https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109536
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:3d3145e9e1461e92bef02d55d36990261dd0444d commit r14-8252-g3d3145e9e1461e92bef02d55d36990261dd0444d Author: Patrick Palka <ppa...@redhat.com> Date: Thu Jan 18 10:36:07 2024 -0500 libstdc++/debug: Fix constexpr _Safe_iterator in C++20 mode [PR109536] Some _Safe_iterator member functions define a variable of non-literal type __gnu_cxx::__scoped_lock, which automatically disqualifies them from being constexpr in C++20 mode even if that code path is never constant evaluated. This restriction was lifted by P2242R3 for C++23, but we need to work around it in C++20 mode. To that end this patch defines a pair of macros that encapsulate the lambda-based workaround mentioned in that paper and uses it to make these functions valid C++20 constexpr functions. The augmented std::vector test element_access/constexpr.cc now successfully compiles in C++20 mode with -D_GLIBCXX_DEBUG (and it should test all member functions modified by this patch). PR libstdc++/109536 libstdc++-v3/ChangeLog: * include/debug/safe_base.h (_Safe_sequence_base::_M_swap): Remove _GLIBCXX20_CONSTEXPR from non-inline member function. * include/debug/safe_iterator.h (_GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN): Define. (_GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END): Define. (_Safe_iterator::operator=): Use them around the code path that defines a variable of type __gnu_cxx::__scoped_lock. (_Safe_iterator::operator++): Likewise. (_Safe_iterator::operator--): Likewise. (_Safe_iterator::operator+=): Likewise. (_Safe_iterator::operator-=): Likewise. * testsuite/23_containers/vector/element_access/constexpr.cc (test_iterators): Test more iterator operations. * testsuite/23_containers/vector/bool/element_access/constexpr.cc (test_iterators): Likewise. * testsuite/std/ranges/adaptors/all.cc (test08) [_GLIBCXX_DEBUG]: Remove. Reviewed-by: Jonathan Wakely <jwak...@redhat.com>
