From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-413261-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 18759 invoked by alias); 25 Jan 2013 17:12:54 -0000
Received: (qmail 18635 invoked by uid 48); 25 Jan 2013 17:12:26 -0000
From: "tilman@code-monkey.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/56110] New: Sub-optimal code: unnecessary CMP after AND
Date: Fri, 25 Jan 2013 17:12:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: tilman@code-monkey.de
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-56110-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2013-01/txt/msg02380.txt.bz2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56110

             Bug #: 56110
           Summary: Sub-optimal code: unnecessary CMP after AND
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tilman@code-monkey.de
            Target: arm


Compiling this code

unsigned f1 (unsigned x, unsigned m)
{
    if (m & 0x008080)
        x >>= 8;

    return x;
}

with gcc 4.7.2 gives this code for ARMv5:

$ armv5tel-softfloat-linux-gnueabi-gcc -O2 -S -o- f1.c
[...]
    ldr    r3, .L6
    and    r3, r1, r3       @ XXX
    cmp    r3, #0           @ XXX
    movne    r0, r0, lsr #8
    bx    lr
[...]

AFAICS we could get rid of the CMP if we used ANDS instead of AND:

    ldr    r3, .L6
    ands    r3, r1, r3
    movne    r0, r0, lsr #8
    bx    lr