diff mbox series

Add iterator concepts and range access customization points for C++20

Message ID 20191029174356.GA31962@redhat.com
State New
Headers show
Series Add iterator concepts and range access customization points for C++20 | expand

Commit Message

Jonathan Wakely Oct. 29, 2019, 5:43 p.m. UTC
This adds most of the new C++20 features to <iterator>, as well as a few
initial pieces of <ranges> (but no actual <ranges> header just yet).

Tested powerpc64le-linux, committed to trunk.
commit 0fe795c21dc4fd72fe103c8418b8bdcea1b59721
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Oct 25 23:41:45 2019 +0100

    Add iterator concepts and range access customization points for C++20
    
    This adds most of the new C++20 features to <iterator>, as well as a few
    initial pieces of <ranges> (but no actual <ranges> header just yet).
    
            * include/Makefile.am: Add new header.
            * include/Makefile.in: Regenerate.
            * include/bits/iterator_concepts.h: New header.
            (contiguous_iterator_tag, iter_reference_t, ranges::iter_move)
            (iter_rvalue_reference_t, incrementable_traits, iter_difference_t)
            (readable_traits, iter_value_t, readable, iter_common_reference_t)
            (writable, waekly_incrementable, incrementable)
            (input_or_output_iterator, sentinel_for, disable_sized_sentinel)
            (sized_sentinel_for, input_iterator, output_iterator)
            (forward_iterator, bidirectional_iterator, random_access_iterator)
            (contiguous_iterator, indirectly_unary_invocable)
            (indirectly_regular_unary_invocable, indirect_unary_predicate)
            (indirect_relation, indirect_strict_weak_order, indirect_result_t)
            (projected, indirectly_movable, indirectly_movable_storable)
            (indirectly_copyable, indirectly_copyable_storable, ranges::iter_swap)
            (indirectly_swappable, indirectly_comparable, permutable, mergeable)
            (sortable, unreachable_sentinel_t, unreachable_sentinel)
            (default_sentinel_t, default_sentinel): Define.
            (__detail::__cpp17_iterator, __detail::__cpp17_input_iterator)
            (__detail::__cpp17_fwd_iterator, __detail::__cpp17_bidi_iterator)
            (__detail::__cpp17_randacc_iterator): Define.
            (__iterator_traits): Define constrained specializations.
            * include/bits/move.h (move): Only use old concept check for C++98.
            * include/bits/range_access.h (ranges::disable_sized_range)
            (ranges::begin, ranges::end, ranges::cbegin, ranges::cend)
            (ranges::rbegin, ranges::rend, ranges::crbegin, ranges::crend)
            (ranges::size, ranges::empty, ranges::data, ranges::cdata): Define
            new customization points for C++20.
            (ranges::range, ranges::sized_range): Define new concepts for C++20.
            (ranges::advance, ranges::distance, ranges::next, ranges::prev):
            Define new functions for C++20.
            (__adl_end, __adl_cdata, __adl_cbegin, __adl_cend, __adl_rbegin)
            (__adl_rend, __adl_crbegin, __adl_crend, __adl_cdata, __adl_size)
            (__adl_empty): Remove.
            * include/bits/stl_iterator.h (disable_sized_sentinel): Specialize
            for reverse_iterator.
            * include/bits/stl_iterator_base_types.h (contiguous_iterator_tag):
            Define new struct for C++20.
            (iterator_traits<_Tp*>): Constrain partial specialization in C++20.
            * include/std/concepts (__is_class_or_enum): Move to __detail
            namespace.
            * testsuite/20_util/forward/c_neg.cc: Adjust dg-error line number.
            * testsuite/20_util/forward/f_neg.cc: Likewise.
            * testsuite/24_iterators/associated_types/incrementable.traits.cc: New
            test.
            * testsuite/24_iterators/associated_types/readable.traits.cc: New test.
            * testsuite/24_iterators/contiguous/concept.cc: New test.
            * testsuite/24_iterators/contiguous/tag.cc: New test.
            * testsuite/24_iterators/customization_points/iter_move.cc: New test.
            * testsuite/24_iterators/customization_points/iter_swap.cc: New test.
            * testsuite/24_iterators/headers/iterator/synopsis_c++20.cc: New test.
            * testsuite/24_iterators/range_operations/advance.cc: New test.
            * testsuite/24_iterators/range_operations/distance.cc: New test.
            * testsuite/24_iterators/range_operations/next.cc: New test.
            * testsuite/24_iterators/range_operations/prev.cc: New test.
            * testsuite/26_numerics/adjacent_difference/requirements/
            explicit_instantiation/2.cc: Rename types that conflict with C++20
            concepts.
            * testsuite/26_numerics/adjacent_difference/requirements/
            explicit_instantiation/pod.cc: Likewise.
            * testsuite/26_numerics/partial_sum/requirements/
            explicit_instantiation/2.cc: Likewise.
            * testsuite/26_numerics/partial_sum/requirements/
            explicit_instantiation/pod.cc: Likewise.
            * testsuite/experimental/iterator/requirements.cc: Likewise.
            * testsuite/std/ranges/access/begin.cc: New test.
            * testsuite/std/ranges/access/cbegin.cc: New test.
            * testsuite/std/ranges/access/cdata.cc: New test.
            * testsuite/std/ranges/access/cend.cc: New test.
            * testsuite/std/ranges/access/crbegin.cc: New test.
            * testsuite/std/ranges/access/crend.cc: New test.
            * testsuite/std/ranges/access/data.cc: New test.
            * testsuite/std/ranges/access/empty.cc: New test.
            * testsuite/std/ranges/access/end.cc: New test.
            * testsuite/std/ranges/access/rbegin.cc: New test.
            * testsuite/std/ranges/access/rend.cc: New test.
            * testsuite/std/ranges/access/size.cc: New test.
            * testsuite/util/testsuite_iterators.h (contiguous_iterator_wrapper)
            (test_range, test_sized_range): New test utilities.

Comments

Jonathan Wakely Oct. 29, 2019, 8:17 p.m. UTC | #1
On 29/10/19 17:43 +0000, Jonathan Wakely wrote:
>This adds most of the new C++20 features to <iterator>, as well as a few
>initial pieces of <ranges> (but no actual <ranges> header just yet).

I broke Clang again with this. Fixed by the attached patch.

