re PR middle-end/42509 (nonoverlapping_memrefs_p misinterprets NULL MEM_OFFSET as const0_rtx)

2010-04-03  Richard Guenther  <rguenther@suse.de>

	PR middle-end/42509
	* alias.c (nonoverlapping_memrefs_p): For spill-slot accesses
	require a non-NULL MEM_OFFSET.

From-SVN: r157954

gcc/ChangeLog

+2010-04-03  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/42509
+	* alias.c (nonoverlapping_memrefs_p): For spill-slot accesses
+	require a non-NULL MEM_OFFSET.
+
 2010-04-02  Steven Bosscher  <steven@gcc.gnu.org>
 
 	* ada/gcc-interface/Make-lang.in, alias.c, attribs.c, auto-inc-dec.c, 

gcc/alias.c

@@ -2147,6 +2147,13 @@ nonoverlapping_memrefs_p (const_rtx x, const_rtx y)
   if (exprx == 0 || expry == 0)
     return 0;
 
+  /* For spill-slot accesses make sure we have valid offsets.  */
+  if ((exprx == get_spill_slot_decl (false)
+       && ! MEM_OFFSET (x))
+      || (expry == get_spill_slot_decl (false)
+	  && ! MEM_OFFSET (y)))
+    return 0;
+
   /* If both are field references, we may be able to determine something.  */
   if (TREE_CODE (exprx) == COMPONENT_REF
       && TREE_CODE (expry) == COMPONENT_REF