[libc++] Implement C++20 atomic_ref (#76647)

Implement the std::atomic_ref class template by reusing atomic_base_impl.
Based on the work from https://reviews.llvm.org/D72240

46 files changed, 3888 insertions, 30 deletions

diff --git a/libcxx/docs/ReleaseNotes/19.rst b/libcxx/docs/ReleaseNotes/19.rst
index 83fcd40..0bc343a 100644
--- a/libcxx/docs/ReleaseNotes/19.rst
+++ b/libcxx/docs/ReleaseNotes/19.rst
@@ -53,6 +53,7 @@ Implemented Papers
 - P2387R3 - Pipe support for user-defined range adaptors
 - P2713R1 - Escaping improvements in ``std::format``
 - P2231R1 - Missing ``constexpr`` in ``std::optional`` and ``std::variant``
+- P0019R8 - ``std::atomic_ref``
 
 Improvements and New Features
 -----------------------------
diff --git a/libcxx/docs/Status/Cxx20Papers.csv b/libcxx/docs/Status/Cxx20Papers.csv
index 955aa5f..6598cd18 100644
--- a/libcxx/docs/Status/Cxx20Papers.csv
+++ b/libcxx/docs/Status/Cxx20Papers.csv
@@ -26,7 +26,7 @@
 "`P0905R1 <https://wg21.link/P0905R1>`__","CWG","Symmetry for spaceship","Jacksonville","|Complete|","7.0","|spaceship|"
 "`P0966R1 <https://wg21.link/P0966R1>`__","LWG","``string::reserve``\  Should Not Shrink","Jacksonville","|Complete| [#note-P0966]_","12.0"
 "","","","","","",""
-"`P0019R8 <https://wg21.link/P0019R8>`__","LWG","Atomic Ref","Rapperswil","",""
+"`P0019R8 <https://wg21.link/P0019R8>`__","LWG","Atomic Ref","Rapperswil","|Complete|","19.0"
 "`P0458R2 <https://wg21.link/P0458R2>`__","LWG","Checking for Existence of an Element in Associative Containers","Rapperswil","|Complete|","13.0"
 "`P0475R1 <https://wg21.link/P0475R1>`__","LWG","LWG 2511: guaranteed copy elision for piecewise construction","Rapperswil","|Complete|",""
 "`P0476R2 <https://wg21.link/P0476R2>`__","LWG","Bit-casting object representations","Rapperswil","|Complete|","14.0"
@@ -125,7 +125,7 @@
 "`P1612R1 <https://wg21.link/P1612R1>`__","LWG","Relocate Endian's Specification","Cologne","|Complete|","10.0"
 "`P1614R2 <https://wg21.link/P1614R2>`__","LWG","The Mothership has Landed","Cologne","|In Progress|",""
 "`P1638R1 <https://wg21.link/P1638R1>`__","LWG","basic_istream_view::iterator should not be copyable","Cologne","|Complete|","16.0","|ranges|"
-"`P1643R1 <https://wg21.link/P1643R1>`__","LWG","Add wait/notify to atomic_ref","Cologne","",""
+"`P1643R1 <https://wg21.link/P1643R1>`__","LWG","Add wait/notify to atomic_ref","Cologne","|Complete|","19.0"
 "`P1644R0 <https://wg21.link/P1644R0>`__","LWG","Add wait/notify to atomic<shared_ptr>","Cologne","",""
 "`P1650R0 <https://wg21.link/P1650R0>`__","LWG","Output std::chrono::days with 'd' suffix","Cologne","|Complete|","16.0"
 "`P1651R0 <https://wg21.link/P1651R0>`__","LWG","bind_front should not unwrap reference_wrapper","Cologne","|Complete|","13.0"
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 01e9c24..954e0c0 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -224,6 +224,7 @@ set(files
   __atomic/atomic_flag.h
   __atomic/atomic_init.h
   __atomic/atomic_lock_free.h
+  __atomic/atomic_ref.h
   __atomic/atomic_sync.h
   __atomic/check_memory_order.h
   __atomic/contention_t.h
@@ -232,6 +233,7 @@ set(files
   __atomic/is_always_lock_free.h
   __atomic/kill_dependency.h
   __atomic/memory_order.h
+  __atomic/to_gcc_order.h
   __availability
   __bit/bit_cast.h
   __bit/bit_ceil.h
diff --git a/libcxx/include/__atomic/atomic_ref.h b/libcxx/include/__atomic/atomic_ref.h
new file mode 100644
index 0000000..156f196
--- /dev/null
+++ b/libcxx/include/__atomic/atomic_ref.h
@@ -0,0 +1,360 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ATOMIC_ATOMIC_REF_H
+#define _LIBCPP___ATOMIC_ATOMIC_REF_H
+
+#include <__assert>
+#include <__atomic/atomic_sync.h>
+#include <__atomic/check_memory_order.h>
+#include <__atomic/to_gcc_order.h>
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__memory/addressof.h>
+#include <__type_traits/has_unique_object_representation.h>
+#include <__type_traits/is_trivially_copyable.h>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _Tp>
+struct __atomic_ref_base {
+protected:
+  _Tp* __ptr_;
+
+  _LIBCPP_HIDE_FROM_ABI __atomic_ref_base(_Tp& __obj) : __ptr_(std::addressof(__obj)) {}
+
+private:
+  _LIBCPP_HIDE_FROM_ABI static _Tp* __clear_padding(_Tp& __val) noexcept {
+    _Tp* __ptr = std::addressof(__val);
+#  if __has_builtin(__builtin_clear_padding)
+    __builtin_clear_padding(__ptr);
+#  endif
+    return __ptr;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI static bool __compare_exchange(
+      _Tp* __ptr, _Tp* __expected, _Tp* __desired, bool __is_weak, int __success, int __failure) noexcept {
+    if constexpr (
+#  if __has_builtin(__builtin_clear_padding)
+        has_unique_object_representations_v<_Tp> || floating_point<_Tp>
+#  else
+        true // NOLINT(readability-simplify-boolean-expr)
+#  endif
+    ) {
+      return __atomic_compare_exchange(__ptr, __expected, __desired, __is_weak, __success, __failure);
+    } else { // _Tp has padding bits and __builtin_clear_padding is available
+      __clear_padding(*__desired);
+      _Tp __copy = *__expected;
+      __clear_padding(__copy);
+      // The algorithm we use here is basically to perform `__atomic_compare_exchange` on the
+      // values until it has either succeeded, or failed because the value representation of the
+      // objects involved was different. This is why we loop around __atomic_compare_exchange:
+      // we basically loop until its failure is caused by the value representation of the objects
+      // being different, not only their object representation.
+      while (true) {
+        _Tp __prev = __copy;
+        if (__atomic_compare_exchange(__ptr, std::addressof(__copy), __desired, __is_weak, __success, __failure)) {
+          return true;
+        }
+        _Tp __curr = __copy;
+        if (std::memcmp(__clear_padding(__prev), __clear_padding(__curr), sizeof(_Tp)) != 0) {
+          // Value representation without padding bits do not compare equal ->
+          // write the current content of *ptr into *expected
+          std::memcpy(__expected, std::addressof(__copy), sizeof(_Tp));
+          return false;
+        }
+      }
+    }
+  }
+
+  friend struct __atomic_waitable_traits<__atomic_ref_base<_Tp>>;
+
+public:
+  using value_type = _Tp;
+
+  static constexpr size_t required_alignment = alignof(_Tp);
+
+  // The __atomic_always_lock_free builtin takes into account the alignment of the pointer if provided,
+  // so we create a fake pointer with a suitable alignment when querying it. Note that we are guaranteed
+  // that the pointer is going to be aligned properly at runtime because that is a (checked) precondition
+  // of atomic_ref's constructor.
+  static constexpr bool is_always_lock_free =
+      __atomic_always_lock_free(sizeof(_Tp), reinterpret_cast<void*>(-required_alignment));
+
+  _LIBCPP_HIDE_FROM_ABI bool is_lock_free() const noexcept { return __atomic_is_lock_free(sizeof(_Tp), __ptr_); }
+
+  _LIBCPP_HIDE_FROM_ABI void store(_Tp __desired, memory_order __order = memory_order::seq_cst) const noexcept
+      _LIBCPP_CHECK_STORE_MEMORY_ORDER(__order) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __order == memory_order::relaxed || __order == memory_order::release || __order == memory_order::seq_cst,
+        "atomic_ref: memory order argument to atomic store operation is invalid");
+    __atomic_store(__ptr_, __clear_padding(__desired), std::__to_gcc_order(__order));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator=(_Tp __desired) const noexcept {
+    store(__desired);
+    return __desired;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp load(memory_order __order = memory_order::seq_cst) const noexcept
+      _LIBCPP_CHECK_LOAD_MEMORY_ORDER(__order) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __order == memory_order::relaxed || __order == memory_order::consume || __order == memory_order::acquire ||
+            __order == memory_order::seq_cst,
+        "atomic_ref: memory order argument to atomic load operation is invalid");
+    alignas(_Tp) byte __mem[sizeof(_Tp)];
+    auto* __ret = reinterpret_cast<_Tp*>(__mem);
+    __atomic_load(__ptr_, __ret, std::__to_gcc_order(__order));
+    return *__ret;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI operator _Tp() const noexcept { return load(); }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp exchange(_Tp __desired, memory_order __order = memory_order::seq_cst) const noexcept {
+    alignas(_Tp) byte __mem[sizeof(_Tp)];
+    auto* __ret = reinterpret_cast<_Tp*>(__mem);
+    __atomic_exchange(__ptr_, __clear_padding(__desired), __ret, std::__to_gcc_order(__order));
+    return *__ret;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI bool
+  compare_exchange_weak(_Tp& __expected, _Tp __desired, memory_order __success, memory_order __failure) const noexcept
+      _LIBCPP_CHECK_EXCHANGE_MEMORY_ORDER(__success, __failure) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __failure == memory_order::relaxed || __failure == memory_order::consume ||
+            __failure == memory_order::acquire || __failure == memory_order::seq_cst,
+        "atomic_ref: failure memory order argument to weak atomic compare-and-exchange operation is invalid");
+    return __compare_exchange(
+        __ptr_,
+        std::addressof(__expected),
+        std::addressof(__desired),
+        true,
+        std::__to_gcc_order(__success),
+        std::__to_gcc_order(__failure));
+  }
+  _LIBCPP_HIDE_FROM_ABI bool
+  compare_exchange_strong(_Tp& __expected, _Tp __desired, memory_order __success, memory_order __failure) const noexcept
+      _LIBCPP_CHECK_EXCHANGE_MEMORY_ORDER(__success, __failure) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __failure == memory_order::relaxed || __failure == memory_order::consume ||
+            __failure == memory_order::acquire || __failure == memory_order::seq_cst,
+        "atomic_ref: failure memory order argument to strong atomic compare-and-exchange operation is invalid");
+    return __compare_exchange(
+        __ptr_,
+        std::addressof(__expected),
+        std::addressof(__desired),
+        false,
+        std::__to_gcc_order(__success),
+        std::__to_gcc_order(__failure));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI bool
+  compare_exchange_weak(_Tp& __expected, _Tp __desired, memory_order __order = memory_order::seq_cst) const noexcept {
+    return __compare_exchange(
+        __ptr_,
+        std::addressof(__expected),
+        std::addressof(__desired),
+        true,
+        std::__to_gcc_order(__order),
+        std::__to_gcc_failure_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI bool
+  compare_exchange_strong(_Tp& __expected, _Tp __desired, memory_order __order = memory_order::seq_cst) const noexcept {
+    return __compare_exchange(
+        __ptr_,
+        std::addressof(__expected),
+        std::addressof(__desired),
+        false,
+        std::__to_gcc_order(__order),
+        std::__to_gcc_failure_order(__order));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI void wait(_Tp __old, memory_order __order = memory_order::seq_cst) const noexcept
+      _LIBCPP_CHECK_WAIT_MEMORY_ORDER(__order) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __order == memory_order::relaxed || __order == memory_order::consume || __order == memory_order::acquire ||
+            __order == memory_order::seq_cst,
