From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 15939 invoked by alias); 31 Aug 2012 00:31:24 -0000 Received: (qmail 15926 invoked by uid 22791); 31 Aug 2012 00:31:22 -0000 X-SWARE-Spam-Status: No, hits=-4.3 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00,KHOP_THREADED X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 31 Aug 2012 00:31:09 +0000 From: "sje at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/54369] Delayed-branch pass in reorg.c removes too many instructions Date: Fri, 31 Aug 2012 00:31:00 -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-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: sje at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Status Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2012-08/txt/msg02027.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54369 Steve Ellcey changed: What |Removed |Added ---------------------------------------------------------------------------- Status|WAITING |NEW --- Comment #2 from Steve Ellcey 2012-08-31 00:30:01 UTC --- I think I see where delete_related_insns is going wrong. We call it with a JUMP instruction that we want to remove because we are just jumping to the next instruction (a label) which we would get to anyway without the jump, then after delete_related_insns removes the jump it checks the label it was jumping to, and if it finds no uses it calls delete_related_insns with that label. When delete_related_insns is called with a label, it assumes it can remove all the code after that label as unreachable. But the code after the label can be reached by the default fall-through code sequence. So after removing a jump and finding a label with no uses we should call delete_insn with that label, not delete_related_insns. So my proposed fix would be: diff --git a/gcc/jump.c b/gcc/jump.c index 9721fe1..fa3d65a 100644 --- a/gcc/jump.c +++ b/gcc/jump.c @@ -1207,7 +1207,7 @@ delete_related_insns (rtx insn) /* This can delete NEXT or PREV, either directly if NEXT is JUMP_LABEL (INSN), or indirectly through more levels of jumps. */ - delete_related_insns (lab); + delete_insn (lab); else if (tablejump_p (insn, NULL, &lab_next)) { /* If we're deleting the tablejump, delete the dispatch table.