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 48F8F3858D3C; Sun,  3 Oct 2021 14:01:34 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 48F8F3858D3C
From: "gabravier at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/102575] New: Failure to optimize double _Complex stores
 to use largest loads/stores possible
Date: Sun, 03 Oct 2021 14:01:34 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: gabravier at gmail dot com
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-102575-4@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: Sun, 03 Oct 2021 14:01:34 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102575

            Bug ID: 102575
           Summary: Failure to optimize double _Complex stores to use
                    largest loads/stores possible
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

void test(double _Complex *a)
{
    a[0] =3D 1;
    a[1] =3D 1;
}

With -O3, on AMD64 GCC outputs this:

test(double _Complex*):
        movsd   xmm1, QWORD PTR .LC0[rip]
        movsd   xmm0, QWORD PTR .LC0[rip+8]
        movsd   QWORD PTR [rdi], xmm1
        movsd   QWORD PTR [rdi+8], xmm0
        movsd   QWORD PTR [rdi+16], xmm1
        movsd   QWORD PTR [rdi+24], xmm0
        ret

Clang instead outputs this:

test(double _Complex*):
        movsd   xmm0, qword ptr [rip + .LCPI0_0] # xmm0 =3D mem[0],zero
        movups  xmmword ptr [rdi], xmm0
        movups  xmmword ptr [rdi + 16], xmm0
        ret

It seems to me like the second output should always be faster.

PS: The difference is even larger with `-mavx2`.=