text: //== RangedConstraintManager.cpp --------------------------------*- C++ -*--==//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file defines RangedConstraintManager, a class that provides a
  //  range-based constraint manager interface.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h"
  
  namespace clang {
  
  namespace ento {
  
  RangedConstraintManager::~RangedConstraintManager() {}
  
  ProgramStateRef RangedConstraintManager::assumeSym(ProgramStateRef State,
                                                     SymbolRef Sym,
                                                     bool Assumption) {
    Sym = simplify(State, Sym);
  
    // Handle SymbolData.
    if (isa<SymbolData>(Sym))
      return assumeSymUnsupported(State, Sym, Assumption);
  
    // Handle symbolic expression.
    if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) {
      // We can only simplify expressions whose RHS is an integer.
  
      BinaryOperator::Opcode op = SIE->getOpcode();
      if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) {
        if (!Assumption)
          op = BinaryOperator::negateComparisonOp(op);
  
        return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());
      }
  
    } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(Sym)) {
      BinaryOperator::Opcode Op = SSE->getOpcode();
      assert(BinaryOperator::isComparisonOp(Op));
  
      // We convert equality operations for pointers only.
      if (Loc::isLocType(SSE->getLHS()->getType()) &&
          Loc::isLocType(SSE->getRHS()->getType())) {
        // Translate "a != b" to "(b - a) != 0".
        // We invert the order of the operands as a heuristic for how loop
        // conditions are usually written ("begin != end") as compared to length
        // calculations ("end - begin"). The more correct thing to do would be to
        // canonicalize "a - b" and "b - a", which would allow us to treat
        // "a != b" and "b != a" the same.
  
        SymbolManager &SymMgr = getSymbolManager();
        QualType DiffTy = SymMgr.getContext().getPointerDiffType();
        SymbolRef Subtraction =
            SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
  
        const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
        Op = BinaryOperator::reverseComparisonOp(Op);
        if (!Assumption)
          Op = BinaryOperator::negateComparisonOp(Op);
        return assumeSymRel(State, Subtraction, Op, Zero);
      }
  
      if (BinaryOperator::isEqualityOp(Op)) {
        SymbolManager &SymMgr = getSymbolManager();
  
        QualType ExprType = SSE->getType();
        SymbolRef CanonicalEquality =
            SymMgr.getSymSymExpr(SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType);
  
        bool WasEqual = SSE->getOpcode() == BO_EQ;
        bool IsExpectedEqual = WasEqual == Assumption;
  
        const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType);
  
        if (IsExpectedEqual) {
          return assumeSymNE(State, CanonicalEquality, Zero, Zero);
        }
  
        return assumeSymEQ(State, CanonicalEquality, Zero, Zero);
      }
    }
  
    // If we get here, there's nothing else we can do but treat the symbol as
    // opaque.
    return assumeSymUnsupported(State, Sym, Assumption);
  }
  
  ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
      ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
      const llvm::APSInt &To, bool InRange) {
  
    Sym = simplify(State, Sym);
  
    // Get the type used for calculating wraparound.
    BasicValueFactory &BVF = getBasicVals();
    APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
  
    llvm::APSInt Adjustment = WraparoundType.getZeroValue();
    SymbolRef AdjustedSym = Sym;
    computeAdjustment(AdjustedSym, Adjustment);
  
    // Convert the right-hand side integer as necessary.
    APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
    llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
    llvm::APSInt ConvertedTo = ComparisonType.convert(To);
  
    // Prefer unsigned comparisons.
    if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
        ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
      Adjustment.setIsSigned(false);
  
    if (InRange)
      return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
                                           ConvertedTo, Adjustment);
    return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
                                          ConvertedTo, Adjustment);
  }
  
  ProgramStateRef
  RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,
                                                SymbolRef Sym, bool Assumption) {
    Sym = simplify(State, Sym);
  
    BasicValueFactory &BVF = getBasicVals();
    QualType T = Sym->getType();
  
    // Non-integer types are not supported.
    if (!T->isIntegralOrEnumerationType())
      return State;
  
    // Reverse the operation and add directly to state.
    const llvm::APSInt &Zero = BVF.getValue(0, T);
    if (Assumption)
      return assumeSymNE(State, Sym, Zero, Zero);
    else
      return assumeSymEQ(State, Sym, Zero, Zero);
  }
  
  ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,
                                                        SymbolRef Sym,
                                                        BinaryOperator::Opcode Op,
                                                        const llvm::APSInt &Int) {
    assert(BinaryOperator::isComparisonOp(Op) &&
           "Non-comparison ops should be rewritten as comparisons to zero.");
  
    // Simplification: translate an assume of a constraint of the form
    // "(exp comparison_op expr) != 0" to true into an assume of
    // "exp comparison_op expr" to true. (And similarly, an assume of the form
    // "(exp comparison_op expr) == 0" to true into an assume of
    // "exp comparison_op expr" to false.)
    if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
      if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))
        if (BinaryOperator::isComparisonOp(SE->getOpcode()))
          return assumeSym(State, Sym, (Op == BO_NE ? true : false));
    }
  
    // Get the type used for calculating wraparound.
    BasicValueFactory &BVF = getBasicVals();
    APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
  
    // We only handle simple comparisons of the form "$sym == constant"
    // or "($sym+constant1) == constant2".
    // The adjustment is "constant1" in the above expression. It's used to
    // "slide" the solution range around for modular arithmetic. For example,
    // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
    // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
    // the subclasses of SimpleConstraintManager to handle the adjustment.
    llvm::APSInt Adjustment = WraparoundType.getZeroValue();
    computeAdjustment(Sym, Adjustment);
  
    // Convert the right-hand side integer as necessary.
    APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
    llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
  
    // Prefer unsigned comparisons.
    if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
        ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
      Adjustment.setIsSigned(false);
  
    switch (Op) {
    default:
      llvm_unreachable("invalid operation not caught by assertion above");
  
    case BO_EQ:
      return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);
  
    case BO_NE:
      return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
  
    case BO_GT:
      return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
  
    case BO_GE:
      return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
  
    case BO_LT:
      return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
  
    case BO_LE:
      return assumeSymLE(State, Sym, ConvertedInt, Adjustment);
    } // end switch
  }
  
  void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
                                                  llvm::APSInt &Adjustment) {
    // Is it a "($sym+constant1)" expression?
    if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
      BinaryOperator::Opcode Op = SE->getOpcode();
      if (Op == BO_Add || Op == BO_Sub) {
        Sym = SE->getLHS();
        Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
  
        // Don't forget to negate the adjustment if it's being subtracted.
        // This should happen /after/ promotion, in case the value being
        // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
        if (Op == BO_Sub)
          Adjustment = -Adjustment;
      }
    }
  }
  
  SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {
    SValBuilder &SVB = State->getStateManager().getSValBuilder();
    SVal SimplifiedVal = SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));
    if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol())
      return SimplifiedSym;
    return Sym;
  }
  
  } // end of namespace ento
  } // end of namespace clang
  