Tested powerpc64le-linux, committed to trunk.
diff mbox series

Patch

diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 9ff12f10fb1..401c87ad103 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -129,6 +129,7 @@  bits_headers = \
 	${bits_srcdir}/invoke.h \
 	${bits_srcdir}/ios_base.h \
 	${bits_srcdir}/istream.tcc \
+	${bits_srcdir}/iterator_concepts.h \
 	${bits_srcdir}/list.tcc \
 	${bits_srcdir}/locale_classes.h \
 	${bits_srcdir}/locale_classes.tcc \
diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
new file mode 100644
index 00000000000..323689e63ea
--- /dev/null
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -0,0 +1,828 @@ 
+// Concepts and traits for use with iterators -*- C++ -*-
+
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/iterator_concepts.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly. @headername{iterator}
+ */
+
+#ifndef _ITERATOR_CONCEPTS_H
+#define _ITERATOR_CONCEPTS_H 1
+
+#pragma GCC system_header
+
+#include <concepts>
+#include <bits/ptr_traits.h>	// to_address
+#include <bits/range_cmp.h>	// identity, ranges::less
+
+#if __cpp_lib_concepts
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  struct input_iterator_tag;
+  struct output_iterator_tag;
+  struct forward_iterator_tag;
+  struct bidirectional_iterator_tag;
+  struct random_access_iterator_tag;
+  struct contiguous_iterator_tag;
+
+  template<typename _Iterator>
+    struct iterator_traits;
+
+  template<typename _Tp> requires is_object_v<_Tp>
+    struct iterator_traits<_Tp*>;
+
+  template<typename _Iterator, typename>
+    struct __iterator_traits;
+
+  namespace __detail
+  {
+    template<typename _Tp>
+      using __with_ref = _Tp&;
+
+    template<typename _Tp>
+      concept __can_reference = requires { typename __with_ref<_Tp>; };
+
+    template<typename _Tp>
+      concept __dereferenceable = requires(_Tp& __t)
+	{
+	  { *__t } -> __can_reference;
+	};
+
+    // FIXME: needed due to PR c++/67704
+    template<__detail::__dereferenceable _Tp>
+      struct __iter_ref
+      {
+	using type = decltype(*std::declval<_Tp&>());
+      };
+  } // namespace __detail
+
+  template<typename _Tp>
+    using iter_reference_t = typename __detail::__iter_ref<_Tp>::type;
+
+  namespace ranges
+  {
+    namespace __cust_imove
+    {
+      template<typename _Tp>
+	concept __adl_imove
+	  = (std::__detail::__class_or_enum<remove_reference_t<_Tp>>)
+	  && requires(_Tp&& __t) { iter_move(static_cast<_Tp&&>(__t)); };
+
+      struct _IMove
+      {
+      private:
+	template<typename _Tp>
+	  static constexpr bool
+	  _S_noexcept()
+	  {
+	    if constexpr (__adl_imove<_Tp>)
+	      return noexcept(iter_move(std::declval<_Tp>()));
+	    else
+	      return noexcept(*std::declval<_Tp>());
+	  }
+
+      public:
+	template<typename _Tp>
+	  requires __adl_imove<_Tp> || requires(_Tp& __e) { *__e; }
+	  constexpr decltype(auto)
+	  operator()(_Tp&& __e) const
+	  noexcept(_S_noexcept<_Tp>())
+	  {
+	    if constexpr (__adl_imove<_Tp>)
+	      return iter_move(static_cast<_Tp&&>(__e));
+	    else if constexpr (is_reference_v<iter_reference_t<_Tp>>)
+	      return std::move(*__e);
+	    else
+	      return *__e;
+	  }
+      };
+    } // namespace __cust_imove
+
+    inline namespace __cust
+    {
+      inline constexpr __cust_imove::_IMove iter_move{};
+    } // inline namespace __cust
+  } // namespace ranges
+
+  namespace __detail
+  {
+    // FIXME: needed due to PR c++/67704
+    template<__detail::__dereferenceable _Tp>
+      struct __iter_rvalue_ref
+      { };
+
+    template<__detail::__dereferenceable _Tp>
+      requires requires(_Tp& __t)
+      {
+	{ ranges::iter_move(__t) } -> __detail::__can_reference;
+      }
+      struct __iter_rvalue_ref<_Tp>
+      { using type = decltype(ranges::iter_move(std::declval<_Tp&>())); };
+
+  } // namespace __detail
+
+  template<typename _Tp>
+    using iter_rvalue_reference_t
+      = typename __detail::__iter_rvalue_ref<_Tp>::type;
+
+  template<typename> struct incrementable_traits { };
+
+  template<typename _Tp> requires is_object_v<_Tp>
+    struct incrementable_traits<_Tp*>
+    { using difference_type = ptrdiff_t; };
+
+  template<typename _Iter>
+    struct incrementable_traits<const _Iter>
+    : incrementable_traits<_Iter> { };
+
+  template<typename _Tp> requires requires { typename _Tp::difference_type; }
+    struct incrementable_traits<_Tp>
+    { using difference_type = typename _Tp::difference_type; };
+
+  template<typename _Tp>
+    requires (!requires { typename _Tp::difference_type; }
+	      && requires(const _Tp& __a, const _Tp& __b)
+	      {
+		requires (!is_void_v<remove_pointer_t<_Tp>>); // PR c++/78173
+		{ __a - __b } -> integral;
+	      })
+    struct incrementable_traits<_Tp>
+    {
+      using difference_type
+	= make_signed_t<decltype(std::declval<_Tp>() - std::declval<_Tp>())>;
+    };
+
+  namespace __detail
+  {
+    // An iterator such that iterator_traits<_Iter> names a specialization
+    // generated from the primary template.
+    template<typename _Iter>
+      concept __primary_traits_iter
+	= __is_base_of(__iterator_traits<_Iter, void>, iterator_traits<_Iter>);
+
+    template<typename _Iter, typename _Tp>
+      struct __iter_traits_impl
+      { using type = iterator_traits<_Iter>; };
+
+    template<typename _Iter, typename _Tp>
+      requires __primary_traits_iter<_Iter>
+      struct __iter_traits_impl<_Iter, _Tp>
+      { using type = _Tp; };
+
+    // ITER_TRAITS
+    template<typename _Iter, typename _Tp = _Iter>
+      using __iter_traits = typename __iter_traits_impl<_Iter, _Tp>::type;
+  } // namespace __detail
+
+  template<typename _Tp>
+    using iter_difference_t = typename
+      __detail::__iter_traits<_Tp, incrementable_traits<_Tp>>::difference_type;
+
+  namespace __detail
+  {
+    template<typename> struct __cond_value_type { };
+
+    template<typename _Tp> requires is_object_v<_Tp>
+      struct __cond_value_type<_Tp>
+      { using value_type = remove_cv_t<_Tp>; };
+  } // namespace __detail
+
+  template<typename> struct readable_traits { };
+
+  template<typename _Tp>
+    struct readable_traits<_Tp*>
+    : __detail::__cond_value_type<_Tp>
+    { };
+
+  template<typename _Iter> requires is_array_v<_Iter>
+    struct readable_traits<_Iter>
+    { using value_type = remove_cv_t<remove_extent_t<_Iter>>; };
+
+  template<typename _Iter>
+    struct readable_traits<const _Iter>
+    : readable_traits<_Iter>
+    { };
+
+  template<typename _Tp> requires requires { typename _Tp::value_type; }
+    struct readable_traits<_Tp>
+    : __detail::__cond_value_type<typename _Tp::value_type>
+    { };
+
+  template<typename _Tp> requires requires { typename _Tp::element_type; }
+    struct readable_traits<_Tp>
+    : __detail::__cond_value_type<typename _Tp::element_type>
+    { };
+
+  template<typename _Tp>
+    using iter_value_t = typename
+      __detail::__iter_traits<_Tp, readable_traits<_Tp>>::value_type;
+
+  namespace __detail
+  {
+    template<typename _Iter>
+      concept __cpp17_iterator = copyable<_Iter>
+	&& requires(_Iter __it)
+	{
+	  { *__it } -> __can_reference;
+	  { ++__it } -> same_as<_Iter&>;
+	  { *__it++ } -> __can_reference;
+	};
+
+    template<typename _Iter>
+      concept __cpp17_input_iterator = __cpp17_iterator<_Iter>
+	&& equality_comparable<_Iter>
+	&& requires(_Iter __it)
+	{
+	  typename incrementable_traits<_Iter>::difference_type;
+	  typename readable_traits<_Iter>::value_type;
+	  typename common_reference_t<iter_reference_t<_Iter>&&,
+		   typename readable_traits<_Iter>::value_type&>;
+	  typename common_reference_t<decltype(*__it++)&&,
+		   typename readable_traits<_Iter>::value_type&>;
+	  requires signed_integral<typename incrementable_traits<_Iter>::difference_type>;
+	};
+
+    template<typename _Iter>
+      concept __cpp17_fwd_iterator = __cpp17_input_iterator<_Iter>
+	&& constructible_from<_Iter>
+	&& is_lvalue_reference_v<iter_reference_t<_Iter>>
+	&& same_as<remove_cvref_t<iter_reference_t<_Iter>>,
+		   typename readable_traits<_Iter>::value_type>
+	&& requires(_Iter __it)
+	{
+	  {  __it++ } -> convertible_to<const _Iter&>;
+	  { *__it++ } -> same_as<iter_reference_t<_Iter>>;
+	};
+
+    template<typename _Iter>
+      concept __cpp17_bidi_iterator = __cpp17_fwd_iterator<_Iter>
+	&& requires(_Iter __it)
+	{
+	  {  --__it } -> same_as<_Iter&>;
+	  {  __it-- } -> convertible_to<const _Iter&>;
+	  { *__it-- } -> same_as<iter_reference_t<_Iter>>;
+	};
+
+    template<typename _Iter>
+      concept __cpp17_randacc_iterator = __cpp17_bidi_iterator<_Iter>
+	&& totally_ordered<_Iter>
+	&& requires(_Iter __it,
+		    typename incrementable_traits<_Iter>::difference_type __n)
+	{
+	  { __it += __n } -> same_as<_Iter&>;
+	  { __it -= __n } -> same_as<_Iter&>;
+	  { __it +  __n } -> same_as<_Iter>;
+	  { __n +  __it } -> same_as<_Iter>;
+	  { __it -  __n } -> same_as<_Iter>;
+	  { __it -  __it } -> same_as<decltype(__n)>;
+	  {  __it[__n]  } -> convertible_to<iter_reference_t<_Iter>>;
+	};
+
+    template<typename _Iter>
+      concept __iter_with_nested_types = requires {
+	typename _Iter::iterator_category;
+	typename _Iter::value_type;
+	typename _Iter::difference_type;
+	typename _Iter::reference;
+      };
+
+    // FIXME: needed due to PR c++/92102
+    template<typename _Iter>
+      concept __iter_without_nested_types = !__iter_with_nested_types<_Iter>;
+
+    template<typename _Iter, bool __use_arrow = false>
+      struct __ptr
+      { using type = void; };
+
+    template<typename _Iter> requires requires { typename _Iter::pointer; }
+      struct __ptr<_Iter, true>
+      { using type = typename _Iter::pointer; };
+
+    template<typename _Iter> requires requires { typename _Iter::pointer; }
+      struct __ptr<_Iter, false>
+      { using type = typename _Iter::pointer; };
+
+    template<typename _Iter>
+      requires (!requires { typename _Iter::pointer; }
+	  && requires(_Iter& __it) { __it.operator->(); })
+      struct __ptr<_Iter, true>
+      { using type = decltype(std::declval<_Iter&>().operator->()); };
+
+    template<typename _Iter>
+      struct __ref
+      { using type = iter_reference_t<_Iter>; };
+
+    template<typename _Iter> requires requires { typename _Iter::reference; }
+      struct __ref<_Iter>
+      { using type = typename _Iter::reference; };
+
+    template<typename _Iter>
+      struct __cat
+      { using type = input_iterator_tag; };
+
+    template<typename _Iter>
+      requires requires { typename _Iter::iterator_category; }
+      struct __cat<_Iter>
+      { using type = typename _Iter::iterator_category; };
+
+    template<typename _Iter>
+      requires (!requires { typename _Iter::iterator_category; }
+		&& __detail::__cpp17_randacc_iterator<_Iter>)
+      struct __cat<_Iter>
+      { using type = random_access_iterator_tag; };
+
+    template<typename _Iter>
+      requires (!requires { typename _Iter::iterator_category; }
+		&& __detail::__cpp17_bidi_iterator<_Iter>)
+      struct __cat<_Iter>
+      { using type = bidirectional_iterator_tag; };
+
+    template<typename _Iter>
+      requires (!requires { typename _Iter::iterator_category; }
+		&& __detail::__cpp17_fwd_iterator<_Iter>)
+      struct __cat<_Iter>
+      { using type = forward_iterator_tag; };
+
+    template<typename _Iter>
+      struct __diff
+      { using type = void; };
+
+    template<typename _Iter>
+      requires requires {
+	typename incrementable_traits<_Iter>::difference_type;
+      }
+      struct __diff<_Iter>
+      {
+	using type = typename incrementable_traits<_Iter>::difference_type;
+      };
+
+  } // namespace __detail
+
+  template<typename _Iterator>
+    requires __detail::__iter_with_nested_types<_Iterator>
+    struct __iterator_traits<_Iterator, void>
+    {
+      using iterator_category = typename _Iterator::iterator_category;
+      using value_type	      = typename _Iterator::value_type;
+      using difference_type   = typename _Iterator::difference_type;
+      using pointer	      = typename __detail::__ptr<_Iterator>::type;
+      using reference	      = typename _Iterator::reference;
+    };
+
+  template<typename _Iterator>
+    requires __detail::__iter_without_nested_types<_Iterator>
+	      && __detail::__cpp17_input_iterator<_Iterator>
+    struct __iterator_traits<_Iterator, void>
+    {
+      using iterator_category = typename __detail::__cat<_Iterator>::type;
+      using value_type
+	= typename readable_traits<_Iterator>::value_type;
+      using difference_type
+	= typename incrementable_traits<_Iterator>::difference_type;
+      using pointer	      = typename __detail::__ptr<_Iterator, true>::type;
+      using reference	      = typename __detail::__ref<_Iterator>::type;
+    };
+
+  template<typename _Iterator>
+    requires __detail::__iter_without_nested_types<_Iterator>
+	      && __detail::__cpp17_iterator<_Iterator>
+    struct __iterator_traits<_Iterator, void>
+    {
+      using iterator_category = output_iterator_tag;
+      using value_type	      = void;
+      using difference_type   = typename __detail::__diff<_Iterator>::type;
+      using pointer	      = void;
+      using reference	      = void;
+    };
+
+  namespace __detail
+  {
+    template<typename _Iter>
+      struct __iter_concept_impl
+      { };
+
+    template<typename _Iter>
+      requires requires { typename __iter_traits<_Iter>::iterator_concept; }
+      struct __iter_concept_impl<_Iter>
+      { using type = typename __iter_traits<_Iter>::iterator_concept; };
+
+    template<typename _Iter>
+      requires (!requires { typename __iter_traits<_Iter>::iterator_concept; }
+	  && requires { typename __iter_traits<_Iter>::iterator_category; })
+      struct __iter_concept_impl<_Iter>
+      { using type = typename __iter_traits<_Iter>::iterator_category; };
+
+    template<typename _Iter>
+      requires (!requires { typename __iter_traits<_Iter>::iterator_concept; }
+	  && !requires { typename __iter_traits<_Iter>::iterator_category; }
+	  && __primary_traits_iter<_Iter>)
+      struct __iter_concept_impl<_Iter>
+      { using type = random_access_iterator_tag; };
+
+    // ITER_TRAITS
+    template<typename _Iter>
+      using __iter_concept = typename __iter_concept_impl<_Iter>::type;
+  } // namespace __detail
+
+  /// Requirements for types that are readable by applying operator*.
+  template<typename _In>
+    concept readable = requires
+      {
+	typename iter_value_t<_In>;
+	typename iter_reference_t<_In>;
+	typename iter_rvalue_reference_t<_In>;
+      }
+      && common_reference_with<iter_reference_t<_In>&&, iter_value_t<_In>&>
+      && common_reference_with<iter_reference_t<_In>&&,
+			      iter_rvalue_reference_t<_In>&&>
+      && common_reference_with<iter_rvalue_reference_t<_In>&&,
+			       const iter_value_t<_In>&>;
+
+  namespace __detail
+  {
+    // FIXME: needed due to PR c++/67704
+    template<readable _Tp>
+      struct __iter_common_ref
+      : common_reference<iter_reference_t<_Tp>, iter_value_t<_Tp>&>
+      { };
+
+    // FIXME: needed due to PR c++/67704
+    template<typename _Fn, typename... _Is>
+      struct __indirect_result
+      { };
+
+    template<typename _Fn, typename... _Is>
+      requires (readable<_Is> && ...)
+	&& invocable<_Fn, iter_reference_t<_Is>...>
+      struct __indirect_result<_Fn, _Is...>
+      : invoke_result<_Fn, iter_reference_t<_Is>...>
+      { };
+  } // namespace __detail
+
+  template<typename _Tp>
+    using iter_common_reference_t
+      = typename __detail::__iter_common_ref<_Tp>::type;
+
+  /// Requirements for writing a value into an iterator's referenced object.
+  template<typename _Out, typename _Tp>
+    concept writable = requires(_Out&& __o, _Tp&& __t)
+      {
+	*__o = std::forward<_Tp>(__t);
+	*std::forward<_Out>(__o) = std::forward<_Tp>(__t);
+	const_cast<const iter_reference_t<_Out>&&>(*__o)
+	  = std::forward<_Tp>(__t);
+	const_cast<const iter_reference_t<_Out>&&>(*std::forward<_Out>(__o))
+	  = std::forward<_Tp>(__t);
+      };
+
+  /// Requirements on types that can be incremented with ++.
+  template<typename _Iter>
+    concept weakly_incrementable = default_constructible<_Iter>
+      && movable<_Iter>
+      && requires(_Iter __i)
+      {
+	typename iter_difference_t<_Iter>;
+	requires signed_integral<iter_difference_t<_Iter>>;
+	{ ++__i } -> same_as<_Iter&>;
+	__i++;
+      };
+
+  template<typename _Iter>
+    concept incrementable = regular<_Iter> && weakly_incrementable<_Iter>
+      && requires(_Iter __i) { { __i++ } -> same_as<_Iter>; };
+
+  template<typename _Iter>
+    concept input_or_output_iterator
+      = requires(_Iter __i) { { *__i } -> __detail::__can_reference; }
+	&& weakly_incrementable<_Iter>;
+
+  template<typename _Sent, typename _Iter>
+    concept sentinel_for = semiregular<_Sent>
+      && input_or_output_iterator<_Iter>
+      && __detail::__weakly_eq_cmp_with<_Sent, _Iter>;
+
+  template<typename _Sent, typename _Iter>
+    inline constexpr bool disable_sized_sentinel = false;
+
+  template<typename _Sent, typename _Iter>
+    concept sized_sentinel_for = sentinel_for<_Sent, _Iter>
+    && !disable_sized_sentinel<remove_cv_t<_Sent>, remove_cv_t<_Iter>>
+    && requires(const _Iter& __i, const _Sent& __s)
+    {
+      { __s - __i } -> same_as<iter_difference_t<_Iter>>;
+      { __i - __s } -> same_as<iter_difference_t<_Iter>>;
+    };
+
+  template<typename _Iter>
+    concept input_iterator = input_or_output_iterator<_Iter>
+      && readable<_Iter>
+      && requires { typename __detail::__iter_concept<_Iter>; }
+      && derived_from<__detail::__iter_concept<_Iter>, input_iterator_tag>;
+
+  template<typename _Iter, typename _Tp>
+    concept output_iterator = input_or_output_iterator<_Iter>
+      && writable<_Iter, _Tp>
+      && requires(_Iter __i, _Tp&& __t) { *__i++ = std::forward<_Tp>(__t); };
+
+  template<typename _Iter>
+    concept forward_iterator = input_iterator<_Iter>
+      && derived_from<__detail::__iter_concept<_Iter>, forward_iterator_tag>
+      && incrementable<_Iter> && sentinel_for<_Iter, _Iter>;
+
+  template<typename _Iter>
+    concept bidirectional_iterator = forward_iterator<_Iter>
+      && derived_from<__detail::__iter_concept<_Iter>,
+		      bidirectional_iterator_tag>
+      && requires(_Iter __i)
+      {
+	{ --__i } -> same_as<_Iter&>;
+	{ __i-- } -> same_as<_Iter>;
+      };
+
+  template<typename _Iter>
+    concept random_access_iterator = bidirectional_iterator<_Iter>
+      && derived_from<__detail::__iter_concept<_Iter>,
+		      random_access_iterator_tag>
+      && totally_ordered<_Iter> && sized_sentinel_for<_Iter, _Iter>
+      && requires(_Iter __i, const _Iter __j,
+		  const iter_difference_t<_Iter> __n)
+      {
+	{ __i += __n } -> same_as<_Iter&>;
+	{ __j +  __n } -> same_as<_Iter>;
+	{ __n +  __j } -> same_as<_Iter>;
+	{ __i -= __n } -> same_as<_Iter&>;
+	{ __j -  __n } -> same_as<_Iter>;
+	{  __j[__n]  } -> same_as<iter_reference_t<_Iter>>;
+      };
+
+  template<typename _Iter>
+    concept contiguous_iterator = random_access_iterator<_Iter>
+      && derived_from<__detail::__iter_concept<_Iter>, contiguous_iterator_tag>
+      && is_lvalue_reference_v<iter_reference_t<_Iter>>
+      && same_as<iter_value_t<_Iter>, remove_cvref_t<iter_reference_t<_Iter>>>
+      && requires(const _Iter& __i)
+      {
+	{ std::to_address(__i) }
+	  -> same_as<add_pointer_t<iter_reference_t<_Iter>>>;
+      };
+
+  // [indirectcallable], indirect callable requirements
+
+  // [indirectcallable.indirectinvocable], indirect callables
+
+  template<typename _Fn, typename _Iter>
+    concept indirectly_unary_invocable = readable<_Iter>
+      && copy_constructible<_Fn> && invocable<_Fn&, iter_value_t<_Iter>&>
+      && invocable<_Fn&, iter_reference_t<_Iter>>
+      && invocable<_Fn&, iter_common_reference_t<_Iter>>
+      && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
+			       invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
+
+  template<typename _Fn, typename _Iter>
+    concept indirectly_regular_unary_invocable = readable<_Iter>
+      && copy_constructible<_Fn>
+      && regular_invocable<_Fn&, iter_value_t<_Iter>&>
+      && regular_invocable<_Fn&, iter_reference_t<_Iter>>
+      && regular_invocable<_Fn&, iter_common_reference_t<_Iter>>
+      && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
+			       invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
+
+  template<typename _Fn, typename _Iter>
+    concept indirect_unary_predicate = readable<_Iter>
+      && copy_constructible<_Fn> && predicate<_Fn&, iter_value_t<_Iter>&>
+      && predicate<_Fn&, iter_reference_t<_Iter>>
+      && predicate<_Fn&, iter_common_reference_t<_Iter>>;
+
+  template<typename _Fn, typename _I1, typename _I2 = _I1>
+    concept indirect_relation = readable<_I1> && readable<_I2>
+      && copy_constructible<_Fn>
+      && relation<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
+      && relation<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
+      && relation<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
+      && relation<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
+      && relation<_Fn&, iter_common_reference_t<_I1>,
+		  iter_common_reference_t<_I2>>;
+
+  template<typename _Fn, typename _I1, typename _I2 = _I1>
+    concept indirect_strict_weak_order = readable<_I1> && readable<_I2>
+      && copy_constructible<_Fn>
+      && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
+      && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
+      && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
+      && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
+      && strict_weak_order<_Fn&, iter_common_reference_t<_I1>,
+			   iter_common_reference_t<_I2>>;
+
+  template<typename _Fn, typename... _Is>
+    using indirect_result_t = typename
+      __detail::__indirect_result<_Fn, iter_reference_t<_Is>...>::type;
+
+  /// [projected], projected
+  template<readable _Iter, indirectly_regular_unary_invocable<_Iter> _Proj>
+    struct projected
+    {
+      using value_type = remove_cvref_t<indirect_result_t<_Proj&, _Iter>>;
+      indirect_result_t<_Proj&, _Iter> operator*() const; // not defined
+    };
+
+  template<weakly_incrementable _Iter, typename _Proj>
+    struct incrementable_traits<projected<_Iter, _Proj>>
+    { using difference_type = iter_difference_t<_Iter>; };
+
+  // [alg.req], common algorithm requirements
+
+  /// [alg.req.ind.move], concept `indirectly_movable`
+
+  template<typename _In, typename _Out>
+    concept indirectly_movable = readable<_In>
+      && writable<_Out, iter_rvalue_reference_t<_In>>;
+
+  template<typename _In, typename _Out>
+    concept indirectly_movable_storable = indirectly_movable<_In, _Out>
+      && writable<_Out, iter_value_t<_In>> && movable<iter_value_t<_In>>
+      && constructible_from<iter_value_t<_In>, iter_rvalue_reference_t<_In>>
+      && assignable_from<iter_value_t<_In>&, iter_rvalue_reference_t<_In>>;
+
+  /// [alg.req.ind.copy], concept `indirectly_copyable`
+  template<typename _In, typename _Out>
+    concept indirectly_copyable = readable<_In>
+      && writable<_Out, iter_reference_t<_In>>;
+
+  template<typename _In, typename _Out>
+    concept indirectly_copyable_storable = indirectly_copyable<_In, _Out>
+      && writable<_Out, const iter_value_t<_In>&>
+      && copyable<iter_value_t<_In>>
+      && constructible_from<iter_value_t<_In>, iter_reference_t<_In>>
+      && assignable_from<iter_value_t<_In>&, iter_reference_t<_In>>;
+
+namespace ranges
+{
+  namespace __cust_iswap
+  {
+    template<typename _It1, typename _It2>
+      void iter_swap(_It1&, _It2&) = delete;
+
+    template<typename _Tp, typename _Up>
+      concept __adl_iswap
+	= (std::__detail::__class_or_enum<remove_reference_t<_Tp>>
+	  || std::__detail::__class_or_enum<remove_reference_t<_Up>>)
+	&& requires(_Tp&& __t, _Up&& __u) {
+	  iter_swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
+	};
+
+    template<typename _Xp, typename _Yp>
+      constexpr iter_value_t<remove_reference_t<_Xp>>
+      __iter_exchange_move(_Xp&& __x, _Yp&& __y)
+      noexcept(noexcept(iter_value_t<remove_reference_t<_Xp>>(iter_move(__x)))
+	       && noexcept(*__x = iter_move(__y)))
+      {
+	iter_value_t<remove_reference_t<_Xp>> __old_value(iter_move(__x));
+	*__x = iter_move(__y);
+	return __old_value;
+      }
+
+    struct _IterSwap
+    {
+    private:
+      template<typename _Tp, typename _Up>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__adl_iswap<_Tp, _Up>)
+	    return noexcept(iter_swap(std::declval<_Tp>(),
+				      std::declval<_Up>()));
+	  else if constexpr (readable<_Tp> && readable<_Up>
+	    && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
+	    return noexcept(ranges::swap(*std::declval<_Tp>(),
+					 *std::declval<_Up>()));
+	  else
+	    return noexcept(*std::declval<_Tp>()
+		= __iter_exchange_move(std::declval<_Up>(),
+				       std::declval<_Tp>()));
+	}
+
+    public:
+      template<typename _Tp, typename _Up>
+	requires __adl_iswap<_Tp, _Up>
+	|| (readable<_Tp> && readable<_Up>
+	    && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
+	|| (indirectly_movable_storable<_Tp, _Up>
+	    && indirectly_movable_storable<_Up, _Tp>)
+	constexpr void
+	operator()(_Tp&& __e1, _Up&& __e2) const
+	noexcept(_S_noexcept<_Tp, _Up>())
+	{
+	  if constexpr (__adl_iswap<_Tp, _Up>)
+	    iter_swap(static_cast<_Tp&&>(__e1), static_cast<_Up&&>(__e2));
+	  else if constexpr (readable<_Tp> && readable<_Up>
+	    && swappable_with<iter_reference_t<_Tp>, iter_reference_t<_Up>>)
+	    ranges::swap(*__e1, *__e2);
+	  else
+	    *__e1 = __iter_exchange_move(__e2, __e1);
+	}
+    };
+  } // namespace __cust_iswap
+
+  inline namespace __cust
+  {
+    inline constexpr __cust_iswap::_IterSwap iter_swap{};
+  } // inline namespace __cust
+
+} // namespace ranges
+
+  /// [alg.req.ind.swap], concept `indirectly_swappable`
+  template<typename _I1, typename _I2 = _I1>
+    concept indirectly_swappable = readable<_I1> && readable<_I2>
+      && requires(_I1& __i1, _I2& __i2)
+      {
+	ranges::iter_swap(__i1, __i1);
+	ranges::iter_swap(__i2, __i2);
+	ranges::iter_swap(__i1, __i2);
+	ranges::iter_swap(__i2, __i1);
+      };
+
+  /// [alg.req.ind.cmp], concept `indirectly_comparable`
+  template<typename _I1, typename _I2, typename _Rel, typename _P1 = identity,
+	   typename _P2 = identity>
+    concept indirectly_comparable
+      = indirect_relation<_Rel, projected<_I1, _P1>, projected<_I2, _P2>>;
+
+  /// [alg.req.permutable], concept `permutable`
+  template<typename _Iter>
+    concept permutable = forward_iterator<_Iter>
+      && indirectly_movable_storable<_Iter, _Iter>
+      && indirectly_swappable<_Iter, _Iter>;
+
+  /// [alg.req.mergeable], concept `mergeable`
+  template<typename _I1, typename _I2, typename _Out,
+	   typename _Rel = ranges::less, typename _P1 = identity,
+	   typename _P2 = identity>
+    concept mergeable = input_iterator<_I1> && input_iterator<_I2>
+      && weakly_incrementable<_Out> && indirectly_copyable<_I1, _Out>
+      && indirectly_copyable<_I2, _Out>
+      && indirect_strict_weak_order<_Rel, projected<_I1, _P1>,
+				    projected<_I2, _P2>>;
+
+  /// [alg.req.sortable], concept `sortable`
+  template<typename _Iter, typename _Rel = ranges::less,
+	   typename _Proj = identity>
+    concept sortable = permutable<_Iter>
+      && indirect_strict_weak_order<_Rel, projected<_Iter, _Proj>>;
+
+  struct unreachable_sentinel_t
+  {
+    template<weakly_incrementable _It>
+      friend constexpr bool
+      operator==(unreachable_sentinel_t, const _It&) noexcept
+      { return false; }
+
+#ifndef __cpp_lib_three_way_comparison
+    template<weakly_incrementable _It>
+      friend constexpr bool
+      operator!=(unreachable_sentinel_t, const _It&) noexcept
+      { return true; }
+
+    template<weakly_incrementable _It>
+      friend constexpr bool
+      operator==(const _It&, unreachable_sentinel_t) noexcept
+      { return false; }
+
+    template<weakly_incrementable _It>
+      friend constexpr bool
+      operator!=(const _It&, unreachable_sentinel_t) noexcept
+      { return true; }
+#endif
+  };
+
+  inline constexpr unreachable_sentinel_t unreachable_sentinel{};
+
+  struct default_sentinel_t { };
+  inline constexpr default_sentinel_t default_sentinel{};
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif // C++20 library concepts
+#endif // _ITERATOR_CONCEPTS_H
diff --git a/libstdc++-v3/include/bits/move.h b/libstdc++-v3/include/bits/move.h
index d7c7068e29c..5d6541d193f 100644
--- a/libstdc++-v3/include/bits/move.h
+++ b/libstdc++-v3/include/bits/move.h
@@ -31,7 +31,9 @@ 
 #define _MOVE_H 1
 
