text: // SimpleSValBuilder.cpp - A basic SValBuilder -----------------------*- C++ -*-
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file defines SimpleSValBuilder, a basic implementation of SValBuilder.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/SValVisitor.h"
  
  using namespace clang;
  using namespace ento;
  
  namespace {
  class SimpleSValBuilder : public SValBuilder {
  protected:
    SVal dispatchCast(SVal val, QualType castTy) override;
    SVal evalCastFromNonLoc(NonLoc val, QualType castTy) override;
    SVal evalCastFromLoc(Loc val, QualType castTy) override;
  
  public:
    SimpleSValBuilder(llvm::BumpPtrAllocator &alloc, ASTContext &context,
                      ProgramStateManager &stateMgr)
                      : SValBuilder(alloc, context, stateMgr) {}
    ~SimpleSValBuilder() override {}
  
    SVal evalMinus(NonLoc val) override;
    SVal evalComplement(NonLoc val) override;
    SVal evalBinOpNN(ProgramStateRef state, BinaryOperator::Opcode op,
                     NonLoc lhs, NonLoc rhs, QualType resultTy) override;
    SVal evalBinOpLL(ProgramStateRef state, BinaryOperator::Opcode op,
                     Loc lhs, Loc rhs, QualType resultTy) override;
    SVal evalBinOpLN(ProgramStateRef state, BinaryOperator::Opcode op,
                     Loc lhs, NonLoc rhs, QualType resultTy) override;
  
    /// getKnownValue - evaluates a given SVal. If the SVal has only one possible
    ///  (integer) value, that value is returned. Otherwise, returns NULL.
    const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal V) override;
  
    /// Recursively descends into symbolic expressions and replaces symbols
    /// with their known values (in the sense of the getKnownValue() method).
    SVal simplifySVal(ProgramStateRef State, SVal V) override;
  
    SVal MakeSymIntVal(const SymExpr *LHS, BinaryOperator::Opcode op,
                       const llvm::APSInt &RHS, QualType resultTy);
  };
  } // end anonymous namespace
  
  SValBuilder *ento::createSimpleSValBuilder(llvm::BumpPtrAllocator &alloc,
                                             ASTContext &context,
                                             ProgramStateManager &stateMgr) {
    return new SimpleSValBuilder(alloc, context, stateMgr);
  }
  
  //===----------------------------------------------------------------------===//
  // Transfer function for Casts.
  //===----------------------------------------------------------------------===//
  
  SVal SimpleSValBuilder::dispatchCast(SVal Val, QualType CastTy) {
    assert(Val.getAs<Loc>() || Val.getAs<NonLoc>());
    return Val.getAs<Loc>() ? evalCastFromLoc(Val.castAs<Loc>(), CastTy)
                             : evalCastFromNonLoc(Val.castAs<NonLoc>(), CastTy);
  }
  
  SVal SimpleSValBuilder::evalCastFromNonLoc(NonLoc val, QualType castTy) {
  
    bool isLocType = Loc::isLocType(castTy);
  
    if (val.getAs<nonloc::PointerToMember>())
      return val;
  
    if (Optional<nonloc::LocAsInteger> LI = val.getAs<nonloc::LocAsInteger>()) {
      if (isLocType)
        return LI->getLoc();
  
      // FIXME: Correctly support promotions/truncations.
      unsigned castSize = Context.getTypeSize(castTy);
      if (castSize == LI->getNumBits())
        return val;
      return makeLocAsInteger(LI->getLoc(), castSize);
    }
  
    if (const SymExpr *se = val.getAsSymbolicExpression()) {
      QualType T = Context.getCanonicalType(se->getType());
      // If types are the same or both are integers, ignore the cast.
      // FIXME: Remove this hack when we support symbolic truncation/extension.
      // HACK: If both castTy and T are integers, ignore the cast.  This is
      // not a permanent solution.  Eventually we want to precisely handle
      // extension/truncation of symbolic integers.  This prevents us from losing
      // precision when we assign 'x = y' and 'y' is symbolic and x and y are
      // different integer types.
     if (haveSameType(T, castTy))
        return val;
  
      if (!isLocType)
        return makeNonLoc(se, T, castTy);
      return UnknownVal();
    }
  
    // If value is a non-integer constant, produce unknown.
    if (!val.getAs<nonloc::ConcreteInt>())
      return UnknownVal();
  
    // Handle casts to a boolean type.
    if (castTy->isBooleanType()) {
      bool b = val.castAs<nonloc::ConcreteInt>().getValue().getBoolValue();
      return makeTruthVal(b, castTy);
    }
  
    // Only handle casts from integers to integers - if val is an integer constant
    // being cast to a non-integer type, produce unknown.
    if (!isLocType && !castTy->isIntegralOrEnumerationType())
      return UnknownVal();
  
    llvm::APSInt i = val.castAs<nonloc::ConcreteInt>().getValue();
    BasicVals.getAPSIntType(castTy).apply(i);
  
    if (isLocType)
      return makeIntLocVal(i);
    else
      return makeIntVal(i);
  }
  
  SVal SimpleSValBuilder::evalCastFromLoc(Loc val, QualType castTy) {
  
    // Casts from pointers -> pointers, just return the lval.
    //
    // Casts from pointers -> references, just return the lval.  These
    //   can be introduced by the frontend for corner cases, e.g
    //   casting from va_list* to __builtin_va_list&.
    //
    if (Loc::isLocType(castTy) || castTy->isReferenceType())
      return val;
  
