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 F303B385380B; Mon, 17 May 2021 22:02:47 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org F303B385380B
From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/100622] Conversion to smaller unsigned type in
 loop
Date: Mon, 17 May 2021 22:02:47 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: segher at gcc dot gnu.org
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: bug_status everconfirmed
Message-ID: <bug-100622-4-5R1b8p3BdW@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-100622-4@http.gcc.gnu.org/bugzilla/>
References: <bug-100622-4@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: Mon, 17 May 2021 22:02:48 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100622

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #5 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Thomas Koenig from comment #4)
> Yes, the masking should be only performed at the end.
>=20
> However, the inner loop could be further simplified to
>=20
> label:
>     lwzu r8,4(r10)
>     add r3,r8,r3
>     bdnz label
>=20
> without the need to do anything with r9, so this is probably
> more than one topic in one test case.

Please use -O2 instead, no one will care much about -O1.  You can use
-fno-unroll-loops to make it easier to read.

The core for foo is

.L3:
        lwzu 10,4(9)
        add 3,10,3
        rldicl 3,3,0,32
        bdnz .L3

and for foo2 is

.L10:
        lwzu 10,4(9)
        add 3,3,10
        bdnz .L10

This is this way in Gimple already: the IV is a DImode, while it would
be better as a SImode.  That is the root of the problem here.  Sinking
extensions could well help, but the IV should not be DImode in the first
place!

Confirmed.=