From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id E582D3858C60; Wed, 29 Sep 2021 16:52:46 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E582D3858C60
From: "redbeard0531 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102528] Unused out-of-line functions emitted for trivial
 coroutines
Date: Wed, 29 Sep 2021 16:52:46 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redbeard0531 at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-102528-4-xdq16piKNz@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-102528-4@http.gcc.gnu.org/bugzilla/>
References: <bug-102528-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 29 Sep 2021 16:52:47 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102528

--- Comment #1 from Mathias Stearn <redbeard0531 at gmail dot com> ---
Sorry, there was a typo in the initial code. I forgot the trivial
implementation of await_resume(). (D'oh!)

Now I can see that test() is just a ret instruction, but there is still a l=
ot
of dead code emitted for the coroutine functions. While it isn't too much f=
or
the trivial functions, for a real use case it would be. And it seems like a=
 bug
anyway  that unused code makes it to the obj file in -O3:
https://godbolt.org/z/bTncofrzd

#include <coroutine>

struct simple {
    struct promise_type {
        void return_void() {}
        std::suspend_never initial_suspend() { return {}; }
        std::suspend_never final_suspend() noexcept { return {}; }
        void unhandled_exception() { throw; }
        simple get_return_object() { return {}; }
    };

    std::true_type await_ready() {return {}; }
    void await_suspend(std::coroutine_handle<>) {}
    void await_resume() {}
};

inline simple test1() {
    co_return;
}

inline simple test2() {
    co_await test1();
    co_return;
}

void test() {
    test2();
}

test1(test1()::_Z5test1v.frame*) [clone .actor]:
        movzx   eax, WORD PTR [rdi+18]
        test    al, 1
        je      .L2
        cmp     ax, 5
        ja      .L3
        mov     edx, 42
        bt      rdx, rax
        jnc     .L3
.L4:
        cmp     BYTE PTR [rdi+17], 0
        jne     .L14
.L1:
        ret
.L2:
        cmp     ax, 2
        je      .L5
        cmp     ax, 4
        je      .L4
        test    ax, ax
        jne     .L3
        mov     QWORD PTR [rdi+24], rdi
.L5:
        cmp     BYTE PTR [rdi+17], 0
        mov     BYTE PTR [rdi+32], 1
        mov     QWORD PTR [rdi], 0
        je      .L1
.L14:
        jmp     operator delete(void*)
test1(test1()::_Z5test1v.frame*) [clone .actor] [clone .cold]:
.L3:
        ud2
test2(test2()::_Z5test2v.frame*) [clone .actor]:
        movzx   eax, WORD PTR [rdi+18]
        test    al, 1
        je      .L16
        cmp     ax, 7
        ja      .L17
        mov     edx, 170
        bt      rdx, rax
        jnc     .L17
.L18:
        cmp     BYTE PTR [rdi+17], 0
        jne     .L33
.L15:
        ret
.L16:
        cmp     ax, 4
        je      .L19
        ja      .L20
        test    ax, ax
        jne     .L34
        mov     QWORD PTR [rdi+24], rdi
.L22:
        mov     BYTE PTR [rdi+32], 1
.L19:
        cmp     BYTE PTR [rdi+17], 0
        mov     QWORD PTR [rdi], 0
        je      .L15
.L33:
        jmp     operator delete(void*)
.L34:
        cmp     ax, 2
        je      .L22
        jmp     .L17
.L20:
        cmp     ax, 6
        je      .L18
        jmp     .L17
test2(test2()::_Z5test2v.frame*) [clone .actor] [clone .cold]:
.L17:
        ud2
test1(test1()::_Z5test1v.frame*) [clone .destroy]:
        movzx   eax, WORD PTR [rdi+18]
        or      eax, 1
        mov     WORD PTR [rdi+18], ax
        cmp     ax, 5
        ja      .L36
        mov     edx, 42
        bt      rdx, rax
        jnc     .L36
        cmp     BYTE PTR [rdi+17], 0
        jne     .L39
        ret
.L39:
        jmp     operator delete(void*)
test1(test1()::_Z5test1v.frame*) [clone .destroy] [clone .cold]:
.L36:
        ud2
test2(test2()::_Z5test2v.frame*) [clone .destroy]:
        movzx   eax, WORD PTR [rdi+18]
        or      eax, 1
        mov     WORD PTR [rdi+18], ax
        cmp     ax, 7
        ja      .L41
        mov     edx, 170
        bt      rdx, rax
        jnc     .L41
        cmp     BYTE PTR [rdi+17], 0
        jne     .L44
        ret
.L44:
        jmp     operator delete(void*)
test2(test2()::_Z5test2v.frame*) [clone .destroy] [clone .cold]:
.L41:
        ud2
test():
        ret=