https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99181
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-9 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:03e18a40070c6fe89397a73d85a38a99371cf8a1 commit r9-9424-g03e18a40070c6fe89397a73d85a38a99371cf8a1 Author: Jakub Jelinek <ja...@redhat.com> Date: Tue Feb 23 09:30:18 2021 +0100 libstdc++: Fix up constexpr std::char_traits<char>::compare [PR99181] Because of LWG 467, std::char_traits<char>::lt compares the values cast to unsigned char rather than char, so even when char is signed we get unsigned comparision. std::char_traits<char>::compare uses __builtin_memcmp and that works the same, but during constexpr evaluation we were calling __gnu_cxx::char_traits<char_type>::compare. As char_traits::lt is not virtual, __gnu_cxx::char_traits<char_type>::compare used __gnu_cxx::char_traits<char_type>::lt rather than std::char_traits<char>::lt and thus compared chars as signed if char is signed. This change fixes it by inlining __gnu_cxx::char_traits<char_type>::compare into std::char_traits<char>::compare by hand, so that it calls the right lt method. 2021-02-23 Jakub Jelinek <ja...@redhat.com> PR libstdc++/99181 * include/bits/char_traits.h (char_traits<char>::compare): For constexpr evaluation don't call __gnu_cxx::char_traits<char_type>::compare but do the comparison loop directly. * testsuite/21_strings/char_traits/requirements/char/99181.cc: New test. (cherry picked from commit 311c57f6d8f285d69e44bf94152c753900cb1a0a)
