On Mon, Oct 23, 2023 at 10:00 AM Patrick Palka <ppalka@redhat.com> wrote:

> On Sun, 22 Oct 2023, Ken Matsui wrote:
>
> > Hi Patrick,
> >
> > There is an issue with the code in
> > libstdc++-v3/include/bits/cpp_type_traits.h. Specifically, Clang 16
> > does not accept the code, while Clang 17 does. Given that we aim to
> > support the last two versions of Clang, we need to ensure that Clang
> > 16 accepts this code. Can you please advise on the best course of
> > action regarding this matter?
>
> The following workaround seems to make Clang happy:
>
>     #include <type_traits>
>
>     template<typename T, bool B = __is_pointer(T)>
>     struct __is_pointer : std::bool_constant<B> { };
>

Ooh, this makes sense. Thank you!


> >
> > https://godbolt.org/z/PbxhYcb7q
> >
> > Sincerely,
> > Ken Matsui
> >
> > On Fri, Oct 20, 2023 at 7:12 AM Ken Matsui <kmatsui@gcc.gnu.org> 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.
> > >         * include/std/type_traits (is_pointer): Likewise. Optimize its
> > >         implementation.
> > >         (is_pointer_v): Likewise.
> > >
> > > Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
> > > Signed-off-by: Ken Matsui <kmatsui@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..246f2cc0b17 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>
> > > +    struct __is_pointer : __truth_type<__is_pointer(_Tp)>
> > > +    {
> > > +      enum { __value = __is_pointer(_Tp) };
> > > +    };
> > > +#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 0641ecfdf2b..75a94cb8d7e 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;
> > > +#endif
> > > +
> > >  template <typename _Tp>
> > >    inline constexpr bool is_lvalue_reference_v = false;
> > >  template <typename _Tp>
> > > --
> > > 2.42.0
> > >
> >
> >