    // FIXME: Handle transparent unions where a value can be "transparently"
    //  lifted into a union type.
    if (castTy->isUnionType())
      return UnknownVal();
  
    // Casting a Loc to a bool will almost always be true,
    // unless this is a weak function or a symbolic region.
    if (castTy->isBooleanType()) {
      switch (val.getSubKind()) {
        case loc::MemRegionValKind: {
          const MemRegion *R = val.castAs<loc::MemRegionVal>().getRegion();
          if (const FunctionCodeRegion *FTR = dyn_cast<FunctionCodeRegion>(R))
            if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(FTR->getDecl()))
              if (FD->isWeak())
                // FIXME: Currently we are using an extent symbol here,
                // because there are no generic region address metadata
                // symbols to use, only content metadata.
                return nonloc::SymbolVal(SymMgr.getExtentSymbol(FTR));
  
          if (const SymbolicRegion *SymR = R->getSymbolicBase())
            return nonloc::SymbolVal(SymR->getSymbol());
  
          // FALL-THROUGH
        }
  
        case loc::GotoLabelKind:
          // Labels and non-symbolic memory regions are always true.
          return makeTruthVal(true, castTy);
      }
    }
  
    if (castTy->isIntegralOrEnumerationType()) {
      unsigned BitWidth = Context.getTypeSize(castTy);
  
      if (!val.getAs<loc::ConcreteInt>())
        return makeLocAsInteger(val, BitWidth);
  
      llvm::APSInt i = val.castAs<loc::ConcreteInt>().getValue();
      BasicVals.getAPSIntType(castTy).apply(i);
      return makeIntVal(i);
    }
  
    // All other cases: return 'UnknownVal'.  This includes casting pointers
    // to floats, which is probably badness it itself, but this is a good
    // intermediate solution until we do something better.
    return UnknownVal();
  }
  
  //===----------------------------------------------------------------------===//
  // Transfer function for unary operators.
  //===----------------------------------------------------------------------===//
  
  SVal SimpleSValBuilder::evalMinus(NonLoc val) {
    switch (val.getSubKind()) {
    case nonloc::ConcreteIntKind:
      return val.castAs<nonloc::ConcreteInt>().evalMinus(*this);
    default:
      return UnknownVal();
    }
  }
  
  SVal SimpleSValBuilder::evalComplement(NonLoc X) {
    switch (X.getSubKind()) {
    case nonloc::ConcreteIntKind:
      return X.castAs<nonloc::ConcreteInt>().evalComplement(*this);
    default:
      return UnknownVal();
    }
  }
  
  //===----------------------------------------------------------------------===//
  // Transfer function for binary operators.
  //===----------------------------------------------------------------------===//
  
  SVal SimpleSValBuilder::MakeSymIntVal(const SymExpr *LHS,
                                      BinaryOperator::Opcode op,
                                      const llvm::APSInt &RHS,
                                      QualType resultTy) {
    bool isIdempotent = false;
  
    // Check for a few special cases with known reductions first.
    switch (op) {
    default:
      // We can't reduce this case; just treat it normally.
      break;
    case BO_Mul:
      // a*0 and a*1
      if (RHS == 0)
        return makeIntVal(0, resultTy);
      else if (RHS == 1)
        isIdempotent = true;
      break;
    case BO_Div:
      // a/0 and a/1
      if (RHS == 0)
        // This is also handled elsewhere.
        return UndefinedVal();
      else if (RHS == 1)
        isIdempotent = true;
      break;
    case BO_Rem:
      // a%0 and a%1
      if (RHS == 0)
        // This is also handled elsewhere.
        return UndefinedVal();
      else if (RHS == 1)
        return makeIntVal(0, resultTy);
      break;
    case BO_Add:
    case BO_Sub:
    case BO_Shl:
    case BO_Shr:
    case BO_Xor:
      // a+0, a-0, a<<0, a>>0, a^0
      if (RHS == 0)
        isIdempotent = true;
      break;
    case BO_And:
      // a&0 and a&(~0)
      if (RHS == 0)
        return makeIntVal(0, resultTy);
      else if (RHS.isAllOnesValue())
        isIdempotent = true;
      break;
    case BO_Or:
      // a|0 and a|(~0)
      if (RHS == 0)
        isIdempotent = true;
      else if (RHS.isAllOnesValue()) {
        const llvm::APSInt &Result = BasicVals.Convert(resultTy, RHS);
        return nonloc::ConcreteInt(Result);
      }
      break;
    }
  
    // Idempotent ops (like a*1) can still change the type of an expression.
    // Wrap the LHS up in a NonLoc again and let evalCastFromNonLoc do the
    // dirty work.
    if (isIdempotent)
        return evalCastFromNonLoc(nonloc::SymbolVal(LHS), resultTy);
  
    // If we reach this point, the expression cannot be simplified.
    // Make a SymbolVal for the entire expression, after converting the RHS.
    const llvm::APSInt *ConvertedRHS = &RHS;
    if (BinaryOperator::isComparisonOp(op)) {
      // We're looking for a type big enough to compare the symbolic value
      // with the given constant.
      // FIXME: This is an approximation of Sema::UsualArithmeticConversions.
      ASTContext &Ctx = getContext();
      QualType SymbolType = LHS->getType();
      uint64_t ValWidth = RHS.getBitWidth();
      uint64_t TypeWidth = Ctx.getTypeSize(SymbolType);
  
      if (ValWidth < TypeWidth) {
        // If the value is too small, extend it.
        ConvertedRHS = &BasicVals.Convert(SymbolType, RHS);
      } else if (ValWidth == TypeWidth) {
        // If the value is signed but the symbol is unsigned, do the comparison
        // in unsigned space. [C99 6.3.1.8]
        // (For the opposite case, the value is already unsigned.)
        if (RHS.isSigned() && !SymbolType->isSignedIntegerOrEnumerationType())
          ConvertedRHS = &BasicVals.Convert(SymbolType, RHS);
      }
    } else
      ConvertedRHS = &BasicVals.Convert(resultTy, RHS);
  
    return makeNonLoc(LHS, op, *ConvertedRHS, resultTy);
  }
  
  SVal SimpleSValBuilder::evalBinOpNN(ProgramStateRef state,
                                    BinaryOperator::Opcode op,
                                    NonLoc lhs, NonLoc rhs,
                                    QualType resultTy)  {
    NonLoc InputLHS = lhs;
    NonLoc InputRHS = rhs;
  
    // Handle trivial case where left-side and right-side are the same.
    if (lhs == rhs)
      switch (op) {
        default:
          break;
        case BO_EQ:
        case BO_LE:
        case BO_GE:
          return makeTruthVal(true, resultTy);
        case BO_LT:
        case BO_GT:
        case BO_NE:
          return makeTruthVal(false, resultTy);
        case BO_Xor:
        case BO_Sub:
          if (resultTy->isIntegralOrEnumerationType())
            return makeIntVal(0, resultTy);
          return evalCastFromNonLoc(makeIntVal(0, /*Unsigned=*/false), resultTy);
        case BO_Or:
        case BO_And:
          return evalCastFromNonLoc(lhs, resultTy);
      }
  
    while (1) {
      switch (lhs.getSubKind()) {
      default:
        return makeSymExprValNN(state, op, lhs, rhs, resultTy);
      case nonloc::PointerToMemberKind: {
        assert(rhs.getSubKind() == nonloc::PointerToMemberKind &&
               "Both SVals should have pointer-to-member-type");
        auto LPTM = lhs.castAs<nonloc::PointerToMember>(),
             RPTM = rhs.castAs<nonloc::PointerToMember>();
        auto LPTMD = LPTM.getPTMData(), RPTMD = RPTM.getPTMData();
        switch (op) {
          case BO_EQ:
            return makeTruthVal(LPTMD == RPTMD, resultTy);
          case BO_NE:
            return makeTruthVal(LPTMD != RPTMD, resultTy);
          default:
            return UnknownVal();
        }
      }
      case nonloc::LocAsIntegerKind: {
        Loc lhsL = lhs.castAs<nonloc::LocAsInteger>().getLoc();
        switch (rhs.getSubKind()) {
          case nonloc::LocAsIntegerKind:
            return evalBinOpLL(state, op, lhsL,
                               rhs.castAs<nonloc::LocAsInteger>().getLoc(),
                               resultTy);
          case nonloc::ConcreteIntKind: {
            // Transform the integer into a location and compare.
            // FIXME: This only makes sense for comparisons. If we want to, say,
            // add 1 to a LocAsInteger, we'd better unpack the Loc and add to it,
            // then pack it back into a LocAsInteger.
            llvm::APSInt i = rhs.castAs<nonloc::ConcreteInt>().getValue();
            BasicVals.getAPSIntType(Context.VoidPtrTy).apply(i);
            return evalBinOpLL(state, op, lhsL, makeLoc(i), resultTy);
          }
          default:
            switch (op) {
              case BO_EQ:
                return makeTruthVal(false, resultTy);
              case BO_NE:
                return makeTruthVal(true, resultTy);
              default:
                // This case also handles pointer arithmetic.
                return makeSymExprValNN(state, op, InputLHS, InputRHS, resultTy);
            }
        }
      }
      case nonloc::ConcreteIntKind: {
        llvm::APSInt LHSValue = lhs.castAs<nonloc::ConcreteInt>().getValue();
  
        // If we're dealing with two known constants, just perform the operation.
        if (const llvm::APSInt *KnownRHSValue = getKnownValue(state, rhs)) {
          llvm::APSInt RHSValue = *KnownRHSValue;
          if (BinaryOperator::isComparisonOp(op)) {
            // We're looking for a type big enough to compare the two values.
            // FIXME: This is not correct. char + short will result in a promotion
            // to int. Unfortunately we have lost types by this point.
            APSIntType CompareType = std::max(APSIntType(LHSValue),
                                              APSIntType(RHSValue));
            CompareType.apply(LHSValue);
            CompareType.apply(RHSValue);
          } else if (!BinaryOperator::isShiftOp(op)) {
            APSIntType IntType = BasicVals.getAPSIntType(resultTy);
            IntType.apply(LHSValue);
            IntType.apply(RHSValue);
          }
  
          const llvm::APSInt *Result =
            BasicVals.evalAPSInt(op, LHSValue, RHSValue);
          if (!Result)
            return UndefinedVal();
  
