[PATCH v26 01/13] libstdc++: Optimize std::is_const compilation performance

[Patrick Palka]

On Sat, 11 May 2024, Ken Matsui wrote:

> This patch optimizes the compilation performance of std::is_const
> by dispatching to the new __is_const built-in trait.

This patch series LGTM

> 
> 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 | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
> index b441bf9908f..8df0cf3ac3b 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -835,6 +835,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    // Type properties.
>  
>    /// is_const
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_const)
> +  template<typename _Tp>
> +    struct is_const
> +    : public __bool_constant<__is_const(_Tp)>
> +    { };
> +#else
>    template<typename>
>      struct is_const
>      : public false_type { };
> @@ -842,6 +848,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>    template<typename _Tp>
>      struct is_const<_Tp const>
>      : public true_type { };
> +#endif
>  
>    /// is_volatile
>    template<typename>
> @@ -3331,10 +3338,15 @@ template <typename _Tp>
>    inline constexpr bool is_member_pointer_v = is_member_pointer<_Tp>::value;
>  #endif
>  
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__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
>  
>  #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_function)
>  template <typename _Tp>
> -- 
> 2.44.0
> 
>