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 04F40383D82D; Tue, 17 Aug 2021 11:24:11 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 04F40383D82D
From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101944] suboptimal SLP for reduced case from
 namd_r
Date: Tue, 17 Aug 2021 11:24:11 +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: 12.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: linkw at gcc dot gnu.org
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-101944-4-L8a2SfYOfw@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-101944-4@http.gcc.gnu.org/bugzilla/>
References: <bug-101944-4@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: Tue, 17 Aug 2021 11:24:12 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101944

--- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #3)
> On x86 we even have
>=20
>   Vector cost: 136
>   Scalar cost: 196
>=20
> note that we seem to vectorize the reduction but that only happens with
> -ffast-math, not -O2 -ftree-slp-vectorize?
>=20

I don't quite follow this question, may misunderstand it. Yes, -ffast-math =
is
required, now -O2 doesn't implicitly enable vectorization, it needs the
explicit slp option.

> One issue is the association of
>=20
> (diffa * vdw_d * (1 / 6.) + vdw_c * (1 / 4.)) * diffa + vdw_b * (1 / 2.))=
 *
> diffa + vdw_a
>=20
> which we fail to reduce as
>=20
>  diffa*diffa*diffa*(1/6.)*vdw_d + diffa*diffa*(1/4.)*vdw_c +
> diffa*(1/2.)*vdw_b + 1.0*vdw_a

Good point!=