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carbon-lang/toolchain/check/testdata/interop/cpp/import.carbon
T
Boaz Brickner 3c9d267388 Generate and use a C++ thunk to call non simple ABI C++ functions (#5850) 
When the C++ function has a parameter that is not a pointer and not a
signed integer of 32 or 64 bits, generate a thunk.

Terminology:
* Callee function: The C++ function we actually want to call.
* Thunk function: The C++ function we generated that calls the callee
function.
* A simple ABI type, for now, is one of:
  * A pointer
  * signed integer with 32 bits
  * signed integer with 64 bits

The thunk function is marked `always_inline` and uses the `asm`
attribute to set its mangled to the callee function mangled name
suffixed with `".carbon_thunk"`.

When importing a C++ function, we decide whether calling it requires a
thunk and if so we generate it and import it as well, which is currently
a recursive call.

When calling the thunk function, we initialize a temporary storage for
each non simple ABI parameter type and take its address. This can be
optimized when the variable is already in storage.

Not supported yet:
* Functions with non void return values.
* Member methods.

Moved unsigned int param test from `arithmetic_types_direct.carbon` to
`arithmetic_types_bridged.carbon`, since only signed integers aren't
bridged using a thunk.

C++ Interop Demo:

```c++
// hello_world.h

struct S {
  S() {}
  S(const S&) { x = 1; }
  int x;
};

void hello_world(S s);
```

```c++
// hello_world.cpp

#include "hello_world.h"

#include <cstdio>

void hello_world2(S s) { printf("hello_world2: %d\n", s.x); }

void hello_world(S s) {
  printf("hello_world: %d\n", s.x);
  hello_world2(s);
}
```

```carbon
// main.carbon

library "Main";

import Cpp library "hello_world.h";

fn Run() -> i32 {
  var s : Cpp.S;
  Cpp.hello_world(s);
  return 0;
}
```

```shell
$ clang -c hello_world.cpp
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link hello_world.o main.o --output=demo
$ ./demo
hello_world: 1
hello_world2: 1
```

Before this change (no thunk - copy constructor not called when calling
`hello_world()`):
```shell
$ ./demo
hello_world: -1219172304
hello_world2: 1
```
2025-08-06 10:27:33 +00:00

