF information or DWARF debugging information which indicates that filename NAME is the current source file to the stdio stream STREAM.

     This macro need not be defined if the standard form of output for the file format in use is appropriate.

TARGET_ASM_OUTPUT_SOURCE_FILENAME

TARGET_ASM_OUTPUT_IDENT

 -- Macro: OUTPUT_QUOTED_STRING (STREAM, STRING)
     A C statement to output the string STRING to the stdio stream STREAM.  If you do not call the function 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.

TARGET_ASM_NAMED_SECTION

TARGET_ASM_ELF_FLAGS_NUMERIC

TARGET_ASM_FUNCTION_SECTION

TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS

TARGET_HAVE_NAMED_SECTIONS
This flag is true if the target supports TARGET_ASM_NAMED_SECTION. It must not be modified by command-line option processing.

TARGET_HAVE_SWITCHABLE_BSS_SECTIONS

TARGET_SECTION_TYPE_FLAGS

TARGET_ASM_RECORD_GCC_SWITCHES

TARGET_ASM_RECORD_GCC_SWITCHES_SECTION

Output of Data
--------------

TARGET_ASM_BYTE_OP

TARGET_ASM_INTEGER

TARGET_ASM_DECL_END

TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA

 -- Macro: ASM_OUTPUT_ASCII (STREAM, PTR, LEN)
     A C statement to output to the stdio stream STREAM an assembler instruction to assemble a string constant containing the LEN bytes at PTR.  PTR will be a C expression of type char * and LEN a C expression of type int.

     If the assembler has a .ascii pseudo-op as found in the Berkeley Unix assembler, do not define the macro ASM_OUTPUT_ASCII.

 -- Macro: ASM_OUTPUT_FDESC (STREAM, DECL, N)
     A C statement to output word N of a function descriptor for DECL.  This must be defined if TARGET_VTABLE_USES_DESCRIPTORS is defined, and is otherwise unused.

 -- Macro: 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.

 -- Macro: ASM_OUTPUT_POOL_PROLOGUE (FILE, FUNNAME, FUNDECL, SIZE)
     A C statement to output assembler commands to define the start of the constant pool for a function.  FUNNAME is a string giving the name of the function.  Should the return type of the function be required, it can be obtained via FUNDECL.  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.

 -- Macro: ASM_OUTPUT_SPECIAL_POOL_ENTRY (FILE, X, MODE, ALIGN, LABELNO, 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 FILE is the standard I/O stream to output the assembler code on.  X is the RTL expression for the constant to output, and MODE is the machine mode (in case X is a const_int).  ALIGN is the required alignment for the value X; you should output an assembler directive to force this much alignment.

     The argument 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:

          (*targetm.asm_out.internal_label) (FILE, "LC", LABELNO);

     When you output a pool entry specially, you should end with a goto to the label 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.

 -- Macro: ASM_OUTPUT_POOL_EPILOGUE (FILE FUNNAME FUNDECL SIZE)
     A C statement to output assembler commands to at the end of the constant pool for a function.  FUNNAME is a string giving the name of the function.  Should the return type of the function be required, you can obtain it via FUNDECL.  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.

 -- Macro: IS_ASM_LOGICAL_LINE_SEPARATOR (C, STR)
     Define this macro as a C expression which is nonzero if C is used as a logical line separator by the assembler.  STR points to the position in the string where C was found; this can be used if a line separator uses multiple characters.

     If you do not define this macro, the default is that only the character ; is treated as a logical line separator.

TARGET_ASM_OPEN_PAREN

These macros are provided by real.h for writing the definitions of ASM_OUTPUT_DOUBLE and the like:

 -- Macro: REAL_VALUE_TO_TARGET_SINGLE (X, L)
 -- Macro: REAL_VALUE_TO_TARGET_DOUBLE (X, L)
 -- Macro: REAL_VALUE_TO_TARGET_LONG_DOUBLE (X, L)
 -- Macro: REAL_VALUE_TO_TARGET_DECIMAL32 (X, L)
 -- Macro: REAL_VALUE_TO_TARGET_DECIMAL64 (X, L)
 -- Macro: REAL_VALUE_TO_TARGET_DECIMAL128 (X, L)
     These translate X, of type REAL_VALUE_TYPE, to the target's floating point representation, and store its bit pattern in the variable L.  For REAL_VALUE_TO_TARGET_SINGLE and REAL_VALUE_TO_TARGET_DECIMAL32, this variable should be a simple long int.  For the others, it should be an array of 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 long int array element.  Each array element holds 32 bits of the result, even if 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 fprintf in the order they should appear in the target machine's memory.

Output of Uninitialized Variables
---------------------------------

Each of the macros in this section is used to do the whole job of outputting a single uninitialized variable.

 -- Macro: ASM_OUTPUT_COMMON (STREAM, NAME, SIZE, ROUNDED)
     A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a common-label named NAME whose size is SIZE bytes.  The variable ROUNDED is the size rounded up to whatever alignment the caller wants.  It is possible that SIZE may be zero, for instance if a struct with no other member than a zero-length array is defined.  In this case, the backend must output a symbol definition that allocates at least one byte, both so that the address of the resulting object does not compare equal to any other, and because some object formats cannot even express the concept of a zero-sized common symbol, as that is how they represent an ordinary undefined external.

     Use the expression assemble_name (STREAM, 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.

 -- Macro: ASM_OUTPUT_ALIGNED_COMMON (STREAM, NAME, SIZE, ALIGNMENT)
     Like ASM_OUTPUT_COMMON except takes the required alignment as a separate, explicit argument.  If you define this macro, it is used in place of 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.

 -- Macro: ASM_OUTPUT_ALIGNED_DECL_COMMON (STREAM, DECL, NAME, SIZE, ALIGNMENT)
     Like ASM_OUTPUT_ALIGNED_COMMON except that DECL of the variable to be output, if there is one, or NULL_TREE if there is no corresponding variable.  If you define this macro, GCC will use it in place of both ASM_OUTPUT_COMMON and ASM_OUTPUT_ALIGNED_COMMON.  Define this macro when you need to see the variable's decl in order to chose what to output.

 -- Macro: ASM_OUTPUT_ALIGNED_BSS (STREAM, DECL, NAME, SIZE, ALIGNMENT)
     A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of uninitialized global DECL named NAME whose size is SIZE bytes.  The variable ALIGNMENT is the alignment specified as the number of bits.

     Try to use function asm_output_aligned_bss defined in file varasm.c when defining this macro.  If unable, use the expression assemble_name (STREAM, 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 this macro. The other is to have TARGET_ASM_SELECT_SECTION return a switchable BSS section (see TARGET_HAVE_SWITCHABLE_BSS_SECTIONS). You do not need to do both.

     Some languages do not have 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.

 -- Macro: ASM_OUTPUT_LOCAL (STREAM, NAME, SIZE, ROUNDED)
     A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a local-common-label named NAME whose size is SIZE bytes.  The variable ROUNDED is the size rounded up to whatever alignment the caller wants.

     Use the expression assemble_name (STREAM, 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.

 -- Macro: ASM_OUTPUT_ALIGNED_LOCAL (STREAM, NAME, SIZE, ALIGNMENT)
     Like ASM_OUTPUT_LOCAL except takes the required alignment as a separate, explicit argument.  If you define this macro, it is used in place of 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.

 -- Macro: ASM_OUTPUT_ALIGNED_DECL_LOCAL (STREAM, DECL, NAME, SIZE, ALIGNMENT)
     Like ASM_OUTPUT_ALIGNED_LOCAL except that DECL of the variable to be output, if there is one, or NULL_TREE if there is no corresponding variable.  If you define this macro, GCC will use it in place of both ASM_OUTPUT_LOCAL and ASM_OUTPUT_ALIGNED_LOCAL.  Define this macro when you need to see the variable's decl in order to chose what to output.

Output and Generation of Labels
-------------------------------

This is about outputting labels.

 -- Macro: ASM_OUTPUT_LABEL (STREAM, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a label named NAME. Use the expression assemble_name (STREAM, 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.

 -- Macro: ASM_OUTPUT_FUNCTION_LABEL (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a label named NAME of a function. Use the expression assemble_name (STREAM, 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.

     If this macro is not defined, then the function name is defined in the usual manner as a label (by means of ASM_OUTPUT_LABEL).

 -- Macro: ASM_OUTPUT_INTERNAL_LABEL (STREAM, NAME)
     Identical to ASM_OUTPUT_LABEL, except that NAME is known to refer to a compiler-generated label.  The default definition uses assemble_name_raw, which is like assemble_name except that it is more efficient.

 -- Macro: 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 config/elfos.h) is "\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 ASM_OUTPUT_SIZE_DIRECTIVE and 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.

 -- Macro: ASM_OUTPUT_SIZE_DIRECTIVE (STREAM, NAME, SIZE)
     A C statement (sans semicolon) to output to the stdio stream STREAM a directive telling the assembler that the size of the symbol NAME is SIZE.  SIZE is a HOST_WIDE_INT. If you define SIZE_ASM_OP, a default definition of this macro is provided.

 -- Macro: ASM_OUTPUT_MEASURED_SIZE (STREAM, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM a directive telling the assembler to calculate the size of the symbol NAME by subtracting its address from the current address.

     If you define SIZE_ASM_OP, a default definition of this macro is provided.  The default assumes that the assembler recognizes a special . symbol as referring to the current address, and can calculate the difference between this and another symbol.  If your assembler does not recognize . or cannot do calculations with it, you will need to redefine ASM_OUTPUT_MEASURED_SIZE to use some other technique.

