Add {ReadOnly}Span ctor (internal for now) that takes a ref and no length (#67447)

* Add {ReadOnly}Span ctor (internal for now) that takes an in and no length

* Address PR feedback

* Fix native references to _pointer

Author: stephentoub

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs

@@ -268,7 +268,7 @@ public override bool IsCollectible
 
             char c = Type.Delimiter;
             string resourceName = nameSpace != null && name != null ?
-                string.Concat(nameSpace, new ReadOnlySpan<char>(ref c, 1), name) :
+                string.Concat(nameSpace, new ReadOnlySpan<char>(in c), name) :
                 string.Concat(nameSpace, name);
 
             return GetManifestResourceStream(resourceName);

src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeMethodInfo.CoreCLR.cs

@@ -338,7 +338,7 @@ public override MethodImplAttributes GetMethodImplementationFlags()
             }
 
             StackAllocedArguments stackArgs = default;
-            Span<object?> arguments = CheckArguments(ref stackArgs, new ReadOnlySpan<object?>(ref parameter, 1), binder, invokeAttr, culture, sig.Arguments);
+            Span<object?> arguments = CheckArguments(ref stackArgs, new ReadOnlySpan<object?>(in parameter), binder, invokeAttr, culture, sig.Arguments);
 
             bool wrapExceptions = (invokeAttr & BindingFlags.DoNotWrapExceptions) == 0;
             return RuntimeMethodHandle.InvokeMethod(obj, arguments, Signature, constructor: false, wrapExceptions);

src/coreclr/System.Private.CoreLib/src/System/StubHelpers.cs

@@ -35,7 +35,7 @@ internal static unsafe byte ConvertToNative(char managedChar, bool fBestFit, boo
 
         internal static char ConvertToManaged(byte nativeChar)
         {
-            var bytes = new ReadOnlySpan<byte>(ref nativeChar, 1);
+            var bytes = new ReadOnlySpan<byte>(in nativeChar);
             string str = Encoding.Default.GetString(bytes);
             return str[0];
         }

src/coreclr/jit/importer.cpp

@@ -4080,7 +4080,7 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
                 // For Span<T>
                 //   Comma
                 //     BoundsCheck(index, s->_length)
-                //     s->_pointer + index * sizeof(T)
+                //     s->_reference + index * sizeof(T)
                 //
                 // For ReadOnlySpan<T> -- same expansion, as it now returns a readonly ref
                 //

src/coreclr/jit/morphblock.cpp

@@ -895,7 +895,7 @@ void MorphCopyBlockHelper::MorphStructCases()
         }
         else if (m_srcDoFldAsg && srcFldIsProfitable)
         {
-            // Check for the symmetric case (which happens for the _pointer field of promoted spans):
+            // Check for the symmetric case (which happens for the _reference field of promoted spans):
             //
             //               [000240] -----+------             /--*  lclVar    struct(P) V18 tmp9
             //                                                  /--*    byref  V18._value (offs=0x00) -> V30

src/coreclr/vm/object.h

@@ -748,7 +748,7 @@ class Span
 {
 private:
     /* Keep fields below in sync with managed Span / ReadOnlySpan layout. */
-    KIND* _pointer;
+    KIND* _reference;
     unsigned int _length;
 
 public:
@@ -762,7 +762,7 @@ class Span
         LIMITED_METHOD_CONTRACT;
         SUPPORTS_DAC;
         _ASSERTE(index < GetLength());
-        return _pointer[index];
+        return _reference[index];
     }
 
     // Gets the length (in elements) of this span.

src/libraries/System.Private.CoreLib/src/System/Array.cs

@@ -239,12 +239,12 @@ public static void Copy(Array sourceArray, long sourceIndex, Array destinationAr
             return InternalGetValue(GetFlattenedIndex(new ReadOnlySpan<int>(indices)));
         }
 
-        public unsafe object? GetValue(int index)
+        public object? GetValue(int index)
         {
             if (Rank != 1)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_Need1DArray);
 
-            return InternalGetValue(GetFlattenedIndex(new ReadOnlySpan<int>(&index, 1)));
+            return InternalGetValue(GetFlattenedIndex(new ReadOnlySpan<int>(in index)));
         }
 
         public object? GetValue(int index1, int index2)
@@ -263,12 +263,12 @@ public static void Copy(Array sourceArray, long sourceIndex, Array destinationAr
             return InternalGetValue(GetFlattenedIndex(stackalloc int[] { index1, index2, index3 }));
         }
 
