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Import C++ vtables (#7174)

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This correctly renders the vtable in SemIR, including allowing overrides
in
Carbon-derived-from-C++ classes.

It doesn't work in lowering because clang walks the methods of the
CXXRecordDecl - and we currently don't export anything into the
CXXRecordDecl's methods (we do export the fields) - so that's next.

This also doesn't teach Clang to affirmatively emit the vtable
regardless of the types use in C++ code - or to have Carbon use the
vtable in an object's initialization.
This commit is contained in:
David Blaikie
2026-05-11 17:33:08 +00:00
committed by GitHub
parent 0f5de499d6
commit df8b25522e
8 changed files with 508 additions and 46 deletions
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toolchain/check/testdata/interop/cpp/class/import/dynamic.carbon
Vendored
+112
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@@ -0,0 +1,112 @@
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/primitives.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/class/import/dynamic.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/class/import/dynamic.carbon
// --- dynamic_base_from_cpp.carbon
library "[[@TEST_NAME]]";
import Cpp;
inline Cpp '''
struct FurtherBase {
virtual auto further_base_func() -> int {
return 11;
}
};
struct Base: FurtherBase {
int i;
virtual auto func() -> int {
return 7;
}
};
auto Use(Base& b) -> int {
return b.func();
}
''';
base class Derived {
extend base: Cpp.Base;
virtual fn other_func[unused self: Self]() -> i32 {
return 3;
}
}
//@dump-sem-ir-begin
inline Cpp '''
// TODO: Carbon lowering should request clang to generate the vtable.
void WorkaroundToEmitCtorAndVtable() {
Carbon::Derived d;
}
// TODO: Carbon lowering should emit initialization that refers to the
// Clang-lowered vtable.
auto DoThing() -> int {
Carbon::Derived d;
return Use(d);
}
''';
//@dump-sem-ir-end
// CHECK:STDOUT: --- dynamic_base_from_cpp.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %Base: type = class_type @Base [concrete]
// CHECK:STDOUT: %FurtherBase.further_base_func.type: type = fn_type @FurtherBase.further_base_func [concrete]
// CHECK:STDOUT: %FurtherBase.further_base_func: %FurtherBase.further_base_func.type = struct_value () [concrete]
// CHECK:STDOUT: %Base.func.type: type = fn_type @Base.func [concrete]
// CHECK:STDOUT: %Base.func: %Base.func.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
// CHECK:STDOUT: .Base = %Base.decl
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %Base.decl: type = class_decl @Base [concrete = constants.%Base] {} {}
// CHECK:STDOUT: %FurtherBase.further_base_func.decl: %FurtherBase.further_base_func.type = fn_decl @FurtherBase.further_base_func [concrete = constants.%FurtherBase.further_base_func] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %Base.func.decl: %Base.func.type = fn_decl @Base.func [concrete = constants.%Base.func] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Cpp.ref.loc35: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: inline_cpp "\n// TODO: Carbon lowering should request clang to generate the vtable.\nvoid WorkaroundToEmitCtorAndVtable() {\n Carbon::Derived d;\n}\n\n// TODO: Carbon lowering should emit initialization that refers to the\n// Clang-lowered vtable.\nauto DoThing() -> int {\n Carbon::Derived d;\n return Use(d);\n}\n\n"
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: vtable @Base.vtable {
// CHECK:STDOUT: imports.%FurtherBase.further_base_func.decl
// CHECK:STDOUT: imports.%Base.func.decl
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: vtable @FurtherBase.vtable {
// CHECK:STDOUT: imports.%FurtherBase.further_base_func.decl
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: vtable @Derived.vtable {
// CHECK:STDOUT: constants.%FurtherBase.further_base_func
// CHECK:STDOUT: constants.%Base.func
// CHECK:STDOUT: @Derived.%Derived.other_func.decl
// CHECK:STDOUT: }
// CHECK:STDOUT: