[backport gcc-4.8/trunk r193341 <mikpe@it.uu.se>]

gcc/

2012-11-08  Steven Bosscher  <steven@gcc.gnu.org>

	PR tree-optimization/55191
	* cfganal.c (connect_infinite_loops_to_exit): Call dfs_deadend here.
	(flow_dfs_compute_reverse_execute): Don't call it here.

gcc/testsuite/

2012-11-08  Steven Bosscher  <steven@gcc.gnu.org>

	PR tree-optimization/55191
	* gcc.dg/pr55191.c: New test.

--- gcc-4.6.3/gcc/cfganal.c.~1~	2012-11-10 17:32:42.000000000 +0100
+++ gcc-4.6.3/gcc/cfganal.c	2012-11-10 17:35:23.000000000 +0100
@@ -626,6 +626,7 @@ void
 connect_infinite_loops_to_exit (void)
 {
   basic_block unvisited_block = EXIT_BLOCK_PTR;
+  basic_block deadend_block;
   struct depth_first_search_dsS dfs_ds;
 
   /* Perform depth-first search in the reverse graph to find nodes
@@ -641,8 +642,9 @@ connect_infinite_loops_to_exit (void)
       if (!unvisited_block)
 	break;
 
-      make_edge (unvisited_block, EXIT_BLOCK_PTR, EDGE_FAKE);
-      flow_dfs_compute_reverse_add_bb (&dfs_ds, unvisited_block);
+      deadend_block = dfs_find_deadend (unvisited_block);
+      make_edge (deadend_block, EXIT_BLOCK_PTR, EDGE_FAKE);
+      flow_dfs_compute_reverse_add_bb (&dfs_ds, deadend_block);
     }
 
   flow_dfs_compute_reverse_finish (&dfs_ds);
@@ -1132,7 +1134,7 @@ flow_dfs_compute_reverse_execute (depth_
   /* Determine if there are unvisited basic blocks.  */
   FOR_BB_BETWEEN (bb, last_unvisited, NULL, prev_bb)
     if (!TEST_BIT (data->visited_blocks, bb->index))
-      return dfs_find_deadend (bb);
+      return bb;
 
   return NULL;
 }
--- gcc-4.6.3/gcc/testsuite/gcc.dg/pr55191.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.3/gcc/testsuite/gcc.dg/pr55191.c	2012-11-10 17:35:23.000000000 +0100
@@ -0,0 +1,14 @@
+/* PR tree-optimization/55191 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int a, b;
+
+void f(void)
+{
+  b = a || b;
+
+  for(a = 0; a < 2; a++);
+  while(1);
+}
+