From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 18119 invoked by alias); 24 Apr 2005 15:27:44 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 18098 invoked by alias); 24 Apr 2005 15:27:41 -0000 Date: Sun, 24 Apr 2005 15:27:00 -0000 Message-ID: <20050424152741.18097.qmail@sourceware.org> From: "dberlin at dberlin dot org" To: gcc-bugs@gcc.gnu.org In-Reply-To: <20050423092333.21173.mikpe@csd.uu.se> References: <20050423092333.21173.mikpe@csd.uu.se> Reply-To: gcc-bugzilla@gcc.gnu.org Subject: [Bug tree-optimization/21173] [4.0/4.1 regression] miscompiled pointer subtraction broke Linux kernel X-Bugzilla-Reason: CC X-SW-Source: 2005-04/txt/msg03412.txt.bz2 List-Id: ------- Additional Comments From dberlin at gcc dot gnu dot org 2005-04-24 15:27 ------- Subject: Re: [4.0/4.1 regression] miscompiled pointer subtraction broke Linux kernel > tree-ssa-pre uses force_gimple_operand with SIMPLE==false, so if > expr is already a valid rhs, force_gimple_operand should do nothing. > If it does, I consider that to be a bug. > > Your patch to use unshare_expr is IMHO unnecessarily expensive. > > > Here's the gdb trace, btw: Breakpoint 3, create_expression_by_pieces (block=0x400c4870, expr=0x88403f0, stmts=0x400c6510) at tree-ssa-pre.c:1322 expr came from a node in ANTIC_IN, we *can't* modify it, because it's not a copy. (gdb) p debug_generic_stmt (expr) (charD.3 *) &0B->typeD.1681; ... 1388 newexpr = force_gimple_operand (folded, (gdb) n 1390 if (forced_stmts) (gdb) p debug_generic_stmt (expr) (charD.3 *) &D.1708_3->typeD.1681; tada! This is the reason we have to unshare it before passing it in. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21173