https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121789
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> (In reply to Avi Kivity from comment #0)
> > Likely the memcpyable detection web gets confused by the move_iterator
>
> Yes, I think that is the reason.
IIRC I thought that move_iterator would match this condition:
else if constexpr (contiguous_iterator<_ForwardIterator>
&& contiguous_iterator<_InputIterator>)
but its iterator_concept is clamped to be no higher than
random_access_iterator_tag, even if it adapts a contiguous iterator.
The __memcpyable<_Dest, _Src>::__value condition is false because we only
unwrap __normal_iterator and not move_iterator:
using _Dest = decltype(std::__niter_base(__result));
using _Src = decltype(std::__niter_base(__first));
We would need to also use __miter_base.
