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Add constant-bound shortcut for string comparison constraints

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copilot-swe-agent[bot] 2026-07-13 05:05:11 +00:00 • committed by GitHub
parent da82c003c9
commit be7e8d7820
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2 changed files with 77 additions and 0 deletions
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59
src/smt/theory_seq.cpp
View file

@ -696,6 +696,14 @@ bool theory_seq::check_lts() {
literal eq = (b == c) ? true_literal : mk_eq(b, c, false);
bool is_strict = is_strict1 || is_strict2;
zstring sa, sd;
if (m_util.str.is_string(a, sa) && m_util.str.is_string(d, sd)) {
bool ok = is_strict ? sa < sd : !(sd < sa);
if (!ok) {
add_axiom(~r1, ~r2, ~eq);
}
continue;
}
if (is_strict) {
add_axiom(~r1, ~r2, ~eq, mk_literal(m_util.str.mk_lex_lt(a, d)));
}
@ -3155,6 +3163,57 @@ void theory_seq::assign_eh(bool_var v, bool is_true) {
}
else if (m_util.str.is_lt(e) || m_util.str.is_le(e)) {
m_lts.push_back(e);
expr* a = nullptr, *b = nullptr;
zstring c;
bool is_lower = false;
expr* x = nullptr;
if (is_true && m_util.str.is_lt(e, a, b)) {
if (m_util.str.is_string(a, c) && !m_util.str.is_string(b)) {
is_lower = true;
x = b;
}
else if (!m_util.str.is_string(a) && m_util.str.is_string(b, c)) {
is_lower = false;
x = a;
}
}
if (x && ctx.get_enode(x)) {
enode* x_root = ctx.get_enode(x)->get_root();
for (expr* p : m_lts) {
if (p == e)
continue;
expr* pa = nullptr, *pb = nullptr;
zstring pc;
bool p_is_lower = false;
expr* px = nullptr;
if (!m_util.str.is_lt(p, pa, pb))
continue;
literal p_lit = ctx.get_literal(p);
if (p_lit == true_literal || p_lit == false_literal || ctx.get_assignment(p_lit) != l_true)
continue;
if (m_util.str.is_string(pa, pc) && !m_util.str.is_string(pb)) {
p_is_lower = true;
px = pb;
}
else if (!m_util.str.is_string(pa) && m_util.str.is_string(pb, pc)) {
p_is_lower = false;
px = pa;
}
if (!px || p_is_lower == is_lower || !ctx.get_enode(px))
continue;
if (ctx.get_enode(px)->get_root() != x_root)
continue;
zstring const& lower = is_lower ? c : pc;
zstring const& upper = is_lower ? pc : c;
if (!(lower < upper)) {
literal_vector lits;
lits.push_back(lit);
lits.push_back(p_lit);
set_conflict(nullptr, lits);
return;
}
}
}
}
else if (m_util.str.is_nth_i(e) || m_util.str.is_nth_u(e)) {
// no-op

18
src/test/seq_rewriter.cpp
View file

@ -15,6 +15,7 @@ Tests:
17. Solver: (str.in_re x (re.range x x)) sat when len(x)=1
18. Solver: (str.in_re x (re.range x x)) unsat when len(x)=2
19. Solver: inverted symbolic bounds make membership unsatisfiable
20. Solver: contradictory constant lexical bounds are unsatisfiable
--*/
#include "ast/arith_decl_plugin.h"
@ -253,6 +254,23 @@ void tst_seq_rewriter() {
std::cout << "symbolic range solver inverted bounds unsat: " << res << "\n";
ENSURE(res == l_false);
}
// 20. unsat: contradictory constant lexical bounds.
// "2024-01-01" < x < "2024-12-31" and x < "2023-01-01".
{
smt_params sp;
smt::context ctx(m, sp);
app_ref x(m.mk_fresh_const("x", str_sort), m);
expr_ref b1(su.str.mk_string("2024-01-01"), m);
expr_ref b2(su.str.mk_string("2024-12-31"), m);
expr_ref b3(su.str.mk_string("2023-01-01"), m);
ctx.assert_expr(su.str.mk_lex_lt(b1, x));
ctx.assert_expr(su.str.mk_lex_lt(x, b2));
ctx.assert_expr(su.str.mk_lex_lt(x, b3));
lbool res = ctx.check();
std::cout << "constant lexical bounds unsat: " << res << "\n";
ENSURE(res == l_false);
}
}
std::cout << "tst_seq_rewriter: all tests passed\n";