diff --git a/libcxx/include/__algorithm/in_in_out_result.h b/libcxx/include/__algorithm/in_in_out_result.h
index d020b918ac73..3a163d1a75b6 100644
--- a/libcxx/include/__algorithm/in_in_out_result.h
+++ b/libcxx/include/__algorithm/in_in_out_result.h
@@ -26,9 +26,9 @@ namespace ranges {
 
 template <class _I1, class _I2, class _O1>
 struct in_in_out_result {
-  [[no_unique_address]] _I1 in1;
-  [[no_unique_address]] _I2 in2;
-  [[no_unique_address]] _O1 out;
+  _LIBCPP_NO_UNIQUE_ADDRESS _I1 in1;
+  _LIBCPP_NO_UNIQUE_ADDRESS _I2 in2;
+  _LIBCPP_NO_UNIQUE_ADDRESS _O1 out;
 
   template <class _II1, class _II2, class _OO1>
     requires convertible_to<const _I1&, _II1> && convertible_to<const _I2&, _II2> && convertible_to<const _O1&, _OO1>
diff --git a/libcxx/include/__algorithm/in_in_result.h b/libcxx/include/__algorithm/in_in_result.h
index e2585a709c1c..159092189a53 100644
--- a/libcxx/include/__algorithm/in_in_result.h
+++ b/libcxx/include/__algorithm/in_in_result.h
@@ -26,8 +26,8 @@ namespace ranges {
 
 template <class _I1, class _I2>
 struct in_in_result {
-  [[no_unique_address]] _I1 in1;
-  [[no_unique_address]] _I2 in2;
+  _LIBCPP_NO_UNIQUE_ADDRESS _I1 in1;
+  _LIBCPP_NO_UNIQUE_ADDRESS _I2 in2;
 
   template <class _II1, class _II2>
     requires convertible_to<const _I1&, _II1> && convertible_to<const _I2&, _II2>
diff --git a/libcxx/include/__algorithm/in_out_out_result.h b/libcxx/include/__algorithm/in_out_out_result.h
index e97a89147378..9788fbfa2e74 100644
--- a/libcxx/include/__algorithm/in_out_out_result.h
+++ b/libcxx/include/__algorithm/in_out_out_result.h
@@ -25,9 +25,9 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 namespace ranges {
 template <class _I1, class _O1, class _O2>
 struct in_out_out_result {
-  [[no_unique_address]] _I1 in;
-  [[no_unique_address]] _O1 out1;
-  [[no_unique_address]] _O2 out2;
+  _LIBCPP_NO_UNIQUE_ADDRESS _I1 in;
+  _LIBCPP_NO_UNIQUE_ADDRESS _O1 out1;
+  _LIBCPP_NO_UNIQUE_ADDRESS _O2 out2;
 
   template <class _II1, class _OO1, class _OO2>
     requires convertible_to<const _I1&, _II1> && convertible_to<const _O1&, _OO1> && convertible_to<const _O2&, _OO2>
diff --git a/libcxx/include/__algorithm/in_out_result.h b/libcxx/include/__algorithm/in_out_result.h
index cdd6ab48fbd2..124b4d6ffb6c 100644
--- a/libcxx/include/__algorithm/in_out_result.h
+++ b/libcxx/include/__algorithm/in_out_result.h
@@ -26,8 +26,8 @@ namespace ranges {
 
 template<class _InputIterator, class _OutputIterator>
 struct in_out_result {
-  [[no_unique_address]] _InputIterator in;
-  [[no_unique_address]] _OutputIterator out;
+  _LIBCPP_NO_UNIQUE_ADDRESS _InputIterator in;
+  _LIBCPP_NO_UNIQUE_ADDRESS _OutputIterator out;
 
   template <class _InputIterator2, class _OutputIterator2>
     requires convertible_to<const _InputIterator&, _InputIterator2> && convertible_to<const _OutputIterator&,
diff --git a/libcxx/include/__config b/libcxx/include/__config
index 2f0e8d4cf81e..e455eacc1948 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1398,6 +1398,28 @@ extern "C" _LIBCPP_FUNC_VIS void __sanitizer_annotate_contiguous_container(
 # define _LIBCPP_ATTRIBUTE_FORMAT(archetype, format_string_index, first_format_arg_index) /* nothing */
 #endif
 
