[patch] jump.c: avoid clobbers when combining jumps

[DJ Delorie]

Pre-approved by rth, and committed by me.  Fixes
gcc.c-torture/execute/20001130-2.c (for sparc targets, at least) with
no regressions on sparc or x86.  Let me know if it should go in 3.0
also.

2001-02-14  Richard Henderson  <rth@redhat.com>
	    DJ Delorie  <dj@redhat.com>

	* jump.c (jump_optimize_1): When we delete a conditional jump
	preceeding a non-conditional jump to effectively the same place,
	make sure that the combined jump skips any clobber insns between
	the two labels.

  
Index: jump.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/jump.c,v
retrieving revision 1.153
diff -p -2 -r1.153 jump.c
*** jump.c	2001/02/11 06:19:29	1.153
--- jump.c	2001/02/14 18:31:30
*************** jump_optimize_1 (f, cross_jump, noop_mov
*** 421,424 ****
--- 421,446 ----
  	      if (temp2 == temp)
  		{
+ 		  /* Ensure that we jump to the later of the two labels.  
+ 		     Consider:
+ 
+ 			if (test) goto L2;
+ 			goto L1;
+ 			...
+ 		      L1:
+ 			(clobber return-reg)
+ 		      L2:
+ 			(use return-reg)
+ 
+ 		     If we leave the goto L1, we'll incorrectly leave
+ 		     return-reg dead for TEST true.  */
+ 
+ 		  temp2 = next_active_insn (JUMP_LABEL (insn));
+ 		  if (!temp2)
+ 		    temp2 = get_last_insn ();
+ 		  if (GET_CODE (temp2) != CODE_LABEL)
+ 		    temp2 = prev_label (temp2);
+ 		  if (temp2 != JUMP_LABEL (temp))
+ 		    redirect_jump (temp, temp2, 1);
+ 
  		  delete_jump (insn);
  		  changed = 1;