Re: RFC: Putting target-dependent global state into switchable structures

[Mike Stump <mikestump at comcast dot net>]

On Jun 26, 2010, at 12:24 PM, Richard Sandiford wrote:
> GCC has a fair number of global variables that cache target-dependent
> data.  This makes it difficult to switch between subtargets on the fly,
> such as when switching between a MIPS16 and a non-MIPS16 function.
> 
> Our current approach is to call target_reinit each time we make such
> a switch.  This function goes off and redoes a fair chunk of the target
> initialisation process, and although it works (or least worked) pretty well,
> it is very slow.
> 

> 	* doc/tm.texi (SWITCHABLE_TARGET): Document.
> 	* Makefile.in (target_globals_def): New variable.
> 	(target_globals_h): Likewise.
> 	(TARGET_GLOBALS_H): Likewise.
> 	(OBJS-common): Add target-globals.o.
> 	(gtype-desc.o): Depend on $(TARGET_GLOBALS_H).
> 	(target-globals.o): New rule.
> 	($(target_globals_h)): Likewise.
> 	(s-target-globals): Likewise.
> 	(GTFILES): Add $(target_globals_h).
> 	(build/gentarget-globals.o): New rule.
> 	* defaults.h (SWITCHABLE_TARGET): Define.
> 	* gengtype.c (open_base_files): Add target-globals.h to the
> 	include list.
> 	* target-globals.def: New file.
> 	* gentarget-globals.c: Likewise.
> 	* target-globals.c: Likewise.

First, thanks for the work.  I have a switchable port, I seem to be seeing:

../../gcc/gcc/target-globals.c: In function ‘target_globals* save_target_globals()’:
../../gcc/gcc/target-globals.c:69:33: error: ‘ggc_alloc_target_globals’ was not declared in this scope
make: *** [target-globals.o] Error 1

after the switch to C++.  I was wondering if your switchable target port compiles post the switch to C++?  Before the switch, I saw a C warning for using ggc_alloc_target_globals undeclared.

With:

diff --git a/gcc/target-globals.c b/gcc/target-globals.c
index e679f21..4e33359 100644
--- a/gcc/target-globals.c
+++ b/gcc/target-globals.c
@@ -65,6 +65,7 @@ struct target_globals *
 save_target_globals (void)
 {
   struct target_globals *g;
+  extern struct target_globals *ggc_alloc_target_globals (void);
 
   g = ggc_alloc_target_globals ();
   g->flag_state = XCNEW (struct target_flag_state);

my port again compiles.  Certainly I hate block scoped external function declarations, it is wrong...  could you decide where it goes and drop in that line someplace?  Thanks.