anchor.diff:  
   (defun find-unused-lexical-locations (program)
     (ensure-location-assign-use program)
  -  (let ((*program* program))
  -    (loop for procedure in (procedures program)
  -	  append (loop for location in (locations procedure)
  -		       when (and (typep location 'sicl-mir:lexical-location)
  -				 (null (using-instructions location)))
  -			 collect location))))
  +  (let ((*program* program)
  +	(result '()))
  +    (map-locations
  +     (lambda (location)
  +       (when (and (typep location 'sicl-mir:lexical-location)
  +		  (null (using-instructions location)))
  +	 (push location result))))
  +    result))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code:     :initarg :initial-instruction :accessor initial-instruction)
     ;; This time stamp is set when the instruction graph is altered in
     ;; some way.
     (%instructions-timestemp 
      :initform 0 :accessor instructions-timestamp)
     ;; This table maps each instruction of the program to an
     ;; instruction-info instance.
  
negative.code: (defun eliminate-redundant-locations (program)
    (ensure-location-assign-use program)
    (let ((*program* program))
      (map-instructions
       (lambda (instruction)
         (let* ((inputs (inputs instruction))
  	      (in  (car inputs))
  	      (outputs (outputs instruction))
  	      (out  (car outputs)))
  	 (when (and (typep instruction 'sicl-mir:assignment-instruction)
  		    (typep in 'sicl-mir:lexical-location)
  		    (= (length (using-instructions in)) 1)
  		    (typep out 'sicl-mir:lexical-location)
  		    (= (length (assigning-instructions out)) 1))
  	   (loop for inst in (using-instructions out)
  		 do (nsubstitute IN OUT (inputs inst)))
  	   (change-class instruction
  			 'sicl-mir:nop-instruction)))))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Remove instances of NOP-INSTRUCTION.
  
  (defun remove-nop-instructions (program)
    (ensure-instruction-info program)
    (let ((*program* program))
      (map-instructions
       (lambda (instruction)
         (loop for rest on (successors instruction)
  	     do (loop while (typep (car rest) 'sicl-mir:nop-instruction)
  		      do (setf (car rest) (car (successors (car rest)))))))))
    (setf (instructions-timestamp program)
  	(incf (current-timestamp program))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  