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

[François Dumont via Gcc-patches]

On 17/07/2023 06:48, Ken Matsui wrote:
On Sun, Jul 16, 2023 at 5:32 AM François Dumont <frs.dum...@gmail.com> wrote:

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

Thank you for your review! This is from the type_traits header, so the
name should be as-is.

Here I meant that current libstdc++ implementation of 
std::__is_arithmetic in cpp_type_traits.h should also make use of the 
builtin __is_arithmetic that you are introducing. That is to say replace 
this:

  template<typename _Tp>
    struct __is_arithmetic
    : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
    { };

by:

#if __has_builtin(__is_arithmetic)

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

#else

  template<typename _Tp>
    struct __is_arithmetic_t
    : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
    { };

#endif

if you replace '__is_arithmetic' by '__is_arithmetic_t' for the 
libstdc++, just adapt to the name you eventually adopt.