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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-4924] libstdc++: Optimize std::tuple_element and std::tuple_size_v Date: Thu, 4 Nov 2021 18:32:56 +0000 (GMT) [thread overview] Message-ID: <20211104183256.2BC94385840B@sourceware.org> (raw) https://gcc.gnu.org/g:09aab7e699dcbd79fd64959cf259567bdca94022 commit r12-4924-g09aab7e699dcbd79fd64959cf259567bdca94022 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Nov 4 09:31:50 2021 +0000 libstdc++: Optimize std::tuple_element and std::tuple_size_v This reduces the number of class template instantiations needed for code using tuples, by reusing _Nth_type in tuple_element and specializing tuple_size_v for tuple, pair and array (and const-qualified versions of them). Also define the _Nth_type primary template as a complete type (but with no nested 'type' member). This avoids "invalid use of incomplete type" errors for out-of-range specializations of tuple_element. Those errors would probably be confusing and unhelpful for users. We already have a user-friendly static assert in tuple_element itself. Also ensure that tuple_size_v is available whenever tuple_size is (as proposed by LWG 3387). We already do that for tuple_element_t. libstdc++-v3/ChangeLog: * include/bits/stl_pair.h (tuple_size_v): Define partial specializations for std::pair. * include/bits/utility.h (_Nth_type): Move definition here and define primary template. (tuple_size_v): Move definition here. * include/std/array (tuple_size_v): Define partial specializations for std::array. * include/std/tuple (tuple_size_v): Move primary template to <bits/utility.h>. Define partial specializations for std::tuple. (tuple_element): Change definition to use _Nth_type. * include/std/variant (_Nth_type): Move to <bits/utility.h>. (variant_alternative, variant): Adjust qualification of _Nth_type. * testsuite/20_util/tuple/element_access/get_neg.cc: Prune additional errors from _Nth_type. Diff: --- libstdc++-v3/include/bits/stl_pair.h | 8 +++ libstdc++-v3/include/bits/utility.h | 51 ++++++++++++++++++- libstdc++-v3/include/std/array | 8 +++ libstdc++-v3/include/std/tuple | 39 +++++---------- libstdc++-v3/include/std/variant | 58 ++-------------------- .../20_util/tuple/element_access/get_neg.cc | 1 + 6 files changed, 84 insertions(+), 81 deletions(-) diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h index 5b400daf97f..6081e0c7fe9 100644 --- a/libstdc++-v3/include/bits/stl_pair.h +++ b/libstdc++-v3/include/bits/stl_pair.h @@ -771,6 +771,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct tuple_element<1, pair<_Tp1, _Tp2>> { typedef _Tp2 type; }; +#if __cplusplus >= 201703L + template<typename _Tp1, typename _Tp2> + inline constexpr size_t tuple_size_v<pair<_Tp1, _Tp2>> = 2; + + template<typename _Tp1, typename _Tp2> + inline constexpr size_t tuple_size_v<const pair<_Tp1, _Tp2>> = 2; +#endif + /// @cond undocumented template<size_t _Int> struct __pair_get; diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h index fce52a4530d..c9ffa008217 100644 --- a/libstdc++-v3/include/bits/utility.h +++ b/libstdc++-v3/include/bits/utility.h @@ -70,6 +70,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct tuple_size<const volatile __enable_if_has_tuple_size<_Tp>> : public tuple_size<_Tp> { }; +#if __cplusplus >= 201703L + template<typename _Tp> + inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value; +#endif + /// Gives the type of the ith element of a given tuple type. template<size_t __i, typename _Tp> struct tuple_element; @@ -97,8 +102,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION }; #if __cplusplus >= 201402L -// The standard says this macro and alias template should be in <tuple> -// but we define them here, to be available in <utility> and <array> too. +// The standard says this macro and alias template should be in <tuple> but we +// we define them here, to be available in <array>, <utility> and <ranges> too. +// _GLIBCXX_RESOLVE_LIB_DEFECTS +// 3378. tuple_size_v/tuple_element_t should be available when +// tuple_size/tuple_element are #define __cpp_lib_tuple_element_t 201402L template<size_t __i, typename _Tp> @@ -195,6 +203,45 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #endif // C++17 #endif // C++14 + template<size_t _Np, typename... _Types> + struct _Nth_type + { }; + + template<typename _Tp0, typename... _Rest> + struct _Nth_type<0, _Tp0, _Rest...> + { using type = _Tp0; }; + + template<typename _Tp0, typename _Tp1, typename... _Rest> + struct _Nth_type<1, _Tp0, _Tp1, _Rest...> + { using type = _Tp1; }; + + template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> + struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...> + { using type = _Tp2; }; + + template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2, + typename... _Rest> +#if __cpp_concepts + requires (_Np >= 3) +#endif + struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...> + : _Nth_type<_Np - 3, _Rest...> + { }; + +#if ! __cpp_concepts // Need additional specializations to avoid ambiguities. + template<typename _Tp0, typename _Tp1, typename... _Rest> + struct _Nth_type<0, _Tp0, _Tp1, _Rest...> + { using type = _Tp0; }; + + template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> + struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...> + { using type = _Tp0; }; + + template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> + struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...> + { using type = _Tp1; }; +#endif + _GLIBCXX_END_NAMESPACE_VERSION } // namespace diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array index 3e12d35157c..413f8e2be01 100644 --- a/libstdc++-v3/include/std/array +++ b/libstdc++-v3/include/std/array @@ -481,6 +481,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using type = _Tp; }; +#if __cplusplus >= 201703L + template<typename _Tp, size_t _Nm> + inline constexpr size_t tuple_size_v<array<_Tp, _Nm>> = _Nm; + + template<typename _Tp, size_t _Nm> + inline constexpr size_t tuple_size_v<const array<_Tp, _Nm>> = _Nm; +#endif + template<typename _Tp, size_t _Nm> struct __is_tuple_like_impl<array<_Tp, _Nm>> : true_type { }; diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple index aaee0b8826a..b82cdf12569 100644 --- a/libstdc++-v3/include/std/tuple +++ b/libstdc++-v3/include/std/tuple @@ -1344,36 +1344,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct tuple_size<tuple<_Elements...