anchor.diff:         for i from 0
          for inst in (allocator-instruction-ordering allocator)
          do (format t "~D: " i) (ir::print-instruction inst)))
  -  (let ((result (make-hash-table))
  +  (let ((result (make-hash-table :synchronized nil :test 'eq))
           (spilled-ranges (sort (all-spilled-ranges allocator)
                                 #'<
                                 :key #'live-range-start))
  
positive.code:                                           (< (live-range-end range) index))
                                          active-ranges))
           (dolist (new-range (gethash index starts))
             (push new-range active-ranges))
           (loop
              for (variable vreg repr) in (gethash inst original-debug-map)
              for range = (find vreg active-ranges :key #'live-range-vreg) ; might be worth maintaining this as a hash-table.
              for location = (if (interval-spilled-p allocator range)
                                 vreg
                                 (gethash range range-allocations))
  
negative.code:              (setf (gethash current-vreg result) '()))
             ;; Add new interference edges.
             (dolist (range live)
               (when (not (eq (live-range-vreg range) current-vreg))
                 (pushnew current-vreg (gethash (live-range-vreg range) result) :test 'eq)
                 (pushnew (live-range-vreg range) (gethash current-vreg result) :test 'eq)))
             (push range live)))
      result))
  
  