-        public unsafe void SetValue(object? value, int index)
+        public void SetValue(object? value, int index)
         {
             if (Rank != 1)
                 ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_Need1DArray);
 
-            InternalSetValue(value, GetFlattenedIndex(new ReadOnlySpan<int>(&index, 1)));
+            InternalSetValue(value, GetFlattenedIndex(new ReadOnlySpan<int>(in index)));
         }
 
         public void SetValue(object? value, int index1, int index2)

src/libraries/System.Private.CoreLib/src/System/Globalization/CompareInfo.cs

@@ -110,7 +110,7 @@ public static CompareInfo GetCompareInfo(string name!!)
 
         public static bool IsSortable(char ch)
         {
-            return IsSortable(MemoryMarshal.CreateReadOnlySpan(ref ch, 1));
+            return IsSortable(new ReadOnlySpan<char>(in ch));
         }
 
         public static bool IsSortable(string text!!)
@@ -785,7 +785,7 @@ public int IndexOf(string source, char value, CompareOptions options)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            return IndexOf(source, MemoryMarshal.CreateReadOnlySpan(ref value, 1), options);
+            return IndexOf(source, new ReadOnlySpan<char>(in value), options);
         }
 
         public int IndexOf(string source, string value, CompareOptions options)
@@ -865,7 +865,7 @@ public unsafe int IndexOf(string source, char value, int startIndex, int count,
                 }
             }
 
-            int result = IndexOf(sourceSpan, MemoryMarshal.CreateReadOnlySpan(ref value, 1), options);
+            int result = IndexOf(sourceSpan, new ReadOnlySpan<char>(in value), options);
             if (result >= 0)
             {
                 result += startIndex;
@@ -1118,7 +1118,7 @@ public int LastIndexOf(string source, char value, CompareOptions options)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            return LastIndexOf(source, MemoryMarshal.CreateReadOnlySpan(ref value, 1), options);
+            return LastIndexOf(source, new ReadOnlySpan<char>(in value), options);
         }
 
         public int LastIndexOf(string source, string value, CompareOptions options)
@@ -1213,7 +1213,7 @@ public int LastIndexOf(string source, char value, int startIndex, int count, Com
                 ThrowHelper.ThrowCountArgumentOutOfRange_ArgumentOutOfRange_Count();
             }
 
-            int retVal = LastIndexOf(sourceSpan, MemoryMarshal.CreateReadOnlySpan(ref value, 1), options);
+            int retVal = LastIndexOf(sourceSpan, new ReadOnlySpan<char>(in value), options);
             if (retVal >= 0)
             {
                 retVal += startIndex;

src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormat.cs

@@ -715,7 +715,7 @@ private static StringBuilder FormatCustomized(
                         if (nextChar >= 0 && nextChar != '%')
                         {
                             char nextCharChar = (char)nextChar;
-                            StringBuilder origStringBuilder = FormatCustomized(dateTime, MemoryMarshal.CreateReadOnlySpan<char>(ref nextCharChar, 1), dtfi, offset, result);
+                            StringBuilder origStringBuilder = FormatCustomized(dateTime, new ReadOnlySpan<char>(in nextCharChar), dtfi, offset, result);
                             Debug.Assert(ReferenceEquals(origStringBuilder, result));
                             tokenLen = 2;
                         }

src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs

@@ -437,7 +437,7 @@ private static StringBuilder FormatCustomized(TimeSpan value, ReadOnlySpan<char>
                         if (nextChar >= 0 && nextChar != (int)'%')
                         {
                             char nextCharChar = (char)nextChar;
-                            StringBuilder origStringBuilder = FormatCustomized(value, MemoryMarshal.CreateReadOnlySpan<char>(ref nextCharChar, 1), dtfi, result);
+                            StringBuilder origStringBuilder = FormatCustomized(value, new ReadOnlySpan<char>(in nextCharChar), dtfi, result);
                             Debug.Assert(ReferenceEquals(origStringBuilder, result));
                             tokenLen = 2;
                         }

src/libraries/System.Private.CoreLib/src/System/Guid.cs

@@ -385,7 +385,7 @@ private static bool TryParseExactD(ReadOnlySpan<char> guidString, ref GuidResult
                 return false;
             }
 
-            Span<byte> bytes = MemoryMarshal.AsBytes(new Span<GuidResult>(ref result, 1));
+            Span<byte> bytes = MemoryMarshal.AsBytes(new Span<GuidResult>(ref result));
             int invalidIfNegative = 0;
             bytes[0] = DecodeByte(guidString[6],   guidString[7],  ref invalidIfNegative);
             bytes[1] = DecodeByte(guidString[4],   guidString[5],  ref invalidIfNegative);
@@ -471,7 +471,7 @@ private static bool TryParseExactN(ReadOnlySpan<char> guidString, ref GuidResult
                 return false;
             }
 
