//== 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/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
namespace clang {
namespace ento {
SimpleConstraintManager::~SimpleConstraintManager() {}
bool SimpleConstraintManager::canReasonAbout(SVal X) const {
Optional<nonloc::SymbolVal> SymVal = X.getAs<nonloc::SymbolVal>();
if (SymVal && SymVal->isExpression()) {
const SymExpr *SE = SymVal->getSymbol();
if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SE)) {
switch (SIE->getOpcode()) {
// We don't reason yet about bitwise-constraints on symbolic values.
case BO_And:
case BO_Or:
case BO_Xor:
return false;
// We don't reason yet about these arithmetic constraints on
// symbolic values.
case BO_Mul:
case BO_Div:
case BO_Rem:
case BO_Shl:
case BO_Shr:
return false;
// All other cases.
default:
return true;
}
}
if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(SE)) {
if (BinaryOperator::isComparisonOp(SSE->getOpcode())) {
// We handle Loc <> Loc comparisons, but not (yet) NonLoc <> NonLoc.
if (Loc::isLocType(SSE->getLHS()->getType())) {
assert(Loc::isLocType(SSE->getRHS()->getType()));
return true;
}
}
}
return false;
}
return true;
}
ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
DefinedSVal Cond,
bool Assumption) {
// If we have a Loc value, cast it to a bool NonLoc first.
if (Optional<Loc> LV = Cond.getAs<Loc>()) {
SValBuilder &SVB = state->getStateManager().getSValBuilder();
QualType T;
const MemRegion *MR = LV->getAsRegion();
if (const TypedRegion *TR = dyn_cast_or_null<TypedRegion>(MR))
T = TR->getLocationType();
else
T = SVB.getContext().VoidPtrTy;
Cond = SVB.evalCast(*LV, SVB.getContext().BoolTy, T).castAs<DefinedSVal>();
}
return assume(state, Cond.castAs<NonLoc>(), Assumption);
}
ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
NonLoc cond,
bool assumption) {
state = assumeAux(state, cond, assumption);
if (NotifyAssumeClients && SU)
return SU->processAssume(state, cond, assumption);
return state;
}
ProgramStateRef
SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State,
SymbolRef Sym, bool Assumption) {
BasicValueFactory &BVF = getBasicVals();
QualType T = Sym->getType();
// None of the constraint solvers currently support non-integer types.
if (!T->isIntegralOrEnumerationType())
return 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 SimpleConstraintManager::assumeAux(ProgramStateRef state,
NonLoc Cond,
bool Assumption) {
// We cannot reason about SymSymExprs, and can only reason about some
// SymIntExprs.
if (!canReasonAbout(Cond)) {
// Just add the constraint to the expression without trying to simplify.
SymbolRef sym = Cond.getAsSymExpr();
return assumeAuxForSymbol(state, sym, Assumption);
}
switch (Cond.getSubKind()) {
default:
llvm_unreachable("'Assume' not implemented for this NonLoc");
case nonloc::SymbolValKind: {
nonloc::SymbolVal SV = Cond.castAs<nonloc::SymbolVal>();
SymbolRef sym = SV.getSymbol();
assert(sym);
// Handle SymbolData.
if (!SV.isExpression()) {
return assumeAuxForSymbol(state, sym, Assumption);
// Handle symbolic expression.
} else if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym)) {
// We can only simplify expressions whose RHS is an integer.
BinaryOperator::Opcode op = SE->getOpcode();
if (BinaryOperator::isComparisonOp(op)) {
if (!Assumption)
op = BinaryOperator::negateComparisonOp(op);
return assumeSymRel(state, SE->getLHS(), op, SE->getRHS());
}
} else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(sym)) {
// 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();
BinaryOperator::Opcode Op = SSE->getOpcode();
assert(BinaryOperator::isComparisonOp(Op));
// For now, we only support comparing pointers.
assert(Loc::isLocType(SSE->getLHS()->getType()));
assert(Loc::isLocType(SSE->getRHS()->getType()));
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 we get here, there's nothing else we can do but treat the symbol as
// opaque.
return assumeAuxForSymbol(state, sym, Assumption);
}
case nonloc::ConcreteIntKind: {
bool b = Cond.castAs<nonloc::ConcreteInt>().getValue() != 0;
bool isFeasible = b ? Assumption : !Assumption;
return isFeasible ? state : nullptr;
}
case nonloc::LocAsIntegerKind:
return assume(state, Cond.castAs<nonloc::LocAsInteger>().getLoc(),
Assumption);
} // end switch
}
static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) {
// Is it a "($sym+constant1)" expression?
if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
BinaryOperator::Opcode Op = SE->getOpcode();
if (Op == BO_Add || Op == BO_Sub) {
Sym = SE->getLHS();
Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
// Don't forget to negate the adjustment if it's being subtracted.
// This should happen /after/ promotion, in case the value being
// subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
if (Op == BO_Sub)
Adjustment = -Adjustment;
}
}
}
ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state,
const SymExpr *LHS,
BinaryOperator::Opcode op,
const llvm::APSInt& Int) {
assert(BinaryOperator::isComparisonOp(op) &&
"Non-comparison ops should be rewritten as comparisons to zero.");
// Get the type used for calculating wraparound.
BasicValueFactory &BVF = getBasicVals();
APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType());
// We only handle simple comparisons of the form "$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.
SymbolRef Sym = LHS;
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
}
} // end of namespace ento
} // end of namespace clang
