lib/Checker/SimpleConstraintManager.cpp

//== SimpleConstraintManager.cpp --------------------------------*- 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 SimpleConstraintManager, a class that holds code shared
//  between BasicConstraintManager and RangeConstraintManager.
//
//===----------------------------------------------------------------------===//

#include "SimpleConstraintManager.h"
#include "clang/Checker/PathSensitive/GRExprEngine.h"
#include "clang/Checker/PathSensitive/GRState.h"
#include "clang/Checker/PathSensitive/Checker.h"

namespace clang {

SimpleConstraintManager::~SimpleConstraintManager() {}

bool SimpleConstraintManager::canReasonAbout(SVal X) const {
  if (nonloc::SymExprVal *SymVal = dyn_cast<nonloc::SymExprVal>(&X)) {
    const SymExpr *SE = SymVal->getSymbolicExpression();

    if (isa<SymbolData>(SE))
      return true;

    if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SE)) {
      switch (SIE->getOpcode()) {
          // We don't reason yet about bitwise-constraints on symbolic values.
        case BinaryOperator::And:
        case BinaryOperator::Or:
        case BinaryOperator::Xor:
          return false;
        // We don't reason yet about these arithmetic constraints on
        // symbolic values.
        case BinaryOperator::Mul:
        case BinaryOperator::Div:
        case BinaryOperator::Rem:
        case BinaryOperator::Shl:
        case BinaryOperator::Shr:
          return false;
        // All other cases.
        default:
          return true;
      }
    }

    return false;
  }

  return true;
}

const GRState *SimpleConstraintManager::Assume(const GRState *state,
                                               DefinedSVal Cond,
                                               bool Assumption) {
  if (isa<NonLoc>(Cond))
    return Assume(state, cast<NonLoc>(Cond), Assumption);
  else
    return Assume(state, cast<Loc>(Cond), Assumption);
}

const GRState *SimpleConstraintManager::Assume(const GRState *state, Loc cond,
                                               bool assumption) {
  state = AssumeAux(state, cond, assumption);
  return SU.ProcessAssume(state, cond, assumption);
}

const GRState *SimpleConstraintManager::AssumeAux(const GRState *state,
                                                  Loc Cond, bool Assumption) {

  BasicValueFactory &BasicVals = state->getBasicVals();

  switch (Cond.getSubKind()) {
  default:
    assert (false && "'Assume' not implemented for this Loc.");
    return state;

  case loc::MemRegionKind: {
    // FIXME: Should this go into the storemanager?

    const MemRegion *R = cast<loc::MemRegionVal>(Cond).getRegion();
    const SubRegion *SubR = dyn_cast<SubRegion>(R);

    while (SubR) {
      // FIXME: now we only find the first symbolic region.
      if (const SymbolicRegion *SymR = dyn_cast<SymbolicRegion>(SubR)) {
        const llvm::APSInt &zero = BasicVals.getZeroWithPtrWidth();
        if (Assumption)
          return AssumeSymNE(state, SymR->getSymbol(), zero, zero);
        else
          return AssumeSymEQ(state, SymR->getSymbol(), zero, zero);
      }
      SubR = dyn_cast<SubRegion>(SubR->getSuperRegion());
    }

    // FALL-THROUGH.
  }

  case loc::GotoLabelKind:
    return Assumption ? state : NULL;

  case loc::ConcreteIntKind: {
    bool b = cast<loc::ConcreteInt>(Cond).getValue() != 0;
    bool isFeasible = b ? Assumption : !Assumption;
    return isFeasible ? state : NULL;
  }
  } // end switch
}

const GRState *SimpleConstraintManager::Assume(const GRState *state,
                                               NonLoc cond,
                                               bool assumption) {
  state = AssumeAux(state, cond, assumption);
  return SU.ProcessAssume(state, cond, assumption);
}

static BinaryOperator::Opcode NegateComparison(BinaryOperator::Opcode op) {
  // FIXME: This should probably be part of BinaryOperator, since this isn't
  // the only place it's used. (This code was copied from SimpleSValuator.cpp.)
  switch (op) {
  default:
    assert(false && "Invalid opcode.");
  case BinaryOperator::LT: return BinaryOperator::GE;
  case BinaryOperator::GT: return BinaryOperator::LE;
  case BinaryOperator::LE: return BinaryOperator::GT;
  case BinaryOperator::GE: return BinaryOperator::LT;
  case BinaryOperator::EQ: return BinaryOperator::NE;
  case BinaryOperator::NE: return BinaryOperator::EQ;
  }
}

const GRState *SimpleConstraintManager::AssumeAux(const GRState *state,
                                                  NonLoc Cond,
                                                  bool Assumption) {

  // We cannot reason about SymSymExprs,
  // and can only reason about some SymIntExprs.
  if (!canReasonAbout(Cond)) {
    // Just return the current state indicating that the path is feasible.
    // This may be an over-approximation of what is possible.
    return state;
  }

  BasicValueFactory &BasicVals = state->getBasicVals();
  SymbolManager &SymMgr = state->getSymbolManager();

  switch (Cond.getSubKind()) {
  default:
    assert(false && "'Assume' not implemented for this NonLoc");

  case nonloc::SymbolValKind: {
    nonloc::SymbolVal& SV = cast<nonloc::SymbolVal>(Cond);
    SymbolRef sym = SV.getSymbol();
    QualType T =  SymMgr.getType(sym);
    const llvm::APSInt &zero = BasicVals.getValue(0, T);
    if (Assumption)
      return AssumeSymNE(state, sym, zero, zero);
    else
      return AssumeSymEQ(state, sym, zero, zero);
  }

  case nonloc::SymExprValKind: {
    nonloc::SymExprVal V = cast<nonloc::SymExprVal>(Cond);

