[PING][PATCH v3 2/2] libstdc++: use new built-in trait __is_const

[Ken Matsui <kmatsui@cs.washington.edu>]

Ping for the use of __is_const built-in.

Sincerely,
Ken Matsui

On Fri, Jul 7, 2023 at 10:27 PM Ken Matsui <kmatsui@gcc.gnu.org> wrote:
>
> This patch lets libstdc++ use new built-in trait __is_const.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_const): Use __is_const built-in trait.
>         (is_const_v): Likewise.
>
> Signed-off-by: Ken Matsui <kmatsui@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..3a46eca5377 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -764,6 +764,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    // Type properties.
>
>    /// is_const
> +#if __has_builtin(__is_const)
> +  template<typename _Tp>
> +    struct is_const
> +    : public __bool_constant<__is_const(_Tp)>
> +    { };
> +#else
>    template<typename>
>      struct is_const
>      : public false_type { };
> @@ -771,6 +777,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    template<typename _Tp>
>      struct is_const<_Tp const>
>      : public true_type { };
> +#endif
>
>    /// is_volatile
>    template<typename>
> @@ -3210,10 +3217,17 @@ template <typename _Tp>
>    inline constexpr bool is_compound_v = is_compound<_Tp>::value;
>  template <typename _Tp>
>    inline constexpr bool is_member_pointer_v = is_member_pointer<_Tp>::value;
> +
> +#if __has_builtin(__is_const)
> +template <typename _Tp>
> +  inline constexpr bool is_const_v = __is_const(_Tp);
> +#else
>  template <typename _Tp>
>    inline constexpr bool is_const_v = false;
>  template <typename _Tp>
>    inline constexpr bool is_const_v<const _Tp> = true;
> +#endif
> +
>  template <typename _Tp>
>    inline constexpr bool is_volatile_v = false;
>  template <typename _Tp>
> --
> 2.41.0
>