249 lines · cpp
1//== RangedConstraintManager.cpp --------------------------------*- C++ -*--==//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file defines RangedConstraintManager, a class that provides a10// range-based constraint manager interface.11//12//===----------------------------------------------------------------------===//13 14#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"15#include "clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h"16 17namespace clang {18 19namespace ento {20 21RangedConstraintManager::~RangedConstraintManager() {}22 23ProgramStateRef RangedConstraintManager::assumeSym(ProgramStateRef State,24 SymbolRef Sym,25 bool Assumption) {26 Sym = simplify(State, Sym);27 28 // Handle SymbolData.29 if (isa<SymbolData>(Sym))30 return assumeSymUnsupported(State, Sym, Assumption);31 32 // Handle symbolic expression.33 if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) {34 // We can only simplify expressions whose RHS is an integer.35 36 BinaryOperator::Opcode op = SIE->getOpcode();37 if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) {38 if (!Assumption)39 op = BinaryOperator::negateComparisonOp(op);40 41 return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());42 }43 44 // Handle adjustment with non-comparison ops.45 const llvm::APSInt &Zero = getBasicVals().getValue(0, SIE->getType());46 return assumeSymRel(State, SIE, (Assumption ? BO_NE : BO_EQ), Zero);47 }48 49 if (const auto *SSE = dyn_cast<SymSymExpr>(Sym)) {50 BinaryOperator::Opcode Op = SSE->getOpcode();51 if (BinaryOperator::isComparisonOp(Op)) {52 53 // We convert equality operations for pointers only.54 if (Loc::isLocType(SSE->getLHS()->getType()) &&55 Loc::isLocType(SSE->getRHS()->getType())) {56 // Translate "a != b" to "(b - a) != 0".57 // We invert the order of the operands as a heuristic for how loop58 // conditions are usually written ("begin != end") as compared to length59 // calculations ("end - begin"). The more correct thing to do would be60 // to canonicalize "a - b" and "b - a", which would allow us to treat61 // "a != b" and "b != a" the same.62 63 SymbolManager &SymMgr = getSymbolManager();64 QualType DiffTy = SymMgr.getContext().getPointerDiffType();65 SymbolRef Subtraction = SymMgr.acquire<SymSymExpr>(66 SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);67 68 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);69 Op = BinaryOperator::reverseComparisonOp(Op);70 if (!Assumption)71 Op = BinaryOperator::negateComparisonOp(Op);72 return assumeSymRel(State, Subtraction, Op, Zero);73 }74 75 if (BinaryOperator::isEqualityOp(Op)) {76 SymbolManager &SymMgr = getSymbolManager();77 78 QualType ExprType = SSE->getType();79 SymbolRef CanonicalEquality = SymMgr.acquire<SymSymExpr>(80 SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType);81 82 bool WasEqual = SSE->getOpcode() == BO_EQ;83 bool IsExpectedEqual = WasEqual == Assumption;84 85 const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType);86 87 if (IsExpectedEqual) {88 return assumeSymNE(State, CanonicalEquality, Zero, Zero);89 }90 91 return assumeSymEQ(State, CanonicalEquality, Zero, Zero);92 }93 }94 }95 96 // If we get here, there's nothing else we can do but treat the symbol as97 // opaque.98 return assumeSymUnsupported(State, Sym, Assumption);99}100 101ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(102 ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,103 const llvm::APSInt &To, bool InRange) {104 105 Sym = simplify(State, Sym);106 107 // Get the type used for calculating wraparound.108 BasicValueFactory &BVF = getBasicVals();109 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());110 111 llvm::APSInt Adjustment = WraparoundType.getZeroValue();112 SymbolRef AdjustedSym = Sym;113 computeAdjustment(AdjustedSym, Adjustment);114 115 // Convert the right-hand side integer as necessary.116 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));117 llvm::APSInt ConvertedFrom = ComparisonType.convert(From);118 llvm::APSInt ConvertedTo = ComparisonType.convert(To);119 120 // Prefer unsigned comparisons.121 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&122 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())123 Adjustment.setIsSigned(false);124 125 if (InRange)126 return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,127 