anchor.diff:      St = #live{bl=fun check_used_block/3,lbl=D,res=gb_trees:empty()},
       case check_liveness_at(R, Lbl, St) of
   	{killed,_} -> true;
  -	{used,_} -> false;
  -	{unknown,_} -> false
  +	{used,_} -> false
       end.
   
   %% index_labels(FunctionIs) -> State
  
positive.code: 	none ->
  	    {Res,St} = case gb_trees:lookup(Lbl, Ll) of
  			   {value,Is} -> check_liveness(R, Is, St0);
  			   none -> {unknown,St0}
  		       end,
  	    {Res,St#live{res=gb_trees:insert(Lbl, Res, St#live.res)}}
      end.
  
negative.code: 	{x,_} ->
  	    {killed,St};
  	_ ->
  	    %% y register. Rarely happens. Be very conversative and
  	    %% assume it's used.
  	    {used,St}
      end;
  check_liveness(R, [{loop_rec_end,{f,Fail}}|_], St) ->
      check_liveness_at(R, Fail, St);
  