support byte and char array natively in ObjectReader/Writer

src/Compilers/Core/Portable/Serialization/ObjectReader.cs

@@ -335,6 +335,18 @@ private Array ReadArray(DataKind kind)
             }
 
             Type elementType = this.ReadType();
+
+            // optimizations for supported array type by binary reader
+            if (elementType == typeof(byte))
+            {
+                return _reader.ReadBytes(length);
+            }
+
+            if (elementType == typeof(char))
+            {
+                return _reader.ReadChars(length);
+            }
+
             Array array = Array.CreateInstance(elementType, length);
             for (int i = 0; i < length; i++)
             {
@@ -353,6 +365,17 @@ private Type ReadType()
 
         private Type ReadType(DataKind kind)
         {
+            // optimization for primitive types
+            if (kind == DataKind.UInt8)
+            {
+                return typeof(byte);
+            }
+
+            if (kind == DataKind.Char)
+            {
+                return typeof(char);
+            }
+
             switch (kind)
             {
                 case DataKind.TypeRef_B:

src/Compilers/Core/Portable/Serialization/ObjectWriter.cs

@@ -472,7 +472,21 @@ private void WriteArray(Array instance)
                     break;
             }
 
-            this.WriteType(instance.GetType().GetElementType());
+            var elementType = instance.GetType().GetElementType();
+            this.WriteType(elementType);
+
+            // optimizations for supported array type by binary writer
+            if (elementType == typeof(byte))
+            {
+                _writer.Write((byte[])instance);
+                return;
+            }
+
+            if (elementType == typeof(char))
+            {
+                _writer.Write((char[])instance);
+                return;
+            }
 
             for (int i = 0; i < length; i++)
             {
@@ -482,6 +496,19 @@ private void WriteArray(Array instance)
 
         private void WriteType(Type type)
         {
+            // optimization. primitive types
+            if (type == typeof(byte))
+            {
+                _writer.Write((byte)DataKind.UInt8);
+                return;
+            }
+
+            if (type == typeof(char))
+            {
+                _writer.Write((byte)DataKind.Char);
+                return;
+            }
+
             int id;
             if (_dataMap.TryGetId(type, out id))
             {