          return nonloc::ConcreteInt(*Result);
        }
  
        // Swap the left and right sides and flip the operator if doing so
        // allows us to better reason about the expression (this is a form
        // of expression canonicalization).
        // While we're at it, catch some special cases for non-commutative ops.
        switch (op) {
        case BO_LT:
        case BO_GT:
        case BO_LE:
        case BO_GE:
          op = BinaryOperator::reverseComparisonOp(op);
          // FALL-THROUGH
        case BO_EQ:
        case BO_NE:
        case BO_Add:
        case BO_Mul:
        case BO_And:
        case BO_Xor:
        case BO_Or:
          std::swap(lhs, rhs);
          continue;
        case BO_Shr:
          // (~0)>>a
          if (LHSValue.isAllOnesValue() && LHSValue.isSigned())
            return evalCastFromNonLoc(lhs, resultTy);
          // FALL-THROUGH
        case BO_Shl:
          // 0<<a and 0>>a
          if (LHSValue == 0)
            return evalCastFromNonLoc(lhs, resultTy);
          return makeSymExprValNN(state, op, InputLHS, InputRHS, resultTy);
        default:
          return makeSymExprValNN(state, op, InputLHS, InputRHS, resultTy);
        }
      }
      case nonloc::SymbolValKind: {
        // We only handle LHS as simple symbols or SymIntExprs.
        SymbolRef Sym = lhs.castAs<nonloc::SymbolVal>().getSymbol();
  
        // LHS is a symbolic expression.
        if (const SymIntExpr *symIntExpr = dyn_cast<SymIntExpr>(Sym)) {
  
          // Is this a logical not? (!x is represented as x == 0.)
          if (op == BO_EQ && rhs.isZeroConstant()) {
            // We know how to negate certain expressions. Simplify them here.
  
            BinaryOperator::Opcode opc = symIntExpr->getOpcode();
            switch (opc) {
            default:
              // We don't know how to negate this operation.
              // Just handle it as if it were a normal comparison to 0.
              break;
            case BO_LAnd:
            case BO_LOr:
              llvm_unreachable("Logical operators handled by branching logic.");
            case BO_Assign:
            case BO_MulAssign:
            case BO_DivAssign:
            case BO_RemAssign:
            case BO_AddAssign:
            case BO_SubAssign:
            case BO_ShlAssign:
            case BO_ShrAssign:
            case BO_AndAssign:
            case BO_XorAssign:
            case BO_OrAssign:
            case BO_Comma:
              llvm_unreachable("'=' and ',' operators handled by ExprEngine.");
            case BO_PtrMemD:
            case BO_PtrMemI:
              llvm_unreachable("Pointer arithmetic not handled here.");
            case BO_LT:
            case BO_GT:
            case BO_LE:
            case BO_GE:
            case BO_EQ:
            case BO_NE:
              assert(resultTy->isBooleanType() ||
                     resultTy == getConditionType());
              assert(symIntExpr->getType()->isBooleanType() ||
                     getContext().hasSameUnqualifiedType(symIntExpr->getType(),
                                                         getConditionType()));
              // Negate the comparison and make a value.
              opc = BinaryOperator::negateComparisonOp(opc);
              return makeNonLoc(symIntExpr->getLHS(), opc,
                  symIntExpr->getRHS(), resultTy);
            }
          }
  
          // For now, only handle expressions whose RHS is a constant.
          if (const llvm::APSInt *RHSValue = getKnownValue(state, rhs)) {
            // If both the LHS and the current expression are additive,
            // fold their constants and try again.
            if (BinaryOperator::isAdditiveOp(op)) {
              BinaryOperator::Opcode lop = symIntExpr->getOpcode();
              if (BinaryOperator::isAdditiveOp(lop)) {
                // Convert the two constants to a common type, then combine them.
  
                // resultTy may not be the best type to convert to, but it's
                // probably the best choice in expressions with mixed type
                // (such as x+1U+2LL). The rules for implicit conversions should
                // choose a reasonable type to preserve the expression, and will
                // at least match how the value is going to be used.
                APSIntType IntType = BasicVals.getAPSIntType(resultTy);
                const llvm::APSInt &first = IntType.convert(symIntExpr->getRHS());
                const llvm::APSInt &second = IntType.convert(*RHSValue);
  
                const llvm::APSInt *newRHS;
                if (lop == op)
                  newRHS = BasicVals.evalAPSInt(BO_Add, first, second);
                else
                  newRHS = BasicVals.evalAPSInt(BO_Sub, first, second);
  
                assert(newRHS && "Invalid operation despite common type!");
                rhs = nonloc::ConcreteInt(*newRHS);
                lhs = nonloc::SymbolVal(symIntExpr->getLHS());
                op = lop;
                continue;
              }
            }
  
            // Otherwise, make a SymIntExpr out of the expression.
            return MakeSymIntVal(symIntExpr, op, *RHSValue, resultTy);
          }
        }
  
        // Does the symbolic expression simplify to a constant?
        // If so, "fold" the constant by setting 'lhs' to a ConcreteInt
        // and try again.
        SVal simplifiedLhs = simplifySVal(state, lhs);
        if (simplifiedLhs != lhs)
          if (auto simplifiedLhsAsNonLoc = simplifiedLhs.getAs<NonLoc>()) {
            lhs = *simplifiedLhsAsNonLoc;
            continue;
          }
  
