From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 1F84E3857C4A; Tue, 29 Mar 2022 13:24:03 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1F84E3857C4A From: "amacleod at redhat dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/105086] [12 Regression] Dead Code Elimination Regression at -Os (trunk vs. 11.2.0) 25 Date: Tue, 29 Mar 2022 13:24:02 +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: amacleod at redhat 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: 12.0 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 29 Mar 2022 13:24:03 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105086 --- Comment #4 from Andrew Macleod --- (In reply to Richard Biener from comment #3) > (In reply to Andrew Macleod from comment #2) >=20 > > I have an alternate question. it looks like when we utilize scev to pi= ck up > > ranges we just give up if scev_probably_wraps_p() is true. > >=20 > > Analyzing # of iterations of loop 1 > > exit condition 1 < [4294967273, + , 1] > > bounds on difference of bases: 4294967272 ... 4294967272 > > result: > > # of iterations 23, bounded by 23 > >=20 > > Statement (exit)if (a_1 > 1) > > is executed at most 23 (bounded by 23) + 1 times in loop 1. > >=20 > > but we neglect to create range for the PHI. We should be able to proper= ly > > create a range for this from the SCEV info rather than giving up? It = would > > be [0,0][4294967273, 4294967295].=20 >=20 > Well, we give up if the IV wraps because then the logic we have to compute > the IV range doesn't work. I'm talking about bounds_of_var_in_loop > which basically computes the range as [base, base + step * niter] with > adjustments to create proper ranges for negative step. >=20 Yeah, that is exactly where I was looking, and it looked like it was just to keep things simple. > > And even with the old value_range we could use anti-range and produce > > ~[1, 4294967272]? >=20 > It should use the range as computed by the "iteration", just not use > SCEV to refine it. >=20 > > Is there a practical reason we don't look any closer at wrap cases to s= ee if > > they are "simple wraps" or not? I think that would also solve this iss= ue. >=20 > The only reason is that nobody implemented it. The important thing is to > compute that it will wrap exactly once of course. I suspected as much. I think we can enhance this next stage 1.=