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 04BB438460B4; Mon, 17 May 2021 03:11:45 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 04BB438460B4
From: "guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/59371] [9/10/11/12 Regression] Performance regression in
 GCC 4.8/9/10/11/12 and later versions.
Date: Mon, 17 May 2021 03:11:44 +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: 4.9.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: guojiufu at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 9.4
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-59371-4-sacK32yOyZ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-59371-4@http.gcc.gnu.org/bugzilla/>
References: <bug-59371-4@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, 17 May 2021 03:11:45 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D59371

--- Comment #28 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
If change code as below, 'i' is not starting from '0', and 'compare code' is
'!=3D'
then wrap/overflow on 'i' may happen, and optimizations (e.g. vectorization)
are not applied.
The below patch is trying to optimize this kind of loop.
https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570424.html

int foo (int *p, unsigned short u_n, unsigned short i)
{
  int x =3D 0;
  for (; i !=3D u_n; i++) {
    x =3D x + p[i];
  }
  return x;
}=