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/******************************************************************************
* Top contributors (to current version):
* Mathias Preiner, Liana Hadarean, Aina Niemetz
*
* This file is part of the cvc5 project.
*
* Copyright (c) 2009-2021 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.
* ****************************************************************************
*
* The BvIntroPow2 preprocessing pass.
*
* Traverses the formula and applies the IsPowerOfTwo rewrite rule. This
* preprocessing pass is particularly useful on QF_BV/pspace benchmarks and
* can be enabled via option `--bv-intro-pow2`.
*/
#include "preprocessing/passes/bv_intro_pow2.h"
#include <unordered_map>
#include "preprocessing/assertion_pipeline.h"
#include "preprocessing/preprocessing_pass_context.h"
#include "theory/bv/theory_bv_utils.h"
namespace cvc5 {
namespace preprocessing {
namespace passes {
using NodeMap = std::unordered_map<Node, Node>;
using namespace cvc5::theory;
BvIntroPow2::BvIntroPow2(PreprocessingPassContext* preprocContext)
: PreprocessingPass(preprocContext, "bv-intro-pow2"){};
PreprocessingPassResult BvIntroPow2::applyInternal(
AssertionPipeline* assertionsToPreprocess)
{
std::unordered_map<Node, Node> cache;
for (size_t i = 0, size = assertionsToPreprocess->size(); i < size; ++i)
{
Node cur = (*assertionsToPreprocess)[i];
Node res = pow2Rewrite(cur, cache);
if (res != cur)
{
res = rewrite(res);
assertionsToPreprocess->replace(i, res);
}
}
return PreprocessingPassResult::NO_CONFLICT;
}
bool BvIntroPow2::isPowerOfTwo(TNode node)
{
if (node.getKind() != kind::EQUAL)
{
return false;
}
if (node[0].getKind() != kind::BITVECTOR_AND
&& node[1].getKind() != kind::BITVECTOR_AND)
{
return false;
}
if (!bv::utils::isZero(node[0]) && !bv::utils::isZero(node[1]))
{
return false;
}
TNode t = !bv::utils::isZero(node[0]) ? node[0] : node[1];
if (t.getNumChildren() != 2) return false;
TNode a = t[0];
TNode b = t[1];
if (bv::utils::getSize(t) < 2) return false;
Node diff =
rewrite(NodeManager::currentNM()->mkNode(kind::BITVECTOR_SUB, a, b));
return (diff.isConst()
&& (bv::utils::isOne(diff) || bv::utils::isOnes(diff)));
}
Node BvIntroPow2::rewritePowerOfTwo(TNode node)
{
NodeManager* nm = NodeManager::currentNM();
TNode term = bv::utils::isZero(node[0]) ? node[1] : node[0];
TNode a = term[0];
TNode b = term[1];
uint32_t size = bv::utils::getSize(term);
Node diff = rewrite(nm->mkNode(kind::BITVECTOR_SUB, a, b));
Assert(diff.isConst());
Node one = bv::utils::mkOne(size);
TNode x = diff == one ? a : b;
Node sk = bv::utils::mkVar(size);
Node sh = nm->mkNode(kind::BITVECTOR_SHL, one, sk);
Node x_eq_sh = nm->mkNode(kind::EQUAL, x, sh);
return x_eq_sh;
}
Node BvIntroPow2::pow2Rewrite(Node node, std::unordered_map<Node, Node>& cache)
{
const auto& ci = cache.find(node);
if (ci != cache.end())
{
Node incache = (*ci).second;
return incache.isNull() ? node : incache;
}
Node res = Node::null();
switch (node.getKind())
{
case kind::AND:
{
bool changed = false;
std::vector<Node> children;
for (unsigned i = 0, size = node.getNumChildren(); i < size; ++i)
{
Node child = node[i];
Node found = pow2Rewrite(child, cache);
changed = changed || (child != found);
children.push_back(found);
}
if (changed)
{
res = NodeManager::currentNM()->mkNode(kind::AND, children);
}
}
break;
case kind::EQUAL:
if (node[0].getType().isBitVector() && isPowerOfTwo(node))
{
res = rewritePowerOfTwo(node);
}
break;
default: break;
}
cache.insert(std::make_pair(node, res));
return res.isNull() ? node : res;
}
} // namespace passes
} // namespace preprocessing
} // namespace cvc5
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