re PR middle-end/54838 (ICE: in merge_latch_edges, at cfgloop.c:678 with -ftracer)

PR54838

From-SVN: r194060

gcc/ChangeLog

+2012-12-02  Marek Polacek  <polacek@redhat.com>
+
+	PR middle-end/54838
+	* cprop.c (bypass_block): Determine number of latches.  Return
+	when there is more than one latch edge.
+
 2012-12-02  Teresa Johnson  <tejohnson@google.com>
 
 	PR gcov-profile/55551

gcc/cprop.c

@@ -1510,13 +1510,28 @@ bypass_block (basic_block bb, rtx setcc, rtx jump)
   if (note)
     find_used_regs (&XEXP (note, 0), NULL);
 
-  may_be_loop_header = false;
-  FOR_EACH_EDGE (e, ei, bb->preds)
-    if (e->flags & EDGE_DFS_BACK)
-      {
-	may_be_loop_header = true;
-	break;
-      }
+  /* Determine whether there are more latch edges.  Threading through
+     a loop header with more than one latch is delicate, see e.g.
+     tree-ssa-threadupdate.c:thread_through_loop_header.  */
+  if (current_loops)
+    {
+      may_be_loop_header = bb == bb->loop_father->header;
+      if (may_be_loop_header
+	  && bb->loop_father->latch == NULL)
+	return 0;
+    }
+  else
+    {
+      unsigned n_back_edges = 0;
+      FOR_EACH_EDGE (e, ei, bb->preds)
+	if (e->flags & EDGE_DFS_BACK)
+	  n_back_edges++;
+
+      may_be_loop_header = n_back_edges > 0;
+
+      if (n_back_edges > 1)
+        return 0;
+    }
 
   change = 0;
   for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )

gcc/testsuite/ChangeLog

+2012-12-02  Marek Polacek  <polacek@redhat.com>
+
+	PR middle-end/54838
+	* gcc.dg/pr54838.c: New test.
+
 2012-12-01  Xinliang David Li  <davidxl@google.com>
 
 	* gcc.target/i386/ifcvt-onecmpl-abs-1.c: Check for

gcc/testsuite/gcc.dg/pr54838.c

+/* PR middle-end/54838 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-forward-propagate -ftracer" } */
+
+void bar (void);
+
+void
+foo (void *b, int *c)
+{
+again:
+  switch (*c)
+    {
+    case 1:
+      if (!b)
+	{
+	  bar ();
+	  return;
+	}
+      goto again;
+    case 3:
+      if (!b)
+	goto again;
+    }
+}