https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120777
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:f86ebb00406dafed3b8ebeae6e9e9d613abdf2ec commit r16-1751-gf86ebb00406dafed3b8ebeae6e9e9d613abdf2ec Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Jun 27 23:39:30 2025 +0200 c++: Implement C++26 P3533R2 - constexpr virtual inheritance [PR120777] The following patch implements the C++26 P3533R2 - constexpr virtual inheritance paper. The changes include not rejecting it for C++26, tweaking the error wording to show that it is valid in C++26, adjusting synthesized_method_walk not to make synthetized cdtors non-constexpr just because of virtual base classes in C++26 and various tweaks in constexpr.cc so that it can deal with the expressions used for virtual base member accesses or cdtor calls which need __in_chrg and/or __vtt_parm arguments to be passed in some cases implicitly when they aren't passed explicitly. And dynamic_cast constant evaluation tweaks so that it handles also expressions with types with virtual bases. 2025-06-27 Jakub Jelinek <ja...@redhat.com> PR c++/120777 gcc/ * gimple-fold.cc (gimple_get_virt_method_for_vtable): Revert 2018-09-18 changes. gcc/c-family/ * c-cppbuiltin.cc (c_cpp_builtins): Predefine __cpp_constexpr_virtual_inheritance=202506L for C++26. gcc/cp/ * constexpr.cc: Implement C++26 P3533R2 - constexpr virtual inheritance. (is_valid_constexpr_fn): Don't reject constexpr cdtors in classes with virtual bases for C++26, adjust error wording. (cxx_bind_parameters_in_call): Add ORIG_FUN argument, add values for __in_chrg and __vtt_parm arguments when needed. (cxx_eval_dynamic_cast_fn): Adjust function comment, HINT -1 should be possible. For C++26 if obj is cast from POINTER_PLUS_EXPR, attempt to use cxx_fold_indirect_ref to simplify it and if successful, build ADDR_EXPR of that. (cxx_eval_call_expression): Add orig_fun variable, set it to fun before looking through clones, pass it to cxx_bind_parameters_in_call. (reduced_constant_expression_p): Add SZ argument, pass DECL_SIZE of FIELD_DECL e.index to recursive calls and don't return false if SZ is non-NULL and there are unfilled fields with bit position at or above SZ. (cxx_fold_indirect_ref_1): Handle reading of vtables using ptrdiff_t dynamic type instead of some pointer type. Set el_sz to DECL_SIZE_UNIT value rather than TYPE_SIZE_UNIT of DECL_FIELD_IS_BASE fields in classes with virtual bases. (cxx_fold_indirect_ref): In canonicalize_obj_off lambda look through COMPONENT_REFs with DECL_FIELD_IS_BASE in classes with virtual bases and adjust off correspondingly. Remove assertion that off is integer_zerop, pass tree_to_uhwi (off) instead of 0 to the cxx_fold_indirect_ref_1 call. * cp-tree.h (publicly_virtually_derived_p): Declare. (reduced_constant_expression_p): Add another tree argument defaulted to NULL_TREE. * method.cc (synthesized_method_walk): Don't clear *constexpr_p if there are virtual bases for C++26. * class.cc (build_base_path): Compute fixed_type_p and virtual_access before checks for build_simple_base_path instead of after that and conditional cp_build_addr_expr. Use build_simple_path if !virtual_access even when v_binfo is non-NULL. (layout_virtual_bases): For build_base_field calls use access_public_node rather than access_private_node if publicly_virtually_derived_p. (build_vtbl_initializer): Revert 2018-09-18 and 2018-12-11 changes. (publicly_virtually_derived_p): New function. gcc/testsuite/ * g++.dg/cpp26/constexpr-virt-inherit1.C: New test. * g++.dg/cpp26/constexpr-virt-inherit2.C: New test. * g++.dg/cpp26/constexpr-virt-inherit3.C: New test. * g++.dg/cpp26/feat-cxx26.C: Add __cpp_constexpr_virtual_inheritance tersts. * g++.dg/cpp2a/constexpr-dtor3.C: Don't expect one error for C++26. * g++.dg/cpp2a/constexpr-dtor16.C: Don't expect errors for C++26. * g++.dg/cpp2a/constexpr-dynamic10.C: Likewise. * g++.dg/cpp0x/constexpr-ice21.C: Likewise. * g++.dg/cpp0x/constexpr-ice4.C: Likewise. * g++.dg/abi/mangle1.C: Guard the test on c++23_down. * g++.dg/abi/mangle81.C: New test. * g++.dg/ipa/ipa-icf-4.C (A::A): For __cpp_constexpr_virtual_inheritance >= 202506L add user provided non-constexpr constructor.
