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 B1A4A3858406; Mon, 21 Feb 2022 06:29:17 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B1A4A3858406
From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/51954] __int128_t (and long long on x86) negation can be
 optimized
Date: Mon, 21 Feb 2022 06:29:17 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 4.7.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: crazylht at gmail dot com
X-Bugzilla-Status: NEW
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-51954-4-nI6VtLc8hV@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-51954-4@http.gcc.gnu.org/bugzilla/>
References: <bug-51954-4@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: Mon, 21 Feb 2022 06:29:17 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D51954

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> We get this now:
>=20
>         movq    %rdi, %rax
>         movq    %rsi, %rdx
>         negq    %rax
>         adcq    $0, %rdx
>         negq    %rdx
>=20
> ICC produces:
>         xorl      %edx, %edx                                    #3.10
>         xorl      %eax, %eax                                    #3.10
>         subq      %rdi, %rax                                    #3.10
>         sbbq      %rsi, %rdx                                    #3.10
>         ret                                                     #3.10
>=20
> Which seems even better.
>=20
> LLVM does produce:
>         movq    %rdi, %rax
>         xorl    %edx, %edx
>         negq    %rax
>         sbbq    %rsi, %rdx
>=20
> Which basically combines the addcq and negq together and changes one mov
> into an exor.

Yes, neg rdx =3D (0 - rdx) =3D (0 - (rdx + CF)(last def)) =3D (sbb 0, rdx)=