https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101244
Bug ID: 101244 Summary: Wrong path in coroutine returning ternary Product: gcc Version: 11.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: victor.burckel at gmail dot com Target Milestone: --- In a coroutine returning a ternary expression with co_await, the co_await part seems to be evaluated whatever the result of the condition: See it on godbolt, I added a check of coro.done in the resume operation to avoid a crash in the clang part as the coroutine is voluntarily resumed one extra time https://godbolt.org/z/vzGKoP8d3 #include <fmt/core.h> #include <coroutine> #include <functional> #ifdef __clang__ namespace std::experimental { using std::coroutine_handle; using std::coroutine_traits; } // namespace std::experimental #endif struct task { struct promise_type; using handle_type = std::coroutine_handle<promise_type>; struct promise_type { auto initial_suspend() noexcept { return std::suspend_always{}; } auto final_suspend() noexcept { return std::suspend_always{}; } void return_value(int v) noexcept { value = v; } task get_return_object() noexcept { return task{handle_type::from_promise(*this)}; } void unhandled_exception() noexcept {} int value{}; }; task(handle_type h) : h{h} {} ~task() { if (h) { fmt::print("destroying coroutine\n"); h.destroy(); fmt::print("coroutine destroyed\n"); } } bool await_ready() const noexcept { return false; } bool await_suspend(std::coroutine_handle<>) noexcept { h.resume(); return true; } int await_resume() noexcept { return h.promise().value; } void resume() { if (!h.done()) h.resume(); } handle_type h; }; struct S { S() { fmt::print("S::S()\n"); } S(const S&) { fmt::print("S::S(const S&)\n"); } S(S&&) { fmt::print("S::S(S&&)\n"); } ~S() { fmt::print("S::~S()\n"); } }; task g(S) { fmt::print("in g()\n"); co_return 1; } task f(bool b) { fmt::print("calling g()\n"); co_return b ? co_await g(S{}) : 2; } int main() { auto task = f(false); fmt::print("resuming f\n"); task.resume(); fmt::print("resuming f\n"); task.resume(); } Gcc outputs resuming f calling g() S::S() S::S(S&&) in g() resuming f destroying coroutine S::~S() coroutine destroyed S::~S() destroying coroutine coroutine destroyed While clang outputs resuming f calling g() resuming f destroying coroutine coroutine destroyed