anchor.diff:              case [{P,V} || {#b_var{}=V,P} <- PhiArgs] of
                   [_|_]=PhiVars ->
                       PhiLive0 = rel2fam(PhiVars),
  -                    PhiLive = [{{L,P},ordsets:union(ordsets:from_list(Vs), Live0)} ||
  +                    PhiLive = [{{L,P},cerl_sets:union(cerl_sets:from_list(Vs), Live0)} ||
                                     {P,Vs} <- PhiLive0],
                       maps:merge(UsedVars, maps:from_list(PhiLive));
                   [] ->
  
positive.code: -import(lists, [append/1,keymember/3,last/1,member/2,
                  takewhile/2,reverse/1]).
  
  -type used_vars() :: #{beam_ssa:label():=ordsets:ordset(beam_ssa:var_name())}.
  
  -type basic_type_test() :: atom() | {'is_tagged_tuple',pos_integer(),atom()}.
  -type type_test() :: basic_type_test() | {'not',basic_type_test()}.
  
negative.code:     %% shortcut_opt/1.
  
      Defined0 = [Def || #b_set{dst=Def} <- Is],
      Defined = cerl_sets:from_list(Defined0),
      MaySkip = cerl_sets:is_disjoint(Defined, Used0),
      case MaySkip of
          true ->
              Skip = Skip0#{L=>true},
  