On Sun, 15 Oct 2023, Ken Matsui wrote:
> This patch optimizes the performance of the is_object trait by dispatching to
> the new __is_function and __is_reference built-in traits.
>
> libstdc++-v3/ChangeLog:
> * include/std/type_traits (is_object): Use __is_function and
> __is_reference built-in traits.
> (is_object_v): Likewise.
>
> Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
> ---
> libstdc++-v3/include/std/type_traits | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index bd57488824b..674d398c075 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -725,11 +725,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { };
>
> /// is_object
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_function) \
> + && _GLIBCXX_USE_BUILTIN_TRAIT(__is_reference)
> + template<typename _Tp>
> + struct is_object
> + : public __bool_constant<!(__is_function(_Tp) || __is_reference(_Tp)
> + || is_void<_Tp>::value)>
> + { };
Since is_object is one of the more commonly used traits, we should
probably just define a built-in for it. (Either way we'd have to
repeat the logic twice, either once in the frontend and once in
the library, or twice in the library (is_object and is_object_v),
so might as well do the more efficient approach).
> +#else
> template<typename _Tp>
> struct is_object
> : public __not_<__or_<is_function<_Tp>, is_reference<_Tp>,
> is_void<_Tp>>>::type
> { };
> +#endif
>
> template<typename>
> struct is_member_pointer;
> @@ -3305,8 +3314,17 @@ template <typename _Tp>
> inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
> template <typename _Tp>
> inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
> +
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_function) \
> + && _GLIBCXX_USE_BUILTIN_TRAIT(__is_reference)
> +template <typename _Tp>
> + inline constexpr bool is_object_v
> + = !(__is_function(_Tp) || __is_reference(_Tp) || is_void<_Tp>::value);
> +#else
> template <typename _Tp>
> inline constexpr bool is_object_v = is_object<_Tp>::value;
> +#endif
> +
> template <typename _Tp>
> inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
> template <typename _Tp>
> --
> 2.42.0
>
>