 -- Macro: NO_DOLLAR_IN_LABEL
     Define this macro if the assembler does not accept the character $ in label names.  By default constructors and destructors in G++ have $ in the identifiers.  If this macro is defined, . is used instead.

 -- Macro: NO_DOT_IN_LABEL
     Define this macro if the assembler does not accept the character . in label names.  By default constructors and destructors in G++ have names that use ..  If this macro is defined, these names are rewritten to avoid ..

 -- Macro: 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 config/elfos.h) is "\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 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.

 -- Macro: TYPE_OPERAND_FMT
     A C string which specifies (using printf syntax) the format of the second operand to TYPE_ASM_OP.  On systems that use ELF, the default (in config/elfos.h) is "@%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 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.

 -- Macro: ASM_OUTPUT_TYPE_DIRECTIVE (STREAM, TYPE)
     A C statement (sans semicolon) to output to the stdio stream STREAM a directive telling the assembler that the type of the symbol NAME is TYPE.  TYPE is a C string; currently, that string is always either "function" or "object", but you should not count on this.

     If you define TYPE_ASM_OP and TYPE_OPERAND_FMT, a default definition of this macro is provided.

 -- Macro: ASM_DECLARE_FUNCTION_NAME (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name NAME of a function which is being defined.  This macro is responsible for outputting the label definition (perhaps using ASM_OUTPUT_FUNCTION_LABEL).  The argument DECL is the 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 ASM_OUTPUT_FUNCTION_LABEL).

     You may wish to use ASM_OUTPUT_TYPE_DIRECTIVE in the definition of this macro.

 -- Macro: ASM_DECLARE_FUNCTION_SIZE (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the size of a function which is being defined.  The argument NAME is the name of the function.  The argument DECL is the 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 ASM_OUTPUT_MEASURED_SIZE in the definition of this macro.

 -- Macro: ASM_DECLARE_COLD_FUNCTION_NAME (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name NAME of a cold function partition which is being defined.  This macro is responsible for outputting the label definition (perhaps using ASM_OUTPUT_FUNCTION_LABEL).  The argument DECL is the FUNCTION_DECL tree node representing the function.

     If this macro is not defined, then the cold partition name is defined in the usual manner as a label (by means of ASM_OUTPUT_LABEL).

     You may wish to use ASM_OUTPUT_TYPE_DIRECTIVE in the definition of this macro.

 -- Macro: ASM_DECLARE_COLD_FUNCTION_SIZE (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the size of a cold function partition which is being defined.  The argument NAME is the name of the cold partition of the function.  The argument DECL is the FUNCTION_DECL tree node representing the function.

     If this macro is not defined, then the partition size is not defined.

     You may wish to use ASM_OUTPUT_MEASURED_SIZE in the definition of this macro.

 -- Macro: ASM_DECLARE_OBJECT_NAME (STREAM, NAME, DECL)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name NAME of an initialized variable which is being defined.  This macro must output the label definition (perhaps using ASM_OUTPUT_LABEL).  The argument DECL is the 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 ASM_OUTPUT_LABEL).

     You may wish to use ASM_OUTPUT_TYPE_DIRECTIVE and/or ASM_OUTPUT_SIZE_DIRECTIVE in the definition of this macro.

TARGET_ASM_DECLARE_CONSTANT_NAME

 -- Macro: ASM_DECLARE_REGISTER_GLOBAL (STREAM, DECL, REGNO, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for claiming a register REGNO for a global variable DECL with name NAME.

     If you don't define this macro, that is equivalent to defining it to do nothing.

 -- Macro: ASM_FINISH_DECLARE_OBJECT (STREAM, DECL, TOPLEVEL, 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 ASM_OUTPUT_SIZE_DIRECTIVE and/or ASM_OUTPUT_MEASURED_SIZE in the definition of this macro.

TARGET_ASM_GLOBALIZE_LABEL

TARGET_ASM_GLOBALIZE_DECL_NAME

TARGET_ASM_ASSEMBLE_UNDEFINED_DECL

 -- Macro: ASM_WEAKEN_LABEL (STREAM, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM some commands that will make the label NAME weak; that is, available for reference from other files but only used if no other definition is available.  Use the expression assemble_name (STREAM, 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 ASM_WEAKEN_DECL, GCC will not support weak symbols and you should not define the SUPPORTS_WEAK macro.

 -- Macro: ASM_WEAKEN_DECL (STREAM, DECL, NAME, VALUE)
     Combines (and replaces) the function of ASM_WEAKEN_LABEL and ASM_OUTPUT_WEAK_ALIAS, allowing access to the associated function or variable decl.  If VALUE is not NULL, this C statement should output to the stdio stream STREAM assembler code which defines (equates) the weak symbol NAME to have the value VALUE.  If VALUE is NULL, it should output commands to make NAME weak.

 -- Macro: ASM_OUTPUT_WEAKREF (STREAM, DECL, NAME, VALUE)
     Outputs a directive that enables NAME to be used to refer to symbol VALUE with weak-symbol semantics.  decl is the declaration of name.

 -- Macro: SUPPORTS_WEAK
     A preprocessor constant expression which evaluates to true if the target supports weak symbols.

     If you don't define this macro, defaults.h provides a default definition.  If either ASM_WEAKEN_LABEL or ASM_WEAKEN_DECL is defined, the default definition is 1; otherwise, it is 0.

 -- Macro: TARGET_SUPPORTS_WEAK
     A C expression which evaluates to true if the target supports weak symbols.

     If you don't define this macro, defaults.h provides a default definition.  The default definition is (SUPPORTS_WEAK).  Define this macro if you want to control weak symbol support with a compiler flag such as -melf.

 -- Macro: MAKE_DECL_ONE_ONLY (DECL)
     A C statement (sans semicolon) to mark 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 COMDAT section flags in the Microsoft Windows PE/COFF format, and this support requires changes to DECL, such as putting it in a separate section.

 -- Macro: SUPPORTS_ONE_ONLY
     A C expression which evaluates to true if the target supports one-only semantics.

     If you don't define this macro, varasm.c provides a default definition.  If MAKE_DECL_ONE_ONLY is defined, the default definition is 1; otherwise, it is 0.  Define this macro if you want to control one-only symbol support with a compiler flag, or if setting the DECL_ONE_ONLY flag is enough to mark a declaration to be emitted as one-only.

TARGET_ASM_ASSEMBLE_VISIBILITY

 -- Macro: 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 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.

 -- Macro: ASM_OUTPUT_EXTERNAL (STREAM, DECL, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name of an external symbol named NAME which is referenced in this compilation but not defined.  The value of 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.

TARGET_ASM_EXTERNAL_LIBCALL

TARGET_ASM_MARK_DECL_PRESERVED

 -- Macro: ASM_OUTPUT_LABELREF (STREAM, NAME)
     A C statement (sans semicolon) to output to the stdio stream STREAM a reference in assembler syntax to a label named NAME.  This should add _ 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 assemble_name.

TARGET_MANGLE_ASSEMBLER_NAME

 -- Macro: ASM_OUTPUT_SYMBOL_REF (STREAM, SYM)
     A C statement (sans semicolon) to output a reference to SYMBOL_REF SYM.  If not defined, 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 TARGET_ENCODE_SECTION_INFO.

 -- Macro: ASM_OUTPUT_LABEL_REF (STREAM, BUF)
     A C statement (sans semicolon) to output a reference to BUF, the result of ASM_GENERATE_INTERNAL_LABEL.  If not defined, assemble_name will be used to output the name of the symbol. This macro is not used by output_asm_label, or the %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.

TARGET_ASM_INTERNAL_LABEL

 -- Macro: ASM_OUTPUT_DEBUG_LABEL (STREAM, PREFIX, NUM)
     A C statement to output to the stdio stream STREAM a debug info label whose name is made from the string PREFIX and the number 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 (*targetm.asm_out.internal_label) will be used.

 -- Macro: ASM_GENERATE_INTERNAL_LABEL (STRING, PREFIX, NUM)
     A C statement to store into the string STRING a label whose name is made from the string PREFIX and the number NUM.

     This string, when output subsequently by assemble_name, should produce the output that (*targetm.asm_out.internal_label) would produce with the same PREFIX and NUM.

     If the string begins with *, then assemble_name will output the rest of the string unchanged.  It is often convenient for ASM_GENERATE_INTERNAL_LABEL to use * in this way.  If the string doesn't start with *, then ASM_OUTPUT_LABELREF gets to output the string, and may change it.  (Of course, ASM_OUTPUT_LABELREF is also part of your machine description, so you should know what it does on your machine.)

 -- Macro: ASM_FORMAT_PRIVATE_NAME (OUTVAR, NAME, NUMBER)
     A C expression to assign to OUTVAR (which is a variable of type char *) a newly allocated string made from the string NAME and the number NUMBER, with some suitable punctuation added.  Use alloca to get space for the string.

     The string will be used as an argument to ASM_OUTPUT_LABELREF to produce an assembler label for an internal static variable whose name is NAME.  Therefore, the string must be such as to result in valid assembler code.  The argument 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.

 -- Macro: ASM_OUTPUT_DEF (STREAM, NAME, VALUE)
     A C statement to output to the stdio stream STREAM assembler code which defines (equates) the symbol NAME to have the value VALUE.

     If SET_ASM_OP is defined, a default definition is provided which is correct for most systems.

 -- Macro: ASM_OUTPUT_DEF_FROM_DECLS (STREAM, DECL_OF_NAME, DECL_OF_VALUE)
     A C statement to output to the stdio stream STREAM assembler code which defines (equates) the symbol whose tree node is DECL_OF_NAME to have the value of the tree node DECL_OF_VALUE.  This macro will be used in preference to ASM_OUTPUT_DEF if it is defined and if the tree nodes are available.

