anchor.diff:  	  `(sys.lap-x86:sar64 :rdx 3)
   	  ;; Write.
   	  `(sys.lap-x86:mov16 (:rax :rcx) :dx))
  -    (setf *r8-value* (list (gensym)))))
  +    *r8-value*))
   
   (defbuiltin sys.int::memref-unsigned-byte-64 (base offset)
     (let ((overflow-error-label (gensym))
  
positive.code:              `(sys.lap-x86:cmp8 :al ,',tag)
               `(sys.lap-x86:jne ,type-error-label)
               `(sys.lap-x86:mov64 (,',slot :r9) :r8))
         (setf *r8-value* (list (gensym))))))
  
  (defmacro define-accessor (name type tag slot)
    `(progn (define-reader ,name ,type ,tag ,slot)
  
negative.code:     (fixnum-check :r9)
      (load-in-reg :r8 x t)
      (fixnum-check :r8)
      (smash-r8)
      (emit `(sys.lap-x86:mov64 :rax :r8)
            ;; Convert RAX to raw integer.
            `(sys.lap-x86:sar64 :rax 3)
  