anchor.diff:  		#'compiler-macroexpand-pass)
   	#'compile-pass
   	#'make-post-process-obj
  +	#'check-stemcells
   	#'post-process-ast
   	#'filter-used-items
  -	#'check-stemcells
   	#'gen-in-arg-strings
   	#'gen-out-var-strings
   	#'final-uniform-strings
  
positive.code: 		 :used-symbol-macros (dedup-used (used-symbol-macros env))
  		 :used-macros (dedup-used (used-macros env))
  		 :used-compiler-macros (dedup-used (used-compiler-macros env))))
  
  ;;----------------------------------------------------------------------
  
  (defun filter-used-items (post-proc-obj)
    "This changes the code-object so that used-types only contains used
     'user' defined structs."
    (with-slots (code env) post-proc-obj
      (setf (used-types post-proc-obj)
  	  (loop :for i :in (find-used-user-structs code env)
  	     :collect (type-spec->type i :env env))))
    post-proc-obj)
  
  ;;----------------------------------------------------------------------
  
  
negative.code: 
  ;;----------------------------------------------------------------------
  
  (defclass post-compile-process ()
    ((code :initarg :code :accessor code)
     (env :initarg :env :accessor env)
  