[Bug libstdc++/100287] New: Using iterator after std::move in ranges::partition

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100287

            Bug ID: 100287
           Summary: Using iterator after std::move in ranges::partition
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

Hi, in ranges::partition in ranges_algo.h#L2540:

  if (__first == __last)
    return {std::move(__first), std::move(__first)};

  while (std::__invoke(__pred, std::__invoke(__proj, *__first)))
    if (++__first == __last)
      return {std::move(__first), std::move(__first)};

The above two return statements std::move on __first twice. If the previous one
changes the original state of the __first, it may cause a problem.