re PR rtl-optimization/59446 (loop2_doloop creates constant comparison and dead jump)

	PR rtl-optimization/59446
	* tree-ssa-threadupdate.c (mark_threaded_blocks): Properly
	test for crossing a loop header.

From-SVN: r205905

gcc/ChangeLog

+2013-12-11  Jeff Law  <law@redhat.com>
+
+	PR rtl-optimization/59446
+	* tree-ssa-threadupdate.c (mark_threaded_blocks): Properly
+	test for crossing a loop header.
+
 2013-12-11  Sriraman Tallam  <tmsriram@google.com>
 
 	PR target/59390

gcc/tree-ssa-threadupdate.c

@@ -1449,20 +1449,13 @@ mark_threaded_blocks (bitmap threaded_blocks)
 	    {
 	      vec<jump_thread_edge *> *path = THREAD_PATH (e);
 
-	      /* Basically we're looking for a situation where we can see
-	  	 3 or more loop structures on a jump threading path.  */
-
-	      struct loop *first_father = (*path)[0]->e->src->loop_father;
-	      struct loop *second_father = NULL;
-	      for (unsigned int i = 0; i < path->length (); i++)
+	      for (unsigned int i = 0, crossed_headers = 0;
+		   i < path->length ();
+		   i++)
 		{
-		  /* See if this is a loop father we have not seen before.  */
-		  if ((*path)[i]->e->dest->loop_father != first_father
-		      && (*path)[i]->e->dest->loop_father != second_father)
-		    {
-		      /* We've already seen two loop fathers, so we
-			 need to trim this jump threading path.  */
-		      if (second_father != NULL)
+		  basic_block dest = (*path)[i]->e->dest;
+		  crossed_headers += (dest == dest->loop_father->header);
+		  if (crossed_headers > 1)
 		    {
 		      /* Trim from entry I onwards.  */
 		      for (unsigned int j = i; j < path->length (); j++)
@@ -1483,11 +1476,6 @@ mark_threaded_blocks (bitmap threaded_blocks)
 			}
 		      break;
 		    }
-		      else
-			{
-			  second_father = (*path)[i]->e->dest->loop_father;
-			}
-		    }
 		}
 	    }
 	}