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 169663896837; Wed, 24 Feb 2021 09:05:17 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 169663896837
From: "bina2374 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94092] Code size and performance degradations
 after -ftree-loop-distribute-patterns was enabled at -O[2s]+
Date: Wed, 24 Feb 2021 09:05:16 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: bina2374 at gmail dot com
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: aoliva at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-94092-4-ortPNozInJ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-94092-4@http.gcc.gnu.org/bugzilla/>
References: <bug-94092-4@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, 24 Feb 2021 09:05:17 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94092

--- Comment #8 from Mel Chen <bina2374 at gmail dot com> ---
Sorry for using the bad example to describe the problem I am facing. Let me
clarify my question with a more precise example.

void array_mul(int N, int *C, short *A, short *B) {
  int i, j;
  for (i =3D 0; i < N; i++) {
    C[i] =3D 0; // Will be transformed to __builtin_memset
    for (j =3D 0; j < N; j++) {
      C[i] +=3D (int)A[i * N + j] * (int)B[j];
    }
  }
}

If I compile the case with -O2 -fno-tree-loop-distribute-patterns, the store
operation 'C[i] =3D 0' can be eliminated by dead store elimination (dse3). =
But
without -fno-tree-loop-distribute-patterns, it will be transformed to memse=
t by
loop distribution (ldist) because ldist executes before dse3. Finally the
memset will not be eliminated.

Another point is if there are other operations in the same level loop as the
store operation, is it really beneficial to do loop distribution and then
convert to builtin function?=