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? - : 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? > > 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. > >
