diff --git a/libcxx/docs/Cxx2aStatusIssuesStatus.csv b/libcxx/docs/Cxx2aStatusIssuesStatus.csv
--- a/libcxx/docs/Cxx2aStatusIssuesStatus.csv
+++ b/libcxx/docs/Cxx2aStatusIssuesStatus.csv
@@ -297,3 +297,4 @@
 "`3396 <https://wg21.link/LWG3396>`__","Clarify point of reference for ``source_location::current()``\  (DE 169)","Prague","",""
 "`3397 <https://wg21.link/LWG3397>`__","``ranges::basic_istream_view::iterator``\  should not provide ``iterator_category``\ ","Prague","",""
 "`3398 <https://wg21.link/LWG3398>`__","``tuple_element_t``\  is also wrong for ``const subrange``\ ","Prague","",""
+"`3446 <https://wg21.link/LWG3446>`__","``indirectly_readable_traits``\ ambiguity for types with both ``value_type``\ and ``element_type``\ ","November virtual meeting","|Complete|","13.0"
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -17,7 +17,8 @@
 
 namespace std
 {
-template<class> struct incrementable_traits; // since C++20
+template<class> struct incrementable_traits;       // since C++20
+template<class> struct indirectly_readable_traits; // since C++20
 
 template<class Iterator>
 struct iterator_traits
@@ -50,6 +51,9 @@
     typedef Category  iterator_category;
 };
 
+template<dereferenceable T>
+  using iter_reference_t = decltype(*declval<T&>());
+
 struct input_iterator_tag  {};
 struct output_iterator_tag {};
 struct forward_iterator_tag       : public input_iterator_tag         {};
@@ -472,6 +476,69 @@
 };
 
 // TODO(cjdb): add iter_difference_t once iterator_traits is cleaned up.
+
+// [readable.traits]
+template<class> struct __cond_value_type {};
+
+template<class _Tp>
+requires is_object_v<_Tp>
+struct __cond_value_type<_Tp> { using value_type = remove_cv_t<_Tp>; };
+
+template<class _Tp>
+concept __has_member_value_type = requires { typename _Tp::value_type; };
+
+template<class _Tp>
+concept __has_member_element_type = requires { typename _Tp::element_type; };
+
+template<class> struct indirectly_readable_traits {};
+
+template<class _Ip>
+requires is_array_v<_Ip>
+struct indirectly_readable_traits<_Ip> {
+  using value_type = remove_cv_t<remove_extent_t<_Ip>>;
+};
+
+template<class _Ip>
+struct indirectly_readable_traits<const _Ip> : indirectly_readable_traits<_Ip> {};
+
+template<class _Tp>
+struct indirectly_readable_traits<_Tp*> : __cond_value_type<_Tp> {};
+
+template<__has_member_value_type _Tp>
+struct indirectly_readable_traits<_Tp>
+  : __cond_value_type<typename _Tp::value_type> {};
+
+template<__has_member_element_type _Tp>
+struct indirectly_readable_traits<_Tp>
+  : __cond_value_type<typename _Tp::element_type> {};
+
+// Pre-emptively applying LWG3541.
+template<__has_member_value_type _Tp>
+requires __has_member_element_type<_Tp>
+struct indirectly_readable_traits<_Tp> {};
+
+template<__has_member_value_type _Tp>
+requires __has_member_element_type<_Tp> &&
+         same_as<remove_cv_t<typename _Tp::element_type>,
+                 remove_cv_t<typename _Tp::value_type>>
+struct indirectly_readable_traits<_Tp>
+  : __cond_value_type<typename _Tp::value_type> {};
+
+template<class _Tp>
+using __with_reference = _Tp&;
+
+template<class _Tp>
+concept __referenceable = requires {
+  typename __with_reference<_Tp>;
+};
+
+template<class _Tp>
+concept __dereferenceable = requires(_Tp& __t) {
+  { *__t } -> __referenceable; // not required to be equality-preserving
+};
+
+template<__dereferenceable _Tp>
+using iter_reference_t = decltype(*declval<_Tp&>());
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
 
 template <class _Iter>
@@ -582,6 +649,71 @@
     typedef typename _Iter::iterator_category iterator_category;
 };
 
+#if !defined(_LIBCPP_HAS_NO_RANGES)
+
+// The `cpp17.*-iterator` concepts have been dubbed `__legacy.*_iterator` because the name is both
+// clearer (C++98 iterators are still valid `cpp17-iterators`, for example), and because it's the
+// term that C++ Reference uses (which is what most users will look to when issued diagnostics).
