[Bug c++/107488] [13 Regression] -Werror=dangling-reference false positives in cppunit

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107488

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:32a06ce38a38bf37db468f0e6c83520fcc221534

commit r13-3642-g32a06ce38a38bf37db468f0e6c83520fcc221534
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Nov 1 17:05:52 2022 -0400

    c++: Quash -Wdangling-reference for member operator* [PR107488]

    -Wdangling-reference complains here:

      std::vector<int> v = ...;
      std::vector<int>::const_iterator it = v.begin();
      while (it != v.end()) {
        const int &r = *it++; // warning
      }

    because it sees a call to
    __gnu_cxx::__normal_iterator<const int*, std::vector<int> >::operator*
    which returns a reference and its argument is a TARGET_EXPR representing
    the result of
    __gnu_cxx::__normal_iterator<const int*, std::vector<int> >::operator++
    But 'r' above refers to one of the int elements of the vector 'v', not
    to a temporary object.  Therefore the warning is a false positive.

    I suppose code like the above is relatively common (the warning broke
    cppunit-1.15.1 and a few other projects), so presumably it makes sense
    to suppress the warning when it comes to member operator*.  In this case
    it's defined as

          reference
          operator*() const _GLIBCXX_NOEXCEPT
          { return *_M_current; }

    and I'm guessing a lot of member operator* are like that, at least when
    it comes to iterators.  I've looked at _Fwd_list_iterator,
    _Fwd_list_const_iterator, __shared_ptr_access, _Deque_iterator,
    istream_iterator, etc, and they're all like that, so adding #pragmas
    would be quite tedious.  :/

            PR c++/107488

    gcc/cp/ChangeLog:

            * call.cc (do_warn_dangling_reference): Quash -Wdangling-reference
            for member operator*.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wdangling-reference5.C: New test.