See <https://wg21.link/p2647>.
Patch: <https://gcc.gnu.org/pipermail/gcc-patches/2022-November/605773.html>.
https://gcc.gnu.org/g:32d16fe9d7e347bc58e7fad316ed7923e1d0f65c commit r13-4161-g32d16fe9d7e347bc58e7fad316ed7923e1d0f65c Author: Jakub Jelinek <jakub@redhat.com> Date: Sat Nov 19 09:26:44 2022 +0100 c++: Implement C++23 P2647R1 - Permitting static constexpr variables in constexpr functions The following patch implements this paper. Per further discussions it is implemented for C++23 only, so isn't treated as a DR, e.g. because the part of the standard the paper is changing didn't even exist in C++20. And we gave up on trying to implement it as a pedwarn rather than error for C++20 and older, because of implicit constexpr lambdas or -fimplicit-constexpr reasons. For C++20 and older, the only change is that passing through definitions of static or thread_local vars usable in constant expressions is now accepted in statement expressions if they aren't inside of constexpr or consteval functions. 2022-11-19 Jakub Jelinek <jakub@redhat.com> gcc/c-family/ * c-cppbuiltin.cc (c_cpp_builtins): Bump __cpp_constexpr value from 202207L to 202211L. gcc/cp/ * constexpr.cc (cxx_eval_constant_expression): Implement C++23 P2647R1 - Permitting static constexpr variables in constexpr functions. Allow DECL_EXPRs of decl_constant_var_p static or thread_local vars. (potential_constant_expression_1): Similarly, except use decl_maybe_constant_var_p instead of decl_constant_var_p if processing_template_decl. gcc/testsuite/ * g++.dg/cpp23/constexpr-nonlit17.C: New test. * g++.dg/cpp23/constexpr-nonlit18.C: New test. * g++.dg/cpp23/feat-cxx2b.C: Adjust expected __cpp_constexpr value. * g++.dg/ext/stmtexpr19.C: Don't expect an error. * g++.dg/ext/stmtexpr25.C: New test.