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fix #7745

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axioms for len(substr(...)) escaped due to nested rewriting
This commit is contained in:
Nikolaj Bjorner 2025-07-26 12:30:42 -07:00
parent 95be0cf9ba
commit 0528c86905
2 changed files with 28 additions and 7 deletions
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29
src/ast/rewriter/seq_axioms.cpp
View file

@ -1224,16 +1224,39 @@ namespace seq {
let n = len(x)
- len(a ++ b) = len(a) + len(b) if x = a ++ b
- len(unit(u)) = 1 if x = unit(u)
- len(extract(x, o, l)) = l if len(x) >= o + l etc
- len(str) = str.length() if x = str
- len(empty) = 0 if x = empty
- len(int.to.str(i)) >= 1 if x = int.to.str(i) and more generally if i = 0 then 1 else 1+floor(log(|i|))
- len(x) >= 0 otherwise
*/
void axioms::length_axiom(expr* n) {
expr* x = nullptr;
expr* x = nullptr, * y = nullptr, * offs = nullptr, * l = nullptr;
VERIFY(seq.str.is_length(n, x));
if (seq.str.is_concat(x) ||
seq.str.is_unit(x) ||
if (seq.str.is_concat(x) && to_app(x)->get_num_args() != 0) {
ptr_vector<expr> args;
for (auto arg : *to_app(x))
args.push_back(seq.str.mk_length(arg));
expr_ref len(a.mk_add(args), m);
add_clause(mk_eq(len, n));
}
else if (seq.str.is_extract(x, y, offs, l)) {
// len(extract(y, o, l)) = l if len(y) >= o + l, o >= 0, l >= 0
// len(extract(y, o, l)) = 0 if o < 0 or l <= 0 or len(y) < o
// len(extract(y, o, l)) = o + l - len(y) if o <= len(y) < o + l
expr_ref len_y(mk_len(y), m);
expr_ref z(a.mk_int(0), m);
expr_ref y_ge_l(a.mk_ge(len_y, a.mk_add(offs, l)), m);
expr_ref y_ge_o(a.mk_ge(len_y, offs), m);
expr_ref offs_ge_0(a.mk_ge(offs, z), m);
expr_ref l_ge_0(a.mk_ge(l, z), m);
add_clause(~offs_ge_0, ~l_ge_0, ~y_ge_l, mk_eq(n, l));
add_clause(offs_ge_0, mk_eq(n, z));
add_clause(l_ge_0, mk_eq(n, z));
add_clause(y_ge_o, mk_eq(n, z));
add_clause(~y_ge_o, y_ge_l, mk_eq(n, a.mk_sub(a.mk_add(offs, l), len_y)));
}
else if (seq.str.is_unit(x) ||
seq.str.is_empty(x) ||
seq.str.is_string(x)) {
expr_ref len(n, m);

6
src/smt/theory_seq.cpp
View file

@ -439,7 +439,6 @@ final_check_status theory_seq::final_check_eh() {
}
bool theory_seq::set_empty(expr* x) {
add_axiom(~mk_eq(m_autil.mk_int(0), mk_len(x), false), mk_eq_empty(x));
return true;
@ -475,9 +474,8 @@ bool theory_seq::check_fixed_length(bool is_zero, bool check_long_strings) {
bool found = false;
for (unsigned i = 0; i < m_length.size(); ++i) {
expr* e = m_length.get(i);
if (fixed_length(e, is_zero, check_long_strings)) {
found = true;
}
if (fixed_length(e, is_zero, check_long_strings))
found = true;
}
return found;
}