Re: [PATCH 2/2] libstdc++: Optimize is_scoped_enum trait performance

[Jonathan Wakely <jwakely.gcc@gmail.com>]

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On Tue, 12 Sept 2023, 01:21 Ken Matsui via Libstdc++, <libstdc++@gcc.gnu.org>
wrote:

> This patch optimizes the performance of the is_scoped_enum trait
> by dispatching to the new __is_scoped_enum built-in trait.
>

OK for trunk (after the built-in is in the front end), thanks.



> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_scoped_enum): Use
>         __is_scoped_enum built-in trait.
>         (is_scoped_enum_v): Likewise.
>
> Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> ---
>  libstdc++-v3/include/std/type_traits | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index 677cd934b94..26ae491fa69 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -3585,6 +3585,12 @@ template<typename _Ret, typename _Fn, typename...
> _Args>
>    /// True if the type is a scoped enumeration type.
>    /// @since C++23
>
> +# if _GLIBCXX_USE_BUILTIN_TRAIT(__is_scoped_enum)
> +  template<typename _Tp>
> +    struct is_scoped_enum
> +    : bool_constant<__is_scoped_enum(_Tp)>
> +    { };
> +# else
>    template<typename _Tp>
>      struct is_scoped_enum
>      : false_type
> @@ -3596,11 +3602,17 @@ template<typename _Ret, typename _Fn, typename...
> _Args>
>      struct is_scoped_enum<_Tp>
>      : bool_constant<!requires(_Tp __t, void(*__f)(int)) { __f(__t); }>
>      { };
> +# endif
>
>    /// @ingroup variable_templates
>    /// @since C++23
> +# if _GLIBCXX_USE_BUILTIN_TRAIT(__is_scoped_enum)
> +  template<typename _Tp>
> +    inline constexpr bool is_scoped_enum_v = __is_scoped_enum(_Tp);
> +# else
>    template<typename _Tp>
>      inline constexpr bool is_scoped_enum_v = is_scoped_enum<_Tp>::value;
> +# endif
>  #endif
>
>  #ifdef __cpp_lib_reference_from_temporary // C++ >= 23 &&
> ref_{converts,constructs}_from_temp
> --
> 2.42.0
>
>