On Tue, Aug 8, 2023 at 1:19 PM Jonathan Wakely <jwak...@redhat.com> wrote: > > > > On Tue, 18 Jul 2023 at 07:25, Ken Matsui via Libstdc++ > <libstd...@gcc.gnu.org> wrote: >> >> 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% > > > But what about the fallback implementation of is_fundamental where we don't > have the __is_arithmetic built-in?
That fallback implementation would be this: https://github.com/ken-matsui/gsoc23/blob/967e20770599f2a8925c9794669111faef11beb7/is_fundamental.cc#L11-L15. The is_fundamental-disjunction.cc benchmark used the USE_BUILTIN macro, but in this benchmark, I used it to just switch two different implementations that use the __is_arithmetic built-in. > - : public __or_<is_arithmetic<_Tp>, is_void<_Tp>, > - is_null_pointer<_Tp>>::type > + : public __bool_constant<is_arithmetic<_Tp>::value > + || is_void<_Tp>::value > + || is_null_pointer<_Tp>::value> > > Here the use of __or_ means that for is_fundamental<int> we don't instantiate > is_void<int> and is_null_pointer<int>. Isn't that still worthwhile? > Let me take a benchmark with __or_ later! We may see a difference. > > > >> >> >> 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. >>
