https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94066
--- Comment #8 from CVS 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:b599bf9d6d1e180d350b71e51e08a66a1bb1546a commit r10-7313-gb599bf9d6d1e180d350b71e51e08a66a1bb1546a Author: Patrick Palka <ppa...@redhat.com> Date: Thu Mar 19 09:58:28 2020 -0400 c++: Reject changing active member of union during initialization [PR94066] This patch adds a check to detect changing the active union member during initialization of another member of the union in cxx_eval_store_expression. It uses the CONSTRUCTOR_NO_CLEARING flag as a proxy for whether the non-empty CONSTRUCTOR of UNION_TYPE we're assigning to is in the process of being initialized. This patch additionally fixes an issue in reduced_constant_expression_p where we were returning false for an uninitialized union with no active member. This lets us correctly reject the uninitialized use in the testcase testconstexpr-union4.C that we weren't before. gcc/cp/ChangeLog: PR c++/94066 * constexpr.c (reduced_constant_expression_p) [CONSTRUCTOR]: Properly handle unions without an initializer. (cxx_eval_component_reference): Emit a different diagnostic when the constructor element corresponding to a union member is NULL. (cxx_eval_bare_aggregate): When constructing a union, always set the active union member before evaluating the initializer. Relax assertion that verifies the index of the constructor element we're initializing hasn't been changed. (cxx_eval_store_expression): Diagnose changing the active union member while the union is in the process of being initialized. After setting an active union member, clear CONSTRUCTOR_NO_CLEARING on the underlying CONSTRUCTOR. (cxx_eval_constant_expression) [PLACEHOLDER_EXPR]: Don't re-reduce a CONSTRUCTOR returned by lookup_placeholder. gcc/testsuite/ChangeLog: PR c++/94066 * g++.dg/cpp1y/constexpr-union2.C: New test. * g++.dg/cpp1y/constexpr-union3.C: New test. * g++.dg/cpp1y/constexpr-union4.C: New test. * g++.dg/cpp1y/constexpr-union5.C: New test. * g++.dg/cpp1y/pr94066.C: New test. * g++.dg/cpp1y/pr94066-2.C: New test. * g++.dg/cpp1y/pr94066-3.C: New test. * g++.dg/cpp2a/constexpr-union1.C: New test.
