path: root/src/theory/arrays/theory_arrays_rewriter.cpp

/******************************************************************************
 * Top contributors (to current version):
 *   Morgan Deters
 *
 * 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.
 * ****************************************************************************
 *
 * [[ Add one-line brief description here ]]
 *
 * [[ Add lengthier description here ]]
 * \todo document this file
 */

#include "theory/arrays/theory_arrays_rewriter.h"

#include "expr/array_store_all.h"
#include "expr/attribute.h"
#include "util/cardinality.h"

namespace cvc5 {
namespace theory {
namespace arrays {

namespace attr {
  struct ArrayConstantMostFrequentValueTag { };
  struct ArrayConstantMostFrequentValueCountTag { };
  }  // namespace attr

typedef expr::Attribute<attr::ArrayConstantMostFrequentValueCountTag, uint64_t> ArrayConstantMostFrequentValueCountAttr;
typedef expr::Attribute<attr::ArrayConstantMostFrequentValueTag, Node> ArrayConstantMostFrequentValueAttr;

Node getMostFrequentValue(TNode store) {
  return store.getAttribute(ArrayConstantMostFrequentValueAttr());
}
uint64_t getMostFrequentValueCount(TNode store) {
  return store.getAttribute(ArrayConstantMostFrequentValueCountAttr());
}

void setMostFrequentValue(TNode store, TNode value) {
  return store.setAttribute(ArrayConstantMostFrequentValueAttr(), value);
}
void setMostFrequentValueCount(TNode store, uint64_t count) {
  return store.setAttribute(ArrayConstantMostFrequentValueCountAttr(), count);
}

Node TheoryArraysRewriter::normalizeConstant(TNode node)
{
  return normalizeConstant(node, node[1].getType().getCardinality());
}

// this function is called by printers when using the option "--model-u-dt-enum"
Node TheoryArraysRewriter::normalizeConstant(TNode node, Cardinality indexCard)
{
  TNode store = node[0];
  TNode index = node[1];
  TNode value = node[2];

  std::vector<TNode> indices;
  std::vector<TNode> elements;

  // Normal form for nested stores is just ordering by index - but also need
  // to check if we are writing to default value

  // Go through nested stores looking for where to insert index
  // Also check whether we are replacing an existing store
  TNode replacedValue;
  uint32_t depth = 1;
  uint32_t valCount = 1;
  while (store.getKind() == kind::STORE)
  {
    if (index == store[1])
    {
      replacedValue = store[2];
      store = store[0];
      break;
    }
    else if (index >= store[1])
    {
      break;
    }
    if (value == store[2])
    {
      valCount += 1;
    }
    depth += 1;
    indices.push_back(store[1]);
    elements.push_back(store[2]);
    store = store[0];
  }
  Node n = store;

  // Get the default value at the bottom of the nested stores
  while (store.getKind() == kind::STORE)
  {
    if (value == store[2])
    {
      valCount += 1;
    }
    depth += 1;
    store = store[0];
  }
  Assert(store.getKind() == kind::STORE_ALL);
  ArrayStoreAll storeAll = store.getConst<ArrayStoreAll>();
  Node defaultValue = storeAll.getValue();
  NodeManager* nm = NodeManager::currentNM();

  // Check if we are writing to default value - if so the store
  // to index can be ignored
  if (value == defaultValue)
  {
    if (replacedValue.isNull())
    {
      // Quick exit - if writing to default value and nothing was
      // replaced, we can just return node[0]
      return node[0];
    }
    // else rebuild the store without the replaced write and then exit
  }
  else
  {
    n = nm->mkNode(kind::STORE, n, index, value);
  }

  // Build the rest of the store after inserting/deleting
  while (!indices.empty())
  {
    n = nm->mkNode(kind::STORE, n, indices.back(), elements.back());
    indices.pop_back();
    elements.pop_back();
  }

  // Ready to exit if write was to the default value (see previous comment)
  if (value == defaultValue)
  {
    return n;
  }

  if (indexCard.isInfinite())
  {
    return n;
  }

  // When index sort is finite, we have to check whether there is any value
  // that is written to more than the default value.  If so, it must become
  // the new default value

  TNode mostFrequentValue;
  uint32_t mostFrequentValueCount = 0;
  store = node[0];
  if (store.getKind() == kind::STORE)
  {
    mostFrequentValue = getMostFrequentValue(store);
    mostFrequentValueCount = getMostFrequentValueCount(store);
  }

  // Compute the most frequently written value for n
  if (valCount > mostFrequentValueCount
      || (valCount == mostFrequentValueCount && value < mostFrequentValue))
  {
    mostFrequentValue = value;
    mostFrequentValueCount = valCount;
  }

  // Need to make sure the default value count is larger, or the same and the
  // default value is expression-order-less-than nextValue
  Cardinality::CardinalityComparison compare =
      indexCard.compare(mostFrequentValueCount + depth);
  Assert(compare != Cardinality::UNKNOWN);
  if (compare == Cardinality::GREATER
      || (compare == Cardinality::EQUAL && (defaultValue < mostFrequentValue)))
  {
    return n;
  }

  // Bad case: have to recompute value counts and/or possibly switch out
  // default value
  store = n;
  std::unordered_set<TNode> indexSet;
  std::unordered_map<TNode, uint32_t> elementsMap;
  std::unordered_map<TNode, uint32_t>::iterator it;
  uint32_t count;
  uint32_t max = 0;
  TNode maxValue;
  while (store.getKind() == kind::STORE)
  {
    indices.push_back(store[1]);
    indexSet.insert(store[1]);
    elements.push_back(store[2]);
    it = elementsMap.find(store[2]);
    if (it != elementsMap.end())
    {
      (*it).second = (*it).second + 1;
      count = (*it).second;
    }
    else
    {
      elementsMap[store[2]] = 1;
      count = 1;
    }
    if (count > max || (count == max && store[2] < maxValue))
    {
      max = count;
      maxValue = store[2];
    }
    store = store[0];
  }

  Assert(depth == indices.size());
  compare = indexCard.compare(max + depth);
  Assert(compare != Cardinality::UNKNOWN);
  if (compare == Cardinality::GREATER
      || (compare == Cardinality::EQUAL && (defaultValue < maxValue)))
  {
    Assert(!replacedValue.isNull() && mostFrequentValue == replacedValue);
    return n;
  }

  // Out of luck: have to swap out default value

  // Enumerate values from index type into newIndices and sort
  std::vector<Node> newIndices;
  TypeEnumerator te(index.getType());
  bool needToSort = false;
  uint32_t numTe = 0;
  while (!te.isFinished()
         && (!indexCard.isFinite()
             || numTe < indexCard.getFiniteCardinality().toUnsignedInt()))
  {
    if (indexSet.find(*te) == indexSet.end())
    {
      if (!newIndices.empty() && (!(newIndices.back() < (*te))))
      {
        needToSort = true;
      }
      newIndices.push_back(*te);
    }
    ++numTe;
    ++te;
  }
  Assert(indexCard.compare(newIndices.size() + depth) == Cardinality::EQUAL);
  if (needToSort)
  {
    std::sort(newIndices.begin(), newIndices.end());
  }

  n = nm->mkConst(ArrayStoreAll(node.getType(), maxValue));
  std::vector<Node>::iterator itNew = newIndices.begin(),
                              it_end = newIndices.end();
  while (itNew != it_end || !indices.empty())
  {
    if (itNew != it_end && (indices.empty() || (*itNew) < indices.back()))
    {
      n = nm->mkNode(kind::STORE, n, (*itNew), defaultValue);
      ++itNew;
    }
    else if (itNew == it_end || indices.back() < (*itNew))
    {
      if (elements.back() != maxValue)
      {
        n = nm->mkNode(kind::STORE, n, indices.back(), elements.back());
      }
      indices.pop_back();
      elements.pop_back();
    }
  }
  return n;
}