+
+template<class _Ip>
+concept __legacy_iterator =
+  requires(_Ip __i) {
+    {   *__i } -> __referenceable;
+    {  ++__i } -> same_as<_Ip&>;
+    { *__i++ } -> __referenceable;
+  } &&
+  copyable<_Ip>;
+
+template<class _Ip>
+concept __legacy_input_iterator =
+  __legacy_iterator<_Ip> &&
+  equality_comparable<_Ip> &&
+  requires(_Ip __i) {
+    typename incrementable_traits<_Ip>::difference_type;
+    typename indirectly_readable_traits<_Ip>::value_type;
+    typename common_reference_t<iter_reference_t<_Ip>&&,
+                                typename indirectly_readable_traits<_Ip>::value_type&>;
+    typename common_reference_t<decltype(*__i++)&&,
+                                typename indirectly_readable_traits<_Ip>::value_type&>;
+    requires signed_integral<typename incrementable_traits<_Ip>::difference_type>;
+  };
+
+template<class _Ip>
+concept __legacy_forward_iterator =
+  __legacy_input_iterator<_Ip> &&
+  constructible_from<_Ip> &&
+  is_lvalue_reference_v<iter_reference_t<_Ip>> &&
+  same_as<remove_cvref_t<iter_reference_t<_Ip>>,
+          typename indirectly_readable_traits<_Ip>::value_type> &&
+  requires(_Ip __i) {
+    {  __i++ } -> convertible_to<_Ip const&>;
+    { *__i++ } -> same_as<iter_reference_t<_Ip>>;
+  };
+
+template<class _Ip>
+concept __legacy_bidirectional_iterator =
+  __legacy_forward_iterator<_Ip> &&
+  requires(_Ip __i) {
+    {  --__i } -> same_as<_Ip&>;
+    {  __i-- } -> convertible_to<_Ip const&>;
+    { *__i-- } -> same_as<iter_reference_t<_Ip>>;
+  };
+
+template<class _Ip>
+concept __legacy_random_access_iterator =
+  __legacy_bidirectional_iterator<_Ip> and
+  totally_ordered<_Ip> and
+  requires(_Ip __i, typename incrementable_traits<_Ip>::difference_type __n) {
+    { __i += __n } -> same_as<_Ip&>;
+    { __i -= __n } -> same_as<_Ip&>;
+    { __i +  __n } -> same_as<_Ip>;
+    { __n +  __i } -> same_as<_Ip>;
+    { __i -  __n } -> same_as<_Ip>;
+    { __i -  __i } -> same_as<decltype(__n)>;
+    {  __i[__n]  } -> convertible_to<iter_reference_t<_Ip>>;
+  };
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
 template <class _Iter, bool> struct __iterator_traits {};
 
 template <class _Iter>
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_bidirectional_iterator.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_bidirectional_iterator.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_bidirectional_iterator.compile.pass.cpp
@@ -0,0 +1,151 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class I>
+// concept __legacy_bidirectional_iterator;
+
+#include <iterator>
+
+#include <array>
+#include <deque>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+#include <filesystem>
+#endif
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+static_assert(std::__legacy_bidirectional_iterator<int*>);
+static_assert(std::__legacy_bidirectional_iterator<int const*>);
+static_assert(std::__legacy_bidirectional_iterator<int volatile*>);
+static_assert(std::__legacy_bidirectional_iterator<int const volatile*>);
+
+// <array>
+static_assert(std::__legacy_bidirectional_iterator<std::array<int, 10>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::array<int, 10>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::array<int, 10>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::array<int, 10>::const_reverse_iterator>);
+
+// <deque>
+static_assert(std::__legacy_bidirectional_iterator<std::deque<int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::deque<int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::deque<int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::deque<int>::const_reverse_iterator>);
+
+// <filesystem>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+static_assert(!std::__legacy_bidirectional_iterator<std::filesystem::directory_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::filesystem::recursive_directory_iterator>);
+#endif
+
+// <forward_list>
+static_assert(!std::__legacy_bidirectional_iterator<std::forward_list<int>::iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::forward_list<int>::const_iterator>);
+
+// <iterator>
+static_assert(!std::__legacy_bidirectional_iterator<std::back_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_bidirectional_iterator<std::front_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_bidirectional_iterator<std::insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_bidirectional_iterator<std::move_iterator<std::vector<int>::iterator> >);
+
+// <list>
+static_assert(std::__legacy_bidirectional_iterator<std::list<int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::list<int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::list<int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::list<int>::const_reverse_iterator>);
+
+// <map>
+static_assert(std::__legacy_bidirectional_iterator<std::map<int, int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::map<int, int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::map<int, int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::map<int, int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_bidirectional_iterator<std::multimap<int, int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multimap<int, int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multimap<int, int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multimap<int, int>::const_reverse_iterator>);
+
+// <set>
+static_assert(std::__legacy_bidirectional_iterator<std::set<int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::set<int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::set<int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::set<int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_bidirectional_iterator<std::multiset<int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multiset<int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multiset<int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::multiset<int>::const_reverse_iterator>);
+
+// <string>
+static_assert(std::__legacy_bidirectional_iterator<std::string::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string::const_reverse_iterator>);
+
+// <string_view>
+static_assert(std::__legacy_bidirectional_iterator<std::string_view::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string_view::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string_view::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::string_view::const_reverse_iterator>);
