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/********************* */
/*! \file bv_ackermann.cpp
** \verbatim
** Top contributors (to current version):
** Aina Niemetz
** This file is part of the CVC4 project.
** Copyright (c) 2009-2017 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 Ackermannization preprocessing pass.
**
** This implements the Ackermannization preprocessing pass, which enables
** very limited theory combination support for eager bit-blasting via
** Ackermannization. It reduces constraints over the combination of the
** theories of fixed-size bit-vectors and uninterpreted functions as
** described in
** Liana Hadarean, An Efficient and Trustworthy Theory Solver for
** Bit-vectors in Satisfiability Modulo Theories.
** https://cs.nyu.edu/media/publications/hadarean_liana.pdf
**/
#include "preprocessing/passes/bv_ackermann.h"
#include "expr/node.h"
#include "options/bv_options.h"
#include "theory/bv/theory_bv_utils.h"
#include <unordered_set>
using namespace CVC4;
using namespace CVC4::theory;
namespace CVC4 {
namespace preprocessing {
namespace passes {
/* -------------------------------------------------------------------------- */
namespace
{
void storeFunction(
TNode func,
TNode term,
FunctionToArgsMap& fun_to_args,
SubstitutionMap& fun_to_skolem)
{
if (fun_to_args.find(func) == fun_to_args.end())
{
fun_to_args.insert(make_pair(func, NodeSet()));
}
NodeSet& set = fun_to_args[func];
if (set.find(term) == set.end())
{
set.insert(term);
Node skolem = bv::utils::mkVar(bv::utils::getSize(term));
fun_to_skolem.addSubstitution(term, skolem);
}
}
void collectFunctionSymbols(
TNode term,
FunctionToArgsMap& fun_to_args,
SubstitutionMap& fun_to_skolem,
std::unordered_set<TNode, TNodeHashFunction>& seen)
{
if (seen.find(term) != seen.end()) return;
if (term.getKind() == kind::APPLY_UF)
{
storeFunction(term.getOperator(), term, fun_to_args, fun_to_skolem);
}
else if (term.getKind() == kind::SELECT)
{
storeFunction(term[0], term, fun_to_args, fun_to_skolem);
}
else
{
AlwaysAssert(term.getKind() != kind::STORE,
"Cannot use eager bitblasting on QF_ABV formula with stores");
}
for (const TNode& n : term)
{
collectFunctionSymbols(n, fun_to_args, fun_to_skolem, seen);
}
seen.insert(term);
}
} // namespace
/* -------------------------------------------------------------------------- */
BVAckermann::BVAckermann(PreprocessingPassContext* preprocContext)
: PreprocessingPass(preprocContext, "bv-ackermann"),
d_funcToSkolem(preprocContext->getUserContext())
{
}
PreprocessingPassResult BVAckermann::applyInternal(
AssertionPipeline* assertionsToPreprocess)
{
Assert(options::bitblastMode() == theory::bv::BITBLAST_MODE_EAGER);
AlwaysAssert(!options::incrementalSolving());
std::unordered_set<TNode, TNodeHashFunction> seen;
for (const Node& a : assertionsToPreprocess->ref())
{
collectFunctionSymbols(a, d_funcToArgs, d_funcToSkolem, seen);
}
NodeManager* nm = NodeManager::currentNM();
for (const auto& p : d_funcToArgs)
{
TNode func = p.first;
const NodeSet& args = p.second;
NodeSet::const_iterator it1 = args.begin();
for (; it1 != args.end(); ++it1)
{
for (NodeSet::const_iterator it2 = it1; it2 != args.end(); ++it2)
{
TNode args1 = *it1;
TNode args2 = *it2;
Node args_eq;
if (args1.getKind() == kind::APPLY_UF)
{
AlwaysAssert(args1.getKind() == kind::APPLY_UF
&& args1.getOperator() == func);
AlwaysAssert(args2.getKind() == kind::APPLY_UF
&& args2.getOperator() == func);
AlwaysAssert(args1.getNumChildren() == args2.getNumChildren());
std::vector<Node> eqs(args1.getNumChildren());
for (unsigned i = 0, n = args1.getNumChildren(); i < n; ++i)
{
eqs[i] = nm->mkNode(kind::EQUAL, args1[i], args2[i]);
}
args_eq = bv::utils::mkAnd(eqs);
}
else
{
AlwaysAssert(args1.getKind() == kind::SELECT && args1[0] == func);
AlwaysAssert(args2.getKind() == kind::SELECT && args2[0] == func);
AlwaysAssert(args1.getNumChildren() == 2);
AlwaysAssert(args2.getNumChildren() == 2);
args_eq = nm->mkNode(kind::EQUAL, args1[1], args2[1]);
}
Node func_eq = nm->mkNode(kind::EQUAL, args1, args2);
Node lemma = nm->mkNode(kind::IMPLIES, args_eq, func_eq);
assertionsToPreprocess->push_back(lemma);
}
}
}
/* replace applications of UF by skolems */
// FIXME for model building, github issue #1118)
for (unsigned i = 0, size = assertionsToPreprocess->size(); i < size; ++i)
{
assertionsToPreprocess->replace(
i, d_funcToSkolem.apply((*assertionsToPreprocess)[i]));
}
return PreprocessingPassResult::NO_CONFLICT;
}
/* -------------------------------------------------------------------------- */
} // namespace passes
} // namespace preprocessing
} // namespace CVC4
|