+        "atomic_ref: memory order argument to atomic wait operation is invalid");
+    std::__atomic_wait(*this, __old, __order);
+  }
+  _LIBCPP_HIDE_FROM_ABI void notify_one() const noexcept { std::__atomic_notify_one(*this); }
+  _LIBCPP_HIDE_FROM_ABI void notify_all() const noexcept { std::__atomic_notify_all(*this); }
+};
+
+template <class _Tp>
+struct __atomic_waitable_traits<__atomic_ref_base<_Tp>> {
+  static _LIBCPP_HIDE_FROM_ABI _Tp __atomic_load(const __atomic_ref_base<_Tp>& __a, memory_order __order) {
+    return __a.load(__order);
+  }
+  static _LIBCPP_HIDE_FROM_ABI const _Tp* __atomic_contention_address(const __atomic_ref_base<_Tp>& __a) {
+    return __a.__ptr_;
+  }
+};
+
+template <class _Tp>
+struct atomic_ref : public __atomic_ref_base<_Tp> {
+  static_assert(is_trivially_copyable_v<_Tp>, "std::atomic_ref<T> requires that 'T' be a trivially copyable type");
+
+  using __base = __atomic_ref_base<_Tp>;
+
+  _LIBCPP_HIDE_FROM_ABI explicit atomic_ref(_Tp& __obj) : __base(__obj) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        reinterpret_cast<uintptr_t>(std::addressof(__obj)) % __base::required_alignment == 0,
+        "atomic_ref ctor: referenced object must be aligned to required_alignment");
+  }
+
+  _LIBCPP_HIDE_FROM_ABI atomic_ref(const atomic_ref&) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator=(_Tp __desired) const noexcept { return __base::operator=(__desired); }
+
+  atomic_ref& operator=(const atomic_ref&) = delete;
+};
+
+template <class _Tp>
+  requires(std::integral<_Tp> && !std::same_as<bool, _Tp>)
+struct atomic_ref<_Tp> : public __atomic_ref_base<_Tp> {
+  using __base = __atomic_ref_base<_Tp>;
+
+  using difference_type = __base::value_type;
+
+  _LIBCPP_HIDE_FROM_ABI explicit atomic_ref(_Tp& __obj) : __base(__obj) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        reinterpret_cast<uintptr_t>(std::addressof(__obj)) % __base::required_alignment == 0,
+        "atomic_ref ctor: referenced object must be aligned to required_alignment");
+  }
+
+  _LIBCPP_HIDE_FROM_ABI atomic_ref(const atomic_ref&) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator=(_Tp __desired) const noexcept { return __base::operator=(__desired); }
+
+  atomic_ref& operator=(const atomic_ref&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_add(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_add(this->__ptr_, __arg, std::__to_gcc_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_sub(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_sub(this->__ptr_, __arg, std::__to_gcc_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_and(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_and(this->__ptr_, __arg, std::__to_gcc_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_or(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_or(this->__ptr_, __arg, std::__to_gcc_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_xor(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_xor(this->__ptr_, __arg, std::__to_gcc_order(__order));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator++(int) const noexcept { return fetch_add(_Tp(1)); }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator--(int) const noexcept { return fetch_sub(_Tp(1)); }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator++() const noexcept { return fetch_add(_Tp(1)) + _Tp(1); }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator--() const noexcept { return fetch_sub(_Tp(1)) - _Tp(1); }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator+=(_Tp __arg) const noexcept { return fetch_add(__arg) + __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator-=(_Tp __arg) const noexcept { return fetch_sub(__arg) - __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator&=(_Tp __arg) const noexcept { return fetch_and(__arg) & __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator|=(_Tp __arg) const noexcept { return fetch_or(__arg) | __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator^=(_Tp __arg) const noexcept { return fetch_xor(__arg) ^ __arg; }
+};
+
+template <class _Tp>
+  requires std::floating_point<_Tp>
+struct atomic_ref<_Tp> : public __atomic_ref_base<_Tp> {
+  using __base = __atomic_ref_base<_Tp>;
+
+  using difference_type = __base::value_type;
+
+  _LIBCPP_HIDE_FROM_ABI explicit atomic_ref(_Tp& __obj) : __base(__obj) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        reinterpret_cast<uintptr_t>(std::addressof(__obj)) % __base::required_alignment == 0,
+        "atomic_ref ctor: referenced object must be aligned to required_alignment");
+  }
+
+  _LIBCPP_HIDE_FROM_ABI atomic_ref(const atomic_ref&) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator=(_Tp __desired) const noexcept { return __base::operator=(__desired); }
+
+  atomic_ref& operator=(const atomic_ref&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_add(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    _Tp __old = this->load(memory_order_relaxed);
+    _Tp __new = __old + __arg;
+    while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed)) {
+      __new = __old + __arg;
+    }
+    return __old;
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp fetch_sub(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    _Tp __old = this->load(memory_order_relaxed);
+    _Tp __new = __old - __arg;
+    while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed)) {
+      __new = __old - __arg;
+    }
+    return __old;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator+=(_Tp __arg) const noexcept { return fetch_add(__arg) + __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp operator-=(_Tp __arg) const noexcept { return fetch_sub(__arg) - __arg; }
+};
+
+template <class _Tp>
+struct atomic_ref<_Tp*> : public __atomic_ref_base<_Tp*> {
+  using __base = __atomic_ref_base<_Tp*>;
+
+  using difference_type = ptrdiff_t;
+
+  _LIBCPP_HIDE_FROM_ABI explicit atomic_ref(_Tp*& __ptr) : __base(__ptr) {}
+
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator=(_Tp* __desired) const noexcept { return __base::operator=(__desired); }
+
+  atomic_ref& operator=(const atomic_ref&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _Tp* fetch_add(ptrdiff_t __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_add(this->__ptr_, __arg * sizeof(_Tp), std::__to_gcc_order(__order));
+  }
+  _LIBCPP_HIDE_FROM_ABI _Tp* fetch_sub(ptrdiff_t __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+    return __atomic_fetch_sub(this->__ptr_, __arg * sizeof(_Tp), std::__to_gcc_order(__order));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator++(int) const noexcept { return fetch_add(1); }
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator--(int) const noexcept { return fetch_sub(1); }
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator++() const noexcept { return fetch_add(1) + 1; }
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator--() const noexcept { return fetch_sub(1) - 1; }
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator+=(ptrdiff_t __arg) const noexcept { return fetch_add(__arg) + __arg; }
+  _LIBCPP_HIDE_FROM_ABI _Tp* operator-=(ptrdiff_t __arg) const noexcept { return fetch_sub(__arg) - __arg; }
+};
+
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(atomic_ref);
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP__ATOMIC_ATOMIC_REF_H
diff --git a/libcxx/include/__atomic/atomic_sync.h b/libcxx/include/__atomic/atomic_sync.h
index e583dca..175700be 100644
--- a/libcxx/include/__atomic/atomic_sync.h
+++ b/libcxx/include/__atomic/atomic_sync.h
@@ -12,6 +12,7 @@
 #include <__atomic/contention_t.h>
 #include <__atomic/cxx_atomic_impl.h>
 #include <__atomic/memory_order.h>
+#include <__atomic/to_gcc_order.h>
 #include <__availability>
 #include <__chrono/duration.h>
 #include <__config>
diff --git a/libcxx/include/__atomic/check_memory_order.h b/libcxx/include/__atomic/check_memory_order.h
index 3012aec0..536f764 100644
--- a/libcxx/include/__atomic/check_memory_order.h
+++ b/libcxx/include/__atomic/check_memory_order.h
@@ -27,4 +27,8 @@
   _LIBCPP_DIAGNOSE_WARNING(__f == memory_order_release || __f == memory_order_acq_rel,                                 \
                            "memory order argument to atomic operation is invalid")
 
+#define _LIBCPP_CHECK_WAIT_MEMORY_ORDER(__m)                                                                           \
+  _LIBCPP_DIAGNOSE_WARNING(__m == memory_order_release || __m == memory_order_acq_rel,                                 \
+                           "memory order argument to atomic operation is invalid")
+
 #endif // _LIBCPP___ATOMIC_CHECK_MEMORY_ORDER_H
diff --git a/libcxx/include/__atomic/cxx_atomic_impl.h b/libcxx/include/__atomic/cxx_atomic_impl.h
index b900cc1..18e88aa 100644
--- a/libcxx/include/__atomic/cxx_atomic_impl.h
+++ b/libcxx/include/__atomic/cxx_atomic_impl.h
@@ -10,6 +10,7 @@
 #define _LIBCPP___ATOMIC_CXX_ATOMIC_IMPL_H
 
 #include <__atomic/memory_order.h>
+#include <__atomic/to_gcc_order.h>
 #include <__config>
 #include <__memory/addressof.h>
 #include <__type_traits/is_assignable.h>
@@ -54,32 +55,6 @@ struct __cxx_atomic_base_impl {
   _Tp __a_value;
 };
 
-_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_order(memory_order __order) {
-  // Avoid switch statement to make this a constexpr.
-  return __order == memory_order_relaxed
-           ? __ATOMIC_RELAXED
-           : (__order == memory_order_acquire
-                  ? __ATOMIC_ACQUIRE
-                  : (__order == memory_order_release
-                         ? __ATOMIC_RELEASE
-                         : (__order == memory_order_seq_cst
-                                ? __ATOMIC_SEQ_CST
-                                : (__order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_CONSUME))));
-}
-
-_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_failure_order(memory_order __order) {
-  // Avoid switch statement to make this a constexpr.
-  return __order == memory_order_relaxed
-           ? __ATOMIC_RELAXED
-           : (__order == memory_order_acquire
-                  ? __ATOMIC_ACQUIRE
-                  : (__order == memory_order_release
-                         ? __ATOMIC_RELAXED
-                         : (__order == memory_order_seq_cst
-                                ? __ATOMIC_SEQ_CST
-                                : (__order == memory_order_acq_rel ? __ATOMIC_ACQUIRE : __ATOMIC_CONSUME))));
-}
-
 template <typename _Tp>
 _LIBCPP_HIDE_FROM_ABI void __cxx_atomic_init(volatile __cxx_atomic_base_impl<_Tp>* __a, _Tp __val) {
   __cxx_atomic_assign_volatile(__a->__a_value, __val);
diff --git a/libcxx/include/__atomic/to_gcc_order.h b/libcxx/include/__atomic/to_gcc_order.h
new file mode 100644
index 0000000..d04c111
--- /dev/null
+++ b/libcxx/include/__atomic/to_gcc_order.h
@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ATOMIC_TO_GCC_ORDER_H
+#define _LIBCPP___ATOMIC_TO_GCC_ORDER_H
+
+#include <__atomic/memory_order.h>
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if defined(__ATOMIC_RELAXED) && defined(__ATOMIC_CONSUME) && defined(__ATOMIC_ACQUIRE) &&                             \
+    defined(__ATOMIC_RELEASE) && defined(__ATOMIC_ACQ_REL) && defined(__ATOMIC_SEQ_CST)
+
+_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_order(memory_order __order) {
+  // Avoid switch statement to make this a constexpr.
