|GNU Compiler Collection (GCC) Internals|
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_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_asserttakes a string in the form you pass to the command-line option -A, such as
cpu=mips, and creates the assertion.
builtin_definetakes a string in the form accepted by option -D and unconditionally defines the macro.
builtin_define_stdtakes a string representing the name of an object-like macro. If it doesn't lie in the user's namespace,
builtin_define_stddefines 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
_mips, and passing
You can also test for the C dialect being compiled. The variable
c_languageis set to one of
clk_objective_c. Note that if we are preprocessing assembler, this variable will be
clk_cbut 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_isocan be used. The function-like macro
preprocessing_trad_p()can be used to check for traditional preprocessing.
TARGET_CPU_CPP_BUILTINSbut this macro is optional and is used for the target operating system instead.
TARGET_CPU_CPP_BUILTINSbut 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.
This variable is declared in options.h, which is included before any target-specific headers.
This variable specifies the initial value of
target_flags. Its default setting is 0.
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_optionsstructures to be used for storing option state, and loc is the location at which the option was passed (
UNKNOWN_LOCATIONexcept for options passed via attributes).
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_OPTIONto 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
Targets may provide a string object type that can be used within and between C, C++ and their respective Objective-C dialects. A string object might, for example, embed encoding and length information. These objects are considered opaque to the compiler and handled as references. An ideal implementation makes the composition of the string object match that of the Objective-C
NXStringfor GNUStep), allowing efficient interworking between C-only and Objective-C code. If a target implements string objects then this hook should return a reference to such an object constructed from the normal `C' string representation provided in string. At present, the hook is used by Objective-C only, to obtain a common-format string object when the target provides one.
If a target implements string objects then this hook should return
trueif stringref is a valid reference to such an object.
If a target implements string objects then this hook should should provide a facility to check the function arguments in args_list against the format specifiers in format_arg where the type of format_arg is one recognized as a valid string reference type.
This target function is similar to the hook
TARGET_OPTION_OVERRIDEbut is called when the optimize level is changed via an attribute or pragma or when it is reset at the end of the code affected by the attribute or pragma. It is not called at the beginning of compilation when
TARGET_OPTION_OVERRIDEis called so if you want to perform these actions then, you should have
This is similar to the
TARGET_OPTION_OVERRIDEhook 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.
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 optimizeor by using the
Set target-dependent initial values of fields in opts.
Set target-dependent default values for --param settings, using calls to
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
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.