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 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 loop 58 // conditions are usually written ("begin != end") as compared to length 59 // calculations ("end - begin"). The more correct thing to do would be 60 // to 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 96 // If we get here, there's nothing else we can do but treat the symbol as 97 // opaque. 98 return assumeSymUnsupported(State, Sym, Assumption); 99 } 100 101 ProgramStateRef 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 } 131 132 ProgramStateRef 133 RangedConstraintManager::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 else 149 return assumeSymEQ(State, Sym, Zero, Zero); 150 } 151 152 ProgramStateRef 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 form 160 // "(exp comparison_op expr) != 0" to true into an assume of 161 // "exp comparison_op expr" to true. (And similarly, an assume of the form 162 // "(exp comparison_op expr) == 0" to true into an assume of 163 // "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 to 177 // "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], which 179 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to 180 // 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 switch 215 } 216 217 void 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 being 228 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'. 229 if (Op == BO_Sub) 230 Adjustment = -Adjustment; 231 } 232 } 233 } 234 235 SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) { 236 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 237 return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym)); 238 } 239 240 SymbolRef 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 ento 248 } // end of namespace clang 249