From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id B71A13858C2C for ; Wed, 22 Dec 2021 10:27:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B71A13858C2C Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-551-L1FQ5zxCMd2VOfkmwpzaYQ-1; Wed, 22 Dec 2021 05:27:44 -0500 X-MC-Unique: L1FQ5zxCMd2VOfkmwpzaYQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C43D681EE61; Wed, 22 Dec 2021 10:27:43 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.104]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4586D7B9C5; Wed, 22 Dec 2021 10:27:38 +0000 (UTC) From: Florian Weimer To: Adrian Moreno via Gcc-help Cc: David Brown , Stefan Ring , Adrian Moreno Subject: Re: broken code only when optimized "-O2" References: <9b28799e-71f8-2ef9-1cc9-01345993cc11@redhat.com> Date: Wed, 22 Dec 2021 11:27:36 +0100 In-Reply-To: <9b28799e-71f8-2ef9-1cc9-01345993cc11@redhat.com> (Adrian Moreno via Gcc-help's message of "Wed, 22 Dec 2021 10:24:28 +0100") Message-ID: <877dbx7x47.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-help@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-help mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Dec 2021 10:27:50 -0000 * Adrian Moreno via Gcc-help: > So here I do not know what the compiler would think about "pos" if it > happens to point to some invalid stack address. In such cases, the compiler typically assumes that the code in question is never executed. This means that the comparison does not need to be performed, among other things. Thanks, Florian