Index: include/__hash_table
===================================================================
--- include/__hash_table
+++ include/__hash_table
@@ -858,12 +858,13 @@
 #endif  // !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) && !defined(_LIBCPP_HAS_NO_VARIADICS)
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
-    template <class _ValueTp>
+    template <class _KeyTp, class _ValueTp>
     _LIBCPP_INLINE_VISIBILITY
-    pair<iterator, bool> __insert_unique_value(_ValueTp&& __x);
+    pair<iterator, bool> __insert_unique_key_value(const _KeyTp& __key, _ValueTp&& __x);
 #else
+    template <class _KeyTp, class _ValueTp>
     _LIBCPP_INLINE_VISIBILITY
-    pair<iterator, bool> __insert_unique_value(const value_type& __x);
+    pair<iterator, bool> __insert_unique_key_value(const _KeyTp& __key, const _ValueTp& __x);
 #endif
 
     pair<iterator, bool> __insert_unique(const value_type& __x);
@@ -1690,27 +1691,28 @@
 pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
 __hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique(const value_type& __x)
 {
-    return __insert_unique_value(__x);
+    return __insert_unique_key_value(__x, __x);
 }
 
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
-template <class _ValueTp>
+template <class _KeyTp, class _ValueTp>
 _LIBCPP_INLINE_VISIBILITY
 pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique_value(_ValueTp&& __x)
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique_key_value(const _KeyTp& __key, _ValueTp&& __x)
 #else
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
+template <class _KeyTp, class _RawValueTp>
 _LIBCPP_INLINE_VISIBILITY
 pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique_value(const value_type& __x)
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique_key_value(const _KeyTp& __key, const _RawValueTp& __x)
 #endif
 {
 #if defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
-    typedef const value_type& _ValueTp;
+    typedef const _RawValueTp& _ValueTp;
 #endif
-    size_t __hash = hash_function()(__x);
+    size_t __hash = hash_function()(__key);
     size_type __bc = bucket_count();
     bool __inserted = false;
     __node_pointer __nd;
@@ -1725,7 +1727,7 @@
                                        __constrain_hash(__nd->__hash_, __bc) == __chash;
                                                            __nd = __nd->__next_)
             {
-                if (key_eq()(__nd->__value_, __x))
+                if (key_eq()(__nd->__value_, __key))
                     goto __done;
             }
         }
@@ -1818,7 +1820,7 @@
 pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
 __hash_table<_Tp, _Hash, _Equal, _Alloc>::__insert_unique(value_type&& __x)
 {
-    return __insert_unique_value(_VSTD::move(__x));
+    return __insert_unique_key_value(__x, _VSTD::move(__x));
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
Index: include/unordered_map
===================================================================
--- include/unordered_map
+++ include/unordered_map
@@ -399,6 +399,9 @@
     size_t operator()(const _Cp& __x) const
         {return static_cast<const _Hash&>(*this)(__x.__cc.first);}
     _LIBCPP_INLINE_VISIBILITY
+    size_t operator()(const typename _Cp::value_type& __x) const
+        {return static_cast<const _Hash&>(*this)(__x.first);}
+    _LIBCPP_INLINE_VISIBILITY
     size_t operator()(const _Key& __x) const
         {return static_cast<const _Hash&>(*this)(__x);}
     void swap(__unordered_map_hasher&__y)
@@ -429,6 +432,9 @@
     size_t operator()(const _Cp& __x) const
         {return __hash_(__x.__cc.first);}
     _LIBCPP_INLINE_VISIBILITY
+    size_t operator()(const typename _Cp::value_type& __x) const
+        {return __hash_(__x.first);}
+    _LIBCPP_INLINE_VISIBILITY
     size_t operator()(const _Key& __x) const
         {return __hash_(__x);}
     void swap(__unordered_map_hasher&__y)
@@ -475,6 +481,9 @@
     _LIBCPP_INLINE_VISIBILITY
     bool operator()(const _Key& __x, const _Cp& __y) const
         {return static_cast<const _Pred&>(*this)(__x, __y.__cc.first);}
+    _LIBCPP_INLINE_VISIBILITY
+    bool operator()(const _Cp& __x, const typename _Cp::value_type& __y) const
+        {return static_cast<const _Pred&>(*this)(__x.__cc.first, __y.first);}
     void swap(__unordered_map_equal&__y)
         _NOEXCEPT_(__is_nothrow_swappable<_Pred>::value)
     {
@@ -508,6 +517,9 @@
     _LIBCPP_INLINE_VISIBILITY
     bool operator()(const _Key& __x, const _Cp& __y) const
         {return __pred_(__x, __y.__cc.first);}
+    _LIBCPP_INLINE_VISIBILITY
+    bool operator()(const _Cp& __x, const typename _Cp::value_type& __y) const
+        {return __pred_(__x.__cc.first, __y.first);}
     void swap(__unordered_map_equal&__y)
         _NOEXCEPT_(__is_nothrow_swappable<_Pred>::value)
     {
@@ -755,6 +767,13 @@
     template <class> friend class _LIBCPP_TYPE_VIS_ONLY __hash_const_local_iterator;
 };
 
