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/********************* */
/*! \file model_blocker.cpp
** \verbatim
** Top contributors (to current version):
** Andrew Reynolds
** This file is part of the CVC4 project.
** Copyright (c) 2009-2018 by the authors listed in the file AUTHORS
** in the top-level source directory) and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief Implementation of utility for blocking models.
**/
#include "smt/model_blocker.h"
#include "expr/node.h"
#include "expr/node_algorithm.h"
#include "theory/quantifiers/term_util.h"
using namespace CVC4::kind;
namespace CVC4 {
Expr ModelBlocker::getModelBlocker(const std::vector<Expr>& assertions,
theory::TheoryModel* m,
BlockModelsMode mode)
{
NodeManager* nm = NodeManager::currentNM();
// convert to nodes
std::vector<Node> tlAsserts;
for (unsigned i = 0, size = assertions.size(); i < size; i++)
{
Node a = Node::fromExpr(assertions[i]);
tlAsserts.push_back(a);
}
Trace("model-blocker") << "Compute model blocker, assertions:" << std::endl;
Node blocker;
if (mode == BLOCK_MODELS_LITERALS) {
// optimization: filter to only top-level disjunctions
unsigned counter = 0;
std::vector<Node> asserts;
while (counter < tlAsserts.size())
{
Node cur = tlAsserts[counter];
counter++;
Node catom = cur.getKind() == NOT ? cur[0] : cur;
bool cpol = cur.getKind() != NOT;
if (catom.getKind() == NOT)
{
tlAsserts.push_back(catom[0]);
}
else if (catom.getKind() == AND && cpol)
{
for (const Node& c : catom)
{
tlAsserts.push_back(c);
}
}
else if (theory::quantifiers::TermUtil::isBoolConnectiveTerm(catom))
{
asserts.push_back(cur);
Trace("model-blocker") << " " << cur << std::endl;
}
}
if (asserts.empty())
{
Node blockTriv = nm->mkConst(false);
Trace("model-blocker") << "...model blocker is (trivially) " << blockTriv
<< std::endl;
return blockTriv.toExpr();
}
Node formula = asserts.size() > 1 ? nm->mkNode(AND, asserts) : asserts[0];
std::unordered_map<TNode, Node, TNodeHashFunction> visited;
std::unordered_map<TNode, Node, TNodeHashFunction> implicant;
std::unordered_map<TNode, Node, TNodeHashFunction>::iterator it;
std::vector<TNode> visit;
TNode cur;
visit.push_back(formula);
do
{
cur = visit.back();
visit.pop_back();
it = visited.find(cur);
Trace("model-blocker-debug") << "Visit : " << cur << std::endl;
if (it == visited.end())
{
visited[cur] = Node::null();
Node catom = cur.getKind() == NOT ? cur[0] : cur;
bool cpol = cur.getKind() != NOT;
// compute the implicant
// impl is a formula that implies cur that is also satisfied by m
Node impl;
if (catom.getKind() == NOT)
{
// double negation
impl = catom[0];
}
else if (catom.getKind() == OR || catom.getKind() == AND)
{
// if disjunctive
if ((catom.getKind() == OR) == cpol)
{
// take the first literal that is satisfied
for (Node n : catom)
{
// rewrite, this ensures that e.g. the propositional value of
// quantified formulas can be queried
n = theory::Rewriter::rewrite(n);
Node vn = Node::fromExpr(m->getValue(n.toExpr()));
Assert(vn.isConst());
if (vn.getConst<bool>() == cpol)
{
impl = cpol ? n : n.negate();
break;
}
}
}
else if (catom.getKind() == OR)
{
// one step NNF
std::vector<Node> children;
for (const Node& cn : catom)
{
children.push_back(cn.negate());
}
impl = nm->mkNode(AND, children);
}
}
else if (catom.getKind() == ITE)
{
Node vcond = Node::fromExpr(m->getValue(cur[0].toExpr()));
Assert(vcond.isConst());
Node cond = cur[0];
Node branch;
if (vcond.getConst<bool>())
{
branch = cur[1];
}
else
{
cond = cond.negate();
branch = cur[2];
}
impl = nm->mkNode(AND, cond, cpol ? branch : branch.negate());
}
else if ((catom.getKind() == EQUAL && catom[0].getType().isBoolean())
|| catom.getKind() == XOR)
{
// based on how the children evaluate in the model
std::vector<Node> children;
for (const Node& cn : catom)
{
Node vn = Node::fromExpr(m->getValue(cn.toExpr()));
Assert(vn.isConst());
children.push_back(vn.getConst<bool>() ? cn : cn.negate());
}
impl = nm->mkNode(AND, children);
}
else
{
// literals justified by themselves
visited[cur] = cur;
Trace("model-blocker-debug") << "...self justified" << std::endl;
}
if (visited[cur].isNull())
{
visit.push_back(cur);
if (impl.isNull())
{
Assert(cur.getKind() == AND);
Trace("model-blocker-debug") << "...recurse" << std::endl;
for (const Node& cn : cur)
{
visit.push_back(cn);
}
}
else
{
Trace("model-blocker-debug") << "...implicant : " << impl << std::endl;
implicant[cur] = impl;
visit.push_back(impl);
}
}
}
else if (it->second.isNull())
{
Node ret = cur;
it = implicant.find(cur);
if (it != implicant.end())
{
Node impl = it->second;
it = visited.find(impl);
Assert(it != visited.end());
Assert(!it->second.isNull());
ret = it->second;
Trace("model-blocker-debug") << "...implicant res: " << ret << std::endl;
}
else
{
bool childChanged = false;
std::vector<Node> children;
// we never recurse to parameterized nodes
Assert(cur.getMetaKind() != metakind::PARAMETERIZED);
for (const Node& cn : cur)
{
it = visited.find(cn);
Assert(it != visited.end());
Assert(!it->second.isNull());
childChanged = childChanged || cn != it->second;
children.push_back(it->second);
}
if (childChanged)
{
ret = nm->mkNode(cur.getKind(), children);
}
Trace("model-blocker-debug") << "...recons res: " << ret << std::endl;
}
visited[cur] = ret;
}
} while (!visit.empty());
Assert(visited.find(formula) != visited.end());
Assert(!visited.find(formula)->second.isNull());
blocker = visited[formula].negate();
} else {
Assert(mode == BLOCK_MODELS_VALUES);
std::unordered_set<Node, NodeHashFunction> symbols;
for (Node n: tlAsserts) {
expr::getSymbols(n, symbols);
}
std::vector<Node> blockers;
for (Node s : symbols) {
if (s.getType().getKind() != kind::FUNCTION_TYPE) {
Node v = m->getValue(s);
Node a = nm->mkNode(DISTINCT, s, v);
blockers.push_back(a);
}
}
if (blockers.size() == 0) {
blocker = nm->mkConst<bool>(true);
} else if (blockers.size() == 1) {
blocker = blockers[0];
} else {
blocker = nm->mkNode(OR, blockers);
}
}
Trace("model-blocker") << "...model blocker is " << blocker << std::endl;
return blocker.toExpr();
}
} /* namespace CVC4 */
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