Re: [PATCH 12/14] libstdc++: Optimize std::is_signed compilation performance

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 10 Jan 2024 at 19:47, Ken Matsui <kmatsui@gcc.gnu.org> wrote:
>
> This patch optimizes the compilation performance of std::is_signed
> by dispatching to the new __is_signed built-in trait.

OK for trunk (if the new built-in is approved).


>
> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_signed): Use __is_signed built-in
>         trait.
>         (is_signed_v): Likewise.
>
> Signed-off-by: Ken Matsui <kmatsui@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 4bcfb1389e3..b917c743aea 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -968,6 +968,13 @@ _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>
> @@ -980,11 +987,11 @@ _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)
> @@ -3418,8 +3425,13 @@ 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>
> --
> 2.43.0
>