     If SET_ASM_OP is defined, a default definition is provided which is correct for most systems.

 -- Macro: TARGET_DEFERRED_OUTPUT_DEFS (DECL_OF_NAME, DECL_OF_VALUE)
     A C statement that evaluates to true if the assembler code which defines (equates) the symbol whose tree node is DECL_OF_NAME to have the value of the tree node 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 ASM_OUTPUT_DEF and ASM_OUTPUT_DEF_FROM_DECLS.

 -- Macro: ASM_OUTPUT_WEAK_ALIAS (STREAM, NAME, VALUE)
     A C statement to output to the stdio stream STREAM assembler code which defines (equates) the weak symbol NAME to have the value VALUE.  If VALUE is NULL, it defines NAME as an undefined weak symbol.

     Define this macro if the target only supports weak aliases; define ASM_OUTPUT_DEF instead if possible.

 -- Macro: OBJC_GEN_METHOD_LABEL (BUF, IS_INST, CLASS_NAME, CAT_NAME, 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. _1_Foo).  For methods in categories, the name of the category is also included in the assembler name (e.g. _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.

     BUF is an expression of type char * which gives you a buffer in which to store the name; its length is as long as CLASS_NAME, CAT_NAME and SEL_NAME put together, plus 50 characters extra.

     The argument IS_INST specifies whether the method is an instance method or a class method; CLASS_NAME is the name of the class; CAT_NAME is the name of the category (or NULL if the method is not in a category); and 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.

How Initialization Functions Are Handled
----------------------------------------

The compiled code for certain languages includes constructors (also called 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 main is called.

Compiling some languages generates destructors (also called 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.

The linker must build two lists of these functions---a list of initialization functions, called __CTOR_LIST__, and a list of termination functions, called __DTOR_LIST__.

Each list always begins with an ignored function pointer (which may hold 0, -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 crtstuff.c or 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 .ctors and .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 .ctors section. Termination functions are handled similarly.

This method will be chosen as the default by target-def.h if 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 CTORS_SECTION_ASM_OP and DTORS_SECTION_ASM_OP to achieve the same effect.

When arbitrary sections are available, there are two variants, depending upon how the code in crtstuff.c is called.  On systems that support a .init section which is executed at program startup, parts of crtstuff.c are compiled into that section.  The program is linked by the gcc driver like this:

     ld -o OUTPUT_FILE crti.o crtbegin.o ... -lgcc crtend.o crtn.o

The prologue of a function (__init) appears in the .init section of crti.o; the epilogue appears in crtn.o.  Likewise for the function __fini in the .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 crtbegin.o and crtend.o are (for most targets) compiled from crtstuff.c.  They contain, among other things, code fragments within the .init and .fini sections that branch to routines in the .text section.  The linker will pull all parts of a section together, which results in a complete __init function that invokes the routines we need at startup.

To use this variant, you must define the INIT_SECTION_ASM_OP macro properly.

If no init section is available, when GCC compiles any function called main (or more accurately, any function designated as a program entry point by the language front end calling expand_main_function), it inserts a procedure call to __main as the first executable code after the function prologue.  The __main function is defined in 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 ld) and an `a.out' format must be used.  In this case, TARGET_ASM_CONSTRUCTOR is defined to produce a .stabs entry of type N_SETT, referencing the name __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 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. TARGET_ASM_DESTRUCTOR is handled similarly.  Since no init section is available, the absence of INIT_SECTION_ASM_OP causes the compilation of main to call __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, 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 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 __main as described above.  In order to use this method, use_collect2 must be defined in the target in config.gcc.

The following section describes the specific macros that control and customize the handling of initialization and termination functions.

Macros Controlling Initialization Routines
------------------------------------------

Here are the macros that control how the compiler handles initialization and termination functions:

 -- Macro: 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 crtstuff.c and libgcc2.c arrange to run the initialization functions.

 -- Macro: HAS_INIT_SECTION
     If defined, main will not call __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 INIT_SECTION_ASM_OP.

 -- Macro: LD_INIT_SWITCH
     If defined, a C string constant for a switch that tells the linker that the following symbol is an initialization routine.

 -- Macro: LD_FINI_SWITCH
     If defined, a C string constant for a switch that tells the linker that the following symbol is a finalization routine.

 -- Macro: COLLECT_SHARED_INIT_FUNC (STREAM, 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 FUNC, which takes no arguments.  If not defined, and the object format requires an explicit initialization function, then a function called _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.

 -- Macro: COLLECT_SHARED_FINI_FUNC (STREAM, 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 FUNC, which takes no arguments.  If not defined, and the object format requires an explicit finalization function, then a function called _GLOBAL__DD will be generated.

 -- Macro: INVOKE__main
     If defined, main will call __main despite the presence of 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.

 -- Macro: SUPPORTS_INIT_PRIORITY
     If nonzero, the C++ 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 init_priority attribute.

TARGET_HAVE_CTORS_DTORS

TARGET_DTORS_FROM_CXA_ATEXIT

TARGET_ASM_CONSTRUCTOR

TARGET_ASM_DESTRUCTOR

If TARGET_HAVE_CTORS_DTORS is true, the initialization routine generated for the generated object file will have static linkage.

If your system uses collect2 as the means of processing constructors, then that program normally uses nm to scan an object file for constructor functions to be called.

On certain kinds of systems, you can define this macro to make collect2 work faster (and, in some cases, make it work at all):

 -- Macro: OBJECT_FORMAT_COFF
     Define this macro if the system uses COFF (Common Object File Format) object files, so that collect2 can assume this format and scan object files directly for dynamic constructor/destructor functions.

     This macro is effective only in a native compiler; collect2 as part of a cross compiler always uses nm for the target machine.

 -- Macro: REAL_NM_FILE_NAME
     Define this macro as a C string constant containing the file name to use to execute nm.  The default is to search the path normally for nm.

 -- Macro: NM_FLAGS
     collect2 calls nm to scan object files for static constructors and destructors and LTO info.  By default, -n is passed.  Define NM_FLAGS to a C string constant if other options are needed to get the same output format as GNU nm -n produces.

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:

 -- Macro: LDD_SUFFIX
     Define this macro to a C string constant containing the name of the program which lists dynamic dependencies, like ldd under SunOS 4.

 -- Macro: PARSE_LDD_OUTPUT (PTR)
     Define this macro to be C code that extracts filenames from the output of the program denoted by LDD_SUFFIX.  PTR is a variable of type char * that points to the beginning of a line of output from LDD_SUFFIX.  If the line lists a dynamic dependency, the code must advance PTR to the beginning of the filename on that line.  Otherwise, it must set PTR to NULL.

 -- Macro: SHLIB_SUFFIX
     Define this macro to a C string constant containing the default shared library extension of the target (e.g., ".so").  collect2 strips version information after this suffix when generating global constructor and destructor names.  This define is only needed on targets that use collect2 to process constructors and destructors.

Output of Assembler Instructions
--------------------------------

This describes assembler instruction output.

 -- Macro: 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.

 -- Macro: 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 asm option in declarations to refer to registers using alternate names.

 -- Macro: OVERLAPPING_REGISTER_NAMES
     If defined, a C initializer for an array of structures containing a name, a register number and a count of the number of consecutive machine registers the name overlaps.  This macro defines additional names for hard registers, thus allowing the asm option in declarations to refer to registers using alternate names.  Unlike ADDITIONAL_REGISTER_NAMES, this macro should be used when the register name implies multiple underlying registers.

     This macro should be used when it is important that a clobber in an asm statement clobbers all the underlying values implied by the register name.  For example, on ARM, clobbering the double-precision VFP register ``d0'' implies clobbering both single-precision registers ``s0'' and ``s1''.

 -- Macro: ASM_OUTPUT_OPCODE (STREAM, 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 STREAM.  The macro-operand PTR is a variable of type 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 STREAM, performing any translation you desire, and increment the variable 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 %-sequences to substitute operands, you must take care of the substitution yourself.  Just be sure to increment PTR over whatever text should not be output normally.

     If you need to look at the operand values, they can be found as the elements of recog_data.operand.

     If the macro definition does nothing, the instruction is output in the usual way.

 -- Macro: FINAL_PRESCAN_INSN (INSN, OPVEC, NOPERANDS)
     If defined, a C statement to be executed just prior to the output of assembler code for INSN, to modify the extracted operands so they will be output differently.

     Here the argument OPVEC is the vector containing the operands extracted from INSN, and 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.

TARGET_ASM_FINAL_POSTSCAN_INSN

 -- Macro: PRINT_OPERAND (STREAM, X, CODE)
     A C compound statement to output to stdio stream STREAM the assembler syntax for an instruction operand X.  X is an RTL expression.

     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.  CODE comes from the % specification that was used to request printing of the operand.  If the specification was just %DIGIT then CODE is 0; if the specification was %LTR DIGIT then CODE is the ASCII code for LTR.

     If X is a register, this macro should print the register's name. The names can be found in an array reg_names whose type is char *[].  reg_names is initialized from REGISTER_NAMES.

     When the machine description has a specification %PUNCT (a % followed by a punctuation character), this macro is called with a null pointer for X and the punctuation character for CODE.

 -- Macro: PRINT_OPERAND_PUNCT_VALID_P (CODE)
     A C expression which evaluates to true if CODE is a valid punctuation character for use in the PRINT_OPERAND macro.  If PRINT_OPERAND_PUNCT_VALID_P is not defined, it means that no punctuation characters (except for the standard one, %) are used in this way.

 -- Macro: PRINT_OPERAND_ADDRESS (STREAM, X)
     A C compound statement to output to stdio stream STREAM the assembler syntax for an instruction operand that is a memory reference whose address is X.  X is an RTL expression.

