tm.texi.in (SWITCHABLE_TARGET): Document.

gcc/
	* doc/tm.texi.in (SWITCHABLE_TARGET): Document.
	* doc/tm.texi: Regenerate.
	* Makefile.in (OBJS-common): Add target-globals.o.
	(gtype-desc.o): Depend on $(IPA_PROP_H), $(LTO_STREAMER_H)
	and target-globals.h.
	(target-globals.o): New rule.
	(GTFILES): Include $(srcdir)/target-globals.h.
	* defaults.h (SWITCHABLE_TARGET): Define.
	* gengtype.c (open_base_files): Add target-globals.h to the
	list of includes.
	* target-globals.h: New file.
	* target-globals.c: Likewise.

	* Makefile.in (target-globals.o): Depend on $(FLAGS_H).
	* flags.h (target_flag_state): New structure.
	(default_target_flag_state): Declare.
	(this_target_flag_state): Declare as a variable or define as a macro.
	(align_loops_log): Redefine as a macro.
	(align_loops_max_skip, align_jumps_log): Likewise.
	(align_jumps_max_skip, align_labels_log): Likewise.
	(align_labels_max_skip, align_functions_log): Likewise.
	* toplev.c (default_target_flag_state): New variable.
	(this_target_flag_state): New conditional variable.
	(align_loops_log): Delete.
	(align_loops_max_skip, align_jumps_log): Likewise.
	(align_jumps_max_skip, align_labels_log): Likewise.
	(align_labels_max_skip, align_functions_log): Likewise.
	* target-globals.h (this_target_flag_state): Declare.
	(target_globals): Add a flag_state field.
	(restore_target_globals): Copy the flag_state field to
	this_target_flag_state.
	* target-globals.c: Include flags.h.
	(default_target_globals): Initialize the flag_state field.
	(save_target_globals): Likewise.

From-SVN: r162086

1 files changed, 19 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index d3d9c1e..78f2f2f 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -842,6 +842,25 @@ pointer.  If this macro is defined, GCC will turn on the
 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
 @end defmac
 
+@defmac 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 @code{mips16}
+and @code{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 @file{target-globals.h} for details.
+
+Define this macro to 1 if your target needs this facility.  The default
+is 0.
+@end defmac
+
 @node Per-Function Data
 @section Defining data structures for per-function information.
 @cindex per-function data