https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118035
--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-12 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:d14333852ebd77b898b3bf1030f9bf5152497345 commit r12-11054-gd14333852ebd77b898b3bf1030f9bf5152497345 Author: Jonathan Wakely <jwak...@redhat.com> Date: Mon Dec 16 17:42:24 2024 +0000 libstdc++: Fix std::deque::insert(pos, first, last) undefined behaviour [PR118035] Inserting an empty range into a std::deque results in undefined calls to either std::copy, std::copy_backward, std::move, or std::move_backward. We call those algos with invalid arguments where the output range is the same as the input range, e.g. std::copy(first, last, first) which violates the preconditions for the algorithms. This fix simply returns early if there's nothing to insert. Most callers already ensure that we don't even call _M_range_insert_aux with an empty range, but some callers don't. Rather than checking for n == 0 in each of the callers, this just does the check once and uses __builtin_expect to treat empty insertions as unlikely. libstdc++-v3/ChangeLog: PR libstdc++/118035 * include/bits/deque.tcc (_M_range_insert_aux): Return immediately if inserting an empty range. * testsuite/23_containers/deque/modifiers/insert/118035.cc: New test. (cherry picked from commit b273e25e11c842a5729d0e03c85088cf5ba8e06c)