    // For now, we only handle expressions whose RHS is an integer.
    // All other expressions are assumed to be feasible.
    const SymIntExpr *SE = dyn_cast<SymIntExpr>(V.getSymbolicExpression());
    if (!SE)
      return state;

    GRStateManager &StateMgr = state->getStateManager();
    ASTContext &Ctx = StateMgr.getContext();
    BasicValueFactory &BasicVals = StateMgr.getBasicVals();

    // FIXME: This is a hack.  It silently converts the RHS integer to be
    // of the same type as on the left side.  This should be removed once
    // we support truncation/extension of symbolic values.   
    const SymExpr *LHS = SE->getLHS();
    QualType LHSType = LHS->getType(Ctx);
    const llvm::APSInt &RHS = BasicVals.Convert(LHSType, SE->getRHS());

    BinaryOperator::Opcode op = SE->getOpcode();
    // FIXME: We should implicitly compare non-comparison expressions to 0.
    if (!BinaryOperator::isComparisonOp(op))
      return state;

    // From here on out, op is the real comparison we'll be testing.
    if (!Assumption)
      op = NegateComparison(op);
  
    return AssumeSymRel(state, LHS, op, RHS);
  }

  case nonloc::ConcreteIntKind: {
    bool b = cast<nonloc::ConcreteInt>(Cond).getValue() != 0;
    bool isFeasible = b ? Assumption : !Assumption;
    return isFeasible ? state : NULL;
  }

  case nonloc::LocAsIntegerKind:
    return AssumeAux(state, cast<nonloc::LocAsInteger>(Cond).getLoc(),
                     Assumption);
  } // end switch
}

const GRState *SimpleConstraintManager::AssumeSymRel(const GRState *state,
                                                     const SymExpr *LHS,
                                                     BinaryOperator::Opcode op,
                                                     const llvm::APSInt& Int) {
  assert(BinaryOperator::isComparisonOp(op) &&
         "Non-comparison ops should be rewritten as comparisons to zero.");

   // 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(Int.getBitWidth(), Int.isUnsigned());

  // First check if the LHS is a simple symbol reference.
  SymbolRef Sym = dyn_cast<SymbolData>(LHS);
  if (!Sym) {
    // Next, see if it's a "($sym+constant1)" expression.
    const SymIntExpr *SE = dyn_cast<SymIntExpr>(LHS);

    // We don't handle "($sym1+$sym2)".
    // Give up and assume the constraint is feasible.
    if (!SE)
      return state;

    // We don't handle "(<expr>+constant1)".
    // Give up and assume the constraint is feasible.
    Sym = dyn_cast<SymbolData>(SE->getLHS());
    if (!Sym)
      return state;

    // Get the constant out of the expression "($sym+constant1)".
    switch (SE->getOpcode()) {
    case BinaryOperator::Add:
      Adjustment = SE->getRHS();
      break;
    case BinaryOperator::Sub:
      Adjustment = -SE->getRHS();
      break;
    default:
      // We don't handle non-additive operators.
      // Give up and assume the constraint is feasible.
      return state;
    }
  }

  switch (op) {
  default:
    // No logic yet for other operators.  Assume the constraint is feasible.
    return state;

  case BinaryOperator::EQ:
    return AssumeSymEQ(state, Sym, Int, Adjustment);

  case BinaryOperator::NE:
    return AssumeSymNE(state, Sym, Int, Adjustment);

  case BinaryOperator::GT:
    return AssumeSymGT(state, Sym, Int, Adjustment);

  case BinaryOperator::GE:
    return AssumeSymGE(state, Sym, Int, Adjustment);

  case BinaryOperator::LT:
    return AssumeSymLT(state, Sym, Int, Adjustment);

  case BinaryOperator::LE:
    return AssumeSymLE(state, Sym, Int, Adjustment);
  } // end switch
}

const GRState *SimpleConstraintManager::AssumeInBound(const GRState *state,
                                                      DefinedSVal Idx,
                                                      DefinedSVal UpperBound,
                                                      bool Assumption) {

  // Only support ConcreteInt for now.
  if (!(isa<nonloc::ConcreteInt>(Idx) && isa<nonloc::ConcreteInt>(UpperBound)))
    return state;

  const llvm::APSInt& Zero = state->getBasicVals().getZeroWithPtrWidth(false);
  llvm::APSInt IdxV = cast<nonloc::ConcreteInt>(Idx).getValue();
  // IdxV might be too narrow.
  if (IdxV.getBitWidth() < Zero.getBitWidth())
    IdxV.extend(Zero.getBitWidth());
  // UBV might be too narrow, too.
  llvm::APSInt UBV = cast<nonloc::ConcreteInt>(UpperBound).getValue();
  if (UBV.getBitWidth() < Zero.getBitWidth())
    UBV.extend(Zero.getBitWidth());

  bool InBound = (Zero <= IdxV) && (IdxV < UBV);
  bool isFeasible = Assumption ? InBound : !InBound;
  return isFeasible ? state : NULL;
}

}  // end of namespace clang