[Bug tree-optimization/31522] False overflow warning with phi nodes

[ian at airs dot com]

------- Comment #8 from ian at airs dot com  2007-04-11 08:04 -------
That's not an infinite loop, it's just a loop with 2^31 iterations.

This patch takes a rather different approach.

Index: tree-vrp.c
===================================================================
--- tree-vrp.c  (revision 123521)
+++ tree-vrp.c  (working copy)
@@ -95,6 +95,11 @@ static sbitmap blocks_visited;
    of values that SSA name N_I may take.  */
 static value_range_t **vr_value;

+/* For a PHI node which sets SSA name N_I, VR_COUNTS[I] holds the
+   number of executable edges we saw the last time we visited the
+   node.  */
+static int *vr_counts;
+

 /* Return whether TYPE should use an overflow infinity distinct from
    TYPE_{MIN,MAX}_VALUE.  We use an overflow infinity value to
@@ -4306,6 +4311,7 @@ vrp_initialize (void)
   basic_block bb;

   vr_value = XCNEWVEC (value_range_t *, num_ssa_names);
+  vr_counts = XCNEWVEC (int, num_ssa_names);

   FOR_EACH_BB (bb)
     {
@@ -5059,7 +5065,7 @@ vrp_visit_phi_node (tree phi)
   tree lhs = PHI_RESULT (phi);
   value_range_t *lhs_vr = get_value_range (lhs);
   value_range_t vr_result = { VR_UNDEFINED, NULL_TREE, NULL_TREE, NULL };
-  bool all_const = true;
+  int edges, old_edges;

   copy_value_range (&vr_result, lhs_vr);

@@ -5069,6 +5075,7 @@ vrp_visit_phi_node (tree phi)
       print_generic_expr (dump_file, phi, dump_flags);
     }

+  edges = 0;
   for (i = 0; i < PHI_NUM_ARGS (phi); i++)
     {
       edge e = PHI_ARG_EDGE (phi, i);
@@ -5086,10 +5093,11 @@ vrp_visit_phi_node (tree phi)
          tree arg = PHI_ARG_DEF (phi, i);
          value_range_t vr_arg;

+         ++edges;
+
          if (TREE_CODE (arg) == SSA_NAME)
            {
              vr_arg = *(get_value_range (arg));
-             all_const = false;
            }
          else
            {
@@ -5115,6 +5123,9 @@ vrp_visit_phi_node (tree phi)
        }
     }

+  old_edges = vr_counts[SSA_NAME_VERSION (lhs)];
+  vr_counts[SSA_NAME_VERSION (lhs)] = edges;
+
   if (vr_result.type == VR_VARYING)
     goto varying;

@@ -5122,7 +5133,7 @@ vrp_visit_phi_node (tree phi)
      when the new value is slightly bigger or smaller than the
      previous one.  */
   if (lhs_vr->type == VR_RANGE && vr_result.type == VR_RANGE
-      && !all_const)
+      && edges <= old_edges)
     {
       if (!POINTER_TYPE_P (TREE_TYPE (lhs)))
        {


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31522