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// 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/int.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/import.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/import.carbon
// --- header.h
auto foo_short(short x) -> void;
auto foo_int(int x) -> void;
// --- api.carbon
library "[[@TEST_NAME]]";
import Cpp library "header.h";
alias FooShort = Cpp.foo_short;
alias FooInt = Cpp.foo_int;
// --- fail_todo_import_api.carbon
// CHECK:STDERR: fail_todo_import_api.carbon: error: semantics TODO: `Unsupported: Importing C++ functions that require thunks indirectly` [SemanticsTodo]
// CHECK:STDERR:
library "[[@TEST_NAME]]";
import library "api";
fn F() {
//@dump-sem-ir-begin
FooShort(8 as i16);
FooInt(9);
//@dump-sem-ir-end
}
// CHECK:STDOUT: --- fail_todo_import_api.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %foo_short.type: type = fn_type @foo_short [concrete]
// CHECK:STDOUT: %foo_short: %foo_short.type = struct_value () [concrete]
// CHECK:STDOUT: %int_16: Core.IntLiteral = int_value 16 [concrete]
// CHECK:STDOUT: %i16: type = class_type @Int, @Int(%int_16) [concrete]
// CHECK:STDOUT: %int_8.b85: Core.IntLiteral = int_value 8 [concrete]
// CHECK:STDOUT: %As.type.f58: type = facet_type <@As, @As(%i16)> [concrete]
// CHECK:STDOUT: %As.Convert.type.8b6: type = fn_type @As.Convert, @As(%i16) [concrete]
// CHECK:STDOUT: %To: Core.IntLiteral = bind_symbolic_name To, 0 [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.0b2: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%To) [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.6d7: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.0b2 = struct_value () [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.type.6c8: type = fn_type @Core.IntLiteral.as.As.impl.Convert, @Core.IntLiteral.as.As.impl(%To) [symbolic]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.1ee: %Core.IntLiteral.as.As.impl.Convert.type.6c8 = struct_value () [symbolic]
// CHECK:STDOUT: %As.impl_witness.ef2: <witness> = impl_witness imports.%As.impl_witness_table.a72, @Core.IntLiteral.as.As.impl(%int_16) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.type.fee: type = fn_type @Core.IntLiteral.as.As.impl.Convert, @Core.IntLiteral.as.As.impl(%int_16) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.dc5: %Core.IntLiteral.as.As.impl.Convert.type.fee = struct_value () [concrete]
// CHECK:STDOUT: %As.facet: %As.type.f58 = facet_value Core.IntLiteral, (%As.impl_witness.ef2) [concrete]
// CHECK:STDOUT: %.026: type = fn_type_with_self_type %As.Convert.type.8b6, %As.facet [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.bound: <bound method> = bound_method %int_8.b85, %Core.IntLiteral.as.As.impl.Convert.dc5 [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.specific_fn: <specific function> = specific_function %Core.IntLiteral.as.As.impl.Convert.dc5, @Core.IntLiteral.as.As.impl.Convert(%int_16) [concrete]
// CHECK:STDOUT: %bound_method.b6e: <bound method> = bound_method %int_8.b85, %Core.IntLiteral.as.As.impl.Convert.specific_fn [concrete]
// CHECK:STDOUT: %int_8.892: %i16 = int_value 8 [concrete]
// CHECK:STDOUT: %foo_int.type: type = fn_type @foo_int [concrete]
// CHECK:STDOUT: %foo_int: %foo_int.type = struct_value () [concrete]
// CHECK:STDOUT: %int_32: Core.IntLiteral = int_value 32 [concrete]
// CHECK:STDOUT: %i32: type = class_type @Int, @Int(%int_32) [concrete]
// CHECK:STDOUT: %int_9.988: Core.IntLiteral = int_value 9 [concrete]
// CHECK:STDOUT: %ImplicitAs.type.9ba: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
// CHECK:STDOUT: %ImplicitAs.Convert.type.6da: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%i32) [concrete]
// CHECK:STDOUT: %ImplicitAs.impl_witness.e34: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.e36, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.ed5: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.16d: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.ed5 = struct_value () [concrete]
// CHECK:STDOUT: %ImplicitAs.facet: %ImplicitAs.type.9ba = facet_value Core.IntLiteral, (%ImplicitAs.impl_witness.e34) [concrete]
// CHECK:STDOUT: %.d6a: type = fn_type_with_self_type %ImplicitAs.Convert.type.6da, %ImplicitAs.facet [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound: <bound method> = bound_method %int_9.988, %Core.IntLiteral.as.ImplicitAs.impl.Convert.16d [concrete]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn: <specific function> = specific_function %Core.IntLiteral.as.ImplicitAs.impl.Convert.16d, @Core.IntLiteral.as.ImplicitAs.impl.Convert(%int_32) [concrete]
