Utilize the new ref readonly language feature

src/coreclr/System.Private.CoreLib/src/System/Threading/Interlocked.CoreCLR.cs

@@ -170,8 +170,8 @@ public static long Add(ref long location1, long value) =>
         /// <summary>Returns a 64-bit signed value, loaded as an atomic operation.</summary>
         /// <param name="location">The 64-bit value to be loaded.</param>
         /// <returns>The loaded value.</returns>
-        public static long Read(ref long location) =>
-            CompareExchange(ref location, 0, 0);
+        public static long Read(ref readonly long location) =>
+            CompareExchange(ref Unsafe.AsRef(in location), 0, 0);
         #endregion
 
         #region MemoryBarrierProcessWide

src/coreclr/nativeaot/System.Private.CoreLib/src/System/CrashInfo.cs

@@ -365,7 +365,7 @@ private void CloseValue(char marker)
 
         private bool WriteSeparator() => _isCommaNeeded ? WriteChar(',') : true;
 
-        private bool WriteChar(char source) => WriteChars(new ReadOnlySpan<char>(source));
+        private bool WriteChar(char source) => WriteChars(new ReadOnlySpan<char>(in source));
 
         private bool WriteChars(ReadOnlySpan<char> chars)
         {

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/InteropServices/ComWrappers.NativeAot.cs

@@ -27,9 +27,9 @@ public abstract partial class ComWrappers
         internal static IntPtr TaggedImplVftblPtr { get; } = CreateTaggedImplVftbl();
         internal static IntPtr DefaultIReferenceTrackerTargetVftblPtr { get; } = CreateDefaultIReferenceTrackerTargetVftbl();
 
-        internal static Guid IID_IUnknown = new Guid(0x00000000, 0x0000, 0x0000, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46);
-        internal static Guid IID_IReferenceTrackerTarget = new Guid(0x64bd43f8, 0xbfee, 0x4ec4, 0xb7, 0xeb, 0x29, 0x35, 0x15, 0x8d, 0xae, 0x21);
-        internal static Guid IID_TaggedImpl = new Guid(0x5c13e51c, 0x4f32, 0x4726, 0xa3, 0xfd, 0xf3, 0xed, 0xd6, 0x3d, 0xa3, 0xa0);
+        internal static readonly Guid IID_IUnknown = new Guid(0x00000000, 0x0000, 0x0000, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x46);
+        internal static readonly Guid IID_IReferenceTrackerTarget = new Guid(0x64bd43f8, 0xbfee, 0x4ec4, 0xb7, 0xeb, 0x29, 0x35, 0x15, 0x8d, 0xae, 0x21);
+        internal static readonly Guid IID_TaggedImpl = new Guid(0x5c13e51c, 0x4f32, 0x4726, 0xa3, 0xfd, 0xf3, 0xed, 0xd6, 0x3d, 0xa3, 0xa0);
 
         private static readonly ConditionalWeakTable<object, NativeObjectWrapper> s_rcwTable = new ConditionalWeakTable<object, NativeObjectWrapper>();
 
@@ -46,7 +46,7 @@ public static unsafe bool TryGetComInstance(object obj, out IntPtr unknown)
                 return false;
             }
 
-            return Marshal.QueryInterface(wrapper._externalComObject, ref IID_IUnknown, out unknown) == 0;
+            return Marshal.QueryInterface(wrapper._externalComObject, in IID_IUnknown, out unknown) == 0;
         }
 
         public static unsafe bool TryGetObject(IntPtr unknown, [NotNullWhen(true)] out object? obj)
@@ -675,7 +675,7 @@ public object GetOrRegisterObjectForComInstance(IntPtr externalComObject, Create
             {
                 // It is possible the user has defined their own IUnknown impl so
                 // we fallback to the tagged interface approach to be sure.
-                if (0 != Marshal.QueryInterface(comObject, ref IID_TaggedImpl, out nint implMaybe))
+                if (0 != Marshal.QueryInterface(comObject, in IID_TaggedImpl, out nint implMaybe))
                 {
                     return null;
                 }
@@ -737,8 +737,7 @@ private unsafe bool TryGetOrCreateObjectForComInstanceInternal(
                     {
                         // The unwrapped object has a CCW in this context. Get the IUnknown for the externalComObject
                         // so we can see if it's the CCW for the unwrapped object in this context.
-                        Guid iid = IID_IUnknown;
-                        int hr = Marshal.QueryInterface(externalComObject, ref iid, out IntPtr externalIUnknown);
+                        int hr = Marshal.QueryInterface(externalComObject, in IID_IUnknown, out IntPtr externalIUnknown);
                         Debug.Assert(hr == 0); // An external COM object that came from a ComWrappers instance
                                                // will always be well-formed.
                         if (unwrappedWrapperInThisContext.ComIp == externalIUnknown)

src/libraries/Common/src/Interop/Windows/SChannel/Interop.Sec_Application_Protocols.cs

