1 // SimpleSValBuilder.cpp - A basic SValBuilder -----------------------*- 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 SimpleSValBuilder, a basic implementation of SValBuilder. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h" 14 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h" 15 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 16 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h" 17 #include "clang/StaticAnalyzer/Core/PathSensitive/SValVisitor.h" 18 #include <optional> 19 20 using namespace clang; 21 using namespace ento; 22 23 namespace { 24 class SimpleSValBuilder : public SValBuilder { 25 26 // Query the constraint manager whether the SVal has only one possible 27 // (integer) value. If that is the case, the value is returned. Otherwise, 28 // returns NULL. 29 // This is an implementation detail. Checkers should use `getKnownValue()` 30 // instead. 31 static const llvm::APSInt *getConstValue(ProgramStateRef state, SVal V); 32 33 // Helper function that returns the value stored in a nonloc::ConcreteInt or 34 // loc::ConcreteInt. 35 static const llvm::APSInt *getConcreteValue(SVal V); 36 37 // With one `simplifySValOnce` call, a compound symbols might collapse to 38 // simpler symbol tree that is still possible to further simplify. Thus, we 39 // do the simplification on a new symbol tree until we reach the simplest 40 // form, i.e. the fixpoint. 41 // Consider the following symbol `(b * b) * b * b` which has this tree: 42 // * 43 // / \ 44 // * b 45 // / \ 46 // / b 47 // (b * b) 48 // Now, if the `b * b == 1` new constraint is added then during the first 49 // iteration we have the following transformations: 50 // * * 51 // / \ / \ 52 // * b --> b b 53 // / \ 54 // / b 55 // 1 56 // We need another iteration to reach the final result `1`. 57 SVal simplifyUntilFixpoint(ProgramStateRef State, SVal Val); 58 59 // Recursively descends into symbolic expressions and replaces symbols 60 // with their known values (in the sense of the getConstValue() method). 61 // We traverse the symbol tree and query the constraint values for the 62 // sub-trees and if a value is a constant we do the constant folding. 63 SVal simplifySValOnce(ProgramStateRef State, SVal V); 64 65 public: 66 SimpleSValBuilder(llvm::BumpPtrAllocator &alloc, ASTContext &context, 67 ProgramStateManager &stateMgr) 68 : SValBuilder(alloc, context, stateMgr) {} 69 ~SimpleSValBuilder() override {} 70 71 SVal evalBinOpNN(ProgramStateRef state, BinaryOperator::Opcode op, 72 NonLoc lhs, NonLoc rhs, QualType resultTy) override; 73 SVal evalBinOpLL(ProgramStateRef state, BinaryOperator::Opcode op, 74 Loc lhs, Loc rhs, QualType resultTy) override; 75 SVal evalBinOpLN(ProgramStateRef state, BinaryOperator::Opcode op, 76 Loc lhs, NonLoc rhs, QualType resultTy) override; 77 78 /// Evaluates a given SVal by recursively evaluating and 79 /// simplifying the children SVals. If the SVal has only one possible 80 /// (integer) value, that value is returned. Otherwise, returns NULL. 81 const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal V) override; 82 83 /// Evaluates a given SVal by recursively evaluating and simplifying the 84 /// children SVals, then returns its minimal possible (integer) value. If the 85 /// constraint manager cannot provide a meaningful answer, this returns NULL. 86 const llvm::APSInt *getMinValue(ProgramStateRef state, SVal V) override; 87 88 /// Evaluates a given SVal by recursively evaluating and simplifying the 89 /// children SVals, then returns its maximal possible (integer) value. If the 90 /// constraint manager cannot provide a meaningful answer, this returns NULL. 91 const llvm::APSInt *getMaxValue(ProgramStateRef state, SVal V) override; 92 93 SVal simplifySVal(ProgramStateRef State, SVal V) override; 94 95 SVal MakeSymIntVal(const SymExpr *LHS, BinaryOperator::Opcode op, 96 const llvm::APSInt &RHS, QualType resultTy); 97 }; 98 } // end anonymous namespace 99 100 SValBuilder *ento::createSimpleSValBuilder(llvm::BumpPtrAllocator &alloc, 101 ASTContext &context, 102 ProgramStateManager &stateMgr) { 103 return new SimpleSValBuilder(alloc, context, stateMgr); 104 } 105 106 // Checks if the negation the value and flipping sign preserve 107 // the semantics on the operation in the resultType 108 static bool isNegationValuePreserving(const llvm::APSInt &Value, 109 APSIntType ResultType) { 110 const unsigned ValueBits = Value.getSignificantBits(); 111 if (ValueBits == ResultType.getBitWidth()) { 112 // The value is the lowest negative value that is representable 113 // in signed integer with bitWith of result type. The 114 // negation is representable if resultType is unsigned. 115 return ResultType.isUnsigned(); 116 } 117 118 // If resultType bitWith is higher that number of bits required 119 // to represent RHS, the sign flip produce same value. 120 return ValueBits < ResultType.getBitWidth(); 121 } 122 123 //===----------------------------------------------------------------------===// 124 // Transfer function for binary operators. 125 //===----------------------------------------------------------------------===// 126 127 SVal SimpleSValBuilder::MakeSymIntVal(const SymExpr *LHS, 128 BinaryOperator::Opcode op, 129 const llvm::APSInt &RHS, 130 QualType resultTy) { 131 bool isIdempotent = false; 132 133 // Check for a few special cases with known reductions first. 134 switch (op) { 135 default: 136 // We can't reduce this case; just treat it normally. 137 break; 138 case BO_Mul: 139 // a*0 and a*1 140 if (RHS == 0) 141 return makeIntVal(0, resultTy); 142 else if (RHS == 1) 143 isIdempotent = true; 144 break; 145 case BO_Div: 146 // a/0 and a/1 147 if (RHS == 0) 148 // This is also handled elsewhere. 149 return UndefinedVal(); 150 else if (RHS == 1) 151 isIdempotent = true; 152 break; 153 case BO_Rem: 154 // a%0 and a%1 155 if (RHS == 0) 156 // This is also handled elsewhere. 157 return UndefinedVal(); 158 else if (RHS == 1) 159 return makeIntVal(0, resultTy); 160 break; 161 case BO_Add: 162 case BO_Sub: 163 case BO_Shl: 164 case BO_Shr: 165 case BO_Xor: 166 // a+0, a-0, a<<0, a>>0, a^0 167 if (RHS == 0) 168 isIdempotent = true; 169 break; 170 case BO_And: 171 // a&0 and a&(~0) 172 if (RHS == 0) 173 return makeIntVal(0, resultTy); 174 else if (RHS.isAllOnes()) 175 isIdempotent = true; 176 break; 177 case BO_Or: 178 // a|0 and a|(~0) 179 if (RHS == 0) 180 isIdempotent = true; 181 else if (RHS.isAllOnes()) { 182 const llvm::APSInt &Result = BasicVals.Convert(resultTy, RHS); 183 return nonloc::ConcreteInt(Result); 184 } 185 break; 186 } 187 188 // Idempotent ops (like a*1) can still change the type of an expression. 189 // Wrap the LHS up in a NonLoc again and let evalCast do the 190 // dirty work. 191 if (isIdempotent) 192 return evalCast(nonloc::SymbolVal(LHS), resultTy, QualType{}); 193 194 // If we reach this point, the expression cannot be simplified. 