 #include <bits/c++config.h>
-#include <bits/concept_check.h>
+#if __cplusplus < 201103L
+# include <bits/concept_check.h>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -188,9 +190,10 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
 				is_nothrow_move_assignable<_Tp>>::value)
     {
+#if __cplusplus < 201103L
       // concept requirements
       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
-
+#endif
       _Tp __tmp = _GLIBCXX_MOVE(__a);
       __a = _GLIBCXX_MOVE(__b);
       __b = _GLIBCXX_MOVE(__tmp);
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index bc137d7396e..3b6ed9aa66a 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -34,6 +34,8 @@ 
 
 #if __cplusplus >= 201103L
 #include <initializer_list>
+#include <bits/iterator_concepts.h>
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -342,62 +344,724 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __adl_begin(_Container& __cont) noexcept(noexcept(begin(__cont)))
     { return begin(__cont); }
 
-  template <typename _Container>
-    constexpr auto
-    __adl_end(_Container& __cont) noexcept(noexcept(end(__cont)))
-    { return end(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_cbegin(_Container& __cont) noexcept(noexcept(cbegin(__cont)))
-    { return cbegin(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_cend(_Container& __cont) noexcept(noexcept(cend(__cont)))
-    { return cend(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_rbegin(_Container& __cont) noexcept(noexcept(rbegin(__cont)))
-    { return rbegin(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_rend(_Container& __cont) noexcept(noexcept(rend(__cont)))
-    { return rend(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_crbegin(_Container& __cont) noexcept(noexcept(crbegin(__cont)))
-    { return crbegin(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_crend(_Container& __cont) noexcept(noexcept(crend(__cont)))
-    { return crend(__cont); }
-
   template <typename _Container>
     constexpr auto
     __adl_data(_Container& __cont) noexcept(noexcept(data(__cont)))
     { return data(__cont); }
 
-  template <typename _Container>
-    constexpr auto
-    __adl_cdata(_Container& __cont) noexcept(noexcept(cdata(__cont)))
-    { return cdata(__cont); }
+namespace ranges
+{
+  template<typename>
+    inline constexpr bool disable_sized_range = false;
 
-  template <typename _Container>
-    constexpr auto
-    __adl_size(_Container& __cont) noexcept(noexcept(size(__cont)))
-    { return size(__cont); }
+  namespace __detail
+  {
+    using __max_diff_type = long long;
+    using __max_size_type = unsigned long long;
 
-  template <typename _Container>
-    constexpr auto
-    __adl_empty(_Container& __cont) noexcept(noexcept(empty(__cont)))
-    { return empty(__cont); }
+    template<typename _Tp>
+      concept __is_integer_like = integral<_Tp>
+	|| same_as<_Tp, __max_diff_type> || same_as<_Tp, __max_size_type>;
+
+    template<typename _Tp>
+      concept __is_signed_integer_like = signed_integral<_Tp>
+	|| same_as<_Tp, __max_diff_type>;
+
+    template<integral _Tp>
+      constexpr make_unsigned_t<_Tp>
+      __to_unsigned_like(_Tp __t) noexcept
+      { return __t; }
+  } // namespace __detail
+
+  namespace __cust_access
+  {
+    template<typename _Tp>
+      constexpr decay_t<_Tp>
+      __decay_copy(_Tp&& __t)
+      noexcept(is_nothrow_convertible_v<_Tp, decay_t<_Tp>>)
+      { return std::forward<_Tp>(__t); }
+
+    template<typename _Tp>
+      concept __member_begin = is_lvalue_reference_v<_Tp>
+	&& requires(_Tp __t)
+	{ { __decay_copy(__t.begin()) } -> input_or_output_iterator; };
+
+    template<typename _Tp> void begin(_Tp&&) = delete;
+    template<typename _Tp> void begin(initializer_list<_Tp>&&) = delete;
+
+    template<typename _Tp>
+      concept __adl_begin = requires(_Tp&& __t)
+	{
+	  { __decay_copy(begin(std::forward<_Tp>(__t))) }
+	    -> input_or_output_iterator;
+	};
+
+    template<typename _Tp>
+      concept __complete_type = requires(_Tp* __p) { __p + 1; };
+
+    struct _Begin
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_begin<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().begin()));
+	  else
+	    return noexcept(__decay_copy(begin(std::declval<_Tp>())));
+	}
+
+    public:
+      template<__complete_type _Tp, size_t _Nm>
+	constexpr _Tp*
+	operator()(_Tp (&__e)[_Nm]) const noexcept
+	{ return __e; }
+
+      template<typename _Tp> requires __member_begin<_Tp> || __adl_begin<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_begin<_Tp>)
+	    return __e.begin();
+	  else
+	    return begin(std::forward<_Tp>(__e));
+	}
+    };
+
+    template<typename _Tp>
+      concept __member_end = is_lvalue_reference_v<_Tp>
+	&& requires(_Tp __t)
+	{
+	  { __decay_copy(__t.end()) }
+	    -> sentinel_for<decltype(_Begin{}(__t))>;
+	};
+
+    template<typename _Tp> void end(_Tp&&) = delete;
+    template<typename _Tp> void end(initializer_list<_Tp>&&) = delete;
+
+    template<typename _Tp>
+      concept __adl_end = requires(_Tp&& __t)
+	{
+	  { __decay_copy(end(std::forward<_Tp>(__t))) }
+	    -> sentinel_for<decltype(_Begin{}(std::forward<_Tp>(__t)))>;
+	};
+
+    struct _End
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_end<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().end()));
+	  else
+	    return noexcept(__decay_copy(end(std::declval<_Tp>())));
+	}
+
+    public:
+      template<__complete_type _Tp, size_t _Nm>
+	constexpr _Tp*
+	operator()(_Tp (&__e)[_Nm]) const noexcept
+	{ return __e + _Nm; }
+
+      template<typename _Tp> requires __member_end<_Tp> || __adl_end<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_end<_Tp>)
+	    return __e.end();
+	  else
+	    return end(std::forward<_Tp>(__e));
+	}
+    };
+
+    template<typename _Tp>
+      constexpr decltype(auto)
+      __as_const(_Tp&& __t) noexcept
+      {
+	if constexpr (is_lvalue_reference_v<_Tp>)
+	  return static_cast<const remove_reference_t<_Tp>&>(__t);
+	else
+	  return static_cast<const _Tp&&>(__t);
+      }
+
+    struct _CBegin
+    {
+      template<typename _Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(noexcept(_Begin{}(__cust_access::__as_const((_Tp&&)__e))))
+	requires requires { _Begin{}(__cust_access::__as_const((_Tp&&)__e)); }
+	{
+	  return _Begin{}(__cust_access::__as_const(std::forward<_Tp>(__e)));
+	}
+    };
+
+    struct _CEnd
+    {
+      template<typename _Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(noexcept(_End{}(__cust_access::__as_const((_Tp&&)__e))))
+	requires requires { _End{}(__cust_access::__as_const((_Tp&&)__e)); }
+	{
+	  return _End{}(__cust_access::__as_const(std::forward<_Tp>(__e)));
+	}
+    };
+
+    template<typename _Tp>
+      concept __member_rbegin = is_lvalue_reference_v<_Tp>
+	&& requires(_Tp __t)
+	{ { __decay_copy(__t.rbegin()) } -> input_or_output_iterator; };
+
+    template<typename _Tp> void rbegin(_Tp&&) = delete;
+
+    template<typename _Tp>
+      concept __adl_rbegin = requires(_Tp&& __t)
+	{
+	  { __decay_copy(rbegin(std::forward<_Tp>(__t))) }
+	    -> input_or_output_iterator;
+	};
+
+    template<typename _Tp>
+      concept __reversable = requires(_Tp&& __t)
+	{
+	  { _Begin{}(std::forward<_Tp>(__t)) } -> bidirectional_iterator;
+	  { _End{}(std::forward<_Tp>(__t)) }
+	    -> same_as<decltype(_Begin{}(std::forward<_Tp>(__t)))>;
+	};
+
+    struct _RBegin
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_rbegin<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().rbegin()));
+	  else if constexpr (__adl_rbegin<_Tp>)
+	    return noexcept(__decay_copy(rbegin(std::declval<_Tp>())));
+	  else if constexpr (noexcept(_End{}(std::declval<_Tp>())))
+	    {
+	      using _It = decltype(_End{}(std::declval<_Tp>()));
+	      // std::reverse_iterator copy-initializes its member.
+	      return is_nothrow_copy_constructible_v<_It>;
+	    }
+	  else
+	    return false;
+	}
+
+    public:
+      template<typename _Tp>
+	requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_rbegin<_Tp>)
+	    return __e.rbegin();
+	  else if constexpr (__adl_rbegin<_Tp>)
+	    return rbegin(std::forward<_Tp>(__e));
+	  else
+	    return std::make_reverse_iterator(_End{}(std::forward<_Tp>(__e)));
+	}
+    };
+
+    template<typename _Tp>
+      concept __member_rend = is_lvalue_reference_v<_Tp>
+	&& requires(_Tp __t)
+	{
+	  { __decay_copy(__t.rend()) }
+	    -> sentinel_for<decltype(_RBegin{}(__t))>;
+	};
+
+    template<typename _Tp> void rend(_Tp&&) = delete;
+
+    template<typename _Tp>
+      concept __adl_rend = requires(_Tp&& __t)
+	{
+	  { __decay_copy(rend(std::forward<_Tp>(__t))) }
+	    -> sentinel_for<decltype(_RBegin{}(std::forward<_Tp>(__t)))>;
+	};
+
+    struct _REnd
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_rend<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().rend()));
+	  else if constexpr (__adl_rend<_Tp>)
+	    return noexcept(__decay_copy(rend(std::declval<_Tp>())));
+	  else if constexpr (noexcept(_Begin{}(std::declval<_Tp>())))
+	    {
+	      using _It = decltype(_Begin{}(std::declval<_Tp>()));
+	      // std::reverse_iterator copy-initializes its member.
+	      return is_nothrow_copy_constructible_v<_It>;
+	    }
+	  else
+	    return false;
+	}
+
+    public:
+      template<typename _Tp>
+	requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_rend<_Tp>)
+	    return __e.rend();
+	  else if constexpr (__adl_rend<_Tp>)
+	    return rend(std::forward<_Tp>(__e));
+	  else
+	    return std::make_reverse_iterator(_Begin{}(std::forward<_Tp>(__e)));
+	}
+    };
+
+    struct _CRBegin
+    {
+      template<typename _Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(noexcept(_RBegin{}(__cust_access::__as_const((_Tp&&)__e))))
+	requires requires { _RBegin{}(__cust_access::__as_const((_Tp&&)__e)); }
+	{
+	  return _RBegin{}(__cust_access::__as_const(std::forward<_Tp>(__e)));
+	}
+    };
+
+    struct _CREnd
+    {
+      template<typename _Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(noexcept(_REnd{}(__cust_access::__as_const((_Tp&&)__e))))
+	requires requires { _REnd{}(__cust_access::__as_const((_Tp&&)__e)); }
+	{
+	  return _REnd{}(__cust_access::__as_const(std::forward<_Tp>(__e)));
+	}
+    };
+
+    template<typename _Tp>
+      concept __member_size = !disable_sized_range<remove_cvref_t<_Tp>>
+	&& requires(_Tp&& __t)
+	{
+	  { __decay_copy(std::forward<_Tp>(__t).size()) }
+	    -> __detail::__is_integer_like;
+	};
+
+    template<typename _Tp> void size(_Tp&&) = delete;
+
+    template<typename _Tp>
+      concept __adl_size = !disable_sized_range<remove_cvref_t<_Tp>>
+	&& requires(_Tp&& __t)
+	{
+	  { __decay_copy(size(std::forward<_Tp>(__t))) }
+	    -> __detail::__is_integer_like;
+	};
+
+    // FIXME: needed due to PR c++/92268
+    template<forward_iterator _It, sized_sentinel_for<_It> _End>
+      requires requires (_It __it, _End __end)
+      { { __end - __it } -> __detail::__is_integer_like; }
+      void
+      __subtractable_fwd_iter(_It, _End)
+      { }
+
+    template<typename _Tp>
+      concept __sizable = requires(_Tp&& __t)
+	{
+	  __subtractable_fwd_iter(_Begin{}(std::forward<_Tp>(__t)),
+				  _End{}(std::forward<_Tp>(__t)));
+	};
+
+    struct _Size
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_size<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().size()));
+	  else if constexpr (__adl_size<_Tp>)
+	    return noexcept(__decay_copy(size(std::declval<_Tp>())));
+	  else if constexpr (__sizable<_Tp>)
+	    return noexcept(_End{}(std::declval<_Tp>())
+			    - _Begin{}(std::declval<_Tp>()));
+	}
+
+    public:
+      template<__complete_type _Tp, size_t _Nm>
+	constexpr size_t
+	operator()(_Tp (&__e)[_Nm]) const noexcept
+	{ return _Nm; }
+
+      template<typename _Tp>
+	requires __member_size<_Tp> || __adl_size<_Tp> || __sizable<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_size<_Tp>)
+	    return std::forward<_Tp>(__e).size();
+	  else if constexpr (__adl_size<_Tp>)
+	    return size(std::forward<_Tp>(__e));
+	  else if constexpr (__sizable<_Tp>)
+	    return __detail::__to_unsigned_like(
+		_End{}(std::forward<_Tp>(__e))
+		- _Begin{}(std::forward<_Tp>(__e)));
+	}
+    };
+
+    template<typename _Tp>
+      concept __member_empty = requires(_Tp&& __t)
+	{ bool(std::forward<_Tp>(__t).empty()); };
+
+    template<typename _Tp>
+      concept __size0_empty = requires(_Tp&& __t)
+	{ _Size{}(std::forward<_Tp>(__t)) == 0; };
+
+    template<typename _Tp>
+      concept __eq_iter_empty = requires(_Tp&& __t)
+	{
+	  { _Begin{}(std::forward<_Tp>(__t)) } -> forward_iterator;
+	  bool(_Begin{}(std::forward<_Tp>(__t))
+	      == _End{}(std::forward<_Tp>(__t)));
+	};
+
+    struct _Empty
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_empty<_Tp>)
+	    return noexcept(std::declval<_Tp>().empty());
+	  else if constexpr (__size0_empty<_Tp>)
+	    return noexcept(_Size{}(std::declval<_Tp>()) == 0);
+	  else
+	    return noexcept(bool(_Begin{}(std::declval<_Tp>())
+		== _End{}(std::declval<_Tp>())));
+	}
+
+    public:
+      template<typename _Tp>
+	requires __member_empty<_Tp> || __size0_empty<_Tp>
+	|| __eq_iter_empty<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_empty<_Tp>)
+	    return bool(std::forward<_Tp>(__e).empty());
+	  else if constexpr (__size0_empty<_Tp>)
+	    return _Size{}(std::forward<_Tp>(__e)) == 0;
+	  else
+	    return bool(_Begin{}(std::forward<_Tp>(__e))
+		== _End{}(std::forward<_Tp>(__e)));
+	}
+    };
+
+    template<typename _Tp>
+      concept __pointer_to_object = is_pointer_v<_Tp>
+				    && is_object_v<remove_pointer_t<_Tp>>;
+
+    template<typename _Tp>
+      concept __member_data = is_lvalue_reference_v<_Tp>
+	&& requires(_Tp __t) { { __t.data() } -> __pointer_to_object; };
+
+    template<typename _Tp>
+      concept __begin_data = requires(_Tp&& __t)
+	{ { _Begin{}(std::forward<_Tp>(__t)) } -> contiguous_iterator; };
+
+    struct _Data
+    {
+    private:
+      template<typename _Tp>
+	static constexpr bool
+	_S_noexcept()
+	{
+	  if constexpr (__member_data<_Tp>)
+	    return noexcept(__decay_copy(std::declval<_Tp>().data()));
+	  else
+	    return noexcept(_Begin{}(std::declval<_Tp>()));
+	}
+
+    public:
+      template<typename _Tp> requires __member_data<_Tp> || __begin_data<_Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>())
+	{
+	  if constexpr (__member_data<_Tp>)
+	    return __e.data();
+	  else
+	    return std::to_address(_Begin{}(std::forward<_Tp>(__e)));
+	}
+    };
+
+    struct _CData
+    {
+      template<typename _Tp>
+	constexpr auto
+	operator()(_Tp&& __e) const
+	noexcept(noexcept(_Data{}(__cust_access::__as_const((_Tp&&)__e))))
+	requires requires { _Data{}(__cust_access::__as_const((_Tp&&)__e)); }
+	{
+	  return _Data{}(__cust_access::__as_const(std::forward<_Tp>(__e)));
+	}
+    };
+
+  } // namespace __cust_access
+
+  inline namespace __cust
+  {
+    inline constexpr __cust_access::_Begin begin{};
+    inline constexpr __cust_access::_End end{};
+    inline constexpr __cust_access::_CBegin cbegin{};
+    inline constexpr __cust_access::_CEnd cend{};
+    inline constexpr __cust_access::_RBegin rbegin{};
+    inline constexpr __cust_access::_REnd rend{};
+    inline constexpr __cust_access::_CRBegin crbegin{};
+    inline constexpr __cust_access::_CREnd crend{};
+    inline constexpr __cust_access::_Size size{};
+    inline constexpr __cust_access::_Empty empty{};
+    inline constexpr __cust_access::_Data data{};
+    inline constexpr __cust_access::_CData cdata{};
+  }
+
+  namespace __detail
+  {
+    template<typename _Tp>
+      concept __range_impl = requires(_Tp&& __t) {
+	ranges::begin(std::forward<_Tp>(__t));
+	ranges::end(std::forward<_Tp>(__t));
+      };
+
+  } // namespace __detail
+
+  /// [range.range] The range concept.
+  template<typename _Tp>
+    concept range = __detail::__range_impl<_Tp&>;
+
+  /// [range.sized] The sized_range concept.
+  template<typename _Tp>
+    concept sized_range = range<_Tp>
+      && requires(_Tp& __t) { ranges::size(__t); };
+
+    // [range.iter.ops] range iterator operations
+
+  template<input_or_output_iterator _It>
+    constexpr void
+    advance(_It& __it, iter_difference_t<_It> __n)
+    {
+      if constexpr (random_access_iterator<_It>)
+	__it += __n;
+      else if constexpr (bidirectional_iterator<_It>)
+	{
+	  if (__n > 0)
+	    {
+	      do
+		{
+		  ++__it;
+		}
+	      while (--__n);
+	    }
+	  else if (__n < 0)
+	    {
+	      do
+		{
+		  --__it;
+		}
+	      while (++__n);
+	    }
+	}
+      else
+	{
+#ifdef __cpp_lib_is_constant_evaluated
+	  if (std::is_constant_evaluated() && __n < 0)
+	    throw "attempt to decrement a non-bidirectional iterator";
+#endif
+	  __glibcxx_assert(__n >= 0);
+	  while (__n-- > 0)
+	    ++__it;
+	}
+    }
+
+  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+    constexpr void
+    advance(_It& __it, _Sent __bound)
+    {
+      if constexpr (assignable_from<_It&, _Sent>)
+	__it = std::move(__bound);
+      else if constexpr (sized_sentinel_for<_Sent, _It>)
+	ranges::advance(__it, __bound - __it);
+      else
+	{
+	  while (__it != __bound)
+	    ++__it;
+	}
+    }
+
+  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+    constexpr iter_difference_t<_It>
+    advance(_It& __it, iter_difference_t<_It> __n, _Sent __bound)
+    {
+      if constexpr (sized_sentinel_for<_Sent, _It>)
+	{
+	  const auto __diff = __bound - __it;
+#ifdef __cpp_lib_is_constant_evaluated
+	  if (std::is_constant_evaluated()
+	      && !(__n == 0 || __diff == 0 || (__n < 0 == __diff < 0)))
+	    throw "inconsistent directions for distance and bound";
+#endif
+	  // n and bound must not lead in opposite directions:
+	  __glibcxx_assert(__n == 0 || __diff == 0 || (__n < 0 == __diff < 0));
+	  const auto __absdiff = __diff < 0 ? -__diff : __diff;
+	  const auto __absn = __n < 0 ? -__n : __n;;
+	  if (__absn >= __absdiff)
+	    {
+	      ranges::advance(__it, __bound);
+	      return __n - __diff;
+	    }
+	  else
+	    {
+	      ranges::advance(__it, __n);
+	      return 0;
+	    }
+	}
+      else if (__it == __bound || __n == 0)
+	return iter_difference_t<_It>(0);
+      else if (__n > 0)
+	{
+	  iter_difference_t<_It> __m = 0;
+	  do
+	    {
+	      ++__it;
+	      ++__m;
+	    }
+	  while (__m != __n && __it != __bound);
+	  return __n - __m;
+	}
+      else if constexpr (bidirectional_iterator<_It> && same_as<_It, _Sent>)
+	{
+	  iter_difference_t<_It> __m = 0;
+	  do
+	    {
+	      --__it;
+	      --__m;
+	    }
+	  while (__m != __n && __it != __bound);
+	  return __n - __m;
+	}
+      else
+	{
+#ifdef __cpp_lib_is_constant_evaluated
+	  if (std::is_constant_evaluated() && __n < 0)
+	    throw "attempt to decrement a non-bidirectional iterator";
+#endif
+	  __glibcxx_assert(__n >= 0);
+	  return __n;
+	}
+    }
+
+  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+    constexpr iter_difference_t<_It>
+    distance(_It __first, _Sent __last)
+    {
+      if constexpr (sized_sentinel_for<_Sent, _It>)
+	return __last - __first;
+      else
+	{
+	  iter_difference_t<_It> __n = 0;
+	  while (__first != __last)
+	    {
+	      ++__first;
+	      ++__n;
+	    }
+	  return __n;
+	}
+    }
+
+  template<range _Range>
+    using iterator_t = decltype(ranges::begin(std::declval<_Range&>()));
+
+  template<range _Range>
+    using range_difference_t = iter_difference_t<iterator_t<_Range>>;
+
+  template<range _Range>
+    constexpr range_difference_t<_Range>
+    distance(_Range&& __r)
+    {
+      if constexpr (sized_range<_Range>)
+	return static_cast<range_difference_t<_Range>>(ranges::size(__r));
+      else
+	return ranges::distance(ranges::begin(__r), ranges::end(__r));
+    }
+
+  template<input_or_output_iterator _It>
+    constexpr _It
+    next(_It __x)
+    {
+      ++__x;
+      return __x;
+    }
+
+  template<input_or_output_iterator _It>
+    constexpr _It
+    next(_It __x, iter_difference_t<_It> __n)
+    {
+      ranges::advance(__x, __n);
+      return __x;
+    }
+
+  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+    constexpr _It
+    next(_It __x, _Sent __bound)
+    {
+      ranges::advance(__x, __bound);
+      return __x;
+    }
+
+  template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+    constexpr _It
+    next(_It __x, iter_difference_t<_It> __n, _Sent __bound)
+    {
+      ranges::advance(__x, __n, __bound);
+      return __x;
+    }
+
+  template<bidirectional_iterator _It>
+    constexpr _It
+    prev(_It __x)
+    {
+      --__x;
+      return __x;
+    }
+
+  template<bidirectional_iterator _It>
+    constexpr _It
+    prev(_It __x, iter_difference_t<_It> __n)
+    {
+      ranges::advance(__x, -__n);
+      return __x;
+    }
+
+  template<bidirectional_iterator _It>
+    constexpr _It
+    prev(_It __x, iter_difference_t<_It> __n, _It __bound)
+    {
+      ranges::advance(__x, -__n, __bound);
+      return __x;
+    }
+
+} // namespace ranges
 #endif // C++20
-
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 420fea687b5..966087598f4 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -431,7 +431,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __make_reverse_iterator(_Iterator __i)
     { return reverse_iterator<_Iterator>(__i); }
 
