anchor.diff:             (%make-array-header +object-tag-array+
                                  memory
                                  fill-pointer
  -                               (specialized-array-definition-tag
  -                                (upgraded-array-info element-type))
  +                               (specialized-array-definition-tag element-type-info)
                                  dimensions
                                  area))
             (displaced-to
  
positive.code: (defun bit-vector-p (object)
    (typep object '(array bit (*))))
  
  (defun make-simple-array (length &optional (element-type 't) area (initial-element nil initial-element-p))
    (let* ((info (upgraded-array-info element-type))
           (array (make-simple-array-1 length info area)))
      (when initial-element-p
        (unless (typep initial-element element-type)
          (error 'type-error :expected-type element-type :datum initial-element))
        (unless (eql initial-element (specialized-array-definition-zero-element info))
          (fill array initial-element)))
      array))
  
negative.code:           (t (let* ((total-size (if (integerp dimensions)
                                      dimensions
                                      (apply #'* dimensions)))
                      (backing-array (make-simple-array total-size element-type-info area initial-element initial-element-p))
                      (array (%make-array-header (if (and (not fill-pointer)
                                                          (not adjustable))
                                                     +object-tag-simple-array+
  