https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105491
--- 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:0c7bce0ac184c057bacad9c8e615ce82923835fd commit r13-211-g0c7bce0ac184c057bacad9c8e615ce82923835fd Author: Patrick Palka <ppa...@redhat.com> Date: Mon May 9 09:53:27 2022 -0400 c++: constexpr init of union sub-aggr w/ base [PR105491] Here ever since r10-7313-gb599bf9d6d1e18, reduced_constant_expression_p in C++11/14 is rejecting the marked sub-aggregate initializer (of type S) W w = {.D.2445={.s={.D.2387={.m=0}, .b=0}}}; ^ ultimately because said initializer has CONSTRUCTOR_NO_CLEARING set, hence the function must verify that all fields of S are initialized. And before C++17 it doesn't expect to see base class fields (since next_initializable_field skips over them), so the presence thereof causes r_c_e_p to return false. The reason r10-7313-gb599bf9d6d1e18 causes this is because in that commit we began using CONSTRUCTOR_NO_CLEARING to precisely track whether we're in middle of activating a union member. This ends up affecting clear_no_implicit_zero, which recurses into sub-aggregate initializers only if the outer initializer has CONSTRUCTOR_NO_CLEARING set. After that commit, the outer union initializer above no longer has the flag set at this point and so clear_no_implicit_zero no longer recurses into the marked inner initializer. But arguably r_c_e_p should be able to accept the marked initializer regardless of whether CONSTRUCTOR_NO_CLEARING is set. The primary bug therefore seems to be that r_c_e_p relies on next_initializable_field which skips over base class fields in C++11/14. To fix this, this patch introduces a new helper function next_subobject_field which is like next_initializable_field except that it never skips base class fields, and makes r_c_e_p use it. This patch then renames next_initializable_field to next_aggregate_field (and makes it skip over vptr fields again). PR c++/105491 gcc/cp/ChangeLog: * call.cc (field_in_pset): Adjust after next_initializable_field renaming. (build_aggr_conv): Likewise. (convert_like_internal): Likewise. (type_has_extended_temps): Likewise. * class.cc (default_init_uninitialized_part): Likewise. (finish_struct): Likewise. * constexpr.cc (cx_check_missing_mem_inits): Likewise. (reduced_constant_expression_p): Use next_subobject_field instead. * cp-gimplify.cc (get_source_location_impl_type): Adjust after next_initializable_field renaming. (fold_builtin_source_location): Likewise. * cp-tree.h (next_initializable_field): Rename to ... (next_aggregate_field): ... this. (next_subobject_field): Declare. * decl.cc (next_aggregate_field): Renamed from ... (next_initializable_field): ... this. Skip over vptr fields again. (next_subobject_field): Define. (reshape_init_class): Adjust after next_initializable_field renaming. * init.cc (build_value_init_noctor): Likewise. (emit_mem_initializers): Likewise. * lambda.cc (build_capture_proxy): Likewise. * method.cc (build_comparison_op): Likewise. * pt.cc (maybe_aggr_guide): Likewise. * tree.cc (structural_type_p): Likewise. * typeck2.cc (split_nonconstant_init_1): Likewise. (digest_init_r): Likewise. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/constexpr-union7.C: New test. * g++.dg/cpp0x/constexpr-union7a.C: New test. * g++.dg/cpp2a/constinit17.C: New test.