-# if __cplusplus > 201103L
+# if __cplusplus >= 201402L
 #  define __cpp_lib_make_reverse_iterator 201402
 
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
@@ -441,10 +441,16 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
     make_reverse_iterator(_Iterator __i)
     { return reverse_iterator<_Iterator>(__i); }
-# endif
-#endif
 
-#if __cplusplus >= 201103L
+#  if __cplusplus > 201703L
+  template<typename _Iterator1, typename _Iterator2>
+    requires (!sized_sentinel_for<_Iterator1, _Iterator2>)
+    inline constexpr bool disable_sized_sentinel<reverse_iterator<_Iterator1>,
+						 reverse_iterator<_Iterator2>>
+						   = true;
+#  endif // C++20
+# endif // C++14
+
   template<typename _Iterator>
     _GLIBCXX20_CONSTEXPR
     auto
@@ -463,7 +469,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __miter_base(reverse_iterator<_Iterator> __it)
     -> decltype(__make_reverse_iterator(__miter_base(__it.base())))
     { return __make_reverse_iterator(__miter_base(__it.base())); }
-#endif
+#endif // C++11
 
   // 24.4.2.2.1 back_insert_iterator
   /**
diff --git a/libstdc++-v3/include/bits/stl_iterator_base_types.h b/libstdc++-v3/include/bits/stl_iterator_base_types.h
index 951e704e468..3fad5869b40 100644
--- a/libstdc++-v3/include/bits/stl_iterator_base_types.h
+++ b/libstdc++-v3/include/bits/stl_iterator_base_types.h
@@ -67,6 +67,10 @@ 
 # include <type_traits>  // For __void_t, is_convertible
 #endif
 
+#if __cplusplus > 201703L && __cpp_concepts
+# include <bits/iterator_concepts.h>
+#endif
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -101,6 +105,11 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// Random-access iterators support a superset of bidirectional
   /// iterator operations.
   struct random_access_iterator_tag : public bidirectional_iterator_tag { };
+
+#if __cplusplus > 201703L
+  /// Contiguous iterators point to objects stored contiguously in memory.
+  struct contiguous_iterator_tag : public random_access_iterator_tag { };
+#endif
   //@}
 
   /**
@@ -137,12 +146,17 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  argument.  Specialized versions for pointers and pointers-to-const
    *  provide tighter, more correct semantics.
   */
+  template<typename _Iterator>
+    struct iterator_traits;
+
 #if __cplusplus >= 201103L
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2408. SFINAE-friendly common_type/iterator_traits is missing in C++14
   template<typename _Iterator, typename = __void_t<>>
     struct __iterator_traits { };
 
+#if ! __cpp_lib_concepts
+
   template<typename _Iterator>
     struct __iterator_traits<_Iterator,
 			     __void_t<typename _Iterator::iterator_category,
@@ -157,11 +171,13 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename _Iterator::pointer           pointer;
       typedef typename _Iterator::reference         reference;
     };
+#endif // ! concepts
 
   template<typename _Iterator>
     struct iterator_traits
     : public __iterator_traits<_Iterator> { };
-#else
+
+#else // ! C++11
   template<typename _Iterator>
     struct iterator_traits
     {
@@ -171,8 +187,24 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename _Iterator::pointer           pointer;
       typedef typename _Iterator::reference         reference;
     };
-#endif
+#endif // C++11
 
+#if __cplusplus > 201703L
+  /// Partial specialization for object pointer types.
+  template<typename _Tp>
+#if __cpp_concepts
+    requires is_object_v<_Tp>
+#endif
+    struct iterator_traits<_Tp*>
+    {
+      using iterator_concept  = contiguous_iterator_tag;
+      using iterator_category = random_access_iterator_tag;
+      using value_type	      = remove_cv_t<_Tp>;
+      using difference_type   = ptrdiff_t;
+      using pointer	      = _Tp*;
+      using reference	      = _Tp&;
+    };
+#else
   /// Partial specialization for pointer types.
   template<typename _Tp>
     struct iterator_traits<_Tp*>
@@ -194,6 +226,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef const _Tp*                  pointer;
       typedef const _Tp&                  reference;
     };
+#endif
 
   /**
    *  This function is not a part of the C++ standard but is syntactic
diff --git a/libstdc++-v3/include/std/concepts b/libstdc++-v3/include/std/concepts
index 6d740eb663c..68cbba9b8a7 100644
--- a/libstdc++-v3/include/std/concepts
+++ b/libstdc++-v3/include/std/concepts
@@ -114,6 +114,10 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
   {
     template<typename _Tp>
       using __cref = const remove_reference_t<_Tp>&;
+
+      template<typename _Tp>
+	concept __class_or_enum
+	  = is_class_v<_Tp> || is_union_v<_Tp> || is_enum_v<_Tp>;
   } // namespace __detail
 
   /// [concept.assignable], concept assignable_from
@@ -159,14 +163,10 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       template<typename _Tp> void swap(_Tp&, _Tp&) = delete;
 
-      template<typename _Tp>
-	concept __class_or_enum
-	  = is_class_v<_Tp> || is_union_v<_Tp> || is_enum_v<_Tp>;
-
       template<typename _Tp, typename _Up>
 	concept __adl_swap
-	  = (__class_or_enum<remove_cvref_t<_Tp>>
-	    || __class_or_enum<remove_cvref_t<_Up>>)
+	  = (__detail::__class_or_enum<remove_reference_t<_Tp>>
+	    || __detail::__class_or_enum<remove_reference_t<_Up>>)
 	  && requires(_Tp&& __t, _Up&& __u) {
 	    swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
 	  };
@@ -175,7 +175,8 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
 	template<typename _Tp, typename _Up>
 	  requires __adl_swap<_Tp, _Up>
-	  constexpr void operator()(_Tp&& __t, _Up&& __u) const
+	  constexpr void
+	  operator()(_Tp&& __t, _Up&& __u) const
 	  noexcept(noexcept(swap(std::declval<_Tp>(), std::declval<_Up>())))
 	  { swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
 
diff --git a/libstdc++-v3/testsuite/20_util/forward/c_neg.cc b/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
index ecbac1fd2b8..6b719eb988f 100644
--- a/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/forward/c_neg.cc
@@ -17,7 +17,7 @@ 
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-error "static assertion failed" "" { target *-*-* } 87 }
+// { dg-error "static assertion failed" "" { target *-*-* } 89 }
 
 #include <list>
 
diff --git a/libstdc++-v3/testsuite/20_util/forward/f_neg.cc b/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
index a073adc7fb6..7161f47760c 100644
--- a/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/forward/f_neg.cc
@@ -17,7 +17,7 @@ 
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-error "static assertion failed" "" { target *-*-* } 87 }
+// { dg-error "static assertion failed" "" { target *-*-* } 89 }
 