RewriteResponse TheoryArraysRewriter::postRewrite(TNode node)
{
  Trace("arrays-postrewrite")
      << "Arrays::postRewrite start " << node << std::endl;
  switch (node.getKind())
  {
    case kind::SELECT:
    {
      TNode store = node[0];
      TNode index = node[1];
      Node n;
      bool val;
      while (store.getKind() == kind::STORE)
      {
        if (index == store[1])
        {
          val = true;
        }
        else if (index.isConst() && store[1].isConst())
        {
          val = false;
        }
        else
        {
          n = Rewriter::rewrite(mkEqNode(store[1], index));
          if (n.getKind() != kind::CONST_BOOLEAN)
          {
            break;
          }
          val = n.getConst<bool>();
        }
        if (val)
        {
          // select(store(a,i,v),j) = v if i = j
          Trace("arrays-postrewrite")
              << "Arrays::postRewrite returning " << store[2] << std::endl;
          return RewriteResponse(REWRITE_DONE, store[2]);
        }
        // select(store(a,i,v),j) = select(a,j) if i /= j
        store = store[0];
      }
      if (store.getKind() == kind::STORE_ALL)
      {
        // select(store_all(v),i) = v
        ArrayStoreAll storeAll = store.getConst<ArrayStoreAll>();
        n = storeAll.getValue();
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning " << n << std::endl;
        Assert(n.isConst());
        return RewriteResponse(REWRITE_DONE, n);
      }
      else if (store != node[0])
      {
        n = NodeManager::currentNM()->mkNode(kind::SELECT, store, index);
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning " << n << std::endl;
        return RewriteResponse(REWRITE_DONE, n);
      }
      break;
    }
    case kind::STORE:
    {
      TNode store = node[0];
      TNode value = node[2];
      // store(a,i,select(a,i)) = a
      if (value.getKind() == kind::SELECT && value[0] == store
          && value[1] == node[1])
      {
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning " << store << std::endl;
        return RewriteResponse(REWRITE_DONE, store);
      }
      TNode index = node[1];
      if (store.isConst() && index.isConst() && value.isConst())
      {
        // normalize constant
        Node n = normalizeConstant(node);
        Assert(n.isConst());
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning " << n << std::endl;
        return RewriteResponse(REWRITE_DONE, n);
      }
      if (store.getKind() == kind::STORE)
      {
        // store(store(a,i,v),j,w)
        bool val;
        if (index == store[1])
        {
          val = true;
        }
        else if (index.isConst() && store[1].isConst())
        {
          val = false;
        }
        else
        {
          Node eqRewritten = Rewriter::rewrite(mkEqNode(store[1], index));
          if (eqRewritten.getKind() != kind::CONST_BOOLEAN)
          {
            Trace("arrays-postrewrite")
                << "Arrays::postRewrite returning " << node << std::endl;
            return RewriteResponse(REWRITE_DONE, node);
          }
          val = eqRewritten.getConst<bool>();
        }
        NodeManager* nm = NodeManager::currentNM();
        if (val)
        {
          // store(store(a,i,v),i,w) = store(a,i,w)
          Node result = nm->mkNode(kind::STORE, store[0], index, value);
          Trace("arrays-postrewrite")
              << "Arrays::postRewrite returning " << result << std::endl;
          return RewriteResponse(REWRITE_AGAIN, result);
        }
        else if (index < store[1])
        {
          // store(store(a,i,v),j,w) = store(store(a,j,w),i,v)
          //    IF i != j and j comes before i in the ordering
          std::vector<TNode> indices;
          std::vector<TNode> elements;
          indices.push_back(store[1]);
          elements.push_back(store[2]);
          store = store[0];
          Node n;
          while (store.getKind() == kind::STORE)
          {
            if (index == store[1])
            {
              val = true;
            }
            else if (index.isConst() && store[1].isConst())
            {
              val = false;
            }
            else
            {
              n = Rewriter::rewrite(mkEqNode(store[1], index));
              if (n.getKind() != kind::CONST_BOOLEAN)
              {
                break;
              }
              val = n.getConst<bool>();
            }
            if (val)
            {
              store = store[0];
              break;
            }
            else if (!(index < store[1]))
            {
              break;
            }
            indices.push_back(store[1]);
            elements.push_back(store[2]);
            store = store[0];
          }
          if (value.getKind() == kind::SELECT && value[0] == store
              && value[1] == index)
          {
            n = store;
          }
          else
          {
            n = nm->mkNode(kind::STORE, store, index, value);
          }
          while (!indices.empty())
          {
            n = nm->mkNode(kind::STORE, n, indices.back(), elements.back());
            indices.pop_back();
            elements.pop_back();
          }
          Assert(n != node);
          Trace("arrays-postrewrite")
              << "Arrays::postRewrite returning " << n << std::endl;
          return RewriteResponse(REWRITE_AGAIN, n);
        }
      }
      break;
    }
    case kind::EQUAL:
    {
      if (node[0] == node[1])
      {
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning true" << std::endl;
        return RewriteResponse(REWRITE_DONE,
                               NodeManager::currentNM()->mkConst(true));
      }
      else if (node[0].isConst() && node[1].isConst())
      {
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning false" << std::endl;
        return RewriteResponse(REWRITE_DONE,
                               NodeManager::currentNM()->mkConst(false));
      }
      if (node[0] > node[1])
      {
        Node newNode =
            NodeManager::currentNM()->mkNode(node.getKind(), node[1], node[0]);
        Trace("arrays-postrewrite")
            << "Arrays::postRewrite returning " << newNode << std::endl;
        return RewriteResponse(REWRITE_DONE, newNode);
      }
      break;
    }
    default: break;
  }
  Trace("arrays-postrewrite")
      << "Arrays::postRewrite returning " << node << std::endl;
  return RewriteResponse(REWRITE_DONE, node);
}

