philnik added a comment.
TBH I don't think adding these builtins is worth the extra maintenance cost.
libc++'s implementation is already really simple, and actually //uses//
`__is_constructible`, contrary to the statement in the summary. This is the
whole implementation currently:
template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_copy_constructible
: public integral_constant<
bool,
__is_constructible(_Tp, __add_lvalue_reference_t<typename
add_const<_Tp>::type>)> {};
#if _LIBCPP_STD_VER > 14
template <class _Tp>
inline constexpr bool is_copy_constructible_v =
is_copy_constructible<_Tp>::value;
#endif
I don't think adding an extra `#if __has_builtin(...)` is worth it in this
case, since we already use builtins for most of it. IMO the effort would be
better spent adding a builtin for `add_const`; that would probably make the
implementation about as efficient as adding a builtin specifically for
`is_copy_constructible`. It would effectively just be `__is_constructible(_Tp,
__add_lvalue_reference(__add_const(_Tp)))`. The `trivially` and `nothrow`
versions look very similar, just with `__is_trivially_constructible` and
`__is_nothrow_constructible` respectively.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D135238/new/
https://reviews.llvm.org/D135238
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