[Bug tree-optimization/30567] [4.2 Regression] -O3 optimizer bug

["rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #26 from rguenth at gcc dot gnu dot org  2007-04-25 14:22 -------
We fail to add the SFTs to the may_alias set of SMT.11, so add_virtual_operand
sees NULL may_aliases and doesn't add SFTs as clobbered.

I believe compute_flow_insensitive_aliasing is the culprit here as one can
easily
see that if we enter the

  for (i = 0; i < ai->num_pointers; i++)
    {
      size_t j;
      struct alias_map_d *p_map1 = ai->pointers[i];
      tree tag1 = var_ann (p_map1->var)->symbol_mem_tag;
      bitmap may_aliases1 = p_map1->may_aliases;

      if (PTR_IS_REF_ALL (p_map1->var))
        continue;

      for (j = i + 1; j < ai->num_pointers; j++)
        {
          struct alias_map_d *p_map2 = ai->pointers[j];
          tree tag2 = var_ann (p_map2->var)->symbol_mem_tag;
          bitmap may_aliases2 = p_map2->may_aliases;


loop with may_aliases2 empty it will stay so.  So as a fix I suggest to
add may aliases symmetrically like with

Index: tree-ssa-alias.c
===================================================================
*** tree-ssa-alias.c    (revision 124151)
--- tree-ssa-alias.c    (working copy)
*************** compute_flow_insensitive_aliasing (struc
*** 1287,1292 ****
--- 1287,1294 ----
          struct alias_map_d *p_map2 = ai->pointers[j];
          tree tag2 = var_ann (p_map2->var)->symbol_mem_tag;
          bitmap may_aliases2 = p_map2->may_aliases;
+         unsigned int k;
+         bitmap_iterator bi;

          if (PTR_IS_REF_ALL (p_map2->var))
            continue;
*************** compute_flow_insensitive_aliasing (struc
*** 1301,1323 ****
            continue;

          if (!bitmap_empty_p (may_aliases2))
!           {
!             unsigned int k;
!             bitmap_iterator bi;
! 
!             /* Add all the aliases for TAG2 into TAG1's alias set.
!                FIXME, update grouping heuristic counters.  */
!             EXECUTE_IF_SET_IN_BITMAP (may_aliases2, 0, k, bi)
!               add_may_alias (tag1, referenced_var (k));
!             bitmap_ior_into (may_aliases1, may_aliases2);
!           }
          else
!           {
!             /* Since TAG2 does not have any aliases of its own, add
!                TAG2 itself to the alias set of TAG1.  */
!             add_may_alias (tag1, tag2);
!             bitmap_set_bit (may_aliases1, DECL_UID (tag2));
!           }
        }
      }

--- 1303,1325 ----
            continue;

          if (!bitmap_empty_p (may_aliases2))
!           /* Add all the aliases for TAG2 into TAG1's alias set.
!              FIXME, update grouping heuristic counters.  */
!           EXECUTE_IF_SET_IN_BITMAP (may_aliases2, 0, k, bi)
!             add_may_alias (tag1, referenced_var (k));
!         else
!           add_may_alias (tag1, tag2);
! 
!         if (!bitmap_empty_p (may_aliases1))
!           /* Add all the aliases for TAG2 into TAG1's alias set.
!              FIXME, update grouping heuristic counters.  */
!           EXECUTE_IF_SET_IN_BITMAP (may_aliases1, 0, k, bi)
!             add_may_alias (tag2, referenced_var (k));
          else
!           add_may_alias (tag2, tag1);
! 
!         bitmap_ior_into (may_aliases2, may_aliases1);
!         bitmap_ior_into (may_aliases1, may_aliases2);
        }
      }



but I have no clue what I am doing here.  't looks like big mess.

I prepare the workaround as alternative ;)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30567