 #include <utility>
 
diff --git a/libstdc++-v3/testsuite/24_iterators/associated_types/incrementable.traits.cc b/libstdc++-v3/testsuite/24_iterators/associated_types/incrementable.traits.cc
new file mode 100644
index 00000000000..929f0e4121f
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/associated_types/incrementable.traits.cc
@@ -0,0 +1,142 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <iterator>
+
+struct none;
+
+template<typename T>
+  concept has_inc_traits_type
+    = requires { typename std::incrementable_traits<T>::difference_type; };
+
+// Check std::incrementable_traits<T>::difference_type is U (or doesn't exist).
+template<typename T, typename U>
+  concept check_inc_traits = (has_inc_traits_type<T> != std::same_as<U, none>);
+
+static_assert( check_inc_traits<void, none> );
+static_assert( check_inc_traits<const void, none> );
+static_assert( check_inc_traits<void*, none> );
+static_assert( check_inc_traits<const void*, none> );
+
+static_assert( check_inc_traits<int, int> );
+static_assert( check_inc_traits<const int, int> );
+
+static_assert( check_inc_traits<int*, std::ptrdiff_t> );
+static_assert( check_inc_traits<const int*, std::ptrdiff_t> );
+static_assert( check_inc_traits<int[2], std::ptrdiff_t> );
+static_assert( check_inc_traits<const int[2], std::ptrdiff_t> );
+
+struct A { using difference_type = int; };
+static_assert( check_inc_traits<A, int> );
+static_assert( check_inc_traits<const A, int> );
+struct B : private A { };
+static_assert( check_inc_traits<B, none> );
+
+struct C { };
+short operator-(C, C) { return 0; }
+static_assert( check_inc_traits<C, short> );
+static_assert( check_inc_traits<const C, short> );
+
+struct D { };
+unsigned short operator-(D, D) { return 0; }
+static_assert( check_inc_traits<D, short> );
+static_assert( check_inc_traits<const D, short> );
+
+struct E { };
+template<>
+  struct std::incrementable_traits<E> { using difference_type = long; };
+static_assert( check_inc_traits<E, long> );
+static_assert( check_inc_traits<const E, long> );
+
+template<typename T>
+  concept has_alias = requires { typename std::iter_difference_t<T>; };
+
+// Check std::iter_difference_t<T> is U (or doesn't exist).
+template<typename T, typename U>
+  concept check_alias = (has_alias<T> != std::same_as<U, none>);
+
+static_assert( check_alias<void, none> );
+static_assert( check_alias<const void, none> );
+static_assert( check_alias<void*, none> );
+static_assert( check_alias<const void*, none> );
+
+static_assert( check_alias<int, int> );
+static_assert( check_alias<const int, int> );
+static_assert( check_alias<int*, std::ptrdiff_t> );
+static_assert( check_alias<const int*, std::ptrdiff_t> );
+static_assert( check_alias<int[2], std::ptrdiff_t> );
+static_assert( check_alias<const int[2], std::ptrdiff_t> );
+
+static_assert( check_alias<A, int> );
+static_assert( check_alias<const A, int> );
+static_assert( check_alias<B, none> );
+static_assert( check_alias<C, short> );
+static_assert( check_alias<const C, short> );
+static_assert( check_alias<D, short> );
+static_assert( check_alias<const D, short> );
+static_assert( check_alias<E, long> );
+static_assert( check_alias<const E, long> );
+
+struct F { };
+template<>
+  struct std::iterator_traits<F> { using difference_type = F; };
+// iterator_traits<F> is specialized, so use its difference_type.
+static_assert( check_alias<F, std::iterator_traits<F>::difference_type> );
+
+struct G { };
+template<>
+  struct std::incrementable_traits<G> { using difference_type = G; };
+template<>
+  struct std::iterator_traits<G> { using difference_type = int; };
+// iterator_traits<G> is specialized, so use its difference_type.
+static_assert( check_alias<G, std::iterator_traits<G>::difference_type> );
+
+struct H { };
+template<>
+  struct std::incrementable_traits<H> { using difference_type = H; };
+template<>
+  struct std::iterator_traits<H>
+  {
+    using iterator_category = input_iterator_tag;
+    using difference_type = int;
+    using value_type = char;
+    using reference = value_type&;
+  };
+// iterator_traits<H> is specialized, so use its difference_type.
+static_assert( check_alias<H, std::iterator_traits<H>::difference_type> );
+
+struct I
+{
+  using difference_type = I;
+};
+// iterator_traits<I> is not specialized, and no standard specialization
+// matches, so use incrementable_traits.
+static_assert( check_alias<I, std::incrementable_traits<I>::difference_type> );
+
+struct J
+{
+  using iterator_category = std::input_iterator_tag;
+  using difference_type = int;
+  using value_type = char;
+  using reference = value_type&;
+};
+// iterator_traits<J> matches constrained specialization in the library,
+// so use its difference_type.
+static_assert( check_alias<J, int> );
diff --git a/libstdc++-v3/testsuite/24_iterators/associated_types/readable.traits.cc b/libstdc++-v3/testsuite/24_iterators/associated_types/readable.traits.cc
new file mode 100644
index 00000000000..b4678abc1bc
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/associated_types/readable.traits.cc
@@ -0,0 +1,143 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <iterator>
+
+struct none;
+
+template<typename T>
+  concept has_readable_traits_type
+    = requires { typename std::readable_traits<T>::value_type; };
+
+// Check std::readable_traits<T>::value_type is U (or doesn't exist).
+template<typename T, typename U>
+  concept check_readable_traits
+    = (has_readable_traits_type<T> != std::same_as<U, none>);
+
+static_assert( check_readable_traits<void, none> );
+static_assert( check_readable_traits<const void, none> );
+static_assert( check_readable_traits<void*, none> );
+static_assert( check_readable_traits<const void*, none> );
+
+static_assert( check_readable_traits<int, none> );
+static_assert( check_readable_traits<const int, none> );
+
+static_assert( check_readable_traits<int*, int> );
+static_assert( check_readable_traits<const int*, int> );
+static_assert( check_readable_traits<int[2], int> );
+static_assert( check_readable_traits<const int[2], int> );
+
+struct A { using value_type = int; };
+static_assert( check_readable_traits<A, int> );
+static_assert( check_readable_traits<const A, int> );
+struct B : private A { };
+static_assert( check_readable_traits<B, none> );
+
+struct C { };
+short operator-(C, C) { return 0; }
+static_assert( check_readable_traits<C, none> );
+static_assert( check_readable_traits<const C, none> );
+
+struct D { long operator*() const { return 1L; } };
+unsigned short operator-(D, D) { return 0; }
+static_assert( check_readable_traits<D, none> );
+static_assert( check_readable_traits<const D, none> );
+
+struct E { };
+template<>
+  struct std::readable_traits<E> { using value_type = long; };
+static_assert( check_readable_traits<E, long> );
+static_assert( check_readable_traits<const E, long> );
+
+template<typename T>
+  concept has_alias = requires { typename std::iter_value_t<T>; };
+
+// Check std::iter_value_t<T> is U (or doesn't exist).
+template<typename T, typename U>
+  concept check_alias = (has_alias<T> != std::same_as<U, none>);
+
+static_assert( check_alias<void, none> );
+static_assert( check_alias<const void, none> );
+static_assert( check_alias<void*, none> );
+static_assert( check_alias<const void*, none> );
+
+static_assert( check_alias<int, none> );
+static_assert( check_alias<const int, none> );
+static_assert( check_alias<int*, std::ptrdiff_t> );
+static_assert( check_alias<const int*, std::ptrdiff_t> );
+static_assert( check_alias<int[2], std::ptrdiff_t> );
+static_assert( check_alias<const int[2], std::ptrdiff_t> );
+
+static_assert( check_alias<A, int> );
+static_assert( check_alias<const A, int> );
+static_assert( check_alias<B, none> );
+static_assert( check_alias<C, none> );
+static_assert( check_alias<const C, none> );
+static_assert( check_alias<D, none> );
+static_assert( check_alias<const D, none> );
+static_assert( check_alias<E, long> );
+static_assert( check_alias<const E, long> );
+
+struct F { };
+template<>
+  struct std::iterator_traits<F> { using value_type = F; };
+// iterator_traits<F> is specialized, so use its value_type.
+static_assert( check_alias<F, std::iterator_traits<F>::value_type> );
+
+struct G { };
+template<>
+  struct std::readable_traits<G> { using value_type = G; };
+template<>
+  struct std::iterator_traits<G> { using value_type = int; };
+// iterator_traits<G> is specialized, so use its value_type.
+static_assert( check_alias<G, std::iterator_traits<G>::value_type> );
+
+struct H { };
+template<>
+  struct std::readable_traits<H> { using value_type = H; };
+template<>
+  struct std::iterator_traits<H>
+  {
+    using iterator_category = input_iterator_tag;
+    using difference_type = int;
+    using value_type = char;
+    using reference = value_type&;
+  };
+// iterator_traits<H> is specialized, so use its value_type.
+static_assert( check_alias<H, std::iterator_traits<H>::value_type> );
+
+struct I
+{
+  using value_type = I;
+};
+// iterator_traits<I> is not specialized, and no standard specialization
+// matches, so use readable_traits.
+static_assert( check_alias<I, std::readable_traits<I>::value_type> );
+
+struct J
+{
+  using iterator_category = std::input_iterator_tag;
+  using difference_type = int;
+  using value_type = char;
+  using reference = value_type&;
+};
+// iterator_traits<J> matches constrained specialization in the library,
+// so use its value_type.
+static_assert( check_alias<J, int> );
diff --git a/libstdc++-v3/testsuite/24_iterators/contiguous/concept.cc b/libstdc++-v3/testsuite/24_iterators/contiguous/concept.cc
new file mode 100644
index 00000000000..a9bb42e023f
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/contiguous/concept.cc
@@ -0,0 +1,36 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <iterator>
+
+static_assert( std::contiguous_iterator<int*> );
+static_assert( std::contiguous_iterator<const int*> );
+static_assert( std::contiguous_iterator<void**> );
+
+static_assert( ! std::contiguous_iterator<void*> );
+static_assert( ! std::contiguous_iterator<const void*> );
+static_assert( ! std::contiguous_iterator<volatile void*> );
+
+static_assert( ! std::contiguous_iterator<void(*)()> );
+static_assert( ! std::contiguous_iterator<void(*)()> );
+
+struct A;
+static_assert( ! std::contiguous_iterator<void(A::*)()> );
+static_assert( ! std::contiguous_iterator<int A::*> );
diff --git a/libstdc++-v3/testsuite/24_iterators/contiguous/tag.cc b/libstdc++-v3/testsuite/24_iterators/contiguous/tag.cc
new file mode 100644
index 00000000000..7673131f215
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/contiguous/tag.cc
@@ -0,0 +1,34 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <iterator>
+
+static_assert( std::is_empty_v<std::contiguous_iterator_tag> );
+static_assert( std::is_trivially_copy_constructible_v<std::contiguous_iterator_tag> );
+
+static_assert( std::is_base_of_v<std::random_access_iterator_tag,
+				 std::contiguous_iterator_tag> );
+static_assert( std::is_convertible_v<std::contiguous_iterator_tag*,
+				     std::random_access_iterator_tag*> );
+
+static_assert( ! std::is_same_v<std::iterator_traits<int*>::iterator_category,
+				std::contiguous_iterator_tag> );
+static_assert( std::is_same_v<std::iterator_traits<int*>::iterator_concept,
+			      std::contiguous_iterator_tag> );
diff --git a/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc
new file mode 100644
index 00000000000..d32dee39f3a
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc
@@ -0,0 +1,68 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+
+struct X
+{
+  int value;
+
+  constexpr X(int i) : value(i) { }
+
+  X(const X&) = default;
+  X& operator=(const X&) = default;
+
+  constexpr X(X&& x)
+  : value(x.value)
+  {
+    x.value = -2;
+  }
+
+  constexpr X& operator=(X&& x)
+  {
+    value = x.value;
+    x.value = -1;
+    return *this;
+  }
+};
+
+constexpr bool
+test_X(int i, int j)
+{
+  X x1{i}, x2{j};
+  std::ranges::iter_move(&x1); // no-op
+  x1 = std::ranges::iter_move(&x2);
+  return x1.value == j &&  x2.value == -1;
+}
+
+static_assert( test_X(1, 2) );
+
+void
+test01()
+{
+  VERIFY( test_X(3, 4) );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/customization_points/iter_swap.cc b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_swap.cc
new file mode 100644
index 00000000000..4243a162fc6
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_swap.cc
@@ -0,0 +1,61 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+
+struct X
+{
+  int value;
+
+  constexpr X(int i) : value(i) { }
+
+  X(const X&) = default;
+  X& operator=(const X&) = default;
+
+  constexpr X& operator=(X&& x)
+  {
+    value = x.value;
+    x.value = -1;
+    return *this;
+  }
+};
+
+constexpr bool
+test_X(int i, int j)
+{
+  X x1{i}, x2{j};
+  std::ranges::iter_swap(&x1, &x2);
+  return x1.value == j &&  x2.value == i;
+}
+
+static_assert( test_X(1, 2) );
+
+void
+test01()
+{
+  VERIFY( test_X(3, 4) );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/headers/iterator/synopsis_c++20.cc b/libstdc++-v3/testsuite/24_iterators/headers/iterator/synopsis_c++20.cc
new file mode 100644
index 00000000000..2dbfb767fdb
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/headers/iterator/synopsis_c++20.cc
@@ -0,0 +1,95 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+// { dg-require-normal-namespace "" }
+
+#include <iterator>
+#include "./synopsis_c++17.cc"
+
+namespace std
+{
+  template<class> struct incrementable_traits;
+  template<class> struct readable_traits;
+
+  struct contiguous_iterator_tag;
+
+  namespace ranges
+  {
+    template<input_or_output_iterator I, sentinel_for<I> S>
+      constexpr iter_difference_t<I> distance(I first, S last);
+    template<range R>
+      constexpr range_difference_t<R> distance(R&& r);
+
+    template<input_or_output_iterator I>
+      constexpr I next(I x);
+    template<input_or_output_iterator I>
+      constexpr I next(I x, iter_difference_t<I> n);
+    template<input_or_output_iterator I, sentinel_for<I> S>
+      constexpr I next(I x, S bound);
+    template<input_or_output_iterator I, sentinel_for<I> S>
+      constexpr I next(I x, iter_difference_t<I> n, S bound);
+
+    template<bidirectional_iterator I>
+      constexpr I prev(I x);
+    template<bidirectional_iterator I>
+      constexpr I prev(I x, iter_difference_t<I> n);
+    template<bidirectional_iterator I>
+      constexpr I prev(I x, iter_difference_t<I> n, I bound);
+  }
+
+  template<semiregular S> class move_sentinel;
+
+  template<input_or_output_iterator I, sentinel_for<I> S>
+    requires (!same_as<I, S>)
+    class common_iterator;
+
+  template<class I, class S>
+    struct incrementable_traits<common_iterator<I, S>>;
+
+  template<input_iterator I, class S>
+    struct iterator_traits<common_iterator<I, S>>;
+
+  struct default_sentinel_t;
+
+  template<input_or_output_iterator I> class counted_iterator;
+
+  template<class I>
+    struct incrementable_traits<counted_iterator<I>>;
+
+  template<input_iterator I>
+    struct iterator_traits<counted_iterator<I>>;
+
+  struct unreachable_sentinel_t;
+}
+
+namespace __gnu_test
+{
+  // customization points
+  constexpr auto* iter_move = &std::ranges::iter_move;
+  constexpr auto* iter_swap = &std::ranges::iter_swap;
+  // sized sentinels
+  constexpr bool const* disable_sized_sentinel
+    = &std::disable_sized_sentinel<void, void>;
+  // default sentinels
+  constexpr std::default_sentinel_t const* default_sentinel
+    = &std::default_sentinel;
+  // unreachable sentinels
+  constexpr std::unreachable_sentinel_t const* unreachable_sentinel
+    = &std::unreachable_sentinel;
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/advance.cc b/libstdc++-v3/testsuite/24_iterators/range_operations/advance.cc
new file mode 100644
index 00000000000..7f77eca1c4b
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/range_operations/advance.cc
@@ -0,0 +1,204 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::random_access_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::input_iterator_wrapper;
+using __gnu_test::output_iterator_wrapper;
+
+void
+test01()
+{
+  int a[2] = { };
+  test_range<int, random_access_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  std::ranges::advance(iter, 1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, 1);
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, -2);
+  VERIFY( iter == r.begin() );
+
+  std::ranges::advance(iter, r.begin() + 1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, r.begin());
+  VERIFY( iter == r.begin() );
+
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, -222, r.begin());
+  VERIFY( iter == r.begin() );
+}
+
+void
+test02()
+{
+  int a[2] = { };
+  test_range<int, bidirectional_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  std::ranges::advance(iter, 1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, 1);
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, -2);
+  VERIFY( iter == r.begin() );
+
+  auto iter1 = r.begin();
+  ++iter1;
+  std::ranges::advance(iter, iter1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, r.begin());
+  VERIFY( iter == r.begin() );
+
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, -222, r.begin());
+  VERIFY( iter == r.begin() );
+}
+
+void
+test03()
+{
+  int a[2] = { };
+  test_range<int, forward_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  std::ranges::advance(iter, 1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, 1);
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+
+  auto iter1 = r.begin();
+  ++iter1;
+  std::ranges::advance(iter, iter1);
+  VERIFY( iter != r.begin() );
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, r.end());
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, r.end());
+  VERIFY( iter == r.end() );
+
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+  iter = r.begin();
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, 99, r.end());
+  VERIFY( iter == r.end() );
+}
+
+void
+test04()
+{
+  int a[2] = { };
+  test_range<int, input_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  std::ranges::advance(iter, 1);
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, 1);
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+
+  test_range<int, input_iterator_wrapper> r2(a);
+  iter = r2.begin();
+  ++iter;
+  const auto iter1 = iter;
+  std::ranges::advance(iter, iter1);
+  VERIFY( iter == iter1 );
+  VERIFY( iter != r2.end() );
+  std::ranges::advance(iter, r2.end());
+  VERIFY( iter == r2.end() );
+  std::ranges::advance(iter, r2.end());
+  VERIFY( iter == r2.end() );
+
+  std::ranges::advance(iter, 99, r2.end());
+  VERIFY( iter == r2.end() );
+  std::ranges::advance(iter, 99, r2.end());
+  VERIFY( iter == r2.end() );
+
+  test_range<int, input_iterator_wrapper> r3(a);
+  iter = r3.begin();
+  std::ranges::advance(iter, 99, r3.end());
+  VERIFY( iter == r3.end() );
+  std::ranges::advance(iter, 99, r3.end());
+  VERIFY( iter == r3.end() );
+}
+
+void
+test05()
+{
+  int a[2] = { };
+  test_range<int, output_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  std::ranges::advance(iter, 1);
+  VERIFY( iter != r.end() );
+  std::ranges::advance(iter, 1);
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+  std::ranges::advance(iter, 0);
+  VERIFY( iter == r.end() );
+
+  test_range<int, output_iterator_wrapper> r2(a);
+  iter = r2.begin();
+  ++iter;
+  std::ranges::advance(iter, r2.end());
+  VERIFY( iter == r2.end() );
+  std::ranges::advance(iter, r2.end());
+  VERIFY( iter == r2.end() );
+
+  std::ranges::advance(iter, 99, r2.end());
+  VERIFY( iter == r2.end() );
+  std::ranges::advance(iter, 99, r2.end());
+  VERIFY( iter == r2.end() );
+
+  test_range<int, output_iterator_wrapper> r3(a);
+  iter = r3.begin();
+  std::ranges::advance(iter, 99, r3.end());
+  VERIFY( iter == r3.end() );
+  std::ranges::advance(iter, 99, r3.end());
+  VERIFY( iter == r3.end() );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+  test05();
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc b/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
new file mode 100644
index 00000000000..4aa095ff3d7
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/range_operations/distance.cc
@@ -0,0 +1,146 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::test_sized_range;
+using __gnu_test::random_access_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::input_iterator_wrapper;
+using __gnu_test::output_iterator_wrapper;
+
+void
+test01()
+{
+  int a[10] = { };
+  VERIFY( std::ranges::distance(a) == 10 );
+
+  test_range<int, random_access_iterator_wrapper> c(a);
+  VERIFY( std::ranges::distance(c) == 10 );
+
+  auto b = c.begin(), e = c.end();
+  VERIFY( std::ranges::distance(b, e) == 10 );
+  VERIFY( std::ranges::distance(e, b) == -10 );
+
+  const auto cb = b, ce = e;
+  VERIFY( std::ranges::distance(cb, ce) == 10 );
+  VERIFY( std::ranges::distance(ce, cb) == -10 );
+
+  test_sized_range<int, random_access_iterator_wrapper> c2(a);
+  VERIFY( std::ranges::distance(c2) == 10 );
+}
+
+void
+test02()
+{
+  int a[2] = { };
+  VERIFY( std::ranges::distance(a) == 2 );
+
+  test_range<int, bidirectional_iterator_wrapper> c(a);
+  VERIFY( std::ranges::distance(c) == 2 );
+
+  auto b = c.begin(), e = c.end();
+  VERIFY( std::ranges::distance(b, e) == 2 );
+
+  const auto cb = b, ce = e;
+  VERIFY( std::ranges::distance(cb, ce) == 2 );
+
+  test_sized_range<int, bidirectional_iterator_wrapper> c2(a);
+  VERIFY( std::ranges::distance(c2) == 2 );
+}
+
+void
+test03()
+{
+  int a[3] = { };
+  test_range<int, forward_iterator_wrapper> c(a);
+  VERIFY( std::ranges::distance(c) == 3 );
+
+  auto b = c.begin(), e = c.end();
+  VERIFY( std::ranges::distance(b, e) == 3 );
+
+  const auto cb = b, ce = e;
+  VERIFY( std::ranges::distance(cb, ce) == 3 );
+
+  test_sized_range<int, forward_iterator_wrapper> c2(a);
+  VERIFY( std::ranges::distance(c2) == 3 );
+}
+
+void
+test04()
+{
+  int a[4] = { };
+  test_range<int, input_iterator_wrapper> c(a);
+  static_assert( std::ranges::range<decltype(c)> );
+
+  VERIFY( std::ranges::distance(c) == 4 );
+  // first call to distance has traversed the range:
+  VERIFY( std::ranges::distance(c) == 0 );
+
+  c = test_range<int, input_iterator_wrapper>(a);
+  auto b = c.begin(), e = c.end();
+  VERIFY( std::ranges::distance(b, e) == 4 );
+
+  test_range<int, input_iterator_wrapper> c2(a);
+  const auto cb = c2.begin(), ce = c2.end();
+  VERIFY( std::ranges::distance(cb, ce) == 4 );
+
+  test_sized_range<int, input_iterator_wrapper> c3(a);
+  VERIFY( std::ranges::distance(c3) == 4 );
+  // first call to distance just called size() without affecting the range:
+  VERIFY( std::ranges::distance(c3) == 4 );
+}
+
+void
+test05()
+{
+  int a[5] = { };
+  test_range<int, output_iterator_wrapper> c(a);
+  VERIFY( std::ranges::distance(c) == 5 );
+
+  test_range<int, output_iterator_wrapper> c2(a);
+  auto b = c2.begin();
+  auto e = c2.end();
+  VERIFY( std::ranges::distance(b, e) == 5 );
+
+  test_range<int, output_iterator_wrapper> c3(a);
+  const auto cb = c3.begin();
+  const auto ce = c3.end();
+  VERIFY( std::ranges::distance(cb, ce) == 5 );
+
+  test_sized_range<int, output_iterator_wrapper> c4(a);
+  VERIFY( std::ranges::distance(c4) == 5 );
+  // first call to distance just called size() without affecting the range:
+  VERIFY( std::ranges::distance(c4) == 5 );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+  test05();
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/next.cc b/libstdc++-v3/testsuite/24_iterators/range_operations/next.cc
new file mode 100644
index 00000000000..7f04cb23b3c
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/range_operations/next.cc
@@ -0,0 +1,211 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::random_access_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::input_iterator_wrapper;
+using __gnu_test::output_iterator_wrapper;
+
+void
+test01()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, random_access_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  VERIFY( *std::ranges::next(begin) == 1 );
+  VERIFY(  std::ranges::next(begin, 0) == begin );
+  VERIFY( *std::ranges::next(begin, 1) == 1 );
+  VERIFY( *std::ranges::next(begin, 3) == 3 );
+  VERIFY( *std::ranges::next(end, -4) == 6 );
+  VERIFY(  std::ranges::next(begin, begin) == begin );
+  VERIFY(  std::ranges::next(begin, end) == end );
+  VERIFY(  std::ranges::next(end, end) == end );
+  VERIFY(  std::ranges::next(end, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 0, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, -5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 0, end) == begin );
+  VERIFY( *std::ranges::next(begin, 5, end) == 5 );
+  VERIFY(  std::ranges::next(begin, 55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, end) == end );
+  VERIFY(  std::ranges::next(end, -5, end) == end );
+  VERIFY(  std::ranges::next(end, -55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, begin) == end );
+  VERIFY( *std::ranges::next(end, -5, begin) == 5 );
+  VERIFY(  std::ranges::next(end, -55, begin) == begin );
+}
+
+void
+test02()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, bidirectional_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  VERIFY( *std::ranges::next(begin) == 1 );
+  VERIFY(  std::ranges::next(begin, 0) == begin );
+  VERIFY( *std::ranges::next(begin, 1) == 1 );
+  VERIFY( *std::ranges::next(begin, 3) == 3 );
+  VERIFY( *std::ranges::next(end, -4) == 6 );
+  VERIFY(  std::ranges::next(begin, begin) == begin );
+  VERIFY(  std::ranges::next(begin, end) == end );
+  VERIFY(  std::ranges::next(end, end) == end );
+  VERIFY(  std::ranges::next(end, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 0, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, -5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 0, end) == begin );
+  VERIFY( *std::ranges::next(begin, 5, end) == 5 );
+  VERIFY(  std::ranges::next(begin, 55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, end) == end );
+  VERIFY(  std::ranges::next(end, -5, end) == end );
+  VERIFY(  std::ranges::next(end, -55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, begin) == end );
+  VERIFY( *std::ranges::next(end, -5, begin) == 5 );
+  VERIFY(  std::ranges::next(end, -55, begin) == begin );
+}
+
+void
+test03()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, forward_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  VERIFY( *std::ranges::next(begin) == 1 );
+  VERIFY(  std::ranges::next(begin, 0) == begin );
+  VERIFY( *std::ranges::next(begin, 1) == 1 );
+  VERIFY( *std::ranges::next(begin, 3) == 3 );
+  VERIFY(  std::ranges::next(begin, begin) == begin );
+  VERIFY(  std::ranges::next(begin, end) == end );
+  VERIFY(  std::ranges::next(end, end) == end );
+  VERIFY(  std::ranges::next(begin, 0, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, -5, begin) == begin );
+  VERIFY(  std::ranges::next(begin, 0, end) == begin );
+  VERIFY( *std::ranges::next(begin, 5, end) == 5 );
+  VERIFY(  std::ranges::next(begin, 55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, end) == end );
+  VERIFY(  std::ranges::next(end, 5, end) == end );
+  VERIFY(  std::ranges::next(end, 55, end) == end );
+  VERIFY(  std::ranges::next(end, 0, begin) == end );
+}
+
+void
+test04()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, input_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  auto iter = std::ranges::next(begin);
+  VERIFY( *iter == 1 );
+  iter = std::ranges::next(iter, 0);
+  VERIFY( *iter == 1 );
+  iter = std::ranges::next(iter, 1);
+  VERIFY( *iter == 2 );
+  iter = std::ranges::next(iter, 4);
+  VERIFY( *iter == 6 );
+
+  iter = std::ranges::next(iter, iter);
+  VERIFY( *iter == 6 );
+  iter = std::ranges::next(iter, end);
+  VERIFY( iter == end );
+  iter = std::ranges::next(iter, end);
+  VERIFY( iter == end );
+
+  test_range<int, input_iterator_wrapper> r2(a);
+  begin = r2.begin();
+  end = r2.end();
+  iter = std::ranges::next(begin, 0, begin);
+  VERIFY( *iter == 0 );
+  iter = std::ranges::next(begin, 5, begin);
+  VERIFY( *iter == 0 );
+  iter = std::ranges::next(begin, -5, begin);
+  VERIFY( *iter == 0 );
+  iter = std::ranges::next(begin, 0, end);
+  VERIFY( *iter == 0 );
+  iter = std::ranges::next(end, 0, begin);
+  VERIFY( iter == end );
+  iter = std::ranges::next(begin, 5, end); // invalidates begin
+  VERIFY( *iter == 5 );
+  iter = std::ranges::next(iter, 55, end);
+  VERIFY( iter == end );
+  iter = std::ranges::next(end, 0, end);
+  VERIFY( iter == end );
+  iter = std::ranges::next(end, 5, end);
+  VERIFY( iter == end );
+}
+
+void
+test05()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, output_iterator_wrapper> r(a);
+  auto iter = r.begin();
+  auto end = r.end(); // sentinel, !same_as<decltype(iter), decltype(end)>
+
+  iter = std::ranges::next(iter);
+  *iter = 10;
+  VERIFY( a[1] == 10 );
+  iter = std::ranges::next(iter, 0);
+  iter = std::ranges::next(iter, 1);
+  *iter = 20;
+  VERIFY( a[2] == 20 );
+  iter = std::ranges::next(iter, 4);
+  iter = std::ranges::next(iter, 0);
+  *iter = 60;
+  VERIFY( a[6] == 60 );
+
+  iter = std::ranges::next(iter, end);
+  VERIFY( iter == end );
+  iter = std::ranges::next(iter, end);
+  VERIFY( iter == end );
+
+  test_range<int, output_iterator_wrapper> r2(a);
+  iter = std::ranges::next(r2.begin(), 5);
+  end = r2.end();
+
+  iter = std::ranges::next(iter, 0, end);
+  *iter = 50;
+  VERIFY( a[5] == 50 );
+  iter = std::ranges::next(iter, 2, end);
+  *iter = 70;
+  VERIFY( a[7] == 70 );
+  iter = std::ranges::next(iter, 5, end);
+  VERIFY( iter == end );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+  test05();
+}
diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/prev.cc b/libstdc++-v3/testsuite/24_iterators/range_operations/prev.cc
new file mode 100644
index 00000000000..944c02a6052
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/range_operations/prev.cc
@@ -0,0 +1,98 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_range;
+using __gnu_test::random_access_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::input_iterator_wrapper;
+using __gnu_test::output_iterator_wrapper;
+
+void
+test01()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, random_access_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  VERIFY( *std::ranges::prev(end) == 9 );
+  VERIFY(  std::ranges::prev(begin, 0) == begin );
+  VERIFY( *std::ranges::prev(end, 1) == 9 );
+  VERIFY( *std::ranges::prev(end, 3) == 7 );
+  VERIFY( *std::ranges::prev(begin, -4) == 4 );
+  VERIFY(  std::ranges::prev(begin, 0, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, 5, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, -5, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, 0, end) == begin );
+  VERIFY( *std::ranges::prev(end, 5, begin) == 5 );
+  VERIFY(  std::ranges::prev(end, 55, begin) == begin );
+  VERIFY(  std::ranges::prev(end, 0, end) == end );
+  VERIFY(  std::ranges::prev(end, -5, end) == end );
+  VERIFY(  std::ranges::prev(end, -55, end) == end );
+  VERIFY(  std::ranges::prev(end, 0, begin) == end );
+  VERIFY( *std::ranges::prev(begin, -5, end) == 5 );
+  VERIFY(  std::ranges::prev(begin, -55, end) == end );
+}
+
+void
+test02()
+{
+  int a[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+  test_range<int, bidirectional_iterator_wrapper> r(a);
+  auto begin = r.begin();
+  auto end = r.end();
+  VERIFY( *std::ranges::prev(end) == 9 );
+  VERIFY(  std::ranges::prev(begin, 0) == begin );
+  VERIFY( *std::ranges::prev(end, 1) == 9 );
+  VERIFY( *std::ranges::prev(end, 3) == 7 );
+  VERIFY( *std::ranges::prev(begin, -4) == 4 );
+  VERIFY(  std::ranges::prev(begin, 0, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, 5, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, -5, begin) == begin );
+  VERIFY(  std::ranges::prev(begin, 0, end) == begin );
+  VERIFY( *std::ranges::prev(end, 5, begin) == 5 );
+  VERIFY(  std::ranges::prev(end, 55, begin) == begin );
+  VERIFY(  std::ranges::prev(end, 0, end) == end );
+  VERIFY(  std::ranges::prev(end, -5, end) == end );
+  VERIFY(  std::ranges::prev(end, -55, end) == end );
+  VERIFY(  std::ranges::prev(end, 0, begin) == end );
+  VERIFY( *std::ranges::prev(begin, -5, end) == 5 );
+  VERIFY(  std::ranges::prev(begin, -55, end) == end );
+}
+
+template<typename T>
+  concept can_prev = requires(T& t) { std::ranges::prev(t); }
+    || requires(T& t) { std::ranges::prev(t, 1); }
+    || requires(T& t) { std::ranges::prev(t, 1, t); };
+
+static_assert( !can_prev<forward_iterator_wrapper<int>> );
+static_assert( !can_prev<input_iterator_wrapper<int>> );
+static_assert( !can_prev<output_iterator_wrapper<int>> );
+
+int
+main()
+{
+  test01();
+  test02();
+}
diff --git a/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/2.cc b/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/2.cc
index 83bd8bc7eb6..1d44c316086 100644
--- a/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/2.cc
@@ -28,9 +28,10 @@  namespace std
   using __gnu_test::NonDefaultConstructible;
 
