ExpressionPtr ConstantExpression::preOptimize(AnalysisResultConstPtr ar) {
  if (ar->getPhase() < AnalysisResult::FirstPreOptimize) {
    return ExpressionPtr();
  }
  ConstructPtr decl;
  while (!isScalar() && !m_dynamic && !(m_context & LValue)) {
    const Symbol *sym = resolveNS(ar);
    if (!sym) {
      // The constant may be defined in a native extension, so check if its
      // available and persistent.
      auto const cns = Unit::lookupPersistentCns(makeStaticString(m_name));
      if (!cns) break;
      auto const& value = tvAsCVarRef(cns);
      if (!value.isAllowedAsConstantValue()) break;
      auto rep = makeScalarExpression(ar, value);
      rep->setComment(getText());
      copyLocationTo(rep);
      return replaceValue(rep);
    }
    if (!const_cast<Symbol*>(sym)->checkDefined() || sym->isDynamic()) {
      sym = 0;
      m_dynamic = true;
    }
    if (!sym) break;
    if (!sym->isSystem()) BlockScope::s_constMutex.lock();
    auto value = dynamic_pointer_cast<Expression>(sym->getValue());
    if (!sym->isSystem()) BlockScope::s_constMutex.unlock();

    if (!value || !value->isScalar()) {
      if (!m_depsSet && sym->getDeclaration()) {
        sym->getDeclaration()->getScope()->addUse(
          getScope(), BlockScope::UseKindConstRef);
        m_depsSet = true;
      }
      break;
    }

    Variant scalarValue;
    if (value->getScalarValue(scalarValue) &&
        !scalarValue.isAllowedAsConstantValue()) {
      // block further optimization
      const_cast<Symbol*>(sym)->setDynamic();
      m_dynamic = true;
      break;
    }

    if (sym->isSystem() && !value->is(KindOfScalarExpression)) {
      if (ExpressionPtr opt = value->preOptimize(ar)) {
        value = opt;
      }
    }
    ExpressionPtr rep = Clone(value, getScope());
    rep->setComment(getText());
    copyLocationTo(rep);
    return replaceValue(rep);
  }

  return ExpressionPtr();
}
ExpressionPtr ConstantExpression::preOptimize(AnalysisResultConstPtr ar) {
  if (ar->getPhase() < AnalysisResult::FirstPreOptimize) {
    return ExpressionPtr();
  }
  ConstructPtr decl;
  while (!isScalar() && !m_dynamic && !(m_context & LValue)) {
    const Symbol *sym = resolveNS(ar);
    if (sym &&
        (!const_cast<Symbol*>(sym)->checkDefined() || sym->isDynamic())) {
      sym = 0;
      m_dynamic = true;
    }
    if (!sym) break;
    if (!sym->isSystem()) BlockScope::s_constMutex.lock();
    auto value = dynamic_pointer_cast<Expression>(sym->getValue());
    if (!sym->isSystem()) BlockScope::s_constMutex.unlock();

    if (!value || !value->isScalar()) {
      if (!m_depsSet && sym->getDeclaration()) {
        sym->getDeclaration()->getScope()->addUse(
          getScope(), BlockScope::UseKindConstRef);
        m_depsSet = true;
      }
      break;
    }

    Variant scalarValue;
    if (value->getScalarValue(scalarValue) &&
        !scalarValue.isAllowedAsConstantValue()) {
      // block further optimization
      const_cast<Symbol*>(sym)->setDynamic();
      m_dynamic = true;
      break;
    }

    if (sym->isSystem() && !value->is(KindOfScalarExpression)) {
      if (ExpressionPtr opt = value->preOptimize(ar)) {
        value = opt;
      }
    }
    ExpressionPtr rep = Clone(value, getScope());
    rep->setComment(getText());
    copyLocationTo(rep);
    return replaceValue(rep);
  }

  return ExpressionPtr();
}
ExpressionPtr ClassConstantExpression::preOptimize(AnalysisResultConstPtr ar) {
  if (ar->getPhase() < AnalysisResult::FirstPreOptimize) {
    return ExpressionPtr();
  }
  if (m_class) {
    updateClassName();
    if (m_class) {
      return ExpressionPtr();
    }
  }

  ClassScopePtr cls = resolveClass();
  if (!cls || (cls->isVolatile() && !isPresent())) {
    if (cls && !m_depsSet) {
      cls->addUse(getScope(), BlockScope::UseKindConstRef);
      m_depsSet = true;
    }
    return ExpressionPtr();
  }

  ConstantTablePtr constants = cls->getConstants();
  ClassScopePtr defClass = cls;
  ConstructPtr decl = constants->getValueRecur(ar, m_varName, defClass);
  if (decl) {
    BlockScope::s_constMutex.lock();
    ExpressionPtr value = dynamic_pointer_cast<Expression>(decl);
    BlockScope::s_constMutex.unlock();

    if (!value->isScalar() &&
        (value->is(KindOfClassConstantExpression) ||
         value->is(KindOfConstantExpression))) {
      std::set<ExpressionPtr> seen;
      do {
        if (!seen.insert(value).second) return ExpressionPtr();
        value = value->preOptimize(ar);
        if (!value) return ExpressionPtr();
      } while (!value->isScalar() &&
               (value->is(KindOfClassConstantExpression) ||
                value->is(KindOfConstantExpression)));
    }

    ExpressionPtr rep = Clone(value, getScope());
    rep->setComment(getText());
    copyLocationTo(rep);
    return replaceValue(rep);
  }
  return ExpressionPtr();
}