On Tue, Aug 8, 2023 at 1:14 PM Jonathan Wakely <jwak...@redhat.com> wrote: > > > > On Tue, 18 Jul 2023 at 07:28, Ken Matsui via Libstdc++ > <libstd...@gcc.gnu.org> wrote: >> >> I will eventually work on disjunction to somehow optimize, but in the >> meantime, this might be a better implementation. Of course, my >> benchmark could be wrong. > > > You should use __or_ internally in libstdc++ code, not std::disjunction. > > Patrick already optimized both of those, and __or_ is slightly faster > (because it doesn't have to conform to the full requirements of > std::disjunction). > I will! Thank you!
> A compiler built-in for __or_ / __disjunction might perform better. But > eventually if we're going to have built-ins for all of __is_arithmetic, > __is_void, and __is_null_pointer, then we would want simply: > > __is_arithmetic(T) || __is_void(T) || __is_null_pointer(T) > > and so we wouldn't need to avoid instantiating any class templates at all. > I think we are not going to define built-ins for is_void and is_null_pointer as their type trait implementations are already optimal. > >> >> >> On Mon, Jul 17, 2023 at 11:24 PM Ken Matsui <kmat...@cs.washington.edu> >> 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% >> > >> > 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. >>
