path: root/src/theory/strings/term_registry.cpp

/*********************                                                        */
/*! \file term_registry.cpp
 ** \verbatim
 ** Top contributors (to current version):
 **   Andrew Reynolds, Andres Noetzli, Tianyi Liang
 ** This file is part of the CVC4 project.
 ** Copyright (c) 2009-2020 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 term registry for the theory of strings.
 **/

#include "theory/strings/term_registry.h"

#include "expr/attribute.h"
#include "options/smt_options.h"
#include "options/strings_options.h"
#include "smt/logic_exception.h"
#include "theory/rewriter.h"
#include "theory/strings/theory_strings_utils.h"
#include "theory/strings/word.h"

using namespace std;
using namespace CVC4::context;
using namespace CVC4::kind;

namespace CVC4 {
namespace theory {
namespace strings {

struct StringsProxyVarAttributeId
{
};
typedef expr::Attribute<StringsProxyVarAttributeId, bool>
    StringsProxyVarAttribute;

TermRegistry::TermRegistry(SolverState& s,
                           OutputChannel& out,
                           SequencesStatistics& statistics,
                           ProofNodeManager* pnm)
    : d_state(s),
      d_out(out),
      d_statistics(statistics),
      d_hasStrCode(false),
      d_functionsTerms(s.getSatContext()),
      d_inputVars(s.getUserContext()),
      d_preregisteredTerms(s.getUserContext()),
      d_registeredTerms(s.getUserContext()),
      d_registeredTypes(s.getUserContext()),
      d_proxyVar(s.getUserContext()),
      d_proxyVarToLength(s.getUserContext()),
      d_lengthLemmaTermsCache(s.getUserContext()),
      d_epg(nullptr)
{
  NodeManager* nm = NodeManager::currentNM();
  d_zero = nm->mkConst(Rational(0));
  d_one = nm->mkConst(Rational(1));
  d_negOne = NodeManager::currentNM()->mkConst(Rational(-1));
  d_cardSize = utils::getAlphabetCardinality();
}

TermRegistry::~TermRegistry() {}

Node TermRegistry::eagerReduce(Node t, SkolemCache* sc)
{
  NodeManager* nm = NodeManager::currentNM();
  Node lemma;
  Kind tk = t.getKind();
  if (tk == STRING_TO_CODE)
  {
    // ite( str.len(s)==1, 0 <= str.code(s) < |A|, str.code(s)=-1 )
    Node code_len = utils::mkNLength(t[0]).eqNode(nm->mkConst(Rational(1)));
    Node code_eq_neg1 = t.eqNode(nm->mkConst(Rational(-1)));
    Node code_range = nm->mkNode(
        AND,
        nm->mkNode(GEQ, t, nm->mkConst(Rational(0))),
        nm->mkNode(
            LT, t, nm->mkConst(Rational(utils::getAlphabetCardinality()))));
    lemma = nm->mkNode(ITE, code_len, code_range, code_eq_neg1);
  }
  else if (tk == STRING_STRIDOF)
  {
    // (and (>= (str.indexof x y n) (- 1)) (<= (str.indexof x y n) (str.len
    // x)))
    Node l = utils::mkNLength(t[0]);
    lemma = nm->mkNode(AND,
                       nm->mkNode(GEQ, t, nm->mkConst(Rational(-1))),
                       nm->mkNode(LEQ, t, l));
  }
  else if (tk == STRING_STOI)
  {
    // (>= (str.to_int x) (- 1))
    lemma = nm->mkNode(GEQ, t, nm->mkConst(Rational(-1)));
  }
  else if (tk == STRING_STRCTN)
  {
    // ite( (str.contains s r), (= s (str.++ sk1 r sk2)), (not (= s r)))
    Node sk1 =
        sc->mkSkolemCached(t[0], t[1], SkolemCache::SK_FIRST_CTN_PRE, "sc1");
    Node sk2 =
        sc->mkSkolemCached(t[0], t[1], SkolemCache::SK_FIRST_CTN_POST, "sc2");
    lemma = t[0].eqNode(utils::mkNConcat(sk1, t[1], sk2));
    lemma = nm->mkNode(ITE, t, lemma, t[0].eqNode(t[1]).notNode());
  }
  return lemma;
}

