diff --git a/llvm/include/llvm/ADT/PostOrderIterator.h b/llvm/include/llvm/ADT/PostOrderIterator.h
--- a/llvm/include/llvm/ADT/PostOrderIterator.h
+++ b/llvm/include/llvm/ADT/PostOrderIterator.h
@@ -292,15 +292,15 @@
 
   std::vector<NodeRef> Blocks; // Block list in normal PO order
 
-  void Initialize(NodeRef BB) {
-    std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
+  void Initialize(const GraphT &G) {
+    std::copy(po_begin(G), po_end(G), std::back_inserter(Blocks));
   }
 
 public:
   using rpo_iterator = typename std::vector<NodeRef>::reverse_iterator;
   using const_rpo_iterator = typename std::vector<NodeRef>::const_reverse_iterator;
 
-  ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
+  ReversePostOrderTraversal(const GraphT &G) { Initialize(G); }
 
   // Because we want a reverse post order, use reverse iterators from the vector
   rpo_iterator begin() { return Blocks.rbegin(); }
diff --git a/llvm/unittests/ADT/PostOrderIteratorTest.cpp b/llvm/unittests/ADT/PostOrderIteratorTest.cpp
--- a/llvm/unittests/ADT/PostOrderIteratorTest.cpp
+++ b/llvm/unittests/ADT/PostOrderIteratorTest.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 #include "llvm/ADT/PostOrderIterator.h"
+#include "TestGraph.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "gtest/gtest.h"
@@ -33,4 +34,40 @@
   auto PIExt = po_ext_end(NullBB, Ext);
   PIExt.insertEdge(Optional<BasicBlock *>(), NullBB);
 }
+
+// Test post-order and reverse post-order traversals for simple graph type.
+TEST(PostOrderIteratorTest, PostOrderAndReversePostOrderTraverrsal) {
+  Graph<6> G;
+  G.AddEdge(0, 1);
+  G.AddEdge(0, 2);
+  G.AddEdge(0, 3);
+  G.AddEdge(1, 4);
+  G.AddEdge(2, 5);
+  G.AddEdge(5, 2);
+  G.AddEdge(2, 4);
+  G.AddEdge(1, 4);
+
+  SmallVector<int> FromIterator;
+  for (auto N : post_order(G))
+    FromIterator.push_back(N->first);
+  EXPECT_EQ(6u, FromIterator.size());
+  EXPECT_EQ(4, FromIterator[0]);
+  EXPECT_EQ(1, FromIterator[1]);
+  EXPECT_EQ(5, FromIterator[2]);
+  EXPECT_EQ(2, FromIterator[3]);
+  EXPECT_EQ(3, FromIterator[4]);
+  EXPECT_EQ(0, FromIterator[5]);
+  FromIterator.clear();
+
+  ReversePostOrderTraversal<Graph<6>> RPOT(G);
+  for (auto N : RPOT)
+    FromIterator.push_back(N->first);
+  EXPECT_EQ(6u, FromIterator.size());
+  EXPECT_EQ(0, FromIterator[0]);
+  EXPECT_EQ(3, FromIterator[1]);
+  EXPECT_EQ(2, FromIterator[2]);
+  EXPECT_EQ(5, FromIterator[3]);
+  EXPECT_EQ(1, FromIterator[4]);
+  EXPECT_EQ(4, FromIterator[5]);
+}
 }