     On some machines, the syntax for a symbolic address depends on the section that the address refers to.  On these machines, define the hook TARGET_ENCODE_SECTION_INFO to store the information into the symbol_ref, and then check for it here.  See Assembler Format.

 -- Macro: DBR_OUTPUT_SEQEND (FILE)
     A C statement, to be executed after all slot-filler instructions have been output.  If necessary, call 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).

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 final_sequence is null when not processing a sequence, otherwise it contains the sequence rtx being output.

 -- Macro: REGISTER_PREFIX
 -- Macro: LOCAL_LABEL_PREFIX
 -- Macro: USER_LABEL_PREFIX
 -- Macro: IMMEDIATE_PREFIX
     If defined, C string expressions to be used for the %R, %L, %U, and %I options of asm_fprintf (see final.c).  These are useful when a single md file must support multiple assembler formats.  In that case, the various tm.h files can define these macros differently.

 -- Macro: ASM_FPRINTF_EXTENSIONS (FILE, ARGPTR, FORMAT)
     If defined this macro should expand to a series of case statements which will be parsed inside the switch statement of the 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 FILE. The varargs input pointer is ARGPTR and the rest of the format string, starting the character after the one that is being switched upon, is pointed to by FORMAT.

 -- Macro: 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

          {option0|option1|option2...}

     in the output templates of patterns (see Output Template) or in the first argument of asm_fprintf.  This construct outputs option0, option1, option2, etc., if the value of 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 ASSEMBLER_DIALECT, the construct outputs nothing. If it's needed to print curly braces or | character in assembler output directly, %{, %} and %| can be used.

     If you do not define this macro, the characters {, | and } do not have any special meaning when used in templates or operands to asm_fprintf.

     Define the macros REGISTER_PREFIX, LOCAL_LABEL_PREFIX, USER_LABEL_PREFIX and IMMEDIATE_PREFIX if you can express the variations in assembler language syntax with that mechanism.  Define ASSEMBLER_DIALECT and use the {option0|option1} syntax if the syntax variant are larger and involve such things as different opcodes or operand order.

 -- Macro: ASM_OUTPUT_REG_PUSH (STREAM, REGNO)
     A C expression to output to STREAM some assembler code which will push hard register number REGNO onto the stack. The code need not be optimal, since this macro is used only when profiling.

 -- Macro: ASM_OUTPUT_REG_POP (STREAM, REGNO)
     A C expression to output to STREAM some assembler code which will pop hard register number REGNO off of the stack. The code need not be optimal, since this macro is used only when profiling.

Output of Dispatch Tables
-------------------------

This concerns dispatch tables.

 -- Macro: ASM_OUTPUT_ADDR_DIFF_ELT (STREAM, BODY, VALUE, REL)
     A C statement to output to the stdio stream STREAM an assembler pseudo-instruction to generate a difference between two labels. VALUE and REL are the numbers of two internal labels.  The definitions of these labels are output using (*targetm.asm_out.internal_label), and they must be printed in the same way here.  For example,

          fprintf (STREAM, "\t.word L%d-L%d\n",
                   VALUE, REL)

     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. BODY is the body of the ADDR_DIFF_VEC; it is provided so that the mode and flags can be read.

 -- Macro: ASM_OUTPUT_ADDR_VEC_ELT (STREAM, 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 STREAM an assembler pseudo-instruction to generate a reference to a label.  VALUE is the number of an internal label whose definition is output using (*targetm.asm_out.internal_label). For example,

          fprintf (STREAM, "\t.word L%d\n", VALUE)

 -- Macro: ASM_OUTPUT_CASE_LABEL (STREAM, PREFIX, NUM, TABLE)
     Define this if the label before a jump-table needs to be output specially.  The first three arguments are the same as for (*targetm.asm_out.internal_label); the fourth argument is the jump-table which follows (a jump_table_data containing an addr_vec or addr_diff_vec).

     This feature is used on system V to output a swbeg statement for the table.

     If this macro is not defined, these labels are output with (*targetm.asm_out.internal_label).

 -- Macro: ASM_OUTPUT_CASE_END (STREAM, NUM, 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 STREAM.  The argument TABLE is the jump-table insn, and 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.

TARGET_ASM_POST_CFI_STARTPROC

TARGET_ASM_EMIT_UNWIND_LABEL

TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL

TARGET_ASM_EMIT_EXCEPT_PERSONALITY

TARGET_ASM_UNWIND_EMIT

TARGET_ASM_MAKE_EH_SYMBOL_INDIRECT

TARGET_ASM_UNWIND_EMIT_BEFORE_INSN

TARGET_ASM_SHOULD_RESTORE_CFA_STATE

Assembler Commands for Exception Regions
----------------------------------------

This describes commands marking the start and the end of an exception region.

 -- Macro: 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. 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.

 -- Macro: EH_FRAME_THROUGH_COLLECT2
     If defined, DWARF 2 frame unwind information will identified by specially named labels.  The collect2 process will locate these labels and generate code to register the frames.

     This might be necessary, for instance, if the system linker will not place the eh_frames in-between the sentinals from crtstuff.c, or if the system linker does garbage collection and sections cannot be marked as not to be collected.

 -- Macro: 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.

 -- Macro: MASK_RETURN_ADDR
     An rtx used to mask the return address found via RETURN_ADDR_RTX, so that it does not contain any extraneous set bits in it.

 -- Macro: 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 INCOMING_RETURN_ADDR_RTX and OBJECT_FORMAT_ELF), GCC will provide a default definition of 1.

TARGET_EXCEPT_UNWIND_INFO
This hook defines the mechanism that will be used for exception handling by the target.  If the target has ABI specified unwind tables, the hook should return UI_TARGET.  If the target is to use the setjmp/longjmp-based exception handling scheme, the hook should return UI_SJLJ.  If the target supports DWARF 2 frame unwind information, the hook should return UI_DWARF2.

A target may, if exceptions are disabled, choose to return UI_NONE. This may end up simplifying other parts of target-specific code.  The default implementation of this hook never returns UI_NONE.

Note that the value returned by this hook should be constant.  It should not depend on anything except the command-line switches described by OPTS.  In particular, the setting UI_SJLJ must be fixed at compiler start-up as C pre-processor macros and builtin functions related to exception handling are set up depending on this setting.

The default implementation of the hook first honors the --enable-sjlj-exceptions configure option, then DWARF2_UNWIND_INFO, and finally defaults to UI_SJLJ.  If DWARF2_UNWIND_INFO depends on command-line options, the target must define this hook so that OPTS is used correctly.

TARGET_UNWIND_TABLES_DEFAULT
This variable should be set to true if the target ABI requires unwinding tables even when exceptions are not used.  It must not be modified by command-line option processing.

 -- Macro: DONT_USE_BUILTIN_SETJMP
     Define this macro to 1 if the setjmp/longjmp-based scheme should use the setjmp/longjmp functions from the C library instead of the __builtin_setjmp/__builtin_longjmp machinery.

 -- Macro: JMP_BUF_SIZE
     This macro has no effect unless DONT_USE_BUILTIN_SETJMP is also defined.  Define this macro if the default size of jmp_buf buffer for the setjmp/longjmp-based exception handling mechanism is not large enough, or if it is much too large. The default size is FIRST_PSEUDO_REGISTER * sizeof(void *).

 -- Macro: 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 UNITS_PER_WORD.  The definition should be the negative minimum alignment if STACK_GROWS_DOWNWARD is true, and the positive minimum alignment otherwise.  See DWARF.  Only applicable if the target supports DWARF 2 frame unwind information.

TARGET_TERMINATE_DW2_EH_FRAME_INFO

TARGET_DWARF_REGISTER_SPAN

TARGET_DWARF_FRAME_REG_MODE

TARGET_INIT_DWARF_REG_SIZES_EXTRA

TARGET_ASM_TTYPE

TARGET_ARM_EABI_UNWINDER

Assembler Commands for Alignment
--------------------------------

This describes commands for alignment.

 -- Macro: JUMP_ALIGN (LABEL)
     The alignment (log base 2) to put in front of 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 LABEL parameter, it is better to set the variable ALIGN_JUMPS in the target's TARGET_OPTION_OVERRIDE.  Otherwise, you should try to honor the user's selection in ALIGN_JUMPS in a JUMP_ALIGN implementation.

 -- Macro: LABEL_ALIGN_AFTER_BARRIER (LABEL)
     The alignment (log base 2) to put in front of LABEL, which follows a 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.

 -- Macro: LOOP_ALIGN (LABEL)
     The alignment (log base 2) to put in front of LABEL that heads a frequently executed basic block (usually the header of a loop).

     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 LABEL parameter, it is better to set the variable align_loops in the target's TARGET_OPTION_OVERRIDE.  Otherwise, you should try to honor the user's selection in align_loops in a LOOP_ALIGN implementation.

 -- Macro: LABEL_ALIGN (LABEL)
     The alignment (log base 2) to put in front of LABEL. If LABEL_ALIGN_AFTER_BARRIER / LOOP_ALIGN specify a different alignment, the maximum of the specified values is used.

     Unless it's necessary to inspect the LABEL parameter, it is better to set the variable align_labels in the target's TARGET_OPTION_OVERRIDE.  Otherwise, you should try to honor the user's selection in align_labels in a LABEL_ALIGN implementation.

 -- Macro: ASM_OUTPUT_SKIP (STREAM, NBYTES)
     A C statement to output to the stdio stream STREAM an assembler instruction to advance the location counter by NBYTES bytes. Those bytes should be zero when loaded.  NBYTES will be a C expression of type unsigned HOST_WIDE_INT.

