[Bug libstdc++/100153] Undefined behavior in stl_bvector.h

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100153

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:

https://gcc.gnu.org/g:c04b0f63243d4d474daa66f84874ebf6b9e7b0cd

commit r11-9281-gc04b0f63243d4d474daa66f84874ebf6b9e7b0cd
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Apr 20 16:16:13 2021 +0100

    libstdc++: Do not allocate a zero-size vector<bool> [PR 100153]

    The vector<bool>::shrink_to_fit() implementation will allocate new
    storage even if the vector is empty. That then leads to the
    end-of-storage pointer being non-null and equal to the _M_start._M_p
    pointer, which means that _M_end_addr() has undefined behaviour.

    The fix is to stop doing a useless zero-sized allocation in
    shrink_to_fit(), so that _M_start._M_p and _M_end_of_storage are both
    null after an empty vector shrinks.

    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

    libstdc++-v3/ChangeLog:

            PR libstdc++/100153
            * include/bits/vector.tcc (vector<bool>::_M_shrink_to_fit()):
            When size() is zero just deallocate and reset.

    (cherry picked from commit 681707ec28d56494fa61a80c62500724d55f8586)