>> : public integral_constant<size_t, sizeof...(_Elements)> { }; -#if __cplusplus > 201402L - template <typename _Tp> - inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value; -#endif +#if __cplusplus >= 201703L + template<typename... _Types> + inline constexpr size_t tuple_size_v<tuple<_Types>> + = sizeof...(_Types); - /** - * Recursive case for tuple_element: strip off the first element in - * the tuple and retrieve the (i-1)th element of the remaining tuple. - */ - template<size_t __i, typename _Head, typename... _Tail> - struct tuple_element<__i, tuple<_Head, _Tail...> > - : tuple_element<__i - 1, tuple<_Tail...> > { }; + template<typename... _Types> + inline constexpr size_t tuple_size_v<const tuple<_Types>> + = sizeof...(_Types); +#endif - /** - * Basis case for tuple_element: The first element is the one we're seeking. - */ - template<typename _Head, typename... _Tail> - struct tuple_element<0, tuple<_Head, _Tail...> > + /// Trait to get the Ith element type from a tuple. + template<size_t __i, typename... _Types> + struct tuple_element<__i, tuple<_Types...>> { - typedef _Head type; - }; + static_assert(__i < sizeof...(_Types), "tuple index must be in range"); - /** - * Error case for tuple_element: invalid index. - */ - template<size_t __i> - struct tuple_element<__i, tuple<>> - { - static_assert(__i < tuple_size<tuple<>>::value, - "tuple index must be in range"); + using type = typename _Nth_type<__i, _Types...>::type; }; template<size_t __i, typename _Head, typename... _Tail> diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index c4c307b7bb2..993ce3dba91 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -54,51 +54,6 @@ namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION -namespace __detail -{ -namespace __variant -{ - template<size_t _Np, typename... _Types> - struct _Nth_type; - - template<typename _Tp0, typename... _Rest> - struct _Nth_type<0, _Tp0, _Rest...> - { using type = _Tp0; }; - - template<typename _Tp0, typename _Tp1, typename... _Rest> - struct _Nth_type<1, _Tp0, _Tp1, _Rest...> - { using type = _Tp1; }; - - template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> - struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...> - { using type = _Tp2; }; - - template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2, - typename... _Rest> -#if __cpp_concepts - requires (_Np >= 3) -#endif - struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...> - : _Nth_type<_Np - 3, _Rest...> - { }; - -#if ! __cpp_concepts // Need additional specializations to avoid ambiguities. - template<typename _Tp0, typename _Tp1, typename... _Rest> - struct _Nth_type<0, _Tp0, _Tp1, _Rest...> - { using type = _Tp0; }; - - template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> - struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...> - { using type = _Tp0; }; - - template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest> - struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...> - { using type = _Tp1; }; -#endif - -} // namespace __variant -} // namespace __detail - #if __cplusplus >= 202002L && __cpp_concepts // P2231R1 constexpr needs constexpr unions and constrained destructors. # define __cpp_lib_variant 202106L @@ -145,8 +100,7 @@ namespace __variant { static_assert(_Np < sizeof...(_Types)); - using type - = typename __detail::__variant::_Nth_type<_Np, _Types...>::type; + using type = typename _Nth_type<_Np, _Types...>::type; }; template<size_t _Np, typename _Variant> @@ -1442,8 +1396,7 @@ namespace __variant = __detail::__variant::__accepted_index<_Tp, variant>::value; template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>> - using __to_type - = typename __detail::__variant::_Nth_type<_Np, _Types...>::type; + using __to_type = typename _Nth_type<_Np, _Types...>::type; template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>> using __accepted_type = __to_type<__accepted_index<_Tp>>; @@ -1580,7 +1533,7 @@ namespace __variant emplace(_Args&&... __args) { namespace __variant = std::__detail::__variant; - using type = typename __variant::_Nth_type<_Np, _Types...>::type; + using type = typename _Nth_type<_Np, _Types...>::type; // Provide the strong exception-safety guarantee when possible, // to avoid becoming valueless. if constexpr (is_nothrow_constructible_v<type, _Args...>) @@ -1620,7 +1573,7 @@ namespace __variant emplace(initializer_list<_Up> __il, _Args&&... __args) { namespace __variant = std::__detail::__variant; - using type = typename __variant::_Nth_type<_Np, _Types...>::type; + using type = typename _Nth_type<_Np, _Types...>::type; // Provide the strong exception-safety guarantee when possible, // to avoid becoming valueless. if constexpr (is_nothrow_constructible_v<type, @@ -1803,8 +1756,7 @@ namespace __variant constexpr size_t __max = 11; // "These go to eleven." // The type of the first variant in the pack. - using _V0 - = typename __detail::__variant::_Nth_type<0, _Variants...>::type; + using _V0 = typename _Nth_type<0, _Variants...>::type; // The number of alternatives in that first variant. constexpr auto __n = variant_size_v<remove_reference_t<_V0>>; diff --git a/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc b/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc index 225bb6245a6..113a7fd62de 100644 --- a/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc +++ b/libstdc++-v3/testsuite/20_util/tuple/element_access/get_neg.cc @@ -60,3 +60,4 @@ test03() } // { dg-error "tuple index must be in range" "" { target *-*-* } 0 } +// { dg-prune-output "no type named 'type' in .*_Nth_type" }
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