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From: "antoshkka at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/115309] New: Simple coroutine based generator is not optimized well Date: Fri, 31 May 2024 14:41:03 +0000 [thread overview] Message-ID: <bug-115309-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115309 Bug ID: 115309 Summary: Simple coroutine based generator is not optimized well Product: gcc Version: 15.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: antoshkka at gmail dot com Target Milestone: --- Consider the following minimal C++ coroutine based generator: #include <coroutine> namespace { struct generator { struct promise_type { using handle = std::coroutine_handle<promise_type>; unsigned value{}; generator get_return_object() noexcept { return generator{handle::from_promise(*this)}; } std::suspend_never initial_suspend() noexcept { return {}; } std::suspend_always final_suspend() noexcept { return {}; } void return_void() noexcept {} void unhandled_exception() { __builtin_abort(); } std::suspend_always yield_value(unsigned v) noexcept { value = v; return {}; } }; ~generator() noexcept { m_coro.destroy(); } unsigned operator*() { return m_coro.promise().value; } private: promise_type::handle m_coro; explicit generator(promise_type::handle coro) noexcept: m_coro{coro} {} }; generator generate_1() { co_yield 1; } } unsigned test() { auto gen = generate_1(); return *gen; } The expected assembly is: test(): mov eax, 1 ret However, trunk GCC with `-O2 -std=c++23` flags generates 60+ instructions with dynamic merory allocations and function calls. Godbolt playground: https://godbolt.org/z/6PvfTfx9n Looks that the main part of the problem is the missing allocation elision for coroutine. Note that the same problem arises with the Standard C++ std::generator: https://godbolt.org/z/EvEPT7d1T
next reply other threads:[~2024-05-31 14:41 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-05-31 14:41 antoshkka at gmail dot com [this message] 2024-05-31 14:59 ` [Bug ipa/115309] " pinskia at gcc dot gnu.org
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