+template <class _Key, class _Pair, class _RawPair = typename __uncvref<_Pair>::type>
+struct __is_keylike_pair : false_type {};
+
+template <class _Key, class _Pair, class _First, class _Second>
+struct __is_keylike_pair<_Key, _Pair, pair<_First, _Second> >
+    : is_same<typename remove_const<_First>::type, _Key> {};
+
 template <class _Key, class _Tp, class _Hash = hash<_Key>, class _Pred = equal_to<_Key>,
           class _Alloc = allocator<pair<const _Key, _Tp> > >
 class _LIBCPP_TYPE_VIS_ONLY unordered_map
@@ -923,8 +942,34 @@
 
     template <class... _Args>
     pair<iterator, bool> emplace(_Args&&... __args)
-        {return __table_.__emplace_unique(_VSTD::forward<_Args>(__args)...);}
+        {return __emplace_impl(_VSTD::forward<_Args>(__args)...);}
 
+private:
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_impl(_Pp&& __x)
+        {
+            return __emplace_extract_key(_VSTD::forward<_Pp>(__x),
+                                         __is_keylike_pair<key_type, _Pp>());
+        }
+    template <class _Arg1, class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_impl(_Arg1&& __arg1, _Args&&... __args)
+        {
+            return __table_.__emplace_unique(_VSTD::forward<_Arg1>(__arg1),
+                                             _VSTD::forward<_Args>(__args)...);
+        }
+
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_extract_key(_Pp&& __x, false_type)
+        {return __table_.__emplace_unique(std::forward<_Pp>(__x));}
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_extract_key(_Pp&& __x, true_type)
+        {return __table_.__insert_unique_key_value(__x.first, _VSTD::forward<_Pp>(__x));}
+
+public:
     template <class... _Args>
         _LIBCPP_INLINE_VISIBILITY
 #if _LIBCPP_DEBUG_LEVEL >= 2
@@ -943,13 +988,14 @@
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY
     pair<iterator, bool> insert(const value_type& __x)
-        {return __table_.__insert_unique(__x);}
+        {return __table_.__insert_unique_key_value(__x, __x);}
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     template <class _Pp,
               class = typename enable_if<is_constructible<value_type, _Pp>::value>::type>
-        _LIBCPP_INLINE_VISIBILITY
-        pair<iterator, bool> insert(_Pp&& __x)
-            {return __table_.__insert_unique(_VSTD::forward<_Pp>(__x));}
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> insert(_Pp&& __x)
+        {return __emplace_impl(_VSTD::forward<_Pp>(__x));}
+
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY
 #if _LIBCPP_DEBUG_LEVEL >= 2
Index: test/libcxx/containers/unord/unord.map/insert_dup_alloc.pass.cpp
===================================================================
--- /dev/null
+++ test/libcxx/containers/unord/unord.map/insert_dup_alloc.pass.cpp
@@ -0,0 +1,87 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// Check that we don't allocate when trying to insert a duplicate value into a
+// unordered_map.
+
+#include <cassert>
+#include <unordered_map>
+#include "count_new.hpp"
+#include "MoveOnly.h"
+
+int main()
+{
+    {
+    std::unordered_map<int, int> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for(int i=0; i < 100; ++i) {
+        s.insert(std::make_pair(3, i));
+        s.insert(std::make_pair(3, unsigned(i)));
+        s.insert(s.end(), std::make_pair(3, i));
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+        s.emplace(std::make_pair(3, i));
+        s.emplace_hint(s.end(), std::make_pair(3, i));
+#endif
+        {
+            const std::pair<int, int> P(3, i);
+            s.insert(P);
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+            s.emplace(P);
+            s.emplace_hint(s.end(), P);
+#endif
+        }
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(3) == 1);
+    assert(s.at(3) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+    }
+    assert(globalMemCounter.checkOutstandingNewEq(0));
+    globalMemCounter.reset();
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+    {
+    std::unordered_map<MoveOnly, MoveOnly> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for(int i=0; i<100; i++) {
+        s.insert(std::make_pair(MoveOnly(3), MoveOnly(i)));
+        s.insert(s.end(), std::make_pair(MoveOnly(3), MoveOnly(i)));
+        s.emplace(std::make_pair(MoveOnly(3), MoveOnly(i)));
+        s.emplace_hint(s.end(), std::make_pair(MoveOnly(3), MoveOnly(i)));
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(MoveOnly(3)) == 1);
+    assert(s.at(MoveOnly(3)) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+    }
+    assert(globalMemCounter.checkOutstandingNewEq(0));
+    globalMemCounter.reset();
+    {
+    std::unordered_map<int, MoveOnly> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for(int i=0; i<100; i++) {
+        s.insert(std::make_pair(3, MoveOnly(i)));
+        s.insert(s.end(), std::make_pair(3, MoveOnly(i)));
+        s.emplace(std::make_pair(3, MoveOnly(i)));
+        s.emplace_hint(s.end(), std::make_pair(3, MoveOnly(i)));
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(3) == 1);
+    assert(s.at(3) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+    }
+    assert(globalMemCounter.checkOutstandingNewEq(0));
+    globalMemCounter.reset();
+#endif
+}