--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/unittests/Support/ReverseIterationTest.cpp	Fri Oct 27 17:07:41 2017 +0900
@@ -0,0 +1,110 @@
+//===- llvm/unittest/Support/ReverseIterationTest.cpp ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+//
+// Reverse Iteration unit tests.
+//
+//===---------------------------------------------------------------------===//
+
+#include "llvm/Support/ReverseIteration.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseMapInfo.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+TEST(ReverseIterationTest, DenseMapTest1) {
+  static_assert(detail::IsPointerLike<int *>::value,
+                "int * is pointer-like");
+  static_assert(detail::IsPointerLike<uintptr_t>::value,
+                "uintptr_t is pointer-like");
+  static_assert(!detail::IsPointerLike<int>::value,
+                "int is not pointer-like");
+  static_assert(detail::IsPointerLike<void *>::value,
+                "void * is pointer-like");
+  struct IncompleteType;
+  static_assert(detail::IsPointerLike<IncompleteType *>::value,
+                "incomplete * is pointer-like");
+
+  // For a DenseMap with non-pointer-like keys, forward iteration equals
+  // reverse iteration.
+  DenseMap<int, int> Map;
+  int Keys[] = { 1, 2, 3, 4 };
+
+  // Insert keys into the DenseMap.
+  for (auto Key: Keys)
+    Map[Key] = 0;
+
+  // Note: This is the observed order of keys in the DenseMap.
+  // If there is any change in the behavior of the DenseMap, this order
+  // would need to be adjusted accordingly.
+  int IterKeys[] = { 2, 4, 1, 3 };
+
+  // Check that the DenseMap is iterated in the expected order.
+  for (const auto &Tuple : zip(Map, IterKeys))
+    ASSERT_EQ(std::get<0>(Tuple).first, std::get<1>(Tuple));
+
+  // Check operator++ (post-increment).
+  int i = 0;
+  for (auto iter = Map.begin(), end = Map.end(); iter != end; iter++, ++i)
+    ASSERT_EQ(iter->first, IterKeys[i]);
+}
+
+// Define a pointer-like int.
+struct PtrLikeInt { int value; };
+
+namespace llvm {
+
+template<> struct DenseMapInfo<PtrLikeInt *> {
+  static PtrLikeInt *getEmptyKey() {
+    static PtrLikeInt EmptyKey;
+    return &EmptyKey;
+  }
+
+  static PtrLikeInt *getTombstoneKey() {
+    static PtrLikeInt TombstoneKey;
+    return &TombstoneKey;
+  }
+
+  static int getHashValue(const PtrLikeInt *P) {
+    return P->value;
+  }
+
+  static bool isEqual(const PtrLikeInt *LHS, const PtrLikeInt *RHS) {
+    return LHS == RHS;
+  }
+};
+
+} // end namespace llvm
+
+TEST(ReverseIterationTest, DenseMapTest2) {
+  static_assert(detail::IsPointerLike<PtrLikeInt *>::value,
+                "PtrLikeInt * is pointer-like");
+
+  PtrLikeInt a = {4}, b = {8}, c = {12}, d = {16};
+  PtrLikeInt *Keys[] = { &a, &b, &c, &d };
+
+  // Insert keys into the DenseMap.
+  DenseMap<PtrLikeInt *, int> Map;
+  for (auto *Key : Keys)
+    Map[Key] = Key->value;
+
+  // Note: If there is any change in the behavior of the DenseMap,
+  // the observed order of keys would need to be adjusted accordingly.
+  if (shouldReverseIterate<PtrLikeInt *>())
+    std::reverse(&Keys[0], &Keys[4]);
+
+  // Check that the DenseMap is iterated in the expected order.
+  for (const auto &Tuple : zip(Map, Keys))
+    ASSERT_EQ(std::get<0>(Tuple).second, std::get<1>(Tuple)->value);
+
+  // Check operator++ (post-increment).
+  int i = 0;
+  for (auto iter = Map.begin(), end = Map.end(); iter != end; iter++, ++i)
+    ASSERT_EQ(iter->second, Keys[i]->value);
+}