strength_reduce bug fix

[Joern Rennecke <amylaar at cygnus dot co dot uk>]

Reviewed by Jim Wilson.
Applied.

Tue Mar  2 22:03:30 1999  J"orn Rennecke <amylaar@cygnus.co.uk>

	* loop.c (strength_reduce): Don't do biv increment -> DEST_REG giv
	conversion if we don't know the lifetime.

Index: loop.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/loop.c,v
retrieving revision 1.147
diff -p -r1.147 loop.c
*** loop.c	1999/02/25 11:16:17	1.147
--- loop.c	1999/03/02 22:04:17
*************** strength_reduce (scan_start, end, loop_t
*** 4198,4207 ****
  		  VARRAY_GROW (may_not_optimize, nregs);
  		}
      
! 	      validate_change (v->insn, &SET_DEST (set), dest_reg, 1);
! 	      validate_change (next->insn, next->location, add_val, 1);
! 	      if (! apply_change_group ())
  		{
  		  vp = &v->next_iv;
  		  continue;
  		}
--- 4198,4240 ----
  		  VARRAY_GROW (may_not_optimize, nregs);
  		}
      
! 	      if (! validate_change (next->insn, next->location, add_val, 0))
  		{
+ 		  vp = &v->next_iv;
+ 		  continue;
+ 		}
+ 
+ 	      /* Here we can try to eliminate the increment by combining
+ 		 it into the uses.  */
+ 
+ 	      /* Set last_use_insn so that we can check against it.  */
+ 
+ 	      for (last_use_insn = v->insn, p = NEXT_INSN (v->insn);
+ 		   p != next->insn;
+ 		   p = next_insn_in_loop (p, scan_start, end, loop_top))
+ 		{
+ 		  rtx note;
+     
+ 		  if (GET_RTX_CLASS (GET_CODE (p)) != 'i')
+ 		    continue;
+ 		  if (reg_mentioned_p (old_reg, PATTERN (p)))
+ 		    {
+ 		      last_use_insn = p;
+ 		    }
+ 		}
+ 
+ 	      /* If we can't get the LUIDs for the insns, we can't
+ 		 calculate the lifetime.  This is likely from unrolling
+ 		 of an inner loop, so there is little point in making this
+ 		 a DEST_REG giv anyways.  */
+ 	      if (INSN_UID (v->insn) >= max_uid_for_loop
+ 		  || INSN_UID (last_use_insn) >= max_uid_for_loop
+ 		  || ! validate_change (v->insn, &SET_DEST (set), dest_reg, 0))
+ 		{
+ 		  /* Change the increment at NEXT back to what it was.  */
+ 		  if (! validate_change (next->insn, next->location,
+ 		      next->add_val, 0))
+ 		    abort ();
  		  vp = &v->next_iv;
  		  continue;
  		}