libstdc++: Optimize std::is_reference compilation performance

This patch optimizes the compilation performance of std::is_reference
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 <kmatsui@gcc.gnu.org>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 1edd05acb4cbbb5535bd351500faf80f26118de8..db880d87f601c35c4a8516514d2c74c3ce3cd8ab 100644 (file)
--- 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>
@@ -3250,12 +3257,19 @@ 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>