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 9109C3858D3C; Fri, 25 Mar 2022 12:00:00 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9109C3858D3C
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/104049] [12 Regression] vec_select to subreg lowering
 causes superfluous moves
Date: Fri, 25 Mar 2022 12:00:00 +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: 12.0
X-Bugzilla-Keywords: missed-optimization, ra
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 12.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: cc
Message-ID: <bug-104049-4-wCKVpCfvcY@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-104049-4@http.gcc.gnu.org/bugzilla/>
References: <bug-104049-4@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: Fri, 25 Mar 2022 12:00:00 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104049

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps the r12-2288-g8695bf78dad1a42636 change wasn't a good idea?
I mean, if we add some hack for the .REDUC_* stuff so that we don't have the
lowpart vec_select that r12-2288 folds into a subreg, won't we still suffer=
 the
same problem when doing anything similar?
E.g. with -O2:

typedef int V __attribute__((vector_size (4 * sizeof (int))));

int
test (V a)
{
  int sum =3D a[0];
  return (((unsigned short)sum) + ((unsigned int)sum >> 16)) >> 1;
}

The assembly difference is then:
-       fmov    w0, s0
-       lsr     w1, w0, 16
-       add     w0, w1, w0, uxth
+       umov    w0, v0.h[0]
+       fmov    w1, s0
+       add     w0, w0, w1, lsr 16
        lsr     w0, w0, 1
        ret
Dunno how costly on aarch64 is Neon -> GPR register move.
Is fmov w0, s0; fmov w1, s0 or fmov w0, s0; mov w1, w0 cheaper?=