   typedef NonDefaultConstructible 		value_type;
-  typedef value_type* 		input_iterator;
-  typedef value_type* 		output_iterator;
+  typedef value_type* 		input_iterator_type;
+  typedef value_type* 		output_iterator_type;
 
-  template 
-  output_iterator adjacent_difference(input_iterator, input_iterator, output_iterator);
+  template output_iterator_type
+  adjacent_difference(input_iterator_type, input_iterator_type,
+		      output_iterator_type);
 } 
diff --git a/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/pod.cc b/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/pod.cc
index dd8b7dc6494..f7c82ece908 100644
--- a/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/pod.cc
+++ b/libstdc++-v3/testsuite/26_numerics/adjacent_difference/requirements/explicit_instantiation/pod.cc
@@ -28,9 +28,10 @@  namespace std
   using __gnu_test::pod_int;
 
   typedef pod_int 		value_type;
-  typedef value_type* 		input_iterator;
-  typedef value_type* 		output_iterator;
+  typedef value_type* 		input_iterator_type;
+  typedef value_type* 		output_iterator_type;
 
-  template 
-  output_iterator adjacent_difference(input_iterator, input_iterator, output_iterator);
+  template output_iterator_type
+  adjacent_difference(input_iterator_type, input_iterator_type,
+		      output_iterator_type);
 } 
diff --git a/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/2.cc b/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/2.cc
index 707de2f37fc..763d2d1ebe5 100644
--- a/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/2.cc
@@ -28,8 +28,9 @@  namespace std
   using __gnu_test::NonDefaultConstructible;
 
   typedef NonDefaultConstructible 		value_type;
-  typedef value_type* 		input_iterator;
-  typedef value_type* 		output_iterator;
+  typedef value_type* 		input_iterator_type;
+  typedef value_type* 		output_iterator_type;
 
-  template output_iterator partial_sum(input_iterator, input_iterator, output_iterator);
+  template output_iterator_type
+  partial_sum(input_iterator_type, input_iterator_type, output_iterator_type);
 } 
diff --git a/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/pod.cc b/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/pod.cc
index 89c2bd9718b..a5b7a688ccb 100644
--- a/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/pod.cc
+++ b/libstdc++-v3/testsuite/26_numerics/partial_sum/requirements/explicit_instantiation/pod.cc
@@ -28,8 +28,9 @@  namespace std
   using __gnu_test::pod_int;
 
   typedef pod_int 		value_type;
-  typedef value_type* 		input_iterator;
-  typedef value_type* 		output_iterator;
+  typedef value_type* 		input_iterator_type;
+  typedef value_type* 		output_iterator_type;
 