 -- Macro: ASM_NO_SKIP_IN_TEXT
     Define this macro if 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.

 -- Macro: ASM_OUTPUT_ALIGN (STREAM, POWER)
     A C statement to output to the stdio stream STREAM an assembler command to advance the location counter to a multiple of 2 to the POWER bytes.  POWER will be a C expression of type int.

 -- Macro: ASM_OUTPUT_ALIGN_WITH_NOP (STREAM, POWER)
     Like ASM_OUTPUT_ALIGN, except that the ``nop'' instruction is used for padding, if necessary.

 -- Macro: ASM_OUTPUT_MAX_SKIP_ALIGN (STREAM, POWER, MAX_SKIP)
     A C statement to output to the stdio stream STREAM an assembler command to advance the location counter to a multiple of 2 to the POWER bytes, but only if MAX_SKIP or fewer bytes are needed to satisfy the alignment request.  POWER and MAX_SKIP will be a C expression of type int.

Controlling Debugging Information Format
========================================

This describes how to specify debugging information.

Macros Affecting All Debugging Formats
--------------------------------------

These macros affect all debugging formats.

 -- Macro: DBX_REGISTER_NUMBER (REGNO)
     A C expression that returns the DBX register number for the compiler register number REGNO.  In the default macro provided, the value of this expression will be 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 must have consecutive numbers after renumbering with 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 DBX_REGISTER_NUMBER in way that does not preserve register pairs, then what you must do instead is redefine the actual register numbering scheme.

 -- Macro: DEBUGGER_AUTO_OFFSET (X)
     A C expression that returns the integer offset value for an automatic variable having address X (an RTL expression).  The default computation assumes that 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 and allow the frame-pointer to be eliminated when the -g option is used.

 -- Macro: DEBUGGER_ARG_OFFSET (OFFSET, X)
     A C expression that returns the integer offset value for an argument having address X (an RTL expression).  The nominal offset is OFFSET.

 -- Macro: PREFERRED_DEBUGGING_TYPE
     A C expression that returns the type of debugging output GCC should produce when the user specifies just -g.  Define this if you have arranged for GCC to support more than one format of debugging output.  Currently, the allowable values are DBX_DEBUG, DWARF2_DEBUG, XCOFF_DEBUG, VMS_DEBUG, and VMS_AND_DWARF2_DEBUG.

     When the user specifies -ggdb, GCC normally also uses the value of this macro to select the debugging output format, but with two exceptions.  If DWARF2_DEBUGGING_INFO is defined, GCC uses the value DWARF2_DEBUG.  Otherwise, if DBX_DEBUGGING_INFO is defined, GCC uses 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 -gstabs, -gdwarf-2, -gxcoff, or -gvms.

Specific Options for DBX Output
-------------------------------

These are specific options for DBX output.

 -- Macro: DBX_DEBUGGING_INFO
     Define this macro if GCC should produce debugging output for DBX in response to the -g option.

 -- Macro: XCOFF_DEBUGGING_INFO
     Define this macro if GCC should produce XCOFF format debugging output in response to the -g option.  This is a variant of DBX format.

 -- Macro: 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.

 -- Macro: DEBUG_SYMS_TEXT
     Define this macro if all .stabs commands should be output while in the text section.

 -- Macro: ASM_STABS_OP
     A C string constant, including spacing, naming the assembler pseudo op to use instead of "\t.stabs\t" to define an ordinary debugging symbol. If you don't define this macro, "\t.stabs\t" is used.  This macro applies only to DBX debugging information format.

 -- Macro: ASM_STABD_OP
     A C string constant, including spacing, naming the assembler pseudo op to use instead of "\t.stabd\t" to define a debugging symbol whose value is the current location.  If you don't define this macro, "\t.stabd\t" is used.  This macro applies only to DBX debugging information format.

 -- Macro: ASM_STABN_OP
     A C string constant, including spacing, naming the assembler pseudo op to use instead of "\t.stabn\t" to define a debugging symbol with no name.  If you don't define this macro, "\t.stabn\t" is used.  This macro applies only to DBX debugging information format.

 -- Macro: DBX_NO_XREFS
     Define this macro if DBX on your system does not support the construct xsTAGNAME.  On some systems, this construct is used to describe a forward reference to a structure named TAGNAME. On other systems, this construct is not supported at all.

 -- Macro: DBX_CONTIN_LENGTH
     A symbol name in DBX-format debugging information is normally continued (split into two separate .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.

 -- Macro: DBX_CONTIN_CHAR
     Normally continuation is indicated by adding a \ character to the end of a .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.

 -- Macro: DBX_STATIC_STAB_DATA_SECTION
     Define this macro if it is necessary to go to the data section before outputting the .stabs pseudo-op for a non-global static variable.

 -- Macro: DBX_TYPE_DECL_STABS_CODE
     The value to use in the ``code'' field of the .stabs directive for a typedef.  The default is N_LSYM.

 -- Macro: DBX_STATIC_CONST_VAR_CODE
     The value to use in the ``code'' field of the .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 N_FUN.

 -- Macro: DBX_REGPARM_STABS_CODE
     The value to use in the ``code'' field of the .stabs directive for a parameter passed in registers.  DBX format does not provide any ``right'' way to do this.  The default is N_RSYM.

 -- Macro: 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 'P'.

 -- Macro: 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.

 -- Macro: DBX_BLOCKS_FUNCTION_RELATIVE
     Define this macro, with value 1, if the value of a symbol describing the scope of a block (N_LBRAC or N_RBRAC) should be relative to the start of the enclosing function.  Normally, GCC uses an absolute address.

 -- Macro: DBX_LINES_FUNCTION_RELATIVE
     Define this macro, with value 1, if the value of a symbol indicating the current line number (N_SLINE) should be relative to the start of the enclosing function.  Normally, GCC uses an absolute address.

 -- Macro: DBX_USE_BINCL
     Define this macro if GCC should generate N_BINCL and 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 N_BINCL or N_EINCL stabs, and it outputs a single number for a type number.

Open-Ended Hooks for DBX Format
-------------------------------

These are hooks for DBX format.

 -- Macro: DBX_OUTPUT_SOURCE_LINE (STREAM, LINE, COUNTER)
     A C statement to output DBX debugging information before code for line number LINE of the current source file to the stdio stream STREAM.  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 DBX_LINES_FUNCTION_RELATIVE.

 -- Macro: NO_DBX_FUNCTION_END
     Some stabs encapsulation formats (in particular ECOFF), cannot handle the .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.

 -- Macro: NO_DBX_BNSYM_ENSYM
     Some assemblers cannot handle the .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.

File Names in DBX Format
------------------------

This describes file names in DBX format.

 -- Macro: DBX_OUTPUT_MAIN_SOURCE_FILENAME (STREAM, NAME)
     A C statement to output DBX debugging information to the stdio stream STREAM, which indicates that file 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 assemble_name (stream, ltext_label_name) to do so.  If you do this, you must also set the variable USED_LTEXT_LABEL_NAME to true.

 -- Macro: 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.

 -- Macro: 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 N_OPT stab at the beginning of every source file, with gcc2_compiled. for the string and value 0.

 -- Macro: DBX_OUTPUT_MAIN_SOURCE_FILE_END (STREAM, NAME)
     A C statement to output DBX debugging information at the end of compilation of the main source file NAME.  Output should be written to the stdio stream STREAM.

     If you don't define this macro, nothing special is output at the end of compilation, which is correct for most machines.

 -- Macro: DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
     Define this macro instead of defining DBX_OUTPUT_MAIN_SOURCE_FILE_END, if what needs to be output at the end of compilation is an N_SO stab with an empty string, whose value is the highest absolute text address in the file.

Macros for DWARF Output
-----------------------

Here are macros for DWARF output.

 -- Macro: DWARF2_DEBUGGING_INFO
     Define this macro if GCC should produce dwarf version 2 format debugging output in response to the -g option.

     TARGET_DWARF_CALLING_CONVENTION

     To support optional call frame debugging information, you must also define INCOMING_RETURN_ADDR_RTX and either set RTX_FRAME_RELATED_P on the prologue insns if you use RTL for the prologue, or call dwarf2out_def_cfa and dwarf2out_reg_save as appropriate from TARGET_ASM_FUNCTION_PROLOGUE if you don't.

 -- Macro: DWARF2_FRAME_INFO
     Define this macro to a nonzero value if GCC should always output Dwarf 2 frame information.  If TARGET_EXCEPT_UNWIND_INFO (see Exception Region Output) returns UI_DWARF2, and exceptions are enabled, GCC will output this information not matter how you define DWARF2_FRAME_INFO.

TARGET_DEBUG_UNWIND_INFO

 -- Macro: 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.

 -- Macro: DWARF2_ASM_VIEW_DEBUG_INFO
     Define this macro to be a nonzero value if the assembler supports view assignment and verification in .loc.  If it does not, but the user enables location views, the compiler may have to fallback to internal line number tables.

TARGET_RESET_LOCATION_VIEW

TARGET_WANT_DEBUG_PUB_SECTIONS

TARGET_DELAY_SCHED2

TARGET_DELAY_VARTRACK

TARGET_NO_REGISTER_ALLOCATION

 -- Macro: ASM_OUTPUT_DWARF_DELTA (STREAM, SIZE, LABEL1, LABEL2)
     A C statement to issue assembly directives that create a difference LAB1 minus LAB2, using an integer of the given SIZE.

 -- Macro: ASM_OUTPUT_DWARF_VMS_DELTA (STREAM, SIZE, LABEL1, LABEL2)
     A C statement to issue assembly directives that create a difference between the two given labels in system defined units, e.g. instruction slots on IA64 VMS, using an integer of the given size.

