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 BF5A63858D20 for ; Thu, 9 Mar 2023 17:59:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org BF5A63858D20 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1678384755; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5zRtK/yMm1F3JPVZnxBXCtFfq4nZ3th4/6FIjHnEUc0=; b=UE+T64+9xAK8PmOtqDo6QWkviflnkPkpO3mZt3PCbv2Ag0djSxSxhMPtwkosWsvr44ZCAy 7cppbH8jE+QURdNJFgLdfSOMqfeNVJ6nMarruc0VabpvAQVFpstYiQuIpvR/92y4yfZrio CDj11vtAN7Ka3YmktCAQcl1zsfbAGqY= Received: from mail-lj1-f198.google.com (mail-lj1-f198.google.com [209.85.208.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-35-bK8LGry6ON2uBnDRPBV7tw-1; Thu, 09 Mar 2023 12:59:14 -0500 X-MC-Unique: bK8LGry6ON2uBnDRPBV7tw-1 Received: by mail-lj1-f198.google.com with SMTP id y23-20020a05651c021700b002984904d871so839695ljn.6 for ; Thu, 09 Mar 2023 09:59:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678384752; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=5zRtK/yMm1F3JPVZnxBXCtFfq4nZ3th4/6FIjHnEUc0=; b=ONPUVCCCZ5LUSx0QlOK6snuLe7SwCw/P1DNOctv1Y/KNqBgFKzYPVny6IXvRiwCOKC 2GBxphm8D4ioHMqzuEqmnTuJ+UicLimqeqb7WrRDmXxtQrcJcAJwrnNiajHD0gQVtSJi SlpFIYeaOG5nxExX8bw7SIywkNg7xuH1Opfi1oPLPavgHZsyXA1lrYld107FJCDh/XEU xqSina4nBQXhMLRvYiDh24iMKU/22riY5WxyK5tpiJlXZM1eRs29A+K5n3ymN8WxR/wR sSaO4LSdlGdOj0QQsTH1l+YD+y+zmRXXodRyyc/bAb4BRxu8Tw00KDzAyPSuWCyB3Qqz Qv4g== X-Gm-Message-State: AO0yUKXgEl9wyuzuTg3rPv3vYM/jFjTBye8ne+szfeMtTx/Wnup29i8r 8Gylthmo33SrJilp3lwBv53KW3Y8pkx4oP2kM8IWOjCHHwI4trKZZOtJupBI18oO1DjfTQpy/ZJ xbmE0Yjk7XVEAbdmnu3SWgHUs6KZ3Tm0KSQ== X-Received: by 2002:a2e:850a:0:b0:295:ba28:a43 with SMTP id j10-20020a2e850a000000b00295ba280a43mr10686547lji.4.1678384752624; Thu, 09 Mar 2023 09:59:12 -0800 (PST) X-Google-Smtp-Source: AK7set+UuGckNM/6v0iFbN3tRrinv1hVtHM9SUvGPp+7AvxNeeg8pO2vBtHi8acBm5DNBqzSgZAuy+hwZy3gLL+FtTw= X-Received: by 2002:a2e:850a:0:b0:295:ba28:a43 with SMTP id j10-20020a2e850a000000b00295ba280a43mr10686538lji.4.1678384752295; Thu, 09 Mar 2023 09:59:12 -0800 (PST) MIME-Version: 1.0 References: <20230307201335.14969-1-ppalka@redhat.com> <7bdcd946-400f-18db-ed02-d157a0638bba@idea> In-Reply-To: <7bdcd946-400f-18db-ed02-d157a0638bba@idea> From: Jonathan Wakely Date: Thu, 9 Mar 2023 17:59:01 +0000 Message-ID: Subject: Re: [PATCH] libstdc++: extraneous begin in cartesian_product_view::end [PR107572] To: Patrick Palka Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-12.1 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_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP 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: On Tue, 7 Mar 2023 at 20:49, Patrick Palka via Libstdc++ wrote: > > On Tue, 7 Mar 2023, Patrick Palka wrote: > > > ranges::begin() isn't guaranteed to be equality-preserving for > > non-forward ranges, so in cartesian_product_view::end we need to be > > careful about calling begin() on the first range (which could be > > non-forward) in the (non-degenerate) case where __empty_tail is false. > > > > Since we're already using a variadic lambda to compute __empty_tail, we > > might as well use that same lambda to build up the tuple of iterators > > instead of doing it via __tuple_transform. > > > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? > > > > PR libstdc++/107572 > > > > libstdc++-v3/ChangeLog: > > > > * include/std/ranges (cartesian_product_view::end): When > > building the tuple of iterators, avoid calling ranges::begin on > > the first range if __empty_tail is false. > > * testsuite/std/ranges/cartesian_product/1.cc (test07): New test. > > --- > > libstdc++-v3/include/std/ranges | 36 +++++++++++++------ > > .../std/ranges/cartesian_product/1.cc | 22 ++++++++++++ > > 2 files changed, 48 insertions(+), 10 deletions(-) > > > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > > index e0cac15a64f..0de7bdef504 100644 > > --- a/libstdc++-v3/include/std/ranges > > +++ b/libstdc++-v3/include/std/ranges > > @@ -8078,26 +8078,42 @@ namespace views::__adaptor > > end() requires ((!__detail::__simple_view<_First> || ... || !__detail::__simple_view<_Vs>) > > && __detail::__cartesian_product_is_common<_First, _Vs...>) > > { > > - bool __empty_tail = [this](index_sequence<_Is...>) { > > - return (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > > + auto __it = [this](index_sequence<_Is...>) { > > + bool __empty_tail = (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > > + auto& __first = std::get<0>(_M_bases); > > + auto __first_it = __empty_tail > > + ? ranges::begin(__first) > > + : __detail::__cartesian_common_arg_end(__first); > > + // N.B. When implementing P2165R4 this should be changed to always return tuple. > > + if constexpr (sizeof...