1 //== SimpleConstraintManager.cpp --------------------------------*- C++ -*--==// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines SimpleConstraintManager, a class that holds code shared 11 // between BasicConstraintManager and RangeConstraintManager. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "SimpleConstraintManager.h" 16 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h" 17 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h" 19 20 namespace clang { 21 22 namespace ento { 23 24 SimpleConstraintManager::~SimpleConstraintManager() {} 25 26 bool SimpleConstraintManager::canReasonAbout(SVal X) const { 27 Optional<nonloc::SymbolVal> SymVal = X.getAs<nonloc::SymbolVal>(); 28 if (SymVal && SymVal->isExpression()) { 29 const SymExpr *SE = SymVal->getSymbol(); 30 31 if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SE)) { 32 switch (SIE->getOpcode()) { 33 // We don't reason yet about bitwise-constraints on symbolic values. 34 case BO_And: 35 case BO_Or: 36 case BO_Xor: 37 return false; 38 // We don't reason yet about these arithmetic constraints on 39 // symbolic values. 40 case BO_Mul: 41 case BO_Div: 42 case BO_Rem: 43 case BO_Shl: 44 case BO_Shr: 45 return false; 46 // All other cases. 47 default: 48 return true; 49 } 50 } 51 52 if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(SE)) { 53 if (BinaryOperator::isComparisonOp(SSE->getOpcode())) { 54 // We handle Loc <> Loc comparisons, but not (yet) NonLoc <> NonLoc. 55 if (Loc::isLocType(SSE->getLHS()->getType())) { 56 assert(Loc::isLocType(SSE->getRHS()->getType())); 57 return true; 58 } 59 } 60 } 61 62 return false; 63 } 64 65 return true; 66 } 67 68 ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, 69 DefinedSVal Cond, 70 bool Assumption) { 71 if (Optional<NonLoc> NV = Cond.getAs<NonLoc>()) 72 return assume(state, *NV, Assumption); 73 return assume(state, Cond.castAs<Loc>(), Assumption); 74 } 75 76 ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, Loc cond, 77 bool assumption) { 78 state = assumeAux(state, cond, assumption); 79 if (NotifyAssumeClients && SU) 80 return SU->processAssume(state, cond, assumption); 81 return state; 82 } 83 84 ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state, 85 Loc Cond, bool Assumption) { 86 switch (Cond.getSubKind()) { 87 default: 88 assert (false && "'Assume' not implemented for this Loc."); 89 return state; 90 91 case loc::MemRegionKind: { 92 // FIXME: Should this go into the storemanager? 93 const MemRegion *R = Cond.castAs<loc::MemRegionVal>().getRegion(); 94 95 // FIXME: now we only find the first symbolic region. 96 if (const SymbolicRegion *SymR = R->getSymbolicBase()) { 97 const llvm::APSInt &zero = getBasicVals().getZeroWithPtrWidth(); 98 if (Assumption) 99 return assumeSymNE(state, SymR->getSymbol(), zero, zero); 100 else 101 return assumeSymEQ(state, SymR->getSymbol(), zero, zero); 102 } 103 104 // FALL-THROUGH. 105 } 106 107 case loc::GotoLabelKind: 108 return Assumption ? state : NULL; 109 110 case loc::ConcreteIntKind: { 111 bool b = Cond.castAs<loc::ConcreteInt>().getValue() != 0; 112 bool isFeasible = b ? Assumption : !Assumption; 113 return isFeasible ? state : NULL; 114 } 115 } // end switch 116 } 117 118 ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, 119 NonLoc cond, 120 bool assumption) { 121 state = assumeAux(state, cond, assumption); 122 if (NotifyAssumeClients && SU) 123 return SU->processAssume(state, cond, assumption); 124 return state; 125 } 126 127 128 ProgramStateRef 129 SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State, 130 SymbolRef Sym, bool Assumption) { 131 BasicValueFactory &BVF = getBasicVals(); 132 QualType T = Sym->getType(); 133 134 // None of the constraint solvers currently support non-integer types. 135 if (!T->isIntegralOrEnumerationType()) 136 return State; 137 138 const llvm::APSInt &zero = BVF.getValue(0, T); 139 if (Assumption) 140 return assumeSymNE(State, Sym, zero, zero); 141 else 142 return assumeSymEQ(State, Sym, zero, zero); 143 } 144 145 ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state, 146 NonLoc Cond, 147 bool Assumption) { 148 149 // We cannot reason about SymSymExprs, and can only reason about some 150 // SymIntExprs. 151 if (!canReasonAbout(Cond)) { 152 // Just add the constraint to the expression without trying to simplify. 153 SymbolRef sym = Cond.getAsSymExpr(); 154 return assumeAuxForSymbol(state, sym, Assumption); 155 } 156 157 switch (Cond.getSubKind()) { 158 default: 159 llvm_unreachable("'Assume' not implemented for this NonLoc"); 160 161 case nonloc::SymbolValKind: { 162 nonloc::SymbolVal SV = Cond.castAs<nonloc::SymbolVal>(); 163 SymbolRef sym = SV.getSymbol(); 164 assert(sym); 165 166 // Handle SymbolData. 167 if (!SV.isExpression()) { 168 return assumeAuxForSymbol(state, sym, Assumption); 169 170 // Handle symbolic expression. 