From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by sourceware.org (Postfix) with ESMTPS id 3CBE13858D38; Wed, 14 Jun 2023 09:30:06 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 3CBE13858D38 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=linux.ibm.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=linux.ibm.com Received: from pps.filterd (m0353726.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 35E9ICqa023836; Wed, 14 Jun 2023 09:30:03 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=from : to : cc : subject : references : date : in-reply-to : message-id : mime-version : content-type : content-transfer-encoding; s=pp1; bh=khsi1/YiNA7H2MV65NDfnPbDxQRjP9UaRElBEuerPSU=; b=d5+V9DH4ur92wNZLn18U3tC08D7rmw/ptzDPQ2BqAnsu1CuD7IES6/ov1jjMeMh926b6 XZKNRh9CEsEgJ4nFNp1102GZU0w8mVV7Udo3y5uDSH19xrU0L4wgWoMsGH3Rtk3sfL0l aTOjPfPaERNxHBZJhIT5z6PTO4CsuJYKuKRe3QESPx3JVFAjv8wFpmaIuLks9BeuPBQW mG4rJ52XvmdCoAaElpXJe0NlH8Dam8wOUL4+p6/u3aKEiHqOwHz9m/Gsfdbdu+Zk3vQp 4sxhWKsb6qFsIhPsw62LhkF8/8YqCkbqSGoOOlsTMY6CgZGEA9rtQIUVPpG/OyNXgPVH 5g== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3r7asur873-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 14 Jun 2023 09:30:02 +0000 Received: from m0353726.ppops.net (m0353726.ppops.net [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 35E9JFMc028909; Wed, 14 Jun 2023 09:30:02 GMT Received: from ppma04dal.us.ibm.com (7a.29.35a9.ip4.static.sl-reverse.com [169.53.41.122]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3r7asur869-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 14 Jun 2023 09:30:02 +0000 Received: from pps.filterd (ppma04dal.us.ibm.com [127.0.0.1]) by ppma04dal.us.ibm.com (8.17.1.19/8.17.1.19) with ESMTP id 35E7T5aQ011868; Wed, 14 Jun 2023 09:30:01 GMT Received: from smtprelay03.dal12v.mail.ibm.com ([9.208.130.98]) by ppma04dal.us.ibm.com (PPS) with ESMTPS id 3r4gt60jgg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 14 Jun 2023 09:30:01 +0000 Received: from smtpav04.wdc07v.mail.ibm.com (smtpav04.wdc07v.mail.ibm.com [10.39.53.231]) by smtprelay03.dal12v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 35E9TxOK459276 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 14 Jun 2023 09:30:00 GMT Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CB7B258050; Wed, 14 Jun 2023 09:29:59 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 55CA758054; Wed, 14 Jun 2023 09:29:59 +0000 (GMT) Received: from ltcden2-lp1.aus.stglabs.ibm.com (unknown [9.3.90.43]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTPS; Wed, 14 Jun 2023 09:29:59 +0000 (GMT) From: Jiufu Guo To: Richard Biener Cc: Segher Boessenkool , gcc-patches@gcc.gnu.org, dje.gcc@gmail.com, linkw@gcc.gnu.org, bergner@linux.ibm.com, jeffreyalaw@gmail.com, richard.sandiford@arm.com Subject: Re: [PATCH] rs6000: replace '(const_int 0)' to 'unspec:BLK [(const_int 0)]' for stack_tie References: <20230613122335.2108620-1-guojiufu@linux.ibm.com> <20230613183320.GU19790@gate.crashing.org> <7no7liadru.fsf@ltcden2-lp1.aus.stglabs.ibm.com> Date: Wed, 14 Jun 2023 17:29:55 +0800 In-Reply-To: (Richard Sandiford's message of "Wed, 14 Jun 2023 10:04:20 +0100") Message-ID: <7ncz1y9yss.fsf@ltcden2-lp1.aus.stglabs.ibm.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: GlnIij8UsYzWS6jhcOYxz0I9x21Gm56b X-Proofpoint-GUID: N82fS3kEWRv8i4I-GT88nuunf03aA5BS X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-06-14_06,2023-06-12_02,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=2 adultscore=0 phishscore=0 bulkscore=0 clxscore=1015 malwarescore=0 lowpriorityscore=0 mlxlogscore=162 mlxscore=2 spamscore=2 impostorscore=0 priorityscore=1501 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2306140076 X-Spam-Status: No, score=-5.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi, Richard Sandiford writes: > Richard Biener writes: >> AFAIU this special instruction is only supposed to prevent >> code motion (of stack memory accesses?) across this instruction? >> I'd say a >> >> (may_clobber (mem:BLK (reg:DI 1 1))) >> >> might be more to the point? I've used "may_clobber" which doesn't >> exist since I'm not sure whether a clobber is considered a kill. >> The docs say "Represents the storing or possible storing of an=20 >> unpredictable..." - what is it? Storing or possible storing? > > I'd also understood it to be either. As in, it is a may-clobber > that can be used for must-clobber. Alternatively: the value stored > is unpredictable, and can therefore be the same as the current value. > > I think the main difference between: > > (clobber (mem:BLK =E2=80=A6)) > > and > > (set (mem:BLK =E2=80=A6) (unspec:BLK =E2=80=A6)) > > is that the latter must happen for correctness (unless something > that understands the unspec proves otherwise) whereas a clobber > can validly be dropped. So for something like stack_tie, a set > seems more correct than a clobber. Thanks a lot for all your helpful comments! BR, Jeff (Jiufu Guo) > > Thanks, > Richard