195 // Make a SymbolVal for the entire expression, after converting the RHS. 196 const llvm::APSInt *ConvertedRHS = &RHS; 197 if (BinaryOperator::isComparisonOp(op)) { 198 // We're looking for a type big enough to compare the symbolic value 199 // with the given constant. 200 // FIXME: This is an approximation of Sema::UsualArithmeticConversions. 201 ASTContext &Ctx = getContext(); 202 QualType SymbolType = LHS->getType(); 203 uint64_t ValWidth = RHS.getBitWidth(); 204 uint64_t TypeWidth = Ctx.getTypeSize(SymbolType); 205 206 if (ValWidth < TypeWidth) { 207 // If the value is too small, extend it. 208 ConvertedRHS = &BasicVals.Convert(SymbolType, RHS); 209 } else if (ValWidth == TypeWidth) { 210 // If the value is signed but the symbol is unsigned, do the comparison 211 // in unsigned space. [C99 6.3.1.8] 212 // (For the opposite case, the value is already unsigned.) 213 if (RHS.isSigned() && !SymbolType->isSignedIntegerOrEnumerationType()) 214 ConvertedRHS = &BasicVals.Convert(SymbolType, RHS); 215 } 216 } else if (BinaryOperator::isAdditiveOp(op) && RHS.isNegative()) { 217 // Change a+(-N) into a-N, and a-(-N) into a+N 218 // Adjust addition/subtraction of negative value, to 219 // subtraction/addition of the negated value. 220 APSIntType resultIntTy = BasicVals.getAPSIntType(resultTy); 221 if (isNegationValuePreserving(RHS, resultIntTy)) { 222 ConvertedRHS = &BasicVals.getValue(-resultIntTy.convert(RHS)); 223 op = (op == BO_Add) ? BO_Sub : BO_Add; 224 } else { 225 ConvertedRHS = &BasicVals.Convert(resultTy, RHS); 226 } 227 } else 228 ConvertedRHS = &BasicVals.Convert(resultTy, RHS); 229 230 return makeNonLoc(LHS, op, *ConvertedRHS, resultTy); 231 } 232 233 // See if Sym is known to be a relation Rel with Bound. 234 static bool isInRelation(BinaryOperator::Opcode Rel, SymbolRef Sym, 235 llvm::APSInt Bound, ProgramStateRef State) { 236 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 237 SVal Result = 238 SVB.evalBinOpNN(State, Rel, nonloc::SymbolVal(Sym), 239 nonloc::ConcreteInt(Bound), SVB.getConditionType()); 240 if (auto DV = Result.getAs<DefinedSVal>()) { 241 return !State->assume(*DV, false); 242 } 243 return false; 244 } 245 246 // See if Sym is known to be within [min/4, max/4], where min and max 247 // are the bounds of the symbol's integral type. With such symbols, 248 // some manipulations can be performed without the risk of overflow. 249 // assume() doesn't cause infinite recursion because we should be dealing 250 // with simpler symbols on every recursive call. 251 static bool isWithinConstantOverflowBounds(SymbolRef Sym, 252 ProgramStateRef State) { 253 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 254 BasicValueFactory &BV = SVB.getBasicValueFactory(); 255 256 QualType T = Sym->getType(); 257 assert(T->isSignedIntegerOrEnumerationType() && 258 "This only works with signed integers!"); 259 APSIntType AT = BV.getAPSIntType(T); 260 261 llvm::APSInt Max = AT.getMaxValue() / AT.getValue(4), Min = -Max; 262 return isInRelation(BO_LE, Sym, Max, State) && 263 isInRelation(BO_GE, Sym, Min, State); 264 } 265 266 // Same for the concrete integers: see if I is within [min/4, max/4]. 