diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 76a60f0..96bf9cd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -46,6 +46,20 @@
 STATISTIC(PostIndexedNodes, "Number of post-indexed nodes created");
 
 namespace {
+#ifndef NDEBUG
+  static cl::opt<bool>
+    ViewDAGCombine1("view-dag-combine1-dags", cl::Hidden,
+                    cl::desc("Pop up a window to show dags before the first "
+                             "dag combine pass"));
+  static cl::opt<bool>
+    ViewDAGCombine2("view-dag-combine2-dags", cl::Hidden,
+                    cl::desc("Pop up a window to show dags before the second "
+                             "dag combine pass"));
+#else
+  static const bool ViewDAGCombine1 = false;
+  static const bool ViewDAGCombine2 = false;
+#endif
+  
   static cl::opt<bool>
     CombinerAA("combiner-alias-analysis", cl::Hidden,
                cl::desc("Turn on alias analysis during testing"));
@@ -4512,6 +4526,10 @@
 // SelectionDAG::Combine - This is the entry point for the file.
 //
 void SelectionDAG::Combine(bool RunningAfterLegalize, AliasAnalysis &AA) {
+  if (!RunningAfterLegalize && ViewDAGCombine1)
+    viewGraph();
+  if (RunningAfterLegalize && ViewDAGCombine2)
+    viewGraph();
   /// run - This is the main entry point to this class.
   ///
   DAGCombiner(*this, AA).Run(RunningAfterLegalize);