+#if __has_cpp_attribute(msvc::no_unique_address)
+   // MSVC implements [[no_unique_address]] as a silent no-op currently.
+   // (If/when MSVC breaks its C++ ABI, it will be changed to work as intended.)
+   // However, MSVC implements [[msvc::no_unique_address]] which does what
+   // [[no_unique_address]] is supposed to do, in general.
+
+   // Clang-cl does not yet (14.0) implement either [[no_unique_address]] or
+   // [[msvc::no_unique_address]] though. If/when it does implement
+   // [[msvc::no_unique_address]], this should be preferred though.
+#  define _LIBCPP_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]
+#elif __has_cpp_attribute(no_unique_address)
+#  define _LIBCPP_NO_UNIQUE_ADDRESS [[no_unique_address]]
+#else
+#  define _LIBCPP_NO_UNIQUE_ADDRESS /* nothing */
+   // Note that this can be replaced by #error as soon as clang-cl
+   // implements msvc::no_unique_address, since there should be no C++20
+   // compiler that doesn't support one of the two attributes at that point.
+   // We geenrally don't want to use this macro outside of C++20-only code,
+   // because using it conditionally in one language version only would make
+   // the ABI inconsistent.
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG
diff --git a/libcxx/include/__iterator/counted_iterator.h b/libcxx/include/__iterator/counted_iterator.h
index 29de729e5ab1..c67743fbe37f 100644
--- a/libcxx/include/__iterator/counted_iterator.h
+++ b/libcxx/include/__iterator/counted_iterator.h
@@ -65,7 +65,7 @@ class counted_iterator
   , public __counted_iterator_value_type<_Iter>
 {
 public:
-  [[no_unique_address]] _Iter __current_ = _Iter();
+  _LIBCPP_NO_UNIQUE_ADDRESS _Iter __current_ = _Iter();
   iter_difference_t<_Iter> __count_ = 0;
 
   using iterator_type = _Iter;
diff --git a/libcxx/include/__ranges/copyable_box.h b/libcxx/include/__ranges/copyable_box.h
index 8d43b8884565..d092b7f9ba29 100644
--- a/libcxx/include/__ranges/copyable_box.h
+++ b/libcxx/include/__ranges/copyable_box.h
@@ -41,7 +41,7 @@ namespace ranges {
   // Primary template - uses std::optional and introduces an empty state in case assignment fails.
   template<__copy_constructible_object _Tp>
   class __copyable_box {
-    [[no_unique_address]] optional<_Tp> __val_;
+    _LIBCPP_NO_UNIQUE_ADDRESS optional<_Tp> __val_;
 
   public:
     template<class ..._Args>
@@ -116,7 +116,7 @@ namespace ranges {
   template<__copy_constructible_object _Tp>
     requires __doesnt_need_empty_state_for_copy<_Tp> && __doesnt_need_empty_state_for_move<_Tp>
   class __copyable_box<_Tp> {
-    [[no_unique_address]] _Tp __val_;
+    _LIBCPP_NO_UNIQUE_ADDRESS _Tp __val_;
 
   public:
     template<class ..._Args>
diff --git a/libcxx/include/__ranges/drop_view.h b/libcxx/include/__ranges/drop_view.h
index f3701bc71130..64c567416453 100644
--- a/libcxx/include/__ranges/drop_view.h
+++ b/libcxx/include/__ranges/drop_view.h
@@ -45,7 +45,7 @@ namespace ranges {
     // one can't call begin() on it more than once.
     static constexpr bool _UseCache = forward_range<_View> && !(random_access_range<_View> && sized_range<_View>);
     using _Cache = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
-    [[no_unique_address]] _Cache __cached_begin_ = _Cache();
+    _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();
     range_difference_t<_View> __count_ = 0;
     _View __base_ = _View();
 
diff --git a/libcxx/include/__ranges/join_view.h b/libcxx/include/__ranges/join_view.h
index 1472924bdb80..1af22213369a 100644
--- a/libcxx/include/__ranges/join_view.h
+++ b/libcxx/include/__ranges/join_view.h
@@ -67,7 +67,7 @@ namespace ranges {
 
