[PATCH v17 37/39] libstdc++: Optimize is_signed trait performance

[Ken Matsui]

This patch optimizes the performance of the is_signed trait by dispatching to
the new __is_signed built-in trait.

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 | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index f7d3815f332..7e93923f44b 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -982,6 +982,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public __bool_constant<__is_abstract(_Tp)>
     { };
 
+  /// is_signed
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__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>
@@ -994,11 +1001,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
   /// @endcond
 
-  /// is_signed
   template<typename _Tp>
     struct is_signed
     : public __is_signed_helper<_Tp>::type
     { };
+#endif
 
   /// is_unsigned
 #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_unsigned)
@@ -3445,8 +3452,13 @@ template <typename _Tp>
 template <typename _Tp>
   inline constexpr bool is_final_v = __is_final(_Tp);
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__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
 
 #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_unsigned)
 template <typename _Tp>
-- 
2.42.0