        // Is the RHS a constant?
        if (const llvm::APSInt *RHSValue = getKnownValue(state, rhs))
          return MakeSymIntVal(Sym, op, *RHSValue, resultTy);
  
        // Give up -- this is not a symbolic expression we can handle.
        return makeSymExprValNN(state, op, InputLHS, InputRHS, resultTy);
      }
      }
    }
  }
  
  static SVal evalBinOpFieldRegionFieldRegion(const FieldRegion *LeftFR,
                                              const FieldRegion *RightFR,
                                              BinaryOperator::Opcode op,
                                              QualType resultTy,
                                              SimpleSValBuilder &SVB) {
    // Only comparisons are meaningful here!
    if (!BinaryOperator::isComparisonOp(op))
      return UnknownVal();
  
    // Next, see if the two FRs have the same super-region.
    // FIXME: This doesn't handle casts yet, and simply stripping the casts
    // doesn't help.
    if (LeftFR->getSuperRegion() != RightFR->getSuperRegion())
      return UnknownVal();
  
    const FieldDecl *LeftFD = LeftFR->getDecl();
    const FieldDecl *RightFD = RightFR->getDecl();
    const RecordDecl *RD = LeftFD->getParent();
  
    // Make sure the two FRs are from the same kind of record. Just in case!
    // FIXME: This is probably where inheritance would be a problem.
    if (RD != RightFD->getParent())
      return UnknownVal();
  
    // We know for sure that the two fields are not the same, since that
    // would have given us the same SVal.
    if (op == BO_EQ)
      return SVB.makeTruthVal(false, resultTy);
    if (op == BO_NE)
      return SVB.makeTruthVal(true, resultTy);
  
    // Iterate through the fields and see which one comes first.
    // [C99 6.7.2.1.13] "Within a structure object, the non-bit-field
    // members and the units in which bit-fields reside have addresses that
    // increase in the order in which they are declared."
    bool leftFirst = (op == BO_LT || op == BO_LE);
    for (const auto *I : RD->fields()) {
      if (I == LeftFD)
        return SVB.makeTruthVal(leftFirst, resultTy);
      if (I == RightFD)
        return SVB.makeTruthVal(!leftFirst, resultTy);
    }
  
    llvm_unreachable("Fields not found in parent record's definition");
  }
  
  // FIXME: all this logic will change if/when we have MemRegion::getLocation().
  SVal SimpleSValBuilder::evalBinOpLL(ProgramStateRef state,
                                    BinaryOperator::Opcode op,
                                    Loc lhs, Loc rhs,
                                    QualType resultTy) {
    // Only comparisons and subtractions are valid operations on two pointers.
    // See [C99 6.5.5 through 6.5.14] or [C++0x 5.6 through 5.15].
    // However, if a pointer is casted to an integer, evalBinOpNN may end up
    // calling this function with another operation (PR7527). We don't attempt to
    // model this for now, but it could be useful, particularly when the
    // "location" is actually an integer value that's been passed through a void*.
    if (!(BinaryOperator::isComparisonOp(op) || op == BO_Sub))
      return UnknownVal();
  
    // Special cases for when both sides are identical.
    if (lhs == rhs) {
      switch (op) {
      default:
        llvm_unreachable("Unimplemented operation for two identical values");
      case BO_Sub:
        return makeZeroVal(resultTy);
      case BO_EQ:
      case BO_LE:
      case BO_GE:
        return makeTruthVal(true, resultTy);
      case BO_NE:
      case BO_LT:
      case BO_GT:
        return makeTruthVal(false, resultTy);
      }
    }
  
    switch (lhs.getSubKind()) {
    default:
      llvm_unreachable("Ordering not implemented for this Loc.");
  
    case loc::GotoLabelKind:
      // The only thing we know about labels is that they're non-null.
      if (rhs.isZeroConstant()) {
        switch (op) {
        default:
          break;
        case BO_Sub:
          return evalCastFromLoc(lhs, resultTy);
        case BO_EQ:
        case BO_LE:
        case BO_LT:
          return makeTruthVal(false, resultTy);
        case BO_NE:
        case BO_GT:
        case BO_GE:
          return makeTruthVal(true, resultTy);
        }
      }
      // There may be two labels for the same location, and a function region may
      // have the same address as a label at the start of the function (depending
      // on the ABI).
      // FIXME: we can probably do a comparison against other MemRegions, though.
      // FIXME: is there a way to tell if two labels refer to the same location?
      return UnknownVal();
  
    case loc::ConcreteIntKind: {
      // If one of the operands is a symbol and the other is a constant,
      // build an expression for use by the constraint manager.
      if (SymbolRef rSym = rhs.getAsLocSymbol()) {
        // We can only build expressions with symbols on the left,
        // so we need a reversible operator.
        if (!BinaryOperator::isComparisonOp(op))
          return UnknownVal();
  
        const llvm::APSInt &lVal = lhs.castAs<loc::ConcreteInt>().getValue();
        op = BinaryOperator::reverseComparisonOp(op);
        return makeNonLoc(rSym, op, lVal, resultTy);
      }
  
