From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 333A53858403; Sat, 25 Sep 2021 09:40:10 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 333A53858403 From: "pinskia at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/100112] missed optimization for dead code elimination at -O3, -Os (vs. -O1, -O2) Date: Sat, 25 Sep 2021 09:40:10 +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: 11.0 X-Bugzilla-Keywords: alias, missed-optimization X-Bugzilla-Severity: normal X-Bugzilla-Who: pinskia at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cc 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: Sat, 25 Sep 2021 09:40:10 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100112 Andrew Pinski changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |rguenth at gcc dot gnu.org --- Comment #3 from Andrew Pinski --- In the strict aliasing case: # .MEM_10 =3D VDEF <.MEM_9(D)> *a.0_1 =3D _3; # VUSE <.MEM_10> c.1_4 =3D c; # .MEM_11 =3D VDEF <.MEM_10> c =3D c.1_4; # VUSE <.MEM_11> c.2_5 =3D c; We use MEM_9 for the load of c (the one with VUSE of MEM_10) as the vuse for the hashtable. In the non-strict-aliasing case, we use the VUSE of MEM_10 a= nd it works. Richi, You know the SCCVN code the best, maybe you can understand how to fix this better.=