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 EFBF33858291; Mon, 17 Oct 2022 15:59:18 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EFBF33858291
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1666022358;
	bh=h7ZI8B7lMJAepScXJQEB7/DQS0P6bONhIrHJ9OBZS9k=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=AivDXqshQzCa1SY+kDQoMG7GeEduGpeYpFSCr81Wr+tJI2eN/85GMByMdXCwga3K3
	 2vsXda3WActPZ/9mUnQVLmhErmaCcyOY2IGYid7U2FEgALKuqExLxvpYS7kXH1DhqZ
	 JlYUSapSyHfV5CXiWItAhPNq4xnZR/CPDEjTd8+s=
From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107172] [13 Regression] wrong code with "-O1 -ftree-vrp"
 on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e
Date: Mon, 17 Oct 2022 15:59:18 +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: 13.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: hjl.tools at gmail dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 13.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-107172-4-Z29v4UgLBE@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-107172-4@http.gcc.gnu.org/bugzilla/>
References: <bug-107172-4@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
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107172

--- Comment #37 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Segher Boessenkool from comment #33)
> (In reply to H.J. Lu from comment #32)
> > > There is no actual comparison with 0, that is just notation.
> >=20
> > True.  But simplify-rtx.cc simplifies
> >=20
> > (ltu (reg 17) (const_int 0))
> >=20
> > to false when reg 17 is set.
>=20
> Is set?  What does that even mean?  Is set to what?

(reg 17) was set to 1.

> > Use the actual comparison isn't issue.  The issue is how
> >=20
> > (ltu (reg 17) (const_int 0))
> >=20
> > should be simplified when reg 17 is known to be set.
>=20
> You need to look at the setter.  It cannot be simplified otherwise.

The backend knows how to evaluate

(ltu:SI (const_int 1 [0x1]) (const_int 0 [0]))

from

(ltu:SI (reg:CCC 17 flags) (const_int 0 [0]))

where (reg:CCC 17 flags) was set to a constant by backend.=