      // If both operands are constants, just perform the operation.
      if (Optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) {
        SVal ResultVal =
            lhs.castAs<loc::ConcreteInt>().evalBinOp(BasicVals, op, *rInt);
        if (Optional<NonLoc> Result = ResultVal.getAs<NonLoc>())
          return evalCastFromNonLoc(*Result, resultTy);
  
        assert(!ResultVal.getAs<Loc>() && "Loc-Loc ops should not produce Locs");
        return UnknownVal();
      }
  
      // Special case comparisons against NULL.
      // This must come after the test if the RHS is a symbol, which is used to
      // build constraints. The address of any non-symbolic region is guaranteed
      // to be non-NULL, as is any label.
      assert(rhs.getAs<loc::MemRegionVal>() || rhs.getAs<loc::GotoLabel>());
      if (lhs.isZeroConstant()) {
        switch (op) {
        default:
          break;
        case BO_EQ:
        case BO_GT:
        case BO_GE:
          return makeTruthVal(false, resultTy);
        case BO_NE:
        case BO_LT:
        case BO_LE:
          return makeTruthVal(true, resultTy);
        }
      }
  
      // Comparing an arbitrary integer to a region or label address is
      // completely unknowable.
      return UnknownVal();
    }
    case loc::MemRegionValKind: {
      if (Optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) {
        // If one of the operands is a symbol and the other is a constant,
        // build an expression for use by the constraint manager.
        if (SymbolRef lSym = lhs.getAsLocSymbol(true))
          return MakeSymIntVal(lSym, op, rInt->getValue(), resultTy);
  
        // Special case comparisons to NULL.
        // This must come after the test if the LHS is a symbol, which is used to
        // build constraints. The address of any non-symbolic region is guaranteed
        // to be non-NULL.
        if (rInt->isZeroConstant()) {
          if (op == BO_Sub)
            return evalCastFromLoc(lhs, resultTy);
  
          if (BinaryOperator::isComparisonOp(op)) {
            QualType boolType = getContext().BoolTy;
            NonLoc l = evalCastFromLoc(lhs, boolType).castAs<NonLoc>();
            NonLoc r = makeTruthVal(false, boolType).castAs<NonLoc>();
            return evalBinOpNN(state, op, l, r, resultTy);
          }
        }
  
        // Comparing a region to an arbitrary integer is completely unknowable.
        return UnknownVal();
      }
  
      // Get both values as regions, if possible.
      const MemRegion *LeftMR = lhs.getAsRegion();
      assert(LeftMR && "MemRegionValKind SVal doesn't have a region!");
  
      const MemRegion *RightMR = rhs.getAsRegion();
      if (!RightMR)
        // The RHS is probably a label, which in theory could address a region.
        // FIXME: we can probably make a more useful statement about non-code
        // regions, though.
        return UnknownVal();
  
      const MemRegion *LeftBase = LeftMR->getBaseRegion();
      const MemRegion *RightBase = RightMR->getBaseRegion();
      const MemSpaceRegion *LeftMS = LeftBase->getMemorySpace();
      const MemSpaceRegion *RightMS = RightBase->getMemorySpace();
      const MemSpaceRegion *UnknownMS = MemMgr.getUnknownRegion();
  
      // If the two regions are from different known memory spaces they cannot be
      // equal. Also, assume that no symbolic region (whose memory space is
      // unknown) is on the stack.
      if (LeftMS != RightMS &&
          ((LeftMS != UnknownMS && RightMS != UnknownMS) ||
           (isa<StackSpaceRegion>(LeftMS) || isa<StackSpaceRegion>(RightMS)))) {
        switch (op) {
        default:
          return UnknownVal();
        case BO_EQ:
          return makeTruthVal(false, resultTy);
        case BO_NE:
          return makeTruthVal(true, resultTy);
        }
      }
  
      // If both values wrap regions, see if they're from different base regions.
      // Note, heap base symbolic regions are assumed to not alias with
      // each other; for example, we assume that malloc returns different address
      // on each invocation.
      // FIXME: ObjC object pointers always reside on the heap, but currently
      // we treat their memory space as unknown, because symbolic pointers
      // to ObjC objects may alias. There should be a way to construct
      // possibly-aliasing heap-based regions. For instance, MacOSXApiChecker
      // guesses memory space for ObjC object pointers manually instead of
      // relying on us.
      if (LeftBase != RightBase &&
          ((!isa<SymbolicRegion>(LeftBase) && !isa<SymbolicRegion>(RightBase)) ||
           (isa<HeapSpaceRegion>(LeftMS) || isa<HeapSpaceRegion>(RightMS))) ){
        switch (op) {
        default:
          return UnknownVal();
        case BO_EQ:
          return makeTruthVal(false, resultTy);
        case BO_NE:
          return makeTruthVal(true, resultTy);
        }
      }
  
      // Handle special cases for when both regions are element regions.
      const ElementRegion *RightER = dyn_cast<ElementRegion>(RightMR);
      const ElementRegion *LeftER = dyn_cast<ElementRegion>(LeftMR);
      if (RightER && LeftER) {
        // Next, see if the two ERs have the same super-region and matching types.
        // FIXME: This should do something useful even if the types don't match,
        // though if both indexes are constant the RegionRawOffset path will
        // give the correct answer.
        if (LeftER->getSuperRegion() == RightER->getSuperRegion() &&
            LeftER->getElementType() == RightER->getElementType()) {
          // Get the left index and cast it to the correct type.
          // If the index is unknown or undefined, bail out here.
          SVal LeftIndexVal = LeftER->getIndex();
          Optional<NonLoc> LeftIndex = LeftIndexVal.getAs<NonLoc>();
          if (!LeftIndex)
            return UnknownVal();
          LeftIndexVal = evalCastFromNonLoc(*LeftIndex, ArrayIndexTy);
          LeftIndex = LeftIndexVal.getAs<NonLoc>();
          if (!LeftIndex)
            return UnknownVal();
  
          // Do the same for the right index.
          SVal RightIndexVal = RightER->getIndex();
          Optional<NonLoc> RightIndex = RightIndexVal.getAs<NonLoc>();
          if (!RightIndex)
            return UnknownVal();
          RightIndexVal = evalCastFromNonLoc(*RightIndex, ArrayIndexTy);
          RightIndex = RightIndexVal.getAs<NonLoc>();
          if (!RightIndex)
            return UnknownVal();
  
          // Actually perform the operation.
          // evalBinOpNN expects the two indexes to already be the right type.
          return evalBinOpNN(state, op, *LeftIndex, *RightIndex, resultTy);
        }
      }
  
      // Special handling of the FieldRegions, even with symbolic offsets.
      const FieldRegion *RightFR = dyn_cast<FieldRegion>(RightMR);
      const FieldRegion *LeftFR = dyn_cast<FieldRegion>(LeftMR);
      if (RightFR && LeftFR) {
        SVal R = evalBinOpFieldRegionFieldRegion(LeftFR, RightFR, op, resultTy,
                                                 *this);
        if (!R.isUnknown())
          return R;
      }
  
      // Compare the regions using the raw offsets.
      RegionOffset LeftOffset = LeftMR->getAsOffset();
      RegionOffset RightOffset = RightMR->getAsOffset();
  
      if (LeftOffset.getRegion() != nullptr &&
          LeftOffset.getRegion() == RightOffset.getRegion() &&
          !LeftOffset.hasSymbolicOffset() && !RightOffset.hasSymbolicOffset()) {
        int64_t left = LeftOffset.getOffset();
        int64_t right = RightOffset.getOffset();
  
        switch (op) {
          default:
            return UnknownVal();
          case BO_LT:
            return makeTruthVal(left < right, resultTy);
          case BO_GT:
            return makeTruthVal(left > right, resultTy);
          case BO_LE:
            return makeTruthVal(left <= right, resultTy);
          case BO_GE:
            return makeTruthVal(left >= right, resultTy);
          case BO_EQ:
            return makeTruthVal(left == right, resultTy);
          case BO_NE:
            return makeTruthVal(left != right, resultTy);
        }
      }
  
      // At this point we're not going to get a good answer, but we can try
      // conjuring an expression instead.
      SymbolRef LHSSym = lhs.getAsLocSymbol();
      SymbolRef RHSSym = rhs.getAsLocSymbol();
      if (LHSSym && RHSSym)
        return makeNonLoc(LHSSym, op, RHSSym, resultTy);
  
      // If we get here, we have no way of comparing the regions.
      return UnknownVal();
    }
    }
  }
  
  SVal SimpleSValBuilder::evalBinOpLN(ProgramStateRef state,
                                    BinaryOperator::Opcode op,
                                    Loc lhs, NonLoc rhs, QualType resultTy) {
    if (op >= BO_PtrMemD && op <= BO_PtrMemI) {
      if (auto PTMSV = rhs.getAs<nonloc::PointerToMember>()) {
        if (PTMSV->isNullMemberPointer())
          return UndefinedVal();
        if (const FieldDecl *FD = PTMSV->getDeclAs<FieldDecl>()) {
          SVal Result = lhs;
  
          for (const auto &I : *PTMSV)
            Result = StateMgr.getStoreManager().evalDerivedToBase(
                Result, I->getType(),I->isVirtual());
          return state->getLValue(FD, Result);
        }
      }
  
      return rhs;
    }
  
    assert(!BinaryOperator::isComparisonOp(op) &&
           "arguments to comparison ops must be of the same type");
  
    // Special case: rhs is a zero constant.
    if (rhs.isZeroConstant())
      return lhs;
  
    // We are dealing with pointer arithmetic.
  
    // Handle pointer arithmetic on constant values.
    if (Optional<nonloc::ConcreteInt> rhsInt = rhs.getAs<nonloc::ConcreteInt>()) {
      if (Optional<loc::ConcreteInt> lhsInt = lhs.getAs<loc::ConcreteInt>()) {
        const llvm::APSInt &leftI = lhsInt->getValue();
        assert(leftI.isUnsigned());
        llvm::APSInt rightI(rhsInt->getValue(), /* isUnsigned */ true);
  
        // Convert the bitwidth of rightI.  This should deal with overflow
        // since we are dealing with concrete values.
        rightI = rightI.extOrTrunc(leftI.getBitWidth());
  
        // Offset the increment by the pointer size.
        llvm::APSInt Multiplicand(rightI.getBitWidth(), /* isUnsigned */ true);
        rightI *= Multiplicand;
  
        // Compute the adjusted pointer.
        switch (op) {
          case BO_Add:
            rightI = leftI + rightI;
            break;
          case BO_Sub:
            rightI = leftI - rightI;
            break;
          default:
            llvm_unreachable("Invalid pointer arithmetic operation");
        }
        return loc::ConcreteInt(getBasicValueFactory().getValue(rightI));
      }
    }
  