 -- Macro: ASM_OUTPUT_DWARF_OFFSET (STREAM, SIZE, LABEL, OFFSET, SECTION)
     A C statement to issue assembly directives that create a section-relative reference to the given LABEL plus OFFSET, using an integer of the given SIZE.  The label is known to be defined in the given SECTION.

 -- Macro: ASM_OUTPUT_DWARF_PCREL (STREAM, SIZE, LABEL)
     A C statement to issue assembly directives that create a self-relative reference to the given LABEL, using an integer of the given SIZE.

 -- Macro: ASM_OUTPUT_DWARF_DATAREL (STREAM, SIZE, LABEL)
     A C statement to issue assembly directives that create a reference to the given LABEL relative to the dbase, using an integer of the given SIZE.

 -- Macro: ASM_OUTPUT_DWARF_TABLE_REF (LABEL)
     A C statement to issue assembly directives that create a reference to the DWARF table identifier LABEL from the current section.  This is used on some systems to avoid garbage collecting a DWARF table which is referenced by a function.

TARGET_ASM_OUTPUT_DWARF_DTPREL

Macros for VMS Debug Format
---------------------------

Here are macros for VMS debug format.

 -- Macro: VMS_DEBUGGING_INFO
     Define this macro if GCC should produce debugging output for VMS in response to the -g option.  The default behavior for VMS is to generate minimal debug info for a traceback in the absence of -g unless explicitly overridden with -g0.  This behavior is controlled by TARGET_OPTION_OPTIMIZATION and TARGET_OPTION_OVERRIDE.

Cross Compilation and Floating Point
====================================

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 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.

 -- Macro: 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 struct containing an array of HOST_WIDE_INT, but all code should treat it as an opaque quantity.

 -- Macro: HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE X)
     Truncates X to a signed integer, rounding toward zero.

 -- Macro: unsigned HOST_WIDE_INT REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE X)
     Truncates X to an unsigned integer, rounding toward zero.  If X is negative, returns zero.

 -- Macro: REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *STRING, machine_mode MODE)
     Converts STRING into a floating point number in the target machine's representation for mode MODE.  This routine can handle both decimal and hexadecimal floating point constants, using the syntax defined by the C language for both.

 -- Macro: int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE X)
     Returns 1 if X is negative (including negative zero), 0 otherwise.

 -- Macro: int REAL_VALUE_ISINF (REAL_VALUE_TYPE X)
     Determines whether X represents infinity (positive or negative).

 -- Macro: int REAL_VALUE_ISNAN (REAL_VALUE_TYPE X)
     Determines whether X represents a ``NaN'' (not-a-number).

 -- Macro: REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE X)
     Returns the negative of the floating point value X.

 -- Macro: REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE X)
     Returns the absolute value of X.

Mode Switching Instructions
===========================

The following macros control mode switching optimizations:

 -- Macro: OPTIMIZE_MODE_SWITCHING (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 cannot put this into instruction emitting or TARGET_MACHINE_DEPENDENT_REORG.

     You can have multiple entities that are mode-switched, and select at run time which entities actually need it.  OPTIMIZE_MODE_SWITCHING should return nonzero for any ENTITY that needs mode-switching. If you define this macro, you also have to define NUM_MODES_FOR_MODE_SWITCHING, TARGET_MODE_NEEDED, TARGET_MODE_PRIORITY and TARGET_MODE_EMIT. TARGET_MODE_AFTER, TARGET_MODE_ENTRY, and TARGET_MODE_EXIT are optional.

 -- Macro: NUM_MODES_FOR_MODE_SWITCHING
     If you define 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 ... N - 1.  N is used to specify that no mode switch is needed / supplied.

TARGET_MODE_EMIT

TARGET_MODE_NEEDED

TARGET_MODE_AFTER

TARGET_MODE_ENTRY

TARGET_MODE_EXIT

TARGET_MODE_PRIORITY

Defining target-specific uses of __attribute__
==============================================

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 extend.texi.

TARGET_ATTRIBUTE_TABLE

TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P

TARGET_COMP_TYPE_ATTRIBUTES

TARGET_SET_DEFAULT_TYPE_ATTRIBUTES

TARGET_MERGE_TYPE_ATTRIBUTES

TARGET_MERGE_DECL_ATTRIBUTES

TARGET_VALID_DLLIMPORT_ATTRIBUTE_P

 -- Macro: TARGET_DECLSPEC
     Define this macro to a nonzero value if you want to treat __declspec(X) as equivalent to __attribute((X)).  By default, this behavior is enabled only for targets that define TARGET_DLLIMPORT_DECL_ATTRIBUTES.  The current implementation of __declspec is via a built-in macro, but you should not rely on this implementation detail.

TARGET_INSERT_ATTRIBUTES

TARGET_HANDLE_GENERIC_ATTRIBUTE

TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P

TARGET_OPTION_VALID_ATTRIBUTE_P

TARGET_OPTION_SAVE

TARGET_OPTION_RESTORE

TARGET_OPTION_POST_STREAM_IN

TARGET_OPTION_PRINT

TARGET_OPTION_PRAGMA_PARSE

TARGET_OPTION_OVERRIDE

TARGET_OPTION_FUNCTION_VERSIONS

TARGET_CAN_INLINE_P

TARGET_RELAYOUT_FUNCTION

Emulating TLS
=============

For targets whose psABI does not provide Thread Local Storage via specific relocations and instruction sequences, an emulation layer is used.  A set of target hooks allows this emulation layer to be configured for the requirements of a particular target.  For instance the psABI may in fact specify TLS support in terms of an emulation layer.

The emulation layer works by creating a control object for every TLS object.  To access the TLS object, a lookup function is provided which, when given the address of the control object, will return the address of the current thread's instance of the TLS object.

TARGET_EMUTLS_GET_ADDRESS

TARGET_EMUTLS_REGISTER_COMMON

TARGET_EMUTLS_VAR_SECTION

TARGET_EMUTLS_TMPL_SECTION

TARGET_EMUTLS_VAR_PREFIX

TARGET_EMUTLS_TMPL_PREFIX

TARGET_EMUTLS_VAR_FIELDS

TARGET_EMUTLS_VAR_INIT

TARGET_EMUTLS_VAR_ALIGN_FIXED

TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS

Defining coprocessor specifics for MIPS targets.
================================================

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:

       register unsigned int cp0count asm ("c0r1");
       unsigned int d;

       d = cp0count + 3;

(``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 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.

Parameters for Precompiled Header Validity Checking
===================================================

TARGET_GET_PCH_VALIDITY

TARGET_PCH_VALID_P

TARGET_CHECK_PCH_TARGET_FLAGS

TARGET_PREPARE_PCH_SAVE

C++ ABI parameters
==================

TARGET_CXX_GUARD_TYPE

TARGET_CXX_GUARD_MASK_BIT

TARGET_CXX_GET_COOKIE_SIZE

TARGET_CXX_COOKIE_HAS_SIZE

TARGET_CXX_IMPORT_EXPORT_CLASS

TARGET_CXX_CDTOR_RETURNS_THIS

TARGET_CXX_KEY_METHOD_MAY_BE_INLINE

TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY

TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT

TARGET_CXX_LIBRARY_RTTI_COMDAT

TARGET_CXX_USE_AEABI_ATEXIT

TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT

TARGET_CXX_ADJUST_CLASS_AT_DEFINITION

TARGET_CXX_DECL_MANGLING_CONTEXT

D ABI parameters
================

TARGET_D_CPU_VERSIONS

TARGET_D_OS_VERSIONS

TARGET_D_REGISTER_CPU_TARGET_INFO

TARGET_D_REGISTER_OS_TARGET_INFO

TARGET_D_MINFO_SECTION

TARGET_D_MINFO_START_NAME

TARGET_D_MINFO_END_NAME

TARGET_D_HAS_STDCALL_CONVENTION

TARGET_D_TEMPLATES_ALWAYS_COMDAT

Adding support for named address spaces
=======================================

The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275 standards committee, Programming Languages - C - Extensions to support embedded processors, specifies a syntax for embedded processors to specify alternate address spaces.  You can configure a GCC port to support section 5.1 of the draft report to add support for address spaces other than the default address space.  These address spaces are new keywords that are similar to the volatile and const type attributes.

Pointers to named address spaces can have a different size than pointers to the generic address space.

For example, the SPU port uses the __ea address space to refer to memory in the host processor, rather than memory local to the SPU processor.  Access to memory in the __ea address space involves issuing DMA operations to move data between the host processor and the local processor memory address space.  Pointers in the __ea address space are either 32 bits or 64 bits based on the -mea32 or -mea64 switches (native SPU pointers are always 32 bits).

Internally, address spaces are represented as a small integer in the range 0 to 15 with address space 0 being reserved for the generic address space.

To register a named address space qualifier keyword with the C front end, the target may call the c_register_addr_space routine.  For example, the SPU port uses the following to declare __ea as the keyword for named address space #1:

     #define ADDR_SPACE_EA 1
     c_register_addr_space ("__ea", ADDR_SPACE_EA);

TARGET_ADDR_SPACE_POINTER_MODE

TARGET_ADDR_SPACE_ADDRESS_MODE

TARGET_ADDR_SPACE_VALID_POINTER_MODE

TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P

TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS

TARGET_ADDR_SPACE_SUBSET_P

TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID

TARGET_ADDR_SPACE_CONVERT

TARGET_ADDR_SPACE_DEBUG

TARGET_ADDR_SPACE_DIAGNOSE_USAGE

Miscellaneous Parameters
========================

Here are several miscellaneous parameters.

 -- Macro: 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.

