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 SVal SimplifiedVal = simplifyToSVal(State, Sym); 27 if (SimplifiedVal.isConstant()) { 28 bool Feasible = SimplifiedVal.isZeroConstant() != Assumption; 29 return Feasible ? State : nullptr; 30 } 31 32 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol()) 33 Sym = SimplifiedSym; 34 35 // Handle SymbolData. 36 if (isa<SymbolData>(Sym)) 37 return assumeSymUnsupported(State, Sym, Assumption); 38 39 // Handle symbolic expression. 40 if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) { 41 // We can only simplify expressions whose RHS is an integer. 42 43 BinaryOperator::Opcode op = SIE->getOpcode(); 44 if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) { 45 if (!Assumption) 46 op = BinaryOperator::negateComparisonOp(op); 47 48 return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS()); 49 } 50 51 // Handle adjustment with non-comparison ops. 52 const llvm::APSInt &Zero = getBasicVals().getValue(0, SIE->getType()); 53 return assumeSymRel(State, SIE, (Assumption ? BO_NE : BO_EQ), Zero); 54 } 55 56 if (const auto *SSE = dyn_cast<SymSymExpr>(Sym)) { 57 BinaryOperator::Opcode Op = SSE->getOpcode(); 58 if (BinaryOperator::isComparisonOp(Op)) { 59 60 // We convert equality operations for pointers only. 61 if (Loc::isLocType(SSE->getLHS()->getType()) && 62 Loc::isLocType(SSE->getRHS()->getType())) { 63 // Translate "a != b" to "(b - a) != 0". 64 // We invert the order of the operands as a heuristic for how loop 65 // conditions are usually written ("begin != end") as compared to length 66 // calculations ("end - begin"). The more correct thing to do would be 67 // to canonicalize "a - b" and "b - a", which would allow us to treat 68 // "a != b" and "b != a" the same. 69 70 SymbolManager &SymMgr = getSymbolManager(); 71 QualType DiffTy = SymMgr.getContext().getPointerDiffType(); 72 SymbolRef Subtraction = 73 SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy); 74 75 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy); 76 Op = BinaryOperator::reverseComparisonOp(Op); 77 if (!Assumption) 78 Op = BinaryOperator::negateComparisonOp(Op); 79 return assumeSymRel(State, Subtraction, Op, Zero); 80 } 81 82 if (BinaryOperator::isEqualityOp(Op)) { 83 SymbolManager &SymMgr = getSymbolManager(); 84 85 QualType ExprType = SSE->getType(); 86 SymbolRef CanonicalEquality = 87 SymMgr.getSymSymExpr(SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType); 88 89 bool WasEqual = SSE->getOpcode() == BO_EQ; 90 bool IsExpectedEqual = WasEqual == Assumption; 91 92 const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType); 93 94 if (IsExpectedEqual) { 95 return assumeSymNE(State, CanonicalEquality, Zero, Zero); 96 } 97 98 return assumeSymEQ(State, CanonicalEquality, Zero, Zero); 99 } 100 } 101 } 102 103 // If we get here, there's nothing else we can do but treat the symbol as 104 // opaque. 105 return assumeSymUnsupported(State, Sym, Assumption); 106 } 107 108 ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange( 109 ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From, 110 const llvm::APSInt &To, bool InRange) { 111 112 Sym = simplify(State, Sym); 113 114 // Get the type used for calculating wraparound. 115 BasicValueFactory &BVF = getBasicVals(); 116 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType()); 117 118 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 119 SymbolRef AdjustedSym = Sym; 120 computeAdjustment(AdjustedSym, Adjustment); 121 122 // Convert the right-hand side integer as necessary. 123 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From)); 124 llvm::APSInt ConvertedFrom = ComparisonType.convert(From); 125 llvm::APSInt ConvertedTo = ComparisonType.convert(To); 126 127 // Prefer unsigned comparisons. 128 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 129 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 130 Adjustment.setIsSigned(false); 131 132 if (InRange) 133 return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom, 134 ConvertedTo, Adjustment); 135 return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom, 136 ConvertedTo, Adjustment); 137 } 138 139 ProgramStateRef 140 RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State, 141 SymbolRef Sym, bool Assumption) { 142 Sym = simplify(State, Sym); 143 144 BasicValueFactory &BVF = getBasicVals(); 145 QualType T = Sym->getType(); 146 147 // Non-integer types are not supported. 