Open
Description
Hi, clang community
I want to discuss an unusual usage of coroutine and CRTP. The following code gives the expected result using MSVC, but a unpredictable result using GCC and clang. Intert a printf into final_suspend helps clang give the expected result.
A similar discussion is on GCC Bugzilla.
https://godbolt.org/z/5rGjKPhW1
clang version: 16.0.0 ~ trunk
Build option: -std=c++20 -O2
#include <cstdio>
#include <utility>
#include <coroutine>
template<class T>
struct CRCoro { // Curiously Recurring Coroutine
struct RValueWrapper {
T* p;
operator T&&() const noexcept { return std::move(*p); }
};
using promise_type = T;
T& getDerived() noexcept { return *static_cast<T*>(this); }
auto get_return_object() noexcept { return RValueWrapper(&getDerived()); }
std::suspend_never initial_suspend() noexcept { return {}; }
std::suspend_never final_suspend() noexcept {
//printf("final_suspend\n");
return {};
}
void return_value(T&& x) noexcept { getDerived() = std::move(x); }
void unhandled_exception() {}
};
struct A : public CRCoro<A> {
int a;
};
A func() {
A aa{};
aa.a = 5;
co_return std::move(aa);
}
int main() {
printf("%d\n", func().a);
return 0;
}
Expected result(MSVC): 5
Possible result of clang: -387938488