171 } else if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym)) { 172 // We can only simplify expressions whose RHS is an integer. 173 174 BinaryOperator::Opcode op = SE->getOpcode(); 175 if (BinaryOperator::isComparisonOp(op)) { 176 if (!Assumption) 177 op = BinaryOperator::negateComparisonOp(op); 178 179 return assumeSymRel(state, SE->getLHS(), op, SE->getRHS()); 180 } 181 182 } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(sym)) { 183 // Translate "a != b" to "(b - a) != 0". 184 // We invert the order of the operands as a heuristic for how loop 185 // conditions are usually written ("begin != end") as compared to length 186 // calculations ("end - begin"). The more correct thing to do would be to 187 // canonicalize "a - b" and "b - a", which would allow us to treat 188 // "a != b" and "b != a" the same. 189 SymbolManager &SymMgr = getSymbolManager(); 190 BinaryOperator::Opcode Op = SSE->getOpcode(); 191 assert(BinaryOperator::isComparisonOp(Op)); 192 193 // For now, we only support comparing pointers. 194 assert(Loc::isLocType(SSE->getLHS()->getType())); 195 assert(Loc::isLocType(SSE->getRHS()->getType())); 196 QualType DiffTy = SymMgr.getContext().getPointerDiffType(); 197 SymbolRef Subtraction = SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, 198 SSE->getLHS(), DiffTy); 199 200 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy); 201 Op = BinaryOperator::reverseComparisonOp(Op); 202 if (!Assumption) 203 Op = BinaryOperator::negateComparisonOp(Op); 204 return assumeSymRel(state, Subtraction, Op, Zero); 205 } 206 207 // If we get here, there's nothing else we can do but treat the symbol as 208 // opaque. 209 return assumeAuxForSymbol(state, sym, Assumption); 210 } 211 212 case nonloc::ConcreteIntKind: { 213 bool b = Cond.castAs<nonloc::ConcreteInt>().getValue() != 0; 214 bool isFeasible = b ? Assumption : !Assumption; 215 return isFeasible ? state : NULL; 216 } 217 218 case nonloc::LocAsIntegerKind: 219 return assumeAux(state, Cond.castAs<nonloc::LocAsInteger>().getLoc(), 220 Assumption); 221 } // end switch 222 } 223 224 static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) { 225 // Is it a "($sym+constant1)" expression? 226 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) { 227 BinaryOperator::Opcode Op = SE->getOpcode(); 228 if (Op == BO_Add || Op == BO_Sub) { 229 Sym = SE->getLHS(); 230 Adjustment = APSIntType(Adjustment).convert(SE->getRHS()); 231 232 // Don't forget to negate the adjustment if it's being subtracted. 233 // This should happen /after/ promotion, in case the value being 234 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'. 235 if (Op == BO_Sub) 236 Adjustment = -Adjustment; 237 } 238 } 239 } 240 241 ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state, 242 const SymExpr *LHS, 243 BinaryOperator::Opcode op, 244 const llvm::APSInt& Int) { 245 assert(BinaryOperator::isComparisonOp(op) && 246 "Non-comparison ops should be rewritten as comparisons to zero."); 247 248 // Get the type used for calculating wraparound. 249 BasicValueFactory &BVF = getBasicVals(); 250 APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType()); 251 252 // We only handle simple comparisons of the form "$sym == constant" 253 // or "($sym+constant1) == constant2". 254 // The adjustment is "constant1" in the above expression. It's used to 255 // "slide" the solution range around for modular arithmetic. For example, 256 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which 257 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to 258 // the subclasses of SimpleConstraintManager to handle the adjustment. 259 SymbolRef Sym = LHS; 260 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 261 computeAdjustment(Sym, Adjustment); 262 263 // Convert the right-hand side integer as necessary. 264 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int)); 265 llvm::APSInt ConvertedInt = ComparisonType.convert(Int); 266 267 // Prefer unsigned comparisons. 268 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 269 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 270 Adjustment.setIsSigned(false); 271 272 switch (op) { 273 default: 274 llvm_unreachable("invalid operation not caught by assertion above"); 275 276 case BO_EQ: 277 return assumeSymEQ(state, Sym, ConvertedInt, Adjustment); 278 279 case BO_NE: 280 return assumeSymNE(state, Sym, ConvertedInt, Adjustment); 281 282 case BO_GT: 283 return assumeSymGT(state, Sym, ConvertedInt, Adjustment); 284 285 case BO_GE: 286 return assumeSymGE(state, Sym, ConvertedInt, Adjustment); 287 288 case BO_LT: 289 return assumeSymLT(state, Sym, ConvertedInt, Adjustment); 290 291 case BO_LE: 292 return assumeSymLE(state, Sym, ConvertedInt, Adjustment); 293 } // end switch 294 } 295 296 } // end of namespace ento 297 298 } // end of namespace clang 299
