Something like this should probably be backported to GCC 14 too, since my change in r14-9232-g3685fae23bb008 inadvertantly caused ICEs that this fixes. But without the previous patch this patch will cause ABI changes, and I'm not sure how easily it would be to divorce those changes from the fix here.
I suppose probably the true issue is that r14-9232 inadvertantly changed ABI for lambdas in base classes, and we should just revert the parser.cc changes for 14.3? (And accept that it'll regress those modules tests.) -- >8 -- This is a step closer to implementing the suggested changes for https://github.com/itanium-cxx-abi/cxx-abi/pull/85. Most lambdas defined within a class should have an extra scope of that class so that uses across different TUs are properly merged by the linker. This also needs to happen during template instantiation. While I was working on this I found some other cases where the mangling of lambdas was incorrect and causing issues, notably the testcase lambda-ctx3.C which currently emits the same mangling for the base class and member lambdas, causing mysterious assembler errors since r14-9232. This is also the root cause of PR c++/118245. One notable case not handled either here or in the ABI is what is supposed to happen with lambdas declared in alias templates; see lambda-ctx4.C. I believe that by the C++ standard, such lambdas should also dedup across TUs, but this isn't currently implemented (for class-scope or not). I wasn't able to work out how to fix the mangling logic for this case easily so I've just excluded alias templates from the class-scope mangling rules in template instantiation. Since this should only affect usage of lambdas in unevaluated contexts (a C++20 feature) this patch does not add an ABI flag to control this behaviour. PR c++/118245 gcc/cp/ChangeLog: * cp-tree.h (LAMBDA_EXPR_EXTRA_SCOPE): Adjust comment. * parser.cc (cp_parser_class_head): Start (and do not finish) lambda scope for all valid types. (cp_parser_class_specifier): Finish lambda scope after parsing members instead. (cp_parser_member_declaration): Adjust comment to mention missing lambda scoping for static member initializers. * pt.cc (instantiate_class_template): Add lambda scoping. (instantiate_template): Likewise. gcc/testsuite/ChangeLog: * g++.dg/abi/lambda-ctx3.C: New test. * g++.dg/abi/lambda-ctx4.C: New test. * g++.dg/cpp2a/lambda-uneval20.C: New test. Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com> --- gcc/cp/cp-tree.h | 3 ++- gcc/cp/parser.cc | 23 ++++++++++++-------- gcc/cp/pt.cc | 14 +++++++++++- gcc/testsuite/g++.dg/abi/lambda-ctx3.C | 21 ++++++++++++++++++ gcc/testsuite/g++.dg/abi/lambda-ctx4.C | 22 +++++++++++++++++++ gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C | 7 ++++++ 6 files changed, 79 insertions(+), 11 deletions(-) create mode 100644 gcc/testsuite/g++.dg/abi/lambda-ctx3.C create mode 100644 gcc/testsuite/g++.dg/abi/lambda-ctx4.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index f77a325bdd0..824b7bb61ae 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -1562,7 +1562,8 @@ enum cp_lambda_default_capture_mode_type { (((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->locus) /* The mangling scope for the lambda: FUNCTION_DECL, PARM_DECL, VAR_DECL, - FIELD_DECL or NULL_TREE. If this is NULL_TREE, we have no linkage. */ + FIELD_DECL, TYPE_DECL, or NULL_TREE. If this is NULL_TREE, we have no + linkage. */ #define LAMBDA_EXPR_EXTRA_SCOPE(NODE) \ (((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->extra_scope) diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc index dd986444449..c851185a86d 100644 --- a/gcc/cp/parser.cc +++ b/gcc/cp/parser.cc @@ -27313,6 +27313,8 @@ cp_parser_class_specifier (cp_parser* parser) if (!braces.require_open (parser)) { pop_deferring_access_checks (); + if (type != error_mark_node) + finish_lambda_scope (); return error_mark_node; } @@ -27377,7 +27379,10 @@ cp_parser_class_specifier (cp_parser* parser) if (cp_parser_allow_gnu_extensions_p (parser)) attributes = cp_parser_gnu_attributes_opt (parser); if (type != error_mark_node) - type = finish_struct (type, attributes); + { + type = finish_struct (type, attributes); + finish_lambda_scope (); + } if (nested_name_specifier_p) pop_inner_scope (old_scope, scope); @@ -28217,6 +28222,12 @@ cp_parser_class_head (cp_parser* parser, if (flag_concepts) type = associate_classtype_constraints (type); + /* Lambdas