On Tue, Jun 13, 2023 at 10:10 PM François Dumont <frs.dum...@gmail.com> wrote:
>
>
> On 13/06/2023 00:22, Ken Matsui via Libstdc++ wrote:
> > This patch gets std::is_object to dispatch to new built-in traits,
> > __is_function, __is_reference, and __is_void.
> >
> > libstdc++-v3/ChangeLog:
> > * include/std/type_traits (is_object): Use new built-in traits,
> > __is_function, __is_reference, and __is_void.
> > (__is_object): Define this built-in-like macro.
> > (is_object_v): Use built-in traits through the build-in-like macro.
> >
> > Signed-off-by: Ken Matsui <kmat...@cs.washington.edu>
> > ---
> > libstdc++-v3/include/std/type_traits | 19 +++++++++++++++++++
> > 1 file changed, 19 insertions(+)
> >
> > diff --git a/libstdc++-v3/include/std/type_traits
> > b/libstdc++-v3/include/std/type_traits
> > index 780fcc00135..93335f94385 100644
> > --- a/libstdc++-v3/include/std/type_traits
> > +++ b/libstdc++-v3/include/std/type_traits
> > @@ -682,11 +682,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > { };
> >
> > /// is_object
> > +#if __has_builtin(__is_function) && __has_builtin(__is_reference) \
> > + && __has_builtin(__is_void)
> > +
> > +#define __is_object(_Tp) \
> > + (!(__is_function(_Tp) || __is_reference(_Tp) || __is_void(_Tp)))
>
> Is this evaluation order random ? Are all those builtin functions
> performances equivalent ?
>
> I would have felt that __is_void is the simplest/fastest cause only for
> 'void' so would have put it first.
This particular order is derived from the original implementation:
```
template<typename _Tp>
struct is_object
: public __not_<__or_<is_function<_Tp>, is_reference<_Tp>,
is_void<_Tp>>>::type
{ };
```
>From what I can see, it appears there shouldn't be any disparities in
performance based on these implementations in /gcc/cp/semantics.cc:
```
+ case CPTK_IS_FUNCTION:
+ return type_code1 == FUNCTION_TYPE;
+ case CPTK_IS_REFERENCE:
+ return type_code1 == REFERENCE_TYPE;
+ case CPTK_IS_VOID:
+ return VOID_TYPE_P (type1);
```
VOID_TYPE_P: gcc/tree.h
```
/* Nonzero if this type is the (possibly qualified) void type. */
#define VOID_TYPE_P(NODE) (TREE_CODE (NODE) == VOID_TYPE)
```
> > +
> > + template<typename _Tp>
> > + struct is_object
> > + : public __bool_constant<__is_object(_Tp)>
> > + { };
> > +#else
> > template<typename _Tp>
> > struct is_object
> > : public __not_<__or_<is_function<_Tp>, is_reference<_Tp>,
> > is_void<_Tp>>>::type
> > { };
> > +#endif
> >
> > template<typename>
> > struct is_member_pointer;
> > @@ -3235,8 +3247,15 @@ template <typename _Tp>
> > inline constexpr bool is_arithmetic_v = is_arithmetic<_Tp>::value;
> > template <typename _Tp>
> > inline constexpr bool is_fundamental_v = is_fundamental<_Tp>::value;
> > +
> > +#ifdef __is_object
> > +template <typename _Tp>
> > + inline constexpr bool is_object_v = __is_object(_Tp);
> > +#else
> > template <typename _Tp>
> > inline constexpr bool is_object_v = is_object<_Tp>::value;
> > +#endif
> > +
> > template <typename _Tp>
> > inline constexpr bool is_scalar_v = is_scalar<_Tp>::value;
> > template <typename _Tp>