-            Span<byte> bytes = MemoryMarshal.AsBytes(new Span<GuidResult>(ref result, 1));
+            Span<byte> bytes = MemoryMarshal.AsBytes(new Span<GuidResult>(ref result));
             int invalidIfNegative = 0;
             bytes[0] = DecodeByte(guidString[6], guidString[7], ref invalidIfNegative);
             bytes[1] = DecodeByte(guidString[4], guidString[5], ref invalidIfNegative);

src/libraries/System.Private.CoreLib/src/System/IO/BinaryWriter.cs

@@ -194,7 +194,7 @@ public virtual void Write(char ch)
                     buffer = rented;
                 }
 
-                int actualByteCount = _encoding.GetBytes(MemoryMarshal.CreateReadOnlySpan(ref ch, 1), buffer);
+                int actualByteCount = _encoding.GetBytes(new ReadOnlySpan<char>(in ch), buffer);
                 OutStream.Write(buffer.Slice(0, actualByteCount));
 
                 if (rented != null)

src/libraries/System.Private.CoreLib/src/System/IO/Strategies/OSFileStreamStrategy.cs

@@ -202,10 +202,10 @@ protected unsafe void SetLengthCore(long value)
             }
         }
 
-        public sealed override unsafe int ReadByte()
+        public sealed override int ReadByte()
         {
-            byte b;
-            return Read(new Span<byte>(&b, 1)) != 0 ? b : -1;
+            byte b = 0;
+            return Read(new Span<byte>(ref b)) != 0 ? b : -1;
         }
 
         public sealed override int Read(byte[] buffer, int offset, int count) =>
@@ -229,8 +229,8 @@ public sealed override int Read(Span<byte> buffer)
             return r;
         }
 
-        public sealed override unsafe void WriteByte(byte value) =>
-            Write(new ReadOnlySpan<byte>(&value, 1));
+        public sealed override void WriteByte(byte value) =>
+            Write(new ReadOnlySpan<byte>(in value));
 
         public override void Write(byte[] buffer, int offset, int count) =>
             Write(new ReadOnlySpan<byte>(buffer, offset, count));

src/libraries/System.Private.CoreLib/src/System/ReadOnlySpan.cs

@@ -23,7 +23,7 @@ namespace System
     public readonly ref struct ReadOnlySpan<T>
     {
         /// <summary>A byref or a native ptr.</summary>
-        internal readonly ByReference<T> _pointer;
+        internal readonly ByReference<T> _reference;
         /// <summary>The number of elements this ReadOnlySpan contains.</summary>
         private readonly int _length;
 
@@ -41,7 +41,7 @@ public ReadOnlySpan(T[]? array)
                 return; // returns default
             }
 
-            _pointer = new ByReference<T>(ref MemoryMarshal.GetArrayDataReference(array));
+            _reference = new ByReference<T>(ref MemoryMarshal.GetArrayDataReference(array));
             _length = array.Length;
         }
 
@@ -75,7 +75,7 @@ public ReadOnlySpan(T[]? array, int start, int length)
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 #endif
 
-            _pointer = new ByReference<T>(ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(array), (nint)(uint)start /* force zero-extension */));
+            _reference = new ByReference<T>(ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(array), (nint)(uint)start /* force zero-extension */));
             _length = length;
         }
 
@@ -102,17 +102,27 @@ public unsafe ReadOnlySpan(void* pointer, int length)
             if (length < 0)
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 
-            _pointer = new ByReference<T>(ref Unsafe.As<byte, T>(ref *(byte*)pointer));
+            _reference = new ByReference<T>(ref Unsafe.As<byte, T>(ref *(byte*)pointer));
             _length = length;
         }
 
+        // TODO https://github.com/dotnet/runtime/issues/67445: Make this public.
+        /// <summary>Creates a new <see cref="ReadOnlySpan{T}"/> of length 1 around the specified reference.</summary>
+        /// <param name="reference">A reference to data.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal ReadOnlySpan(in T reference)
+        {
+            _reference = new ByReference<T>(ref Unsafe.AsRef(in reference));
+            _length = 1;
+        }
+
         // Constructor for internal use only.
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal ReadOnlySpan(ref T ptr, int length)
+        internal ReadOnlySpan(ref T reference, int length)
         {
             Debug.Assert(length >= 0);
 
