Invalid code emitted after type info pass

[josevalim]

Describe the bug

Take this code:

-module(clean_minimal).
-export([test/0]).

%% This triggers the bug
buggy(X) ->
    _ = id(X),
    case X =:= <<"a">> orelse X =:= <<"b">> of
        false -> outside;
        true ->
            Y = case X of <<"a">> -> 1; _ -> 2 end,
            {inside, Y}
    end.

id(Z) -> Z.

test() ->
    io:format("buggy(<<\"c\">>) = ~p~n", [buggy(<<"c">>)]).

Now compile and execute it:

$ erlc clean_minimal.erl && erl -noshell -eval "clean_minimal:test(), init:stop()" && erlc +no_type_opt clean_minimal.erl && erl -noshell -eval "io:format(\"~nWith +no_type_opt:~n\"), clean_minimal:test(), init:stop()"

It emits:

buggy(<<"c">>) = {inside,2}

With +no_type_opt:
buggy(<<"c">>) = outside

Showing the type optimisation makes it enter the wrong branch.

Affected versions

Checked only on Erlang/OTP 28 [erts-16.2]

Additional context

Originally reported here: elixir-lang/elixir#15069

[SteffenDE]

I tested different OTP versions with Docker and it happens down to OTP 24. OTP 23 is not affected.

Even more minimal:

buggy(X) ->
    case X =:= <<"a">> orelse X =:= <<"b">> of
        false -> outside;
        true ->
            Y = case X of <<"c">> -> never; _ -> ok end,
            {inside, Y}
    end.

#!/bin/bash

VERSION=${1:-28}

docker run --rm erlang:$VERSION sh -c '
cat > bug_test.erl << '\''EOF'\''
-module(bug_test).
-export([test/0]).

buggy(X) ->
    case X =:= <<"a">> orelse X =:= <<"b">> of
        false -> outside;
        true ->
            Y = case X of <<"c">> -> never; _ -> ok end,
            {inside, Y}
    end.

test() ->
    Result = buggy(<<"c">>),
    Expected = outside,
    io:format("Result: ~p, Expected: ~p, Match: ~p~n", [Result, Expected, Result =:= Expected]),
    case Result =:= Expected of
        true -> ok;
        false -> error
    end.
EOF

echo "=== Erlang/OTP version ==="
erl -version 2>&1

echo ""
echo "=== With default optimization ==="
erlc bug_test.erl && erl -noshell -eval "bug_test:test(), halt()."

echo ""
echo "=== With +no_type_opt ==="
erlc +no_type_opt bug_test.erl && erl -noshell -eval "bug_test:test(), halt()."
'

Good with 23:

$ ./test_bug 23
=== Erlang/OTP version ===
Erlang (SMP,ASYNC_THREADS) (BEAM) emulator version 11.2.2.18

=== With default optimization ===
Result: outside, Expected: outside, Match: true

=== With +no_type_opt ===
Result: outside, Expected: outside, Match: true

Same for anything after:

$ ./test_bug 24.0.0
=== Erlang/OTP version ===
Erlang (SMP,ASYNC_THREADS) (BEAM) emulator version 12.0

=== With default optimization ===
Result: {inside,never}, Expected: outside, Match: false

=== With +no_type_opt ===
Result: outside, Expected: outside, Match: true

Using no_ssa_opt also fixes it.

[jhogberg]

Thanks for your report, I've fixed it in #10569