From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 3868E3858C56; Mon, 28 Mar 2022 20:07:15 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 3868E3858C56 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: Mon, 28 Mar 2022 20:07:15 +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: Mon, 28 Mar 2022 20:07:15 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105086 --- Comment #2 from Andrew Macleod --- Ranger VRP doesn't simulate edges the same way VRP does. It looks like VRP simulates the back edge twice and the second time notes that the MAX value = is greater than it was before and "projects" the max to +INF to avoid further simulations and thus executing every instance of the loop.=20 This allows it to refine the range in the loop better, which ranger VRP isn= 't doing as it is still doing a DOM walk and doesn't revisit the node. ANd I haven't added any sort of similar "projection" logic to the back edge processing. I have an alternate question. it looks like when we utilize scev to pick up ranges we just give up if scev_probably_wraps_p() is true. 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 Statement (exit)if (a_1 > 1) is executed at most 23 (bounded by 23) + 1 times in loop 1. but we neglect to create range for the PHI. We should be able to properly create a range for this from the SCEV info rather than giving up? It woul= d be [0,0][4294967273, 4294967295].=20 And even with the old value_range we could use anti-range and produce ~[1, 4294967272]? Is there a practical reason we don't look any closer at wrap cases to see if they are "simple wraps" or not? I think that would also solve this issue.=