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 6785E3854833; Mon, 15 Feb 2021 09:01:53 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6785E3854833
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/99100] Inconsistent vector length used in autovectorizer
 for AVX-512
Date: Mon, 15 Feb 2021 09:01:53 +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: 10.2.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
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: component
Message-ID: <bug-99100-4-xrRPexX9fl@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-99100-4@http.gcc.gnu.org/bugzilla/>
References: <bug-99100-4@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, 15 Feb 2021 09:01:53 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99100

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|tree-optimization           |target

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
What's odd is that with -mavx512f -mtune=3Dskylake-avx512 we don't vectoriz=
e it
at all.  I'm looking at a smaller test:

#pragma omp declare simd simdlen(8) notinbranch
extern double __attribute__((const)) myfunc(double x);

#define N 1024
__attribute__ ((__aligned__(256))) double a[N], b[N], c[N];

void foo()
{
   for (int i =3D 0; i < N; i++) a[i] =3D myfunc(b[i]);
}


we have 3 simd clones here and the only discriminator is the target badness
returned by targetm.simd_clone.usable (n).  I suspect

  switch (node->simdclone->vecsize_mangle)
    {
    case 'b':
      if (!TARGET_SSE2)
        return -1;
      if (!TARGET_AVX)
        return 0;
      return TARGET_AVX2 ? 2 : 1;
    case 'c':
      if (!TARGET_AVX)
        return -1;
      return TARGET_AVX2 ? 1 : 0;
    case 'd':
      if (!TARGET_AVX2)
        return -1;
      return 0;
    case 'e':
      if (!TARGET_AVX512F)
        return -1;
      return 0;

since 'd' behaves the same as 'e' here we prefer 'd' or 'e' dependent on
the order in the simd clones.

Note the odd thing is we produce a 'c' mangling clone _and_ a 'd' mangling
one.  But indeed once we reach 'd' badness is zero and can't improve anymor=
e.

There's also no sign of handling of prefered SIMD modes in the above
function...

Target issue.  Not sure about the -mtune=3Dskylake-avx512 issue though.=