diff --git a/libcxx/include/tuple b/libcxx/include/tuple
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -1116,13 +1116,12 @@
 tuple(allocator_arg_t, _Alloc, tuple<_Tp...>) -> tuple<_Tp...>;
 #endif
 
+template <class ..._Ts>
+struct __all_are_swappable : __all<__is_swappable<_Ts>::value...> {};
+
 template <class ..._Tp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-typename enable_if
-<
-    __all<__is_swappable<_Tp>::value...>::value,
-    void
->::type
+typename enable_if<__all_are_swappable<_Tp...>::value>::type
 swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u)
                  _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
     {__t.swap(__u);}
diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -550,8 +550,6 @@
 
 // is_same
 
-#if __has_keyword(__is_same)
-
 template <class _Tp, class _Up>
 struct _LIBCPP_TEMPLATE_VIS is_same : _BoolConstant<__is_same(_Tp, _Up)> { };
 
@@ -560,36 +558,17 @@
 inline constexpr bool is_same_v = __is_same(_Tp, _Up);
 #endif
 
-#else
-
-template <class _Tp, class _Up> struct _LIBCPP_TEMPLATE_VIS is_same           : public false_type {};
-template <class _Tp>            struct _LIBCPP_TEMPLATE_VIS is_same<_Tp, _Tp> : public true_type {};
-
-#if _LIBCPP_STD_VER > 14
-template <class _Tp, class _Up>
-inline constexpr bool is_same_v = is_same<_Tp, _Up>::value;
-#endif
-
-#endif // __is_same
+// _IsSame<T,U> has the same effect as is_same<T,U> but instantiates fewer types:
+// is_same<A,B> and is_same<C,D> are guaranteed to be different types, but
+// _IsSame<A,B> and _IsSame<C,D> are the same type (namely, false_type).
+// If we ever need to support a compiler without the __is_same builtin,
+// we can make this an alias template for `is_same<T,U>::type`.
 
 template <class _Tp, class _Up>
-using _IsSame = _BoolConstant<
-#ifdef __clang__
-    __is_same(_Tp, _Up)
-#else
-    is_same<_Tp, _Up>::value
-#endif
->;
+using _IsSame = _BoolConstant<__is_same(_Tp, _Up)>;
 
 template <class _Tp, class _Up>
-using _IsNotSame = _BoolConstant<
-#ifdef __clang__
-    !__is_same(_Tp, _Up)
-#else
-    !is_same<_Tp, _Up>::value
-#endif
->;
-
+using _IsNotSame = _BoolConstant<!__is_same(_Tp, _Up)>;
 
 template <class _Tp>
 using __test_for_primary_template = __enable_if_t<
@@ -600,10 +579,6 @@
     __test_for_primary_template, _Tp
   >;
 
-struct __two {char __lx[2];};
-
-// helper class:
-
 // is_const
 
 #if __has_keyword(__is_const)
@@ -958,6 +933,8 @@
 
 // is_class
 
+struct __two {char __lx[2];};
+
 #if __has_feature(is_class) || defined(_LIBCPP_COMPILER_GCC)
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_class