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elaborate on narrow

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-12-15 10:13:33 -08:00
parent 12fe964ea5
commit a6684824c1
4 changed files with 118 additions and 37 deletions
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120
src/math/polysat/op_constraint.cpp
View file

@ -9,6 +9,15 @@ Author:
Jakob Rath, Nikolaj Bjorner (nbjorner) 2021-12-09
Notes:
Additional possible functionality on constraints:
- activate - when operation is first activated. It may be created and only activated later.
- bit-wise assignments - narrow based on bit assignment, not entire word assignment.
- integration with congruence tables
- integration with conflict resolution
--*/
#include "math/polysat/op_constraint.h"
@ -51,7 +60,19 @@ namespace polysat {
default: return false;
}
}
bool op_constraint::is_always_false(bool is_positive) const {
return is_always_false(is_positive, p(), q(), r());
}
bool op_constraint::is_currently_false(assignment_t const& a, bool is_positive) const {
return is_always_false(is_positive, p().subst_val(a), q().subst_val(a), r().subst_val(a));
}
bool op_constraint::is_currently_true(assignment_t const& a, bool is_positive) const {
return is_always_true(is_positive, p().subst_val(a), q().subst_val(a), r().subst_val(a));
}
std::ostream& op_constraint::display(std::ostream& out, lbool status) const {
switch (status) {
case l_true: return display(out);
@ -60,7 +81,7 @@ namespace polysat {
}
}
std::ostream& operator<<(std::ostream & out, op_constraint::code c) {
std::ostream& operator<<(std::ostream& out, op_constraint::code c) {
switch (c) {
case op_constraint::code::ashr_op:
return out << ">>a";
@ -75,29 +96,31 @@ namespace polysat {
case op_constraint::code::xor_op:
return out << "^";
default:
return out << "?";
UNREACHABLE();
return out;
}
return out;
}
std::ostream& op_constraint::display(std::ostream& out) const {
return out << r() << " " << m_op << " " << p() << " << " << q();
if (m_op == code::not_op)
return out << r() << " == ~" << p();
else
return out << r() << " == " << p() << " " << m_op << " " << q();
}
bool op_constraint::is_always_false(bool is_positive) const {
return is_always_false(is_positive, p(), q(), r());
}
bool op_constraint::is_currently_false(assignment_t const& a, bool is_positive) const {
return is_always_false(is_positive, p().subst_val(a), q().subst_val(a), r().subst_val(a));
}
bool op_constraint::is_currently_true(assignment_t const& a, bool is_positive) const {
return is_always_true(is_positive, p().subst_val(a), q().subst_val(a), r().subst_val(a));
}
/**
* Propagate consequences or detect conflicts based on partial assignments.
*
* We can assume that op_constraint is only asserted positive.
*/
void op_constraint::narrow(solver& s, bool is_positive) {
SASSERT(is_positive);
if (is_currently_true(s.assignment(), is_positive))
return;
switch (m_op) {
case code::lshr_op:
narrow_lshr(s);
@ -106,6 +129,10 @@ namespace polysat {
NOT_IMPLEMENTED_YET();
break;
}
if (!s.is_conflict() && is_currently_false(s.assignment(), is_positive)) {
s.set_conflict(signed_constraint(this, is_positive));
return;
}
}
unsigned op_constraint::hash() const {
@ -120,38 +147,61 @@ namespace polysat {
}
/**
* Enforce basic axioms, such as:
* Enforce basic axioms for r == p >> q, such as:
*
* r = p >> q & q >= k -> r[i] = 0 for i > K - k
* r = p >> q & q >= K -> r = 0
* r = p >> q & q = k -> r[i] = p[i+k] for k + i < K
* r = p >> q & q >= k -> r <= 2^{K-k-1}
* r = p >> q => r <= p
* r = p >> q & q != 0 => r < p
* r = p >> q & q = 0 => r = p
* q >= k -> r[i] = 0 for i > K - k
* q >= K -> r = 0
* q = k -> r[i] = p[i+k] for k + i < K
* q >= k -> r <= 2^{K-k-1}
* r <= p
* q != 0 => r <= p
* q = 0 => r = p
*
* when q is a constant, several axioms can be enforced at activation time.
*
* Enforce also inferences and bounds
*
* We can assume that op_constraint is only asserted positive.
*/
void op_constraint::narrow_lshr(solver& s) {
auto pv = p().subst_val(s.assignment());
auto qv = q().subst_val(s.assignment());
auto rv = r().subst_val(s.assignment());
unsigned K = p().manager().power_of_2();
signed_constraint lshl(this, true);
// r <= p
if (pv.is_val() && rv.is_val() && rv.val() > pv.val()) {
s.add_clause(~lshl, s.ule(r(), p()), true);
return;
}
// q >= K -> r = 0
if (qv.is_val() && qv.val() >= K && rv.is_val() && !rv.is_zero()) {
s.add_clause(~lshl, ~s.ule(K, q()), s.eq(r()), true);
return;
}
// q = 0 => r = p
if (qv.is_zero() && pv.is_val() && rv.is_val() && pv != rv) {
s.add_clause(~lshl, ~s.eq(q()), s.eq(p(), r()), true);
return;
}
// q != 0 & p > 0 => r < p
if (qv.is_val() && !qv.is_zero() && pv.is_val() && rv.is_val() && pv <= rv) {
s.add_clause(~lshl, s.eq(q()), s.ule(p, 0), s.ult(r(), p()), true);
return;
}
NOT_IMPLEMENTED_YET();
}
lbool op_constraint::eval_lshr(pdd const& p, pdd const& q, pdd const& r) const {
if (q.is_val() && r.is_val()) {
auto& m = p.manager();
if (q.val() >= m.power_of_2())
return r.is_zero() ? l_true : l_false;
if (p.is_val()) {
pdd rr = p * m.mk_val(rational::power_of_two(q.val().get_unsigned()));
return rr == r ? l_true : l_false;
}
// other cases when we know lower
// bound of q, e.g, q = 2^k*q1 + q2, where q2 is a constant.
}
auto& m = p.manager();
if (p.is_val() && q.is_val() && r.is_val())
return r == p * m.mk_val(rational::power_of_two(q.val().get_unsigned())) ? l_true : l_false;
if (q.is_val() && q.val() >= m.power_of_2() && r.is_val())
return r.is_zero() ? l_true : l_false;
// other cases when we know lower
// bound of q, e.g, q = 2^k*q1 + q2, where q2 is a constant.
return l_undef;
}
}

