[PATCH] Fix PR8967

[Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz>]

Hello,

the patch below should fix the problem. I am not quite sure about its
correctness -- there indeed should be anti_dependence in mark_used_regs,
but it does not handle the pretended set of unchanging mem after its
use. I would be much happier if there were some cleaner way.

Zdenek

Changelog:
   * flow.c (init_propagate_block_info, insn_dead_p, mark_used_regs):
   Eliminate dead unchanging mem stores.

*** flow.c	Fri Dec 20 18:59:43 2002
--- /mnt/extra/gcc_main_rtlopt_merge/gcc/gcc/flow.c	Sat Dec 21 16:38:42 2002
*************** init_propagate_block_info (bb, live, loc
*** 1996,2008 ****
  	    rtx mem = SET_DEST (set);
  	    rtx canon_mem = canon_rtx (mem);
  
- 	    /* This optimization is performed by faking a store to the
- 	       memory at the end of the block.  This doesn't work for
- 	       unchanging memories because multiple stores to unchanging
- 	       memory is illegal and alias analysis doesn't consider it.  */
- 	    if (RTX_UNCHANGING_P (canon_mem))
- 	      continue;
- 
  	    if (XEXP (canon_mem, 0) == frame_pointer_rtx
  		|| (GET_CODE (XEXP (canon_mem, 0)) == PLUS
  		    && XEXP (XEXP (canon_mem, 0), 0) == frame_pointer_rtx
--- 1997,2002 ----
*************** insn_dead_p (pbi, x, call_ok, notes)
*** 2177,2185 ****
  	     If so, this memory write is dead (remember, we're walking
  	     backwards from the end of the block to the start).  Since
  	     rtx_equal_p does not check the alias set or flags, we also
! 	     must have the potential for them to conflict (anti_dependence).  */
  	  for (temp = pbi->mem_set_list; temp != 0; temp = XEXP (temp, 1))
! 	    if (anti_dependence (r, XEXP (temp, 0)))
  	      {
  		rtx mem = XEXP (temp, 0);
  
--- 2171,2179 ----
  	     If so, this memory write is dead (remember, we're walking
  	     backwards from the end of the block to the start).  Since
  	     rtx_equal_p does not check the alias set or flags, we also
! 	     must have the potential for them to conflict (output_dependence).  */
  	  for (temp = pbi->mem_set_list; temp != 0; temp = XEXP (temp, 1))
! 	    if (output_dependence (r, XEXP (temp, 0)))
  	      {
  		rtx mem = XEXP (temp, 0);
  
*************** mark_used_regs (pbi, x, cond, insn)
*** 3791,3798 ****
  
  	      while (temp)
  		{
  		  next = XEXP (temp, 1);
! 		  if (anti_dependence (XEXP (temp, 0), x))
  		    {
  		      /* Splice temp out of the list.  */
  		      if (prev)
--- 3785,3794 ----
  
  	      while (temp)
  		{
+ 		  rtx mem = XEXP (temp, 0);
  		  next = XEXP (temp, 1);
! 		  if (true_dependence (mem, GET_MODE (mem), x,
! 				       rtx_addr_varies_p))
  		    {
  		      /* Splice temp out of the list.  */
  		      if (prev)