-            _pointer = new ByReference<T>(ref ptr);
+            _reference = new ByReference<T>(ref reference);
             _length = length;
         }
 
@@ -133,7 +143,7 @@ public ref readonly T this[int index]
             {
                 if ((uint)index >= (uint)_length)
                     ThrowHelper.ThrowIndexOutOfRangeException();
-                return ref Unsafe.Add(ref _pointer.Value, (nint)(uint)index /* force zero-extension */);
+                return ref Unsafe.Add(ref _reference.Value, (nint)(uint)index /* force zero-extension */);
             }
         }
 
@@ -251,7 +261,7 @@ public ref readonly T GetPinnableReference()
         {
             // Ensure that the native code has just one forward branch that is predicted-not-taken.
             ref T ret = ref Unsafe.NullRef<T>();
-            if (_length != 0) ret = ref _pointer.Value;
+            if (_length != 0) ret = ref _reference.Value;
             return ref ret;
         }
 
@@ -274,7 +284,7 @@ public void CopyTo(Span<T> destination)
 
             if ((uint)_length <= (uint)destination.Length)
             {
-                Buffer.Memmove(ref destination._pointer.Value, ref _pointer.Value, (uint)_length);
+                Buffer.Memmove(ref destination._reference.Value, ref _reference.Value, (uint)_length);
             }
             else
             {
@@ -295,7 +305,7 @@ public bool TryCopyTo(Span<T> destination)
             bool retVal = false;
             if ((uint)_length <= (uint)destination.Length)
             {
-                Buffer.Memmove(ref destination._pointer.Value, ref _pointer.Value, (uint)_length);
+                Buffer.Memmove(ref destination._reference.Value, ref _reference.Value, (uint)_length);
                 retVal = true;
             }
             return retVal;
@@ -307,7 +317,7 @@ public bool TryCopyTo(Span<T> destination)
         /// </summary>
         public static bool operator ==(ReadOnlySpan<T> left, ReadOnlySpan<T> right) =>
             left._length == right._length &&
-            Unsafe.AreSame<T>(ref left._pointer.Value, ref right._pointer.Value);
+            Unsafe.AreSame<T>(ref left._reference.Value, ref right._reference.Value);
 
         /// <summary>
         /// For <see cref="ReadOnlySpan{Char}"/>, returns a new instance of string that represents the characters pointed to by the span.
@@ -317,7 +327,7 @@ public override string ToString()
         {
             if (typeof(T) == typeof(char))
             {
-                return new string(new ReadOnlySpan<char>(ref Unsafe.As<T, char>(ref _pointer.Value), _length));
+                return new string(new ReadOnlySpan<char>(ref Unsafe.As<T, char>(ref _reference.Value), _length));
             }
             return $"System.ReadOnlySpan<{typeof(T).Name}>[{_length}]";
         }
@@ -335,7 +345,7 @@ public ReadOnlySpan<T> Slice(int start)
             if ((uint)start > (uint)_length)
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 
-            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _pointer.Value, (nint)(uint)start /* force zero-extension */), _length - start);
+            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _reference.Value, (nint)(uint)start /* force zero-extension */), _length - start);
         }
 
         /// <summary>
@@ -358,7 +368,7 @@ public ReadOnlySpan<T> Slice(int start, int length)
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 #endif
 
-            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _pointer.Value, (nint)(uint)start /* force zero-extension */), length);
+            return new ReadOnlySpan<T>(ref Unsafe.Add(ref _reference.Value, (nint)(uint)start /* force zero-extension */), length);
         }
 
         /// <summary>
@@ -372,7 +382,7 @@ public T[] ToArray()
                 return Array.Empty<T>();
 
             var destination = new T[_length];
-            Buffer.Memmove(ref MemoryMarshal.GetArrayDataReference(destination), ref _pointer.Value, (uint)_length);
+            Buffer.Memmove(ref MemoryMarshal.GetArrayDataReference(destination), ref _reference.Value, (uint)_length);
             return destination;
         }
     }

src/libraries/System.Private.CoreLib/src/System/Resources/ManifestBasedResourceGroveler.cs

@@ -343,7 +343,7 @@ private static ResourceSet InternalGetResourceSetFromSerializedData(Stream store
 
             char c = Type.Delimiter;
             string resourceName = nameSpace != null && name != null ?
-                string.Concat(nameSpace, new ReadOnlySpan<char>(ref c, 1), name) :
+                string.Concat(nameSpace, new ReadOnlySpan<char>(in c), name) :
                 string.Concat(nameSpace, name);
 
             string? canonicalName = null;