Remove dead SD nodes after the combining pass. Fixes PR12201.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154786 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d1b998f..0914c66 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1080,6 +1080,7 @@
 
   // If the root changed (e.g. it was a dead load, update the root).
   DAG.setRoot(Dummy.getValue());
+  DAG.RemoveDeadNodes();
 }
 
 SDValue DAGCombiner::visit(SDNode *N) {