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add detection of string equalities

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2020-05-29 10:40:47 -07:00
parent e0130f5cf4
commit 3d9d52f742
3 changed files with 37 additions and 15 deletions
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44
src/smt/seq_regex.cpp
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@ -47,19 +47,37 @@ namespace smt {
}
/**
* is_string_equality holds of str.in_re s R, if R is of the form .* ++ x ++ .* ++ y ++ .* ++
* is_string_equality holds of str.in_re s R,
*
* s in (all ++ x ++ all ++ y ++ all)
* =>
* s = fresh1 ++ x ++ fresh2 ++ y ++ fresh3
*
* example rewrite:
* (str.in_re s .* ++ R) => s = x ++ y and (str.in_re y R)
*
* is_string_equality is currently placed under propagate_accept.
* this allows extracting string equalities after processing regexes that are not
* simple unions of simple concatentations. Though, it may produce different equations for
* alternate values of the unfolding index.
* TBD General rewrite possible:
*
* s in (R ++ Q)
* =>
* s = x ++ y and x in R and y in Q
*/
bool seq_regex::is_string_equality(literal lit) {
expr* s = nullptr, *r = nullptr;
expr* e = ctx.bool_var2expr(lit.var());
VERIFY(str().is_in_re(e, s, r));
vector<expr_ref_vector> patterns;
if (seq_rw().is_re_contains_pattern(r, patterns)) {
expr_ref t(m);
expr_ref_vector ts(m);
sort* seq_sort = m.get_sort(s);
ts.push_back(m.mk_fresh_const("seq.cont", seq_sort));
for (auto const& p : patterns) {
ts.append(p);
ts.push_back(m.mk_fresh_const("seq.cont", seq_sort));
}
t = th.mk_concat(ts, seq_sort);
th.propagate_eq(lit, s, t, true);
return true;
}
return false;
}
@ -93,7 +111,12 @@ namespace smt {
if (coallesce_in_re(lit))
return;
#if 0
// Enable/disable to test effect
if (is_string_equality(lit))
return;
#endif
//
// TBD s in R => R != {}
// non-emptiness enforcement could instead of here,
@ -170,9 +193,6 @@ namespace smt {
TRACE("seq", tout << "propagate " << mk_pp(e, m) << "\n";);
if (is_string_equality(lit))
return true;
if (block_unfolding(lit, idx))
return true;