anchor.diff:  %%  Test whether the instruction Instruction always
   %%  causes an exit/failure.
   
  +-spec is_exit_instruction(instruction()) -> boolean().
  +
   is_exit_instruction({call_ext,_,{extfunc,M,F,A}}) ->
       erl_bifs:is_exit_bif(M, F, A);
   is_exit_instruction(if_end) -> true;
  
positive.code: %% remove_unused_labels(Instructions0) -> Instructions
  %%  Remove all unused labels. Also remove unreachable
  %%  instructions following labels that are removed.
  
  remove_unused_labels(Is) ->
      Used0 = initial_labels(Is),
  
negative.code: %%% 
  
  -import(lists, [reverse/1,reverse/2,foldl/3]).
  
  -type instruction() :: beam_utils:instruction().
  
  -spec module(beam_utils:module_code(), [compile:option()]) ->
                      {'ok',beam_utils:module_code()}.
  
  module({Mod,Exp,Attr,Fs0,Lc}, _Opt) ->
      Fs = [function(F) || F <- Fs0],
  