--- gcc/cprop.c.mp	2012-11-26 12:13:08.631193625 +0100
+++ gcc/cprop.c	2012-11-26 14:41:32.864034283 +0100
@@ -1429,14 +1429,26 @@ find_implicit_sets (void)
 
 static int bypass_last_basic_block;
 
+/* Determine whether there is only one constant SRC rtx in the hash table
+   for REGNO.  Here we assume that for the same hash value there won't be
+   more entries with the same SRC rtx.  Return true if there is only one
+   constant, false otherwise.  */
+
+static bool
+only_one_const_p (int regno)
+{
+  struct expr *set = lookup_set (regno, &set_hash_table);
+  return next_set (regno, set) == NULL;
+}
+
 /* Find a set of REGNO to a constant that is available at the end of basic
    block BB.  Return NULL if no such set is found.  Based heavily upon
    find_avail_set.  */
 
 static struct expr *
-find_bypass_set (int regno, int bb)
+find_bypass_set (int regno, int bb, bool multiple_latches)
 {
-  struct expr *result = 0;
+  struct expr *result = NULL;
 
   for (;;)
     {
@@ -1450,9 +1462,15 @@ find_bypass_set (int regno, int bb)
 	  set = next_set (regno, set);
 	}
 
-      if (set == 0)
+      if (set == NULL)
 	break;
 
+      /* If there are more latch edges coming to the BB, we need to
+	 make sure that for the same hash value there aren't
+	 more constants.  */
+      if (multiple_latches && !only_one_const_p (regno))
+	return NULL;
+
       src = set->src;
       if (cprop_constant_p (src))
 	result = set;
@@ -1502,6 +1520,7 @@ bypass_block (basic_block bb, rtx setcc,
   int may_be_loop_header;
   unsigned removed_p;
   unsigned i;
+  unsigned n_latches;
   edge_iterator ei;
 
   insn = (setcc != NULL) ? setcc : jump;
@@ -1514,12 +1533,12 @@ bypass_block (basic_block bb, rtx setcc,
     find_used_regs (&XEXP (note, 0), NULL);
 
   may_be_loop_header = false;
+  n_latches = 0;
   FOR_EACH_EDGE (e, ei, bb->preds)
     if (e->flags & EDGE_DFS_BACK)
-      {
-	may_be_loop_header = true;
-	break;
-      }
+      n_latches++;
+
+  may_be_loop_header = n_latches > 0;
 
   change = 0;
   for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
@@ -1557,7 +1576,7 @@ bypass_block (basic_block bb, rtx setcc,
 	  struct expr *set;
 	  rtx src, new_rtx;
 
-	  set = find_bypass_set (regno, e->src->index);
+	  set = find_bypass_set (regno, e->src->index, n_latches > 1);
 
 	  if (! set)
 	    continue;
--- gcc/testsuite/gcc.dg/pr54838.c.mp	2012-11-26 14:48:43.783980854 +0100
+++ gcc/testsuite/gcc.dg/pr54838.c	2012-11-26 14:49:51.051158719 +0100
@@ -0,0 +1,24 @@
+/* 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;
+    }
+}