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

[Ken Matsui via Gcc-patches]

Hi,

I took a benchmark for this.

https://github.com/ken-matsui/gcc-benches/blob/main/is_fundamental-disjunction.md#mon-jul-17-105937-pm-pdt-2023

template<typename _Tp>
struct is_fundamental
: public std::bool_constant<__is_arithmetic(_Tp)
                            || std::is_void<_Tp>::value
                            || std::is_null_pointer<_Tp>::value>
{ };

is faster than:

template<typename _Tp>
struct is_fundamental
: public std::bool_constant<__is_arithmetic(_Tp)
                            || std::disjunction<std::is_void<_Tp>,
                                                std::is_null_pointer<_Tp>
                                                >::value>
{ };

Time: -32.2871%
Peak Memory: -18.5071%
Total Memory: -20.1991%

Sincerely,
Ken Matsui

On Sun, Jul 16, 2023 at 9:49 PM Ken Matsui <kmat...@cs.washington.edu> wrote:
>
> On Sun, Jul 16, 2023 at 5:41 AM François Dumont <frs.dum...@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 <kmat...@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.