+  return __order == memory_order_relaxed
+           ? __ATOMIC_RELAXED
+           : (__order == memory_order_acquire
+                  ? __ATOMIC_ACQUIRE
+                  : (__order == memory_order_release
+                         ? __ATOMIC_RELEASE
+                         : (__order == memory_order_seq_cst
+                                ? __ATOMIC_SEQ_CST
+                                : (__order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_CONSUME))));
+}
+
+_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_failure_order(memory_order __order) {
+  // Avoid switch statement to make this a constexpr.
+  return __order == memory_order_relaxed
+           ? __ATOMIC_RELAXED
+           : (__order == memory_order_acquire
+                  ? __ATOMIC_ACQUIRE
+                  : (__order == memory_order_release
+                         ? __ATOMIC_RELAXED
+                         : (__order == memory_order_seq_cst
+                                ? __ATOMIC_SEQ_CST
+                                : (__order == memory_order_acq_rel ? __ATOMIC_ACQUIRE : __ATOMIC_CONSUME))));
+}
+
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ATOMIC_TO_GCC_ORDER_H
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
index cb142b0..80a0f9e 100644
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -599,6 +599,7 @@ template <class T>
 #include <__atomic/atomic_flag.h>
 #include <__atomic/atomic_init.h>
 #include <__atomic/atomic_lock_free.h>
+#include <__atomic/atomic_ref.h>
 #include <__atomic/atomic_sync.h>
 #include <__atomic/check_memory_order.h>
 #include <__atomic/contention_t.h>
diff --git a/libcxx/include/libcxx.imp b/libcxx/include/libcxx.imp
new file mode 100644
index 0000000..f6aa1ea
--- /dev/null
+++ b/libcxx/include/libcxx.imp
@@ -0,0 +1,869 @@
+[
+  { include: [ "<__algorithm/adjacent_find.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/all_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/any_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/binary_search.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/clamp.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/comp.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/comp_ref_type.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/copy_backward.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/copy_move_common.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/copy_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/count.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/count_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/equal.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/equal_range.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/fill.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/fill_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find_end.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find_first_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find_if_not.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/find_segment_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/fold.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/for_each.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/for_each_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/for_each_segment.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/generate.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/generate_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/half_positive.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_found_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_fun_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_in_out_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_in_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_out_out_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/in_out_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/includes.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/inplace_merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_heap_until.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_partitioned.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_sorted.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/is_sorted_until.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/iter_swap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/iterator_operations.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/lexicographical_compare.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/lexicographical_compare_three_way.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/lower_bound.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/make_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/make_projected.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/max.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/max_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/min.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/min_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/min_max_result.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/minmax.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/minmax_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/mismatch.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/move.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/move_backward.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/next_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/none_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/nth_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/partial_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/partial_sort_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/partition.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/partition_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/partition_point.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pop_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/prev_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_any_all_none_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backend.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backend.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/any_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/backend.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/fill.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/find_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/for_each.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/libdispatch.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/serial.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/stable_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/thread.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/transform.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_backends/cpu_backends/transform_reduce.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_count.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_equal.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_fill.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_find.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_for_each.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_frontend_dispatch.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_generate.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_is_partitioned.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_move.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_replace.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_rotate_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_stable_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/pstl_transform.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/push_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_adjacent_find.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_all_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_any_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_binary_search.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_clamp.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_contains.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_contains_subrange.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_copy_backward.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_copy_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_count.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_count_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_ends_with.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_equal.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_equal_range.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_fill.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_fill_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_find.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_find_end.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_find_first_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_find_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_find_if_not.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_for_each.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_for_each_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_generate.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_generate_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_includes.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_inplace_merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_heap_until.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_partitioned.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_sorted.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_is_sorted_until.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_iterator_concept.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_lexicographical_compare.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_lower_bound.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_make_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_max.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_max_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_merge.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_min.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_min_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_minmax.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_minmax_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_mismatch.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_move.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_move_backward.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_next_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_none_of.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_nth_element.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_partial_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_partial_sort_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_partition.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_partition_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_partition_point.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_pop_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_prev_permutation.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_push_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_remove.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_remove_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_remove_copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_remove_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_replace.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_replace_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_replace_copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_replace_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_reverse.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_reverse_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_rotate.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_rotate_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_sample.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_search.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_search_n.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_set_difference.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_set_intersection.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_set_symmetric_difference.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_set_union.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_shuffle.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_sort_heap.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_stable_partition.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_stable_sort.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_starts_with.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_swap_ranges.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_transform.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_unique.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_unique_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/ranges_upper_bound.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/remove.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/remove_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/remove_copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/remove_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/replace.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/replace_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/replace_copy_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/replace_if.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/reverse.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/reverse_copy.h>", "private", "<algorithm>", "public" ] },
+  { include: [ "<__algorithm/rotate.h>", "private", "<algorithm>", "public" ] },
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+  { include: [ "<__type_traits/copy_cvref.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/datasizeof.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/decay.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/dependent_type.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/desugars_to.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/disjunction.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/enable_if.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/extent.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/has_unique_object_representation.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/has_virtual_destructor.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/integral_constant.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/invoke.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_abstract.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_aggregate.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_allocator.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_always_bitcastable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_arithmetic.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_array.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_assignable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_base_of.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_bounded_array.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_callable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_char_like_type.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_class.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_compound.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_const.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_constant_evaluated.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_constructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_convertible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_core_convertible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_destructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_empty.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_enum.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_equality_comparable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_execution_policy.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_final.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_floating_point.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_function.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_fundamental.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_implicitly_default_constructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_integral.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_literal_type.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_member_function_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_member_object_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_member_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_nothrow_assignable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_nothrow_constructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_nothrow_convertible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_nothrow_destructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_null_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_object.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_pod.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_polymorphic.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_primary_template.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_reference.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_reference_wrapper.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_referenceable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_same.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_scalar.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_scoped_enum.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_signed.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_signed_integer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_specialization.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_standard_layout.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_swappable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivial.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_assignable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_constructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_copyable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_destructible.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_lexicographically_comparable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_trivially_relocatable.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_unbounded_array.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_union.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_unsigned.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_unsigned_integer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_valid_expansion.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_void.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/is_volatile.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/lazy.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/make_32_64_or_128_bit.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/make_const_lvalue_ref.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/make_signed.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/make_unsigned.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/maybe_const.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/nat.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/negation.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/noexcept_move_assign_container.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/promote.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/rank.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_all_extents.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_const.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_const_ref.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_cv.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_cvref.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_extent.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_pointer.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_reference.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/remove_volatile.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/result_of.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/strip_signature.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/type_identity.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/type_list.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/underlying_type.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/unwrap_ref.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__type_traits/void_t.h>", "private", "<type_traits>", "public" ] },
+  { include: [ "<__utility/as_const.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/as_lvalue.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/auto_cast.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/cmp.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/convert_to_integral.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/declval.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/empty.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/exception_guard.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/exchange.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/forward.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/forward_like.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/in_place.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/integer_sequence.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/is_pointer_in_range.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/move.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/no_destroy.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/pair.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/piecewise_construct.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/priority_tag.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/rel_ops.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/small_buffer.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/swap.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/to_underlying.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__utility/unreachable.h>", "private", "<utility>", "public" ] },
+  { include: [ "<__variant/monostate.h>", "private", "<variant>", "public" ] },
+]
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index 70dac2f..8bc94d7 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -1066,7 +1066,11 @@ module std_private_atomic_atomic_flag         [system] {
 }
 module std_private_atomic_atomic_init         [system] { header "__atomic/atomic_init.h" }
 module std_private_atomic_atomic_lock_free    [system] { header "__atomic/atomic_lock_free.h" }
-module std_private_atomic_atomic_sync         [system] { header "__atomic/atomic_sync.h" }
+module std_private_atomic_atomic_ref          [system] { header "__atomic/atomic_ref.h" }
+module std_private_atomic_atomic_sync         [system] {
+  header "__atomic/atomic_sync.h"
+  export std_private_atomic_to_gcc_order
+}
 module std_private_atomic_check_memory_order  [system] { header "__atomic/check_memory_order.h" }
 module std_private_atomic_contention_t        [system] { header "__atomic/contention_t.h" }
 module std_private_atomic_cxx_atomic_impl     [system] { header "__atomic/cxx_atomic_impl.h" }
@@ -1074,6 +1078,10 @@ module std_private_atomic_fence               [system] { header "__atomic/fence.
 module std_private_atomic_is_always_lock_free [system] { header "__atomic/is_always_lock_free.h" }
 module std_private_atomic_kill_dependency     [system] { header "__atomic/kill_dependency.h" }
 module std_private_atomic_memory_order        [system] { header "__atomic/memory_order.h" }
+module std_private_atomic_to_gcc_order        [system] {
+  header "__atomic/to_gcc_order.h"
+  export std_private_atomic_memory_order
+}
 
 module std_private_bit_bit_cast       [system] { header "__bit/bit_cast.h" }
 module std_private_bit_bit_ceil       [system] { header "__bit/bit_ceil.h" }
diff --git a/libcxx/modules/std/atomic.inc b/libcxx/modules/std/atomic.inc
index d77d7a5..e8cf90d 100644
--- a/libcxx/modules/std/atomic.inc
+++ b/libcxx/modules/std/atomic.inc
@@ -22,7 +22,7 @@ export namespace std {
 
   // [atomics.ref.generic], class template atomic_ref
   // [atomics.ref.pointer], partial specialization for pointers
-  // using std::atomic_ref _LIBCPP_USING_IF_EXISTS;
+  using std::atomic_ref _LIBCPP_USING_IF_EXISTS;
 
   // [atomics.types.generic], class template atomic
   using std::atomic _LIBCPP_USING_IF_EXISTS;
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_strong.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_strong.pass.cpp
new file mode 100644
index 0000000..066ed11
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_strong.pass.cpp
@@ -0,0 +1,58 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+// ADDITIONAL_COMPILE_FLAGS: -Wno-user-defined-warnings
+
+// <atomic>
+
+// bool compare_exchange_strong(T& expected, T desired, memory_order success, memory_order failure) const noexcept;
+//
+// Preconditions: failure is memory_order::relaxed, memory_order::consume, memory_order::acquire, or memory_order::seq_cst.