@@ -54,7 +54,7 @@ public static unsafe byte[] ToByteArray(List<SslApplicationProtocol> application
             byte[] buffer = new byte[sizeof(Sec_Application_Protocols) + protocolListSize];
             int index = 0;
 
-            MemoryMarshal.Write(buffer.AsSpan(index), ref protocols);
+            MemoryMarshal.Write(buffer.AsSpan(index), in protocols);
             index += sizeof(Sec_Application_Protocols);
 
             for (int i = 0; i < applicationProtocols.Count; i++)

src/libraries/System.Collections.Concurrent/tests/ConcurrentDictionary/ConcurrentDictionary.Generic.Tests.cs

@@ -114,13 +114,13 @@ static T AssertNotNull<T>(T value, [CallerArgumentExpression(nameof(value))] str
                     uint hash1 = (5381 << 16) + 5381;
                     uint hash2 = BitOperations.RotateLeft(hash1, 5) + hash1;
 
-                    MemoryMarshal.Write(asBytes, ref seed);
-                    MemoryMarshal.Write(asBytes.Slice(4), ref hash2); // set hash2 := 0 (for Ordinal)
+                    MemoryMarshal.Write(asBytes, in seed);
+                    MemoryMarshal.Write(asBytes.Slice(4), in hash2); // set hash2 := 0 (for Ordinal)
 
                     hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1) ^ (uint)seed;
                     hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1);
 
-                    MemoryMarshal.Write(asBytes.Slice(8), ref hash1); // set hash1 := 0 (for Ordinal)
+                    MemoryMarshal.Write(asBytes.Slice(8), in hash1); // set hash1 := 0 (for Ordinal)
                 });
 
                 int ordinalHashCode = nonRandomizedOrdinal(candidate);

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.cs

@@ -431,7 +431,7 @@ void ICollection.CopyTo(Array array, int index)
         /// <summary>Gets either a reference to a <typeparamref name="TValue"/> in the dictionary or a null reference if the key does not exist in the dictionary.</summary>
         /// <param name="key">The key used for lookup.</param>
         /// <returns>A reference to a <typeparamref name="TValue"/> in the dictionary or a null reference if the key does not exist in the dictionary.</returns>
-        /// <remarks>The null reference can be detected by calling <see cref="Unsafe.IsNullRef{T}(ref T)"/>.</remarks>
+        /// <remarks>The null reference can be detected by calling <see cref="Unsafe.IsNullRef"/>.</remarks>
         public ref readonly TValue GetValueRefOrNullRef(TKey key)
         {
             if (key is null)

src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs

@@ -199,7 +199,7 @@ public void AddRangeDerivedSpan(string[] builderElements, string[] rangeElements
 
             // AddRange
             builder.AddRange(new ReadOnlySpan<string>(rangeElements));
-            
+
             // Assert
             Assert.Equal(expectedResult, builder);
         }
@@ -214,7 +214,7 @@ public void AddRangeDerivedImmutableArray(string[] builderElements, string[] ran
 
             // AddRange
             builder.AddRange(rangeElements.ToImmutableArray());
-            
+
             // Assert
             Assert.Equal(expectedResult, builder);
         }
@@ -226,7 +226,7 @@ public void AddRangeDerivedBuilder(string[] builderElements, string[] rangeEleme
             // Initialize builder
             var builderBase = new ImmutableArray<object>.Builder();
             builderBase.AddRange(builderElements);
-            
+
             // Prepare another builder to add
             var builder = new ImmutableArray<string>.Builder();
             builder.AddRange(rangeElements);
@@ -1108,7 +1108,7 @@ public void ItemRef()
             builder.Add(3);
 
             ref readonly int safeRef = ref builder.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, builder.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs

@@ -2552,7 +2552,7 @@ public void ItemRef()
             var array = new[] { 1, 2, 3 }.ToImmutableArray();
 
             ref readonly int safeRef = ref array.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, array.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs

@@ -228,7 +228,7 @@ public void RemoveRange()
 
             mutable.RemoveRange(new double[] { 2.4, 3.6 });
             Assert.Equal(new[] { 1.5, 4.7 }, mutable);
-            
+
             var absComparer = new DelegateEqualityComparer<double>(equals: (x, y) => Math.Abs(x) == Math.Abs(y));
             mutable.RemoveRange(new double[] { -1.5 }, absComparer);
             Assert.Equal(new[] { 4.7 }, mutable);
@@ -431,7 +431,7 @@ public void ItemRef()
             var builder = new ImmutableList<int>.Builder(list);
 
             ref readonly int safeRef = ref builder.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, builder.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableListTest.cs

@@ -820,7 +820,7 @@ public void ItemRef()
             ImmutableList<int> list = new[] { 1, 2, 3 }.ToImmutableList();
 
             ref readonly int safeRef = ref list.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, list.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableQueueTest.cs

@@ -268,7 +268,7 @@ public void PeekRef()
                 .Enqueue(3);
 
             ref readonly int safeRef = ref queue.PeekRef();
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(1, queue.PeekRef());
 

src/libraries/System.Collections.Immutable/tests/ImmutableSortedDictionaryBuilderTest.cs

@@ -286,7 +286,7 @@ public void ValueRef()
             }.ToImmutableSortedDictionary().ToBuilder();
 
             ref readonly int safeRef = ref builder.ValueRef("a");
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(1, builder.ValueRef("a"));
 

src/libraries/System.Collections.Immutable/tests/ImmutableSortedDictionaryTest.cs

@@ -434,7 +434,7 @@ public void ValueRef()
             }.ToImmutableSortedDictionary();
 
             ref readonly int safeRef = ref dictionary.ValueRef("a");
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(1, dictionary.ValueRef("a"));
 

src/libraries/System.Collections.Immutable/tests/ImmutableSortedSetBuilderTest.nonnetstandard.cs

@@ -19,7 +19,7 @@ public void ItemRef()
             var builder = new ImmutableSortedSet<int>.Builder(array);
 
             ref readonly int safeRef = ref builder.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, builder.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableSortedSetTest.cs

@@ -410,7 +410,7 @@ public void ItemRef()
             var array = new[] { 1, 2, 3 }.ToImmutableSortedSet();
 
             ref readonly int safeRef = ref array.ItemRef(1);
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(2, array.ItemRef(1));
 

src/libraries/System.Collections.Immutable/tests/ImmutableStackTest.cs

@@ -285,7 +285,7 @@ public void PeekRef()
                 .Push(3);
 
             ref readonly int safeRef = ref stack.PeekRef();
-            ref int unsafeRef = ref Unsafe.AsRef(safeRef);
+            ref int unsafeRef = ref Unsafe.AsRef(in safeRef);
 
             Assert.Equal(3, stack.PeekRef());
 

src/libraries/System.Collections/tests/Generic/Dictionary/HashCollisionScenarios/OutOfBoundsRegression.cs

@@ -303,13 +303,13 @@ static string GenerateCollidingStringCandidate(int seed)
                     uint hash1 = (5381 << 16) + 5381;
                     uint hash2 = BitOperations.RotateLeft(hash1, 5) + hash1;
 
-                    MemoryMarshal.Write(asBytes, ref seed);
-                    MemoryMarshal.Write(asBytes.Slice(4), ref hash2); // set hash2 := 0 (for Ordinal)
+                    MemoryMarshal.Write(asBytes, in seed);
+                    MemoryMarshal.Write(asBytes.Slice(4), in hash2); // set hash2 := 0 (for Ordinal)
 
                     hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1) ^ (uint)seed;
                     hash1 = (BitOperations.RotateLeft(hash1, 5) + hash1);
 
