anchor.diff:      end.
   
   opt_ref_used_is([#b_set{op=peek_message,dst=Msg}|Is], Vs0) ->
  -    Vs = Vs0#{{var,Msg}=>message},
  +    Vs = Vs0#{Msg=>message},
       opt_ref_used_is(Is, Vs);
   opt_ref_used_is([#b_set{op={bif,Bif},args=Args,dst=Dst}=I|Is],
                   Vs0) ->
  
positive.code:     beam_ssa:fold_instrs_rpo(F, [0], no, Blocks).
  
  opt_ref_used(RecvLbl, Ref, Blocks) ->
      Vs = #{{var,Ref}=>ref,ref=>Ref,ref_matched=>false},
      case opt_ref_used_1(RecvLbl, Vs, Blocks) of
          used -> true;
          not_used -> false;
  
negative.code: %%  Return 'true' if Args denotes a comparison between the
  %%  reference and message or part of the message.
  
  is_ref_msg_comparison([#b_var{}=V1,#b_var{}=V2], Vs) ->
      case Vs of
          #{V1:=ref,V2:=message} -> true;
          #{V1:=message,V2:=ref} -> true;
  