From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id E96FA3858439; Fri, 11 Feb 2022 10:24:14 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E96FA3858439 From: "cvs-commit at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce Date: Fri, 11 Feb 2022 10:24:14 +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: 12.0 X-Bugzilla-Keywords: compare-debug-failure X-Bugzilla-Severity: normal X-Bugzilla-Who: cvs-commit at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 9.5 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: Fri, 11 Feb 2022 10:24:15 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104459 --- Comment #5 from CVS Commits --- The master branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:18c8086d65f3d539e065ea7c97e3de6f3bbdf684 commit r12-7194-g18c8086d65f3d539e065ea7c97e3de6f3bbdf684 Author: Jakub Jelinek Date: Fri Feb 11 11:21:24 2022 +0100 df: Don't set bbs dirty because of debug insn moves [PR104459] As mentioned in the PR, we get -fcompare-debug failure, which is caused= by cfg_layout_merge_blocks successfully merging two bbs where both bbs contained just CODE_LABEL, NOTE_INSN_BASIC_BLOCK and in the -g case both some debug insns at the end. cfg_layout_merge_blocks calls update_bb_for_insn_chain which for the post-label insns in the second b= lock (except for BARRIERs) calls df_insn_change_bb. This function changes the bb of the insns and for notes just punts, but for other insns calls df_set_bb_dirty. Now the problem is that because there were only debug insns and notes in the second block, df_set_bb_dirty is called on both only in the -g case and not with -g0. df_set_bb_dirty these days sets both the BB_MODIFIED flag and marks the bb as dirty, and the former is what 6 spots in cfgcleanup.cc use in code-generation decisions, in this case may_thread |=3D (target->flags & BB_MODIFIED) !=3D 0; in particular. So, with -g may_thread is true while with -g0 it is not and we diverge from that point onwards. I've thought about introducing df_set_bb_dirty_nondebug that wouldn't set BB_MODIFIED but would mark the bb dirty, but then I went through history and found changes like: https://gcc.gnu.org/legacy-ml/gcc-patches/2010-10/msg00059.html so I've also tried just not calling df_set_bb_dirty for debug insns at all and it passed x86_64-linux and i686-linux --enable-checking=3Dyes,rtl,extra,df bootstraps/regtests, so perhaps that works too. Now that I look at it again, if we don't need those from %d to %d messa= ges for debug insns in the dump files, another way to fix it would be just = to change the very first line in the hunk from if (!INSN_P (insn)) to if (!DEBUG_INSN_P (insn)) Though, df_set_bb_dirty_nondebug which will do everything but set bb->flags |=3D BB_MODIFIED is yet another option I can test. Perhaps even that PR42889 was solely about those 6 decisions in cfgclea= nup (at that point it used df_get_bb_dirty) and not about actually the recomputation of some of the problems causing different code generation= s. 2022-02-11 Jakub Jelinek PR rtl-optimization/104459 * df-scan.cc (df_insn_change_bb): Don't call df_set_bb_dirty wh= en moving DEBUG_INSNs between bbs. * gcc.dg/pr104459.c: New test.=