-                    MemoryMarshal.Write(asBytes.Slice(8), ref hash1); // set hash1 := 0 (for Ordinal)
+                    MemoryMarshal.Write(asBytes.Slice(8), in hash1); // set hash1 := 0 (for Ordinal)
                 });
             }
         }

src/libraries/System.Data.OleDb/src/OleDbComWrappers.cs

@@ -8,6 +8,10 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
+// We need to target netstandard2.0, so keep using ref for MemoryMarshal.Write
+// CS9191: The 'ref' modifier for argument 2 corresponding to 'in' parameter is equivalent to 'in'. Consider using 'in' instead.
+#pragma warning disable CS9191
+
 namespace System.Data.OleDb
 {
     /// <summary>

src/libraries/System.Data.OleDb/src/SafeHandles.cs

@@ -9,6 +9,10 @@
 using System.Runtime.Versioning;
 using static System.Data.Common.UnsafeNativeMethods;
 
+// We need to target netstandard2.0, so keep using ref for MemoryMarshal.Write
+// CS9191: The 'ref' modifier for argument 2 corresponding to 'in' parameter is equivalent to 'in'. Consider using 'in' instead.
+#pragma warning disable CS9191
+
 namespace System.Data.OleDb
 {
     internal sealed class DualCoTaskMem : SafeHandle

src/libraries/System.Management/src/System/Management/InteropClasses/WMIInterop.cs

@@ -9,6 +9,10 @@
 using System.Runtime.Versioning;
 using System.Text;
 
+// We need to target netstandard2.0, so keep using ref for MemoryMarshal.Write
+// CS9191: The 'ref' modifier for argument 2 corresponding to 'in' parameter is equivalent to 'in'. Consider using 'in' instead.
+#pragma warning disable CS9191
+
 namespace WbemClient_v1 { }
 namespace WbemUtilities_v1 { }
 

src/libraries/System.Management/src/System/Management/wmiutil.cs

@@ -3,6 +3,10 @@
 
 using System.Runtime.InteropServices;
 
+// We need to target netstandard2.0, so keep using ref for MemoryMarshal.Write
+// CS9191: The 'ref' modifier for argument 2 corresponding to 'in' parameter is equivalent to 'in'. Consider using 'in' instead.
+#pragma warning disable CS9191
+
 namespace System.Management
 {
 

src/libraries/System.Memory/ref/System.Memory.cs

@@ -693,7 +693,7 @@ public static partial class MemoryMarshal
         public static System.ReadOnlySpan<TTo> Cast<TFrom, TTo>(System.ReadOnlySpan<TFrom> span) where TFrom : struct where TTo : struct { throw null; }
         public static System.Span<TTo> Cast<TFrom, TTo>(System.Span<TFrom> span) where TFrom : struct where TTo : struct { throw null; }
         public static System.Memory<T> CreateFromPinnedArray<T>(T[]? array, int start, int length) { throw null; }
-        public static System.ReadOnlySpan<T> CreateReadOnlySpan<T>(scoped ref T reference, int length) { throw null; }
+        public static System.ReadOnlySpan<T> CreateReadOnlySpan<T>(scoped ref readonly T reference, int length) { throw null; }
         [System.CLSCompliant(false)]
         public static unsafe ReadOnlySpan<byte> CreateReadOnlySpanFromNullTerminated(byte* value) { throw null; }
         [System.CLSCompliant(false)]
@@ -710,8 +710,8 @@ public static partial class MemoryMarshal
         public static bool TryGetMemoryManager<T, TManager>(System.ReadOnlyMemory<T> memory, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out TManager? manager, out int start, out int length) where TManager : System.Buffers.MemoryManager<T> { throw null; }
         public static bool TryGetString(System.ReadOnlyMemory<char> memory, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out string? text, out int start, out int length) { throw null; }
         public static bool TryRead<T>(System.ReadOnlySpan<byte> source, out T value) where T : struct { throw null; }
-        public static bool TryWrite<T>(System.Span<byte> destination, ref T value) where T : struct { throw null; }
-        public static void Write<T>(System.Span<byte> destination, ref T value) where T : struct { }
+        public static bool TryWrite<T>(System.Span<byte> destination, in T value) where T : struct { throw null; }
+        public static void Write<T>(System.Span<byte> destination, in T value) where T : struct { }
     }
 }
 namespace System.Text

src/libraries/System.Memory/src/System/Buffers/SequenceReader.cs

@@ -99,7 +99,7 @@ public readonly long Length
                 if (_length < 0)
                 {
                     // Cast-away readonly to initialize lazy field
-                    Unsafe.AsRef(_length) = Sequence.Length;
+                    Unsafe.AsRef(in _length) = Sequence.Length;
                 }
                 return _length;
             }