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| //== 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) {
// Handle SymbolData.
if (isa<SymbolData>(Sym)) {
return assumeSymUnsupported(State, Sym, Assumption);
// Handle symbolic expression.
} else 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)) {
// 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.
if (Loc::isLocType(SSE->getLHS()->getType()) &&
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 assumeSymUnsupported(State, Sym, Assumption);
}
ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
const llvm::APSInt &To, bool InRange) {
// 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) {
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;
}
}
}
void *ProgramStateTrait<ConstraintRange>::GDMIndex() {
static int Index;
return &Index;
}
} // end of namespace ento
} // end of namespace clang
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