From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 19563 invoked by alias); 7 Nov 2011 13:53:49 -0000 Received: (qmail 19545 invoked by uid 22791); 7 Nov 2011 13:53:48 -0000 X-SWARE-Spam-Status: No, hits=-7.5 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 07 Nov 2011 13:53:29 +0000 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id pA7DrSr1004586 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 7 Nov 2011 08:53:29 -0500 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx02.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id pA7DrSCa012655; Mon, 7 Nov 2011 08:53:28 -0500 Received: from barimba (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id pA7DrRpj025870; Mon, 7 Nov 2011 08:53:27 -0500 From: Tom Tromey To: Jeff Law Cc: gcc-patches Subject: Re: RFA: New pass to delete unexecutable paths in the CFG References: <4EB7AAF6.6060702@redhat.com> Date: Mon, 07 Nov 2011 14:16:00 -0000 In-Reply-To: <4EB7AAF6.6060702@redhat.com> (Jeff Law's message of "Mon, 07 Nov 2011 02:55:02 -0700") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.90 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org X-SW-Source: 2011-11/txt/msg00939.txt.bz2 >>>>> "Jeff" == Jeff Law writes: Jeff> First, it's perfectly fine to have a NULL pointer dereference in a Jeff> program as long as that code is never executed. Once the code is Jeff> executed, we've entered the realm of undefined behavior. Jeff> Thus in a conforming program we can safely assume that a provable NULL Jeff> pointer dereference can never be executed at runtime. This implies Jeff> there is a path through the CFG that is unexecutable. IIUC, then this isn't true for Java. In Java the attempt to dereference NULL throws a NullPointerException, which can be caught, etc. It isn't undefined. Tom