https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119064
--- Comment #8 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:981bd3e62cd271f620892cf5db56f00b4df50156 commit r16-2206-g981bd3e62cd271f620892cf5db56f00b4df50156 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Jul 11 19:05:38 2025 +0200 c++: Implement C++26 P2786R13 - Trivial Relocatability [PR119064] The following patch implements the compiler side of the C++26 paper. Based on the https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119064#c3 feedback, the patch enables the new conditional keywords trivially_relocatable_if_eligible and replaceable_if_eligible only for C++26, for older versions those conditional keywords yield -Wc++26-compat warning and are treated as normal identifiers. Plus __trivially_relocatable_if_eligible and __replaceable_if_eligible are handled as conditional keywords always without diagnostics (similarly to __final in C++98). The patch uses __builtin_ prefix on the new traits (but unlike clang which for some weird reason chose to name one __builtin_is_replaceable and another __builtin_is_cpp_trivially_relocatable this one uses __builtin_is_replaceable and __builtin_is_trivially_relocatable. I'll try to convince clang to change, they've only implemented it recently. The patch computes these properties on demand, only when something needs them (at the expense of eating 2 more bits per lang_type, but I've recently saved 64 bits and a patch to save another 64 bits is pending; and even 4 bits wouldn't fit). The patch doesn't add __builtin_trivially_relocate builtin that clang has, std::trivially_relocate is not constexpr and I think we don't need it for now at least until we implement some kind of vtable pointer signing __builtin_memmove should do the job. Especially if libstdc++ will for clang compatibility use the builtin if available and __builtin_memmove otherwise, we can switch any time. I've cross-tested all testcases also against the clang++ trunk implementation, and both compilers agreed in everything except for https://github.com/llvm/llvm-project/issues/143599 where clang++ was changed already and https://github.com/llvm/llvm-project/issues/144232 where I believe clang++ got it wrong too. The first testcase comes from https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p2786r13.html#simple-worked-examples just tweaked so that the classes are named differently each time and that it compiles. There are 3 differences from the paper vs. the g++ as well as clang++ implementation, I've added comments into trivially-relocatable1.C but I think either that part of the paper wasn't updated through the later changes or it got it wrong. 2025-07-11 Jakub Jelinek <ja...@redhat.com> PR c++/119064 gcc/ * doc/invoke.texi (Wc++26-compat): Document. gcc/c-family/ * c.opt (Wc++26-compat): New option. * c.opt.urls: Regenerate. * c-opts.cc (c_common_post_options): Clear warn_cxx26_compat for C++26 or later. * c-cppbuiltin.cc (c_cpp_builtins): For C++26 predefine __cpp_trivial_relocatability=202502L. gcc/cp/ * cp-tree.h: Implement C++26 P2786R13 - Trivial Relocatability. (struct lang_type): Add trivially_relocatable, trivially_relocatable_computed, replaceable and replaceable_computed bitfields. Change width of dummy from 2 to 30. (CLASSTYPE_TRIVIALLY_RELOCATABLE_BIT, CLASSTYPE_TRIVIALLY_RELOCATABLE_COMPUTED, CLASSTYPE_REPLACEABLE_BIT, CLASSTYPE_REPLACEABLE_COMPUTED): Define. (enum virt_specifier): Add VIRT_SPEC_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE and VIRT_SPEC_REPLACEABLE_IF_ELIGIBLE enumerators. (trivially_relocatable_type_p, replaceable_type_p): Declare. * cp-trait.def (IS_NOTHROW_RELOCATABLE, IS_REPLACEABLE, IS_TRIVIALLY_RELOCATABLE): New traits. * parser.cc (cp_parser_class_property_specifier_seq_opt): Handle trivially_relocatable_if_eligible, __trivially_relocatable_if_eligible, replaceable_if_eligible and __replaceable_if_eligible. (cp_parser_class_head): Set CLASSTYPE_REPLACEABLE_BIT and/or CLASSTYPE_TRIVIALLY_RELOCATABLE_BIT if corresponding conditional keywords were parsed and assert corresponding *_COMPUTED macro is false. * pt.cc (instantiate_class_template): Copy over also CLASSTYPE_TRIVIALLY_RELOCATABLE_{BIT,COMPUTED} and CLASSTYPE_REPLACEABLE_{BIT,COMPUTED} bits. * semantics.cc (referenceable_type_p): Move definition earlier. (trait_expr_value): Handle CPTK_IS_NOTHROW_RELOCATABLE, CPTK_IS_REPLACEABLE and CPTK_IS_TRIVIALLY_RELOCATABLE. (finish_trait_expr): Likewise. * tree.cc (default_movable_type_p): New function. (union_with_no_declared_special_member_fns): Likewise. (trivially_relocatable_type_p): Likewise. (replaceable_type_p): Likewise. * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_NOTHROW_RELOCATABLE, CPTK_IS_REPLACEABLE and CPTK_IS_TRIVIALLY_RELOCATABLE. gcc/testsuite/ * g++.dg/cpp26/feat-cxx26.C: Add test for __cpp_trivial_relocatability. * g++.dg/cpp26/trivially-relocatable1.C: New test. * g++.dg/cpp26/trivially-relocatable2.C: New test. * g++.dg/cpp26/trivially-relocatable3.C: New test. * g++.dg/cpp26/trivially-relocatable4.C: New test. * g++.dg/cpp26/trivially-relocatable5.C: New test. * g++.dg/cpp26/trivially-relocatable6.C: New test. * g++.dg/cpp26/trivially-relocatable7.C: New test. * g++.dg/cpp26/trivially-relocatable8.C: New test. * g++.dg/cpp26/trivially-relocatable9.C: New test. * g++.dg/cpp26/trivially-relocatable10.C: New test. * g++.dg/cpp26/trivially-relocatable11.C: New test.
