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code cleanup, add comments

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This commit is contained in:
Nikolaj Bjorner 2024-12-30 08:51:41 -08:00
parent 322dcec531
commit bcf66f214f
2 changed files with 96 additions and 62 deletions
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156
src/ast/sls/sls_bv_lookahead.cpp
View file

@ -33,11 +33,23 @@ namespace sls {
m(ev.m) {
}
/**
* Main entry point. The lookahead solver is invoked periodically
* before any other propagation with the main BV solver.
*/
void bv_lookahead::start_propagation() {
if (m_stats.m_num_propagations++ % m_config.propagation_base == 0)
search();
}
/**
* Main search loop.
* - Selects candidate variables
* - Applies random moves with a small probability
* - Applies guided moves to reduce cost of false literals
* - Applies random updates if no progress is made
*/
void bv_lookahead::search() {
updt_params(ctx.get_params());
rescore();
@ -53,36 +65,87 @@ namespace sls {
if (vars.empty())
return;
// random walk with probability 1024/wp
// random walk
if (ctx.rand(2047) < m_config.wp && apply_random_move(vars))
continue;
// guided moves, greedily reducing cost of false literals
if (apply_guided_move(vars))
continue;
// bail out if no progress, and try random update
if (apply_random_update(get_candidate_uninterp()))
recalibrate_weights();
}
m_config.max_moves_base += 100;
}
/**
* guided move: apply lookahead search for the selected variables
* and possible moves
*/
bool bv_lookahead::apply_guided_move(ptr_vector<expr> const& vars) {
m_best_expr = nullptr;
m_best_score = m_top_score;
unsigned sz = vars.size();
unsigned start = ctx.rand(sz);
unsigned start = ctx.rand();
for (unsigned i = 0; i < sz; ++i)
add_updates(vars[(start + i) % sz]);
TRACE("bv", tout << "guided update " << m_best_score << " " << (m_best_expr?"no update":"") << "\n";);
CTRACE("bv", !m_best_expr, tout << "no guided move\n";);
if (!m_best_expr)
return false;
apply_update(m_best_expr, m_best_value);
//verbose_stream() << "increasing move " << mk_bounded_pp(m_best_expr, m)
// << " := " << m_best_value << " score: " << m_top_score << "\n";
apply_update(m_best_expr, m_best_value, "increasing move");
return true;
}
/**
* random update: select a variable at random and set bits to random values
*/
bool bv_lookahead::apply_random_update(ptr_vector<expr> const& vars) {
expr* e = vars[ctx.rand(vars.size())];
auto& v = wval(e);
m_v_updated.set_bw(v.bw);
v.get_variant(m_v_updated, m_ev.m_rand);
if (!v.can_set(m_v_updated))
return false;
apply_update(e, m_v_updated, "random update");
return true;
}
/**
* random move: select a variable at random and use one of the moves: flip, add1, sub1
*/
bool bv_lookahead::apply_random_move(ptr_vector<expr> const& vars) {
expr* e = vars[ctx.rand(vars.size())];
auto& v = wval(e);
m_v_updated.set_bw(v.bw);
v.bits().copy_to(v.nw, m_v_updated);
switch (ctx.rand(3)) {
case 0: {
// flip a random bit
auto bit = ctx.rand(v.bw);
m_v_updated.set(bit, !m_v_updated.get(bit));
break;
}
case 1:
v.add1(m_v_updated);
break;
default:
v.sub1(m_v_updated);
break;
}
if (!v.can_set(m_v_updated))
return false;
apply_update(e, m_v_updated, "random move");
return true;
}
/**
* Retrieve a candidate top-level predicate that is false, give preference to
* those with high score, but back off if they are frequently chosen.
*/
ptr_vector<expr> const& bv_lookahead::get_candidate_uninterp() {
auto const& lits = ctx.root_literals();
app* e = nullptr;
@ -93,8 +156,8 @@ namespace sls {
continue;
auto a = to_app(ctx.atom(lit.var()));
auto score = old_score(a);
auto q = score
+ m_config.ucb_constant * sqrt(log((double)m_touched) / get_touched(a))
auto q = score
+ m_config.ucb_constant * sqrt(log((double)m_touched) / get_touched(a))
+ m_config.ucb_noise * ctx.rand(512);
if (q > max)
max = q, e = a;
@ -121,47 +184,6 @@ namespace sls {
return vars;
}
bool bv_lookahead::apply_random_update(ptr_vector<expr> const& vars) {
expr* e = vars[ctx.rand(vars.size())];
auto& v = wval(e);
m_v_updated.set_bw(v.bw);
v.get_variant(m_v_updated, m_ev.m_rand);
if (!v.can_set(m_v_updated))
return false;
apply_update(e, m_v_updated);
//verbose_stream() << "random update " << mk_bounded_pp(e, m) << " := " << m_v_updated << " score " << m_top_score << "\n";
return true;
}
bool bv_lookahead::apply_random_move(ptr_vector<expr> const& vars) {
