From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mengyan1223.wang (mengyan1223.wang [89.208.246.23]) by sourceware.org (Postfix) with ESMTPS id 95A833858408 for ; Wed, 9 Mar 2022 16:12:41 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 95A833858408 Received: from localhost.localdomain (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-384) server-digest SHA384) (Client did not present a certificate) (Authenticated sender: xry111@mengyan1223.wang) by mengyan1223.wang (Postfix) with ESMTPSA id 159D065C24; Wed, 9 Mar 2022 11:12:38 -0500 (EST) Message-ID: Subject: [PATCH v2] cse: avoid signed overflow in compute_const_anchors [PR 104843] From: Xi Ruoyao To: Richard Biener Cc: GCC Patches , Richard Sandiford , Jeff Law Date: Thu, 10 Mar 2022 00:12:36 +0800 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-3037.9 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, JMQ_SPF_NEUTRAL, SPF_HELO_PASS, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE 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-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Mar 2022 16:12:44 -0000 On Wed, 2022-03-09 at 15:55 +0100, Richard Biener wrote: > isn't it better to make targetm.const_anchor unsigned? > The & and ~ are not subject to overflow rules. It's not enough: if n is the minimum value of HOST_WIDE_INT and const_anchor = 0x8000 (the value for MIPS), we'll have a signed 0x7fff in *upper_base. Then the next line, "*upper_offs = n - *upper_base;" will be a signed overflow again. How about the following? -- >8 -- With a non-zero const_anchor, the behavior of this function relied on signed overflow. gcc/ PR rtl-optimization/104843 * cse.cc (compute_const_anchors): Use unsigned HOST_WIDE_INT for n to perform overflow arithmetics safely. --- gcc/cse.cc | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/gcc/cse.cc b/gcc/cse.cc index a18b599d324..052fa0c3490 100644 --- a/gcc/cse.cc +++ b/gcc/cse.cc @@ -1169,12 +1169,12 @@ compute_const_anchors (rtx cst, HOST_WIDE_INT *lower_base, HOST_WIDE_INT *lower_offs, HOST_WIDE_INT *upper_base, HOST_WIDE_INT *upper_offs) { - HOST_WIDE_INT n = INTVAL (cst); - - *lower_base = n & ~(targetm.const_anchor - 1); - if (*lower_base == n) + unsigned HOST_WIDE_INT n = UINTVAL (cst); + unsigned HOST_WIDE_INT lb = n & ~(targetm.const_anchor - 1); + if (lb == n) return false; + *lower_base = lb; *upper_base = (n + (targetm.const_anchor - 1)) & ~(targetm.const_anchor - 1); *upper_offs = n - *upper_base; -- 2.35.1 >