//== 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(Sym)) return assumeSymUnsupported(State, Sym, Assumption); // Handle symbolic expression. if (const SymIntExpr *SIE = dyn_cast(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()); } // Handle adjustment with non-comparison ops. const llvm::APSInt &Zero = getBasicVals().getValue(0, SIE->getType()); return assumeSymRel(State, SIE, (Assumption ? BO_NE : BO_EQ), Zero); } if (const auto *SSE = dyn_cast(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(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(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; } } } SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) { SValBuilder &SVB = State->getStateManager().getSValBuilder(); return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym)); } SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) { SVal SimplifiedVal = simplifyToSVal(State, Sym); if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol()) return SimplifiedSym; return Sym; } } // end of namespace ento } // end of namespace clang