expr* e = vars[ctx.rand(vars.size())];
auto& v = wval(e);
m_v_updated.set_bw(v.bw);
v.bits().copy_to(v.nw, m_v_updated);
switch (ctx.rand(3)) {
case 0: {
// flip a random bit
auto bit = ctx.rand(v.bw);
m_v_updated.set(bit, !m_v_updated.get(bit));
break;
}
case 1:
v.add1(m_v_updated);
break;
default:
v.sub1(m_v_updated);
break;
}
if (!v.can_set(m_v_updated))
return false;
apply_update(e, m_v_updated);
TRACE("bv", tout << "random move " << mk_bounded_pp(e, m) << " := " << m_v_updated << "\n";);
// verbose_stream() << "random move " << mk_bounded_pp(e, m) << " := " << m_v_updated << " score " << m_top_score << "\n";
return true;
}
void bv_lookahead::check_restart() {
if (m_stats.m_moves % m_config.restart_base == 0) {
@ -183,6 +205,9 @@ namespace sls {
rescore();
}
/**
* Reset variables that occur in false literals.
*/
void bv_lookahead::reset_uninterp_in_false_literals() {
auto const& lits = ctx.root_literals();
expr_mark marked;
@ -199,7 +224,7 @@ namespace sls {
m_v_updated.set_bw(v.bw);
m_v_updated.set_zero();
if (v.can_set(m_v_updated)) {
apply_update(e, m_v_updated);
apply_update(e, m_v_updated, "reset");
}
}
}
@ -225,7 +250,6 @@ namespace sls {
void bv_lookahead::updt_params(params_ref const& _p) {
sls_params p(_p);
m_config.walksat = p.walksat();
m_config.walksat_repick = p.walksat_repick();
m_config.paws_sp = p.paws_sp();
@ -236,18 +260,21 @@ namespace sls {
m_config.restart_init = p.restart_init();
m_config.early_prune = p.early_prune();
m_config.ucb = p.walksat_ucb();
m_config.ucb_constant = p.walksat_ucb_constant();
m_config.ucb_forget = p.walksat_ucb_forget();
m_config.ucb_init = p.walksat_ucb_init();
m_config.ucb_noise = p.walksat_ucb_noise();
}
/**
* Score of a predicate based on how close the current
* solution is to satisfying it. The proximity measure is
* based on hamming distance for equalities, and differences
* for inequalities.
*/
double bv_lookahead::new_score(app* a) {
bool is_true = ctx.is_true(a);
bool is_true_new = m_ev.bval1(a);
if (!ctx.is_relevant(a))
return 0;
if (is_true == is_true_new)
return 1;
expr* x, * y;
@ -327,6 +354,10 @@ namespace sls {
return 0;
}
/**
* Rehearse an update. The update is revered while a score is computed and returned.
* Walk all parents, until hitting predicates where their scores are computed.
*/
double bv_lookahead::lookahead_update(expr* e, bvect const& new_value) {
SASSERT(bv.is_bv(e));
SASSERT(is_uninterp(e));
@ -441,16 +472,18 @@ namespace sls {
try_set(u, m_v_updated);
}
void bv_lookahead::apply_update(expr* e, bvect const& new_value) {
TRACE("bv", tout << "apply " << mk_bounded_pp(e, m) << " new value " << new_value << "\n");
/**
* Apply an update to a variable.
* The update is committed.
*/
void bv_lookahead::apply_update(expr* e, bvect const& new_value, char const* reason) {
SASSERT(bv.is_bv(e));
SASSERT(is_uninterp(e));
SASSERT(m_restore.empty());
wval(e).eval = new_value;
double old_top_score = m_top_score;
//verbose_stream() << mk_bounded_pp(e, m) << " := " << new_value << "\n";
VERIFY(wval(e).commit_eval());
insert_update_stack(e);
unsigned max_depth = get_depth(e);
@ -461,7 +494,7 @@ namespace sls {
m_ev.eval(e); // updates wval(e).eval
if (!wval(e).commit_eval()) {
TRACE("bv", tout << "failed to commit " << mk_bounded_pp(e, m) << " " << wval(e) << "\n");
IF_VERBOSE(0, verbose_stream() << "failed to commit " << mk_bounded_pp(e, m) << " " << wval(e) << "\n");
IF_VERBOSE(2, verbose_stream() << "failed to commit " << mk_bounded_pp(e, m) << " " << wval(e) << "\n");
// bv_plugin::is_sat picks up discrepancies
continue;
}
@ -484,8 +517,9 @@ namespace sls {
m_update_stack[depth].reset();
}
m_in_update_stack.reset();
TRACE("bv", tout << mk_bounded_pp(e, m) << " := "
<< new_value << " " << m_top_score << " (" << old_top_score << ")\n");
TRACE("bv", tout << reason << " " << mk_bounded_pp(m_best_expr, m)
<< " := " << new_value
<< " score " << m_top_score << "\n";);
}
bool bv_lookahead::insert_update(expr* e) {

2
src/ast/sls/sls_bv_lookahead.h
View file

@ -108,7 +108,7 @@ namespace sls {
void try_set(expr* u, bvect const& new_value);
void add_updates(expr* u);
void apply_update(expr* e, bvect const& new_value);
void apply_update(expr* e, bvect const& new_value, char const* reason);
bool apply_random_move(ptr_vector<expr> const& vars);
bool apply_guided_move(ptr_vector<expr> const& vars);
bool apply_random_update(ptr_vector<expr> const& vars);