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From: "peter at cordes dot ca" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/39942] Nonoptimal code - leaveq; xchg   %ax,%ax; retq
Date: Tue, 14 Apr 2020 21:20:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D39942

Peter Cordes <peter at cordes dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |peter at cordes dot ca

--- Comment #53 from Peter Cordes <peter at cordes dot ca> ---
I think we can close this as fixed at some point.  The last activity on this
bug was some patches that sound like they were supposed to fix, and the MCV=
Es
from comments I tested no longer has a problem.

GCC9.3 -O3 -march=3Dcore2 -fomit-frame-pointer only uses a `.p2align` to al=
ign
the top of the loop, not between leave and ret or between cmp/jcc.

void wait_for_enter()
{
    volatile int foo =3D 0;  // to get a LEAVE instruction emitted at all
        int u =3D getchar();
        while (!u)
                u =3D getchar()-13;
}

https://godbolt.org/z/RvxzZv

(Note that Godbolt normally filters .p2align so you have to either compile =
to
binary or not filter directives in the asm source.  Otherwise you'll never =
see
NOPs except in the unusual case where GCC actually emits a nop mnemonic.)=