267 static bool isWithinConstantOverflowBounds(llvm::APSInt I) { 268 APSIntType AT(I); 269 assert(!AT.isUnsigned() && 270 "This only works with signed integers!"); 271 272 llvm::APSInt Max = AT.getMaxValue() / AT.getValue(4), Min = -Max; 273 return (I <= Max) && (I >= -Max); 274 } 275 276 static std::pair<SymbolRef, llvm::APSInt> 277 decomposeSymbol(SymbolRef Sym, BasicValueFactory &BV) { 278 if (const auto *SymInt = dyn_cast<SymIntExpr>(Sym)) 279 if (BinaryOperator::isAdditiveOp(SymInt->getOpcode())) 280 return std::make_pair(SymInt->getLHS(), 281 (SymInt->getOpcode() == BO_Add) ? 282 (SymInt->getRHS()) : 283 (-SymInt->getRHS())); 284 285 // Fail to decompose: "reduce" the problem to the "$x + 0" case. 286 return std::make_pair(Sym, BV.getValue(0, Sym->getType())); 287 } 288 289 // Simplify "(LSym + LInt) Op (RSym + RInt)" assuming all values are of the 290 // same signed integral type and no overflows occur (which should be checked 291 // by the caller). 292 static NonLoc doRearrangeUnchecked(ProgramStateRef State, 293 BinaryOperator::Opcode Op, 294 SymbolRef LSym, llvm::APSInt LInt, 295 SymbolRef RSym, llvm::APSInt RInt) { 296 SValBuilder &SVB = State->getStateManager().getSValBuilder(); 297 BasicValueFactory &BV = SVB.getBasicValueFactory(); 298 SymbolManager &SymMgr = SVB.getSymbolManager(); 299 300 QualType SymTy = LSym->getType(); 301 assert(SymTy == RSym->getType() && 302 "Symbols are not of the same type!"); 303 assert(APSIntType(LInt) == BV.getAPSIntType(SymTy) && 304 "Integers are not of the same type as symbols!"); 305 assert(APSIntType(RInt) == BV.getAPSIntType(SymTy) && 306 "Integers are not of the same type as symbols!"); 307 308 QualType ResultTy; 309 if (BinaryOperator::isComparisonOp(Op)) 310 ResultTy = SVB.getConditionType(); 311 else if (BinaryOperator::isAdditiveOp(Op)) 312 ResultTy = SymTy; 313 else 314 llvm_unreachable("Operation not suitable for unchecked rearrangement!"); 315 316 if (LSym == RSym) 317 return SVB.evalBinOpNN(State, Op, nonloc::ConcreteInt(LInt), 318 nonloc::ConcreteInt(RInt), ResultTy) 319 .castAs<NonLoc>(); 320 321 SymbolRef ResultSym = nullptr; 322 BinaryOperator::Opcode ResultOp; 323 llvm::APSInt ResultInt; 324 if (BinaryOperator::isComparisonOp(Op)) { 325 // Prefer comparing to a non-negative number. 326 // FIXME: Maybe it'd be better to have consistency in 327 // "$x - $y" vs. "$y - $x" because those are solver's keys. 328 if (LInt > RInt) { 329 ResultSym = SymMgr.getSymSymExpr(RSym, BO_Sub, LSym, SymTy); 330 ResultOp = BinaryOperator::reverseComparisonOp(Op); 331 ResultInt = LInt - RInt; // Opposite order! 332 } else { 333 ResultSym = SymMgr.getSymSymExpr(LSym, BO_Sub, RSym, SymTy); 334 ResultOp = Op; 335 ResultInt = RInt - LInt; // Opposite order! 336 } 337 } else { 338 ResultSym = SymMgr.getSymSymExpr(LSym, Op, RSym, SymTy); 339 ResultInt = (Op == BO_Add) ? (LInt + RInt) : (LInt - RInt); 340 ResultOp = BO_Add; 341 // Bring back the cosmetic difference. 342 if (ResultInt < 0) { 343 ResultInt = -ResultInt; 344 ResultOp = BO_Sub; 345 } else if (ResultInt == 0) { 346 // Shortcut: Simplify "$x + 0" to "$x". 347 return nonloc::SymbolVal(ResultSym); 348 } 349 } 350 const llvm::APSInt &PersistentResultInt = BV.getValue(ResultInt); 351 return nonloc::SymbolVal( 352 SymMgr.getSymIntExpr(ResultSym, ResultOp, PersistentResultInt, ResultTy)); 353 } 354 355 // Rearrange if symbol type matches the result type and if the operator is a 356 // comparison operator, both symbol and constant must be within constant 357 // overflow bounds. 358 static bool shouldRearrange(ProgramStateRef State, BinaryOperator::Opcode Op, 359 SymbolRef Sym, llvm::APSInt Int, QualType Ty) { 360 return Sym->getType() == Ty && 361 (!BinaryOperator::isComparisonOp(Op) || 362 (isWithinConstantOverflowBounds(Sym, State) && 363 isWithinConstantOverflowBounds(Int))); 364 } 365 366 static std::optional<NonLoc> tryRearrange(ProgramStateRef State, 367 BinaryOperator::Opcode Op, NonLoc Lhs, 368 NonLoc Rhs, QualType ResultTy) { 369 ProgramStateManager &StateMgr = State->getStateManager(); 370 SValBuilder &SVB = StateMgr.getSValBuilder(); 371 372 // We expect everything to be of the same type - this type. 373 QualType SingleTy; 374 375 // FIXME: After putting complexity threshold to the symbols we can always 376 // rearrange additive operations but rearrange comparisons only if 377 // option is set. 378 if (!SVB.getAnalyzerOptions().ShouldAggressivelySimplifyBinaryOperation) 379 return std::nullopt; 380 381 SymbolRef LSym = Lhs.getAsSymbol(); 382 if (!LSym) 383 return std::nullopt; 384 385 if (BinaryOperator::isComparisonOp(Op)) { 386 SingleTy = LSym->getType(); 387 if (ResultTy != SVB.getConditionType()) 388 return std::nullopt; 389 // Initialize SingleTy later with a symbol's type. 390 } else if (BinaryOperator::isAdditiveOp(Op)) { 391 SingleTy = ResultTy; 392 if (LSym->getType() != SingleTy) 393 return std::nullopt; 394 } else { 395 // Don't rearrange other operations. 396 return std::nullopt; 397 } 398 399 assert(!SingleTy.isNull() && "We should have figured out the type by now!"); 400 401 // Rearrange signed symbolic expressions only 402 if (!SingleTy->isSignedIntegerOrEnumerationType()) 403 return std::nullopt; 404 405 SymbolRef RSym = Rhs.getAsSymbol(); 406 if (!RSym || RSym->getType() != SingleTy) 407 return std::nullopt; 408 409 BasicValueFactory &BV = State->getBasicVals(); 410 llvm::APSInt LInt, RInt; 411 std::tie(LSym, LInt) = decomposeSymbol(LSym, BV); 412 std::tie(RSym, RInt) = decomposeSymbol(RSym, BV); 413 if (!shouldRearrange(State, Op, LSym, LInt, SingleTy) || 414 !shouldRearrange(State, Op, RSym, RInt, SingleTy)) 415 return std::nullopt; 416 417 // We know that no overflows can occur anymore. 418 return doRearrangeUnchecked(State, Op, LSym, LInt, RSym, RInt); 419 } 420 421 SVal SimpleSValBuilder::evalBinOpNN(ProgramStateRef state, 422 BinaryOperator::Opcode op, 423 NonLoc lhs, NonLoc rhs, 424 QualType resultTy) { 425 NonLoc InputLHS = lhs; 426 NonLoc InputRHS = rhs; 427 428 // Constraints may have changed since the creation of a bound SVal. Check if 429 // the values can be simplified based on those new constraints. 430 SVal simplifiedLhs = simplifySVal(state, lhs); 431 SVal simplifiedRhs = simplifySVal(state, rhs); 432 if (auto simplifiedLhsAsNonLoc = simplifiedLhs.getAs<NonLoc>()) 433 lhs = *simplifiedLhsAsNonLoc; 434 if (auto simplifiedRhsAsNonLoc = simplifiedRhs.getAs<NonLoc>()) 435 rhs = *simplifiedRhsAsNonLoc; 436 437 // Handle trivial case where left-side and right-side are the same. 438 if (lhs == rhs) 439 switch (op) { 440 default: 441 break; 442 case BO_EQ: 443 case BO_LE: 444 case BO_GE: 445 return makeTruthVal(true, resultTy); 446 case BO_LT: 447 case BO_GT: 448 case BO_NE: 449 return makeTruthVal(false, resultTy); 450 case BO_Xor: 451 case BO_Sub: 452 if (resultTy->isIntegralOrEnumerationType()) 453 return makeIntVal(0, resultTy); 454 return evalCast(makeIntVal(0, /*isUnsigned=*/false), resultTy, 455 QualType{}); 456 case BO_Or: 457 case