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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id i188-20020a37b8c5000000b0073b45004754sm10165217qkf.34.2023.03.07.12.49.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Mar 2023 12:49:25 -0800 (PST) From: Patrick Palka X-Google-Original-From: Patrick Palka Date: Tue, 7 Mar 2023 15:49:24 -0500 (EST) To: Patrick Palka cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org Subject: Re: [PATCH] libstdc++: extraneous begin in cartesian_product_view::end [PR107572] In-Reply-To: <20230307201335.14969-1-ppalka@redhat.com> Message-ID: <7bdcd946-400f-18db-ed02-d157a0638bba@idea> References: <20230307201335.14969-1-ppalka@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-13.9 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, 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): -- >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