[erlc] internal error in beam_kernel_to_ssa:collect_preds

[RobinMorisset]

On master,

f(X, 0) ->
    try
        0 = {
            _ = 0 + 0,
            Z = bnot ok,
            {(_ = ok), (_ = X)}#{ok => ok},
            ok +
                (f1(
                    ok +
                        f1(
                            ok +
                                (f1(
                                    (Y =
                                        -f1(
                                            #{
                                                (ok +
                                                    (ok +
                                                        f1(
                                                            case
                                                                try ok of
                                                                    _ ->
                                                                        fun(_) ->
                                                                            ok
                                                                        end
                                                                after
                                                                    ok
                                                                end
                                                            of
                                                                #{} ->
                                                                    ok
                                                            end
                                                        ))) => ok
                                            } > ok
                                        ))
                                ) + ok)
                        ) >
                        ok
                ))
        }
    of
        _ ->
            Z;
        _ ->
            Y
    after
        ok
    end.

f1(_) ->
    ok.

crashes erlc with the following error message:

Function: f/2
minimized/final_collect_preds.erl: internal error in pass beam_kernel_to_ssa:
exception error: no function clause matching beam_kernel_to_ssa:collect_preds([[]],[{{b_literal,unused},55}],[[]]) 
  in function  beam_kernel_to_ssa:gen_phis/2 (beam_kernel_to_ssa.erl, line 1271)
  in call from beam_kernel_to_ssa:gen_phis/2 (beam_kernel_to_ssa.erl, line 1273)
  in call from beam_kernel_to_ssa:fix_phis_1/3 (beam_kernel_to_ssa.erl, line 1239)
  in call from beam_kernel_to_ssa:fix_phis_1/3 (beam_kernel_to_ssa.erl, line 1263)
  in call from beam_kernel_to_ssa:fix_phis_1/3 (beam_kernel_to_ssa.erl, line 1251)
  in call from beam_kernel_to_ssa:fix_phis_1/3 (beam_kernel_to_ssa.erl, line 1265)
  in call from beam_kernel_to_ssa:fix_phis_1/3 (beam_kernel_to_ssa.erl, line 1251)

I've already minimized the testcase as much as I could; the three expressions in

 _ = 0 + 0,
 Z = bnot ok,
 {(_ = ok), (_ = X)}#{ok => ok},

can be moved rather freely within the function and the bug keeps reproducing, but removing or simplifying any of them makes it disappear.

[RobinMorisset]

This testcase reminds me of the one in #6572 (comment), which was similarly big because it needed to hit the fixpoint iteration limit.