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Diffstat (limited to 'gcc/tm.texi')
| -rw-r--r-- | gcc/tm.texi | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/gcc/tm.texi b/gcc/tm.texi index 795abac65a7..769583eba90 100644 --- a/gcc/tm.texi +++ b/gcc/tm.texi @@ -22,6 +22,7 @@ includes @file{tm.h} and most compiler source files include @menu * Driver:: Controlling how the driver runs the compilation passes. * Run-time Target:: Defining @samp{-m} options like @samp{-m68000} and @samp{-m68020}. +* Per-Function Data:: Defining data structures for per-function information. * Storage Layout:: Defining sizes and alignments of data. * Type Layout:: Defining sizes and properties of basic user data types. * Registers:: Naming and describing the hardware registers. @@ -704,6 +705,80 @@ pointer. If this macro is defined, GCC will turn on the @samp{-fomit-frame-pointer} option whenever @samp{-O} is specified. @end table +@node Per-Function Data +@section Defining data structures for per-function information. +@cindex per-function data +@cindex data structures + +If the target needs to store information on a per-function basis, GCC +provides a macro and a couple of variables to allow this. Note, just +using statics to store the information is a bad idea, since GCC supports +nested functions, so you can be halfway through encoding one function +when another one comes along. + +GCC defines a data structure called @code{struct function} which +contains all of the data specific to an individual function. This +structure contains a field called @code{machine} whose type is +@code{struct machine_function *}, which can be used by targets to point +to their own specific data. + +If a target needs per-function specific data it should define the type +@code{struct machine_function} and also the macro +@code{INIT_EXPANDERS}. This macro should be used to initialise some or +all of the function pointers @code{init_machine_status}, +@code{free_machine_status} and @code{mark_machine_status}. These +pointers are explained below. + +One typical use of per-function, target specific data is to create an +RTX to hold the register containing the function's return address. This +RTX can then be used to implement the @code{__builtin_return_address} +function, for level 0. + +Note - earlier implementations of GCC used a single data area to hold +all of the per-function information. Thus when processing of a nested +function began the old per-function data had to be pushed onto a +stack, and when the processing was finished, it had to be popped off the +stack. GCC used to provide function pointers called +@code{save_machine_status} and @code{restore_machine_status} to handle +the saving and restoring of the target specific information. Since the +single data area approach is no longer used, these pointers are no +longer supported. + +The macro and function pointers are described below. + +@table @code +@findex INIT_EXPANDERS +@item INIT_EXPANDERS +Macro called to initialise 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 initialisation of the +function pointers below. + +@findex init_machine_status +@item init_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +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 initialisation of the @code{struct function} structure. It is +intended that this would be used to initialise the @code{machine} of +that struture. + +@findex free_machine_status +@item free_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +pointer is non-NULL it will be called once per function, after the +function has been compiled, in order to allow any memory allocated +during the @code{init_machine_status} function call to be freed. + +@findex mark_machine_status +@item mark_machine_status +This is a @code{void (*)(struct function *)} function pointer. If this +pointer is non-NULL it will be called once per function in order to mark +any data items in the @code{struct machine_function} structure which +need garbage collection. + +@end table + @node Storage Layout @section Storage Layout @cindex storage layout |