diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 9492353..6785d69 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4929,9 +4929,11 @@
                          &ReturnValues[0], ReturnValues.size()));
   }
 
-  // As a special case, a null chain means that a tail call has been emitted and
-  // the DAG root is already updated.
+  // Assign order to nodes here. If the call does not produce a result, it won't
+  // be mapped to a SDNode and visit() will not assign it an order number.
   if (!Result.second.getNode()) {
+    // As a special case, a null chain means that a tail call has been emitted and
+    // the DAG root is already updated.
     HasTailCall = true;
     ++SDNodeOrder;
     AssignOrderingToNode(DAG.getRoot().getNode());