Node TermRegistry::lengthPositive(Node t)
{
  NodeManager* nm = NodeManager::currentNM();
  Node zero = nm->mkConst(Rational(0));
  Node emp = Word::mkEmptyWord(t.getType());
  Node tlen = nm->mkNode(STRING_LENGTH, t);
  Node tlenEqZero = tlen.eqNode(zero);
  Node tEqEmp = t.eqNode(emp);
  Node caseEmpty = nm->mkNode(AND, tlenEqZero, tEqEmp);
  Node caseNEmpty = nm->mkNode(GT, tlen, zero);
  // (or (and (= (str.len t) 0) (= t "")) (> (str.len t) 0))
  return nm->mkNode(OR, caseEmpty, caseNEmpty);
}

void TermRegistry::preRegisterTerm(TNode n)
{
  if (d_preregisteredTerms.find(n) != d_preregisteredTerms.end())
  {
    return;
  }
  eq::EqualityEngine* ee = d_state.getEqualityEngine();
  d_preregisteredTerms.insert(n);
  Trace("strings-preregister")
      << "TheoryString::preregister : " << n << std::endl;
  // check for logic exceptions
  Kind k = n.getKind();
  if (!options::stringExp())
  {
    if (k == STRING_STRIDOF || k == STRING_ITOS || k == STRING_STOI
        || k == STRING_STRREPL || k == STRING_STRREPLALL
        || k == STRING_REPLACE_RE || k == STRING_REPLACE_RE_ALL
        || k == STRING_STRCTN || k == STRING_LEQ || k == STRING_TOLOWER
        || k == STRING_TOUPPER || k == STRING_REV || k == STRING_UPDATE)
    {
      std::stringstream ss;
      ss << "Term of kind " << k
         << " not supported in default mode, try --strings-exp";
      throw LogicException(ss.str());
    }
  }
  if (k == EQUAL)
  {
    if (n[0].getType().isRegExp())
    {
      std::stringstream ss;
      ss << "Equality between regular expressions is not supported";
      throw LogicException(ss.str());
    }
    ee->addTriggerEquality(n);
    return;
  }
  else if (k == STRING_IN_REGEXP)
  {
    d_out.requirePhase(n, true);
    ee->addTriggerPredicate(n);
    ee->addTerm(n[0]);
    ee->addTerm(n[1]);
    return;
  }
  else if (k == STRING_TO_CODE)
  {
    d_hasStrCode = true;
  }
  registerTerm(n, 0);
  TypeNode tn = n.getType();
  if (tn.isRegExp() && n.isVar())
  {
    std::stringstream ss;
    ss << "Regular expression variables are not supported.";
    throw LogicException(ss.str());
  }
  if (tn.isString())  // string-only
  {
    // all characters of constants should fall in the alphabet
    if (n.isConst())
    {
      std::vector<unsigned> vec = n.getConst<String>().getVec();
      for (unsigned u : vec)
      {
        if (u >= d_cardSize)
        {
          std::stringstream ss;
          ss << "Characters in string \"" << n
             << "\" are outside of the given alphabet.";
          throw LogicException(ss.str());
        }
      }
    }
    ee->addTerm(n);
  }
  else if (tn.isBoolean())
  {
    // Get triggered for both equal and dis-equal
    ee->addTriggerPredicate(n);
  }
  else
  {
    // Function applications/predicates
    ee->addTerm(n);
  }
  // Set d_functionsTerms stores all function applications that are
  // relevant to theory combination. Notice that this is a subset of
  // the applications whose kinds are function kinds in the equality
  // engine. This means it does not include applications of operators
  // like re.++, which is not a function kind in the equality engine.
  // Concatenation terms do not need to be considered here because
  // their arguments have string type and do not introduce any shared
  // terms.
  if (n.hasOperator() && ee->isFunctionKind(k) && k != STRING_CONCAT)
  {
    d_functionsTerms.push_back(n);
  }
  if (options::stringFMF())
  {
    if (tn.isStringLike())
    {
      // Our decision strategy will minimize the length of this term if it is a
      // variable but not an internally generated Skolem, or a term that does
      // not belong to this theory.
      if (n.isVar() ? !d_skCache.isSkolem(n)
                    : kindToTheoryId(k) != THEORY_STRINGS)
      {
        d_inputVars.insert(n);
        Trace("strings-preregister") << "input variable: " << n << std::endl;
      }
    }
  }
}

void TermRegistry::registerTerm(Node n, int effort)
{
  TypeNode tn = n.getType();
  bool do_register = true;
  if (!tn.isStringLike())
  {
    if (options::stringEagerLen())
    {
      do_register = effort == 0;
    }
    else
    {
      do_register = effort > 0 || n.getKind() != STRING_CONCAT;
    }
  }
  if (!do_register)
  {
    return;
  }
  if (d_registeredTerms.find(n) != d_registeredTerms.end())
  {
    return;
  }
  d_registeredTerms.insert(n);
  // ensure the type is registered
  registerType(tn);
  Debug("strings-register") << "TheoryStrings::registerTerm() " << n
                            << ", effort = " << effort << std::endl;
  TrustNode regTermLem;
  if (tn.isStringLike())
  {
    // register length information:
    //  for variables, split on empty vs positive length
    //  for concat/const/replace, introduce proxy var and state length relation
    regTermLem = getRegisterTermLemma(n);
  }
  else if (n.getKind() != STRING_STRCTN)
  {
    // we don't send out eager reduction lemma for str.contains currently
    Node eagerRedLemma = eagerReduce(n, &d_skCache);
    if (!eagerRedLemma.isNull())
    {
      // if there was an eager reduction, we make the trust node for it
      if (d_epg != nullptr)
      {
        regTermLem = d_epg->mkTrustNode(
            eagerRedLemma, PfRule::STRING_EAGER_REDUCTION, {n});
      }
      else
      {
        regTermLem = TrustNode::mkTrustLemma(eagerRedLemma, nullptr);
      }
    }
  }
  if (!regTermLem.isNull())
  {
    Trace("strings-lemma") << "Strings::Lemma REG-TERM : " << regTermLem
                           << std::endl;
    Trace("strings-assert")
        << "(assert " << regTermLem.getNode() << ")" << std::endl;
    ++(d_statistics.d_lemmasRegisterTerm);
    d_out.trustedLemma(regTermLem);
  }
}

void TermRegistry::registerType(TypeNode tn)
{
  if (d_registeredTypes.find(tn) != d_registeredTypes.end())
  {
    return;
  }
  d_registeredTypes.insert(tn);
  if (tn.isStringLike())
  {
    // preregister the empty word for the type
    Node emp = Word::mkEmptyWord(tn);
    if (!d_state.hasTerm(emp))
    {
      preRegisterTerm(emp);
    }
  }
}

TrustNode TermRegistry::getRegisterTermLemma(Node n)
{
  Assert(n.getType().isStringLike());
  NodeManager* nm = NodeManager::currentNM();
  // register length information:
  //  for variables, split on empty vs positive length
  //  for concat/const/replace, introduce proxy var and state length relation
  Node lsum;
  if (n.getKind() != STRING_CONCAT && !n.isConst())
  {
    Node lsumb = nm->mkNode(STRING_LENGTH, n);
    lsum = Rewriter::rewrite(lsumb);
    // can register length term if it does not rewrite
    if (lsum == lsumb)
    {
      registerTermAtomic(n, LENGTH_SPLIT);
      return TrustNode::null();
    }
  }
  Node sk = d_skCache.mkSkolemCached(n, SkolemCache::SK_PURIFY, "lsym");
  StringsProxyVarAttribute spva;
  sk.setAttribute(spva, true);
  Node eq = Rewriter::rewrite(sk.eqNode(n));
  d_proxyVar[n] = sk;
  // If we are introducing a proxy for a constant or concat term, we do not
  // need to send lemmas about its length, since its length is already
  // implied.
  if (n.isConst() || n.getKind() == STRING_CONCAT)
  {
    // do not send length lemma for sk.
    registerTermAtomic(sk, LENGTH_IGNORE);
  }
  Node skl = nm->mkNode(STRING_LENGTH, sk);
  if (n.getKind() == STRING_CONCAT)
  {
    std::vector<Node> nodeVec;
    for (const Node& nc : n)
    {
      if (nc.getAttribute(StringsProxyVarAttribute()))
      {
        Assert(d_proxyVarToLength.find(nc) != d_proxyVarToLength.end());
        nodeVec.push_back(d_proxyVarToLength[nc]);
      }
      else
      {
        Node lni = nm->mkNode(STRING_LENGTH, nc);
        nodeVec.push_back(lni);
      }
    }
    lsum = nm->mkNode(PLUS, nodeVec);
    lsum = Rewriter::rewrite(lsum);
  }
  else if (n.isConst())
  {
    lsum = nm->mkConst(Rational(Word::getLength(n)));
  }
  Assert(!lsum.isNull());
  d_proxyVarToLength[sk] = lsum;
  Node ceq = Rewriter::rewrite(skl.eqNode(lsum));

  Node ret = nm->mkNode(AND, eq, ceq);

  // it is a simple rewrite to justify this
  if (d_epg != nullptr)
  {
    return d_epg->mkTrustNode(ret, PfRule::MACRO_SR_PRED_INTRO, {ret});
  }
  return TrustNode::mkTrustLemma(ret, nullptr);
}

void TermRegistry::registerTermAtomic(Node n, LengthStatus s)
{
  if (d_lengthLemmaTermsCache.find(n) != d_lengthLemmaTermsCache.end())
  {
    return;
  }
  d_lengthLemmaTermsCache.insert(n);

  if (s == LENGTH_IGNORE)
  {
    // ignore it
    return;
  }
  std::map<Node, bool> reqPhase;
  TrustNode lenLem = getRegisterTermAtomicLemma(n, s, reqPhase);
  if (!lenLem.isNull())
  {
    Trace("strings-lemma") << "Strings::Lemma REGISTER-TERM-ATOMIC : " << lenLem
                           << std::endl;
    Trace("strings-assert")
        << "(assert " << lenLem.getNode() << ")" << std::endl;
    ++(d_statistics.d_lemmasRegisterTermAtomic);
    d_out.trustedLemma(lenLem);
  }
  for (const std::pair<const Node, bool>& rp : reqPhase)
  {
    d_out.requirePhase(rp.first, rp.second);
  }
}

SkolemCache* TermRegistry::getSkolemCache() { return &d_skCache; }

const context::CDList<TNode>& TermRegistry::getFunctionTerms() const
{
  return d_functionsTerms;
}

const context::CDHashSet<Node, NodeHashFunction>& TermRegistry::getInputVars()
    const
{
  return d_inputVars;
}

bool TermRegistry::hasStringCode() const { return d_hasStrCode; }

TrustNode TermRegistry::getRegisterTermAtomicLemma(
    Node n, LengthStatus s, std::map<Node, bool>& reqPhase)
{
  if (n.isConst())
  {
    // No need to send length for constant terms. This case may be triggered
    // for cases where the skolem cache automatically replaces a skolem by
    // a constant.
    return TrustNode::null();
  }
  Assert(n.getType().isStringLike());
  NodeManager* nm = NodeManager::currentNM();
  Node n_len = nm->mkNode(kind::STRING_LENGTH, n);
  Node emp = Word::mkEmptyWord(n.getType());
  if (s == LENGTH_GEQ_ONE)
  {
    Node neq_empty = n.eqNode(emp).negate();
    Node len_n_gt_z = nm->mkNode(GT, n_len, d_zero);
    Node len_geq_one = nm->mkNode(AND, neq_empty, len_n_gt_z);
    Trace("strings-lemma") << "Strings::Lemma SK-GEQ-ONE : " << len_geq_one
                           << std::endl;
    Trace("strings-assert") << "(assert " << len_geq_one << ")" << std::endl;
    if (options::proofNewPedantic() > 0)
    {
      Unhandled() << "Unhandled lemma Strings::Lemma SK-GEQ-ONE : "
                  << len_geq_one << std::endl;
    }
    return TrustNode::mkTrustLemma(len_geq_one, nullptr);
  }

  if (s == LENGTH_ONE)
  {
    Node len_one = n_len.eqNode(d_one);
    Trace("strings-lemma") << "Strings::Lemma SK-ONE : " << len_one
                           << std::endl;
    Trace("strings-assert") << "(assert " << len_one << ")" << std::endl;
    if (options::proofNewPedantic() > 0)
    {
      Unhandled() << "Unhandled lemma Strings::Lemma SK-ONE : " << len_one
                  << std::endl;
    }
    return TrustNode::mkTrustLemma(len_one, nullptr);
  }
  Assert(s == LENGTH_SPLIT);

