https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109536
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:7d00a59229ee17af009a3c6c6208b0611740ed49 commit r14-6553-g7d00a59229ee17af009a3c6c6208b0611740ed49 Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed Dec 6 13:39:52 2023 +0000 libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536] This makes constexpr std::vector (mostly) work in Debug Mode. All safe iterator instrumentation and checking is disabled during constant evaluation, because it requires mutex locks and calls to non-inline functions defined in libstdc++.so. It should be OK to disable the safety checks, because most UB should be detected during constant evaluation anyway. We could try to enable the full checking in constexpr, but it would mean wrapping all the non-inline functions like _M_attach with an inline _M_constexpr_attach that does the iterator housekeeping inline without mutex locks when called for constant evaluation, and calls the non-inline function at runtime. That could be done in future if we find that we've lost safety or useful checking by disabling the safe iterators. There are a few test failures in C++20 mode, which I'm unable to explain. The _Safe_iterator::operator++() member gives errors for using non-constexpr functions during constant evaluation, even though those functions are guarded by std::is_constant_evaluated() checks. The same code works fine for C++23 and up. libstdc++-v3/ChangeLog: PR libstdc++/109536 * include/bits/c++config (__glibcxx_constexpr_assert): Remove macro. * include/bits/stl_algobase.h (__niter_base, __copy_move_a) (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux) (__lexicographical_compare_aux): Add constexpr to overloads for debug mode iterators. * include/debug/helper_functions.h (__unsafe): Add constexpr. * include/debug/macros.h (_GLIBCXX_DEBUG_VERIFY_COND_AT): Remove macro, folding it into ... (_GLIBCXX_DEBUG_VERIFY_AT_F): ... here. Do not use __glibcxx_constexpr_assert. * include/debug/safe_base.h (_Safe_iterator_base): Add constexpr to some member functions. Omit attaching, detaching and checking operations during constant evaluation. * include/debug/safe_container.h (_Safe_container): Likewise. * include/debug/safe_iterator.h (_Safe_iterator): Likewise. * include/debug/safe_iterator.tcc (__niter_base, __copy_move_a) (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux) (__lexicographical_compare_aux): Add constexpr. * include/debug/vector (_Safe_vector, vector): Add constexpr. Omit safe iterator operations during constant evaluation. * testsuite/23_containers/vector/bool/capacity/constexpr.cc: Remove dg-xfail-if for debug mode. * testsuite/23_containers/vector/bool/cmp_c++20.cc: Likewise. * testsuite/23_containers/vector/bool/cons/constexpr.cc: Likewise. * testsuite/23_containers/vector/bool/element_access/1.cc: Likewise. * testsuite/23_containers/vector/bool/element_access/constexpr.cc: Likewise. * testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc: Likewise. * testsuite/23_containers/vector/bool/modifiers/constexpr.cc: Likewise. * testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc: Likewise. * testsuite/23_containers/vector/capacity/constexpr.cc: Likewise. * testsuite/23_containers/vector/cmp_c++20.cc: Likewise. * testsuite/23_containers/vector/cons/constexpr.cc: Likewise. * testsuite/23_containers/vector/data_access/constexpr.cc: Likewise. * testsuite/23_containers/vector/element_access/constexpr.cc: Likewise. * testsuite/23_containers/vector/modifiers/assign/constexpr.cc: Likewise. * testsuite/23_containers/vector/modifiers/constexpr.cc: Likewise. * testsuite/23_containers/vector/modifiers/swap/constexpr.cc: Likewise. * testsuite/23_containers/vector/cons/destructible_debug_neg.cc: Adjust dg-error line number.