(_Is) == 1) > > + return std::make_pair(std::move(__first_it), > > + ranges::begin(std::get<1 + _Is>(_M_bases))...); > > + else > > + return std::make_tuple(std::move(__first_it), > > + ranges::begin(std::get<1 + _Is>(_M_bases))...); > > On second thought, it might be better to use __tuple_or_pair_t here > instead of manually determining whether to use a pair or tuple, so that > we don't forget to adjust this site when implementing P2165R4 (which > removes __tuple_or_pair_t): Good idea. OK for trunk. > > -- >8 -- > > Subject: [PATCH] libstdc++: extraneous begin in cartesian_product_view::end > [PR107572] > > ranges::begin() isn't guaranteed to be equality-preserving for > non-forward ranges, so in cartesian_product_view::end we need to avoid > calling begin() on the first range (which could be non-forward) in the > (non-degenerate) case where __empty_tail is false. > > Since we're already using a variadic lambda to compute __empty_tail, we > might as well use that same lambda to build up the tuple of iterators > instead of doing it separately via __tuple_transform. > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? > > PR libstdc++/107572 > > libstdc++-v3/ChangeLog: > > * include/std/ranges (cartesian_product_view::end): When > building the tuple of iterators, avoid calling ranges::begin on > the first range if __empty_tail is false. > * testsuite/std/ranges/cartesian_product/1.cc (test07): New test. > --- > libstdc++-v3/include/std/ranges | 28 ++++++++++++------- > .../std/ranges/cartesian_product/1.cc | 25 +++++++++++++++++ > 2 files changed, 43 insertions(+), 10 deletions(-) > > diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges > index e0cac15a64f..d2ab79179ca 100644 > --- a/libstdc++-v3/include/std/ranges > +++ b/libstdc++-v3/include/std/ranges > @@ -8078,26 +8078,34 @@ namespace views::__adaptor > end() requires ((!__detail::__simple_view<_First> || ... || !__detail::__simple_view<_Vs>) > && __detail::__cartesian_product_is_common<_First, _Vs...>) > { > - bool __empty_tail = [this](index_sequence<_Is...>) { > - return (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > + auto __it = [this](index_sequence<_Is...>) { > + using _Ret = __detail::__tuple_or_pair_t, > + iterator_t<_Vs>...>; > + bool __empty_tail = (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > + auto& __first = std::get<0>(_M_bases); > + return _Ret{(__empty_tail > + ? ranges::begin(__first) > + : __detail::__cartesian_common_arg_end(__first)), > + ranges::begin(std::get<1 + _Is>(_M_bases))...}; > }(make_index_sequence{}); > > - auto __it = __detail::__tuple_transform(ranges::begin, _M_bases); > - if (!__empty_tail) > - std::get<0>(__it) = __detail::__cartesian_common_arg_end(std::get<0>(_M_bases)); > return _Iterator{*this, std::move(__it)}; > } > > constexpr _Iterator > end() const requires __detail::__cartesian_product_is_common > { > - bool __empty_tail = [this](index_sequence<_Is...>) { > - return (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > + auto __it = [this](index_sequence<_Is...>) { > + using _Ret = __detail::__tuple_or_pair_t, > + iterator_t...>; > + bool __empty_tail = (ranges::empty(std::get<1 + _Is>(_M_bases)) || ...); > + auto& __first = std::get<0>(_M_bases); > + return _Ret{(__empty_tail > + ? ranges::begin(__first) > + : __detail::__cartesian_common_arg_end(__first)), > + ranges::begin(std::get<1 + _Is>(_M_bases))...}; > }(make_index_sequence{}); > > - auto __it = __detail::__tuple_transform(ranges::begin, _M_bases); > - if (!__empty_tail) > - std::get<0>(__it) = __detail::__cartesian_common_arg_end(std::get<0>(_M_bases)); > return _Iterator{*this, std::move(__it)}; > } > > diff --git a/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc b/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc > index 1ec4422e6f3..8069eb0ab3c 100644 > --- a/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc > +++ b/libstdc++-v3/testsuite/std/ranges/cartesian_product/1.cc > @@ -3,6 +3,7 @@ > > #include > #include > +#include > #include > #include > > @@ -178,6 +179,29 @@ test06() > return true; > } > > +void > +test07() > +{ > + // PR libstdc++/107572 > + static std::istringstream ints("0 1 2 3 4"); > + struct istream_range > + { > + auto begin() { return std::istream_iterator{ints}; } > + auto end() { return std::istream_iterator{}; } > + using iterator_concept = std::input_iterator_tag; > + }; > + static_assert(!ranges::forward_range > + && ranges::common_range); > + istream_range r; > + int i = 0; > + for (auto [v] : views::cartesian_product(r)) > + { > + VERIFY( v == i ); > + ++i; > + }; > + VERIFY( i == 5 ); > +} > + > int > main() > { > @@ -187,4 +211,5 @@ main() > test04(); > test05(); > static_assert(test06()); > + test07(); > } > -- > 2.40.0.rc0.57.g454dfcbddf >