On Mon, 23 Oct 2023, Ken Matsui wrote:

> On Mon, Oct 23, 2023 at 10:05 AM Patrick Palka <ppalka@redhat.com> wrote:
>       On Fri, Oct 20, 2023 at 12:22 PM Ken Matsui <kmatsui@gcc.gnu.org> wrote:
>       >
>       > This patch optimizes the compilation performance of std::is_invocable
>       > by dispatching to the new __is_invocable built-in trait.
>       >
>       > libstdc++-v3/ChangeLog:
>       >
>       >         * include/std/type_traits (is_invocable): Use __is_invocable
>       >         built-in trait.
> 
>       Nice!  We should use the trait directly in is_invocable_v too.
> 
> 
> Thank you! But we want to take account of static_assert’s in is_invocable, so I think we cannot use the built-in directly?

Good point, I guess that's a great reason to improvement the diagnostic
that check_trait_type emits: it'd speed up the class template version
because we could get rid of the static_asserts (without regressing
diagnostic quality), and it'd speed up the variable template version
because we could use the built-in directly there.

Your patch LGTM as is though, that could be a follow-up if anything.

> 
> 
>       >         * testsuite/20_util/is_invocable/incomplete_args_neg.cc: Handle
>       >         the new error from __is_invocable.
>       >         * testsuite/20_util/is_invocable/incomplete_neg.cc: Likewise.
>       >
>       > Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
>       > ---
>       >  libstdc++-v3/include/std/type_traits                        | 6 ++++++
>       >  .../testsuite/20_util/is_invocable/incomplete_args_neg.cc   | 1 +
>       >  .../testsuite/20_util/is_invocable/incomplete_neg.cc        | 1 +
>       >  3 files changed, 8 insertions(+)
>       >
>       > diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
>       > index 75a94cb8d7e..91851b78c7e 100644
>       > --- a/libstdc++-v3/include/std/type_traits
>       > +++ b/libstdc++-v3/include/std/type_traits
>       > @@ -3167,9 +3167,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       >      using invoke_result_t = typename invoke_result<_Fn, _Args...>::type;
>       >
>       >    /// std::is_invocable
>       > +#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_invocable)
>       > +  template<typename _Fn, typename... _ArgTypes>
>       > +    struct is_invocable
>       > +    : public __bool_constant<__is_invocable(_Fn, _ArgTypes...)>
>       > +#else
>       >    template<typename _Fn, typename... _ArgTypes>
>       >      struct is_invocable
>       >      : __is_invocable_impl<__invoke_result<_Fn, _ArgTypes...>, void>::type
>       > +#endif
>       >      {
>       >        static_assert(std::__is_complete_or_unbounded(__type_identity<_Fn>{}),
>       >         "_Fn must be a complete class or an unbounded array");
>       > diff --git a/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_args_neg.cc b/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_args_neg.cc
>       > index 34d1d9431d1..3f9e5274f3c 100644
>       > --- a/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_args_neg.cc
>       > +++ b/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_args_neg.cc
>       > @@ -18,6 +18,7 @@
>       >  // <http://www.gnu.org/licenses/>.
>       >
>       >  // { dg-error "must be a complete class" "" { target *-*-* } 0 }
>       > +// { dg-prune-output "invalid use of incomplete type" }
>       >
>       >  #include <type_traits>
>       >
>       > diff --git a/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_neg.cc b/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_neg.cc
>       > index e1e54d25ee5..92af48c48b6 100644
>       > --- a/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_neg.cc
>       > +++ b/libstdc++-v3/testsuite/20_util/is_invocable/incomplete_neg.cc
>       > @@ -18,6 +18,7 @@
>       >  // <http://www.gnu.org/licenses/>.
>       >
>       >  // { dg-error "must be a complete class" "" { target *-*-* } 0 }
>       > +// { dg-prune-output "invalid use of incomplete type" }
>       >
>       >  #include <type_traits>
>       >
>       > --
>       > 2.42.0
>       >
> 
> 
>