[Bug libstdc++/108554] Warning "null pointer dereferece" raised when extracting a unique_ptr from a map and any "-O" flag

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108554

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:3376467ce090aa0966d59ca3aea35db4f17a4b47

commit r13-5386-g3376467ce090aa0966d59ca3aea35db4f17a4b47
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jan 26 10:55:28 2023 +0000

    libstdc++: Add returns_nonnull to non-inline std::map detail [PR108554]

    std::map uses a non-inline function to rebalance its tree and the
    compiler can't see that it always returns a valid pointer (assuming
    valid inputs, which is a precondition anyway). This can result in
    -Wnull-derefernce warnings for valid code, because the compiler thinks
    there is a path where the function returns null.

    Adding the returns_nonnull attribute tells the compiler that is can't
    happen. While we're doing that, we might as well also add a nonnull
    attribute to the rebalancing functions too.

    libstdc++-v3/ChangeLog:

            PR libstdc++/108554
            * include/bits/stl_tree.h (_Rb_tree_insert_and_rebalance): Add
            nonnull attribute.
            (_Rb_tree_rebalance_for_erase): Add nonnull and returns_nonnull
            attributes.
            * testsuite/23_containers/map/modifiers/108554.cc: New test.