From 60d0d6b24fc533b349f8de082a8bbd819c8c31bd Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 24 Nov 2020 00:07:37 -0800
Subject: [PATCH 1/3] Fix atomic_ref's static_assert.

---
 stl/inc/atomic | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/stl/inc/atomic b/stl/inc/atomic
index 8dfadf62917..077c8a5dd1b 100644
--- a/stl/inc/atomic
+++ b/stl/inc/atomic
@@ -2346,12 +2346,7 @@ private:
     using _Base = _Choose_atomic_base_t<_Ty, _Ty&>;
 
 public:
-    // clang-format off
-    static_assert(is_trivially_copyable_v<_Ty> && is_copy_constructible_v<_Ty> && is_move_constructible_v<_Ty>
-        && is_copy_assignable_v<_Ty> && is_move_assignable_v<_Ty>,
-        "atomic_ref<T> requires T to be trivially copyable, copy constructible, move constructible, copy assignable, "
-        "and move assignable.");
-    // clang-format on
+    static_assert(is_trivially_copyable_v<_Ty>, "atomic_ref<T> requires T to be trivially copyable.");
 
     using value_type = _Ty;
 

From 27bbf9720883be4c44b24fa26432ea6be558735a Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Tue, 24 Nov 2020 00:43:07 -0800
Subject: [PATCH 2/3] Test atomic_ref<const int>.

---
 tests/std/tests/P0019R8_atomic_ref/test.cpp | 22 +++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tests/std/tests/P0019R8_atomic_ref/test.cpp b/tests/std/tests/P0019R8_atomic_ref/test.cpp
index 1813049d209..91e9ee013b3 100644
--- a/tests/std/tests/P0019R8_atomic_ref/test.cpp
+++ b/tests/std/tests/P0019R8_atomic_ref/test.cpp
@@ -269,6 +269,26 @@ void test_ptr_ops() {
     assert(ry.load() == a + 0x10);
 }
 
+// GH-1497 <atomic>: atomic_ref<const T> fails to compile
+void test_gh_1497() {
+    {
+        const int ci{1729};
+        const std::atomic_ref atom{ci};
+        assert(atom.load() == 1729);
+    }
+
+    {
+        int i{11};
+        const std::atomic_ref<int> atom_modify{i};
+        const std::atomic_ref<const int> atom_observe{i};
+        assert(atom_modify.load() == 11);
+        assert(atom_observe.load() == 11);
+        atom_modify.store(22);
+        assert(atom_modify.load() == 22);
+        assert(atom_observe.load() == 22);
+    }
+}
+
 int main() {
     test_ops<false, char>();
     test_ops<false, signed char>();
@@ -319,4 +339,6 @@ int main() {
 
     test_ptr_ops<char*>();
     test_ptr_ops<long*>();
+
+    test_gh_1497();
 }

From 9a2d3413facef9b51a57538de6341026532d7871 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Mon, 30 Nov 2020 17:50:13 -0800
Subject: [PATCH 3/3] Code review feedback.

---
 tests/std/tests/P0019R8_atomic_ref/test.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/std/tests/P0019R8_atomic_ref/test.cpp b/tests/std/tests/P0019R8_atomic_ref/test.cpp
index 91e9ee013b3..d8398df7f76 100644
--- a/tests/std/tests/P0019R8_atomic_ref/test.cpp
+++ b/tests/std/tests/P0019R8_atomic_ref/test.cpp
@@ -270,9 +270,9 @@ void test_ptr_ops() {
 }
 
 // GH-1497 <atomic>: atomic_ref<const T> fails to compile
-void test_gh_1497() {
+void test_gh_1497_const_type() {
     {
-        const int ci{1729};
+        static constexpr int ci{1729}; // static storage duration, so this is stored in read-only memory
         const std::atomic_ref atom{ci};
         assert(atom.load() == 1729);
     }
@@ -340,5 +340,5 @@ int main() {
     test_ptr_ops<char*>();
     test_ptr_ops<long*>();
 
-    test_gh_1497();
+    test_gh_1497_const_type();
 }