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 898E5388E820; Wed, 17 Jun 2020 13:06:19 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 898E5388E820
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1592399179;
 bh=qgDuaqPPIRvL7bI/AODp4AGFaUtlMtiFw/Z+7FvMcbQ=;
 h=From:To:Subject:Date:In-Reply-To:References:From;
 b=nnXHtmZN48paDPVOGqx6crtIXdeIs3TtpzHCnG3YwOkhmHgYi/2gRDXZidNtzlJnf
 qkMEoqSEamw1PNlp1EK7dZigLnoF7RM053ydclePkAmUg4MxhkGVkZ2es67LsHv9VV
 0uuyEW9hxuHGDEXyJk15i2rL7nt/gv1Ac+C5XstQ=
From: "jens.seifert at de dot ibm.com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/95704] PPC: int128 shifts should be implemented branchless
Date: Wed, 17 Jun 2020 13:06:19 +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: 8.3.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jens.seifert at de dot ibm.com
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: 
Message-ID: <bug-95704-4-EfxZNzhpEm@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-95704-4@http.gcc.gnu.org/bugzilla/>
References: <bug-95704-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 17 Jun 2020 13:06:19 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95704

--- Comment #3 from Jens Seifert <jens.seifert at de dot ibm.com> ---
GCC 8.3 generates:
_Z3shloy:
.LFB0:
        .cfi_startproc
        addi 9,5,-64
        cmpwi 7,9,0
        blt 7,.L2
        sld 4,3,9
        li 3,0
        blr
        .p2align 4,,15
.L2:
        srdi 9,3,1
        subfic 10,5,63
        sld 4,4,5
        srd 9,9,10
        sld 3,3,5
        or 4,9,4
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0
        .cfi_endproc

8 instructions if taking L2. The branch free code I propsed:

_Z15shl_branch_lessoy:
.LFB1:
        .cfi_startproc
        rldicl 5,5,0,32
        subfic 9,5,64
        addi 10,5,-64
        sld 10,3,10
        srd 9,3,9
        sld 4,4,5
        or 9,9,10
        or 4,9,4
        sld 3,3,5
        blr

8 instructions no branch. Almost everything can be executed in parallel.

rldicl 5,5,0,32 gets added by gcc, which is not necessary.=