2010-11-26 Richard Guenther <rguenther@suse.de>

	PR lto/46648
	* gimple.c (gtc_visit): Do not return true for members of an
	SCC still being processed but the current lattice value of
	the member.  Treat SCC members comparison state as lattice,
	starting at equal, eventually dropping to unequal.
	(gimple_types_compatible_p_1): Likewise.

	* gcc.dg/lto/20101125-1_0.c: New testcase.
	* gcc.dg/lto/20101125-1_1.c: Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@167183 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 16 insertions, 17 deletions

diff --git a/gcc/gimple.c b/gcc/gimple.c
index 851e30ffbda..67c80e327c3 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -3515,27 +3515,23 @@ gtc_visit (tree t1, tree t2, enum gtc_mode mode,
 
   if ((slot = pointer_map_contains (sccstate, p)) != NULL)
     cstate = (struct sccs *)*slot;
+  /* Not yet visited.  DFS recurse.  */
   if (!cstate)
     {
-      bool res;
-      /* Not yet visited.  DFS recurse.  */
-      res = gimple_types_compatible_p_1 (t1, t2, mode, p,
-					 sccstack, sccstate, sccstate_obstack);
-      if (!cstate)
-	cstate = (struct sccs *)* pointer_map_contains (sccstate, p);
+      gimple_types_compatible_p_1 (t1, t2, mode, p,
+				   sccstack, sccstate, sccstate_obstack);
+      cstate = (struct sccs *)* pointer_map_contains (sccstate, p);
       state->low = MIN (state->low, cstate->low);
-      /* If the type is no longer on the SCC stack and thus is not part
-	 of the parents SCC, return its state.  Otherwise we will
-	 ignore this pair and assume equality.  */
-      if (!cstate->on_sccstack)
-	return res;
     }
+  /* If the type is still on the SCC stack adjust the parents low.  */
   if (cstate->dfsnum < state->dfsnum
       && cstate->on_sccstack)
     state->low = MIN (cstate->dfsnum, state->low);
 
-  /* We are part of our parents SCC, skip this entry and return true.  */
-  return true;
+  /* Return the current lattice value.  We start with an equality
+     assumption so types part of a SCC will be optimistically
+     treated equal unless proven otherwise.  */
+  return cstate->u.same_p;
 }
 
 /* Worker for gimple_types_compatible.
@@ -3559,6 +3555,9 @@ gimple_types_compatible_p_1 (tree t1, tree t2, enum gtc_mode mode,
   state->dfsnum = gtc_next_dfs_num++;
   state->low = state->dfsnum;
   state->on_sccstack = true;
+  /* Start with an equality assumption.  As we DFS recurse into child
+     SCCs this assumption may get revisited.  */
+  state->u.same_p = 1;
 
   /* If their attributes are not the same they can't be the same type.  */
   if (!attribute_list_equal (TYPE_ATTRIBUTES (t1), TYPE_ATTRIBUTES (t2)))
@@ -3822,22 +3821,22 @@ different_types:
 
   /* Common exit path for types that are compatible.  */
 same_types:
-  state->u.same_p = 1;
-  goto pop;
+  gcc_assert (state->u.same_p == 1);
 
 pop:
   if (state->low == state->dfsnum)
     {
       type_pair_t x;
 
-      /* Pop off the SCC and set its cache values.  */
+      /* Pop off the SCC and set its cache values to the final
+         comparison result.  */
       do
 	{
 	  struct sccs *cstate;
 	  x = VEC_pop (type_pair_t, *sccstack);
 	  cstate = (struct sccs *)*pointer_map_contains (sccstate, x);
 	  cstate->on_sccstack = false;
-	  x->same_p[mode] = cstate->u.same_p;
+	  x->same_p[mode] = state->u.same_p;
 	}
       while (x != p);
     }