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delete_trivially_dead_insns tweek


Identifies and removes no-op patterns of the form

	(set (subreg:SI (reg:DI 99) 1))
	     (subreg:SI (reg:DI 99) 1)))

and has the mildly disconcerting property of curing a regression
on gcc.c-torture/execute/920501-6.c with -O -funroll-all-loops. 

I'm undecided on whether I will at this time continue persuing the
unrolling bug that is no doubt still in there.


r~


	* cse.c (delete_trivially_dead_insns): Identify no-op insns
	containing subregs too.

Index: cse.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cse.c,v
retrieving revision 1.112
diff -c -p -d -r1.112 cse.c
*** cse.c	1999/11/14 11:45:55	1.112
--- cse.c	1999/11/18 00:20:23
*************** delete_trivially_dead_insns (insns, nreg
*** 7176,7183 ****
  	live_insn = ! dead_libcall;
        else if (GET_CODE (PATTERN (insn)) == SET)
  	{
! 	  if (GET_CODE (SET_DEST (PATTERN (insn))) == REG
! 	      && SET_DEST (PATTERN (insn)) == SET_SRC (PATTERN (insn)))
  	    ;
  
  #ifdef HAVE_cc0
--- 7176,7185 ----
  	live_insn = ! dead_libcall;
        else if (GET_CODE (PATTERN (insn)) == SET)
  	{
! 	  if ((GET_CODE (SET_DEST (PATTERN (insn))) == REG
! 	       || GET_CODE (SET_DEST (PATTERN (insn))) == SUBREG)
! 	      && rtx_equal_p (SET_DEST (PATTERN (insn)),
! 			      SET_SRC (PATTERN (insn))))
  	    ;
  
  #ifdef HAVE_cc0
*************** delete_trivially_dead_insns (insns, nreg
*** 7207,7214 ****
  
  	    if (GET_CODE (elt) == SET)
  	      {
! 		if (GET_CODE (SET_DEST (elt)) == REG
! 		    && SET_DEST (elt) == SET_SRC (elt))
  		  ;
  
  #ifdef HAVE_cc0
--- 7209,7217 ----
  
  	    if (GET_CODE (elt) == SET)
  	      {
! 		if ((GET_CODE (SET_DEST (elt)) == REG
! 		     || GET_CODE (SET_DEST (elt)) == SUBREG)
! 		    && rtx_equal_p (SET_DEST (elt), SET_SRC (elt)))
  		  ;
  
  #ifdef HAVE_cc0


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