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:     St = #live{bl=check_killed_block_fun(),lbl=D,res=gb_trees:empty()},
      case check_liveness(R, Is, St) of
  	{killed,_} -> true;
  	{used,_} -> false;
  	{unknown,_} -> false
      end.
  
  %% is_killed_at(Reg, Lbl, State) -> true|false
  
negative.code:     I = {block,[{set,[D1,D2],[S],get_list}]},
      check_liveness(R, [I|Is], St);
  check_liveness(_R, Is, St) when is_list(Is) ->
      %% Not implemented. Conservatively assume that the register is used.
      {used,St}.
      
  check_liveness_everywhere(R, [{f,Lbl}|T], St0) ->
      case check_liveness_at(R, Lbl, St0) of
  