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 we have a Loc value, cast it to a bool NonLoc first. 72 if (Optional<Loc> LV = Cond.getAs<Loc>()) { 73 SValBuilder &SVB = state->getStateManager().getSValBuilder(); 74 QualType T; 75 const MemRegion *MR = LV->getAsRegion(); 76 if (const TypedRegion *TR = dyn_cast_or_null<TypedRegion>(MR)) 77 T = TR->getLocationType(); 78 else 79 T = SVB.getContext().VoidPtrTy; 80 81 Cond = SVB.evalCast(*LV, SVB.getContext().BoolTy, T).castAs<DefinedSVal>(); 82 } 83 84 return assume(state, Cond.castAs<NonLoc>(), Assumption); 85 } 86 87 ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, 88 NonLoc cond, 89 bool assumption) { 90 state = assumeAux(state, cond, assumption); 91 if (NotifyAssumeClients && SU) 92 return SU->processAssume(state, cond, assumption); 93 return state; 94 } 95 96 97 ProgramStateRef 98 SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State, 99 SymbolRef Sym, bool Assumption) { 100 BasicValueFactory &BVF = getBasicVals(); 101 QualType T = Sym->getType(); 102 103 // None of the constraint solvers currently support non-integer types. 104 if (!T->isIntegralOrEnumerationType()) 105 return State; 106 107 const llvm::APSInt &zero = BVF.getValue(0, T); 108 if (Assumption) 109 return assumeSymNE(State, Sym, zero, zero); 110 else 111 return assumeSymEQ(State, Sym, zero, zero); 112 } 113 114 ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state, 115 NonLoc Cond, 116 bool Assumption) { 117 118 // We cannot reason about SymSymExprs, and can only reason about some 119 // SymIntExprs. 120 if (!canReasonAbout(Cond)) { 121 // Just add the constraint to the expression without trying to simplify. 122 SymbolRef sym = Cond.getAsSymExpr(); 123 return assumeAuxForSymbol(state, sym, Assumption); 124 } 125 126 switch (Cond.getSubKind()) { 127 default: 128 llvm_unreachable("'Assume' not implemented for this NonLoc"); 129 130 case nonloc::SymbolValKind: { 131 nonloc::SymbolVal SV = Cond.castAs<nonloc::SymbolVal>(); 132 SymbolRef sym = SV.getSymbol(); 133 assert(sym); 134 135 // Handle SymbolData. 136 if (!SV.isExpression()) { 137 return assumeAuxForSymbol(state, sym, Assumption); 138 139 // Handle symbolic expression. 140 } else if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym)) { 141 // We can only simplify expressions whose RHS is an integer. 142 143 BinaryOperator::Opcode op = SE->getOpcode(); 144 if (BinaryOperator::isComparisonOp(op)) { 145 if (!Assumption) 146 op = BinaryOperator::negateComparisonOp(op); 147 148 return assumeSymRel(state, SE->getLHS(), op, SE->getRHS()); 149 } 150 151 } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(sym)) { 152 // Translate "a != b" to "(b - a) != 0". 153 // We invert the order of the operands as a heuristic for how loop 154 // conditions are usually written ("begin != end") as compared to length 155 // calculations ("end - begin"). The more correct thing to do would be to 156 // canonicalize "a - b" and "b - a", which would allow us to treat 157 // "a != b" and "b != a" the same. 158 SymbolManager &SymMgr = getSymbolManager(); 159 BinaryOperator::Opcode Op = SSE->getOpcode(); 160 assert(BinaryOperator::isComparisonOp(Op)); 161 162 // For now, we only support comparing pointers. 163 assert(Loc::isLocType(SSE->getLHS()->getType())); 164 assert(Loc::isLocType(SSE->getRHS()->getType())); 165 QualType DiffTy = SymMgr.getContext().getPointerDiffType(); 166 SymbolRef Subtraction = SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, 167 SSE->getLHS(), DiffTy); 168 169 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy); 170 Op = BinaryOperator::reverseComparisonOp(Op); 171 if (!Assumption) 172 Op = BinaryOperator::negateComparisonOp(Op); 173 return assumeSymRel(state, Subtraction, Op, Zero); 174 } 175 176 // If we get here, there's nothing else we can do but treat the symbol as 177 // opaque. 178 return assumeAuxForSymbol(state, sym, Assumption); 179 } 180 181 case nonloc::ConcreteIntKind: { 182 bool b = Cond.castAs<nonloc::ConcreteInt>().getValue() != 0; 183 bool isFeasible = b ? Assumption : !Assumption; 184 return isFeasible ? state : nullptr; 185 } 186 187 case nonloc::LocAsIntegerKind: 188 return assume(state, Cond.castAs<nonloc::LocAsInteger>().getLoc(), 189 Assumption); 190 } // end switch 191 } 192 193 ProgramStateRef SimpleConstraintManager::assumeWithinInclusiveRange( 194 ProgramStateRef State, NonLoc Value, const llvm::APSInt &From, 195 const llvm::APSInt &To, bool InRange) { 196 197 assert(From.isUnsigned() == To.isUnsigned() && 198 From.getBitWidth() == To.getBitWidth() && 199 "Values should have same types!"); 200 201 if (!canReasonAbout(Value)) { 202 // Just add the constraint to the expression without trying to simplify. 