https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111703
--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-12 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:6a31302a6c8bec9af3c93f736c2b1a76e9a530e2 commit r12-10016-g6a31302a6c8bec9af3c93f736c2b1a76e9a530e2 Author: Patrick Palka <ppa...@redhat.com> Date: Wed Nov 15 12:03:16 2023 -0500 c++: constantness of local var in constexpr fn [PR111703, PR112269] potential_constant_expression was incorrectly treating most local variables from a constexpr function as constant because it wasn't considering the 'now' parameter. This patch fixes this by relaxing its var_in_maybe_constexpr_fn checks accordingly, which turns out to partially fix two recently reported regressions: PR111703 is a regression caused by r11-550-gf65a3299a521a4 for restricting constexpr evaluation during warning-dependent folding. The mechanism is intended to restrict only constant evaluation of the instantiated non-dependent expression, but it also ends up restricting constant evaluation occurring during instantiation of the expression, in particular when instantiating the converted argument 'x' (a VIEW_CONVERT_EXPR) into a copy constructor call. This seems like a flaw in the mechanism, though I don't know if we want to fix the mechanism or get rid of it completely since the original testcases which motivated the mechanism are fixed more simply by r13-1225-gb00b95198e6720. In any case, this patch partially fixes this by making us correctly treat 'x' as non-constant which prevents the problematic warning-dependent folding from occurring at all. PR112269 is caused by r14-4796-g3e3d73ed5e85e7 for merging tsubst_copy into tsubst_copy_and_build. tsubst_copy used to exit early when 'args' was empty, behavior which that commit deliberately didn't preserve. This early exit masked the fact that COMPLEX_EXPR wasn't handled by tsubst at all, and is a tree code that apparently we could see during warning-dependent folding on some targets. A complete fix is to add handling for this tree code in tsubst_expr, but this patch should fix the reported testsuite failures since the COMPLEX_EXPRs that crop up in <complex> are considered non-constant expressions after this patch. PR c++/111703 PR c++/112269 gcc/cp/ChangeLog: * constexpr.cc (potential_constant_expression_1) <case VAR_DECL>: Only consider var_in_maybe_constexpr_fn if 'now' is false. <case INDIRECT_REF>: Likewise. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-fn8.C: New test. (cherry picked from commit 6665a8572c8f24bd55c6081c91f461442c94dcfb)
