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 94 const MemRegion *R = Cond.castAs<loc::MemRegionVal>().getRegion(); 95 const SubRegion *SubR = dyn_cast<SubRegion>(R); 96 97 while (SubR) { 98 // FIXME: now we only find the first symbolic region. 99 if (const SymbolicRegion *SymR = dyn_cast<SymbolicRegion>(SubR)) { 100 const llvm::APSInt &zero = getBasicVals().getZeroWithPtrWidth(); 101 if (Assumption) 102 return assumeSymNE(state, SymR->getSymbol(), zero, zero); 103 else 104 return assumeSymEQ(state, SymR->getSymbol(), zero, zero); 105 } 106 SubR = dyn_cast<SubRegion>(SubR->getSuperRegion()); 107 } 108 109 // FALL-THROUGH. 110 } 111 112 case loc::GotoLabelKind: 113 return Assumption ? state : NULL; 114 115 case loc::ConcreteIntKind: { 116 bool b = Cond.castAs<loc::ConcreteInt>().getValue() != 0; 117 bool isFeasible = b ? Assumption : !Assumption; 118 return isFeasible ? state : NULL; 119 } 120 } // end switch 121 } 122 123 ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, 124 NonLoc cond, 125 bool assumption) { 126 state = assumeAux(state, cond, assumption); 127 if (NotifyAssumeClients && SU) 128 return SU->processAssume(state, cond, assumption); 129 return state; 130 } 131 132 133 ProgramStateRef 134 SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State, 135 SymbolRef Sym, bool Assumption) { 136 BasicValueFactory &BVF = getBasicVals(); 137 QualType T = Sym->getType(); 138 139 // None of the constraint solvers currently support non-integer types. 140 if (!T->isIntegralOrEnumerationType()) 141 return State; 142 143 const llvm::APSInt &zero = BVF.getValue(0, T); 144 if (Assumption) 145 return assumeSymNE(State, Sym, zero, zero); 146 else 147 return assumeSymEQ(State, Sym, zero, zero); 148 } 149 150 ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state, 151 NonLoc Cond, 152 bool Assumption) { 153 154 // We cannot reason about SymSymExprs, and can only reason about some 155 // SymIntExprs. 156 if (!canReasonAbout(Cond)) { 157 // Just add the constraint to the expression without trying to simplify. 158 SymbolRef sym = Cond.getAsSymExpr(); 159 return assumeAuxForSymbol(state, sym, Assumption); 160 } 161 162 switch (Cond.getSubKind()) { 163 default: 164 llvm_unreachable("'Assume' not implemented for this NonLoc"); 165 166 case nonloc::SymbolValKind: { 167 nonloc::SymbolVal SV = Cond.castAs<nonloc::SymbolVal>(); 168 SymbolRef sym = SV.getSymbol(); 169 assert(sym); 170 171 // Handle SymbolData. 172 if (!SV.isExpression()) { 173 return assumeAuxForSymbol(state, sym, Assumption); 174 175 // Handle symbolic expression. 176 } else if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym)) { 177 // We can only simplify expressions whose RHS is an integer. 178 179 BinaryOperator::Opcode op = SE->getOpcode(); 180 if (BinaryOperator::isComparisonOp(op)) { 181 if (!Assumption) 182 op = BinaryOperator::negateComparisonOp(op); 183 184 return assumeSymRel(state, SE->getLHS(), op, SE->getRHS()); 185 } 186 187 } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(sym)) { 188 // Translate "a != b" to "(b - a) != 0". 189 // We invert the order of the operands as a heuristic for how loop 190 // conditions are usually written ("begin != end") as compared to length 191 // calculations ("end - begin"). The more correct thing to do would be to 192 // canonicalize "a - b" and "b - a", which would allow us to treat 193 // "a != b" and "b != a" the same. 194 SymbolManager &SymMgr = getSymbolManager(); 195 BinaryOperator::Opcode Op = SSE->getOpcode(); 196 assert(BinaryOperator::isComparisonOp(Op)); 197 198 // For now, we only support comparing pointers. 199 assert(Loc::isLocType(SSE->getLHS()->getType())); 200 assert(Loc::isLocType(SSE->getRHS()->getType())); 201 QualType DiffTy = SymMgr.getContext().getPointerDiffType(); 202 SymbolRef Subtraction = SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, 203 SSE->getLHS(), DiffTy); 204 205 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy); 206 Op = BinaryOperator::reverseComparisonOp(Op); 207 if (!Assumption) 208 Op = BinaryOperator::negateComparisonOp(Op); 209 return assumeSymRel(state, Subtraction, Op, Zero); 210 } 211 212 // If we get here, there's nothing else we can do but treat the symbol as 213 // opaque. 214 return assumeAuxForSymbol(state, sym, Assumption); 215 } 216 217 case nonloc::ConcreteIntKind: { 218 bool b = Cond.castAs<nonloc::ConcreteInt>().getValue() != 0; 219 bool isFeasible = b ? Assumption : !Assumption; 220 return isFeasible ? state : NULL; 221 } 222 223 case nonloc::LocAsIntegerKind: 224 return assumeAux(state, Cond.castAs<nonloc::LocAsInteger>().getLoc(), 225 Assumption); 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 } // end of namespace ento 302 303 } // end of namespace clang 304