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 B47C73858D39 for ; Fri, 1 Jul 2022 07:24:49 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B47C73858D39 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-21-LbOg7afAM5WzsxB8RkOFkA-1; Fri, 01 Jul 2022 03:24:46 -0400 X-MC-Unique: LbOg7afAM5WzsxB8RkOFkA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 01328185A79C; Fri, 1 Jul 2022 07:24:46 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B4D4D416154; Fri, 1 Jul 2022 07:24:45 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 2617Ogtn1648723 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Fri, 1 Jul 2022 09:24:43 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 2617OfCV1648722; Fri, 1 Jul 2022 09:24:41 +0200 Date: Fri, 1 Jul 2022 09:24:41 +0200 From: Jakub Jelinek To: Richard Sandiford , Richard Biener Cc: gcc-patches@gcc.gnu.org Subject: [PATCH] wide-int: Fix up wi::shifted_mask [PR106144] Message-ID: Reply-To: Jakub Jelinek MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-4.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, 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 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: Fri, 01 Jul 2022 07:24:50 -0000 Hi! As the following self-test testcase shows, wi::shifted_mask sometimes doesn't create canonicalized wide_ints, which then fail to compare equal to canonicalized wide_ints with the same value. In particular, wi::mask (128, false, 128) gives { -1 } with len 1 and prec 128, while wi::shifted_mask (0, 128, false, 128) gives { -1, -1 } with len 2 and prec 128. The problem is that the code is written with the assumption that there are 3 bit blocks (or 2 if start is 0), but doesn't consider the possibility where there are 2 bit blocks (or 1 if start is 0) where the highest block isn't present. In that case, there is the optional block of negate ? 0 : -1 elts, followed by just one elt (either one from the if (shift) or just negate ? -1 : 0) and the rest is implicit sign-extension. Only if end < prec there is 1 or more bits above it that have different bit value and so we need to emit all the elts till end and then one more elt. if (end == prec) would work too, because we have: if (width > prec - start) width = prec - start; unsigned int end = start + width; so end is guaranteed to be end <= prec, dunno what is preferred. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2022-07-01 Jakub Jelinek PR middle-end/106144 * wide-int.cc (wi::shifted_mask): If end >= prec, return right after emitting element for shift or if shift is 0 first element after start. (wide_int_cc_tests): Add tests for equivalency of wi::mask and wi::shifted_mask with 0 start. --- gcc/wide-int.cc.jj 2022-01-11 23:11:23.592273263 +0100 +++ gcc/wide-int.cc 2022-06-30 20:41:25.506292687 +0200 @@ -842,6 +842,13 @@ wi::shifted_mask (HOST_WIDE_INT *val, un val[i++] = negate ? block : ~block; } + if (end >= prec) + { + if (!shift) + val[i++] = negate ? 0 : -1; + return i; + } + while (i < end / HOST_BITS_PER_WIDE_INT) /* 1111111 */ val[i++] = negate ? 0 : -1; @@ -2583,6 +2590,10 @@ wide_int_cc_tests () run_all_wide_int_tests (); test_overflow (); test_round_for_mask (); + ASSERT_EQ (wi::mask (128, false, 128), + wi::shifted_mask (0, 128, false, 128)); + ASSERT_EQ (wi::mask (128, true, 128), + wi::shifted_mask (0, 128, true, 128)); } } // namespace selftest Jakub