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Rudimentary virtual function call interop support (#6050)

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This is Itanium-specific for now (explicitly downcasting to the itanium
vtable handling code in Clang) - though it doesn't look like it'd be a
big stretch to either have conditional/two codepaths down Itanium and
MSVC in Carbon, or maybe add a virtual function in clang to avoid
needing to conditional+downcast in Carbon.

Here's a working example:
`dynamic_type.h`:
```
#ifndef TEST_H
#define TEST_H

struct A {
  virtual auto virt0() -> int;
  virtual auto virt1() -> int;
};

auto GetVal() -> A* _Nonnull;

#endif
```
`test.carbon`:
```
library "test";

import Cpp library "dynamic_type.h";
import Core library "io";

fn Run() {
  var a: Cpp.A* = Cpp.GetVal();
  Core.Print(a->virt0());
  Core.Print(a->virt1());
}
```
`dynamic_type.cpp`:
```
#include "dynamic_type.h"

auto A::virt0() -> int {
  return 0;
}

auto A::virt1() -> int {
  return 1;
}

struct B: A {
  auto virt0() -> int override {
    return 7;
  }
  auto virt1() -> int override {
    return 42;
  }
};

auto GetVal() -> A* _Nonnull {
  static B b;
  return &b;
}
```
```
$ ./bazel-bin/toolchain/carbon compile test.carbon
$ clang++-tot -g dynamic_type.cpp test.o --output=a.out
$ ./a.out
7
42
```
(linking with `carbon link` failed because we aren't linking to the C++
runtime yet, it seems, so: `ld.lld: error: undefined symbol: vtable for
__cxxabiv1::__class_type_info`)

---------

Co-authored-by: Dana Jansens <danakj@orodu.net>
This commit is contained in:
David Blaikie
2025-09-17 23:30:13 +00:00
committed by GitHub
co-authored by Dana Jansens
parent cac3578b86
commit bff0e5978b
4 changed files with 162 additions and 62 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/testdata/interop/cpp/class/struct.carbon
Vendored
+19 -16
View File
@@ -169,7 +169,7 @@ import Cpp library "dynamic.h";
fn MyF(bar: Cpp.Bar*);
//@dump-sem-ir-end
// --- fail_todo_call_dynamic.carbon
// --- call_dynamic.carbon
library "[[@TEST_NAME]]";
@@ -177,13 +177,6 @@ import Cpp library "dynamic.h";
//@dump-sem-ir-begin
fn MyF(bar: Cpp.Bar*) {
// CHECK:STDERR: fail_todo_call_dynamic.carbon:[[@LINE+7]]:3: error: semantics TODO: `Unsupported: Virtual function` [SemanticsTodo]
// CHECK:STDERR: bar->f();
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR: fail_todo_call_dynamic.carbon:[[@LINE+4]]:3: note: in call to Cpp function here [InCallToCppFunction]
// CHECK:STDERR: bar->f();
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR:
bar->f();
}
//@dump-sem-ir-end
@@ -473,16 +466,19 @@ fn MyF(bar: Cpp.Bar*);
// CHECK:STDOUT:
// CHECK:STDOUT: fn @MyF(%bar.param: %ptr);
// CHECK:STDOUT:
// CHECK:STDOUT: --- fail_todo_call_dynamic.carbon
// CHECK:STDOUT: --- call_dynamic.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %Bar: type = class_type @Bar [concrete]
// CHECK:STDOUT: %ptr.f68: type = ptr_type %Bar [concrete]
// CHECK:STDOUT: %pattern_type: type = pattern_type %ptr.f68 [concrete]
// CHECK:STDOUT: %pattern_type.146: type = pattern_type %ptr.f68 [concrete]
// CHECK:STDOUT: %MyF.type: type = fn_type @MyF [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %MyF: %MyF.type = struct_value () [concrete]
// CHECK:STDOUT: %.2e2: type = cpp_overload_set_type @<null name> [concrete]
// CHECK:STDOUT: %.2e2: type = cpp_overload_set_type @Bar.f [concrete]
// CHECK:STDOUT: %empty_struct: %.2e2 = struct_value () [concrete]
// CHECK:STDOUT: %Bar.f.type: type = fn_type @Bar.f [concrete]
// CHECK:STDOUT: %Bar.f: %Bar.f.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -491,13 +487,18 @@ fn MyF(bar: Cpp.Bar*);
// CHECK:STDOUT: import Cpp//...
// CHECK:STDOUT: }
// CHECK:STDOUT: %Bar.decl: type = class_decl @Bar [concrete = constants.%Bar] {} {}
// CHECK:STDOUT: %.6e0: %.2e2 = cpp_overload_set_value @<null name> [concrete = constants.%empty_struct]
// CHECK:STDOUT: %.6e0: %.2e2 = cpp_overload_set_value @Bar.f [concrete = constants.%empty_struct]
// CHECK:STDOUT: %Bar.f.decl: %Bar.f.type = fn_decl @Bar.f [concrete = constants.%Bar.f] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %MyF.decl: %MyF.type = fn_decl @MyF [concrete = constants.%MyF] {
// CHECK:STDOUT: %bar.patt: %pattern_type = binding_pattern bar [concrete]
// CHECK:STDOUT: %bar.param_patt: %pattern_type = value_param_pattern %bar.patt, call_param0 [concrete]
// CHECK:STDOUT: %bar.patt: %pattern_type.146 = binding_pattern bar [concrete]
// CHECK:STDOUT: %bar.param_patt: %pattern_type.146 = value_param_pattern %bar.patt, call_param0 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %bar.param: %ptr.f68 = value_param call_param0
// CHECK:STDOUT: %.loc7: type = splice_block %ptr [concrete = constants.%ptr.f68] {
@@ -512,9 +513,11 @@ fn MyF(bar: Cpp.Bar*);
// CHECK:STDOUT: fn @MyF(%bar.param: %ptr.f68) {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %bar.ref: %ptr.f68 = name_ref bar, %bar
// CHECK:STDOUT: %.loc15: ref %Bar = deref %bar.ref
// CHECK:STDOUT: %.loc8: ref %Bar = deref %bar.ref
// CHECK:STDOUT: %f.ref: %.2e2 = name_ref f, imports.%.6e0 [concrete = constants.%empty_struct]
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %.loc15, %f.ref
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %.loc8, %f.ref
// CHECK:STDOUT: %addr: %ptr.f68 = addr_of %.loc8
// CHECK:STDOUT: %Bar.f.call: init %empty_tuple.type = call imports.%Bar.f.decl(%addr)
// CHECK:STDOUT: return
// CHECK:STDOUT: }
// CHECK:STDOUT: