anchor.diff:      Vst = prune_x_regs(Live, Vst1),
       extract_term(CtxType, bs_start_match, [Src], Dst, Vst, Vst0);
   validate_bs_start_match({f,Fail}, Live, Slots, Src, Dst, Vst) ->
  +    assert_no_exception(Fail),
  +
       branch(Fail, Vst,
              fun(FailVst) ->
                      update_type(fun subtract/2, #t_bs_matchable{}, Src, FailVst)
  
positive.code:     Type = #t_tuple{exact=true,size=Sz,elements=Es},
      type_test(Lbl, Type, Src, Vst);
  vi_safe({test,is_eq_exact,{f,Lbl},[Src,Val]=Ss}, Vst) ->
      validate_src(Ss, Vst),
      branch(Lbl, Vst,
             fun(FailVst) ->
  
negative.code:     end;
  validate_branch_1(Lbl, [_ | Tags]) ->
      validate_branch_1(Lbl, Tags);
  validate_branch_1(_Lbl, _Tags) ->
      ok.
  
  %% A shorthand version of branch/4 for when the state is only altered on
  