Re: [PATCH v2 3/3] libstdc++: Optimize is_fundamental performance by __is_arithmetic built-in

[Ken Matsui <kmatsui@cs.washington.edu>]

On Sun, Jul 16, 2023 at 5:41 AM François Dumont <frs.dumont@gmail.com> wrote:
>
>
> On 15/07/2023 06:55, Ken Matsui via Libstdc++ wrote:
> > This patch optimizes the performance of the is_fundamental trait by
> > dispatching to the new __is_arithmetic built-in trait.
> >
> > libstdc++-v3/ChangeLog:
> >
> >       * include/std/type_traits (is_fundamental_v): Use __is_arithmetic
> >       built-in trait.
> >       (is_fundamental): Likewise. Optimize the original implementation.
> >
> > Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> > ---
> >   libstdc++-v3/include/std/type_traits | 21 +++++++++++++++++----
> >   1 file changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
> > index 7ebbe04c77b..cf24de2fcac 100644
> > --- a/libstdc++-v3/include/std/type_traits
> > +++ b/libstdc++-v3/include/std/type_traits
> > @@ -668,11 +668,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >   #endif
> >
> >     /// is_fundamental
> > +#if __has_builtin(__is_arithmetic)
> > +  template<typename _Tp>
> > +    struct is_fundamental
> > +    : public __bool_constant<__is_arithmetic(_Tp)
> > +                             || is_void<_Tp>::value
> > +                             || is_null_pointer<_Tp>::value>
> > +    { };
>
> What about doing this ?
>
>    template<typename _Tp>
>      struct is_fundamental
>      : public __bool_constant<__is_arithmetic(_Tp)
>                               || __or_<is_void<_Tp>,
>                                       is_null_pointer<_Tp>>::value>
>      { };
>
> Based on your benches it seems that builtin __is_arithmetic is much better that std::is_arithmetic. But __or_ could still avoid instantiation of is_null_pointer.
>
Let me take a benchmark for this later.