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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines RangedConstraintManager, a class that provides a 10 // 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 17 namespace clang { 18 19 namespace ento { 20 21 RangedConstraintManager::~RangedConstraintManager() {} 22 23 ProgramStateRef 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 assert(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 loop 58 // conditions are usually written ("begin != end") as compared to length 59 // calculations ("end - begin"). The more correct thing to do would be to 60 // canonicalize "a - b" and "b - a", which would allow us to treat 61 // "a != b" and "b != a" the same. 62 63 SymbolManager &SymMgr = getSymbolManager(); 64 QualType DiffTy = SymMgr.getContext().getPointerDiffType(); 65 SymbolRef Subtraction = 66 SymMgr.getSymSymExpr(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 = 80 SymMgr.getSymSymExpr(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 // If we get here, there's nothing else we can do but treat the symbol as 96 // opaque. 97 return assumeSymUnsupported(State, Sym, Assumption); 98 } 99 100 ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange( 101 ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From, 102 const llvm::APSInt &To, bool InRange) { 103 104 Sym = simplify(State, Sym); 105 106 // Get the type used for calculating wraparound. 107 BasicValueFactory &BVF = getBasicVals(); 108 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType()); 109 110 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 111 SymbolRef AdjustedSym = Sym; 112 computeAdjustment(AdjustedSym, Adjustment); 113 114 // Convert the right-hand side integer as necessary. 115 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From)); 116 llvm::APSInt ConvertedFrom = ComparisonType.convert(From); 117 llvm::APSInt ConvertedTo = ComparisonType.convert(To); 118 119 // Prefer unsigned comparisons. 120 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 121 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 122 Adjustment.setIsSigned(false); 123 124 if (InRange) 125 return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom, 126 ConvertedTo, Adjustment); 127 return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom, 128 ConvertedTo, Adjustment); 129 } 130 131 ProgramStateRef 132 RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State, 133 SymbolRef Sym, bool Assumption) { 134 Sym = simplify(State, Sym); 135 136 BasicValueFactory &BVF = getBasicVals(); 137 QualType T = Sym->getType(); 138 139 // Non-integer types are not supported. 140 if (!T->isIntegralOrEnumerationType()) 141 return State; 142 143 // Reverse the operation and add directly to state. 144 const llvm::APSInt &Zero = BVF.getValue(0, T); 145 if (Assumption) 146 return assumeSymNE(State, Sym, Zero, Zero); 147 else 148 return assumeSymEQ(State, Sym, Zero, Zero); 149 } 150 151 ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State, 152 SymbolRef Sym, 153 BinaryOperator::Opcode Op, 154 const llvm::APSInt &Int) { 155 assert(BinaryOperator::isComparisonOp(Op) && 156 "Non-comparison ops should be rewritten as comparisons to zero."); 157 158 // Simplification: translate an assume of a constraint of the form 159 // "(exp comparison_op expr) != 0" to true into an assume of 160 // "exp comparison_op expr" to true. (And similarly, an assume of the form 161 // "(exp comparison_op expr) == 0" to true into an assume of 162 // "exp comparison_op expr" to false.) 163 if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) { 164 if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym)) 165 if (BinaryOperator::isComparisonOp(SE->getOpcode())) 166 return assumeSym(State, Sym, (Op == BO_NE ? true : false)); 167 } 168 169 // Get the type used for calculating wraparound. 170 BasicValueFactory &BVF = getBasicVals(); 171 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType()); 172 173 // We only handle simple comparisons of the form "$sym == constant" 174 // or "($sym+constant1) == constant2". 175 // The adjustment is "constant1" in the above expression. It's used to 176 // "slide" the solution range around for modular arithmetic. For example, 177 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which 178 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to 179 // the subclasses of SimpleConstraintManager to handle the adjustment. 180 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 181 computeAdjustment(Sym, Adjustment); 182 183 // Convert the right-hand side integer as necessary. 184 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int)); 185 llvm::APSInt ConvertedInt = ComparisonType.convert(Int); 186 187 // Prefer unsigned comparisons. 188 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 189 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 190 Adjustment.setIsSigned(false); 191 192 switch (Op) { 193 default: 194 llvm_unreachable("invalid operation not caught by assertion above"); 195 196 case BO_EQ: 197 return assumeSymEQ(State, Sym, ConvertedInt, Adjustment); 198 199 case BO_NE: 200 return assumeSymNE(State, Sym, ConvertedInt, Adjustment); 201 202 case BO_GT: 203 return assumeSymGT(State, Sym, ConvertedInt, Adjustment); 204 205 case BO_GE: 206 return assumeSymGE(State, Sym, ConvertedInt, Adjustment); 207 208 case BO_LT: 209 return assumeSymLT(State, Sym, ConvertedInt, Adjustment); 210 211 case BO_LE: 212 return assumeSymLE(State, Sym, ConvertedInt, Adjustment); 213 } // end switch 214 } 215 216 void RangedConstraintManager::computeAdjustment(SymbolRef &Sym, 217 llvm::APSInt &Adjustment) { 218 // Is it a "($sym+constant1)" expression? 219 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) { 220 BinaryOperator::Opcode Op = SE->getOpcode(); 221 if (Op == BO_Add || Op == BO_Sub) { 222 Sym = SE->getLHS(); 223 Adjustment = APSIntType(Adjustment).convert(SE->getRHS()); 224 225 // Don't forget to negate the adjustment if it's being subtracted. 226 // This should happen /after/ promotion, in case the value being 227 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'. 228 if (Op == BO_Sub) 229 Adjustment = -Adjustment; 230 } 231 } 232 } 233 234 SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) { 235 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 236 return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym)); 237 } 238 239 SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) { 240 SVal SimplifiedVal = simplifyToSVal(State, Sym); 241 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol()) 242 return SimplifiedSym; 243 return Sym; 244 } 245 246 } // end of namespace ento 247 } // end of namespace clang 248