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 0F3A43982C05; Fri,  2 Jul 2021 13:14:56 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 0F3A43982C05
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101223] [11/12 Regression] evrp produces
 wrong code since r11-3685-gfcae5121154d1c33
Date: Fri, 02 Jul 2021 13:14:55 +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: 11.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 11.2
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-101223-4-qURsU7o6Yb@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-101223-4@http.gcc.gnu.org/bugzilla/>
References: <bug-101223-4@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: Fri, 02 Jul 2021 13:14:56 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101223

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to rsandifo@gcc.gnu.org from comment #8)
> (In reply to Andrew Macleod from comment #7)
> > wi::sub  sets the overflow flag for 0 - 1 with 1 bit signed...   so the
> > comparison ends up being undefined, and we then make incorrect choices
> > because we think we can.
> Isn't that a bug in wi::sub though?  I think we should fix it rather
> than work around it in callers.

How can one write 0 - 1 in 1-bit signed though?  1 isn't in the range...
One can only do 0 + -1 which doesn't overflow, or 0 - -1 which does.=