https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61947
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Created attachment 33203 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33203&action=edit proposed patch Add std::allocator_arg_t parameter to unary _Head_base constructors taking a __uses_allocN tag type, so that they are not candidates for calls with one parameter. This allows the !is_convertible constraint to be removed from the _Head_base::_Head_base(__UHead&&) constructor.
