https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100579
Bug ID: 100579
Summary: [coroutines] Poor codegen using an optional-like type
with co_await
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rs2740 at gmail dot com
Target Milestone: ---
#ifdef __clang__
#include <experimental/coroutine>
namespace stdx = std::experimental;
#else
#include <coroutine>
namespace stdx = std;
#endif
struct O {
~O() {}
struct promise_type {
O get_return_object() { return O{this};}
stdx::suspend_never initial_suspend() { return {}; }
stdx::suspend_never final_suspend() noexcept { return {}; }
void return_void(){ value->b = true; }
void unhandled_exception(){ throw; }
auto await_transform(O o) {
struct A {
bool await_ready() {
return o_.b;
}
void await_resume() {}
void await_suspend(stdx::coroutine_handle<> h){
h.destroy();
}
O o_;
};
return A{o};
}
O* value;
};
explicit O(promise_type* p){ p->value = this; }
explicit O(bool b) : b(b) {}
bool b = false;
};
O g();
O f() { co_await g(); co_return; }
This is basically a reduced version of
https://github.com/facebook/folly/blob/99f856ae2009a80b157b5121e44b1f70f61bd7c9/folly/Optional.h#L613-L678
GCC does not appear to be able to optimize away the coroutine frame allocation,
while Clang does: https://gcc.godbolt.org/z/7981o81ne