+
+#include <atomic>
+
+#include "atomic_helpers.h"
+#include "check_assertion.h"
+
+template <typename T>
+struct TestCompareExchangeStrongInvalidMemoryOrder {
+  void operator()() const {
+    { // no assertion should trigger here
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+      T t(T(2));
+      a.compare_exchange_strong(t, T(3), std::memory_order_relaxed, std::memory_order_relaxed);
+    }
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          T t(T(2));
+          a.compare_exchange_strong(t, T(3), std::memory_order_relaxed, std::memory_order_release);
+        }()),
+        "atomic_ref: failure memory order argument to strong atomic compare-and-exchange operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          T t(T(2));
+          a.compare_exchange_strong(t, T(3), std::memory_order_relaxed, std::memory_order_acq_rel);
+        }()),
+        "atomic_ref: failure memory order argument to strong atomic compare-and-exchange operation is invalid");
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestCompareExchangeStrongInvalidMemoryOrder>()();
+  return 0;
+}
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_weak.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_weak.pass.cpp
new file mode 100644
index 0000000..e83a143
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.compare_exchange_weak.pass.cpp
@@ -0,0 +1,58 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+// ADDITIONAL_COMPILE_FLAGS: -Wno-user-defined-warnings
+
+// <atomic>
+
+// bool compare_exchange_weak(T& expected, T desired, memory_order success, memory_order failure) const noexcept;
+//
+// Preconditions: failure is memory_order::relaxed, memory_order::consume, memory_order::acquire, or memory_order::seq_cst.
+
+#include <atomic>
+
+#include "atomic_helpers.h"
+#include "check_assertion.h"
+
+template <typename T>
+struct TestCompareExchangeWeakInvalidMemoryOrder {
+  void operator()() const {
+    { // no assertion should trigger here
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+      T t(T(2));
+      a.compare_exchange_weak(t, T(3), std::memory_order_relaxed, std::memory_order_relaxed);
+    }
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          T t(T(2));
+          a.compare_exchange_weak(t, T(3), std::memory_order_relaxed, std::memory_order_release);
+        }()),
+        "atomic_ref: failure memory order argument to weak atomic compare-and-exchange operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          T t(T(2));
+          a.compare_exchange_weak(t, T(3), std::memory_order_relaxed, std::memory_order_acq_rel);
+        }()),
+        "atomic_ref: failure memory order argument to weak atomic compare-and-exchange operation is invalid");
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestCompareExchangeWeakInvalidMemoryOrder>()();
+  return 0;
+}
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.ctor.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.ctor.pass.cpp
new file mode 100644
index 0000000..ef3705d
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.ctor.pass.cpp
@@ -0,0 +1,40 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+
+// <atomic>
+
+// atomic_ref(T& obj);
+//
+// Preconditions: The referenced object is aligned to required_alignment.
+
+#include <atomic>
+#include <cstddef>
+
+#include "check_assertion.h"
+
+int main(int, char**) {
+  { // no assertion should trigger here
+    alignas(float) std::byte c[sizeof(float)];
+    float* f = new (c) float(3.14f);
+    [[maybe_unused]] std::atomic_ref<float> r(*f);
+  }
+
+  TEST_LIBCPP_ASSERT_FAILURE(
+      ([] {
+        alignas(float) std::byte c[2 * sizeof(float)]; // intentionally larger
+        float* f = new (c + 1) float(3.14f);           // intentionally misaligned
+        [[maybe_unused]] std::atomic_ref<float> r(*f);
+      }()),
+      "atomic_ref ctor: referenced object must be aligned to required_alignment");
+
+  return 0;
+}
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.load.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.load.pass.cpp
new file mode 100644
index 0000000..bc92b3d
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.load.pass.cpp
@@ -0,0 +1,55 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+// ADDITIONAL_COMPILE_FLAGS: -Wno-user-defined-warnings
+
+// <atomic>
+
+// T load(memory_order order = memory_order::seq_cst) const noexcept;
+//
+// Preconditions: order is memory_order::relaxed, memory_order::consume, memory_order::acquire, or memory_order::seq_cst.
+
+#include <atomic>
+
+#include "atomic_helpers.h"
+#include "check_assertion.h"
+
+template <typename T>
+struct TestLoadInvalidMemoryOrder {
+  void operator()() const {
+    { // no assertion should trigger here
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+      (void)a.load(std::memory_order_relaxed);
+    }
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          (void)a.load(std::memory_order_release);
+        }()),
+        "atomic_ref: memory order argument to atomic load operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          (void)a.load(std::memory_order_acq_rel);
+        }()),
+        "atomic_ref: memory order argument to atomic load operation is invalid");
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestLoadInvalidMemoryOrder>()();
+  return 0;
+}
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.store.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.store.pass.cpp
new file mode 100644
index 0000000..ab0d4a2
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.store.pass.cpp
@@ -0,0 +1,63 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+// ADDITIONAL_COMPILE_FLAGS: -Wno-user-defined-warnings
+
+// <atomic>
+
+// void store(T desired, memory_order order = memory_order::seq_cst) const noexcept;
+//
+// Preconditions: order is memory_order::relaxed, memory_order::release, or memory_order::seq_cst.
+
+#include <atomic>
+
+#include "atomic_helpers.h"
+#include "check_assertion.h"
+
+template <typename T>
+struct TestStoreInvalidMemoryOrder {
+  void operator()() const {
+    { // no assertion should trigger here
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+      a.store(T(2), std::memory_order_relaxed);
+    }
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          a.store(T(2), std::memory_order_consume);
+        }()),
+        "atomic_ref: memory order argument to atomic store operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          a.store(T(2), std::memory_order_acquire);
+        }()),
+        "atomic_ref: memory order argument to atomic store operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          a.store(T(2), std::memory_order_acq_rel);
+        }()),
+        "atomic_ref: memory order argument to atomic store operation is invalid");
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestStoreInvalidMemoryOrder>()();
+  return 0;
+}
diff --git a/libcxx/test/libcxx/atomics/atomics.ref/assert.wait.pass.cpp b/libcxx/test/libcxx/atomics/atomics.ref/assert.wait.pass.cpp
new file mode 100644
index 0000000..dcec2fb
--- /dev/null
+++ b/libcxx/test/libcxx/atomics/atomics.ref/assert.wait.pass.cpp
@@ -0,0 +1,55 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-hardening-mode=none || libcpp-hardening-mode=fast
+// XFAIL: libcpp-hardening-mode=debug && availability-verbose_abort-missing
+// ADDITIONAL_COMPILE_FLAGS: -Wno-user-defined-warnings
+
+// <atomic>
+
+// void wait(T old, memory_order order = memory_order::seq_cst) const noexcept;
+//
+// Preconditions: order is memory_order::relaxed, memory_order::consume, memory_order::acquire, or memory_order::seq_cst.
+
+#include <atomic>
+
+#include "atomic_helpers.h"
+#include "check_assertion.h"
+
+template <typename T>
+struct TestWaitInvalidMemoryOrder {
+  void operator()() const {
+    { // no assertion should trigger here
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+      a.wait(T(2), std::memory_order_relaxed);
+    }
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          a.wait(T(2), std::memory_order_release);
+        }()),
+        "atomic_ref: memory order argument to atomic wait operation is invalid");
+
+    TEST_LIBCPP_ASSERT_FAILURE(
+        ([] {
+          T x(T(1));
+          std::atomic_ref<T> const a(x);
+          a.wait(T(2), std::memory_order_acq_rel);
+        }()),
+        "atomic_ref: memory order argument to atomic wait operation is invalid");
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestWaitInvalidMemoryOrder>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/assign.pass.cpp b/libcxx/test/std/atomics/atomics.ref/assign.pass.cpp
new file mode 100644
index 0000000..3887211
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/assign.pass.cpp
@@ -0,0 +1,50 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// T operator=(T) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestAssign {
+  void operator()() const {
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      std::same_as<T> decltype(auto) y = (a = T(2));
+      assert(y == T(2));
+      assert(x == T(2));
+
+      ASSERT_NOEXCEPT(a = T(0));
+      static_assert(std::is_nothrow_assignable_v<std::atomic_ref<T>, T>);
+
+      static_assert(!std::is_copy_assignable_v<std::atomic_ref<T>>);
+    }
+
+    {
+      auto assign = [](std::atomic_ref<T> const& y, T, T new_val) { y = new_val; };
+      auto load   = [](std::atomic_ref<T> const& y) { return y.load(); };
+      test_seq_cst<T>(assign, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestAssign>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/bitwise_and_assign.pass.cpp b/libcxx/test/std/atomics/atomics.ref/bitwise_and_assign.pass.cpp
new file mode 100644
index 0000000..2be1e99
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/bitwise_and_assign.pass.cpp
@@ -0,0 +1,60 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator&=(integral-type) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_bitwise_and_assign = requires { std::declval<T const>() &= std::declval<T>(); };
+
+template <typename T>
+struct TestDoesNotHaveBitwiseAndAssign {
+  void operator()() const { static_assert(!has_bitwise_and_assign<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestBitwiseAndAssign {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    std::same_as<T> decltype(auto) y = (a &= T(1));
+    assert(y == T(1));
+    assert(x == T(1));
+    ASSERT_NOEXCEPT(a &= T(0));
+
+    y = (a &= T(2));
+    assert(y == T(0));
+    assert(x == T(0));
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestBitwiseAndAssign>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveBitwiseAndAssign>()();
+
+  TestEachPointerType<TestDoesNotHaveBitwiseAndAssign>()();
+
+  TestDoesNotHaveBitwiseAndAssign<bool>()();
+  TestDoesNotHaveBitwiseAndAssign<UserAtomicType>()();
+  TestDoesNotHaveBitwiseAndAssign<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/bitwise_or_assign.pass.cpp b/libcxx/test/std/atomics/atomics.ref/bitwise_or_assign.pass.cpp
new file mode 100644
index 0000000..5c22c8a2
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/bitwise_or_assign.pass.cpp
@@ -0,0 +1,56 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator|=(integral-type) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_bitwise_or_assign = requires { std::declval<T const>() |= std::declval<T>(); };
+
+template < typename T>
+struct TestDoesNotHaveBitwiseOrAssign {
+  void operator()() const { static_assert(!has_bitwise_or_assign<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestBitwiseOrAssign {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    std::same_as<T> decltype(auto) y = (a |= T(2));
+    assert(y == T(3));
+    assert(x == T(3));
+    ASSERT_NOEXCEPT(a |= T(0));
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestBitwiseOrAssign>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveBitwiseOrAssign>()();
+
+  TestEachPointerType<TestDoesNotHaveBitwiseOrAssign>()();
+
+  TestDoesNotHaveBitwiseOrAssign<bool>()();
+  TestDoesNotHaveBitwiseOrAssign<UserAtomicType>()();
+  TestDoesNotHaveBitwiseOrAssign<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/bitwise_xor_assign.pass.cpp b/libcxx/test/std/atomics/atomics.ref/bitwise_xor_assign.pass.cpp
new file mode 100644
index 0000000..4dc4fd3
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/bitwise_xor_assign.pass.cpp
@@ -0,0 +1,56 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator|=(integral-type) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_bitwise_xor_assign = requires { std::declval<T const>() ^= std::declval<T>(); };
+
+template <typename T>
+struct TestDoesNotHaveBitwiseXorAssign {
+  void operator()() const { static_assert(!has_bitwise_xor_assign<std::atomic_ref<float>>); }
+};
+
+template <typename T>
+struct TestBitwiseXorAssign {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    std::same_as<T> decltype(auto) y = (a ^= T(2));
+    assert(y == T(3));
+    assert(x == T(3));
+    ASSERT_NOEXCEPT(a ^= T(0));
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestBitwiseXorAssign>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveBitwiseXorAssign>()();
+
+  TestEachPointerType<TestDoesNotHaveBitwiseXorAssign>()();
+
+  TestDoesNotHaveBitwiseXorAssign<bool>()();
+  TestDoesNotHaveBitwiseXorAssign<UserAtomicType>()();
+  TestDoesNotHaveBitwiseXorAssign<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/compare_exchange_strong.pass.cpp b/libcxx/test/std/atomics/atomics.ref/compare_exchange_strong.pass.cpp
new file mode 100644
index 0000000..72b2f44
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/compare_exchange_strong.pass.cpp
@@ -0,0 +1,221 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// bool compare_exchange_strong(T&, T, memory_order, memory_order) const noexcept;
