[Bug libstdc++/66742] abort on sorting list with custom compiler that is not stateless

["mdiluzio at feralinteractive dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66742

--- Comment #3 from Marc Di Luzio <mdiluzio at feralinteractive dot com> ---
Created attachment 35901
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35901&action=edit
main.ii

Updating with a valid ==/!= operator pair and state handling, apologies for the
original bad test case.
gcc output is the same verbatim as above.

However, sort still aborts with any allocator that provides ==/!= operators
based on internal state that is non-default.


sort contains a default constructed list __carry, which will have a different
allocator instance to the parent list if an allocator was passed in on
construction -
list.tcc:402
        list __carry;

__carry is then spliced with the parent list -
list.tcc:409
            __carry.splice(__carry.begin(), *this, begin());


A check then occurs if the two allocators are equal -
stl_list.h:1374
        if (this != &__x)
          _M_check_equal_allocators(__x);

allocator.h:188
      static bool
      _S_do_it(const _Alloc& __one, const _Alloc& __two)
      { return __one != __two; }


This final check will fail if the != operator for the allocator is dependent on
internal state comparison, which has differs from the default.

This appears to be incorrect, unless I'm misunderstanding the purpose of the
==/!= operators for allocators?

If this is still considered an issue, I would suggest that __carry be copy
constructed.