-  template output_iterator partial_sum(input_iterator, input_iterator, output_iterator);
+  template output_iterator_type
+  partial_sum(input_iterator_type, input_iterator_type, output_iterator_type);
 } 
diff --git a/libstdc++-v3/testsuite/experimental/iterator/requirements.cc b/libstdc++-v3/testsuite/experimental/iterator/requirements.cc
index c11857e34a7..734cc170e9e 100644
--- a/libstdc++-v3/testsuite/experimental/iterator/requirements.cc
+++ b/libstdc++-v3/testsuite/experimental/iterator/requirements.cc
@@ -64,4 +64,6 @@  std::move_iterator<int*> mi;
 std::istream_iterator<int> isi;
 std::ostream_iterator<int> osi(os());
 std::istreambuf_iterator<char> isbi;
+
+#include <ostream>
 std::ostreambuf_iterator<char> osbi(os());
diff --git a/libstdc++-v3/testsuite/std/ranges/access/begin.cc b/libstdc++-v3/testsuite/std/ranges/access/begin.cc
new file mode 100644
index 00000000000..1d7db46b68a
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/begin.cc
@@ -0,0 +1,140 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator> // N.B. should be <ranges>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using std::same_as;
+
+void
+test01()
+{
+  int a[2] = {};
+
+  static_assert(same_as<decltype(std::ranges::begin(a)), decltype(a + 0)>);
+  static_assert(noexcept(std::ranges::begin(a)));
+  VERIFY( std::ranges::begin(a) == (a + 0) );
+
+  constexpr long b[2] = { };
+  static_assert( std::ranges::begin(b) == (b + 0) );
+}
+
+void
+test02()
+{
+  using __gnu_test::test_range;
+  using __gnu_test::random_access_iterator_wrapper;
+  using __gnu_test::input_iterator_wrapper;
+  using __gnu_test::output_iterator_wrapper;
+
+  int a[] = { 0, 1 };
+
+  test_range<int, random_access_iterator_wrapper> r(a);
+  static_assert(same_as<decltype(std::ranges::begin(r)), decltype(r.begin())>);
+  VERIFY( std::ranges::begin(r) == r.begin() );
+
+  test_range<int, input_iterator_wrapper> i(a);
+  static_assert(same_as<decltype(std::ranges::begin(i)), decltype(i.begin())>);
+  VERIFY( std::ranges::begin(i) == i.begin() );
+
+  test_range<int, output_iterator_wrapper> o(a);
+  static_assert(same_as<decltype(std::ranges::begin(o)), decltype(o.begin())>);
+  *std::ranges::begin(o) = 99;
+  VERIFY( a[0] == 99 );
+}
+
+struct R
+{
+  int a[4] = { 0, 1, 2, 3 };
+
+  friend int* begin(R& r) { return r.a + 0; }
+  friend int* begin(R&& r) { return r.a + 1; }
+  friend const int* begin(const R& r) noexcept { return r.a + 2; }
+  friend const int* begin(const R&& r) noexcept { return r.a + 3; }
+};
+
+void
+test03()
+{
+  R r;
+  const R& c = r;
+
+  static_assert(same_as<decltype(std::ranges::begin(r)), decltype(begin(r))>);
+  static_assert(!noexcept(std::ranges::begin(r)));
+  VERIFY( std::ranges::begin(r) == begin(r) );
+
+  static_assert(same_as<decltype(std::ranges::begin(std::move(r))),
+		decltype(begin(std::move(r)))>);
+  static_assert(!noexcept(std::ranges::begin(std::move(r))));
+  VERIFY( std::ranges::begin(std::move(r)) == begin(std::move(r)) );
+
+
+  static_assert(same_as<decltype(std::ranges::begin(c)), decltype(begin(c))>);
+  static_assert(noexcept(std::ranges::begin(c)));
+  VERIFY( std::ranges::begin(c) == begin(c) );
+
+  static_assert(same_as<decltype(std::ranges::begin(std::move(c))),
+		decltype(begin(std::move(c)))>);
+  static_assert(noexcept(std::ranges::begin(std::move(c))));
+  VERIFY( std::ranges::begin(std::move(c)) == begin(std::move(c)) );
+}
+
+struct RR
+{
+  short s = 0;
+  long l = 0;
+  int a[4] = { 0, 1, 2, 3 };
+
+  short* begin() noexcept { return &s; }
+  const long* begin() const { return &l; }
+
+  friend int* begin(RR& r) { return r.a + 0; }
+  friend int* begin(RR&& r) { return r.a + 1; }
+  friend const int* begin(const RR& r) { return r.a + 2; }
+  friend const int* begin(const RR&& r) noexcept { return r.a + 3; }
+};
+
+void
+test04()
+{
+  RR r;
+  const RR& c = r;
+  VERIFY( std::ranges::begin(r) == &r.s );
+  static_assert(noexcept(std::ranges::begin(r)));
+
+  VERIFY( std::ranges::begin(std::move(r)) == r.a + 1 );
+  static_assert(!noexcept(std::ranges::begin(std::move(r))));
+
+  VERIFY( std::ranges::begin(c) == &r.l );
+  static_assert(!noexcept(std::ranges::begin(c)));
+
+  VERIFY( std::ranges::begin(std::move(c)) == r.a + 3 );
+  static_assert(noexcept(std::ranges::begin(std::move(c))));
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/cbegin.cc b/libstdc++-v3/testsuite/std/ranges/access/cbegin.cc
new file mode 100644
index 00000000000..34dd7fec3c6
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/cbegin.cc
@@ -0,0 +1,91 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator> // N.B. should be <ranges>
+#include <testsuite_hooks.h>
+using std::same_as;
+
+void
+test01()
+{
+  int a[2] = {};
+
+  static_assert(same_as<decltype(std::ranges::cbegin(a)), const int*>);
+  static_assert(noexcept(std::ranges::cbegin(a)));
+  VERIFY( std::ranges::cbegin(a) == (a + 0) );
+
+  constexpr long b[2] = {};
+  static_assert( std::ranges::cbegin(b) == (b + 0) );
+}
+
+struct R
+{
+  int a[4] = { 0, 1, 2, 3 };
+
+  friend int* begin(R& r) { return r.a + 0; }
+  friend int* begin(R&& r) { return r.a + 1; }
+  friend const int* begin(const R& r) noexcept { return r.a + 2; }
+  friend const int* begin(const R&& r) noexcept { return r.a + 3; }
+};
+
+void
+test03()
+{
+  R r;
+  const R& c = r;
+  VERIFY(std::ranges::cbegin(r) == std::ranges::begin(c));
+  VERIFY(std::ranges::cbegin(std::move(r)) == std::ranges::begin(std::move(c)));
+  VERIFY(std::ranges::cbegin(c) == std::ranges::begin(c));
+  VERIFY(std::ranges::cbegin(std::move(c)) == std::ranges::begin(std::move(c)));
+}
+
+struct RR
+{
+  short s = 0;
+  long l = 0;
+  int a[4] = { 0, 1, 2, 3 };
+
+  short* begin() noexcept { return &s; }
+  const long* begin() const { return &l; }
+
+  friend int* begin(RR& r) { return r.a + 0; }
+  friend int* begin(RR&& r) { return r.a + 1; }
+  friend const int* begin(const RR& r) { return r.a + 2; }
+  friend const int* begin(const RR&& r) noexcept { return r.a + 3; }
+};
+
+void
+test04()
+{
+  RR r;
+  const RR& c = r;
+  VERIFY(std::ranges::cbegin(r) == std::ranges::begin(c));
+  VERIFY(std::ranges::cbegin(std::move(r)) == std::ranges::begin(std::move(c)));
+  VERIFY(std::ranges::cbegin(c) == std::ranges::begin(c));
+  VERIFY(std::ranges::cbegin(std::move(c)) == std::ranges::begin(std::move(c)));
+}
+
+int
+main()
+{
+  test01();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/cdata.cc b/libstdc++-v3/testsuite/std/ranges/access/cdata.cc
new file mode 100644
index 00000000000..9a1ab5b9607
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/cdata.cc
@@ -0,0 +1,73 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  struct R
+  {
+    int i = 0;
+    int j = 0;
+    int* data() { return &j; }
+    const R* data() const noexcept { return nullptr; }
+  };
+  R r;
+  const R& c = r;
+  VERIFY( std::ranges::cdata(r) == (R*)nullptr );
+  static_assert( noexcept(std::ranges::cdata(r)) );
+  VERIFY( std::ranges::cdata(c) == (R*)nullptr );
+  static_assert( noexcept(std::ranges::cdata(c)) );
+}
+
+void
+test02()
+{
+  int a[] = { 0, 1 };
+  VERIFY( std::ranges::cdata(a) == a + 0 );
+}
+
+struct R
+{
+  long l = 0;
+
+  int* data() const { return nullptr; }
+  friend long* begin(R&& r) { return &r.l; }
+  friend const long* begin(const R&& r) { return &r.l + 1; }
+};
+
+void
+test03()
+{
+  R r;
+  const R& c = r;
+  VERIFY( std::ranges::cdata(std::move(r)) == std::ranges::data(std::move(c)) );
+  VERIFY( std::ranges::cdata(std::move(c)) == std::ranges::data(std::move(c)) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/cend.cc b/libstdc++-v3/testsuite/std/ranges/access/cend.cc
new file mode 100644
index 00000000000..789c6ca3837
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/cend.cc
@@ -0,0 +1,98 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator> // N.B. should be <ranges>
+#include <testsuite_hooks.h>
+
+using std::same_as;
+
+void
+test01()
+{
+  int a[2] = {};
+
+  static_assert(same_as<decltype(std::ranges::cend(a)), const int*>);
+  static_assert(noexcept(std::ranges::cend(a)));
+  VERIFY( std::ranges::cend(a) == (a + 2) );
+}
+
+struct R
+{
+  int a[4] = { 0, 1, 2, 3 };
+
+  const int* begin() const { return nullptr; }
+  friend const int* begin(const R&& r) noexcept { return nullptr; }
+
+  // Should be ignored because it doesn't return a sentinel for int*
+  const long* end() const { return nullptr; }
+
+  friend int* end(R& r) { return r.a + 0; }
+  friend int* end(R&& r) { return r.a + 1; }
+  friend const int* end(const R& r) noexcept { return r.a + 2; }
+  friend const int* end(const R&& r) noexcept { return r.a + 3; }
+};
+
+void
+test03()
+{
+  R r;
+  const R& c = r;
+  VERIFY( std::ranges::cend(r) == std::ranges::end(c) );
+  VERIFY( std::ranges::cend(std::move(r)) == std::ranges::end(std::move(c)) );
+  VERIFY( std::ranges::cend(c) == std::ranges::end(c) );
+  VERIFY( std::ranges::cend(std::move(c)) == std::ranges::end(std::move(c)) );
+}
+
+struct RR
+{
+  short s = 0;
+  long l = 0;
+  int a[4] = { 0, 1, 2, 3 };
+
+  const void* begin() const { return nullptr; }
+  friend const void* begin(const RR&&) noexcept { return nullptr; }
+
+  short* end() noexcept { return &s; }
+  const long* end() const { return &l; }
+
+  friend int* end(RR&) { throw 1; }
+  friend int* end(RR&& r) { return r.a + 1; }
+  friend const int* end(const RR&) { throw 1; }
+  friend const int* end(const RR&& r) noexcept { return r.a + 3; }
+};
+
+void
+test04()
+{
+  RR r;
+  const RR& c = r;
+  VERIFY( std::ranges::cend(r) == std::ranges::end(c) );
+  VERIFY( std::ranges::cend(std::move(r)) == std::ranges::end(std::move(c)) );
+  VERIFY( std::ranges::cend(c) == std::ranges::end(c) );
+  VERIFY( std::ranges::cend(std::move(c)) == std::ranges::end(std::move(c)) );
+}
+
+int
+main()
+{
+  test01();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/crbegin.cc b/libstdc++-v3/testsuite/std/ranges/access/crbegin.cc
new file mode 100644
index 00000000000..24939ac658e
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/crbegin.cc
@@ -0,0 +1,73 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+struct R1
+{
+  int i = 0;
+  int j = 0;
+
+  const int* rbegin() const { return &i; }
+  friend const int* rbegin(const R1&& r) { return &r.j; }
+};
+
+void
+test01()
+{
+  R1 r;
+  const R1& c = r;
+  VERIFY( std::ranges::crbegin(r) == std::ranges::rbegin(c) );
+  VERIFY( std::ranges::crbegin(std::move(r)) == std::ranges::rbegin(std::move(c)) );
+  VERIFY( std::ranges::crbegin(c) == std::ranges::rbegin(c) );
+  VERIFY( std::ranges::crbegin(std::move(c)) == std::ranges::rbegin(std::move(c)) );
+}
+
+struct R2
+{
+  int a[2] = { };
+  long l[2] = { };
+
+  const int* begin() const { return a; }
+  const int* end() const { return a + 2; }
+
+  friend const long* begin(const R2&& r) { return r.l; }
+  friend const long* end(const R2&& r) { return r.l + 2; }
+};
+
+void
+test02()
+{
+  R2 r;
+  const R2& c = r;
+  VERIFY( std::ranges::crbegin(r) == std::ranges::rbegin(c) );
+  VERIFY( std::ranges::crbegin(std::move(r)) == std::ranges::rbegin(std::move(c)) );
+  VERIFY( std::ranges::crbegin(c) == std::ranges::rbegin(c) );
+  VERIFY( std::ranges::crbegin(std::move(c)) == std::ranges::rbegin(std::move(c)) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/crend.cc b/libstdc++-v3/testsuite/std/ranges/access/crend.cc
new file mode 100644
index 00000000000..ef0fb0e6b09
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/crend.cc
@@ -0,0 +1,108 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+struct R1
+{
+  int i = 0;
+  int j = 0;
+
+  constexpr const int* rbegin() const { return &i; }
+  constexpr const int* rend() const { return &i + 1; }
+  friend constexpr const int* rbegin(const R1&& r) { return &r.j; }
+  friend constexpr const int* rend(const R1&& r) { return &r.j + 1; }
+};
+
+void
+test01()
+{
+  R1 r;
+  const R1& c = r;
+  VERIFY( std::ranges::crend(r) == std::ranges::rend(c) );
+  VERIFY( std::ranges::crend(std::move(r)) == std::ranges::rend(std::move(c)) );
+  VERIFY( std::ranges::crend(c) == std::ranges::rend(c) );
+  VERIFY( std::ranges::crend(std::move(c)) == std::ranges::rend(std::move(c)) );
+}
+
+struct R2
+{
+  int a[2] = { };
+  long l[2] = { };
+
+  const int* begin() const { return a; }
+  const int* end() const { return a + 2; }
+
+  friend const long* begin(const R2&& r) { return r.l; }
+  friend const long* end(const R2&& r) { return r.l + 2; }
+};
+
+void
+test02()
+{
+  R2 r;
+  const R2& c = r;
+  VERIFY( std::ranges::crend(r) == std::ranges::rend(c) );
+  VERIFY( std::ranges::crend(std::move(r)) == std::ranges::rend(std::move(c)) );
+  VERIFY( std::ranges::crend(c) == std::ranges::rend(c) );
+  VERIFY( std::ranges::crend(std::move(c)) == std::ranges::rend(std::move(c)) );
+}
+
+struct R3
+{
+  int i = 0;
+
+  const int* rbegin() const noexcept { return &i + 1; }
+  const long* rend() const noexcept { return nullptr; } // not a sentinel for rbegin()
+
+  friend const long* rbegin(const R3&) noexcept { return nullptr; }
+  friend const int* rend(const R3& r) { return &r.i; }
+};
+
+void
+test03()
+{
+  R3 r;
+  const R3& c = r;
+  VERIFY( std::ranges::crend(r) == std::ranges::rend(c) );
+  static_assert( !noexcept(std::ranges::crend(r)) );
+  VERIFY( std::ranges::crend(c) == std::ranges::rend(c) );
+  static_assert( !noexcept(std::ranges::crend(c)) );
+}
+
+void
+test04()
+{
+  int a[2] = { };
+  const auto& c = a;
+  VERIFY( std::ranges::crend(a) == std::ranges::rend(c) );
+  VERIFY( std::ranges::crend(c) == std::ranges::rend(c) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/data.cc b/libstdc++-v3/testsuite/std/ranges/access/data.cc
new file mode 100644
index 00000000000..d9129d055fc
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/data.cc
@@ -0,0 +1,78 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+void
+test01()
+{
+  struct R
+  {
+    int i = 0;
+    int j = 0;
+    int* data() { return &j; }
+    const R* data() const noexcept { return nullptr; }
+  };
+  R r;
+  const R& c = r;
+  VERIFY( std::ranges::data(r) == &r.j );
+  static_assert( !noexcept(std::ranges::data(r)) );
+  VERIFY( std::ranges::data(c) == (R*)nullptr );
+  static_assert( noexcept(std::ranges::data(c)) );
+}
+
+
+void
+test02()
+{
+  int a[] = { 0, 1 };
+  VERIFY( std::ranges::data(a) == a + 0 );
+
+  __gnu_test::test_range<int, __gnu_test::contiguous_iterator_wrapper> r(a);
+  VERIFY( std::ranges::data(r) == std::to_address(std::ranges::begin(r)) );
+}
+
+struct R3
+{
+  long l = 0;
+
+  int* data() const { return nullptr; }
+  friend long* begin(R3&& r) { return &r.l; }
+  friend const long* begin(const R3&& r) { return &r.l + 1; }
+};
+
+void
+test03()
+{
+  R3 r;
+  const R3& c = r;
+  VERIFY( std::ranges::data(std::move(r)) == std::to_address(std::ranges::begin(std::move(r))) );
+  VERIFY( std::ranges::data(std::move(c)) == std::to_address(std::ranges::begin(std::move(c))) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/empty.cc b/libstdc++-v3/testsuite/std/ranges/access/empty.cc
new file mode 100644
index 00000000000..64b1e1b5e1b
