anchor.diff:  (defun (setf successors) (new-successors instruction)
     (setf (sicl-mir:successors instruction) new-successors))
   
  +;;; FIXME: we need to deal with non-local transfers one day.
  +;;; 
  +;;;  (remove-if (lambda (successor)
  +;;;	       (not (eq (owner instruction) (owner successor))))
  +;;;	     (successors instruction)))
   (defun local-successors (instruction)
  -  (remove-if (lambda (successor)
  -	       (not (eq (owner instruction) (owner successor))))
  -	     (successors instruction)))
  +  (successors instruction))
   
   (defun inputs (instruction)
     (sicl-mir:inputs instruction))
   
  +(defun (setf inputs) (new-inputs instruction)
  +  (setf (sicl-mir:inputs instruction) new-inputs))
  +
   (defun outputs (instruction)
     (sicl-mir:outputs instruction))
  +
  +(defun (setf outputs) (new-outputs instruction)
  +  (setf (sicl-mir:outputs instruction) new-outputs))
  +
  +(defun defining-instructions (datum)
  +  (sicl-mir:defining-instructions datum))
  +
  +(defun using-instructions (datum)
  +  (sicl-mir:using-instructions datum))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code: (defmethod make-datum-info ((datum sicl-mir:immediate-input))
    (make-instance 'immediate-input-info))
  
  (defun find-datum-info (datum)
    (assert (not (null *program*)))
    (or (gethash datum (datum-info *program*))
  
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))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  