[PATCH v11 23/40] libstdc++: Optimize is_reference trait performance

[Ken Matsui via Gcc-patches]

This patch optimizes the performance of the is_reference trait by dispatching
to the new __is_reference built-in trait.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_reference): Use __is_reference built-in
        trait.
        (is_reference_v): Likewise.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/std/type_traits | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 792213ebfe8..36ad9814047 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -682,6 +682,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Composite type categories.
 
   /// is_reference
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_reference)
+  template<typename _Tp>
+    struct is_reference
+    : public __bool_constant<__is_reference(_Tp)>
+    { };
+#else
   template<typename _Tp>
     struct is_reference
     : public false_type
@@ -696,6 +702,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct is_reference<_Tp&&>
     : public true_type
     { };
+#endif
 
   /// is_arithmetic
   template<typename _Tp>
@@ -3264,12 +3271,19 @@ template <typename _Tp>
   inline constexpr bool is_class_v = __is_class(_Tp);
 template <typename _Tp>
   inline constexpr bool is_function_v = is_function<_Tp>::value;
+
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_reference)
+template <typename _Tp>
+  inline constexpr bool is_reference_v = __is_reference(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_reference_v = false;
 template <typename _Tp>
   inline constexpr bool is_reference_v<_Tp&> = true;
 template <typename _Tp>
   inline constexpr bool is_reference_v<_Tp&&> = true;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
 template <typename _Tp>
-- 
2.42.0