diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a54e9490afe..1a09dcc78c3 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2011-10-26  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/50763
+	* tree-ssa-tail-merge.c (replace_block_by): Update vops if phi_vuse1 or
+	phi_vuse2 is NULL_TREE only if bb1 dominates or is dominated by bb2.
+
 2011-10-26  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/41844
diff --git a/gcc/tree-ssa-tail-merge.c b/gcc/tree-ssa-tail-merge.c
index f7b2f5278d7..eb4bc92bd62 100644
--- a/gcc/tree-ssa-tail-merge.c
+++ b/gcc/tree-ssa-tail-merge.c
@@ -1551,7 +1551,12 @@ replace_block_by (basic_block bb1, basic_block bb2, bool update_vops)
       phi_vuse1 = vop_at_entry (bb1);
 
       /* If both are not found, it means there's no need to update.  */
-      update_vops = phi_vuse1 != NULL_TREE || phi_vuse2 != NULL_TREE;
+      if (phi_vuse1 == NULL_TREE && phi_vuse2 == NULL_TREE)
+	update_vops = false;
+      else if (phi_vuse1 == NULL_TREE)
+	update_vops = dominated_by_p (CDI_DOMINATORS, bb1, bb2);
+      else if (phi_vuse2 == NULL_TREE)
+	update_vops = dominated_by_p (CDI_DOMINATORS, bb2, bb1);
     }
 
   if (phi_vuse1 && gimple_bb (SSA_NAME_DEF_STMT (phi_vuse1)) == bb1)