On Sat, 23 Dec 2023, Ken Matsui wrote:
> This patch optimizes the compilation performance of std::is_pointer
> by dispatching to the new __is_pointer built-in trait.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/cpp_type_traits.h (__is_pointer): Use
> __is_pointer built-in trait. Optimize its implementation.
> * include/std/type_traits (is_pointer): Likewise.
> (is_pointer_v): Likewise.
>
> Co-authored-by: Jonathan Wakely <jwak...@redhat.com>
> Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
> ---
> libstdc++-v3/include/bits/cpp_type_traits.h | 29 ++++++++++++++
> libstdc++-v3/include/std/type_traits | 44 +++++++++++++++++----
> 2 files changed, 65 insertions(+), 8 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h
> b/libstdc++-v3/include/bits/cpp_type_traits.h
> index 4312f32a4e0..c348df97f72 100644
> --- a/libstdc++-v3/include/bits/cpp_type_traits.h
> +++ b/libstdc++-v3/include/bits/cpp_type_traits.h
> @@ -363,6 +363,13 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
> //
> // Pointer types
> //
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
> + template<typename _Tp, bool _IsPtr = __is_pointer(_Tp)>
> + struct __is_pointer : __truth_type<_IsPtr>
> + {
> + enum { __value = _IsPtr };
> + };
> +#else
> template<typename _Tp>
> struct __is_pointer
> {
> @@ -377,6 +384,28 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
> typedef __true_type __type;
> };
>
> + template<typename _Tp>
> + struct __is_pointer<_Tp* const>
> + {
> + enum { __value = 1 };
> + typedef __true_type __type;
> + };
> +
> + template<typename _Tp>
> + struct __is_pointer<_Tp* volatile>
> + {
> + enum { __value = 1 };
> + typedef __true_type __type;
> + };
> +#endif
> +
> + template<typename _Tp>
> + struct __is_pointer<_Tp* const volatile>
> + {
> + enum { __value = 1 };
> + typedef __true_type __type;
> + };
> +
> //
> // An arithmetic type is an integer type or a floating point type
> //
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index 30b0778e58a..d53911b2fa0 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -542,19 +542,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> : public true_type { };
> #endif
>
> - template<typename>
> - struct __is_pointer_helper
> + /// is_pointer
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
> + template<typename _Tp>
> + struct is_pointer
> + : public __bool_constant<__is_pointer(_Tp)>
> + { };
> +#else
> + template<typename _Tp>
> + struct is_pointer
> : public false_type { };
>
> template<typename _Tp>
> - struct __is_pointer_helper<_Tp*>
> + struct is_pointer<_Tp*>
> : public true_type { };
>
> - /// is_pointer
> template<typename _Tp>
> - struct is_pointer
> - : public __is_pointer_helper<__remove_cv_t<_Tp>>::type
> - { };
> + struct is_pointer<_Tp* const>
> + : public true_type { };
> +
> + template<typename _Tp>
> + struct is_pointer<_Tp* volatile>
> + : public true_type { };
> +
> + template<typename _Tp>
> + struct is_pointer<_Tp* const volatile>
> + : public true_type { };
> +#endif
>
> /// is_lvalue_reference
> template<typename>
> @@ -3252,8 +3266,22 @@ template <typename _Tp, size_t _Num>
> inline constexpr bool is_array_v<_Tp[_Num]> = true;
> #endif
>
> +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
> +template <typename _Tp>
> + inline constexpr bool is_pointer_v = __is_pointer(_Tp);
> +#else
> template <typename _Tp>
> - inline constexpr bool is_pointer_v = is_pointer<_Tp>::value;
> + inline constexpr bool is_pointer_v = false;
> +template <typename _Tp>
> + inline constexpr bool is_pointer_v<_Tp*> = true;
> +template <typename _Tp>
> + inline constexpr bool is_pointer_v<_Tp* const> = true;
> +template <typename _Tp>
> + inline constexpr bool is_pointer_v<_Tp* volatile> = true;
> +template <typename _Tp>
> + inline constexpr bool is_pointer_v<_Tp* const volatile> = true;
Is this fallback implementation faster than the current implementation?
LGTM if so.
> +#endif
> +
> template <typename _Tp>
> inline constexpr bool is_lvalue_reference_v = false;
> template <typename _Tp>
> --
> 2.43.0
>
>