     static constexpr bool _UseCache = !is_reference_v<_InnerRange>;
     using _Cache = _If<_UseCache, __non_propagating_cache<remove_cvref_t<_InnerRange>>, __empty_cache>;
-    [[no_unique_address]] _Cache __cache_;
+    _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cache_;
     _View __base_ = _View(); // TODO: [[no_unique_address]] makes clang crash! File a bug :)
 
   public:
diff --git a/libcxx/include/__ranges/reverse_view.h b/libcxx/include/__ranges/reverse_view.h
index 4da16133088f..c7f1ab8f943b 100644
--- a/libcxx/include/__ranges/reverse_view.h
+++ b/libcxx/include/__ranges/reverse_view.h
@@ -43,8 +43,8 @@ namespace ranges {
     // amortized O(1) begin() method.
     static constexpr bool _UseCache = !random_access_range<_View> && !common_range<_View>;
     using _Cache = _If<_UseCache, __non_propagating_cache<reverse_iterator<iterator_t<_View>>>, __empty_cache>;
-    [[no_unique_address]] _Cache __cached_begin_ = _Cache();
-    [[no_unique_address]] _View __base_ = _View();
+    _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();
+    _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
 
   public:
     _LIBCPP_HIDE_FROM_ABI
diff --git a/libcxx/include/__ranges/subrange.h b/libcxx/include/__ranges/subrange.h
index 0ea9d7887590..2450e230f281 100644
--- a/libcxx/include/__ranges/subrange.h
+++ b/libcxx/include/__ranges/subrange.h
@@ -82,9 +82,9 @@ namespace ranges {
     static constexpr bool _MustProvideSizeAtConstruction = !_StoreSize; // just to improve compiler diagnostics
     struct _Empty { constexpr _Empty(auto) noexcept { } };
     using _Size = conditional_t<_StoreSize, make_unsigned_t<iter_difference_t<_Iter>>, _Empty>;
-    [[no_unique_address]] _Iter __begin_ = _Iter();
-    [[no_unique_address]] _Sent __end_ = _Sent();
-    [[no_unique_address]] _Size __size_ = 0;
+    _LIBCPP_NO_UNIQUE_ADDRESS _Iter __begin_ = _Iter();
+    _LIBCPP_NO_UNIQUE_ADDRESS _Sent __end_ = _Sent();
+    _LIBCPP_NO_UNIQUE_ADDRESS _Size __size_ = 0;
 
   public:
     _LIBCPP_HIDE_FROM_ABI
diff --git a/libcxx/include/__ranges/take_view.h b/libcxx/include/__ranges/take_view.h
index 5f8fbaa0bd8b..de44fc1fae72 100644
--- a/libcxx/include/__ranges/take_view.h
+++ b/libcxx/include/__ranges/take_view.h
@@ -39,7 +39,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 namespace ranges {
   template<view _View>
   class take_view : public view_interface<take_view<_View>> {
-    [[no_unique_address]] _View __base_ = _View();
+    _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
     range_difference_t<_View> __count_ = 0;
 
     template<bool> class __sentinel;
@@ -136,7 +136,7 @@ namespace ranges {
     using _Base = __maybe_const<_Const, _View>;
     template<bool _OtherConst>
     using _Iter = counted_iterator<iterator_t<__maybe_const<_OtherConst, _View>>>;
-    [[no_unique_address]] sentinel_t<_Base> __end_ = sentinel_t<_Base>();
+    _LIBCPP_NO_UNIQUE_ADDRESS sentinel_t<_Base> __end_ = sentinel_t<_Base>();
 
     template<bool>
     friend class take_view<_View>::__sentinel;
diff --git a/libcxx/include/__ranges/transform_view.h b/libcxx/include/__ranges/transform_view.h
index a8d2ea3f0ed2..dad46536c75f 100644
--- a/libcxx/include/__ranges/transform_view.h
+++ b/libcxx/include/__ranges/transform_view.h
@@ -61,8 +61,8 @@ class transform_view : public view_interface<transform_view<_View, _Fn>> {
   template<bool> class __iterator;
   template<bool> class __sentinel;
 
-  [[no_unique_address]] __copyable_box<_Fn> __func_;
-  [[no_unique_address]] _View __base_ = _View();
+  _LIBCPP_NO_UNIQUE_ADDRESS __copyable_box<_Fn> __func_;
+  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
 
 public:
   _LIBCPP_HIDE_FROM_ABI