203 SymbolRef Sym = Value.getAsSymExpr(); 204 assert(Sym); 205 return assumeSymWithinInclusiveRange(State, Sym, From, To, InRange); 206 } 207 208 switch (Value.getSubKind()) { 209 default: 210 llvm_unreachable("'assumeWithinInclusiveRange' is not implemented" 211 "for this NonLoc"); 212 213 case nonloc::LocAsIntegerKind: 214 case nonloc::SymbolValKind: { 215 if (SymbolRef Sym = Value.getAsSymbol()) 216 return assumeSymWithinInclusiveRange(State, Sym, From, To, InRange); 217 return State; 218 } // end switch 219 220 case nonloc::ConcreteIntKind: { 221 const llvm::APSInt &IntVal = Value.castAs<nonloc::ConcreteInt>().getValue(); 222 bool IsInRange = IntVal >= From && IntVal <= To; 223 bool isFeasible = (IsInRange == InRange); 224 return isFeasible ? State : nullptr; 225 } 226 } // end switch 227 } 228 229 static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) { 230 // Is it a "($sym+constant1)" expression? 231 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) { 232 BinaryOperator::Opcode Op = SE->getOpcode(); 233 if (Op == BO_Add || Op == BO_Sub) { 234 Sym = SE->getLHS(); 235 Adjustment = APSIntType(Adjustment).convert(SE->getRHS()); 236 237 // Don't forget to negate the adjustment if it's being subtracted. 238 // This should happen /after/ promotion, in case the value being 239 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'. 240 if (Op == BO_Sub) 241 Adjustment = -Adjustment; 242 } 243 } 244 } 245 246 ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state, 247 const SymExpr *LHS, 248 BinaryOperator::Opcode op, 249 const llvm::APSInt& Int) { 250 assert(BinaryOperator::isComparisonOp(op) && 251 "Non-comparison ops should be rewritten as comparisons to zero."); 252 253 // Get the type used for calculating wraparound. 254 BasicValueFactory &BVF = getBasicVals(); 255 APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType()); 256 257 // We only handle simple comparisons of the form "$sym == constant" 258 // or "($sym+constant1) == constant2". 259 // The adjustment is "constant1" in the above expression. It's used to 260 // "slide" the solution range around for modular arithmetic. For example, 261 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which 262 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to 263 // the subclasses of SimpleConstraintManager to handle the adjustment. 264 SymbolRef Sym = LHS; 265 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 266 computeAdjustment(Sym, Adjustment); 267 268 // Convert the right-hand side integer as necessary. 269 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int)); 270 llvm::APSInt ConvertedInt = ComparisonType.convert(Int); 271 272 // Prefer unsigned comparisons. 273 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 274 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 275 Adjustment.setIsSigned(false); 276 277 switch (op) { 278 default: 279 llvm_unreachable("invalid operation not caught by assertion above"); 280 281 case BO_EQ: 282 return assumeSymEQ(state, Sym, ConvertedInt, Adjustment); 283 284 case BO_NE: 285 return assumeSymNE(state, Sym, ConvertedInt, Adjustment); 286 287 case BO_GT: 288 return assumeSymGT(state, Sym, ConvertedInt, Adjustment); 289 290 case BO_GE: 291 return assumeSymGE(state, Sym, ConvertedInt, Adjustment); 292 293 case BO_LT: 294 return assumeSymLT(state, Sym, ConvertedInt, Adjustment); 295 296 case BO_LE: 297 return assumeSymLE(state, Sym, ConvertedInt, Adjustment); 298 } // end switch 299 } 300 301 ProgramStateRef 302 SimpleConstraintManager::assumeSymWithinInclusiveRange(ProgramStateRef State, 303 SymbolRef Sym, 304 const llvm::APSInt &From, 305 const llvm::APSInt &To, 306 bool InRange) { 307 // Get the type used for calculating wraparound. 308 BasicValueFactory &BVF = getBasicVals(); 309 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType()); 310 311 llvm::APSInt Adjustment = WraparoundType.getZeroValue(); 312 SymbolRef AdjustedSym = Sym; 313 computeAdjustment(AdjustedSym, Adjustment); 314 315 // Convert the right-hand side integer as necessary. 316 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From)); 317 llvm::APSInt ConvertedFrom = ComparisonType.convert(From); 318 llvm::APSInt ConvertedTo = ComparisonType.convert(To); 319 320 // Prefer unsigned comparisons. 321 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() && 322 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned()) 323 Adjustment.setIsSigned(false); 324 325 if (InRange) 326 return assumeSymbolWithinInclusiveRange(State, AdjustedSym, ConvertedFrom, 327 ConvertedTo, Adjustment); 328 return assumeSymbolOutOfInclusiveRange(State, AdjustedSym, ConvertedFrom, 329 ConvertedTo, Adjustment); 330 } 331 332 } // end of namespace ento 333 334 } // end of namespace clang 335
