Add more restriction in 'peep2_find_free_register'

[Anatoly Sokolov <aesok@post.ru>]

Hello.

This patch add two more check in 'peep2_find_free_register' function, which
find free hard registers for use as scratch registers in peephole2.

  * It is not allowed to use register that are being declared as global, as
  scratch register.

  * For an interrupt function it is safety to use only call-used registers
  which are saved in prologue. In 'rename_registers' optimization pass this
  check is done in HARD_REGNO_RENAME_OK macro. This patch add
  HARD_REGNO_SCRATCH_OK macro for 'peephole2' pass. The
  HARD_REGNO_SCRATCH_OK macro sould be difined for target which use interrupt
  and 'match_scratch' in peephole2 (avr, m68k).

  For example for avr target:

avr.h:
#define  HARD_REGNO_SCRATCH_OK(REGNO) avr_hard_regno_scrath_ok (REGNO)

avr.c:
int
avr_hard_regno_scrath_ok (unsigned int regno)
{
  /* Interrupt functions can only use registers that have already been
     saved by the prologue, even if they would normally be
     call-clobbered.  */

  if ((cfun->machine->is_interrupt || cfun->machine->is_signal)
      && !df_regs_ever_live_p (regno))
    return 0;

  return 1;
}


2008-06-17  Anatoly Sokolov <aesok@post.ru>

        * recog.c (peep2_find_free_register): Add check for global regs. 
        Add target specific check.

Index: gcc/doc/tm.texi
===================================================================
--- gcc/doc/tm.texi     (revision 136872)
+++ gcc/doc/tm.texi     (working copy)
@@ -2242,6 +2242,16 @@
 allocation.
 @end defmac
 
+@defmac HARD_REGNO_SCRATCH_OK (@var{regno})
+A C expression that is nonzero if it is OK to use a hard register 
+@var{regno} as scratch reg in peephole2.
+
+One common use of this macro is to prevent using of a register that 
+is not saved by a prologue in an interrupt handler.
+
+The default is always nonzero.
+@end defmac
+
 @defmac AVOID_CCMODE_COPIES
 Define this macro if the compiler should avoid copies to/from @code{CCmode}
 registers.  You should only define this macro if support for copying to/from
Index: gcc/recog.c
===================================================================
--- gcc/recog.c	(revision 136872)
+++ gcc/recog.c	(working copy)
@@ -2898,6 +2898,9 @@
       /* Don't allocate fixed registers.  */
       if (fixed_regs[regno])
        continue;
+      /* Don't allocate global registers.  */
+      if (global_regs[regno])
+       continue;
       /* Make sure the register is of the right class.  */
       if (! TEST_HARD_REG_BIT (reg_class_contents[cl], regno))
        continue;
@@ -2907,6 +2910,10 @@
       /* And that we don't create an extra save/restore.  */
       if (! call_used_regs[regno] && ! df_regs_ever_live_p (regno))
        continue;
+#ifdef HARD_REGNO_SCRATCH_OK
+      if (! HARD_REGNO_SCRATCH_OK(regno))
+       continue;
+#endif
       /* And we don't clobber traceback for noreturn functions.  */
       if ((regno == FRAME_POINTER_REGNUM || regno == HARD_FRAME_POINTER_REGNUM)
          && (! reload_completed || frame_pointer_needed))


Anatoly.