+// bool compare_exchange_strong(T&, T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestCompareExchangeStrong {
+  void operator()() const {
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y = a.compare_exchange_strong(t, T(2));
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3));
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2)));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y = a.compare_exchange_strong(t, T(2), std::memory_order_seq_cst);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3), std::memory_order_seq_cst);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2), std::memory_order_seq_cst));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y =
+          a.compare_exchange_strong(t, T(2), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2), std::memory_order_release, std::memory_order_relaxed));
+    }
+
+    // success memory_order::release
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::release, std::memory_order::relaxed);
+        assert(r);
+      };
+
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(std::memory_order::acquire); };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::release);
+        assert(r);
+      };
+      test_acquire_release<T>(store_one_arg, load);
+    }
+
+    // success memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acquire, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acquire)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load_one_arg);
+    }
+
+    // success memory_order::acq_rel
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::acq_rel, std::memory_order::relaxed);
+        assert(r);
+      };
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acq_rel, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::acq_rel);
+        assert(r);
+      };
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acq_rel)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store_one_arg, load_one_arg);
+    }
+
+    // success memory_order::seq_cst
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::seq_cst, std::memory_order::relaxed);
+        assert(r);
+      };
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::seq_cst, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_seq_cst<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::seq_cst);
+        assert(r);
+      };
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::seq_cst)) {
+        }
+        return val;
+      };
+      test_seq_cst<T>(store_one_arg, load_one_arg);
+    }
+
+    // failure memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r =
+            x.compare_exchange_strong(unexpected, unexpected, std::memory_order::relaxed, std::memory_order::acquire);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r = x.compare_exchange_strong(unexpected, unexpected, std::memory_order::acquire);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load_one_arg);
+
+      // acq_rel replaced by acquire
+      auto load_one_arg_acq_rel = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r = x.compare_exchange_strong(unexpected, unexpected, std::memory_order::acq_rel);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load_one_arg_acq_rel);
+    }
+
+    // failure memory_order::seq_cst
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::seq_cst); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r =
+            x.compare_exchange_strong(unexpected, unexpected, std::memory_order::relaxed, std::memory_order::seq_cst);
+        assert(!r);
+        return result;
+      };
+      test_seq_cst<T>(store, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestCompareExchangeStrong>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/compare_exchange_weak.pass.cpp b/libcxx/test/std/atomics/atomics.ref/compare_exchange_weak.pass.cpp
new file mode 100644
index 0000000..5219a8e
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/compare_exchange_weak.pass.cpp
@@ -0,0 +1,226 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// bool compare_exchange_weak(T&, T, memory_order, memory_order) const noexcept;
+// bool compare_exchange_weak(T&, T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <concepts>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestCompareExchangeWeak {
+  void operator()() const {
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y = a.compare_exchange_weak(t, T(2));
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_weak(t, T(3));
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_weak(t, T(2)));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y = a.compare_exchange_weak(t, T(2), std::memory_order_seq_cst);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_weak(t, T(3), std::memory_order_seq_cst);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_weak(t, T(2), std::memory_order_seq_cst));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> decltype(auto) y =
+          a.compare_exchange_weak(t, T(2), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_weak(t, T(3), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_weak(t, T(2), std::memory_order_release, std::memory_order_relaxed));
+    }
+
+    // success memory_order::release
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::release, std::memory_order::relaxed)) {
+        }
+      };
+
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(std::memory_order::acquire); };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::release)) {
+        }
+      };
+      test_acquire_release<T>(store_one_arg, load);
+    }
+
+    // success memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::acquire, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::acquire)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load_one_arg);
+    }
+
+    // success memory_order::acq_rel
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::acq_rel, std::memory_order::relaxed)) {
+        }
+      };
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::acq_rel, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::acq_rel)) {
+        }
+      };
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::acq_rel)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store_one_arg, load_one_arg);
+    }
+
+    // success memory_order::seq_cst
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::seq_cst, std::memory_order::relaxed)) {
+        }
+      };
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::seq_cst, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_seq_cst<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        // could fail spuriously, so put it in a loop
+        while (!x.compare_exchange_weak(old_val, new_val, std::memory_order::seq_cst)) {
+        }
+      };
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_weak(val, val, std::memory_order::seq_cst)) {
+        }
+        return val;
+      };
+      test_seq_cst<T>(store_one_arg, load_one_arg);
+    }
+
+    // failure memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r =
+            x.compare_exchange_weak(unexpected, unexpected, std::memory_order::relaxed, std::memory_order::acquire);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r = x.compare_exchange_weak(unexpected, unexpected, std::memory_order::acquire);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load_one_arg);
+
+      // acq_rel replaced by acquire
+      auto load_one_arg_acq_rel = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r = x.compare_exchange_weak(unexpected, unexpected, std::memory_order::acq_rel);
+        assert(!r);
+        return result;
+      };
+      test_acquire_release<T>(store, load_one_arg_acq_rel);
+    }
+
+    // failure memory_order::seq_cst
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::seq_cst); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        T unexpected(T(255));
+        bool r =
+            x.compare_exchange_weak(unexpected, unexpected, std::memory_order::relaxed, std::memory_order::seq_cst);
+        assert(!r);
+        return result;
+      };
+      test_seq_cst<T>(store, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestCompareExchangeWeak>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/convert.pass.cpp b/libcxx/test/std/atomics/atomics.ref/convert.pass.cpp
new file mode 100644
index 0000000..2a58a5e
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/convert.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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// operator T() const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestConvert {
+  void operator()() const {
+    T x(T(1));
+
+    T copy = x;
+    std::atomic_ref<T> const a(copy);
+
+    T converted = a;
+    assert(converted == x);
+
+    ASSERT_NOEXCEPT(T(a));
+    static_assert(std::is_nothrow_convertible_v<std::atomic_ref<T>, T>);
+
+    auto store = [](std::atomic_ref<T> const& y, T, T new_val) { y.store(new_val); };
+    auto load  = [](std::atomic_ref<T> const& y) { return static_cast<T>(y); };
+    test_seq_cst<T>(store, load);
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestConvert>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/ctor.pass.cpp b/libcxx/test/std/atomics/atomics.ref/ctor.pass.cpp
new file mode 100644
index 0000000..d6c6474
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/ctor.pass.cpp
@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <atomic>
+
+// explicit atomic_ref(T&);
+
+#include <atomic>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestCtor {
+  void operator()() const {
+    // check that the constructor is explicit
+    static_assert(!std::is_convertible_v<T, std::atomic_ref<T>>);
+    static_assert(std::is_constructible_v<std::atomic_ref<T>, T&>);
+
+    T x(T(0));
+    std::atomic_ref<T> a(x);
+    (void)a;
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestCtor>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/deduction.pass.cpp b/libcxx/test/std/atomics/atomics.ref/deduction.pass.cpp
new file mode 100644
index 0000000..24a399a
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/deduction.pass.cpp
@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <atomic>
+
+// explicit atomic_ref(T&);
+
+#include <atomic>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestDeduction {
+  void operator()() const {
+    T x(T(0));
+    std::atomic_ref a(x);
+    ASSERT_SAME_TYPE(decltype(a), std::atomic_ref<T>);
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestDeduction>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/exchange.pass.cpp b/libcxx/test/std/atomics/atomics.ref/exchange.pass.cpp
new file mode 100644
index 0000000..cd998d4
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/exchange.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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// T exchange(T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestExchange {
+  void operator()() const {
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = a.exchange(T(2));
+      assert(y == T(1));
+      ASSERT_NOEXCEPT(a.exchange(T(2)));
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a.exchange(T(3), std::memory_order_seq_cst);
+      assert(y == T(2));
+      ASSERT_NOEXCEPT(a.exchange(T(3), std::memory_order_seq_cst));
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestExchange>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_add.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_add.pass.cpp
new file mode 100644
index 0000000..908a687
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_add.pass.cpp
@@ -0,0 +1,113 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_add(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+// floating-point-type fetch_add(floating-point-type, memory_order = memory_order::seq_cst) const noexcept;
+// T* fetch_add(difference_type, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_add = requires {
+  std::declval<T const>().fetch_add(std::declval<T>());
+  std::declval<T const>().fetch_add(std::declval<T>(), std::declval<std::memory_order>());
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchAdd {
+  void operator()() const { static_assert(!has_fetch_add<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestFetchAdd {
+  void operator()() const {
+    if constexpr (std::is_arithmetic_v<T>) {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_add(T(2));
+        assert(y == T(1));
+        assert(x == T(3));
+        ASSERT_NOEXCEPT(a.fetch_add(T(0)));
+      }
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_add(T(4), std::memory_order_relaxed);
+        assert(y == T(3));
+        assert(x == T(7));
+        ASSERT_NOEXCEPT(a.fetch_add(T(0), std::memory_order_relaxed));
+      }
+    } else if constexpr (std::is_pointer_v<T>) {
+      using U = std::remove_pointer_t<T>;
+      U t[9]  = {};
+      T p{&t[1]};
+      std::atomic_ref<T> const a(p);
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_add(2);
+        assert(y == &t[1]);
+        assert(a == &t[3]);
+        ASSERT_NOEXCEPT(a.fetch_add(0));
+      }
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_add(4, std::memory_order_relaxed);
+        assert(y == &t[3]);
+        assert(a == &t[7]);
+        ASSERT_NOEXCEPT(a.fetch_add(0, std::memory_order_relaxed));
+      }
+    } else {
+      static_assert(std::is_void_v<T>);
+    }
+
+    // memory_order::release
+    {
+      auto fetch_add = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        x.fetch_add(new_val - old_val, std::memory_order::release);
+      };
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(std::memory_order::acquire); };
+      test_acquire_release<T>(fetch_add, load);
+    }
+
+    // memory_order::seq_cst