RewriteResponse TheoryArraysRewriter::preRewrite(TNode node)
{
  Trace("arrays-prerewrite")
      << "Arrays::preRewrite start " << node << std::endl;
  switch (node.getKind())
  {
    case kind::SELECT:
    {
      TNode store = node[0];
      TNode index = node[1];
      Node n;
      bool val;
      while (store.getKind() == kind::STORE)
      {
        if (index == store[1])
        {
          val = true;
        }
        else if (index.isConst() && store[1].isConst())
        {
          val = false;
        }
        else
        {
          n = Rewriter::rewrite(mkEqNode(store[1], index));
          if (n.getKind() != kind::CONST_BOOLEAN)
          {
            break;
          }
          val = n.getConst<bool>();
        }
        if (val)
        {
          // select(store(a,i,v),j) = v if i = j
          Trace("arrays-prerewrite")
              << "Arrays::preRewrite returning " << store[2] << std::endl;
          return RewriteResponse(REWRITE_AGAIN, store[2]);
        }
        // select(store(a,i,v),j) = select(a,j) if i /= j
        store = store[0];
      }
      if (store.getKind() == kind::STORE_ALL)
      {
        // select(store_all(v),i) = v
        ArrayStoreAll storeAll = store.getConst<ArrayStoreAll>();
        n = storeAll.getValue();
        Trace("arrays-prerewrite")
            << "Arrays::preRewrite returning " << n << std::endl;
        Assert(n.isConst());
        return RewriteResponse(REWRITE_DONE, n);
      }
      else if (store != node[0])
      {
        n = NodeManager::currentNM()->mkNode(kind::SELECT, store, index);
        Trace("arrays-prerewrite")
            << "Arrays::preRewrite returning " << n << std::endl;
        return RewriteResponse(REWRITE_DONE, n);
      }
      break;
    }
    case kind::STORE:
    {
      TNode store = node[0];
      TNode value = node[2];
      // store(a,i,select(a,i)) = a
      if (value.getKind() == kind::SELECT && value[0] == store
          && value[1] == node[1])
      {
        Trace("arrays-prerewrite")
            << "Arrays::preRewrite returning " << store << std::endl;
        return RewriteResponse(REWRITE_AGAIN, store);
      }
      if (store.getKind() == kind::STORE)
      {
        // store(store(a,i,v),j,w)
        TNode index = node[1];
        bool val;
        if (index == store[1])
        {
          val = true;
        }
        else if (index.isConst() && store[1].isConst())
        {
          val = false;
        }
        else
        {
          Node eqRewritten = Rewriter::rewrite(mkEqNode(store[1], index));
          if (eqRewritten.getKind() != kind::CONST_BOOLEAN)
          {
            break;
          }
          val = eqRewritten.getConst<bool>();
        }
        NodeManager* nm = NodeManager::currentNM();
        if (val)
        {
          // store(store(a,i,v),i,w) = store(a,i,w)
          Node newNode = nm->mkNode(kind::STORE, store[0], index, value);
          Trace("arrays-prerewrite")
              << "Arrays::preRewrite returning " << newNode << std::endl;
          return RewriteResponse(REWRITE_DONE, newNode);
        }
      }
      break;
    }
    case kind::EQUAL:
    {
      if (node[0] == node[1])
      {
        Trace("arrays-prerewrite")
            << "Arrays::preRewrite returning true" << std::endl;
        return RewriteResponse(REWRITE_DONE,
                               NodeManager::currentNM()->mkConst(true));
      }
      break;
    }
    default: break;
  }

  Trace("arrays-prerewrite")
      << "Arrays::preRewrite returning " << node << std::endl;
  return RewriteResponse(REWRITE_DONE, node);
}

TrustNode TheoryArraysRewriter::expandDefinition(Node node)
{
  NodeManager* nm = NodeManager::currentNM();
  Kind kind = node.getKind();

  /* Expand
   *
   *   (eqrange a b i j)
   *
   * to
   *
   *  forall k . i <= k <= j => a[k] = b[k]
   *
   */
  if (kind == kind::EQ_RANGE)
  {
    TNode a = node[0];
    TNode b = node[1];
    TNode i = node[2];
    TNode j = node[3];
    Node k = nm->mkBoundVar(i.getType());
    Node bvl = nm->mkNode(kind::BOUND_VAR_LIST, k);
    TypeNode type = k.getType();

    Kind kle;
    Node range;
    if (type.isBitVector())
    {
      kle = kind::BITVECTOR_ULE;
    }
    else if (type.isFloatingPoint())
    {
      kle = kind::FLOATINGPOINT_LEQ;
    }
    else if (type.isInteger() || type.isReal())
    {
      kle = kind::LEQ;
    }
    else
    {
      Unimplemented() << "Type " << type << " is not supported for predicate "
                      << kind;
    }

    range = nm->mkNode(kind::AND, nm->mkNode(kle, i, k), nm->mkNode(kle, k, j));

    Node eq = nm->mkNode(kind::EQUAL,
                         nm->mkNode(kind::SELECT, a, k),
                         nm->mkNode(kind::SELECT, b, k));
    Node implies = nm->mkNode(kind::IMPLIES, range, eq);
    Node ret = nm->mkNode(kind::FORALL, bvl, implies);
    return TrustNode::mkTrustRewrite(node, ret, nullptr);
  }
  return TrustNode::null();
}

}  // namespace arrays
}  // namespace theory
}  // namespace cvc5