+
+// <unordered_map>
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_local_iterator>);
+
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_local_iterator>);
+
+// <unordered_set>
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::const_local_iterator>);
+
+// <vector>
+static_assert(std::__legacy_bidirectional_iterator<std::vector<int>::iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::vector<int>::const_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::vector<int>::reverse_iterator>);
+static_assert(std::__legacy_bidirectional_iterator<std::vector<int>::const_reverse_iterator>);
+
+// Not iterators
+static_assert(!std::__legacy_bidirectional_iterator<void>);
+static_assert(!std::__legacy_bidirectional_iterator<void*>);
+static_assert(!std::__legacy_bidirectional_iterator<int* const>);
+static_assert(!std::__legacy_bidirectional_iterator<std::vector<int>::iterator volatile>);
+static_assert(!std::__legacy_bidirectional_iterator<std::vector<int>::iterator&>);
+static_assert(!std::__legacy_bidirectional_iterator<std::vector<int>::iterator&&>);
+static_assert(!std::__legacy_bidirectional_iterator<int>);
+static_assert(!std::__legacy_bidirectional_iterator<int[]>);
+static_assert(!std::__legacy_bidirectional_iterator<int[10]>);
+static_assert(!std::__legacy_bidirectional_iterator<int()>);
+static_assert(!std::__legacy_bidirectional_iterator<int (*)()>);
+static_assert(!std::__legacy_bidirectional_iterator<int (&)()>);
+
+struct S {};
+static_assert(!std::__legacy_bidirectional_iterator<S>);
+static_assert(!std::__legacy_bidirectional_iterator<int S::*>);
+static_assert(!std::__legacy_bidirectional_iterator<int (S::*)()>);
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_forward_iterator.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_forward_iterator.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_forward_iterator.compile.pass.cpp
@@ -0,0 +1,151 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class I>
+// concept __legacy_forward_iterator;
+
+#include <iterator>
+
+#include <array>
+#include <deque>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+#include <filesystem>
+#endif
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+static_assert(std::__legacy_forward_iterator<int*>);
+static_assert(std::__legacy_forward_iterator<int const*>);
+static_assert(std::__legacy_forward_iterator<int volatile*>);
+static_assert(std::__legacy_forward_iterator<int const volatile*>);
+
+// <array>
+static_assert(std::__legacy_forward_iterator<std::array<int, 10>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::array<int, 10>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::array<int, 10>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::array<int, 10>::const_reverse_iterator>);
+
+// <deque>
+static_assert(std::__legacy_forward_iterator<std::deque<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::deque<int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::deque<int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::deque<int>::const_reverse_iterator>);
+
+// <filesystem>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+static_assert(!std::__legacy_forward_iterator<std::filesystem::directory_iterator>);
+static_assert(!std::__legacy_forward_iterator<std::filesystem::recursive_directory_iterator>);
+#endif
+
+// <forward_list>
+static_assert(std::__legacy_forward_iterator<std::forward_list<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::forward_list<int>::const_iterator>);
+
+// <iterator>
+static_assert(!std::__legacy_forward_iterator<std::back_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_forward_iterator<std::front_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_forward_iterator<std::insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_forward_iterator<std::move_iterator<std::vector<int>::iterator> >);
+
+// <list>
+static_assert(std::__legacy_forward_iterator<std::list<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::list<int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::list<int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::list<int>::const_reverse_iterator>);
+
+// <map>
+static_assert(std::__legacy_forward_iterator<std::map<int, int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::map<int, int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::map<int, int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::map<int, int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_forward_iterator<std::multimap<int, int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::multimap<int, int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::multimap<int, int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::multimap<int, int>::const_reverse_iterator>);
+
+// <set>
+static_assert(std::__legacy_forward_iterator<std::set<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::set<int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::set<int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::set<int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_forward_iterator<std::multiset<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::multiset<int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::multiset<int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::multiset<int>::const_reverse_iterator>);
+
+// <string>
+static_assert(std::__legacy_forward_iterator<std::string::iterator>);
+static_assert(std::__legacy_forward_iterator<std::string::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::string::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::string::const_reverse_iterator>);
+
+// <string_view>
+static_assert(std::__legacy_forward_iterator<std::string_view::iterator>);
+static_assert(std::__legacy_forward_iterator<std::string_view::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::string_view::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::string_view::const_reverse_iterator>);
+
+// <unordered_map>
+static_assert(std::__legacy_forward_iterator<std::unordered_map<int, int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::unordered_map<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_local_iterator>);
+
