anchor.diff:    (setf (owner (find-datum-info datum))
   	new))
   
  -(defmethod assigning-instructions ((datum sicl-mir:lexical-location))
  -  (assigning-instructions (find-datum-info datum)))
  -
  -(defmethod (setf assigning-instructions)
  -    (new (datum sicl-mir:lexical-location))
  -  (setf (assigning-instructions (find-datum-info datum))
  -	new))
  -
  -(defmethod using-instructions ((datum sicl-mir:datum))
  -  (using-instructions (find-datum-info datum)))
  -
  -(defmethod (setf using-instructions) (new (datum sicl-mir:datum))
  -  (setf (using-instructions (find-datum-info datum))
  +(defmethod spill-cost ((datum sicl-mir:datum))
  +  (spill-cost (find-datum-info datum)))
  +
  +(defmethod (setf spill-cost) (new (datum sicl-mir:datum))
  +  (setf (spill-cost (find-datum-info datum))
   	new))
   
   (defmethod required-register ((datum sicl-mir:datum))
  
positive.code: (defun simplify-instructions (program)
    (let ((*program* program))
      (loop for location in (find-unused-lexical-locations program)
  	  do (loop for instruction in (assigning-instructions location)
  		   do (simplify-instruction instruction)))))
  
  (set-processor 'simplified-instructions 'simplify-instructions)
  
negative.code: 
  (defun merge-similar-constants (program)
    (let ((*program* program)
  	(constants '()))
      (flet ((canonicalize (constant)
  	     (or (find (sicl-mir:value constant) constants
  		       :key #'sicl-mir:value :test #'equal)
  		 (push constant constants))))
        (map-instructions
         (lambda (instruction)
  	 (let ((new-inputs
  		 (loop for input in (inputs instruction)
  		       collect (if (typep input 'sicl-mir:constant-input)
  				   (canonicalize input)
  				   input))))
  	   (unless (every #'eq (inputs instruction) new-inputs)
  	     (setf (inputs instruction) new-inputs))))))))
  
  (set-processor 'unique-constants 'merge-similar-constants)
  
  (add-dependencies 'unique-constants
  		  '(instruction-info
  		    backend-specific-constants))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  