On Wed, 12 Jul 2023 at 21:42, Ken Matsui <kmat...@cs.washington.edu> wrote: > > On Wed, Jul 12, 2023 at 3:01 AM Jonathan Wakely <jwak...@redhat.com> wrote: > > > > On Mon, 10 Jul 2023 at 06:51, Ken Matsui via Libstdc++ > > <libstd...@gcc.gnu.org> wrote: > > > > > > Hi, > > > > > > Here is the benchmark result for is_pointer: > > > > > > https://github.com/ken-matsui/gcc-benches/blob/main/is_pointer.md#sun-jul--9-103948-pm-pdt-2023 > > > > > > Time: -62.1344% > > > Peak Memory Usage: -52.4281% > > > Total Memory Usage: -53.5889% > > > > Wow! > > > > Although maybe we could have improved our std::is_pointer_v anyway, like so: > > > > template <typename _Tp> > > inline constexpr bool is_pointer_v = false; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp*> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* const> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* volatile> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* const volatile> = true; > > > > I'm not sure why I didn't already do that. > > > > Could you please benchmark that? And if it is better than the current > > impl using is_pointer<_Tp>::value then we should do this in the > > library: > > > > #if __has_builtin(__is_pointer) > > template <typename _Tp> > > inline constexpr bool is_pointer_v = __is_pointer(_Tp); > > #else > > template <typename _Tp> > > inline constexpr bool is_pointer_v = false; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp*> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* const> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* volatile> = true; > > template <typename _Tp> > > inline constexpr bool is_pointer_v<_Tp* const volatile> = true; > > #endif > > Hi François and Jonathan, > > Thank you for your reviews! I will rename the four underscores to the > appropriate name and take a benchmark once I get home. > > If I apply your change on is_pointer_v, is it better to add the > `Co-authored-by:` line in the commit?
Yes, that would be the correct thing to do (although in this case the change is small enough that I don't really care about getting credit for it :-)
