As proposed in [Carbon: C++ interop for overloaded functions and
function
templates](https://docs.google.com/document/d/1KUxumZtNe3mY3TsjW2s_ZADOlAaFlrtsLKHVILtqIaM/edit?tab=t.0),
Clang is used to perform the overload resolution using C++ rules, when
an overloaded C++ set is called from Carbon. Once a function is
selected, it's converted into a Carbon function and called using the
Carbon rules including argument conversions.
A single non-templated function is treated the same way as an overload
set and the same rules apply for its call.
Template functions are not supported yet.
Demo:
a) Non-templated function calls:
```c++
// --- overloads.h
auto foo(int a, short b) -> void;
auto foo(double a) -> void;
auto foo(int a) -> void;
```
```c++
// overloads.cpp
#include "overloads.h"
#include <cstdio>
auto foo(int a, short b) -> void {
printf("hello from foo_int_short(%d, %d) \n", a, b);
}
auto foo(double a) -> void { printf("hello from foo_double(%f) \n", a); }
auto foo(int a) -> void { printf("hello from foo_int(%d) \n", a); }
```
```c++
library "Main";
import Cpp library "overloads.h";
fn Run() -> i32 {
Cpp.foo(1.1 as f64);
return 0;
}
```
```
$ clang -c overloads.cpp
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link overloads.o main.o --output=demo
$ ./demo
hello from foo_double(1.100000)
```
b) Constructors:
```c++
// --- constructor_overloads.h
class C {
public:
C();
C(int a, int b);
};
```
```c++
// constructor_overloads.cpp
#include "constructor_overloads.h"
#include <cstdio>
C::C() { printf("hello from C() \n"); }
C::C(int a, int b) { printf("hello from C(%d, %d) \n", a, b); }
```
```c++
library "Main";
import Cpp library "constructor_overloads.h";
fn Run() -> i32 {
let c1: Cpp.C = Cpp.C.C();
let c2: Cpp.C = Cpp.C.C(1, 2);
return 0;
}
```
```
$ clang -c constructor_overloads.cpp
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link constructor_overloads.o main.o \--output=demo
$ ./demo
hello from C()
hello from C(1, 2)
```
Follow-ups:
- `Cpp.foo({})` - proper handling of struct literals as call args.
- Fix access for overloaded sets.
- Fix tests:
- Method calls: `error: missing object argument in method call
[MissingObjectInMethodCall]` in tests.
- Fix `toolchain/check/testdata/interop/cpp/import.carbon` test.
- Fix `enums` support.
- Fix `str` -> `std::string_view` mapping.
Part of #5915
Instead of hardcoding which types are copyable, add a `Core.Copy`
interface to perform copying. Move almost all the current copy support
to that interface. Some remaining pieces are still using builtin logic
after this PR:
* For tuples and structs, builtin logic is used to perform elementwise
copies. This also supports copying *adapters of* tuples and structs,
which seems like it may not be desirable, especially for non-extending
adapters. A `Copy` impl is provided for tuples of at most 2 elements, so
that `Core.Copy` constraints are satisfied, but we can't implement this
generally until we have variadics support, and don't yet have a
mechanism to generalize this to structs.
* For `enum` types imported from C++, builtin logic is used to perform a
copy. This is temporary until we have a mechanism to identify these
types from an impl in the prelude.
One lowering test in `toolchain/lower/testdata/class/generic.carbon` is
disabled for now, as it causes a crash in the lowering code due to an
ABI mismatch between the call signature in the lowered declaration of a
specific function and the call that is generated in the specific callee.
Fixing this is a little involved, and will be done in a separate PR.
---------
Co-authored-by: Geoff Romer <gromer@google.com>
This avoids impl lookups involving, say, `Core.Int` pulling in all ~65
impls in "prelude/types/int", which resulted in a lot of unnecessary
importing work, followed by a lot of unnecessary inst namer and inst
formatter work.
Before:
```
Ran 1335 tests in 6186 ms wall time, 146818 ms across threads
Slowest tests:
- toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon: 5611 ms, 5532 ms in Run
- toolchain/check/testdata/interop/cpp/function/operators.carbon: 2034 ms, 1981 ms in Run
- toolchain/check/testdata/primitives/import_symbolic.carbon: 1796 ms, 1786 ms in Run
- toolchain/lower/testdata/operators/arithmetic.carbon: 1729 ms, 1728 ms in Run
- toolchain/lower/testdata/function/generic/call_recursive_sccs_deep.carbon: 1700 ms, 1697 ms in Run
[==========] 1335 tests from 1 test suite ran. (682 ms total)
```
After:
```
Ran 1335 tests in 2419 ms wall time, 109587 ms across threads
Slowest tests:
- toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon: 1748 ms, 1665 ms in Run
- toolchain/check/testdata/interop/cpp/function/operators.carbon: 1106 ms, 1057 ms in Run
- toolchain/lower/testdata/function/generic/call_recursive_diamond.carbon: 1044 ms, 1041 ms in Run
- toolchain/lower/testdata/function/generic/call_recursive_sccs_deep.carbon: 1015 ms, 1012 ms in Run
- toolchain/lower/testdata/operators/arithmetic.carbon: 998 ms, 997 ms in Run
[==========] 1335 tests from 1 test suite ran. (652 ms total)
```
That's still slower than it should be, but a large improvement
nonetheless.
Fixes#6029
This uses each vector's size as a barrier between lists, to eliminate
the possibility of incidental collisions between entries of different
lists. This is the same as is done inside `AddBlock`.
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
```
Ivana Ivanovska
Richard SmithandGeoff Romer
Jon Ross-Perkins
Boaz Brickner