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