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 452E53857C66; Fri,  6 Oct 2023 17:30:04 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 452E53857C66
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1696613404;
	bh=pv9a1Ao+tmnvQ2eozATpicCNy4F4h8OFdBsqfwv2rJo=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=K4HVVY14YcakqU4W7V41PIHFW4xbhNsXgihdnp5fEIvGAjEe+MPyMmfE/ieZdKvA5
	 mP6lsDqaGzV250MJu6xK3aIo+nblAakoiVjfO1g9oENE0Hg8Z1ltkHdieIb/oOGRBn
	 1cfJ5G4TO8rpVrTbqoZ+OvaUBwub1zQ/d12Jitsk=
From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111694] [13/14 Regression] Wrong behavior for
 signbit of negative zero when optimizing
Date: Fri, 06 Oct 2023 17:30:03 +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: 13.2.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: amacleod at redhat dot com
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: 13.3
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-111694-4-CXx2VXBtJZ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-111694-4@http.gcc.gnu.org/bugzilla/>
References: <bug-111694-4@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=3D111694

--- Comment #4 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Richard Biener from comment #3)
> Looks like some frange / relation mistake then.


l_3(D)  [frange] double [-Inf, +Inf]
Equivalence set : [l_3(D), r_4(D)]
    <bb 3> :
    _1 =3D __builtin_signbit (l_3(D));
    if (_1 !=3D 0)
      goto <bb 6>; [INV]
    else
      goto <bb 4>; [INV]

3->6  (T) _1 :  [irange] int [-INF, -1][1, +INF]
3->6  (T) l_3(D) :      [frange] double [-Inf, -0.0 (-0x0.0p+0)]
3->4  (F) _1 :  [irange] int [0, 0]
3->4  (F) l_3(D) :      [frange] double [0.0 (0x0.0p+0), +Inf]

    <bb 4> :
    _2 =3D __builtin_signbit (r_4(D));

Yeah, we know l_3 and r_4 are equivalent, and we also know that on the edge
3->4 l_3 has the range  double [0.0 (0x0.0p+0), +Inf]

When we miss is that with an equivalence, we also have to put -0.0 back into
the range.  We currently don't so we think we can fold the second signbit c=
all.

If I fix that, we then see=20
r_4(D)  [frange] double [-0.0 (-0x0.0p+0), +Inf]
which prevents the folding.=20=20

I need to audit to see if there are other places where we may have to "adju=
st"
equivalence range, or how best to deal with this in the general case.=