+    {
+      auto fetch_add_no_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) { x.fetch_add(new_val - old_val); };
+      auto fetch_add_with_order = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        x.fetch_add(new_val - old_val, std::memory_order::seq_cst);
+      };
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(); };
+      test_seq_cst<T>(fetch_add_no_arg, load);
+      test_seq_cst<T>(fetch_add_with_order, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestFetchAdd>()();
+
+  TestFetchAdd<float>()();
+  TestFetchAdd<double>()();
+
+  TestEachPointerType<TestFetchAdd>()();
+
+  TestDoesNotHaveFetchAdd<bool>()();
+  TestDoesNotHaveFetchAdd<UserAtomicType>()();
+  TestDoesNotHaveFetchAdd<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_and.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_and.pass.cpp
new file mode 100644
index 0000000..8f0bec2
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_and.pass.cpp
@@ -0,0 +1,69 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_and(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_and = requires {
+  std::declval<T const>().fetch_and(std::declval<T>());
+  std::declval<T const>().fetch_and(std::declval<T>(), std::declval<std::memory_order>());
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchAnd {
+  void operator()() const { static_assert(!has_fetch_and<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestFetchAnd {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_and(T(2));
+      assert(y == T(1));
+      assert(x == T(0));
+      ASSERT_NOEXCEPT(a.fetch_and(T(0)));
+    }
+
+    x = T(1);
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_and(T(2), std::memory_order_relaxed);
+      assert(y == T(1));
+      assert(x == T(0));
+      ASSERT_NOEXCEPT(a.fetch_and(T(0), std::memory_order_relaxed));
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestFetchAnd>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveFetchAnd>()();
+
+  TestEachPointerType<TestDoesNotHaveFetchAnd>()();
+
+  TestDoesNotHaveFetchAnd<bool>()();
+  TestDoesNotHaveFetchAnd<UserAtomicType>()();
+  TestDoesNotHaveFetchAnd<LargeUserAtomicType>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_or.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_or.pass.cpp
new file mode 100644
index 0000000..2045868
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_or.pass.cpp
@@ -0,0 +1,68 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_or(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <concepts>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_or = requires {
+  std::declval<T const>().fetch_or(std::declval<T>());
+  std::declval<T const>().fetch_or(std::declval<T>(), std::declval<std::memory_order>());
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchOr {
+  void operator()() const { static_assert(!has_fetch_or<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestFetchOr {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_or(T(2));
+      assert(y == T(1));
+      assert(x == T(3));
+      ASSERT_NOEXCEPT(a.fetch_or(T(0)));
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_or(T(2), std::memory_order_relaxed);
+      assert(y == T(3));
+      assert(x == T(3));
+      ASSERT_NOEXCEPT(a.fetch_or(T(0), std::memory_order_relaxed));
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestFetchOr>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveFetchOr>()();
+
+  TestEachPointerType<TestDoesNotHaveFetchOr>()();
+
+  TestDoesNotHaveFetchOr<bool>()();
+  TestDoesNotHaveFetchOr<UserAtomicType>()();
+  TestDoesNotHaveFetchOr<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_sub.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_sub.pass.cpp
new file mode 100644
index 0000000..5456045
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_sub.pass.cpp
@@ -0,0 +1,113 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_sub(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+// floating-point-type fetch_sub(floating-point-type, memory_order = memory_order::seq_cst) const noexcept;
+// T* fetch_sub(difference_type, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_sub = requires {
+  std::declval<T const>().fetch_sub(std::declval<T>());
+  std::declval<T const>().fetch_sub(std::declval<T>(), std::declval<std::memory_order>());
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchSub {
+  void operator()() const { static_assert(!has_fetch_sub<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestFetchSub {
+  void operator()() const {
+    if constexpr (std::is_arithmetic_v<T>) {
+      T x(T(7));
+      std::atomic_ref<T> const a(x);
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_sub(T(4));
+        assert(y == T(7));
+        assert(x == T(3));
+        ASSERT_NOEXCEPT(a.fetch_sub(T(0)));
+      }
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_sub(T(2), std::memory_order_relaxed);
+        assert(y == T(3));
+        assert(x == T(1));
+        ASSERT_NOEXCEPT(a.fetch_sub(T(0), std::memory_order_relaxed));
+      }
+    } else if constexpr (std::is_pointer_v<T>) {
+      using U = std::remove_pointer_t<T>;
+      U t[9]  = {};
+      T p{&t[7]};
+      std::atomic_ref<T> const a(p);
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_sub(4);
+        assert(y == &t[7]);
+        assert(a == &t[3]);
+        ASSERT_NOEXCEPT(a.fetch_sub(0));
+      }
+
+      {
+        std::same_as<T> decltype(auto) y = a.fetch_sub(2, std::memory_order_relaxed);
+        assert(y == &t[3]);
+        assert(a == &t[1]);
+        ASSERT_NOEXCEPT(a.fetch_sub(0, std::memory_order_relaxed));
+      }
+    } else {
+      static_assert(std::is_void_v<T>);
+    }
+
+    // memory_order::release
+    {
+      auto fetch_sub = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        x.fetch_sub(old_val - new_val, std::memory_order::release);
+      };
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(std::memory_order::acquire); };
+      test_acquire_release<T>(fetch_sub, load);
+    }
+
+    // memory_order::seq_cst
+    {
+      auto fetch_sub_no_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) { x.fetch_sub(old_val - new_val); };
+      auto fetch_sub_with_order = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        x.fetch_sub(old_val - new_val, std::memory_order::seq_cst);
+      };
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(); };
+      test_seq_cst<T>(fetch_sub_no_arg, load);
+      test_seq_cst<T>(fetch_sub_with_order, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestFetchSub>()();
+
+  TestFetchSub<float>()();
+  TestFetchSub<double>()();
+
+  TestEachPointerType<TestFetchSub>()();
+
+  TestDoesNotHaveFetchSub<bool>()();
+  TestDoesNotHaveFetchSub<UserAtomicType>()();
+  TestDoesNotHaveFetchSub<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_xor.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_xor.pass.cpp
new file mode 100644
index 0000000..aade87f
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_xor.pass.cpp
@@ -0,0 +1,68 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_xor(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <concepts>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_xor = requires {
+  std::declval<T const>().fetch_xor(std::declval<T>());
+  std::declval<T const>().fetch_xor(std::declval<T>(), std::declval<std::memory_order>());
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchXor {
+  void operator()() const { static_assert(!has_fetch_xor<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestFetchXor {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_xor(T(2));
+      assert(y == T(1));
+      assert(x == T(3));
+      ASSERT_NOEXCEPT(a.fetch_xor(T(0)));
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a.fetch_xor(T(2), std::memory_order_relaxed);
+      assert(y == T(3));
+      assert(x == T(1));
+      ASSERT_NOEXCEPT(a.fetch_xor(T(0), std::memory_order_relaxed));
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestFetchXor>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveFetchXor>()();
+
+  TestEachPointerType<TestDoesNotHaveFetchXor>()();
+
+  TestDoesNotHaveFetchXor<bool>()();
+  TestDoesNotHaveFetchXor<UserAtomicType>()();
+  TestDoesNotHaveFetchXor<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/increment_decrement.pass.cpp b/libcxx/test/std/atomics/atomics.ref/increment_decrement.pass.cpp
new file mode 100644
index 0000000..c84c89b
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/increment_decrement.pass.cpp
@@ -0,0 +1,97 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator++(int) const noexcept;
+// integral-type operator--(int) const noexcept;
+// integral-type operator++() const noexcept;
+// integral-type operator--() const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_pre_increment_operator = requires { ++std::declval<T const>(); };
+
+template <typename T>
+concept has_post_increment_operator = requires { std::declval<T const>()++; };
+
+template <typename T>
+concept has_pre_decrement_operator = requires { --std::declval<T const>(); };
+
+template <typename T>
+concept has_post_decrement_operator = requires { std::declval<T const>()--; };
+
+template <typename T>
+constexpr bool does_not_have_increment_nor_decrement_operators() {
+  return !has_pre_increment_operator<T> && !has_pre_decrement_operator<T> && !has_post_increment_operator<T> &&
+         !has_post_decrement_operator<T>;
+}
+
+template <typename T>
+struct TestDoesNotHaveIncrementDecrement {
+  void operator()() const { static_assert(does_not_have_increment_nor_decrement_operators<T>()); }
+};
+
+template <typename T>
+struct TestIncrementDecrement {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = ++a;
+      assert(y == T(2));
+      assert(x == T(2));
+      ASSERT_NOEXCEPT(++a);
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = --a;
+      assert(y == T(1));
+      assert(x == T(1));
+      ASSERT_NOEXCEPT(--a);
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a++;
+      assert(y == T(1));
+      assert(x == T(2));
+      ASSERT_NOEXCEPT(a++);
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a--;
+      assert(y == T(2));
+      assert(x == T(1));
+      ASSERT_NOEXCEPT(a--);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestIncrementDecrement>()();
+
+  TestEachFloatingPointType<TestDoesNotHaveIncrementDecrement>()();
+
+  TestEachPointerType<TestDoesNotHaveIncrementDecrement>()();
+
+  TestDoesNotHaveIncrementDecrement<bool>()();
+  TestDoesNotHaveIncrementDecrement<UserAtomicType>()();
+  TestDoesNotHaveIncrementDecrement<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/is_always_lock_free.pass.cpp b/libcxx/test/std/atomics/atomics.ref/is_always_lock_free.pass.cpp
new file mode 100644
index 0000000..94f65e3b4
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/is_always_lock_free.pass.cpp
@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <atomic>
+
+// static constexpr bool is_always_lock_free;
+// bool is_lock_free() const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+
+#include "test_macros.h"
+
+template <typename T>
+void check_always_lock_free(std::atomic_ref<T> const a) {
+  std::same_as<const bool> decltype(auto) is_always_lock_free = std::atomic_ref<T>::is_always_lock_free;
+  if (is_always_lock_free) {
+    std::same_as<bool> decltype(auto) is_lock_free = a.is_lock_free();
+    assert(is_lock_free);
+  }
+  ASSERT_NOEXCEPT(a.is_lock_free());
+}
+
+#define CHECK_ALWAYS_LOCK_FREE(T)                                                                                      \
+  do {                                                                                                                 \
+    typedef T type;                                                                                                    \
+    type obj{};                                                                                                        \
+    check_always_lock_free(std::atomic_ref<type>(obj));                                                                \
+  } while (0)
+
+void test() {
+  int i = 0;
+  check_always_lock_free(std::atomic_ref<int>(i));
+
+  float f = 0.f;
+  check_always_lock_free(std::atomic_ref<float>(f));
+
+  int* p = &i;
+  check_always_lock_free(std::atomic_ref<int*>(p));
+
+  CHECK_ALWAYS_LOCK_FREE(struct Empty{});
+  CHECK_ALWAYS_LOCK_FREE(struct OneInt { int i; });
+  CHECK_ALWAYS_LOCK_FREE(struct IntArr2 { int i[2]; });
+  CHECK_ALWAYS_LOCK_FREE(struct FloatArr3 { float i[3]; });
+  CHECK_ALWAYS_LOCK_FREE(struct LLIArr2 { long long int i[2]; });
+  CHECK_ALWAYS_LOCK_FREE(struct LLIArr4 { long long int i[4]; });
+  CHECK_ALWAYS_LOCK_FREE(struct LLIArr8 { long long int i[8]; });
+  CHECK_ALWAYS_LOCK_FREE(struct LLIArr16 { long long int i[16]; });
+  CHECK_ALWAYS_LOCK_FREE(struct Padding {
+    char c; /* padding */
+    long long int i;
+  });
+  CHECK_ALWAYS_LOCK_FREE(union IntFloat {
+    int i;
+    float f;
+  });
+  CHECK_ALWAYS_LOCK_FREE(enum class CharEnumClass : char{foo});
+}
+
+int main(int, char**) {
+  test();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/load.pass.cpp b/libcxx/test/std/atomics/atomics.ref/load.pass.cpp
new file mode 100644
index 0000000..feed0fb
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/load.pass.cpp
@@ -0,0 +1,62 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// T load(memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <concepts>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestLoad {
+  void operator()() const {
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    {
+      std::same_as<T> decltype(auto) y = a.load();
+      assert(y == T(1));
+      ASSERT_NOEXCEPT(a.load());
+    }
+