+static_assert(std::__legacy_forward_iterator<std::unordered_multimap<int, int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::unordered_multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_local_iterator>);
+
+// <unordered_set>
+static_assert(std::__legacy_forward_iterator<std::unordered_set<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::unordered_set<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+static_assert(std::__legacy_forward_iterator<std::unordered_multiset<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::unordered_multiset<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+// <vector>
+static_assert(std::__legacy_forward_iterator<std::vector<int>::iterator>);
+static_assert(std::__legacy_forward_iterator<std::vector<int>::const_iterator>);
+static_assert(std::__legacy_forward_iterator<std::vector<int>::reverse_iterator>);
+static_assert(std::__legacy_forward_iterator<std::vector<int>::const_reverse_iterator>);
+
+// Not iterators
+static_assert(!std::__legacy_forward_iterator<void>);
+static_assert(!std::__legacy_forward_iterator<void*>);
+static_assert(!std::__legacy_forward_iterator<int* const>);
+static_assert(!std::__legacy_forward_iterator<std::vector<int>::iterator volatile>);
+static_assert(!std::__legacy_forward_iterator<std::vector<int>::iterator&>);
+static_assert(!std::__legacy_forward_iterator<std::vector<int>::iterator&&>);
+static_assert(!std::__legacy_forward_iterator<int>);
+static_assert(!std::__legacy_forward_iterator<int[]>);
+static_assert(!std::__legacy_forward_iterator<int[10]>);
+static_assert(!std::__legacy_forward_iterator<int()>);
+static_assert(!std::__legacy_forward_iterator<int (*)()>);
+static_assert(!std::__legacy_forward_iterator<int (&)()>);
+
+struct S {};
+static_assert(!std::__legacy_forward_iterator<S>);
+static_assert(!std::__legacy_forward_iterator<int S::*>);
+static_assert(!std::__legacy_forward_iterator<int (S::*)()>);
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_input_iterator.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_input_iterator.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_input_iterator.compile.pass.cpp
@@ -0,0 +1,151 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class I>
+// concept __legacy_input_iterator;
+
+#include <iterator>
+
+#include <array>
+#include <deque>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+#include <filesystem>
+#endif
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+static_assert(std::__legacy_input_iterator<int*>);
+static_assert(std::__legacy_input_iterator<int const*>);
+static_assert(std::__legacy_input_iterator<int volatile*>);
+static_assert(std::__legacy_input_iterator<int const volatile*>);
+
+// <array>
+static_assert(std::__legacy_input_iterator<std::array<int, 10>::iterator>);
+static_assert(std::__legacy_input_iterator<std::array<int, 10>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::array<int, 10>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::array<int, 10>::const_reverse_iterator>);
+
+// <deque>
+static_assert(std::__legacy_input_iterator<std::deque<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::deque<int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::deque<int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::deque<int>::const_reverse_iterator>);
+
+// <filesystem>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+static_assert(std::__legacy_input_iterator<std::filesystem::directory_iterator>);
+static_assert(std::__legacy_input_iterator<std::filesystem::recursive_directory_iterator>);
+#endif
+
+// <forward_list>
+static_assert(std::__legacy_input_iterator<std::forward_list<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::forward_list<int>::const_iterator>);
+
+// <iterator>
+static_assert(!std::__legacy_input_iterator<std::back_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_input_iterator<std::front_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_input_iterator<std::insert_iterator<std::vector<int> > >);
+static_assert(std::__legacy_input_iterator<std::move_iterator<std::vector<int>::iterator> >);
+
+// <list>
+static_assert(std::__legacy_input_iterator<std::list<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::list<int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::list<int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::list<int>::const_reverse_iterator>);
+
+// <map>
+static_assert(std::__legacy_input_iterator<std::map<int, int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::map<int, int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::map<int, int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::map<int, int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_input_iterator<std::multimap<int, int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::multimap<int, int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::multimap<int, int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::multimap<int, int>::const_reverse_iterator>);
+
+// <set>
+static_assert(std::__legacy_input_iterator<std::set<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::set<int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::set<int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::set<int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_input_iterator<std::multiset<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::multiset<int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::multiset<int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::multiset<int>::const_reverse_iterator>);
+
+// <string>
+static_assert(std::__legacy_input_iterator<std::string::iterator>);
+static_assert(std::__legacy_input_iterator<std::string::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::string::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::string::const_reverse_iterator>);
+
+// <string_view>
+static_assert(std::__legacy_input_iterator<std::string_view::iterator>);
+static_assert(std::__legacy_input_iterator<std::string_view::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::string_view::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::string_view::const_reverse_iterator>);
+
+// <unordered_map>
+static_assert(std::__legacy_input_iterator<std::unordered_map<int, int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::unordered_map<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_local_iterator>);
+
