Re: [PATCH v2 2/3] libstdc++: Optimize is_arithmetic performance by __is_arithmetic built-in

[François Dumont via Gcc-patches]

On 15/07/2023 06:55, Ken Matsui via Libstdc++ wrote:
This patch optimizes the performance of the is_arithmetic trait by
dispatching to the new __is_arithmetic built-in trait.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (is_arithmetic): Use __is_arithmetic
        built-in trait.
        (is_arithmetic_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 0e7a9c9c7f3..7ebbe04c77b 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -655,10 +655,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
      { };
  
    /// is_arithmetic
+#if __has_builtin(__is_arithmetic)
+  template<typename _Tp>
+    struct is_arithmetic
+    : public __bool_constant<__is_arithmetic(_Tp)>
+    { };
+#else
    template<typename _Tp>
      struct is_arithmetic
      : public __or_<is_integral<_Tp>, is_floating_point<_Tp>>::type
      { };
+#endif
  
    /// is_fundamental
    template<typename _Tp>
@@ -3198,8 +3205,15 @@ template <typename _Tp>
    inline constexpr bool is_reference_v<_Tp&> = true;
  template <typename _Tp>
    inline constexpr bool is_reference_v<_Tp&&> = true;
+
+#if __has_builtin(__is_arithmetic)
+template <typename _Tp>
+  inline constexpr bool is_arithmetic_v = __is_arithmetic(_Tp);
+#else
  template <typename _Tp>
    inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
+#endif
+
  template <typename _Tp>
    inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
  template <typename _Tp>

Same remark as the one I did for __is_pointer in cpp_type_traits.h. You 
could implement it as:

  template<typename _Tp>
    struct __is_arithmetic_t
    : public __truth_type<__is_arithmetic(_Tp)>
    { };

François