anchor.diff:  ;;             slot-value-1
   ;;             slot-value-2)))
   (defbuiltin sys.int::%dcas-object (object offset old-1 old-2 new-1 new-2) ()
  -  (let ((constant-offset (and (constant-type-p offset `(signed-byte ,(- 64 sys.int::+n-fixnum-bits+)))
  +  (let ((constant-offset (and (constant-type-p offset `(signed-byte ,(- 32 sys.int::+n-fixnum-bits+)))
                                 (second offset))))
       (unless constant-offset
         (load-in-reg :rdi offset t)
  
positive.code: (defmacro define-u-b-object-ref (name width read-op write-op register)
    `(progn
       (defbuiltin ,name (object offset) ()
         (let ((constant-offset (and (constant-type-p offset `(signed-byte ,(- 64 sys.int::+n-fixnum-bits+)))
                                     (second offset))))
           (unless constant-offset
             (load-in-reg :rdi offset t)
  
negative.code:   (let ((type-error-label (gensym))
          (bignum-path (gensym "alr-sb64-bignum"))
          (value-extracted (gensym "alr-sb64-value-extracted"))
          (constant-offset (and (constant-type-p offset `(signed-byte ,(- 32 sys.int::+n-fixnum-bits+)))
                                (second offset))))
      (emit-trailer (bignum-path)
        ;; Check for bignumness.
  