in bases and members must have the same mangling scope for ABI. + We open this scope now, and will close it in cp_parser_class_specifier + after parsing the member list. */ + if (type && type != error_mark_node) + start_lambda_scope (TYPE_NAME (type)); + /* We will have entered the scope containing the class; the names of base classes should be looked up in that context. For example: @@ -28231,16 +28242,10 @@ cp_parser_class_head (cp_parser* parser, if (cp_lexer_next_token_is (parser->lexer, CPP_COLON)) { if (type) - { - pushclass (type); - start_lambda_scope (TYPE_NAME (type)); - } + pushclass (type); bases = cp_parser_base_clause (parser); if (type) - { - finish_lambda_scope (); - popclass (); - } + popclass (); } else bases = NULL_TREE; diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index dfaa8906a2c..cb234b53a55 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -12604,6 +12604,10 @@ instantiate_class_template (tree type) gcc_assert (!DECL_CLASS_SCOPE_P (TYPE_MAIN_DECL (pattern)) || COMPLETE_OR_OPEN_TYPE_P (TYPE_CONTEXT (type))); + /* When instantiating nested lambdas, ensure that they get the mangling + scope of the new class type. */ + start_lambda_scope (TYPE_NAME (type)); + base_list = NULL_TREE; /* Defer access checking while we substitute into the types named in the base-clause. */ @@ -12965,6 +12969,8 @@ instantiate_class_template (tree type) finish_struct_1 (type); TYPE_BEING_DEFINED (type) = 0; + finish_lambda_scope (); + /* Remember if instantiating this class ran into errors, so we can avoid instantiating member functions in limit_bad_template_recursion. We set this flag even if the problem was in another instantiation triggered by @@ -22530,6 +22536,8 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain) ctx = tsubst_entering_scope (DECL_CONTEXT (gen_tmpl), targ_ptr, complain, gen_tmpl); push_nested_class (ctx); + if (!DECL_ALIAS_TEMPLATE_P (gen_tmpl)) + start_lambda_scope (TYPE_NAME (ctx)); } tree pattern = DECL_TEMPLATE_RESULT (gen_tmpl); @@ -22559,7 +22567,11 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain) if (fndecl == NULL_TREE) fndecl = tsubst_decl (pattern, targ_ptr, complain, /*use_spec_table=*/false); if (DECL_CLASS_SCOPE_P (gen_tmpl)) - pop_nested_class (); + { + if (!DECL_ALIAS_TEMPLATE_P (gen_tmpl)) + finish_lambda_scope (); + pop_nested_class (); + } pop_from_top_level (); if (fndecl == error_mark_node) diff --git a/gcc/testsuite/g++.dg/abi/lambda-ctx3.C b/gcc/testsuite/g++.dg/abi/lambda-ctx3.C new file mode 100644 index 00000000000..f92f2500531 --- /dev/null +++ b/gcc/testsuite/g++.dg/abi/lambda-ctx3.C @@ -0,0 +1,21 @@ +// { dg-do compile { target c++20 } } +// { dg-additional-options "-fkeep-inline-functions" } +// See also https://github.com/itanium-cxx-abi/cxx-abi/pull/85 + +struct A { + decltype([]{ return 1; }) f; +}; + +struct B : decltype([]{ return 2; }) { + decltype([]{ return 3; }) f; +}; + +struct C : decltype([]{ return 4; }) { + decltype([]{ return 5; }) f; +}; + +// { dg-final { scan-assembler {_ZNK1AUlvE_clEv:} } } +// { dg-final { scan-assembler {_ZNK1BUlvE_clEv:} } } +// { dg-final { scan-assembler {_ZNK1BUlvE0_clEv:} } } +// { dg-final { scan-assembler {_ZNK1CUlvE_clEv:} } } +// { dg-final { scan-assembler {_ZNK1CUlvE0_clEv:} } } diff --git a/gcc/testsuite/g++.dg/abi/lambda-ctx4.C b/gcc/testsuite/g++.dg/abi/lambda-ctx4.C new file mode 100644 index 00000000000..d6544a84652 --- /dev/null +++ b/gcc/testsuite/g++.dg/abi/lambda-ctx4.C @@ -0,0 +1,22 @@ +// { dg-do compile { target c++20 } } +// { dg-additional-options "-fkeep-inline-functions" } + +struct S { + template <int I> + using T = decltype([]{ return I; }); +}; + +S::T<0> a; +S::T<1> b; + +int main() { + a(); + b(); +} + +// Currently we don't implement any special mangling rules for template aliases +// (though we probably should; an alias template is a definable item by +// [basic.def.odr] p1.5 and as such contained lambdas in different TUs should have +// the same type, see [basic.def.odr] p15.6) +// { scan_assembler {_ZNK1SUlvE_clEv:} } +// { scan_assembler {_ZNK1SUlvE0_clEv:} } diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C new file mode 100644 index 00000000000..fa009f53ff2 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C @@ -0,0 +1,7 @@ +// PR c++/118245 +// { dg-do compile { target c++20 } } + +template<auto> struct Cask {}; +struct T1 : Cask<[]{}> { + Cask<[]{}> c{}; +}; -- 2.47.0
