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 838793858414; Wed,  8 Sep 2021 11:55:20 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 838793858414
From: "npiggin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/102239] New: powerpc suboptimal boolean test of contiguous bits
Date: Wed, 08 Sep 2021 11:55:20 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 11.2.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: npiggin 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
 cf_gcctarget
Message-ID: <bug-102239-4@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: Wed, 08 Sep 2021 11:55:20 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102239

            Bug ID: 102239
           Summary: powerpc suboptimal boolean test of contiguous bits
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npiggin at gmail dot com
  Target Milestone: ---
            Target: powerpc64le-linux-gnu

gcc version 11.2.1 20210815 (Debian 11.2.0-2)=20

Build flags -O2

--- test.c ---
void foo(long arg)
{
        if (arg & ((1UL << 33) | (1UL << 34)))
                asm volatile("# if");
        else
                asm volatile("# else");
}
---

generates:

foo:
        rldicr 3,3,29,1
        srdi. 3,3,29
        beq 0,.L6
        # if
        blr
.L6:
        # else
        blr

This test of multiple contiguous bits could be tested with a single instruc=
tion
with rldicr. or rldicl.

Those instructions do tend to be more expensive than the Rc=3D0 form (C2 cr=
acked
on POWER9, slower pipe class on POWER10), but I think they should be better
than the current 2-instruction sequence.=