+    {
+      std::same_as<T> decltype(auto) y = a.load(std::memory_order_seq_cst);
+      assert(y == T(1));
+      ASSERT_NOEXCEPT(a.load(std::memory_order_seq_cst));
+    }
+
+    // memory_order::seq_cst
+    {
+      auto store           = [](std::atomic_ref<T> const& y, T, T new_val) { y.store(new_val); };
+      auto load_no_arg     = [](std::atomic_ref<T> const& y) { return y.load(); };
+      auto load_with_order = [](std::atomic_ref<T> const& y) { return y.load(std::memory_order::seq_cst); };
+      test_seq_cst<T>(store, load_no_arg);
+      test_seq_cst<T>(store, load_with_order);
+    }
+
+    // memory_order::release
+    {
+      auto store = [](std::atomic_ref<T> const& y, T, T new_val) { y.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& y) { return y.load(std::memory_order::acquire); };
+      test_acquire_release<T>(store, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestLoad>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/member_types.pass.cpp b/libcxx/test/std/atomics/atomics.ref/member_types.pass.cpp
new file mode 100644
index 0000000..d4e2f01
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/member_types.pass.cpp
@@ -0,0 +1,132 @@
+//===----------------------------------------------------------------------===//
+//
+// 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, c++20
+
+// <atomic>
+
+// template <class T>
+// struct atomic_ref
+// {
+//    using value_type = T;
+//    using difference_type = value_type;      // only for atomic_ref<Integral> and
+//                                             // atomic_ref<Floating> specializations
+//    using difference_type = std::ptrdiff_t;  // only for atomic_ref<T*> specializations
+//
+//    explicit atomic_ref(T&);
+//    atomic_ref(const atomic_ref&) noexcept;
+//    atomic_ref& operator=(const atomic_ref&) = delete;
+// };
+
+#include <atomic>
+#include <type_traits>
+
+#include "test_macros.h"
+
+template <class T>
+concept has_difference_type = requires { typename T::difference_type; };
+
+template <class T>
+void check_member_types() {
+  if constexpr ((std::is_integral_v<T> && !std::is_same_v<T, bool>) || std::is_floating_point_v<T>) {
+    ASSERT_SAME_TYPE(typename std::atomic_ref<T>::value_type, T);
+    ASSERT_SAME_TYPE(typename std::atomic_ref<T>::difference_type, T);
+  } else if constexpr (std::is_pointer_v<T>) {
+    ASSERT_SAME_TYPE(typename std::atomic_ref<T>::value_type, T);
+    ASSERT_SAME_TYPE(typename std::atomic_ref<T>::difference_type, std::ptrdiff_t);
+  } else {
+    ASSERT_SAME_TYPE(typename std::atomic_ref<T>::value_type, T);
+    static_assert(!has_difference_type<std::atomic_ref<T>>);
+  }
+}
+
+template <class T>
+void test() {
+  // value_type and difference_type (except for primary template)
+  check_member_types<T>();
+
+  static_assert(std::is_nothrow_copy_constructible_v<std::atomic_ref<T>>);
+
+  static_assert(!std::is_copy_assignable_v<std::atomic_ref<T>>);
+
+  // explicit constructor
+  static_assert(!std::is_convertible_v<T, std::atomic_ref<T>>);
+  static_assert(std::is_constructible_v<std::atomic_ref<T>, T&>);
+}
+
+void testall() {
+  // Primary template
+  struct Empty {};
+  test<Empty>();
+  struct Trivial {
+    int a;
+    float b;
+  };
+  test<Trivial>();
+  test<bool>();
+
+  // Partial specialization for pointer types
+  test<void*>();
+
+  // Specialization for integral types
+  // + character types
+  test<char>();
+  test<char8_t>();
+  test<char16_t>();
+  test<char32_t>();
+  test<wchar_t>();
+  // + standard signed integer types
+  test<signed char>();
+  test<short>();
+  test<int>();
+  test<long>();
+  test<long long>();
+  // + standard unsigned integer types
+  test<unsigned char>();
+  test<unsigned short>();
+  test<unsigned int>();
+  test<unsigned long>();
+  test<unsigned long long>();
+  // + any other types needed by the typedefs in the header <cstdint>
+  test<int8_t>();
+  test<int16_t>();
+  test<int32_t>();
+  test<int64_t>();
+  test<int_fast8_t>();
+  test<int_fast16_t>();
+  test<int_fast32_t>();
+  test<int_fast64_t>();
+  test<int_least8_t>();
+  test<int_least16_t>();
+  test<int_least32_t>();
+  test<int_least64_t>();
+  test<intmax_t>();
+  test<intptr_t>();
+  test<uint8_t>();
+  test<uint16_t>();
+  test<uint32_t>();
+  test<uint64_t>();
+  test<uint_fast8_t>();
+  test<uint_fast16_t>();
+  test<uint_fast32_t>();
+  test<uint_fast64_t>();
+  test<uint_least8_t>();
+  test<uint_least16_t>();
+  test<uint_least32_t>();
+  test<uint_least64_t>();
+  test<uintmax_t>();
+  test<uintptr_t>();
+
+  // Specialization for floating-point types
+  // + floating-point types
+  test<float>();
+  test<double>();
+  test<long double>();
+  // + TODO extended floating-point types
+}
+
+int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/atomics/atomics.ref/notify_all.pass.cpp b/libcxx/test/std/atomics/atomics.ref/notify_all.pass.cpp
new file mode 100644
index 0000000..382b19f
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/notify_all.pass.cpp
@@ -0,0 +1,78 @@
+//
+// 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: no-threads
+// XFAIL: availability-synchronization_library-missing
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// void notify_all() const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <thread>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_helpers.h"
+#include "make_test_thread.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestNotifyAll {
+  void operator()() const {
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    bool done                      = false;
+    std::atomic<int> started_num   = 0;
+    std::atomic<int> wait_done_num = 0;
+
+    constexpr auto number_of_threads = 8;
+    std::vector<std::thread> threads;
+    threads.reserve(number_of_threads);
+
+    for (auto j = 0; j < number_of_threads; ++j) {
+      threads.push_back(support::make_test_thread([&a, &started_num, &done, &wait_done_num] {
+        started_num.fetch_add(1, std::memory_order::relaxed);
+
+        a.wait(T(1));
+        wait_done_num.fetch_add(1, std::memory_order::relaxed);
+
+        // likely to fail if wait did not block
+        assert(done);
+      }));
+    }
+
+    while (started_num.load(std::memory_order::relaxed) != number_of_threads) {
+      std::this_thread::yield();
+    }
+
+    std::this_thread::sleep_for(std::chrono::milliseconds(1));
+
+    done = true;
+    a.store(T(3));
+    a.notify_all();
+
+    // notify_all should unblock all the threads so that the loop below won't stuck
+    while (wait_done_num.load(std::memory_order::relaxed) != number_of_threads) {
+      std::this_thread::yield();
+    }
+
+    for (auto& thread : threads) {
+      thread.join();
+    }
+
+    ASSERT_NOEXCEPT(a.notify_all());
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestNotifyAll>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/notify_one.pass.cpp b/libcxx/test/std/atomics/atomics.ref/notify_one.pass.cpp
new file mode 100644
index 0000000..611e674
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/notify_one.pass.cpp
@@ -0,0 +1,46 @@
+//
+// 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: no-threads
+// XFAIL: availability-synchronization_library-missing
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// void notify_one() const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <thread>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_helpers.h"
+#include "make_test_thread.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestNotifyOne {
+  void operator()() const {
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    std::thread t = support::make_test_thread([&]() {
+      a.store(T(3));
+      a.notify_one();
+    });
+    a.wait(T(1));
+    assert(a.load() == T(3));
+    t.join();
+    ASSERT_NOEXCEPT(a.notify_one());
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestNotifyOne>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/operator_minus_equals.pass.cpp b/libcxx/test/std/atomics/atomics.ref/operator_minus_equals.pass.cpp
new file mode 100644
index 0000000..571d626
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/operator_minus_equals.pass.cpp
@@ -0,0 +1,79 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator-=(integral-type) const noexcept;
+// floating-point-type operator-=(floating-point-type) const noexcept;
+// T* operator-=(difference_type) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_operator_minus_equals = requires { std::declval<T const>() -= std::declval<T>(); };
+
+template <typename T>
+struct TestDoesNotHaveOperatorMinusEquals {
+  void operator()() const { static_assert(!has_operator_minus_equals<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestOperatorMinusEquals {
+  void operator()() const {
+    if constexpr (std::is_arithmetic_v<T>) {
+      T x(T(3));
+      std::atomic_ref<T> const a(x);
+
+      std::same_as<T> decltype(auto) y = (a -= T(2));
+      assert(y == T(1));
+      assert(x == T(1));
+      ASSERT_NOEXCEPT(a -= T(0));
+    } else if constexpr (std::is_pointer_v<T>) {
+      using U = std::remove_pointer_t<T>;
+      U t[9]  = {};
+      T p{&t[3]};
+      std::atomic_ref<T> const a(p);
+
+      std::same_as<T> decltype(auto) y = (a -= 2);
+      assert(y == &t[1]);
+      assert(a == &t[1]);
+      ASSERT_NOEXCEPT(a -= 0);
+    } else {
+      static_assert(std::is_void_v<T>);
+    }
+
+    // memory_order::seq_cst
+    {
+      auto minus_equals = [](std::atomic_ref<T> const& x, T old_val, T new_val) { x -= (old_val - new_val); };
+      auto load         = [](std::atomic_ref<T> const& x) { return x.load(); };
+      test_seq_cst<T>(minus_equals, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestOperatorMinusEquals>()();
+
+  TestOperatorMinusEquals<float>()();
+  TestOperatorMinusEquals<double>()();
+
+  TestEachPointerType<TestOperatorMinusEquals>()();
+
+  TestDoesNotHaveOperatorMinusEquals<bool>()();
+  TestDoesNotHaveOperatorMinusEquals<UserAtomicType>()();
+  TestDoesNotHaveOperatorMinusEquals<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/operator_plus_equals.pass.cpp b/libcxx/test/std/atomics/atomics.ref/operator_plus_equals.pass.cpp
new file mode 100644
index 0000000..de48ea5
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/operator_plus_equals.pass.cpp
@@ -0,0 +1,79 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+
+// integral-type operator+=(integral-type) const noexcept;
+// floating-point-type operator+=(floating-point-type) const noexcept;
+// T* operator+=(difference_type) const noexcept;
+
+#include <atomic>
+#include <concepts>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_operator_plus_equals = requires { std::declval<T const>() += std::declval<T>(); };
+
+template <typename T>
+struct TestDoesNotHaveOperatorPlusEquals {
+  void operator()() const { static_assert(!has_operator_plus_equals<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestOperatorPlusEquals {
+  void operator()() const {
+    if constexpr (std::is_arithmetic_v<T>) {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      std::same_as<T> decltype(auto) y = (a += T(2));
+      assert(y == T(3));
+      assert(x == T(3));
+      ASSERT_NOEXCEPT(a += T(0));
+    } else if constexpr (std::is_pointer_v<T>) {
+      using U = std::remove_pointer_t<T>;
+      U t[9]  = {};
+      T p{&t[1]};
+      std::atomic_ref<T> const a(p);
+
+      std::same_as<T> decltype(auto) y = (a += 2);
+      assert(y == &t[3]);
+      assert(a == &t[3]);
+      ASSERT_NOEXCEPT(a += 0);
+    } else {
+      static_assert(std::is_void_v<T>);
+    }
+
+    // memory_order::seq_cst
+    {
+      auto plus_equals = [](std::atomic_ref<T> const& x, T old_val, T new_val) { x += (new_val - old_val); };
+      auto load        = [](std::atomic_ref<T> const& x) { return x.load(); };
+      test_seq_cst<T>(plus_equals, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachIntegralType<TestOperatorPlusEquals>()();
+
+  TestOperatorPlusEquals<float>()();
+  TestOperatorPlusEquals<double>()();
+
+  TestEachPointerType<TestOperatorPlusEquals>()();
+
+  TestDoesNotHaveOperatorPlusEquals<bool>()();
+  TestDoesNotHaveOperatorPlusEquals<UserAtomicType>()();
+  TestDoesNotHaveOperatorPlusEquals<LargeUserAtomicType>()();
+
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/required_alignment.pass.cpp b/libcxx/test/std/atomics/atomics.ref/required_alignment.pass.cpp
new file mode 100644
index 0000000..86e0cba
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/required_alignment.pass.cpp
@@ -0,0 +1,39 @@
+//
+// 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
+
+// static constexpr size_t required_alignment;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+
+template <typename T>
+constexpr void check_required_alignment() {
+  std::same_as<const std::size_t> decltype(auto) required_alignment = std::atomic_ref<T>::required_alignment;
+  assert(required_alignment >= alignof(T));
+}
+
+constexpr bool test() {
+  check_required_alignment<int>();
+  check_required_alignment<float>();
+  check_required_alignment<int*>();
+  struct Empty {};
+  check_required_alignment<Empty>();
+  struct Trivial {
+    int a;
+  };
+  check_required_alignment<Trivial>();
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/requires-trivially-copyable.verify.cpp b/libcxx/test/std/atomics/atomics.ref/requires-trivially-copyable.verify.cpp
new file mode 100644
index 0000000..9a8b036
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/requires-trivially-copyable.verify.cpp
@@ -0,0 +1,26 @@
+//
+// 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
+
+// <atomic_ref>
+
+// template<class T>
+// class atomic_ref;
+
+// The program is ill-formed if is_trivially_copyable_v<T> is false.