    // Handle cases where 'lhs' is a region.
    if (const MemRegion *region = lhs.getAsRegion()) {
      rhs = convertToArrayIndex(rhs).castAs<NonLoc>();
      SVal index = UnknownVal();
      const SubRegion *superR = nullptr;
      // We need to know the type of the pointer in order to add an integer to it.
      // Depending on the type, different amount of bytes is added.
      QualType elementType;
  
      if (const ElementRegion *elemReg = dyn_cast<ElementRegion>(region)) {
        assert(op == BO_Add || op == BO_Sub);
        index = evalBinOpNN(state, op, elemReg->getIndex(), rhs,
                            getArrayIndexType());
        superR = cast<SubRegion>(elemReg->getSuperRegion());
        elementType = elemReg->getElementType();
      }
      else if (isa<SubRegion>(region)) {
        assert(op == BO_Add || op == BO_Sub);
        index = (op == BO_Add) ? rhs : evalMinus(rhs);
        superR = cast<SubRegion>(region);
        // TODO: Is this actually reliable? Maybe improving our MemRegion
        // hierarchy to provide typed regions for all non-void pointers would be
        // better. For instance, we cannot extend this towards LocAsInteger
        // operations, where result type of the expression is integer.
        if (resultTy->isAnyPointerType())
          elementType = resultTy->getPointeeType();
      }
  
      if (Optional<NonLoc> indexV = index.getAs<NonLoc>()) {
        return loc::MemRegionVal(MemMgr.getElementRegion(elementType, *indexV,
                                                         superR, getContext()));
      }
    }
    return UnknownVal();
  }
  
  const llvm::APSInt *SimpleSValBuilder::getKnownValue(ProgramStateRef state,
                                                     SVal V) {
    if (V.isUnknownOrUndef())
      return nullptr;
  
    if (Optional<loc::ConcreteInt> X = V.getAs<loc::ConcreteInt>())
      return &X->getValue();
  
    if (Optional<nonloc::ConcreteInt> X = V.getAs<nonloc::ConcreteInt>())
      return &X->getValue();
  
    if (SymbolRef Sym = V.getAsSymbol())
      return state->getConstraintManager().getSymVal(state, Sym);
  
    // FIXME: Add support for SymExprs.
    return nullptr;
  }
  
  SVal SimpleSValBuilder::simplifySVal(ProgramStateRef State, SVal V) {
    // For now, this function tries to constant-fold symbols inside a
    // nonloc::SymbolVal, and does nothing else. More simplifications should
    // be possible, such as constant-folding an index in an ElementRegion.
  
    class Simplifier : public FullSValVisitor<Simplifier, SVal> {
      ProgramStateRef State;
      SValBuilder &SVB;
  
    public:
      Simplifier(ProgramStateRef State)
          : State(State), SVB(State->getStateManager().getSValBuilder()) {}
  
      SVal VisitSymbolData(const SymbolData *S) {
        if (const llvm::APSInt *I =
                SVB.getKnownValue(State, nonloc::SymbolVal(S)))
          return Loc::isLocType(S->getType()) ? (SVal)SVB.makeIntLocVal(*I)
                                              : (SVal)SVB.makeIntVal(*I);
        return nonloc::SymbolVal(S);
      }
  
      // TODO: Support SymbolCast. Support IntSymExpr when/if we actually
      // start producing them.
  
      SVal VisitSymIntExpr(const SymIntExpr *S) {
        SVal LHS = Visit(S->getLHS());
        SVal RHS;
        // By looking at the APSInt in the right-hand side of S, we cannot
        // figure out if it should be treated as a Loc or as a NonLoc.
        // So make our guess by recalling that we cannot multiply pointers
        // or compare a pointer to an integer.
        if (Loc::isLocType(S->getLHS()->getType()) &&
            BinaryOperator::isComparisonOp(S->getOpcode())) {
          // The usual conversion of $sym to &SymRegion{$sym}, as they have
          // the same meaning for Loc-type symbols, but the latter form
          // is preferred in SVal computations for being Loc itself.
          if (SymbolRef Sym = LHS.getAsSymbol()) {
            assert(Loc::isLocType(Sym->getType()));
            LHS = SVB.makeLoc(Sym);
          }
          RHS = SVB.makeIntLocVal(S->getRHS());
        } else {
          RHS = SVB.makeIntVal(S->getRHS());
        }
        return SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType());
      }
  
      SVal VisitSymSymExpr(const SymSymExpr *S) {
        SVal LHS = Visit(S->getLHS());
        SVal RHS = Visit(S->getRHS());
        return SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType());
      }
  
      SVal VisitSymExpr(SymbolRef S) { return nonloc::SymbolVal(S); }
  
      SVal VisitMemRegion(const MemRegion *R) { return loc::MemRegionVal(R); }
  
      SVal VisitNonLocSymbolVal(nonloc::SymbolVal V) {
        // Simplification is much more costly than computing complexity.
        // For high complexity, it may be not worth it.
        if (V.getSymbol()->computeComplexity() > 100)
          return V;
        return Visit(V.getSymbol());
      }
  
      SVal VisitSVal(SVal V) { return V; }
    };
  
    return Simplifier(State).Visit(V);
  }
  