On Mon, Oct 16, 2023 at 9:36 AM Patrick Palka <ppa...@redhat.com> wrote:
>
> On Sun, 15 Oct 2023, Ken Matsui wrote:
>
> > This patch optimizes the performance of the is_pointer trait 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.
> > * include/std/type_traits (is_pointer): Likewise. Optimize its
> > implementation.
> > (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 | 8 ++++
> > libstdc++-v3/include/std/type_traits | 44 +++++++++++++++++----
> > 2 files changed, 44 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..cd5ce45951f 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 __has_builtin(__is_pointer)
>
> Why not _GLIBCXX_USE_BUILTIN_TRAIT? LGTM besides this.
>
Oops, thank you for pointing this out :)
> > + template<typename _Tp>
> > + struct __is_pointer : __truth_type<__is_pointer(_Tp)>
> > + {
> > + enum { __value = __is_pointer(_Tp) };
> > + };
>
> Nice :D
>
Yeees! But I thought this might be very confusing for someone who does
not know the new built-in behavior.
> > +#else
> > template<typename _Tp>
> > struct __is_pointer
> > {
> > @@ -376,6 +383,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
> > enum { __value = 1 };
> > typedef __true_type __type;
> > };
> > +#endif
> >
> > //
> > // 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 9c56d15c0b7..3acd843f2f2 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>
> > @@ -3254,8 +3268,22 @@ 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;
> > +#endif
> > +
> > template <typename _Tp>
> > inline constexpr bool is_lvalue_reference_v = false;
> > template <typename _Tp>
> > --
> > 2.42.0
> >
> >
>
