From 00ff3b3776a62402e7977fd9172a926ad62ea449 Mon Sep 17 00:00:00 2001 From: Stavros Aronis Date: Thu, 23 Apr 2015 11:15:47 +0200 Subject: Fix a bug related to constraints generated for erlang:'*'/2 For Rst = A1 * A2, typesig for erlang:'*'/2 was constraining the arguments A1 and A2 in the 'reverse' direction by requiring that A2 is a subtype of Rst div A1, unless A1 is a hard zero. This is not correct: if for example both Rst and A1 are non_negative, such a constraint will first force A1 to be non-zero for the division to go through and then require A2 to be non_negative as non_negative div positive = non_negative, always (see commited test). In the fixed version, we are not constraining an argument if the other operand *may* be zero. --- lib/dialyzer/src/dialyzer_typesig.erl | 8 ++++---- lib/dialyzer/test/small_SUITE_data/src/inv_mult.erl | 15 +++++++++++++++ 2 files changed, 19 insertions(+), 4 deletions(-) create mode 100644 lib/dialyzer/test/small_SUITE_data/src/inv_mult.erl (limited to 'lib/dialyzer') diff --git a/lib/dialyzer/src/dialyzer_typesig.erl b/lib/dialyzer/src/dialyzer_typesig.erl index 1737bfd3a9..6c14860d7d 100644 --- a/lib/dialyzer/src/dialyzer_typesig.erl +++ b/lib/dialyzer/src/dialyzer_typesig.erl @@ -1579,11 +1579,11 @@ get_bif_constr({M, F, A} = _BIF, Dst, Args, _State) -> eval_inv_arith('+', _Pos, Dst, Arg) -> bif_return(erlang, '-', 2, [Dst, Arg]); eval_inv_arith('*', _Pos, Dst, Arg) -> - case t_number_vals(Arg) of - [0] -> t_integer(); - _ -> + Zero = t_from_term(0), + case t_is_none(t_inf(Arg, Zero)) of + false -> t_integer(); + true -> TmpRet = bif_return(erlang, 'div', 2, [Dst, Arg]), - Zero = t_from_term(0), %% If 0 is not part of the result, it cannot be part of the argument. case t_is_subtype(Zero, Dst) of false -> t_subtract(TmpRet, Zero); diff --git a/lib/dialyzer/test/small_SUITE_data/src/inv_mult.erl b/lib/dialyzer/test/small_SUITE_data/src/inv_mult.erl new file mode 100644 index 0000000000..3413556813 --- /dev/null +++ b/lib/dialyzer/test/small_SUITE_data/src/inv_mult.erl @@ -0,0 +1,15 @@ +%% Dialyzer was too constraining when checking the relation between the +%% arguments and result of a multiplication. We should not constrain an argument +%% if the other operand *may* be zero. +%% +%% Bug found by Kostis Sagonas, fixed by Stavros Aronis + +-module(inv_mult). +-compile(export_all). + +main(L) -> + N = -1 * length(L), + fact(N). + +fact(0) -> 1; +fact(N) -> N * fact(N-1). -- cgit v1.2.1