+static_assert(std::__legacy_input_iterator<std::unordered_multimap<int, int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::unordered_multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_local_iterator>);
+
+// <unordered_set>
+static_assert(std::__legacy_input_iterator<std::unordered_set<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::unordered_set<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+static_assert(std::__legacy_input_iterator<std::unordered_multiset<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::unordered_multiset<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::const_local_iterator>);
+
+// <vector>
+static_assert(std::__legacy_input_iterator<std::vector<int>::iterator>);
+static_assert(std::__legacy_input_iterator<std::vector<int>::const_iterator>);
+static_assert(std::__legacy_input_iterator<std::vector<int>::reverse_iterator>);
+static_assert(std::__legacy_input_iterator<std::vector<int>::const_reverse_iterator>);
+
+// Not iterators
+static_assert(!std::__legacy_input_iterator<void>);
+static_assert(!std::__legacy_input_iterator<void*>);
+static_assert(!std::__legacy_input_iterator<int* const>);
+static_assert(!std::__legacy_input_iterator<std::vector<int>::iterator volatile>);
+static_assert(!std::__legacy_input_iterator<std::vector<int>::iterator&>);
+static_assert(!std::__legacy_input_iterator<std::vector<int>::iterator&&>);
+static_assert(!std::__legacy_input_iterator<int>);
+static_assert(!std::__legacy_input_iterator<int[]>);
+static_assert(!std::__legacy_input_iterator<int[10]>);
+static_assert(!std::__legacy_input_iterator<int()>);
+static_assert(!std::__legacy_input_iterator<int (*)()>);
+static_assert(!std::__legacy_input_iterator<int (&)()>);
+
+struct S {};
+static_assert(!std::__legacy_input_iterator<S>);
+static_assert(!std::__legacy_input_iterator<int S::*>);
+static_assert(!std::__legacy_input_iterator<int (S::*)()>);
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_iterator.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_iterator.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_iterator.compile.pass.cpp
@@ -0,0 +1,151 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class I>
+// concept __legacy_iterator;
+
+#include <iterator>
+
+#include <array>
+#include <deque>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+#include <filesystem>
+#endif
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+static_assert(std::__legacy_iterator<int*>);
+static_assert(std::__legacy_iterator<int const*>);
+static_assert(std::__legacy_iterator<int volatile*>);
+static_assert(std::__legacy_iterator<int const volatile*>);
+
+// <array>
+static_assert(std::__legacy_iterator<std::array<int, 10>::iterator>);
+static_assert(std::__legacy_iterator<std::array<int, 10>::const_iterator>);
+static_assert(std::__legacy_iterator<std::array<int, 10>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::array<int, 10>::const_reverse_iterator>);
+
+// <deque>
+static_assert(std::__legacy_iterator<std::deque<int>::iterator>);
+static_assert(std::__legacy_iterator<std::deque<int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::deque<int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::deque<int>::const_reverse_iterator>);
+
+// <filesystem>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+static_assert(std::__legacy_iterator<std::filesystem::directory_iterator>);
+static_assert(std::__legacy_iterator<std::filesystem::recursive_directory_iterator>);
+#endif
+
+// <forward_list>
+static_assert(std::__legacy_iterator<std::forward_list<int>::iterator>);
+static_assert(std::__legacy_iterator<std::forward_list<int>::const_iterator>);
+
+// <iterator>
+static_assert(std::__legacy_iterator<std::back_insert_iterator<std::vector<int> > >);
+static_assert(std::__legacy_iterator<std::front_insert_iterator<std::vector<int> > >);
+static_assert(std::__legacy_iterator<std::insert_iterator<std::vector<int> > >);
+static_assert(std::__legacy_iterator<std::move_iterator<std::vector<int>::iterator> >);
+
+// <list>
+static_assert(std::__legacy_iterator<std::list<int>::iterator>);
+static_assert(std::__legacy_iterator<std::list<int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::list<int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::list<int>::const_reverse_iterator>);
+
+// <map>
+static_assert(std::__legacy_iterator<std::map<int, int>::iterator>);
+static_assert(std::__legacy_iterator<std::map<int, int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::map<int, int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::map<int, int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_iterator<std::multimap<int, int>::iterator>);
+static_assert(std::__legacy_iterator<std::multimap<int, int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::multimap<int, int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::multimap<int, int>::const_reverse_iterator>);
+
+// <set>
+static_assert(std::__legacy_iterator<std::set<int>::iterator>);
+static_assert(std::__legacy_iterator<std::set<int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::set<int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::set<int>::const_reverse_iterator>);
+
+static_assert(std::__legacy_iterator<std::multiset<int>::iterator>);
+static_assert(std::__legacy_iterator<std::multiset<int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::multiset<int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::multiset<int>::const_reverse_iterator>);
+
+// <string>
+static_assert(std::__legacy_iterator<std::string::iterator>);
+static_assert(std::__legacy_iterator<std::string::const_iterator>);
+static_assert(std::__legacy_iterator<std::string::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::string::const_reverse_iterator>);
+
+// <string_view>
+static_assert(std::__legacy_iterator<std::string_view::iterator>);
+static_assert(std::__legacy_iterator<std::string_view::const_iterator>);
+static_assert(std::__legacy_iterator<std::string_view::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::string_view::const_reverse_iterator>);
+
+// <unordered_map>
+static_assert(std::__legacy_iterator<std::unordered_map<int, int>::iterator>);
+static_assert(std::__legacy_iterator<std::unordered_map<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_local_iterator>);
+
+static_assert(std::__legacy_iterator<std::unordered_multimap<int, int>::iterator>);