 -- Macro: 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.

 -- Macro: CASE_VECTOR_MODE
     An alias for a machine mode name.  This is the machine mode that elements of a jump-table should have.

 -- Macro: CASE_VECTOR_SHORTEN_MODE (MIN_OFFSET, MAX_OFFSET, BODY)
     Optional: return the preferred mode for an 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 addr_diff_vec. To make this work, you also have to define INSN_ALIGN and make the alignment for addr_diff_vec explicit. The BODY argument is provided so that the offset_unsigned and scale flags can be updated.

 -- Macro: 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 -fPIC or -fPIC is in effect.

TARGET_CASE_VALUES_THRESHOLD

 -- Macro: WORD_REGISTER_OPERATIONS
     Define this macro to 1 if operations between registers with integral mode smaller than a word are always performed on the entire register.  To be more explicit, if you start with a pair of word_mode registers with known values and you do a subword, for example QImode, addition on the low part of the registers, then the compiler may consider that the result has a known value in word_mode too if the macro is defined to 1.  Most RISC machines have this property and most CISC machines do not.

TARGET_MIN_ARITHMETIC_PRECISION

 -- Macro: LOAD_EXTEND_OP (MEM_MODE)
     Define this macro to be a C expression indicating when insns that read memory in MEM_MODE, an integral mode narrower than a word, set the bits outside of MEM_MODE to be either the sign-extension or the zero-extension of the data read.  Return SIGN_EXTEND for values of MEM_MODE for which the insn sign-extends, ZERO_EXTEND for which it zero-extends, and UNKNOWN for other modes.

     This macro is not called with MEM_MODE non-integral or with a width greater than or equal to BITS_PER_WORD, so you may return any value in this case.  Do not define this macro if it would always return UNKNOWN.  On machines where this macro is defined, you will normally define it as the constant SIGN_EXTEND or ZERO_EXTEND.

     You may return a non-UNKNOWN value even if for some hard registers the sign extension is not performed, if for the REGNO_REG_CLASS of these hard registers TARGET_CAN_CHANGE_MODE_CLASS returns false when the FROM mode is MEM_MODE and the TO mode is any integral mode larger than this but not larger than word_mode.

     You must return UNKNOWN if for some hard registers that allow this mode, TARGET_CAN_CHANGE_MODE_CLASS says that they cannot change to word_mode, but that they can change to another integral mode that is larger then MEM_MODE but still smaller than word_mode.

 -- Macro: SHORT_IMMEDIATES_SIGN_EXTEND
     Define this macro to 1 if loading short immediate values into registers sign extends.

TARGET_MIN_DIVISIONS_FOR_RECIP_MUL

 -- Macro: MOVE_MAX
     The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations.

 -- Macro: 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 MOVE_MAX.  Otherwise, it is the constant value that is the largest value that MOVE_MAX can have at run-time.

 -- Macro: 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 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 SHIFT_COUNT_TRUNCATED to be zero on such machines.  Instead, add patterns to the 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.

TARGET_SHIFT_TRUNCATION_MASK

TARGET_TRULY_NOOP_TRUNCATION

TARGET_MODE_REP_EXTENDED

TARGET_SETJMP_PRESERVES_NONVOLATILE_REGS_P

 -- Macro: 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 (cstoreMODE4) when the condition is true.  This description must apply to all the cstoreMODE4 patterns and all the comparison operators whose results have a MODE_INT mode.

     A value of 1 or -1 means that the instruction implementing the comparison operator returns exactly 1 or -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 cstoreMODE4 pattern.  Either the low bit or the sign bit of STORE_FLAG_VALUE be on.  Presently, only those bits are used by the compiler.

     If STORE_FLAG_VALUE is neither 1 or -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 SImode value and where STORE_FLAG_VALUE is defined as 0x80000000, saying that just the sign bit is relevant, the expression

          (ne:SI (and:SI X (const_int POWER-OF-2)) (const_int 0))

     can be converted to

          (ashift:SI X (const_int N))

     where 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 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 STORE_FLAG_VALUE, and hence the instructions to be used:

       * Use the shortest sequence that yields a valid definition for 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.

       * For equal-length sequences, use a value of 1 or -1, with -1 being slightly preferred on machines with expensive jumps and 1 preferred on other machines.

       * As a second choice, choose a value of 0x80000001 if instructions exist that set both the sign and low-order bits but do not define the others.

       * Otherwise, use a value of 0x80000000.

     Many machines can produce both the value chosen for 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

          (set A (neg:M (ne:M B C)))

     Some machines can also perform and or plus operations on condition code values with less instructions than the corresponding cstoreMODE4 insn followed by and or plus.  On those machines, define the appropriate patterns.  Use the names incscc and decscc, respectively, for the patterns which perform plus or minus operations on condition code values.  See rs6000.md for some examples.  The GNU Superoptimizer 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 STORE_FLAG_VALUE if the machine has no store-flag instructions, or if the value generated by these instructions is 1.

 -- Macro: FLOAT_STORE_FLAG_VALUE (MODE)
     A C expression that gives a nonzero 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.

 -- Macro: VECTOR_STORE_FLAG_VALUE (MODE)
     A C expression that gives an rtx representing the nonzero true element for vector comparisons.  The returned rtx should be valid for the inner mode of 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 const1_rtx or constm1_rtx.  This macro may return NULL_RTX to prevent the compiler optimizing such vector comparison operations for the given mode.

 -- Macro: CLZ_DEFINED_VALUE_AT_ZERO (MODE, VALUE)
 -- Macro: CTZ_DEFINED_VALUE_AT_ZERO (MODE, VALUE)
     A C expression that indicates whether the architecture defines a value for clz or ctz with a zero operand. A result of 0 indicates the value is undefined. If the value is defined for only the RTL expression, the macro should evaluate to 1; if the value applies also to the corresponding optab entry (which is normally the case if it expands directly into the corresponding RTL), then the macro should evaluate to 2. In the cases where the value is defined, VALUE should be set to this value.

     If this macro is not defined, the value of clz or ctz at zero is assumed to be undefined.

     This macro must be defined if the target's expansion for 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, and to provide a default expansion for the ffs optab.

     Note that regardless of this macro the ``definedness'' of clz and ctz at zero do 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.

 -- Macro: 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; SImode on 32-bit machine or DImode on 64-bit machines. On some machines you must define this to be one of the partial integer modes, such as PSImode.

     The width of Pmode must be at least as large as the value of POINTER_SIZE.  If it is not equal, you must define the macro POINTERS_EXTEND_UNSIGNED to specify how pointers are extended to Pmode.

 -- Macro: FUNCTION_MODE
     An alias for the machine mode used for memory references to functions being called, in call RTL expressions.  On most CISC machines, where an instruction can begin at any byte address, this should be QImode.  On most RISC machines, where all instructions have fixed size and alignment, this should be a mode with the same size and alignment as the machine instruction words - typically SImode or HImode.

 -- Macro: STDC_0_IN_SYSTEM_HEADERS
     In normal operation, the preprocessor expands __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 __STDC__ is normally 0, but is 1 if the user specifies strict conformance to the C Standard.

     Defining STDC_0_IN_SYSTEM_HEADERS makes GNU CPP follows the host convention when processing system header files, but when processing user files __STDC__ will always expand to 1.

TARGET_C_PREINCLUDE

TARGET_CXX_IMPLICIT_EXTERN_C

 -- Macro: SYSTEM_IMPLICIT_EXTERN_C
     Define this macro if the system header files do not support C++. This macro handles system header files by pretending that system header files are enclosed in extern "C" {...}.

 -- Macro: 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 c_register_pragma or 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 TARGET_INSERT_ATTRIBUTES as well.

     Preprocessor macros that appear on pragma lines are not expanded.  All #pragma directives that do not match any registered pragma are silently ignored, unless the user specifies -Wunknown-pragmas.

 -- Function: void c_register_pragma (const char *SPACE, const char *NAME, void (*CALLBACK) (struct cpp_reader *))
 -- Function: void c_register_pragma_with_expansion (const char *SPACE, const char *NAME, void (*CALLBACK) (struct cpp_reader *))

     Each call to c_register_pragma or c_register_pragma_with_expansion establishes one pragma.  The CALLBACK routine will be called when the preprocessor encounters a pragma of the form

          #pragma [SPACE] NAME ...

     SPACE is the case-sensitive namespace of the pragma, or NULL to put the pragma in the global namespace.  The callback routine receives PFILE as its first argument, which can be passed on to cpplib's functions if necessary.  You can lex tokens after the NAME by calling 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 CPP_EOF.  Macro expansion occurs on the arguments of pragmas registered with c_register_pragma_with_expansion but not on the arguments of pragmas registered with c_register_pragma.

     Note that the use of 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 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 c_target_objs and cxx_target_objs in the target entry in the config.gcc file.  These variables should name the target-specific, language-specific object file which contains the code that uses pragma_lex.  Note it will also be necessary to add a rule to the makefile fragment pointed to by tmake_file that shows how to build this object file.

 -- Macro: HANDLE_PRAGMA_PACK_WITH_EXPANSION
     Define this macro if macros should be expanded in the arguments of #pragma pack.

 -- Macro: 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 #pragma pack() (that is, a small power of two).

 -- Macro: DOLLARS_IN_IDENTIFIERS
     Define this macro to control use of the character $ in identifier names for the C family of languages.  0 means $ 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.

 -- Macro: INSN_SETS_ARE_DELAYED (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 INSN, even if they appear to use a resource set or clobbered in INSN. INSN is always a jump_insn or an insn; GCC knows that every call_insn has this behavior.  On machines where some insn or 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.

