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 99DAD393D011; Mon,  8 Mar 2021 08:32:46 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 99DAD393D011
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/99412] s352 benchmark of TSVC is vectorized
 by clang and not by gcc
Date: Mon, 08 Mar 2021 08:32:46 +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: 11.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: component assigned_to blocked keywords
 everconfirmed dependson bug_status cf_reconfirmed_on
Message-ID: <bug-99412-4-ceMZeBXHzi@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-99412-4@http.gcc.gnu.org/bugzilla/>
References: <bug-99412-4@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, 08 Mar 2021 08:32:46 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99412

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|middle-end                  |tree-optimization
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot =
gnu.org
             Blocks|                            |53947
           Keywords|                            |missed-optimization
     Ever confirmed|0                           |1
         Depends on|                            |97832
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-03-08

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
With -fno-tree-reassoc we detect the reduction chain and produce

.L3:
        vmovaps b(%rax), %ymm5
        vmovaps b+32(%rax), %ymm6
        addq    $160, %rax
        vfmadd231ps     a-160(%rax), %ymm5, %ymm1
        vmovaps b-96(%rax), %ymm7
        vfmadd231ps     a-128(%rax), %ymm6, %ymm0
        vmovaps b-64(%rax), %ymm5
        vmovaps b-32(%rax), %ymm6
        vfmadd231ps     a-96(%rax), %ymm7, %ymm2
        vfmadd231ps     a-64(%rax), %ymm5, %ymm3
        vfmadd231ps     a-32(%rax), %ymm6, %ymm4
        cmpq    $128000, %rax
        jne     .L3
        vaddps  %ymm1, %ymm0, %ymm0
        vaddps  %ymm2, %ymm0, %ymm0
        vaddps  %ymm3, %ymm0, %ymm0
        vaddps  %ymm4, %ymm0, %ymm0
        vextractf128    $0x1, %ymm0, %xmm1
        vaddps  %xmm0, %xmm1, %xmm1
        vmovhlps        %xmm1, %xmm1, %xmm0
        vaddps  %xmm1, %xmm0, %xmm0
        vshufps $85, %xmm0, %xmm0, %xmm1
        vaddps  %xmm0, %xmm1, %xmm0
        decl    %edx
        jne     .L2

we're not re-rolling and thus are forced to use a VF of 4 here.

Note that LLVM doesn't seem to veectorize the loop but instead vectorizes
the basic-block which isn't what TSVC looks for (but that would work for
non-fast-math).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97832
[Bug 97832] AoSoA complex caxpy-like loops: AVX2+FMA -Ofast 7 times slower =
than
-O3=