+static_assert(std::__legacy_iterator<std::unordered_multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_local_iterator>);
+
+// <unordered_set>
+static_assert(std::__legacy_iterator<std::unordered_set<int>::iterator>);
+static_assert(std::__legacy_iterator<std::unordered_set<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+static_assert(std::__legacy_iterator<std::unordered_multiset<int>::iterator>);
+static_assert(std::__legacy_iterator<std::unordered_multiset<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::const_local_iterator>);
+
+// <vector>
+static_assert(std::__legacy_iterator<std::vector<int>::iterator>);
+static_assert(std::__legacy_iterator<std::vector<int>::const_iterator>);
+static_assert(std::__legacy_iterator<std::vector<int>::reverse_iterator>);
+static_assert(std::__legacy_iterator<std::vector<int>::const_reverse_iterator>);
+
+// Not iterators
+static_assert(!std::__legacy_iterator<void>);
+static_assert(!std::__legacy_iterator<void*>);
+static_assert(!std::__legacy_iterator<int* const>);
+static_assert(!std::__legacy_iterator<std::vector<int>::iterator volatile>);
+static_assert(!std::__legacy_iterator<std::vector<int>::iterator&>);
+static_assert(!std::__legacy_iterator<std::vector<int>::iterator&&>);
+static_assert(!std::__legacy_iterator<int>);
+static_assert(!std::__legacy_iterator<int[]>);
+static_assert(!std::__legacy_iterator<int[10]>);
+static_assert(!std::__legacy_iterator<int()>);
+static_assert(!std::__legacy_iterator<int (*)()>);
+static_assert(!std::__legacy_iterator<int (&)()>);
+
+struct S {};
+static_assert(!std::__legacy_iterator<S>);
+static_assert(!std::__legacy_iterator<int S::*>);
+static_assert(!std::__legacy_iterator<int (S::*)()>);
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_random_access_iterator.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_random_access_iterator.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/legacy_random_access_iterator.compile.pass.cpp
@@ -0,0 +1,151 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class I>
+// concept __legacy_random_access_iterator;
+
+#include <iterator>
+
+#include <array>
+#include <deque>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+#include <filesystem>
+#endif
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+static_assert(std::__legacy_random_access_iterator<int*>);
+static_assert(std::__legacy_random_access_iterator<int const*>);
+static_assert(std::__legacy_random_access_iterator<int volatile*>);
+static_assert(std::__legacy_random_access_iterator<int const volatile*>);
+
+// <array>
+static_assert(std::__legacy_random_access_iterator<std::array<int, 10>::iterator>);
+static_assert(std::__legacy_random_access_iterator<std::array<int, 10>::const_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::array<int, 10>::reverse_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::array<int, 10>::const_reverse_iterator>);
+
+// <deque>
+static_assert(std::__legacy_random_access_iterator<std::deque<int>::iterator>);
+static_assert(std::__legacy_random_access_iterator<std::deque<int>::const_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::deque<int>::reverse_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::deque<int>::const_reverse_iterator>);
+
+// <filesystem>
+#ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
+static_assert(!std::__legacy_random_access_iterator<std::filesystem::directory_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::filesystem::recursive_directory_iterator>);
+#endif
+
+// <forward_list>
+static_assert(!std::__legacy_random_access_iterator<std::forward_list<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::forward_list<int>::const_iterator>);
+
+// <iterator>
+static_assert(!std::__legacy_random_access_iterator<std::back_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_random_access_iterator<std::front_insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_random_access_iterator<std::insert_iterator<std::vector<int> > >);
+static_assert(!std::__legacy_random_access_iterator<std::move_iterator<std::vector<int>::iterator> >);
+
+// <list>
+static_assert(!std::__legacy_random_access_iterator<std::list<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::list<int>::const_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::list<int>::reverse_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::list<int>::const_reverse_iterator>);
+
+// <map>
+static_assert(!std::__legacy_random_access_iterator<std::map<int, int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::map<int, int>::const_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::map<int, int>::reverse_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::map<int, int>::const_reverse_iterator>);
+
+static_assert(!std::__legacy_random_access_iterator<std::multimap<int, int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multimap<int, int>::reverse_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multimap<int, int>::const_reverse_iterator>);
+
+// <set>
+static_assert(!std::__legacy_random_access_iterator<std::set<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::set<int>::const_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::set<int>::reverse_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::set<int>::const_reverse_iterator>);
+
+static_assert(!std::__legacy_random_access_iterator<std::multiset<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multiset<int>::const_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multiset<int>::reverse_iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::multiset<int>::const_reverse_iterator>);
+
+// <string>
+static_assert(std::__legacy_random_access_iterator<std::string::iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string::const_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string::reverse_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string::const_reverse_iterator>);
+
+// <string_view>
+static_assert(std::__legacy_random_access_iterator<std::string_view::iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string_view::const_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string_view::reverse_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::string_view::const_reverse_iterator>);
+
+// <unordered_map>