 -- Macro: INSN_REFERENCES_ARE_DELAYED (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 INSN, even if they appear to set or clobber a resource referenced in INSN. INSN is always a jump_insn or an insn.  On machines where some insn or 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 INSN.

     You need not define this macro if it would always return zero.

 -- Macro: 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.

TARGET_MD_ASM_ADJUST

 -- Macro: MATH_LIBRARY
     Define this macro as a C string constant for the linker argument to link in the system math library, minus the initial "-l", or "" if the target does not have a separate math library.

     You need only define this macro if the default of "m" is wrong.

 -- Macro: 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 "LIBRARY_PATH" is wrong.

 -- Macro: 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 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.

 -- Macro: 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 BRANCH_COST+1 is the default if the machine does not use cc0, and 1 if it does use cc0.

 -- Macro: IFCVT_MODIFY_TESTS (CE_INFO, TRUE_EXPR, FALSE_EXPR)
     Used if the target needs to perform machine-dependent modifications on the conditionals used for turning basic blocks into conditionally executed code. CE_INFO points to a data structure, struct ce_if_block, which contains information about the currently processed blocks.  TRUE_EXPR and FALSE_EXPR are the tests that are used for converting the then-block and the else-block, respectively.  Set either TRUE_EXPR or FALSE_EXPR to a null pointer if the tests cannot be converted.

 -- Macro: IFCVT_MODIFY_MULTIPLE_TESTS (CE_INFO, BB, TRUE_EXPR, FALSE_EXPR)
     Like IFCVT_MODIFY_TESTS, but used when converting more complicated if-statements into conditions combined by and and or operations. BB contains the basic block that contains the test that is currently being processed and about to be turned into a condition.

 -- Macro: IFCVT_MODIFY_INSN (CE_INFO, PATTERN, INSN)
     A C expression to modify the PATTERN of an INSN that is to be converted to conditional execution format.  CE_INFO points to a data structure, struct ce_if_block, which contains information about the currently processed blocks.

 -- Macro: IFCVT_MODIFY_FINAL (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 struct ce_if_block structure that is pointed to by CE_INFO.

 -- Macro: IFCVT_MODIFY_CANCEL (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 struct ce_if_block structure that is pointed to by CE_INFO.

 -- Macro: IFCVT_MACHDEP_INIT (CE_INFO)
     A C expression to initialize any machine specific data for if-conversion of the if-block in the struct ce_if_block structure that is pointed to by CE_INFO.

TARGET_MACHINE_DEPENDENT_REORG

TARGET_INIT_BUILTINS

TARGET_BUILTIN_DECL

TARGET_EXPAND_BUILTIN

TARGET_RESOLVE_OVERLOADED_BUILTIN

TARGET_CHECK_BUILTIN_CALL

TARGET_FOLD_BUILTIN

TARGET_GIMPLE_FOLD_BUILTIN

TARGET_COMPARE_VERSION_PRIORITY

TARGET_GET_FUNCTION_VERSIONS_DISPATCHER

TARGET_GENERATE_VERSION_DISPATCHER_BODY

TARGET_PREDICT_DOLOOP_P

TARGET_HAVE_COUNT_REG_DECR_P

TARGET_DOLOOP_COST_FOR_GENERIC

TARGET_DOLOOP_COST_FOR_ADDRESS

TARGET_CAN_USE_DOLOOP_P

TARGET_INVALID_WITHIN_DOLOOP

TARGET_LEGITIMATE_COMBINED_INSN

TARGET_CAN_FOLLOW_JUMP

TARGET_COMMUTATIVE_P

TARGET_ALLOCATE_INITIAL_VALUE

TARGET_UNSPEC_MAY_TRAP_P

TARGET_SET_CURRENT_FUNCTION

 -- Macro: 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 .o as the suffix for object files.

 -- Macro: 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.

 -- Macro: COLLECT_EXPORT_LIST
     If defined, 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 main and uses export lists.

TARGET_CANNOT_MODIFY_JUMPS_P

TARGET_HAVE_CONDITIONAL_EXECUTION

TARGET_GEN_CCMP_FIRST

TARGET_GEN_CCMP_NEXT

TARGET_LOOP_UNROLL_ADJUST

 -- Macro: 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 pow, powf or powl routines. The default value places no upper bound on the multiplication count.

 -- Macro: void TARGET_EXTRA_INCLUDES (const char *SYSROOT, const char *IPREFIX, int STDINC)
     This target hook should register any extra include files for the target.  The parameter STDINC indicates if normal include files are present.  The parameter SYSROOT is the system root directory. The parameter IPREFIX is the prefix for the gcc directory.

 -- Macro: void TARGET_EXTRA_PRE_INCLUDES (const char *SYSROOT, const char *IPREFIX, int STDINC)
     This target hook should register any extra include files for the target before any standard headers.  The parameter STDINC indicates if normal include files are present.  The parameter SYSROOT is the system root directory.  The parameter IPREFIX is the prefix for the gcc directory.

 -- Macro: void TARGET_OPTF (char *PATH)
     This target hook should register special include paths for the target. The parameter PATH is the include to register.  On Darwin systems, this is used for Framework includes, which have semantics that are different from -I.

 -- Macro: bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree FNDECL)
     This target macro returns true if it is safe to use a local alias for a virtual function FNDECL when constructing thunks, false otherwise.  By default, the macro returns true for all functions, if a target supports aliases (i.e. defines ASM_OUTPUT_DEF), false otherwise,

 -- Macro: TARGET_FORMAT_TYPES
     If defined, this macro is the name of a global variable containing target-specific format checking information for the -Wformat option.  The default is to have no target-specific format checks.

 -- Macro: TARGET_N_FORMAT_TYPES
     If defined, this macro is the number of entries in TARGET_FORMAT_TYPES.

 -- Macro: TARGET_OVERRIDES_FORMAT_ATTRIBUTES
     If defined, this macro is the name of a global variable containing target-specific format overrides for the -Wformat option. The default is to have no target-specific format overrides. If defined, TARGET_FORMAT_TYPES must be defined, too.

 -- Macro: TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
     If defined, this macro specifies the number of entries in TARGET_OVERRIDES_FORMAT_ATTRIBUTES.

 -- Macro: TARGET_OVERRIDES_FORMAT_INIT
     If defined, this macro specifies the optional initialization routine for target specific customizations of the system printf and scanf formatter settings.

TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN

TARGET_INVALID_CONVERSION

TARGET_INVALID_UNARY_OP

TARGET_INVALID_BINARY_OP

TARGET_PROMOTED_TYPE

TARGET_CONVERT_TO_TYPE

TARGET_VERIFY_TYPE_CONTEXT

 -- Macro: 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.

 -- Macro: LIBGCC2_UNWIND_ATTRIBUTE
     Define this macro if any target-specific attributes need to be attached to the functions in libgcc that provide low-level support for call stack unwinding.  It is used in declarations in unwind-generic.h and the associated definitions of those functions.

TARGET_UPDATE_STACK_BOUNDARY

TARGET_GET_DRAP_RTX

TARGET_ZERO_CALL_USED_REGS

TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS

TARGET_CONST_ANCHOR

TARGET_ASAN_SHADOW_OFFSET

TARGET_MEMMODEL_CHECK

TARGET_ATOMIC_TEST_AND_SET_TRUEVAL

TARGET_HAS_IFUNC_P

TARGET_ATOMIC_ALIGN_FOR_MODE

TARGET_ATOMIC_ASSIGN_EXPAND_FENV

TARGET_RECORD_OFFLOAD_SYMBOL

TARGET_OFFLOAD_OPTIONS

 -- Macro: TARGET_SUPPORTS_WIDE_INT

     On older ports, large integers are stored in CONST_DOUBLE rtl objects.  Newer ports define TARGET_SUPPORTS_WIDE_INT to be nonzero to indicate that large integers are stored in CONST_WIDE_INT rtl objects.  The CONST_WIDE_INT allows very large integer constants to be represented.  CONST_DOUBLE is limited to twice the size of the host's HOST_WIDE_INT representation.

     Converting a port mostly requires looking for the places where CONST_DOUBLEs are used with VOIDmode and replacing that code with code that accesses CONST_WIDE_INTs.  "grep -i const_double" at the port level gets you to 95% of the changes that need to be made.  There are a few places that require a deeper look.

       * There is no equivalent to hval and lval for CONST_WIDE_INTs.  This would be difficult to express in the md language since there are a variable number of elements.

          Most ports only check that hval is either 0 or -1 to see if the value is small.  As mentioned above, this will no longer be necessary since small constants are always CONST_INT.  Of course there are still a few exceptions, the alpha's constraint used by the zap instruction certainly requires careful examination by C code. However, all the current code does is pass the hval and lval to C code, so evolving the c code to look at the CONST_WIDE_INT is not really a large change.

       * Because there is no standard template that ports use to materialize constants, there is likely to be some futzing that is unique to each port in this code.

       * The rtx costs may have to be adjusted to properly account for larger constants that are represented as CONST_WIDE_INT.

     All and all it does not take long to convert ports that the maintainer is familiar with.

TARGET_HAVE_SPECULATION_SAFE_VALUE

TARGET_SPECULATION_SAFE_VALUE

TARGET_RUN_TARGET_SELFTESTS

TARGET_MEMTAG_CAN_TAG_ADDRESSES

TARGET_MEMTAG_TAG_SIZE

TARGET_MEMTAG_GRANULE_SIZE

TARGET_MEMTAG_INSERT_RANDOM_TAG

TARGET_MEMTAG_ADD_TAG

TARGET_MEMTAG_SET_TAG

TARGET_MEMTAG_EXTRACT_TAG

TARGET_MEMTAG_UNTAGGED_POINTER