ConvertedTo, Adjustment);128 return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,129 ConvertedTo, Adjustment);130}131 132ProgramStateRef133RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,134 SymbolRef Sym, bool Assumption) {135 Sym = simplify(State, Sym);136 137 BasicValueFactory &BVF = getBasicVals();138 QualType T = Sym->getType();139 140 // Non-integer types are not supported.141 if (!T->isIntegralOrEnumerationType())142 return State;143 144 // Reverse the operation and add directly to state.145 const llvm::APSInt &Zero = BVF.getValue(0, T);146 if (Assumption)147 return assumeSymNE(State, Sym, Zero, Zero);148 else149 return assumeSymEQ(State, Sym, Zero, Zero);150}151 152ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,153 SymbolRef Sym,154 BinaryOperator::Opcode Op,155 const llvm::APSInt &Int) {156 assert(BinaryOperator::isComparisonOp(Op) &&157 "Non-comparison ops should be rewritten as comparisons to zero.");158 159 // Simplification: translate an assume of a constraint of the form160 // "(exp comparison_op expr) != 0" to true into an assume of161 // "exp comparison_op expr" to true. (And similarly, an assume of the form162 // "(exp comparison_op expr) == 0" to true into an assume of163 // "exp comparison_op expr" to false.)164 if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {165 if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))166 if (BinaryOperator::isComparisonOp(SE->getOpcode()))167 return assumeSym(State, Sym, (Op == BO_NE ? true : false));168 }169 170 // Get the type used for calculating wraparound.171 BasicValueFactory &BVF = getBasicVals();172 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());173 174 // We only handle simple comparisons of the form "$sym == constant"175 // or "($sym+constant1) == constant2".176 // The adjustment is "constant1" in the above expression. It's used to177 // "slide" the solution range around for modular arithmetic. For example,178 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which179 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to180 // the subclasses of SimpleConstraintManager to handle the adjustment.181 llvm::APSInt Adjustment = WraparoundType.getZeroValue();182 computeAdjustment(Sym, Adjustment);183 184 // Convert the right-hand side integer as necessary.185 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));186 llvm::APSInt ConvertedInt = ComparisonType.convert(Int);187 188 // Prefer unsigned comparisons.189 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&190 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())191 Adjustment.setIsSigned(false);192 193 switch (Op) {194 default:195 llvm_unreachable("invalid operation not caught by assertion above");196 197 case BO_EQ:198 return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);199 200 case BO_NE:201 return assumeSymNE(State, Sym, ConvertedInt, Adjustment);202 203 case BO_GT:204 return assumeSymGT(State, Sym, ConvertedInt, Adjustment);205 206 case BO_GE:207 return assumeSymGE(State, Sym, ConvertedInt, Adjustment);208 209 case BO_LT:210 return assumeSymLT(State, Sym, ConvertedInt, Adjustment);211 212 case BO_LE:213 return assumeSymLE(State, Sym, ConvertedInt, Adjustment);214 } // end switch215}216 217void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,218 llvm::APSInt &Adjustment) {219 // Is it a "($sym+constant1)" expression?220 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {221 BinaryOperator::Opcode Op = SE->getOpcode();222 if (Op == BO_Add || Op == BO_Sub) {223 Sym = SE->getLHS();224 Adjustment = APSIntType(Adjustment).convert(SE->getRHS());225 226 // Don't forget to negate the adjustment if it's being subtracted.227 // This should happen /after/ promotion, in case the value being228 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.229 if (Op == BO_Sub)230 Adjustment = -Adjustment;231 }232 }233}234 235SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) {236 SValBuilder &SVB = State->getStateManager().getSValBuilder();237 return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));238}239 240SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {241 SVal SimplifiedVal = simplifyToSVal(State, Sym);242 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol())243 return SimplifiedSym;244 return Sym;245}246 247} // end of namespace ento248} // end of namespace clang249