From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 2BB9B3875A22; Mon, 25 Jul 2022 13:04:51 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 2BB9B3875A22 From: "rearnsha at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/106187] armhf: Miscompilation at O2 level (O0 / O1 are working) Date: Mon, 25 Jul 2022 13:04:51 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: rtl-optimization X-Bugzilla-Version: 10.4.0 X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: rearnsha 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: 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, 25 Jul 2022 13:04:51 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106187 --- Comment #45 from Richard Earnshaw --- The problem with changing rtx_equal_for_cselib_1 is that it is essentially commutative in its operands - it doesn't disambiguate with x substituting f= or y or vice-versa, so we cannot tell if an operation is a load or a store. A minimal fix, which just suppresses stores would be: @@ -81,6 +81,10 @@ reload_cse_noop_set_p (rtx set) if (cselib_reg_set_mode (SET_DEST (set)) !=3D GET_MODE (SET_DEST (set))) return 0; + /* Fixme: we need to check that removing a store doesn't change + the alias computations. */ + if (flag_strict_aliasing && MEM_P (SET_DEST (set))) + return 0; return rtx_equal_for_cselib_p (SET_DEST (set), SET_SRC (set)); } But we could no-doubt improve on that.=