[PATCH v2 2/2] libstdc++: Use new built-in trait __is_signed

[Ken Matsui via Gcc-patches]

This patch lets libstdc++ use new built-in trait __is_signed.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_signed): Use __is_signed built-in trait.
        (is_signed_v): Likewise.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/std/type_traits | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 0e7a9c9c7f3..23ab5a4b1e5 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -865,6 +865,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public __bool_constant<__is_abstract(_Tp)>
     { };
 
+  /// is_signed
+#if __has_builtin(__is_signed)
+  template<typename _Tp>
+    struct is_signed
+    : public __bool_constant<__is_signed(_Tp)>
+    { };
+#else
   /// @cond undocumented
   template<typename _Tp,
           bool = is_arithmetic<_Tp>::value>
@@ -877,11 +884,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
   /// @endcond
 
-  /// is_signed
   template<typename _Tp>
     struct is_signed
     : public __is_signed_helper<_Tp>::type
     { };
+#endif
 
   /// is_unsigned
   template<typename _Tp>
@@ -3240,8 +3247,14 @@ template <typename _Tp>
 template <typename _Tp>
   inline constexpr bool is_final_v = __is_final(_Tp);
 
+#if __has_builtin(__is_signed)
+template <typename _Tp>
+  inline constexpr bool is_signed_v = __is_signed(_Tp);
+#else
 template <typename _Tp>
   inline constexpr bool is_signed_v = is_signed<_Tp>::value;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_unsigned_v = is_unsigned<_Tp>::value;
 
-- 
2.41.0