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-rw-r--r--lib/compiler/src/beam_ssa_type.erl14
-rw-r--r--lib/compiler/src/beam_validator.erl12
2 files changed, 17 insertions, 9 deletions
diff --git a/lib/compiler/src/beam_ssa_type.erl b/lib/compiler/src/beam_ssa_type.erl
index 06b42f1928..fe229d25df 100644
--- a/lib/compiler/src/beam_ssa_type.erl
+++ b/lib/compiler/src/beam_ssa_type.erl
@@ -896,11 +896,15 @@ type(call, [#b_remote{mod=#b_literal{val=Mod},
{_,_} ->
#t_tuple{}
end;
- {erlang,'++',[List1,List2]} ->
- case get_type(List1, Ts) =:= cons orelse
- get_type(List2, Ts) =:= cons of
- true -> cons;
- false -> list
+ {erlang,'++',[LHS,RHS]} ->
+ LType = get_type(LHS, Ts),
+ RType = get_type(RHS, Ts),
+ case LType =:= cons orelse RType =:= cons of
+ true ->
+ cons;
+ false ->
+ %% `[] ++ RHS` yields RHS, even if RHS is not a list.
+ join(list, RType)
end;
{erlang,'--',[_,_]} ->
list;
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 09a5a6c104..ebe9631e09 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -2844,10 +2844,14 @@ call_return_type_1(erlang, setelement, 3, Vst) ->
setelement(3, TupleType, #{})
end;
call_return_type_1(erlang, '++', 2, Vst) ->
- case get_term_type({x,0}, Vst) =:= cons orelse
- get_term_type({x,1}, Vst) =:= cons of
- true -> cons;
- false -> list
+ LType = get_term_type({x,0}, Vst),
+ RType = get_term_type({x,1}, Vst),
+ case LType =:= cons orelse RType =:= cons of
+ true ->
+ cons;
+ false ->
+ %% `[] ++ RHS` yields RHS, even if RHS is not a list
+ join(list, RType)
end;
call_return_type_1(erlang, '--', 2, _Vst) ->
list;