Imported Upstream version 6.4.0.137

Former-commit-id: 943baa9f16a098c33e129777827f3a9d20da00d6

mcs/class/corlib/System.Runtime.CompilerServices/RuntimeHelpers.cs

@@ -195,5 +195,25 @@ namespace System.Runtime.CompilerServices
 			return FormatterServices.GetUninitializedObject (type);
 		}
 #endif
+
+        /// <summary>
+        /// GetSubArray helper method for the compiler to slice an array using a range.
+        /// </summary>
+        public static T[] GetSubArray<T> (T[] array, Range range)
+        {
+            Type elementType = array.GetType ().GetElementType ();
+            Span<T> source = array.AsSpan (range);
+
+            if (elementType.IsValueType)
+            {
+                return source.ToArray ();
+            }
+            else
+            {
+                T[] newArray = (T[]) Array.CreateInstance (elementType, source.Length);
+                source.CopyTo (newArray);
+                return newArray;
+            }
+        }
 	}
 }