libstdc++: Optimize std::add_rvalue_reference compilation performance

This patch optimizes the compilation performance of
std::add_rvalue_reference by dispatching to the new
__add_rvalue_reference built-in trait.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (__add_rval_ref_t): Use
	__add_rvalue_reference built-in trait.

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 79983ea980a18acc5b599991de7a55d7f7b7ea5a..a31de2ee4abb6ebc779961703855ec555ddd6426 100644 (file)
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1184,6 +1184,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 
   /// @cond undocumented
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__add_rvalue_reference)
+  template<typename _Tp>
+    using __add_rval_ref_t = __add_rvalue_reference(_Tp);
+#else
   template<typename _Tp, typename = void>
     struct __add_rvalue_reference_helper
     { using type = _Tp; };
@@ -1194,6 +1198,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Tp>
     using __add_rval_ref_t = typename __add_rvalue_reference_helper<_Tp>::type;
+#endif
   /// @endcond
 
   /// is_move_constructible