From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id E56683858017; Thu, 9 Dec 2021 23:29:49 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E56683858017 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-5882] libstdc++: Fix ambiguous comparisons for iterators in C++20 X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: 9042302ef06dc8484ee188ebd6c4164ba67d347d X-Git-Newrev: 2c7fb16b5283cf90c4a7f7470e91e1010ee80fcc Message-Id: <20211209232949.E56683858017@sourceware.org> Date: Thu, 9 Dec 2021 23:29:49 +0000 (GMT) X-BeenThere: libstdc++-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Dec 2021 23:29:50 -0000 https://gcc.gnu.org/g:2c7fb16b5283cf90c4a7f7470e91e1010ee80fcc commit r12-5882-g2c7fb16b5283cf90c4a7f7470e91e1010ee80fcc Author: Jonathan Wakely Date: Thu Dec 9 22:22:42 2021 +0000 libstdc++: Fix ambiguous comparisons for iterators in C++20 Since r11-1571 (c++: Refinements to "more constrained") was changed in the front end, the following comment from stl_iterator.h stopped being true: // These extra overloads are not needed in C++20, because the ones above // are constrained with a requires-clause and so overload resolution will // prefer them to greedy unconstrained function templates. The requires-clause is no longer considered when comparing unrelated function templates. That means that the constrained operator== specified in the standard is no longer more constrained than the pathological comparison operators defined in the testsuite_greedy_ops.h header. This was causing several tests to FAIL in C++20 mode: FAIL: 23_containers/deque/types/1.cc (test for excess errors) FAIL: 23_containers/vector/types/1.cc (test for excess errors) FAIL: 24_iterators/move_iterator/greedy_ops.cc (test for excess errors) FAIL: 24_iterators/normal_iterator/greedy_ops.cc (test for excess errors) FAIL: 24_iterators/reverse_iterator/greedy_ops.cc (test for excess errors) The solution is to restore some of the non-standard comparison operators that are more specialized than the greedy operators in the testsuite. libstdc++-v3/ChangeLog: * include/bits/stl_iterator.h (operator==, operator<=>): Define overloads for homogeneous specializations of reverse_iterator, __normal_iterator and move_iterator. Diff: --- libstdc++-v3/include/bits/stl_iterator.h | 50 ++++++++++++++++++++++++++++---- 1 file changed, 45 insertions(+), 5 deletions(-) diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index f6504ece560..6bd860b803e 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -574,6 +574,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION operator<=>(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) { return __y.base() <=> __x.base(); } + + // Additional, non-standard overloads to avoid ambiguities with greedy, + // unconstrained overloads in associated namespaces. + + template + [[nodiscard]] + constexpr bool + operator==(const reverse_iterator<_Iterator>& __x, + const reverse_iterator<_Iterator>& __y) + requires requires { { __x.base() == __y.base() } -> convertible_to; } + { return __x.base() == __y.base(); } + + template + [[nodiscard]] + constexpr compare_three_way_result_t<_Iterator, _Iterator> + operator<=>(const reverse_iterator<_Iterator>& __x, + const reverse_iterator<_Iterator>& __y) + { return __y.base() <=> __x.base(); } #endif // C++20 ///@} @@ -1161,6 +1179,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const __normal_iterator<_IteratorR, _Container>& __rhs) noexcept(noexcept(std::__detail::__synth3way(__lhs.base(), __rhs.base()))) { return std::__detail::__synth3way(__lhs.base(), __rhs.base()); } + + template + [[nodiscard]] + constexpr bool + operator==(const __normal_iterator<_Iterator, _Container>& __lhs, + const __normal_iterator<_Iterator, _Container>& __rhs) + noexcept(noexcept(__lhs.base() == __rhs.base())) + requires requires { + { __lhs.base() == __rhs.base() } -> std::convertible_to; + } + { return __lhs.base() == __rhs.base(); } + + template + [[nodiscard]] + constexpr std::__detail::__synth3way_t<_Iterator> + operator<=>(const __normal_iterator<_Iterator, _Container>& __lhs, + const __normal_iterator<_Iterator, _Container>& __rhs) + noexcept(noexcept(std::__detail::__synth3way(__lhs.base(), __rhs.base()))) + { return std::__detail::__synth3way(__lhs.base(), __rhs.base()); } #else // Forward iterator requirements template @@ -1689,14 +1726,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #endif { return !(__x < __y); } -#if ! (__cplusplus > 201703L && __cpp_lib_concepts) // Note: See __normal_iterator operators note from Gaby to understand // why we have these extra overloads for some move_iterator operators. - // These extra overloads are not needed in C++20, because the ones above - // are constrained with a requires-clause and so overload resolution will - // prefer them to greedy unconstrained function templates. - template [[__nodiscard__]] inline _GLIBCXX17_CONSTEXPR bool @@ -1704,6 +1736,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const move_iterator<_Iterator>& __y) { return __x.base() == __y.base(); } +#if __cpp_lib_three_way_comparison + template + [[__nodiscard__]] + constexpr compare_three_way_result_t<_Iterator> + operator<=>(const move_iterator<_Iterator>& __x, + const move_iterator<_Iterator>& __y) + { return __x.base() <=> __y.base(); } +#else template [[__nodiscard__]] inline _GLIBCXX17_CONSTEXPR bool