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fix various nullability checks in seq_regex

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2020-06-03 12:28:32 -07:00
parent 377dbad3b9
commit 3a7df2c6ef
4 changed files with 22 additions and 16 deletions
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22
src/smt/seq_regex.cpp
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@ -195,11 +195,22 @@ namespace smt {
VERIFY(sk().is_accept(e, s, i, idx, r));
expr_ref is_nullable(m), d(r, m);
TRACE("seq", tout << "propagate " << mk_pp(e, m) << "\n";);
if (block_unfolding(lit, idx))
return true;
literal_vector conds;
conds.push_back(~lit);
if (!unfold_cofactors(d, conds))
return false;
if (re().is_empty(d)) {
th.add_axiom(conds);
return true;
}
// s in R & len(s) <= i => nullable(R)
literal len_s_le_i = th.m_ax.mk_le(th.mk_len(s), idx);
switch (ctx.get_assignment(len_s_le_i)) {
@ -207,25 +218,22 @@ namespace smt {
ctx.mark_as_relevant(len_s_le_i);
return false;
case l_true:
is_nullable = seq_rw().is_nullable(r);
is_nullable = seq_rw().is_nullable(d);
rewrite(is_nullable);
th.add_axiom(~lit, ~len_s_le_i, th.mk_literal(is_nullable));
conds.push_back(~len_s_le_i);
conds.push_back(th.mk_literal(is_nullable));
th.add_axiom(conds);
return true;
case l_false:
break;
}
literal_vector conds;
if (!unfold_cofactors(d, conds))
return false;
// (accept s i R) & len(s) > i => (accept s (+ i 1) D(nth(s, i), R)) or conds
expr_ref head = th.mk_nth(s, i);
d = re().mk_derivative(head, r);
rewrite(d);
literal acc_next = th.mk_literal(sk().mk_accept(s, a().mk_int(idx + 1), d));
conds.push_back(~lit);
conds.push_back(len_s_le_i);
conds.push_back(acc_next);
th.add_axiom(conds);