  // get the positive length lemma
  Node lenLemma = lengthPositive(n);
  // split whether the string is empty
  Node n_len_eq_z = n_len.eqNode(d_zero);
  Node n_len_eq_z_2 = n.eqNode(emp);
  Node case_empty = nm->mkNode(AND, n_len_eq_z, n_len_eq_z_2);
  Node case_emptyr = Rewriter::rewrite(case_empty);
  if (!case_emptyr.isConst())
  {
    // prefer trying the empty case first
    // notice that requirePhase must only be called on rewritten literals that
    // occur in the CNF stream.
    n_len_eq_z = Rewriter::rewrite(n_len_eq_z);
    Assert(!n_len_eq_z.isConst());
    reqPhase[n_len_eq_z] = true;
    n_len_eq_z_2 = Rewriter::rewrite(n_len_eq_z_2);
    Assert(!n_len_eq_z_2.isConst());
    reqPhase[n_len_eq_z_2] = true;
  }
  else
  {
    // If n = "" ---> true or len( n ) = 0 ----> true, then we expect that
    // n ---> "". Since this method is only called on non-constants n, it must
    // be that n = "" ^ len( n ) = 0 does not rewrite to true.
    Assert(!case_emptyr.getConst<bool>());
  }

  if (d_epg != nullptr)
  {
    return d_epg->mkTrustNode(lenLemma, PfRule::STRING_LENGTH_POS, {n});
  }
  return TrustNode::mkTrustLemma(lenLemma, nullptr);
}

Node TermRegistry::getSymbolicDefinition(Node n, std::vector<Node>& exp) const
{
  if (n.getNumChildren() == 0)
  {
    Node pn = getProxyVariableFor(n);
    if (pn.isNull())
    {
      return Node::null();
    }
    Node eq = n.eqNode(pn);
    eq = Rewriter::rewrite(eq);
    if (std::find(exp.begin(), exp.end(), eq) == exp.end())
    {
      exp.push_back(eq);
    }
    return pn;
  }
  std::vector<Node> children;
  if (n.getMetaKind() == metakind::PARAMETERIZED)
  {
    children.push_back(n.getOperator());
  }
  for (const Node& nc : n)
  {
    if (n.getType().isRegExp())
    {
      children.push_back(nc);
    }
    else
    {
      Node ns = getSymbolicDefinition(nc, exp);
      if (ns.isNull())
      {
        return Node::null();
      }
      else
      {
        children.push_back(ns);
      }
    }
  }
  return NodeManager::currentNM()->mkNode(n.getKind(), children);
}

Node TermRegistry::getProxyVariableFor(Node n) const
{
  NodeNodeMap::const_iterator it = d_proxyVar.find(n);
  if (it != d_proxyVar.end())
  {
    return (*it).second;
  }
  return Node::null();
}

Node TermRegistry::ensureProxyVariableFor(Node n)
{
  Node proxy = getProxyVariableFor(n);
  if (proxy.isNull())
  {
    registerTerm(n, 0);
    proxy = getProxyVariableFor(n);
  }
  Assert(!proxy.isNull());
  return proxy;
}

void TermRegistry::inferSubstitutionProxyVars(Node n,
                                              std::vector<Node>& vars,
                                              std::vector<Node>& subs,
                                              std::vector<Node>& unproc) const
{
  if (n.getKind() == AND)
  {
    for (const Node& nc : n)
    {
      inferSubstitutionProxyVars(nc, vars, subs, unproc);
    }
    return;
  }
  if (n.getKind() == EQUAL)
  {
    Node ns = n.substitute(vars.begin(), vars.end(), subs.begin(), subs.end());
    ns = Rewriter::rewrite(ns);
    if (ns.getKind() == EQUAL)
    {
      Node s;
      Node v;
      for (unsigned i = 0; i < 2; i++)
      {
        Node ss;
        // determine whether this side has a proxy variable
        if (ns[i].getAttribute(StringsProxyVarAttribute()))
        {
          // it is a proxy variable
          ss = ns[i];
        }
        else if (ns[i].isConst())
        {
          ss = getProxyVariableFor(ns[i]);
        }
        if (!ss.isNull())
        {
          v = ns[1 - i];
          // if the other side is a constant or variable
          if (v.getNumChildren() == 0)
          {
            if (s.isNull())
            {
              s = ss;
            }
            else
            {
              // both sides of the equality correspond to a proxy variable
              if (ss == s)
              {
                // it is a trivial equality, e.g. between a proxy variable
                // and its definition
                return;
              }
              else
              {
                // equality between proxy variables, non-trivial
                s = Node::null();
              }
            }
          }
        }
      }
      if (!s.isNull())
      {
        // the equality can be turned into a substitution
        subs.push_back(s);
        vars.push_back(v);
        return;
      }
    }
    else
    {
      n = ns;
    }
  }
  if (!n.isConst() || !n.getConst<bool>())
  {
    unproc.push_back(n);
  }
}

}  // namespace strings
}  // namespace theory
}  // namespace CVC4