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fixestoconsequences

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2016-09-02 11:00:40 +08:00
parent c746d46d80
commit dc48008d46
3 changed files with 103 additions and 14 deletions
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106
src/smt/smt_consequences.cpp
View file

@ -19,6 +19,7 @@ Revision History:
#include "smt_context.h"
#include "ast_util.h"
#include "datatype_decl_plugin.h"
#include "model_pp.h"
namespace smt {
@ -32,6 +33,15 @@ namespace smt {
return mk_and(premises);
}
//
// The literal lit is assigned at the search level, so it follows from the assumptions.
// We retrieve the set of assumptions it depends on in the set 's'.
// The map m_antecedents contains the association from these literals to the assumptions they depend on.
// We then examine the contents of the literal lit and augment the set of consequences in one of the following cases:
// - e is a propositional atom and it is one of the variables that is to be fixed.
// - e is an equality between a variable and value that is to be fixed.
// - e is a data-type recognizer of a variable that is to be fixed.
//
void context::extract_fixed_consequences(literal lit, obj_map<expr, expr*>& vars, uint_set const& assumptions, expr_ref_vector& conseq) {
ast_manager& m = m_manager;
datatype_util dt(m);
@ -48,6 +58,7 @@ namespace smt {
switch (js.get_kind()) {
case b_justification::CLAUSE: {
clause * cls = js.get_clause();
if (!cls) break;
unsigned num_lits = cls->get_num_literals();
for (unsigned j = 0; j < num_lits; ++j) {
literal lit2 = cls->get_literal(j);
@ -115,6 +126,18 @@ namespace smt {
}
SASSERT(!inconsistent());
}
//
// The assignment stack is assumed consistent.
// For each Boolean variable, we check if there is a literal assigned to the
// opposite value of the reference model, and for non-Boolean variables we
// check if the current state forces the variable to be distinct from the reference value.
//
// For yet to be determined Boolean variables we furthermore force the phase to be opposite
// to the reference value in the attempt to let the sat engine emerge with a model that
// rules out as many non-fixed variables as possible.
//
unsigned context::delete_unfixed(obj_map<expr, expr*>& var2val, expr_ref_vector& unfixed) {
ast_manager& m = m_manager;
@ -158,8 +181,12 @@ namespace smt {
return to_delete.size();
}
#define are_equal(v, k) (e_internalized(k) && e_internalized(v) && get_enode(k)->get_root() == get_enode(v)->get_root())
//
// Extract equalities that are congruent at the search level.
// Add a clause to short-circuit the congruence justifications for
// next rounds.
//
unsigned context::extract_fixed_eqs(obj_map<expr, expr*>& var2val, expr_ref_vector& conseq) {
TRACE("context", tout << "extract fixed consequences\n";);
@ -170,8 +197,7 @@ namespace smt {
for (; it != end; ++it) {
expr* k = it->m_key;
expr* v = it->m_value;
if (!m.is_bool(k) && e_internalized(k) && e_internalized(v) &&
get_enode(k)->get_root() == get_enode(v)->get_root()) {
if (!m.is_bool(k) && are_equal(k, v)) {
literal_vector literals;
m_conflict_resolution->eq2literals(get_enode(v), get_enode(k), literals);
uint_set s;
@ -208,6 +234,7 @@ namespace smt {
expr_ref_vector& unfixed) {
m_antecedents.reset();
pop_to_base_lvl();
lbool is_sat = check(assumptions.size(), assumptions.c_ptr());
if (is_sat != l_true) {
return is_sat;
@ -223,6 +250,7 @@ namespace smt {
expr_ref_vector trail(m);
model_evaluator eval(*mdl.get());
expr_ref val(m);
TRACE("context", model_pp(tout, *mdl););
for (unsigned i = 0; i < vars.size(); ++i) {
eval(vars[i], val);
if (m.is_value(val)) {
@ -249,23 +277,39 @@ namespace smt {
obj_map<expr,expr*>::iterator it = var2val.begin();
expr* e = it->m_key;
expr* val = it->m_value;
push_scope();
TRACE("context", tout << "scope level: " << get_scope_level() << "\n";);
SASSERT(!inconsistent());
//
// The current variable is checked to be a backbone
// We add the negation of the reference assignment to the variable.
// If the variable is a Boolean, it means adding literal that has
// the opposite value of the current reference model.
// If the variable is a non-Boolean, it means adding a disequality.
//
literal lit;
if (m.is_bool(e)) {
lit = literal(get_bool_var(e), m.is_true(val));
}
else {
TRACE("context", tout << mk_pp(e, m) << " " << mk_pp(val, m) << "\n";);
eq = mk_eq_atom(e, val);
internalize_formula(eq, false);
lit = literal(get_bool_var(eq), true);
TRACE("context", tout << mk_pp(e, m) << " " << mk_pp(val, m) << "\n";
display_literal_verbose(tout, lit); tout << "\n";
tout << "Equal: " << are_equal(e, val) << "\n";);
}
mark_as_relevant(lit);
push_scope();
assign(lit, b_justification::mk_axiom(), true);
flet<bool> l(m_searching, true);
//
// We check if the current assignment stack can be extended to a
// satisfying assignment. bounded search may decide to restart,
// in which case it returns l_undef and clears search failure.
//
while (true) {
is_sat = bounded_search();
TRACE("context", tout << "search result: " << is_sat << "\n";);
@ -279,21 +323,41 @@ namespace smt {
}
break;
}
if (is_sat == l_true && get_assignment(lit) == l_true) {
//
// If the state is satisfiable with the current variable assigned to
// a different value from the reference model, it is unfixed.
//
// If it is assigned above the search level we can't conclude anything
// about its value.
// extract_fixed_consequences pops the assignment stack to the search level
// so this sets up the state to retry finding fixed values.
//
// Otherwise, the variable is fixed.
// - it is either assigned at the search level to l_false, or
// - the state is l_false, which means that the variable is fixed by
// the background constraints (and does not depend on assumptions).
//
if (is_sat == l_true && get_assignment(lit) == l_true && is_relevant(lit)) {
var2val.erase(e);
unfixed.push_back(e);
TRACE("context", tout << mk_pp(e, m) << " is unfixed\n";);
SASSERT(!are_equal(e, val));
TRACE("context", tout << mk_pp(e, m) << " is unfixed\n";
display_literal_verbose(tout, lit); tout << "\n";
tout << "relevant: " << is_relevant(lit) << "\n";
display(tout););
}
else if (is_sat == l_true && get_assign_level(lit) > get_search_level()) {
else if (is_sat == l_true && (get_assign_level(lit) > get_search_level() || !is_relevant(lit))) {
TRACE("context", tout << "Retry fixing: " << mk_pp(e, m) << "\n";);
extract_fixed_consequences(num_units, var2val, _assumptions, conseq);
++num_reiterations;
continue;
}
else {
//
// The state can be labeled as inconsistent when the implied consequence does
// not depend on assumptions, then the conflict level sits at the search level
// which causes the conflict resolver to decide that the state is unsat.
//
if (l_false == is_sat) {
SASSERT(inconsistent());
m_conflict = null_b_justification;
@ -305,6 +369,11 @@ namespace smt {
}
++num_iterations;
//
// Check the slow pass: it retrieves an updated model and checks if the
// values in the updated model differ from the values in the reference
// model.
//
bool apply_slow_pass = model_threshold <= num_iterations || num_iterations <= 2;
if (apply_slow_pass && is_sat == l_true) {
num_unfixed += delete_unfixed(var2val, unfixed);
@ -312,11 +381,20 @@ namespace smt {
model_threshold *= 3;
model_threshold /= 2;
}
// repeat until we either have a model with negated literal or
// the literal is implied at base.
//
// Walk the assignment stack at level 1 for learned consequences.
// The current literal should be assigned at the search level unless
// the state is is_sat == l_true and the assignment to lit is l_true.
// This condition is checked above.
//
extract_fixed_consequences(num_units, var2val, _assumptions, conseq);
num_units = assigned_literals().size();
//
// Fixed equalities can be extracted by walking all variables and checking
// if the congruence roots are equal at the search level.
//
if (apply_slow_pass) {
num_fixed_eqs += extract_fixed_eqs(var2val, conseq);
IF_VERBOSE(1, verbose_stream() << "(get-consequences"
@ -338,6 +416,11 @@ namespace smt {
}
TRACE("context", tout << "finishing " << mk_pp(e, m) << "\n";);
SASSERT(!inconsistent());
//
// This becomes unnecessary when the fixed consequence are
// completely extracted.
//
if (var2val.contains(e)) {
TRACE("context", tout << "Fixed value to " << mk_pp(e, m) << " was not processed\n";);
expr_ref fml(m);
@ -348,7 +431,6 @@ namespace smt {
fml = m.mk_implies(antecedent2fml(m_antecedents[lit.var()]), fml);
conseq.push_back(fml);
var2val.erase(e);
SASSERT(get_assignment(lit) == l_false);
}
}
end_search();
@ -356,6 +438,10 @@ namespace smt {
return l_true;
}
//
// Validate, in a slow pass, that the current consequences are correctly
// extracted.
//
void context::validate_consequences(expr_ref_vector const& assumptions, expr_ref_vector const& vars,
expr_ref_vector const& conseq, expr_ref_vector const& unfixed) {
ast_manager& m = m_manager;

