https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99426
--- Comment #11 from Patrick Palka <ppalka at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:716af95fd454871473c4b118b8412b6a68459b75 commit r14-9948-716af95fd454871473c4b118b8412b6a68459b75 Author: Patrick Palka <ppa...@redhat.com> c++/modules: local type merging [PR99426] One known missing piece in the modules implementation is merging of a streamed-in local type (class or enum) with the corresponding in-TU version of the local type. This missing piece turns out to cause a hard-to-reduce use-after-free GC issue due to the entity_ary not being marked as a GC root (deliberately), and manifests as a serialization error on stream-in as in PR99426 (see comment #6 for a reduction). It's also reproducible on trunk when running the xtreme-header tests without -fno-module-lazy. This patch implements this missing piece, making us merge such local types according to their position within the containing function's definition, analogous to how we merge FIELD_DECLs of a class according to their index in the TYPE_FIELDS list. PR c++/99426 gcc/cp/ChangeLog: * module.cc (merge_kind::MK_local_type): New enumerator. (merge_kind_name): Update. (trees_out::chained_decls): Move BLOCK-specific handling of DECL_LOCAL_DECL_P decls to ... (trees_out::core_vals) <case BLOCK>: ... here. Stream BLOCK_VARS manually. (trees_in::core_vals) <case BLOCK>: Stream BLOCK_VARS manually. Handle deduplicated local types.. (trees_out::key_local_type): Define. (trees_in::key_local_type): Define. (trees_out::get_merge_kind) <case FUNCTION_DECL>: Return MK_local_type for a local type. (trees_out::key_mergeable) <case FUNCTION_DECL>: Use key_local_type. (trees_in::key_mergeable) <case FUNCTION_DECL>: Likewise. (trees_in::is_matching_decl): Be flexible with type mismatches for local entities. (trees_in::register_duplicate): Also register the DECL_TEMPLATE_RESULT of a TEMPLATE_DECL as a duplicate. (depset_cmp): Return 0 for equal IDENTIFIER_HASH_VALUEs. gcc/testsuite/ChangeLog: * g++.dg/modules/merge-17.h: New test. * g++.dg/modules/merge-17_a.H: New test. * g++.dg/modules/merge-17_b.C: New test. * g++.dg/modules/xtreme-header-7_a.H: New test. * g++.dg/modules/xtreme-header-7_b.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
