[Bug tree-optimization/22591] [4.0/4.1 Regression] wrong alias information causes an incorrect redundant load elimination

[dnovillo at gcc dot gnu dot org]

------- Additional Comments From dnovillo at gcc dot gnu dot org  2005-07-26 16:19 -------

Testing patch.  The shortcut we were taking in may_alias_p is invalid even with
strict aliasing.

--- tree-ssa-alias.c    25 Jul 2005 12:04:50 -0000      2.107
+++ tree-ssa-alias.c    26 Jul 2005 16:16:34 -0000
@@ -1511,23 +1511,6 @@ may_alias_p (tree ptr, HOST_WIDE_INT mem

   alias_stats.tbaa_queries++;

-  /* If VAR is a pointer with the same alias set as PTR, then dereferencing
-     PTR can't possibly affect VAR.  Note, that we are specifically testing
-     for PTR's alias set here, not its pointed-to type.  We also can't
-     do this check with relaxed aliasing enabled.  */
-  if (POINTER_TYPE_P (TREE_TYPE (var))
-      && var_alias_set != 0
-      && mem_alias_set != 0)
-    {
-      HOST_WIDE_INT ptr_alias_set = get_alias_set (ptr);
-      if (ptr_alias_set == var_alias_set)
-       {
-         alias_stats.alias_noalias++;
-         alias_stats.tbaa_resolved++;
-         return false;
-       }
-    }
-
   /* If the alias sets don't conflict then MEM cannot alias VAR.  */
   if (!alias_sets_conflict_p (mem_alias_set, var_alias_set))
     {

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22591