Optimized swapping of ref array elements.

lib/system.nim

@@ -1744,6 +1744,13 @@ proc swap*[T](a, b: var T) {.magic: "Swap", noSideEffect.}
   ## swaps the values `a` and `b`. This is often more efficient than
   ## ``tmp = a; a = b; b = tmp``. Particularly useful for sorting algorithms.
 
+when not defined(js) and not defined(booting):
+  template swapRefsInArray*{swap(arr[a], arr[b])}(arr: openarray[ref], a, b: int) =
+    # Optimize swapping of array elements if they are refs. Default swap
+    # implementation will cause unsureAsgnRef to be emitted which causes
+    # unnecessary slow down in this case.
+    swap(cast[ptr pointer](addr arr[a])[], cast[ptr pointer](addr arr[b])[])
+
 template `>=%` *(x, y: untyped): untyped = y <=% x
   ## treats `x` and `y` as unsigned and compares them.
   ## Returns true iff ``unsigned(x) >= unsigned(y)``.