[Bug c++/105534] New: -Wmaybe-uninitialized shouldn't suppress -Wuninitialized warnings

["redbeard0531 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105534

            Bug ID: 105534
           Summary: -Wmaybe-uninitialized shouldn't suppress
                    -Wuninitialized warnings
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redbeard0531 at gmail dot com
  Target Milestone: ---

The following function emits a -Wuninitialized warning on ++count with -Wall
https://godbolt.org/z/KfaMEETY1:

int test(bool cond) {
    int count;
    ++count;
    return count;
}

Making the increment be conditional changes it to a -Wmaybe-uninitialized
warning, which is suppressed with -Wno-maybe-uninitialized.
https://godbolt.org/z/qarMrqW7E

int test(bool cond) {
    int count;
    if (cond) ++count;
    return count;
}

This makes no sense. count is never initialized on any path through the
function, and it is returned on all paths.

We use -Wall with -Wno-maybe-uninitialized on our codebase because we were
getting too many false-positives with -Wmaybe-initialized, in particular from
third-party headers that we didn't want to modify. At the time we decided to do
that, we didn't realize that we would also be missing out on clearly
uninitialized cases like this.