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/empty.cc
@@ -0,0 +1,76 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator> // N.B. should be <ranges>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using std::same_as;
+
+void
+test01()
+{
+  struct R
+  {
+    constexpr int empty() const & { return 0; }
+    constexpr const void* empty() const && { return this; }
+  };
+  constexpr R r;
+  static_assert( !std::ranges::empty(r) );
+  static_assert( same_as<decltype(std::ranges::empty(r)), bool> );
+  static_assert( std::ranges::empty(std::move(r)) );
+  static_assert( same_as<decltype(std::ranges::empty(std::move(r))), bool> );
+}
+
+void
+test02()
+{
+  using __gnu_test::test_range;
+  using __gnu_test::test_sized_range;
+  using __gnu_test::random_access_iterator_wrapper;
+  using __gnu_test::forward_iterator_wrapper;
+  using __gnu_test::input_iterator_wrapper;
+  using __gnu_test::output_iterator_wrapper;
+
+  int a[] = { 0, 1 };
+  VERIFY( !std::ranges::empty(a) );
+
+  test_range<int, random_access_iterator_wrapper> r(a);
+  VERIFY( !std::ranges::empty(r) );
+
+  test_range<int, forward_iterator_wrapper> i(a);
+  VERIFY( !std::ranges::empty(i) );
+
+  test_sized_range<int, random_access_iterator_wrapper> sr(a);
+  VERIFY( !std::ranges::empty(sr) );
+
+  test_sized_range<int, input_iterator_wrapper> si(a);
+  VERIFY( !std::ranges::empty(si) );
+
+  test_sized_range<int, output_iterator_wrapper> so(a);
+  VERIFY( !std::ranges::empty(so) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/end.cc b/libstdc++-v3/testsuite/std/ranges/access/end.cc
new file mode 100644
index 00000000000..7f09cc2a4ab
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/end.cc
@@ -0,0 +1,145 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator> // N.B. should be <ranges>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using std::same_as;
+
+void
+test01()
+{
+  int a[2] = {};
+
+  static_assert(same_as<decltype(std::ranges::end(a)), decltype(a + 2)>);
+  static_assert(noexcept(std::ranges::end(a)));
+  VERIFY( std::ranges::end(a) == (a + 2) );
+}
+
+void
+test02()
+{
+  using __gnu_test::test_range;
+  using __gnu_test::random_access_iterator_wrapper;
+  using __gnu_test::input_iterator_wrapper;
+  using __gnu_test::output_iterator_wrapper;
+
+  int a[] = { 0, 1 };
+
+  test_range<int, random_access_iterator_wrapper> r(a);
+  static_assert(same_as<decltype(std::ranges::end(r)), decltype(r.end())>);
+  VERIFY( std::ranges::end(r) == r.end() );
+
+  test_range<int, input_iterator_wrapper> i(a);
+  static_assert(same_as<decltype(std::ranges::end(i)), decltype(i.end())>);
+  VERIFY( std::ranges::end(i) == i.end() );
+
+  test_range<int, output_iterator_wrapper> o(a);
+  static_assert(same_as<decltype(std::ranges::end(o)), decltype(o.end())>);
+  VERIFY( std::ranges::end(o) == std::ranges::next(o.begin(), 2) );
+}
+
+struct R
+{
+  int a[4] = { 0, 1, 2, 3 };
+
+  const int* begin() const { return nullptr; }
+  friend const int* begin(const R&& r) noexcept { return nullptr; }
+
+  // Should be ignored because it doesn't return a sentinel for int*
+  const long* end() const { return nullptr; }
+
+  friend int* end(R& r) { return r.a + 0; }
+  friend int* end(R&& r) { return r.a + 1; }
+  friend const int* end(const R& r) noexcept { return r.a + 2; }
+  friend const int* end(const R&& r) noexcept { return r.a + 3; }
+};
+
+void
+test03()
+{
+  R r;
+  const R& c = r;
+
+  static_assert(same_as<decltype(std::ranges::end(r)), decltype(end(r))>);
+  static_assert(!noexcept(std::ranges::end(r)));
+  VERIFY( std::ranges::end(r) == end(r) );
+
+  static_assert(same_as<decltype(std::ranges::end(std::move(r))),
+		decltype(end(std::move(r)))>);
+  static_assert(!noexcept(std::ranges::end(std::move(r))));
+  VERIFY( std::ranges::end(std::move(r)) == end(std::move(r)) );
+
+
+  static_assert(same_as<decltype(std::ranges::end(c)), decltype(end(c))>);
+  static_assert(noexcept(std::ranges::end(c)));
+  VERIFY( std::ranges::end(c) == end(c) );
+
+  static_assert(same_as<decltype(std::ranges::end(std::move(c))),
+		decltype(end(std::move(c)))>);
+  static_assert(noexcept(std::ranges::end(std::move(c))));
+  VERIFY( std::ranges::end(std::move(c)) == end(std::move(c)) );
+}
+
+struct RR
+{
+  short s = 0;
+  long l = 0;
+  int a[4] = { 0, 1, 2, 3 };
+
+  const void* begin() const { return nullptr; }
+  friend const void* begin(const RR&&) noexcept { return nullptr; }
+
+  short* end() noexcept { return &s; }
+  const long* end() const { return &l; }
+
+  friend int* end(RR&) { throw 1; }
+  friend int* end(RR&& r) { return r.a + 1; }
+  friend const int* end(const RR&) { throw 1; }
+  friend const int* end(const RR&& r) noexcept { return r.a + 3; }
+};
+
+void
+test04()
+{
+  RR r;
+  const RR& c = r;
+  VERIFY( std::ranges::end(r) == &r.s );
+  static_assert(noexcept(std::ranges::end(r)));
+
+  VERIFY( std::ranges::end(std::move(r)) == r.a + 1 );
+  static_assert(!noexcept(std::ranges::end(std::move(r))));
+
+  VERIFY( std::ranges::end(c) == &r.l );
+  static_assert(!noexcept(std::ranges::end(c)));
+
+  VERIFY( std::ranges::end(std::move(c)) == r.a + 3 );
+  static_assert(noexcept(std::ranges::end(std::move(c))));
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/rbegin.cc b/libstdc++-v3/testsuite/std/ranges/access/rbegin.cc
new file mode 100644
index 00000000000..6cfc1a38122
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/rbegin.cc
@@ -0,0 +1,81 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+struct R1
+{
+  int i = 0;
+  int j = 0;
+
+  constexpr const int* rbegin() const { return &i; }
+  friend constexpr const int* rbegin(const R1&& r) { return &r.j; }
+};
+
+void
+test01()
+{
+  constexpr R1 r;
+  static_assert( std::ranges::rbegin(r) == &r.i );
+  static_assert( std::ranges::rbegin(std::move(r)) == &r.j );
+}
+
+struct R2
+{
+  int a[2] = { };
+  long l[2] = { };
+
+  constexpr const int* begin() const { return a; }
+  constexpr const int* end() const { return a + 2; }
+
+  friend constexpr const long* begin(const R2&& r) { return r.l; }
+  friend constexpr const long* end(const R2&& r) { return r.l + 2; }
+};
+
+void
+test02()
+{
+  constexpr R2 r;
+  static_assert( std::ranges::rbegin(r)
+      == std::make_reverse_iterator(std::ranges::end(r)) );
+  static_assert( std::ranges::rbegin(std::move(r))
+      == std::make_reverse_iterator(std::ranges::end(std::move(r))) );
+}
+
+void
+test03()
+{
+  using __gnu_test::test_range;
+  using __gnu_test::bidirectional_iterator_wrapper;
+
+  int a[2] = { };
+  test_range<int, bidirectional_iterator_wrapper> r(a);
+  VERIFY( std::ranges::rbegin(r) == std::make_reverse_iterator(std::ranges::end(r)) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/rend.cc b/libstdc++-v3/testsuite/std/ranges/access/rend.cc
new file mode 100644
index 00000000000..2192825708a
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/rend.cc
@@ -0,0 +1,105 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+struct R1
+{
+  int i = 0;
+  int j = 0;
+
+  constexpr const int* rbegin() const { return &i; }
+  constexpr const int* rend() const { return &i + 1; }
+  friend constexpr const int* rbegin(const R1&& r) { return &r.j; }
+  friend constexpr const int* rend(const R1&& r) { return &r.j + 1; }
+};
+
+void
+test01()
+{
+  constexpr R1 r;
+  static_assert( std::ranges::rend(r) == &r.i + 1 );
+  static_assert( std::ranges::rend(std::move(r)) == &r.j + 1 );
+}
+
+struct R2
+{
+  int a[2] = { };
+  long l[2] = { };
+
+  constexpr const int* begin() const { return a; }
+  constexpr const int* end() const { return a + 2; }
+
+  friend constexpr const long* begin(const R2&& r) { return r.l; }
+  friend constexpr const long* end(const R2&& r) { return r.l + 2; }
+};
+
+void
+test02()
+{
+  constexpr R2 r;
+  static_assert( std::ranges::rend(r)
+      == std::make_reverse_iterator(std::ranges::begin(r)) );
+  static_assert( std::ranges::rend(std::move(r))
+      == std::make_reverse_iterator(std::ranges::begin(std::move(r))) );
+}
+
+struct R3
+{
+  int i = 0;
+
+  int* rbegin() noexcept { return &i + 1; }
+  long* rend() noexcept { return nullptr; } // not a sentinel for rbegin()
+
+  friend long* rbegin(R3&) noexcept { return nullptr; }
+  friend int* rend(R3& r) { return &r.i; }
+};
+
+void
+test03()
+{
+  R3 r;
+  auto i1 = std::ranges::rbegin(r);
+  auto i2 = rend(r);
+  static_assert( std::sentinel_for<decltype(i2), decltype(i1)> );
+  // VERIFY( std::ranges::rend(r) == r.i );
+  // static_assert( !noexcept(std::ranges::rend(r)) );
+}
+
+void
+test04()
+{
+  using __gnu_test::test_range;
+  using __gnu_test::bidirectional_iterator_wrapper;
+
+  int a[2] = { };
+  test_range<int, bidirectional_iterator_wrapper> r(a);
+  VERIFY( std::ranges::rend(r) == std::make_reverse_iterator(std::ranges::begin(r)) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/access/size.cc b/libstdc++-v3/testsuite/std/ranges/access/size.cc
new file mode 100644
index 00000000000..b92e5d50449
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/size.cc
@@ -0,0 +1,116 @@ 
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <iterator>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+void
+test01()
+{
+  constexpr int a[10] = { };
+  static_assert( std::ranges::size(a) == 10 );
+  static_assert( noexcept(std::ranges::size(a)) );
+
+  int a2[2];
+  VERIFY( std::ranges::size(a2) == 2);
+  static_assert( noexcept(std::ranges::size(a2)) );
+}
+
+void
+test02()
+{
+  struct R
+  {
+    int size() { return 1; }
+    long size() const noexcept { return 2; }
+  };
+  R r;
+  const R& c = r;
+  VERIFY( std::ranges::size(r) == 1 );
+  static_assert( !noexcept(std::ranges::size(r)) );
+  VERIFY( std::ranges::size(c) == 2L );
+  static_assert( noexcept(std::ranges::size(c)) );
+
+  int a[3] = { };
+  __gnu_test::test_sized_range<int, __gnu_test::input_iterator_wrapper> ri(a);
+  VERIFY( std::ranges::size(ri) == 3 );
+  static_assert( noexcept(std::ranges::size(ri)) );
+}
+
+struct R3
+{
+  int* size() { return nullptr; }
+  friend int size(R3&) noexcept { return 1; }
+  friend long size(const R3&) { return 2L; }
+  friend unsigned int size(R3&&) { return 3U; }
+  friend unsigned long size(const R3&&) noexcept { return 4UL; }
+};
+
+void
+test03()
+{
+  R3 r;
+  const R3& c = r;
+  VERIFY( std::ranges::size(r) == 1 );
+  static_assert( noexcept(std::ranges::size(r)) );
+  VERIFY( std::ranges::size(std::move(r)) == 3U );
+  static_assert( !noexcept(std::ranges::size(std::move(r))) );
+  VERIFY( std::ranges::size(c) == 2L );
+  static_assert( !noexcept(std::ranges::size(c)) );
+  VERIFY( std::ranges::size(std::move(c)) == 4UL );
+  static_assert( noexcept(std::ranges::size(std::move(c))) );
+}
+
+void
+test04()
+{
+  int a[] = { 0, 1 };
+  __gnu_test::test_range<int, __gnu_test::random_access_iterator_wrapper> r(a);
+  auto& rr = r;
+  VERIFY( std::ranges::size(r) == (std::ranges::end(r) - std::ranges::begin(r)) );
+}
+
+struct R5
+{
+  int size() const noexcept { return 0; }
+  R5* begin() { return this; }
+  R5* end() { return this + 1; }
+};
+
+template<>
+constexpr bool std::ranges::disable_sized_range<R5> = true;
+
+void
+test05()
+{
+  R5 r;
+  VERIFY( std::ranges::size(r) == 1 );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+  test05();
+}
diff --git a/libstdc++-v3/testsuite/util/testsuite_iterators.h b/libstdc++-v3/testsuite/util/testsuite_iterators.h
index 974490b1b6c..70c1f9b6689 100644
--- a/libstdc++-v3/testsuite/util/testsuite_iterators.h
+++ b/libstdc++-v3/testsuite/util/testsuite_iterators.h
@@ -590,5 +590,145 @@  namespace __gnu_test
     size() const
     { return bounds.size(); }
   };
-}
-#endif
+
+#if __cplusplus > 201703L
+  template<typename T>
+    struct contiguous_iterator_wrapper
+    : random_access_iterator_wrapper<T>
+    {
+      using random_access_iterator_wrapper<T>::random_access_iterator_wrapper;
+
+      using iterator_concept = std::contiguous_iterator_tag;
+
+      contiguous_iterator_wrapper&
+      operator++()
+      {
+	random_access_iterator_wrapper<T>::operator++();
+	return *this;
+      }
+
+      contiguous_iterator_wrapper&
+      operator--()
+      {
+	random_access_iterator_wrapper<T>::operator--();
+	return *this;
+      }
+
+      contiguous_iterator_wrapper
+      operator++(int)
+      {
+	auto tmp = *this;
+	++*this;
+	return tmp;
+      }
+
+      contiguous_iterator_wrapper
+      operator--(int)
+      {
+	auto tmp = *this;
+	--*this;
+	return tmp;
+      }
+
+      contiguous_iterator_wrapper&
+      operator+=(std::ptrdiff_t n)
+      {
+	random_access_iterator_wrapper<T>::operator+=(n);
+	return *this;
+      }
+
+      friend contiguous_iterator_wrapper
+      operator+(contiguous_iterator_wrapper iter, std::ptrdiff_t n)
+      { return iter += n; }
+
+      friend contiguous_iterator_wrapper
+      operator+(std::ptrdiff_t n, contiguous_iterator_wrapper iter)
+      { return iter += n; }
+
+      contiguous_iterator_wrapper&
+      operator-=(std::ptrdiff_t n)
+      { return *this += -n; }
+
+      friend contiguous_iterator_wrapper
+      operator-(contiguous_iterator_wrapper iter, std::ptrdiff_t n)
+      { return iter -= n; }
+    };
+
+  // A type meeting the minimum std::range requirements
+  template<typename T, template<typename> class Iter>
+    class test_range
+    {
+      // Adds default constructor to Iter<T> if needed
+      struct iterator : Iter<T>
+      {
+	using Iter<T>::Iter;
+
+	iterator() : Iter<T>(nullptr, nullptr) { }
+
+	using Iter<T>::operator++;
+
+	iterator& operator++() { Iter<T>::operator++(); return *this; }
+      };
+
+      template<typename I>
+	struct sentinel
+	{
+	  T* end;
+
+	  friend bool operator==(const sentinel& s, const I& i)
+	  { return s.end == i.ptr; }
+
+	  friend bool operator!=(const sentinel& s, const I& i)
+	  { return !(s == i); }
+
+	  friend bool operator==(const I& i, const sentinel& s)
+	  { return s == i; }
+
+	  friend bool operator!=(const I& i, const sentinel& s)
+	  { return !(s == i); }
+	};
+
+      auto
+      get_iterator(T* p)
+      {
+	if constexpr (std::default_constructible<Iter<T>>)
+	  return Iter<T>(p, &bounds);
+	else
+	  return iterator(p, &bounds);
+      }
+
+    public:
+      test_range(T* first, T* last) : bounds(first, last)
+      { }
+
+      template<std::size_t N>
+	explicit
+	test_range(T (&arr)[N]) : test_range(arr, arr+N)
+	{ }
+
+      auto begin() & { return get_iterator(bounds.first); }
+
+      auto end() &
+      {
+	using I = decltype(get_iterator(bounds.last));
+	if constexpr (std::sentinel_for<I, I>)
+	  return get_iterator(bounds.last);
+	else
+	  return sentinel<I>{bounds.last};
+      }
+
+      typename Iter<T>::ContainerType bounds;
+    };
+
+  // A type meeting the minimum std::sized_range requirements
+  template<typename T, template<typename> class Iter>
+    struct test_sized_range : test_range<T, Iter>
+    {
+      using test_range<T, Iter>::test_range;
+
+      std::size_t size() const noexcept
+      { return this->bounds.size(); }
+    };
+#endif // C++20
+} // namespace __gnu_test
+#endif // _TESTSUITE_ITERATORS