4
src/math/polysat/op_constraint.h
View file

@ -6,11 +6,11 @@ Module Name:
Op constraint.
lshr: r == p >> q
ashr: r == p >> q
ashr: r == p >>a q
lshl: r == p << q
and: r == p & q
or: r == p | q
neg: r == ~p
not: r == ~p
xor: r == p ^ q
Author:

28
src/math/polysat/solver.cpp
View file

@ -793,6 +793,34 @@ namespace polysat {
add_clause(*clause);
}
void solver::add_clause(signed_constraint c1, signed_constraint c2, signed_constraint c3, bool is_redundant) {
clause_builder cb(*this);
if (!c1.is_always_false())
cb.push(c1);
if (!c2.is_always_false())
cb.push(c2);
if (!c3.is_always_false())
cb.push(c3);
clause_ref clause = cb.build();
clause->set_redundant(is_redundant);
add_clause(*clause);
}
void solver::add_clause(signed_constraint c1, signed_constraint c2, signed_constraint c3, signed_constraint c4, bool is_redundant) {
clause_builder cb(*this);
if (!c1.is_always_false())
cb.push(c1);
if (!c2.is_always_false())
cb.push(c2);
if (!c3.is_always_false())
cb.push(c3);
if (!c4.is_always_false())
cb.push(c4);
clause_ref clause = cb.build();
clause->set_redundant(is_redundant);
add_clause(*clause);
}
void solver::insert_constraint(signed_constraints& cs, signed_constraint c) {
SASSERT(c);
LOG_V("INSERTING: " << c);

3
src/math/polysat/solver.h
View file

@ -56,6 +56,7 @@ namespace polysat {
friend class constraint;
friend class ule_constraint;
friend class mul_ovfl_constraint;
friend class op_constraint;
friend class signed_constraint;
friend class clause;
friend class clause_builder;
@ -207,6 +208,8 @@ namespace polysat {
void backjump(unsigned new_level);
void add_clause(clause& lemma);
void add_clause(signed_constraint c1, signed_constraint c2, bool is_redundant);
void add_clause(signed_constraint c1, signed_constraint c2, signed_constraint c3, bool is_redundant);
void add_clause(signed_constraint c1, signed_constraint c2, signed_constraint c3, signed_constraint c4, bool is_redundant);
signed_constraint lit2cnstr(sat::literal lit) const { return m_constraints.lookup(lit); }