+static_assert(!std::__legacy_random_access_iterator<std::unordered_map<int, int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::unordered_map<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_map<int, int>::const_local_iterator>);
+
+static_assert(!std::__legacy_random_access_iterator<std::unordered_multimap<int, int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::unordered_multimap<int, int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multimap<int, int>::const_local_iterator>);
+
+// <unordered_set>
+static_assert(!std::__legacy_random_access_iterator<std::unordered_set<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::unordered_set<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_set<int>::const_local_iterator>);
+
+static_assert(!std::__legacy_random_access_iterator<std::unordered_multiset<int>::iterator>);
+static_assert(!std::__legacy_random_access_iterator<std::unordered_multiset<int>::const_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::local_iterator>);
+static_assert(!std::__legacy_bidirectional_iterator<std::unordered_multiset<int>::const_local_iterator>);
+
+// <vector>
+static_assert(std::__legacy_random_access_iterator<std::vector<int>::iterator>);
+static_assert(std::__legacy_random_access_iterator<std::vector<int>::const_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::vector<int>::reverse_iterator>);
+static_assert(std::__legacy_random_access_iterator<std::vector<int>::const_reverse_iterator>);
+
+// Not iterators
+static_assert(!std::__legacy_random_access_iterator<void>);
+static_assert(!std::__legacy_random_access_iterator<void*>);
+static_assert(!std::__legacy_random_access_iterator<int* const>);
+static_assert(!std::__legacy_random_access_iterator<std::vector<int>::iterator volatile>);
+static_assert(!std::__legacy_random_access_iterator<std::vector<int>::iterator&>);
+static_assert(!std::__legacy_random_access_iterator<std::vector<int>::iterator&&>);
+static_assert(!std::__legacy_random_access_iterator<int>);
+static_assert(!std::__legacy_random_access_iterator<int[]>);
+static_assert(!std::__legacy_random_access_iterator<int[10]>);
+static_assert(!std::__legacy_random_access_iterator<int()>);
+static_assert(!std::__legacy_random_access_iterator<int (*)()>);
+static_assert(!std::__legacy_random_access_iterator<int (&)()>);
+
+struct S {};
+static_assert(!std::__legacy_random_access_iterator<S>);
+static_assert(!std::__legacy_random_access_iterator<int S::*>);
+static_assert(!std::__legacy_random_access_iterator<int (S::*)()>);
diff --git a/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/locale_dependent.compile.pass.cpp b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/locale_dependent.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/iterators/iterator.requirements/iterator.assoc.types/iterator.traits/locale_dependent.compile.pass.cpp
@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// REQUIRES: locale.en_US.UTF-8
+
+#include <iterator>
+
+#include <istream>
+#include <ostream>
+
+static_assert(std::__legacy_iterator<std::istream_iterator<int, std::istream> >);
+static_assert(std::__legacy_iterator<std::istreambuf_iterator<int, std::istream> >);
+static_assert(std::__legacy_iterator<std::ostream_iterator<int, std::ostream> >);
+static_assert(std::__legacy_iterator<std::ostreambuf_iterator<int, std::ostream> >);
+
+static_assert(std::__legacy_input_iterator<std::istream_iterator<int, std::istream> >);
+static_assert(std::__legacy_input_iterator<std::istreambuf_iterator<int, std::istream> >);
+static_assert(!std::__legacy_input_iterator<std::ostream_iterator<int, std::ostream> >);
+static_assert(!std::__legacy_input_iterator<std::ostreambuf_iterator<int, std::ostream> >);
+
+// This is because the legacy iterator concepts don't care about iterator_category
+static_assert(std::__legacy_forward_iterator<std::istream_iterator<int, std::istream> >);
+
+static_assert(!std::__legacy_forward_iterator<std::istreambuf_iterator<int, std::istream> >);
+static_assert(!std::__legacy_forward_iterator<std::ostream_iterator<int, std::ostream> >);
+static_assert(!std::__legacy_forward_iterator<std::ostreambuf_iterator<int, std::ostream> >);
+
+static_assert(!std::__legacy_bidirectional_iterator<std::istream_iterator<int, std::istream> >);
+static_assert(!std::__legacy_bidirectional_iterator<std::istreambuf_iterator<int, std::istream> >);
+static_assert(!std::__legacy_bidirectional_iterator<std::ostream_iterator<int, std::ostream> >);
+static_assert(!std::__legacy_bidirectional_iterator<std::ostreambuf_iterator<int, std::ostream> >);
+
+static_assert(!std::__legacy_random_access_iterator<std::istream_iterator<int, std::istream> >);
+static_assert(!std::__legacy_random_access_iterator<std::istreambuf_iterator<int, std::istream> >);
+static_assert(!std::__legacy_random_access_iterator<std::ostream_iterator<int, std::ostream> >);
+static_assert(!std::__legacy_random_access_iterator<std::ostreambuf_iterator<int, std::ostream> >);
diff --git a/libcxx/test/std/iterators/iterator.primitives/iterator.traits/iter_reference_t.compile.pass.cpp b/libcxx/test/std/iterators/iterator.primitives/iterator.traits/iter_reference_t.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.primitives/iterator.traits/iter_reference_t.compile.pass.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class T>
+// using iter_reference_t = decltype(*declval<T&>());
+
+#include <iterator>
+
+#include <concepts>
+
+#include "test_iterators.h"
+
+static_assert(std::same_as<std::iter_reference_t<input_iterator<int*> >, int&>);
+static_assert(std::same_as<std::iter_reference_t<forward_iterator<int*> >, int&>);
+static_assert(std::same_as<std::iter_reference_t<bidirectional_iterator<int*> >, int&>);
+static_assert(std::same_as<std::iter_reference_t<random_access_iterator<int*> >, int&>);
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/indirectly_readable_traits.compile.pass.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/indirectly_readable_traits.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.assoc.types/readable.traits/indirectly_readable_traits.compile.pass.cpp
@@ -0,0 +1,187 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class T>
+// struct indirectly_readable_traits;
+
+#include <iterator>
+
+#include <concepts>
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+// `value_type` and `element_type` member aliases aren't actually used to declare anytihng, so GCC
+// thinks they're completely unused.
