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 C96AC3858D3C; Mon, 11 Oct 2021 08:34:27 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C96AC3858D3C
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102650] [12 Regression] Dead Code Elimination
 Regression at -O3 (trunk vs 11.2.0)
Date: Mon, 11 Oct 2021 08:34:27 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth 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: 12.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: keywords target_milestone everconfirmed bug_status
 cf_reconfirmed_on short_desc
Message-ID: <bug-102650-4-mb5TZ4x6aF@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-102650-4@http.gcc.gnu.org/bugzilla/>
References: <bug-102650-4@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, 11 Oct 2021 08:34:27 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102650

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
   Target Milestone|---                         |12.0
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-10-11
            Summary|Dead Code Elimination       |[12 Regression] Dead Code
                   |Regression at -O3 (trunk vs |Elimination Regression at
                   |11.2.0)                     |-O3 (trunk vs 11.2.0)

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Macleod from comment #1)
> This is a result of the vagaries of the single subrange value-range.
>=20
> VRP is seeing:
> # f_11 =3D PHI <-1(2), 2(3)>
>   goto <bb 6>; [100.00%]
>=20
>   <bb 5> [local count: 955630225]:
>   _3 =3D (unsigned short) f_11;
>   _6 =3D _3 + 2;
>   e_19 =3D (short int) _6;
>=20
> It knows f_11 is [-1, 2] and when that is cast to a ushort,  produces ~[3,
> 65534].
>=20
> That is all we knew about it in GCC11, so when we calculate_6 =3D ~[3,655=
34] +
> 2  it comes up with [1,4] and the e_19 =3D=3D 0 later on then can be fold=
ed away.
>=20
> in gcc12, EVRP has figured out that _3 is unsigned short [2, 2][+INF, +IN=
F].
> which if we add 2 to it, would come up with [1,1][4,4] which would be
> perfect.
>=20
> We save this to the value_range global table in EVRP, but alas it gets
> transliterated to a single pair value_range : _3  : unsigned short [2, +I=
NF]

That translation could see whether the corresponding anti-rante ~[3,65534] =
is
smaller (which it is) and use that instead?=