// CHECK:STDOUT: %bound_method.8e3: <bound method> = bound_method %int_9.988, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
// CHECK:STDOUT: %int_9.114: %i32 = int_value 9 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
// CHECK:STDOUT: %Main.FooShort: %foo_short.type = import_ref Main//api, FooShort, loaded [concrete = constants.%foo_short]
// CHECK:STDOUT: %Main.FooInt: %foo_int.type = import_ref Main//api, FooInt, loaded [concrete = constants.%foo_int]
// CHECK:STDOUT: %Core.import_ref.a86c: @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert.type (%Core.IntLiteral.as.ImplicitAs.impl.Convert.type.0b2) = import_ref Core//prelude/parts/int, loc16_39, loaded [symbolic = @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert (constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.6d7)]
// CHECK:STDOUT: %ImplicitAs.impl_witness_table.e36 = impl_witness_table (%Core.import_ref.a86c), @Core.IntLiteral.as.ImplicitAs.impl [concrete]
// CHECK:STDOUT: %Core.import_ref.ea5: @Core.IntLiteral.as.As.impl.%Core.IntLiteral.as.As.impl.Convert.type (%Core.IntLiteral.as.As.impl.Convert.type.6c8) = import_ref Core//prelude/parts/int, loc25_39, loaded [symbolic = @Core.IntLiteral.as.As.impl.%Core.IntLiteral.as.As.impl.Convert (constants.%Core.IntLiteral.as.As.impl.Convert.1ee)]
// CHECK:STDOUT: %As.impl_witness_table.a72 = impl_witness_table (%Core.import_ref.ea5), @Core.IntLiteral.as.As.impl [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: %FooShort.ref: %foo_short.type = name_ref FooShort, imports.%Main.FooShort [concrete = constants.%foo_short]
// CHECK:STDOUT: %int_8: Core.IntLiteral = int_value 8 [concrete = constants.%int_8.b85]
// CHECK:STDOUT: %int_16: Core.IntLiteral = int_value 16 [concrete = constants.%int_16]
// CHECK:STDOUT: %i16: type = class_type @Int, @Int(constants.%int_16) [concrete = constants.%i16]
// CHECK:STDOUT: %impl.elem0.loc10: %.026 = impl_witness_access constants.%As.impl_witness.ef2, element0 [concrete = constants.%Core.IntLiteral.as.As.impl.Convert.dc5]
// CHECK:STDOUT: %bound_method.loc10_14.1: <bound method> = bound_method %int_8, %impl.elem0.loc10 [concrete = constants.%Core.IntLiteral.as.As.impl.Convert.bound]
// CHECK:STDOUT: %specific_fn.loc10: <specific function> = specific_function %impl.elem0.loc10, @Core.IntLiteral.as.As.impl.Convert(constants.%int_16) [concrete = constants.%Core.IntLiteral.as.As.impl.Convert.specific_fn]
// CHECK:STDOUT: %bound_method.loc10_14.2: <bound method> = bound_method %int_8, %specific_fn.loc10 [concrete = constants.%bound_method.b6e]
// CHECK:STDOUT: %Core.IntLiteral.as.As.impl.Convert.call: init %i16 = call %bound_method.loc10_14.2(%int_8) [concrete = constants.%int_8.892]
// CHECK:STDOUT: %.loc10_14.1: %i16 = value_of_initializer %Core.IntLiteral.as.As.impl.Convert.call [concrete = constants.%int_8.892]
// CHECK:STDOUT: %.loc10_14.2: %i16 = converted %int_8, %.loc10_14.1 [concrete = constants.%int_8.892]
// CHECK:STDOUT: %foo_short.call: init %empty_tuple.type = call %FooShort.ref(%.loc10_14.2)
// CHECK:STDOUT: %FooInt.ref: %foo_int.type = name_ref FooInt, imports.%Main.FooInt [concrete = constants.%foo_int]
// CHECK:STDOUT: %int_9: Core.IntLiteral = int_value 9 [concrete = constants.%int_9.988]
// CHECK:STDOUT: %impl.elem0.loc11: %.d6a = impl_witness_access constants.%ImplicitAs.impl_witness.e34, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.16d]
// CHECK:STDOUT: %bound_method.loc11_10.1: <bound method> = bound_method %int_9, %impl.elem0.loc11 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound]
// CHECK:STDOUT: %specific_fn.loc11: <specific function> = specific_function %impl.elem0.loc11, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
// CHECK:STDOUT: %bound_method.loc11_10.2: <bound method> = bound_method %int_9, %specific_fn.loc11 [concrete = constants.%bound_method.8e3]
// CHECK:STDOUT: %Core.IntLiteral.as.ImplicitAs.impl.Convert.call: init %i32 = call %bound_method.loc11_10.2(%int_9) [concrete = constants.%int_9.114]
// CHECK:STDOUT: %.loc11_10.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call [concrete = constants.%int_9.114]
// CHECK:STDOUT: %.loc11_10.2: %i32 = converted %int_9, %.loc11_10.1 [concrete = constants.%int_9.114]
// CHECK:STDOUT: %foo_int.call: init %empty_tuple.type = call %FooInt.ref(%.loc11_10.2)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT:
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