BO_And: 458 return evalCast(lhs, resultTy, QualType{}); 459 } 460 461 while (true) { 462 switch (lhs.getKind()) { 463 default: 464 return makeSymExprValNN(op, lhs, rhs, resultTy); 465 case nonloc::PointerToMemberKind: { 466 assert(rhs.getKind() == nonloc::PointerToMemberKind && 467 "Both SVals should have pointer-to-member-type"); 468 auto LPTM = lhs.castAs<nonloc::PointerToMember>(), 469 RPTM = rhs.castAs<nonloc::PointerToMember>(); 470 auto LPTMD = LPTM.getPTMData(), RPTMD = RPTM.getPTMData(); 471 switch (op) { 472 case BO_EQ: 473 return makeTruthVal(LPTMD == RPTMD, resultTy); 474 case BO_NE: 475 return makeTruthVal(LPTMD != RPTMD, resultTy); 476 default: 477 return UnknownVal(); 478 } 479 } 480 case nonloc::LocAsIntegerKind: { 481 Loc lhsL = lhs.castAs<nonloc::LocAsInteger>().getLoc(); 482 switch (rhs.getKind()) { 483 case nonloc::LocAsIntegerKind: 484 // FIXME: at the moment the implementation 485 // of modeling "pointers as integers" is not complete. 486 if (!BinaryOperator::isComparisonOp(op)) 487 return UnknownVal(); 488 return evalBinOpLL(state, op, lhsL, 489 rhs.castAs<nonloc::LocAsInteger>().getLoc(), 490 resultTy); 491 case nonloc::ConcreteIntKind: { 492 // FIXME: at the moment the implementation 493 // of modeling "pointers as integers" is not complete. 494 if (!BinaryOperator::isComparisonOp(op)) 495 return UnknownVal(); 496 // Transform the integer into a location and compare. 497 // FIXME: This only makes sense for comparisons. If we want to, say, 498 // add 1 to a LocAsInteger, we'd better unpack the Loc and add to it, 499 // then pack it back into a LocAsInteger. 500 llvm::APSInt i = rhs.castAs<nonloc::ConcreteInt>().getValue(); 501 // If the region has a symbolic base, pay attention to the type; it 502 // might be coming from a non-default address space. For non-symbolic 503 // regions it doesn't matter that much because such comparisons would 504 // most likely evaluate to concrete false anyway. FIXME: We might 505 // still need to handle the non-comparison case. 506 if (SymbolRef lSym = lhs.getAsLocSymbol(true)) 507 BasicVals.getAPSIntType(lSym->getType()).apply(i); 508 else 509 BasicVals.getAPSIntType(Context.VoidPtrTy).apply(i); 510 return evalBinOpLL(state, op, lhsL, makeLoc(i), resultTy); 511 } 512 default: 513 switch (op) { 514 case BO_EQ: 515 return makeTruthVal(false, resultTy); 516 case BO_NE: 517 return makeTruthVal(true, resultTy); 518 default: 519 // This case also handles pointer arithmetic. 520 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy); 521 } 522 } 523 } 524 case nonloc::ConcreteIntKind: { 525 llvm::APSInt LHSValue = lhs.castAs<nonloc::ConcreteInt>().getValue(); 526 527 // If we're dealing with two known constants, just perform the operation. 528 if (const llvm::APSInt *KnownRHSValue = getConstValue(state, rhs)) { 529 llvm::APSInt RHSValue = *KnownRHSValue; 530 if (BinaryOperator::isComparisonOp(op)) { 531 // We're looking for a type big enough to compare the two values. 532 // FIXME: This is not correct. char + short will result in a promotion 533 // to int. Unfortunately we have lost types by this point. 