148 if (!T->isIntegralOrEnumerationType()) 149 return State; 150 151 // Reverse the operation and add directly to state. 152 const llvm::APSInt &Zero = BVF.getValue(0, T); 153 if (Assumption) 154 return assumeSymNE(State, Sym, Zero, Zero); 155 else 156 return assumeSymEQ(State, Sym, Zero, Zero); 157 } 158 159 ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State, 160 SymbolRef Sym, 161 BinaryOperator::Opcode Op, 162 const llvm::APSInt &Int) { 163 assert(BinaryOperator::isComparisonOp(Op) && 164 "Non-comparison ops should be rewritten as comparisons to zero."); 165 166 // Simplification: translate an assume of a constraint of the form 167 // "(exp comparison_op expr) != 0" to true into an assume of 168 // "exp comparison_op expr" to true. (And similarly, an assume of the form 169 // "(exp comparison_op expr) == 0" to true into an assume of 170 // "exp comparison_op expr" to false.) 171 if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) { 172 if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym)) 173 if (BinaryOperator::isComparisonOp(SE->getOpcode())) 174 return assumeSym(State, Sym, (Op == BO_NE ? true : false)); 175 } 176 177 // Get the type used for calculating wraparound. 178 BasicValueFactory &BVF = getBasicVals(); 179 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType()); 180 181 // We only handle simple comparisons of the form "$sym == constant" 182 // or "($sym+constant1) == constant2". 183 // The adjustment is "constant1" in the above expression. It's used to 184 // "slide" the solution range around for modular arithmetic. For example, 185 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which 186 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to 187 // the subclasses of SimpleConstraintManager to handle the adjustment. 188 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 189 computeAdjustment(Sym, Adjustment); 190 191 // Convert the right-hand side integer as necessary. 192 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int)); 193 llvm::APSInt ConvertedInt = ComparisonType.convert(Int); 194 195 // Prefer unsigned comparisons. 196 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 197 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 198 Adjustment.setIsSigned(false); 199 200 switch (Op) { 201 default: 202 llvm_unreachable("invalid operation not caught by assertion above"); 203 204 case BO_EQ: 205 return assumeSymEQ(State, Sym, ConvertedInt, Adjustment); 206 207 case BO_NE: 208 return assumeSymNE(State, Sym, ConvertedInt, Adjustment); 209 210 case BO_GT: 211 return assumeSymGT(State, Sym, ConvertedInt, Adjustment); 212 213 case BO_GE: 214 return assumeSymGE(State, Sym, ConvertedInt, Adjustment); 215 216 case BO_LT: 217 return assumeSymLT(State, Sym, ConvertedInt, Adjustment); 218 219 case BO_LE: 220 return assumeSymLE(State, Sym, ConvertedInt, Adjustment); 221 } // end switch 222 } 223 224 void RangedConstraintManager::computeAdjustment(SymbolRef &Sym, 225 llvm::APSInt &Adjustment) { 226 // Is it a "($sym+constant1)" expression? 227 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) { 228 BinaryOperator::Opcode Op = SE->getOpcode(); 229 if (Op == BO_Add || Op == BO_Sub) { 230 Sym = SE->getLHS(); 231 Adjustment = APSIntType(Adjustment).convert(SE->getRHS()); 232 233 // Don't forget to negate the adjustment if it's being subtracted. 234 // This should happen /after/ promotion, in case the value being 235 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'. 236 if (Op == BO_Sub) 237 Adjustment = -Adjustment; 238 } 239 } 240 } 241 242 SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) { 243 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 244 return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym)); 245 } 246 247 SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) { 248 SVal SimplifiedVal = simplifyToSVal(State, Sym); 249 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol()) 250 return SimplifiedSym; 251 return Sym; 252 } 253 254 } // end of namespace ento 255 } // end of namespace clang 256