[backport from gcc-4.7.2 r191031 <mikpe@it.uu.se>]

gcc/

2012-09-06  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/54498
	* tree-ssa-alias.h (get_continuation_for_phi): Add flag to
	abort when reaching an already visited region.
	* tree-ssa-alias.c (maybe_skip_until): Likewise.  And do it.
	(get_continuation_for_phi_1): Likewise.
	(walk_non_aliased_vuses): When we translated the reference,
	abort when we re-visit a region.
	* tree-ssa-pre.c (translate_vuse_through_block): Adjust.

--- gcc-4.6.3/gcc/tree-ssa-alias.c.~1~	2011-09-30 20:13:25.000000000 +0200
+++ gcc-4.6.3/gcc/tree-ssa-alias.c	2012-09-09 19:02:50.000000000 +0200
@@ -1713,7 +1713,7 @@ stmt_kills_ref_p (gimple stmt, tree ref)
 
 static bool
 maybe_skip_until (gimple phi, tree target, ao_ref *ref,
-		  tree vuse, bitmap *visited)
+		  tree vuse, bitmap *visited, bool abort_on_visited)
 {
   if (!*visited)
     *visited = BITMAP_ALLOC (NULL);
@@ -1729,8 +1729,9 @@ maybe_skip_until (gimple phi, tree targe
 	{
 	  /* An already visited PHI node ends the walk successfully.  */
 	  if (bitmap_bit_p (*visited, SSA_NAME_VERSION (PHI_RESULT (def_stmt))))
-	    return true;
-	  vuse = get_continuation_for_phi (def_stmt, ref, visited);
+	    return !abort_on_visited;
+	  vuse = get_continuation_for_phi (def_stmt, ref,
+					   visited, abort_on_visited);
 	  if (!vuse)
 	    return false;
 	  continue;
@@ -1751,7 +1752,8 @@ maybe_skip_until (gimple phi, tree targe
    be found.  */
 
 tree
-get_continuation_for_phi (gimple phi, ao_ref *ref, bitmap *visited)
+get_continuation_for_phi (gimple phi, ao_ref *ref, bitmap *visited,
+			  bool abort_on_visited)
 {
   unsigned nargs = gimple_phi_num_args (phi);
 
@@ -1776,14 +1778,14 @@ get_continuation_for_phi (gimple phi, ao
 		   && dominated_by_p (CDI_DOMINATORS,
 				      gimple_bb (def1), gimple_bb (def0))))
 	{
-	  if (maybe_skip_until (phi, arg0, ref, arg1, visited))
+	  if (maybe_skip_until (phi, arg0, ref, arg1, visited, abort_on_visited))
 	    return arg0;
 	}
       else if (gimple_nop_p (def1)
 	       || dominated_by_p (CDI_DOMINATORS,
 				  gimple_bb (def0), gimple_bb (def1)))
 	{
-	  if (maybe_skip_until (phi, arg1, ref, arg0, visited))
+	  if (maybe_skip_until (phi, arg1, ref, arg0, visited, abort_on_visited))
 	    return arg1;
 	}
       /* Special case of a diamond:
@@ -1836,6 +1838,7 @@ walk_non_aliased_vuses (ao_ref *ref, tre
 {
   bitmap visited = NULL;
   void *res;
+  bool translated = false;
 
   timevar_push (TV_ALIAS_STMT_WALK);
 
@@ -1852,7 +1855,7 @@ walk_non_aliased_vuses (ao_ref *ref, tre
       if (gimple_nop_p (def_stmt))
 	break;
       else if (gimple_code (def_stmt) == GIMPLE_PHI)
-	vuse = get_continuation_for_phi (def_stmt, ref, &visited);
+	vuse = get_continuation_for_phi (def_stmt, ref, &visited, translated);
       else
 	{
 	  if (stmt_may_clobber_ref_p_1 (def_stmt, ref))
@@ -1870,6 +1873,7 @@ walk_non_aliased_vuses (ao_ref *ref, tre
 	      else if (res != NULL)
 		break;
 	      /* Translation succeeded, continue walking.  */
+	      translated = true;
 	    }
 	  vuse = gimple_vuse (def_stmt);
 	}
--- gcc-4.6.3/gcc/tree-ssa-alias.h.~1~	2011-01-03 21:52:22.000000000 +0100
+++ gcc-4.6.3/gcc/tree-ssa-alias.h	2012-09-09 19:01:09.000000000 +0200
@@ -107,7 +107,7 @@ extern bool stmt_may_clobber_ref_p (gimp
 extern bool stmt_may_clobber_ref_p_1 (gimple, ao_ref *);
 extern bool call_may_clobber_ref_p (gimple, tree);
 extern bool stmt_kills_ref_p (gimple, tree);
-extern tree get_continuation_for_phi (gimple, ao_ref *, bitmap *);
+extern tree get_continuation_for_phi (gimple, ao_ref *, bitmap *, bool);
 extern void *walk_non_aliased_vuses (ao_ref *, tree,
 				     void *(*)(ao_ref *, tree, void *),
 				     void *(*)(ao_ref *, tree, void *), void *);
--- gcc-4.6.3/gcc/tree-ssa-pre.c.~1~	2012-01-03 15:46:03.000000000 +0100
+++ gcc-4.6.3/gcc/tree-ssa-pre.c	2012-09-09 19:01:09.000000000 +0200
@@ -1293,7 +1293,7 @@ translate_vuse_through_block (VEC (vn_re
 	  bitmap visited = NULL;
 	  /* Try to find a vuse that dominates this phi node by skipping
 	     non-clobbering statements.  */
-	  vuse = get_continuation_for_phi (phi, &ref, &visited);
+	  vuse = get_continuation_for_phi (phi, &ref, &visited, false);
 	  if (visited)
 	    BITMAP_FREE (visited);
 	}