diff --git a/include/llvm/ADT/Hashing.h b/include/llvm/ADT/Hashing.h
index 06dd76a2ed7..1b0e66947b2 100644
--- a/include/llvm/ADT/Hashing.h
+++ b/include/llvm/ADT/Hashing.h
@@ -350,6 +350,16 @@ template <typename T> struct is_hashable_data
   : integral_constant<bool, ((is_integral<T>::value || is_pointer<T>::value) &&
                              64 % sizeof(T) == 0)> {};
 
+// Special case std::pair to detect when both types are viable and when there
+// is no alignment-derived padding in the pair. This is a bit of a lie because
+// std::pair isn't truly POD, but it's close enough in all reasonable
+// implementations for our use case of hashing the underlying data.
+template <typename T, typename U> struct is_hashable_data<std::pair<T, U> >
+  : integral_constant<bool, (is_hashable_data<T>::value &&
+                             is_hashable_data<U>::value &&
+                             !is_alignment_padded<std::pair<T, U> >::value &&
+                             !is_pod_pair_padded<T, U>::value)> {};
+
 /// \brief Helper to get the hashable data representation for a type.
 /// This variant is enabled when the type itself can be used.
 template <typename T>
diff --git a/include/llvm/Support/type_traits.h b/include/llvm/Support/type_traits.h
index 03f85e99971..f488a29c7af 100644
--- a/include/llvm/Support/type_traits.h
+++ b/include/llvm/Support/type_traits.h
@@ -125,6 +125,24 @@ struct is_integral : is_integral_impl<T> {};
 template <typename T> struct is_pointer : false_type {};
 template <typename T> struct is_pointer<T*> : true_type {};
 
+/// \brief Metafunction to compute whether a type requires alignment padding.
+/// When true, an object of this type will have padding bytes inside its
+/// 'sizeof' bytes.
+template <typename T> class is_alignment_padded {
+  struct pod_size_tester { T t; char c; };
+public:
+  enum { value = offsetof(pod_size_tester, c) != sizeof(T) };
+};
+
+/// \brief Metafunction to determine whether an adjacent pair of two types will
+/// require padding between them due to alignment.
+template <typename T, typename U> class is_pod_pair_padded {
+  struct pod_pair { T t; U u; };
+  struct pod_char_pair { T t; char c; };
+public:
+  enum { value = offsetof(pod_pair, u) != offsetof(pod_char_pair, c) };
+};
+
   
 // enable_if_c - Enable/disable a template based on a metafunction
 template<bool Cond, typename T = void>
diff --git a/unittests/ADT/HashingTest.cpp b/unittests/ADT/HashingTest.cpp
index a9458bb5a5a..19a036cdf53 100644
--- a/unittests/ADT/HashingTest.cpp
+++ b/unittests/ADT/HashingTest.cpp
@@ -66,11 +66,13 @@ TEST(HashingTest, HashValueBasicTest) {
   EXPECT_NE(hash_combine(42, 43), hash_value(std::make_pair(42ull, 43ull)));
   EXPECT_NE(hash_combine(42, 43), hash_value(std::make_pair(42, 43ull)));
   EXPECT_NE(hash_combine(42, 43), hash_value(std::make_pair(42ull, 43)));
-  EXPECT_EQ(hash_combine(42, hash_combine(43, hash_combine(44, 45))),
-            hash_value(
-              std::make_pair(42, std::make_pair(43, std::make_pair(44, 45)))));
-  EXPECT_EQ(hash_combine(42, 43), hash_value(std::make_pair(42, 43)));
-  EXPECT_EQ(hash_combine(42, 43), hash_value(std::make_pair(42, 43)));
+
+  // Note that pairs are implicitly flattened to a direct sequence of data and
+  // hashed efficiently as a consequence.
+  EXPECT_EQ(hash_combine(42, 43, 44),
+            hash_value(std::make_pair(42, std::make_pair(43, 44))));
+  EXPECT_EQ(hash_value(std::make_pair(42, std::make_pair(43, 44))),
+            hash_value(std::make_pair(std::make_pair(42, 43), 44)));
 }
 
 template <typename T, size_t N> T *begin(T (&arr)[N]) { return arr; }