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Cache derivative_cofactors calls in seq_monadic

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Memoize derivative_cofactors per regex in an owning cache so each regex's
cofactors are computed once per top-level solve. The cache is reset at the
start of solve()/solve_and() and freed in the destructor.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 57b9b87e-950a-49ea-bbb3-ed585646a5a9
This commit is contained in:
Nikolaj Bjorner 2026-07-31 19:20:52 -07:00
parent 168b51d332
commit 6212042e80
2 changed files with 30 additions and 10 deletions
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28
src/ast/rewriter/seq_monadic.cpp
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@ -23,7 +23,6 @@ TODOs:
- if perf suffers: use DFS backtracking search instead of DNF expansion (space overhead)
- create a validation harness: expose certificates for correctness that can be checked.
- extend with lower and upper bound constraints
- cache calls to cofactors so they are only computed once per regex.
- consider using expr_ref as alternative to pinned expressions
- encapsulate within general interface:
create: undo_trail x dependency_manager x ast_manager -> regex_membership
@ -61,11 +60,24 @@ expr_ref seq_monadic::der_elem(expr* r, expr* elem) {
return d2;
}
void seq_monadic::derivative_cofactors(expr* r, expr_ref_pair_vector& result) {
expr_ref_pair_vector const& seq_monadic::derivative_cofactors(expr* r) {
expr_ref_pair_vector* v = nullptr;
if (m_cofactor_cache.find(r, v))
return *v;
v = alloc(expr_ref_pair_vector, m);
if (m_mode == transition_mode::light_antimirov)
m_rw.light_ant_derivative_cofactors(r, result);
m_rw.light_ant_derivative_cofactors(r, *v);
else
m_rw.brz_derivative_cofactors(r, result);
m_rw.brz_derivative_cofactors(r, *v);
m_pin.push_back(r); // keep the key alive for the cache's lifetime
m_cofactor_cache.insert(r, v);
return *v;
}
void seq_monadic::reset_cofactor_cache() {
for (auto& kv : m_cofactor_cache)
dealloc(kv.m_value);
m_cofactor_cache.reset();
}
void seq_monadic::live_states(expr* R, ptr_vector<expr>& out, bool& ok) {
@ -89,8 +101,7 @@ void seq_monadic::live_states(expr* R, ptr_vector<expr>& out, bool& ok) {
const unsigned STATE_CAP = 1u << 12;
for (unsigned i = 0; i < states.size(); ++i) {
if (states.size() > STATE_CAP || !m.inc()) { ok = false; return; }
expr_ref_pair_vector cof(m);
derivative_cofactors(states.get(i), cof);
expr_ref_pair_vector const& cof = derivative_cofactors(states.get(i));
for (auto const& [g, t] : cof) {
if (re().is_empty(t)) continue;
unsigned k = intern(t); // MUST precede succ[i] indexing: intern may
@ -195,8 +206,7 @@ lbool seq_monadic::product_nonempty(svector<component> const& comps, expr_ref* w
// per-component cofactor branches (target, guard); pin both, they outlive `cof`.
std::vector<std::vector<std::pair<expr*, expr*>>> branches(n);
for (unsigned i = 0; i < n; ++i) {
expr_ref_pair_vector cof(m);
derivative_cofactors(st[i], cof);
expr_ref_pair_vector const& cof = derivative_cofactors(st[i]);
for (auto const& [g, t] : cof) {
if (re().is_empty(t)) continue;
m_pin.push_back(t);
@ -415,6 +425,7 @@ lbool seq_monadic::decide_dnf(vector<disjunct> const& dnf, obj_map<expr, expr*>*
lbool seq_monadic::solve(expr* term, expr* R, obj_map<expr, expr*>* model) {
m_pin.reset();
reset_cofactor_cache();
m_budget = 200000; // global work budget: bail fast on DNF explosion
m_giveup = false;
vector<disjunct> dnf;
@ -428,6 +439,7 @@ lbool seq_monadic::solve_and(vector<std::pair<expr*, expr*>> const& mems,
if (mems.empty())
return l_undef;
m_pin.reset();
reset_cofactor_cache();
m_budget = 200000;
m_giveup = false;
// Multiply the per-membership DNFs: combined = { d ++ e : d in combined, e in dnf_i }.