[Bug middle-end/52580] [4.8 Regression] 171.swim performance drop on x86 – vectorization doesn’t happen anymore

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52580

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-03-14 
14:52:11 UTC ---
The issue is that with the artificial access functions added for
__BLNK__.uold and __BLK__.vnew we run the subscript dependence tester
but that fails even when only a single access function cannot be
analyzed.

The following fixes that.

Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c (revision 185379)
+++ gcc/tree-data-ref.c (working copy)
@@ -3460,6 +3460,7 @@ subscript_dependence_tester_1 (struct da
   unsigned int i;
   tree last_conflicts;
   struct subscript *subscript;
+  tree res = NULL_TREE;

   for (i = 0; VEC_iterate (subscript_p, DDR_SUBSCRIPTS (ddr), i, subscript);
        i++)
@@ -3471,40 +3472,43 @@ subscript_dependence_tester_1 (struct da
                                      &overlaps_a, &overlaps_b,
                                      &last_conflicts, loop_nest);

+      if (SUB_CONFLICTS_IN_A (subscript))
+       free_conflict_function (SUB_CONFLICTS_IN_A (subscript));
+      if (SUB_CONFLICTS_IN_B (subscript))
+       free_conflict_function (SUB_CONFLICTS_IN_B (subscript));
+
+      SUB_CONFLICTS_IN_A (subscript) = overlaps_a;
+      SUB_CONFLICTS_IN_B (subscript) = overlaps_b;
+      SUB_LAST_CONFLICT (subscript) = last_conflicts;
+
+      /* If there is any undetermined conflict function we have to
+         give a conservative answer in case we cannot prove that
+        no dependence exists when analyzing another subscript.  */
       if (CF_NOT_KNOWN_P (overlaps_a)
          || CF_NOT_KNOWN_P (overlaps_b))
        {
-         finalize_ddr_dependent (ddr, chrec_dont_know);
-         dependence_stats.num_dependence_undetermined++;
-         free_conflict_function (overlaps_a);
-         free_conflict_function (overlaps_b);
-         return false;
+         res = chrec_dont_know;
+         continue;
        }

+      /* When there is a subscript with no dependence we can stop.  */
       else if (CF_NO_DEPENDENCE_P (overlaps_a)
               || CF_NO_DEPENDENCE_P (overlaps_b))
        {
-         finalize_ddr_dependent (ddr, chrec_known);
-         dependence_stats.num_dependence_independent++;
-         free_conflict_function (overlaps_a);
-         free_conflict_function (overlaps_b);
-         return false;
-       }
-
-      else
-       {
-         if (SUB_CONFLICTS_IN_A (subscript))
-           free_conflict_function (SUB_CONFLICTS_IN_A (subscript));
-         if (SUB_CONFLICTS_IN_B (subscript))
-           free_conflict_function (SUB_CONFLICTS_IN_B (subscript));
-
-         SUB_CONFLICTS_IN_A (subscript) = overlaps_a;
-         SUB_CONFLICTS_IN_B (subscript) = overlaps_b;
-         SUB_LAST_CONFLICT (subscript) = last_conflicts;
+         res = chrec_known;
+         break;
        }
     }

-  return true;
+  if (res == NULL_TREE)
+    return true;
+
+  if (res == chrec_known)
+    dependence_stats.num_dependence_independent++;
+  else
+    dependence_stats.num_dependence_undetermined++;
+  finalize_ddr_dependent (ddr, res);
+  return false;
 }

 /* Computes the conflicting iterations in LOOP_NEST, and initialize DDR.  */