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 [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id BEFF83835424 for ; Mon, 17 May 2021 16:47:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org BEFF83835424 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-3coxw9FGM8W4by2YJ5AxFQ-1; Mon, 17 May 2021 12:47:14 -0400 X-MC-Unique: 3coxw9FGM8W4by2YJ5AxFQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DAF0C106BB2B; Mon, 17 May 2021 16:47:12 +0000 (UTC) Received: from localhost (unknown [10.33.36.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8D9E5226F1; Mon, 17 May 2021 16:47:12 +0000 (UTC) Date: Mon, 17 May 2021 17:47:11 +0100 From: Jonathan Wakely To: Patrick Palka Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org Subject: Re: [PATCH] libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621] Message-ID: References: <20210517161743.870382-1-ppalka@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210517161743.870382-1-ppalka@redhat.com> X-Clacks-Overhead: GNU Terry Pratchett X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline X-Spam-Status: No, score=-14.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 May 2021 16:47:17 -0000 On 17/05/21 12:17 -0400, Patrick Palka via Libstdc++ wrote: >A range being a random access range is not a sufficient condition for >ranges::next(iter, sent) to have constant time complexity; the range >must also have a sized sentinel. This adjusts the memoization condition >for reverse_view accordingly. > >Tested on x86_64-pc-linxu-gnu, does this look OK for trunk? Doesn't >seem to be worth backporting. OK for trunk. I agree the backports probably aren't needed, but if it causes anybody problems we can do it later. >libstdc++-v3/ChangeLog: > > * include/std/ranges (reverse_view::_S_needs_cached_begin): > Set to false if the underlying non-common random-access range > doesn't have a sized sentinel. >--- > libstdc++-v3/include/std/ranges | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > >diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges >index bf52074ca05..e93469ca3b4 100644 >--- a/libstdc++-v3/include/std/ranges >+++ b/libstdc++-v3/include/std/ranges >@@ -3340,7 +3340,9 @@ namespace views::__adaptor > { > private: > static constexpr bool _S_needs_cached_begin >- = !common_range<_Vp> && !random_access_range<_Vp>; >+ = !common_range<_Vp> && !(random_access_range<_Vp> >+ && sized_sentinel_for, >+ iterator_t<_Vp>>); > > [[no_unique_address]] > __detail::__maybe_present_t<_S_needs_cached_begin, >-- >2.31.1.621.g97eea85a0a >