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 9D9D0398E43F; Thu,  6 Jun 2024 06:17:13 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9D9D0398E43F
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1717654633;
	bh=lJD2dcLsLBSBvFyydSu9REZWtDemDU2st14kU283MCY=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=Ov7v+5hWrQMXI/Qc0XzKPEk3luJzWM70DO3oMZ1u2CwsSGW4xRoHu8OetKm2s9cqP
	 lJzCGIjR5H9smPXgnni33tKlCLX0+C3K0y5viouwPnu60oAGMlwZP+8DmORFKpIwGl
	 hsihzCL0KSDvrA4CBivvl+pfJLIIJO+XARrG4RyM=
From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114932] IVopts inefficient handling of signed
 IV used for addressing.
Date: Thu, 06 Jun 2024 06:17:10 +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: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenther at suse dot de
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: tnfchris at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-114932-4-A03bBFs2dP@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-114932-4@http.gcc.gnu.org/bugzilla/>
References: <bug-114932-4@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=3D114932

--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 5 Jun 2024, tnfchris at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114932
>=20
> --- Comment #11 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #10)
> > I think the question is why IVOPTs ends up using both the signed and
> > unsigned variant of the same IV instead of expressing all uses of both =
with
> > one IV?
> >=20
> > That's where I'd look into.
>=20
> It looks like this is because of a subtle difference in the expressions.
>=20
> In get_loop_invariant_expr IVOPTs first tries to strip away all casts with
> STRIP_NOPS.
>=20
> The first expression is (unsigned long) (stride.3_27 * 4) and the second
> expression is ((unsigned long) stride.3_27) * 4 (The pretty printing here=
 is
> pretty bad...)
>=20
> So the first one becomes:
>   (unsigned long) (stride.3_27 * 4) -> stride.3_27 * 4
>=20
> and second one:
>   ((unsigned long) stride.3_27) * 4 -> ((unsigned long) stride.3_27) * 4
>=20
> since we don't care about overflow here, it looks like the stripping shou=
ld
> be recursive as long as it's a NOP expression between two integral types.
>=20
> That would get them to hash to the same IV expression.  Trying now..

Note tree-affine is a tool that's used for this kind of "weak" equalities.
Convert both to affine, subtract them and if that's zero they are equal.=