Imported Upstream version 5.16.0.100

Former-commit-id: 38faa55fb9669e35e7d8448b15c25dc447f25767

mcs/class/corlib/ReferenceSources/Buffer.cs

@@ -1,3 +1,12 @@
+#if BIT64
+using nuint = System.UInt64;
+#else
+using nuint = System.UInt32;
+#endif
+
+using System.Runtime.CompilerServices;
+using System.Runtime;
+
 namespace System
 {
 	partial class Buffer
@@ -213,7 +222,28 @@ namespace System
 
 		internal static unsafe void Memmove (byte *dest, byte *src, uint len)
 		{
+            if (((nuint)dest - (nuint)src < len) || ((nuint)src - (nuint)dest < len))
+				goto PInvoke;
 			Memcpy (dest, src, (int) len);
+			return;
+
+            PInvoke:
+            RuntimeImports.Memmove(dest, src, len);
+		}
+
+		internal static void Memmove<T>(ref T destination, ref T source, nuint elementCount)
+		{
+            if (!RuntimeHelpers.IsReferenceOrContainsReferences<T>()) {
+                unsafe {
+                    fixed (byte* pDestination = &Unsafe.As<T, byte>(ref destination), pSource = &Unsafe.As<T, byte>(ref source))
+                        Memmove(pDestination, pSource, (uint)elementCount * (uint)Unsafe.SizeOf<T>());
+                }
+			} else {
+                unsafe {
+                    fixed (byte* pDestination = &Unsafe.As<T, byte>(ref destination), pSource = &Unsafe.As<T, byte>(ref source))
+                        RuntimeImports.Memmove_wbarrier(pDestination, pSource, (uint)elementCount, typeof(T).TypeHandle.Value);
+				}
+			}
 		}
 	}
 }