[erlc] internal error in pass beam_kernel_to_ssa

[RobinMorisset]

On master (with and without cherry-picking #6559), the following testcase:

f(<<X>>) ->
    Y =
        case ok of
            X ->
                true = (ok > ((Y = _) = -1)),
                <<>> =
                    {f1(
                        <<
                            (ok - ok),
                            (bnot ok),
                            (f0() band ok),
                            (f0()),
                            (not ok),
                            (ok or f0()),
                            (f1(
                                f1(
                                    <<
                                        (f1(
                                            <<
                                                (f1(
                                                    <<0 || _ <- []>>
                                                ))
                                            >>
                                        ) * ok)
                                    >>
                                )
                            ))
                        >>
                    )}
        end.

f0() ->
    ok.

f1(_) ->
    ok.

causes the following erlc error:

Function: f/1
minimized/kernel_to_ssa.erl: internal error in pass beam_kernel_to_ssa:
exception error: no function clause matching beam_kernel_to_ssa:cg({k_return,[],[{k_var,[],41},{k_literal,[compiler_generated],-1}]},
 {cg,47,1,none,
     #{0 => {b_var,0},
       4 => {b_var,4},
       12 => {b_var,12},
       13 => {b_var,13},
       14 => {b_var,14},
       15 => {b_var,15},
       16 => {b_var,16},
       17 => {b_var,17},
       18 => {b_var,18},
       19 => {b_var,19},
       20 => {b_var,20},
       21 => {b_var,21},
       22 => {b_var,22},
       23 => {b_var,23},
       24 => {b_var,24},
       25 => {b_var,25},
       26 => {b_var,26},
       27 => {b_var,27},
       28 => {b_var,28},
       29 => {b_var,29},
       30 => {b_var,30},
       41 => {b_var,41},
       42 => {b_var,42},
       43 => {b_var,43},
       44 => {b_var,44},
       '@ssa_bool' => {b_var,{'@ssa_bool',45}},
       '@ssa_ret' => {b_var,'@ssa_ret'}},
     5,0,1,#{},false}) 
  in function  beam_kernel_to_ssa:cg/2 (beam_kernel_to_ssa.erl, line 114)
  in call from beam_kernel_to_ssa:guard_clause_cg/3 (beam_kernel_to_ssa.erl, line 563)
  in call from beam_kernel_to_ssa:match_cg/3 (beam_kernel_to_ssa.erl, line 177)
  in call from beam_kernel_to_ssa:do_match_cg/3 (beam_kernel_to_ssa.erl, line 167)
  in call from beam_kernel_to_ssa:select_bin_end/4 (beam_kernel_to_ssa.erl, line 437)
  in call from beam_kernel_to_ssa:select_bin_seg/4 (beam_kernel_to_ssa.erl, line 397)
  in call from beam_kernel_to_ssa:select_binary/5 (beam_kernel_to_ssa.erl, line 314)

I've been unable to minimize the testcase any further, all parts of it seem required to reproduce this bug.

[bjorng]

The reason you could not minimize the test case is that the fixpoint iteration limit needed be reached for the bug to appear.

[RobinMorisset]

Thank you for the explanation (and for the fix!), I was surprised by the size of the testcase but it makes sense now.