diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f0fb8403400..a774a43341a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2008-04-23  Richard Guenther  <rguenther@suse.de>
+
+	* alias.c (alias_set_subset_of): Correctly handle asking
+	if zero is a subset of an alias set with zero child.
+	* tree-ssa-alias.c (have_common_aliases_p): Simplify logic.
+	(compute_flow_insensitive_aliasing): Correctly walk all
+	pointers.  Do not unnecessarily union sets.
+
 2008-04-23  Richard Guenther  <rguenther@suse.de>
 
 	PR middle-end/36021
diff --git a/gcc/alias.c b/gcc/alias.c
index 2e4f5aebdb4..7b14f26cc13 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -305,8 +305,9 @@ alias_set_subset_of (alias_set_type set1, alias_set_type set2)
   /* Otherwise, check if set1 is a subset of set2.  */
   ase = get_alias_set_entry (set2);
   if (ase != 0
-      && (splay_tree_lookup (ase->children,
-			     (splay_tree_key) set1)))
+      && ((ase->has_zero_child && set1 == 0)
+	  || splay_tree_lookup (ase->children,
+			        (splay_tree_key) set1)))
     return true;
   return false;
 }
diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index a9ae29fa876..eb57010bdda 100644
--- a/gcc/tree-ssa-alias.c
+++ b/gcc/tree-ssa-alias.c
@@ -2390,9 +2390,7 @@ have_common_aliases_p (bitmap tag1aliases, bitmap tag2aliases)
   /* This is the old behavior of have_common_aliases_p, which is to
      return false if both sets are empty, or one set is and the other
      isn't.  */
-     if ((tag1aliases == NULL && tag2aliases != NULL)
-      || (tag2aliases == NULL && tag1aliases != NULL)
-      || (tag1aliases == NULL && tag2aliases == NULL))
+  if (tag1aliases == NULL || tag2aliases == NULL)
     return false;
 
   return bitmap_intersect_p (tag1aliases, tag2aliases);
@@ -2490,12 +2488,16 @@ compute_flow_insensitive_aliasing (struct alias_info *ai)
       if (PTR_IS_REF_ALL (p_map1->var))
 	continue;
 
-      for (j = i + 1; j < ai->num_pointers; j++)
+      for (j = 0; j < ai->num_pointers; j++)
 	{
 	  struct alias_map_d *p_map2 = ai->pointers[j];
 	  tree tag2 = symbol_mem_tag (p_map2->var);
 	  bitmap may_aliases2 = may_aliases (tag2);
 
+	  /* By convention tags don't alias themselves.  */
+	  if (tag1 == tag2)
+	    continue;
+
 	  if (PTR_IS_REF_ALL (p_map2->var))
 	    continue;
 
@@ -2508,18 +2510,8 @@ compute_flow_insensitive_aliasing (struct alias_info *ai)
 	  if (have_common_aliases_p (may_aliases1, may_aliases2))
 	    continue;
 
-	  if (may_aliases2 && !bitmap_empty_p (may_aliases2))
-	    {
-	      union_alias_set_into (tag1, 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);
-	    }
+	  add_may_alias (tag1, tag2);
 	}
-
     }
   timevar_pop (TV_FLOW_INSENSITIVE);
 }