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