[PATCH] Dead store elimination for local memory references

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

this patch makes store motion to remove unused stores to local
variables.  It bootstraps it on amd64; on the other hand I am
not really at all sure whether the local_variable_p is correct.

Zdenek

Changelog:
	* gcse.c (local_variable_p): New static function.
	(build_store_vectors): Arrange for ellimination of dead local memory
	references.

Index: gcse.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/gcse.c,v
retrieving revision 1.250
diff -c -3 -p -r1.250 gcse.c
*** gcse.c	12 Jun 2003 04:15:56 -0000	1.250
--- gcse.c	19 Jun 2003 20:34:26 -0000
*************** static void find_moveable_store		PARAMS 
*** 687,692 ****
--- 687,693 ----
  static int compute_store_table		PARAMS ((void));
  static bool load_kills_store		PARAMS ((rtx, rtx));
  static bool find_loads			PARAMS ((rtx, rtx));
+ static bool local_variable_p (struct ls_expr *ptr);
  static bool store_killed_in_insn	PARAMS ((rtx, rtx, rtx));
  static bool store_killed_after		PARAMS ((rtx, rtx, rtx, basic_block,
  						 int *, rtx *));
*************** find_loads (x, store_pattern)
*** 7441,7446 ****
--- 7442,7466 ----
    return ret;
  }
  
+ /* Checks if mem in PTR corresponds to a local variable.  */
+ static bool
+ local_variable_p (struct ls_expr *ptr)
+ {
+   rtx reg, base;
+       
+   for (reg = ptr->pattern_regs; reg; reg = XEXP (reg, 1))
+     {
+       base = find_base_term (XEXP (reg, 0));
+       if (base
+ 	  && GET_CODE (base) == ADDRESS
+ 	  && GET_MODE (base) == Pmode
+ 	  && XEXP (base, 0) == frame_pointer_rtx)
+ 	return true;
+     }
+ 
+   return false;
+ }
+ 
  /* Check if INSN kills the store pattern X (is aliased with it).
     Return true if it it does.  */
  
*************** static void
*** 7550,7555 ****
--- 7570,7576 ----
  build_store_vectors ()
  {
    basic_block bb;
+   edge e;
    int *regs_set_in_block;
    rtx insn, st;
    struct ls_expr * ptr;
*************** build_store_vectors ()
*** 7621,7626 ****
--- 7642,7666 ----
         	}
      }
  
+   for (e = EXIT_BLOCK_PTR->pred; e; e = e->pred_next)
+     {
+       bb = e->src;
+       if (bb->succ->succ_next)
+ 	continue;
+ 
+       for (ptr = first_ls_expr (); ptr != NULL; ptr = next_ls_expr (ptr))
+ 	{
+ 	  /* If this is a reference to a local variable, add the fake store
+ 	     before end of function.  This takes care of dead code ellimination
+ 	     for them.  */
+ 	  if (!local_variable_p (ptr))
+ 	    continue;
+ 
+ 	  if (!TEST_BIT (ae_kill[bb->index], ptr->index))
+ 	    SET_BIT (st_antloc[bb->index], ptr->index);
+ 	}
+     }
+ 	
    free (regs_set_in_block);
  
    if (gcse_file)