+#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
+
+// clang-format off
+template <class T>
+concept check_has_value_type = requires {
+  typename std::indirectly_readable_traits<T>::value_type;
+};
+
+template <class T, class Expected>
+concept check_value_type_matches =
+  check_has_value_type<T> &&
+  std::same_as<typename std::indirectly_readable_traits<T>::value_type, Expected>;
+// clang-format on
+
+template <class T>
+constexpr bool check_pointer() {
+  constexpr bool result = check_value_type_matches<T*, T>;
+  static_assert(check_value_type_matches<T const*, T> == result);
+  static_assert(check_value_type_matches<T volatile*, T> == result);
+  static_assert(check_value_type_matches<T const volatile*, T> == result);
+
+  static_assert(check_value_type_matches<T* const, T> == result);
+  static_assert(check_value_type_matches<T const* const, T> == result);
+  static_assert(check_value_type_matches<T volatile* const, T> == result);
+  static_assert(check_value_type_matches<T const volatile* const, T> == result);
+
+  return result;
+}
+
+static_assert(!check_pointer<void>());
+static_assert(check_pointer<int>());
+static_assert(check_pointer<long>());
+static_assert(check_pointer<double>());
+static_assert(check_pointer<double*>());
+
+struct S {};
+static_assert(check_pointer<S>());
+
+template <class T>
+constexpr bool check_array() {
+  constexpr bool result = check_value_type_matches<T[], T>;
+  static_assert(check_value_type_matches<T const[], T> == result);
+  static_assert(check_value_type_matches<T volatile[], T> == result);
+  static_assert(check_value_type_matches<T const volatile[], T> == result);
+  static_assert(check_value_type_matches<T[10], T> == result);
+  static_assert(check_value_type_matches<T const[10], T> == result);
+  static_assert(check_value_type_matches<T volatile[10], T> == result);
+  static_assert(check_value_type_matches<T const volatile[10], T> == result);
+  return result;
+}
+
+static_assert(check_array<int>());
+static_assert(check_array<long>());
+static_assert(check_array<double>());
+static_assert(check_array<double*>());
+static_assert(check_array<S>());
+
+template <class T, class Expected>
+constexpr bool check_explicit_member() {
+  constexpr bool result = check_value_type_matches<T, Expected>;
+  static_assert(check_value_type_matches<T const, Expected> == result);
+  return result;
+}
+
+struct has_value_type {
+  using value_type = int;
+};
+static_assert(check_explicit_member<has_value_type, int>());
+static_assert(check_explicit_member<std::vector<int>::iterator, int>());
+
+struct has_element_type {
+  using element_type = S;
+};
+static_assert(check_explicit_member<has_element_type, S>());
+
+struct has_same_value_and_element_type {
+  using value_type = int;
+  using element_type = int;
+};
+static_assert(check_explicit_member<has_same_value_and_element_type, int>());
+static_assert(check_explicit_member<std::shared_ptr<long>, long>());
+static_assert(check_explicit_member<std::shared_ptr<long const>, long>());
+
+// clang-format off
+template<class T, class U>
+requires std::same_as<std::remove_cv_t<T>, std::remove_cv_t<U> >
+struct possibly_different_cv_qualifiers {
+  using value_type = T;
+  using element_type = U;
+};
+// clang-format on
+
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int, int>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int, int const>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int, int volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int, int const volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const, int>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const, int const>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const, int volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const, int const volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int volatile, int>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int volatile, int const>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int volatile, int volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int volatile, int const volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const volatile, int>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const volatile, int const>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const volatile, int volatile>, int>());
+static_assert(check_explicit_member<possibly_different_cv_qualifiers<int const volatile, int const volatile>, int>());
+
+struct S2 {};
+namespace std {
+template <>
+struct indirectly_readable_traits<S2> {
+  using value_type = int;
+};
+} // namespace std
+static_assert(check_value_type_matches<S2, int>);
+static_assert(check_value_type_matches<std::vector<int>, int>);
+static_assert(check_value_type_matches<std::vector<int>::iterator, int>);
+static_assert(check_value_type_matches<std::vector<int>::const_iterator, int>);
+static_assert(check_value_type_matches<std::istream_iterator<int>, int>);
+static_assert(check_value_type_matches<std::istreambuf_iterator<char>, char>);
+static_assert(check_value_type_matches<std::optional<int>, int>);
+
+template <class T>
+constexpr bool check_ref() {
+  struct ref_value {
+    using value_type = T&;
+  };
+  constexpr bool result = check_has_value_type<ref_value>;
+
+  struct ref_element {
+    using element_type = T&;
+  };
+  static_assert(check_has_value_type<ref_element> == result);
+
+  return result;
+}
+
+static_assert(!check_ref<int>());
+static_assert(!check_ref<S>());
+static_assert(!check_ref<std::shared_ptr<long> >());
+
+static_assert(!check_has_value_type<void>);
+static_assert(!check_has_value_type<std::nullptr_t>);
+static_assert(!check_has_value_type<int>);
+static_assert(!check_has_value_type<S>);
+
+struct has_different_value_and_element_type {
+  using value_type = int;
+  using element_type = long;
+};
+static_assert(!check_has_value_type<has_different_value_and_element_type>);
+
+struct void_value {
+  using value_type = void;
+};
+static_assert(!check_has_value_type<void_value>);
+
+struct void_element {
+  using element_type = void;
+};
+static_assert(!check_has_value_type<void_element>);