+
+#include <atomic>
+
+void trivially_copyable() {
+  struct X {
+    X() = default;
+    X(X const&) {} // -> not trivially copyable
+  } x;
+  // expected-error-re@*:* {{static assertion failed {{.*}}atomic_ref<T> requires that 'T' be a trivially copyable type}}
+  std::atomic_ref<X> r(x);
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/store.pass.cpp b/libcxx/test/std/atomics/atomics.ref/store.pass.cpp
new file mode 100644
index 0000000..ea01a3d
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/store.pass.cpp
@@ -0,0 +1,61 @@
+//
+// 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
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// void store(T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestStore {
+  void operator()() const {
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    a.store(T(2));
+    assert(x == T(2));
+    ASSERT_NOEXCEPT(a.store(T(1)));
+
+    a.store(T(3), std::memory_order_seq_cst);
+    assert(x == T(3));
+    ASSERT_NOEXCEPT(a.store(T(0), std::memory_order_seq_cst));
+
+    // TODO memory_order::relaxed
+
+    // memory_order::seq_cst
+    {
+      auto store_no_arg     = [](std::atomic_ref<T> const& y, T, T new_val) { y.store(new_val); };
+      auto store_with_order = [](std::atomic_ref<T> const& y, T, T new_val) {
+        y.store(new_val, std::memory_order::seq_cst);
+      };
+      auto load = [](std::atomic_ref<T> const& y) { return y.load(); };
+      test_seq_cst<T>(store_no_arg, load);
+      test_seq_cst<T>(store_with_order, load);
+    }
+
+    // memory_order::release
+    {
+      auto store = [](std::atomic_ref<T> const& y, T, T new_val) { y.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& y) { return y.load(std::memory_order::acquire); };
+      test_acquire_release<T>(store, load);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestStore>()();
+  return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/test_helper.h b/libcxx/test/std/atomics/atomics.ref/test_helper.h
new file mode 100644
index 0000000..225a70c
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/test_helper.h
@@ -0,0 +1,136 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_STD_ATOMICS_ATOMIC_REF_TEST_HELPER_H
+#define TEST_STD_ATOMICS_ATOMIC_REF_TEST_HELPER_H
+
+#include <atomic>
+#include <cassert>
+#include <cmath>
+#include <vector>
+
+#include "test_macros.h"
+
+#ifndef TEST_HAS_NO_THREADS
+#  include "make_test_thread.h"
+#  include <thread>
+#endif
+
+template <class T>
+bool equals(T x, T y) {
+  return x == y;
+}
+
+template <class T>
+T make_value(int i) {
+  assert(i == 0 || i == 1);
+  if constexpr (std::is_pointer_v<T>) {
+    // So that pointers returned can be subtracted from one another
+    static std::remove_const_t<std::remove_pointer_t<T>> d[2];
+    return &d[i];
+  } else {
+    return T(i);
+  }
+}
+
+// Test that all threads see the exact same sequence of events
+// Test will pass 100% if store_op and load_op are correctly
+// affecting the memory with seq_cst order
+template <class T, class StoreOp, class LoadOp>
+void test_seq_cst(StoreOp store_op, LoadOp load_op) {
+#ifndef TEST_HAS_NO_THREADS
+  for (int i = 0; i < 100; ++i) {
+    T old_value(make_value<T>(0));
+    T new_value(make_value<T>(1));
+
+    T copy_x = old_value;
+    std::atomic_ref<T> const x(copy_x);
+    T copy_y = old_value;
+    std::atomic_ref<T> const y(copy_y);
+
+    std::atomic_bool x_updated_first(false);
+    std::atomic_bool y_updated_first(false);
+
+    auto t1 = support::make_test_thread([&] { store_op(x, old_value, new_value); });
+
+    auto t2 = support::make_test_thread([&] { store_op(y, old_value, new_value); });
+
+    auto t3 = support::make_test_thread([&] {
+      while (!equals(load_op(x), new_value)) {
+        std::this_thread::yield();
+      }
+      if (!equals(load_op(y), new_value)) {
+        x_updated_first.store(true, std::memory_order_relaxed);
+      }
+    });
+
+    auto t4 = support::make_test_thread([&] {
+      while (!equals(load_op(y), new_value)) {
+        std::this_thread::yield();
+      }
+      if (!equals(load_op(x), new_value)) {
+        y_updated_first.store(true, std::memory_order_relaxed);
+      }
+    });
+
+    t1.join();
+    t2.join();
+    t3.join();
+    t4.join();
+    // thread 3 and thread 4 cannot see different orders of storing x and y
+    assert(!(x_updated_first && y_updated_first));
+  }
+#else
+  (void)store_op;
+  (void)load_op;
+#endif
+}
+
+// Test that all writes before the store are seen by other threads after the load
+// Test will pass 100% if store_op and load_op are correctly
+// affecting the memory with acquire-release order
+template <class T, class StoreOp, class LoadOp>
+void test_acquire_release(StoreOp store_op, LoadOp load_op) {
+#ifndef TEST_HAS_NO_THREADS
+  for (auto i = 0; i < 100; ++i) {
+    T old_value(make_value<T>(0));
+    T new_value(make_value<T>(1));
+
+    T copy = old_value;
+    std::atomic_ref<T> const at(copy);
+    int non_atomic = 5;
+
+    constexpr auto number_of_threads = 8;
+    std::vector<std::thread> threads;
+    threads.reserve(number_of_threads);
+
+    for (auto j = 0; j < number_of_threads; ++j) {
+      threads.push_back(support::make_test_thread([&at, &non_atomic, load_op, new_value] {
+        while (!equals(load_op(at), new_value)) {
+          std::this_thread::yield();
+        }
+        // Other thread's writes before the release store are visible
+        // in this thread's read after the acquire load
+        assert(non_atomic == 6);
+      }));
+    }
+
+    non_atomic = 6;
+    store_op(at, old_value, new_value);
+
+    for (auto& thread : threads) {
+      thread.join();
+    }
+  }
+#else
+  (void)store_op;
+  (void)load_op;
+#endif
+}
+
+#endif // TEST_STD_ATOMICS_ATOMIC_REF_TEST_HELPER_H
diff --git a/libcxx/test/std/atomics/atomics.ref/wait.pass.cpp b/libcxx/test/std/atomics/atomics.ref/wait.pass.cpp
new file mode 100644
index 0000000..e5310fe
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/wait.pass.cpp
@@ -0,0 +1,88 @@
+//
+// 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: no-threads
+// XFAIL: availability-synchronization_library-missing
+// XFAIL: !has-64-bit-atomics
+// XFAIL: !has-1024-bit-atomics
+
+// void wait(T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "make_test_thread.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestWait {
+  void operator()() const {
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      assert(a.load() == T(1));
+      a.wait(T(0));
+      std::thread t1 = support::make_test_thread([&]() {
+        a.store(T(3));
+        a.notify_one();
+      });
+      a.wait(T(1));
+      assert(a.load() == T(3));
+      t1.join();
+      ASSERT_NOEXCEPT(a.wait(T(0)));
+
+      assert(a.load() == T(3));
+      a.wait(T(0), std::memory_order_seq_cst);
+      std::thread t2 = support::make_test_thread([&]() {
+        a.store(T(5));
+        a.notify_one();
+      });
+      a.wait(T(3), std::memory_order_seq_cst);
+      assert(a.load() == T(5));
+      t2.join();
+      ASSERT_NOEXCEPT(a.wait(T(0), std::memory_order_seq_cst));
+    }
+
+    // memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+      auto load  = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        x.wait(T(255), std::memory_order::acquire);
+        return result;
+      };
+      test_acquire_release<T>(store, load);
+    }
+
+    // memory_order::seq_cst
+    {
+      auto store       = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val); };
+      auto load_no_arg = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        x.wait(T(255));
+        return result;
+      };
+      auto load_with_order = [](std::atomic_ref<T> const& x) {
+        auto result = x.load(std::memory_order::relaxed);
+        x.wait(T(255), std::memory_order::seq_cst);
+        return result;
+      };
+      test_seq_cst<T>(store, load_no_arg);
+      test_seq_cst<T>(store, load_with_order);
+    }
+  }
+};
+
+int main(int, char**) {
+  TestEachAtomicType<TestWait>()();
+  return 0;
+}