[erlc] Crash in beam_ssa_opt with -0.0

[RobinMorisset]

Describe the bug
Running erlc on the following:

-feature(maybe_expr, enable).
-module(test258136).
-export([f/0]).

f() ->
    <<
        (ok)
     || _ := {_V1} <- ok,
        (maybe
            {} ?= _V1
        else
            -0.0 ->
                [];
            0.0 ->
                []
        end)
    >>.

crashes with the following message:

Function: '-f/0-lbc$^0/2-0-'/2
Sub pass ssa_opt_type_start
/home/rmorisset/minimized/test258136.erl: internal error in pass beam_ssa_opt:
exception error: no case clause matching {{1,{t_float,{-0.0,-0.0}}},{1,{t_float,{0.0,0.0}}}}
  in function  beam_types:join/2 (beam_types.erl, line 256)
  in call from beam_ssa_type:join_types_1/3 (beam_ssa_type.erl, line 2896)
  in call from beam_ssa_type:update_successor/3 (beam_ssa_type.erl, line 2077)
  in call from beam_ssa_type:update_switch/8 (beam_ssa_type.erl, line 2036)
  in call from beam_ssa_type:update_successors/5 (beam_ssa_type.erl, line 2001)
  in call from beam_ssa_type:sig_bs/8 (beam_ssa_type.erl, line 258)
  in call from beam_ssa_type:sig_function_1/4 (beam_ssa_type.erl, line 221)
  in call from beam_ssa_type:do_sig_function/4 (beam_ssa_type.erl, line 169)

Affected versions

• master
• Destructive tuple update #8090

[RobinMorisset]

Another example with a fairly similar error message:

-module(test386949).
-export([a/0, b/0, c/0]).

f(_V1) when ((+_V1) >= ok) ->
    <<(ok) || _ <- ok>>.

a() ->
    f(ok).

b() ->
    f(1.0).

c() ->
    f(2147483647).

crashes erlc with

Sub pass ssa_opt_type_continue
Function: '-f/1-lbc$^0/2-0-'/2
/home/rmorisset/minimized/test386949.erl: internal error in pass beam_ssa_opt:
exception error: no function clause matching beam_types:join([]) 
  in function  beam_ssa_type:join_arg_types/3 (beam_ssa_type.erl, line 447)
  in call from beam_ssa_type:opt_continue/4 (beam_ssa_type.erl, line 430)
  in call from beam_ssa_opt:ssa_opt_type_continue/1 (beam_ssa_opt.erl, line 439)
  in call from compile:run_sub_passes_1/3 (compile.erl, line 1184)
  in call from beam_ssa_opt:phase/4 (beam_ssa_opt.erl, line 118)
  in call from beam_ssa_opt:fixpoint/6 (beam_ssa_opt.erl, line 101)
  in call from beam_ssa_opt:run_phases/3 (beam_ssa_opt.erl, line 87)

This one does not rely on 0.0/-0.0, so it may have been a red herring. I'm also wondering whether it might be yet another instance of #7342.

[jhogberg]

Thanks, these are two separate issues. I've fixed the first in #8101 and will look into the second now :)

[jhogberg]

I've pushed a commit that fixes the second one now too, on the same branch because I'm feeling lazy. :D

Nevermind, it traded one bug for another -- to be continued.