9
src/smt/smt_context.cpp
View file

@ -1094,7 +1094,7 @@ namespace smt {
\brief This method is invoked when a new disequality is asserted.
The disequality is propagated to the theories.
*/
void context::add_diseq(enode * n1, enode * n2) {
bool context::add_diseq(enode * n1, enode * n2) {
enode * r1 = n1->get_root();
enode * r2 = n2->get_root();
TRACE("add_diseq", tout << "assigning: #" << n1->get_owner_id() << " != #" << n2->get_owner_id() << "\n";
@ -1111,7 +1111,7 @@ namespace smt {
if (r1 == r2) {
TRACE("add_diseq_inconsistent", tout << "add_diseq #" << n1->get_owner_id() << " #" << n2->get_owner_id() << " inconsistency, scope_lvl: " << m_scope_lvl << "\n";);
return; // context is inconsistent
return false; // context is inconsistent
}
// Propagate disequalities to theories
@ -1145,6 +1145,7 @@ namespace smt {
l1 = l1->get_next();
}
}
return true;
}
/**
@ -1400,7 +1401,9 @@ namespace smt {
}
else {
TRACE("add_diseq", display_eq_detail(tout, bool_var2enode(v)););
add_diseq(get_enode(lhs), get_enode(rhs));
if (!add_diseq(get_enode(lhs), get_enode(rhs)) && !inconsistent()) {
set_conflict(b_justification(mk_justification(eq_propagation_justification(get_enode(lhs), get_enode(rhs)))), ~l);
}
}
}
else if (d.is_theory_atom()) {

2
src/smt/smt_context.h
View file

@ -942,7 +942,7 @@ namespace smt {
push_eq(n1, n2, eq_justification::mk_cg(used_commutativity));
}
void add_diseq(enode * n1, enode * n2);
bool add_diseq(enode * n1, enode * n2);
void assign_quantifier(quantifier * q);