534 APSIntType CompareType = std::max(APSIntType(LHSValue), 535 APSIntType(RHSValue)); 536 CompareType.apply(LHSValue); 537 CompareType.apply(RHSValue); 538 } else if (!BinaryOperator::isShiftOp(op)) { 539 APSIntType IntType = BasicVals.getAPSIntType(resultTy); 540 IntType.apply(LHSValue); 541 IntType.apply(RHSValue); 542 } 543 544 const llvm::APSInt *Result = 545 BasicVals.evalAPSInt(op, LHSValue, RHSValue); 546 if (!Result) { 547 if (op == BO_Shl || op == BO_Shr) { 548 // FIXME: At this point the constant folding claims that the result 549 // of a bitwise shift is undefined. However, constant folding 550 // relies on the inaccurate type information that is stored in the 551 // bit size of APSInt objects, and if we reached this point, then 552 // the checker core.BitwiseShift already determined that the shift 553 // is valid (in a PreStmt callback, by querying the real type from 554 // the AST node). 555 // To avoid embarrassing false positives, let's just say that we 556 // don't know anything about the result of the shift. 557 return UnknownVal(); 558 } 559 return UndefinedVal(); 560 } 561 562 return nonloc::ConcreteInt(*Result); 563 } 564 565 // Swap the left and right sides and flip the operator if doing so 566 // allows us to better reason about the expression (this is a form 567 // of expression canonicalization). 568 // While we're at it, catch some special cases for non-commutative ops. 569 switch (op) { 570 case BO_LT: 571 case BO_GT: 572 case BO_LE: 573 case BO_GE: 574 op = BinaryOperator::reverseComparisonOp(op); 575 [[fallthrough]]; 576 case BO_EQ: 577 case BO_NE: 578 case BO_Add: 579 case BO_Mul: 580 case BO_And: 581 case BO_Xor: 582 case BO_Or: 583 std::swap(lhs, rhs); 584 continue; 585 case BO_Shr: 586 // (~0)>>a 587 if (LHSValue.isAllOnes() && LHSValue.isSigned()) 588 return evalCast(lhs, resultTy, QualType{}); 589 [[fallthrough]]; 590 case BO_Shl: 591 // 0<<a and 0>>a 592 if (LHSValue == 0) 593 return evalCast(lhs, resultTy, QualType{}); 594 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy); 595 case BO_Div: 596 // 0 / x == 0 597 case BO_Rem: 598 // 0 % x == 0 599 if (LHSValue == 0) 600 return makeZeroVal(resultTy); 601 [[fallthrough]]; 602 default: 603 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy); 604 } 605 } 606 case nonloc::SymbolValKind: { 607 // We only handle LHS as simple symbols or SymIntExprs. 608 SymbolRef Sym = lhs.castAs<nonloc::SymbolVal>().getSymbol(); 609 610 // LHS is a symbolic expression. 611 if (const SymIntExpr *symIntExpr = dyn_cast<SymIntExpr>(Sym)) { 612 613 // Is this a logical not? (!x is represented as x == 0.) 614 if (op == BO_EQ && rhs.isZeroConstant()) { 615 // We know how to negate certain expressions. Simplify them here. 616 617 BinaryOperator::Opcode opc = symIntExpr->getOpcode(); 618 switch (opc) { 619 default: 620 // We don't know how to negate this operation. 621 // Just handle it as if it were a normal comparison to 0. 622 break; 623 case BO_LAnd: 624 case BO_LOr: 625 llvm_unreachable("Logical operators handled by branching logic."); 626 case BO_Assign: 627 case BO_MulAssign: 628 case BO_DivAssign: 629 case BO_RemAssign: 630 case BO_AddAssign: 631 case BO_SubAssign: 632 case BO_ShlAssign: 633 case BO_ShrAssign: 634 case BO_AndAssign: 635 case BO_XorAssign: 636 case BO_OrAssign: 637 case BO_Comma: 638 llvm_unreachable("'=' and ',' operators handled by ExprEngine."); 639 case BO_PtrMemD: 640 case BO_PtrMemI: 641 llvm_unreachable("Pointer arithmetic not handled here."); 642 case BO_LT: 643 case BO_GT: 644 case BO_LE: 645 case BO_GE: 646 case BO_EQ: 647 case BO_NE: 648 assert(resultTy->isBooleanType() || 649 resultTy == getConditionType()); 650 assert(symIntExpr->getType()->isBooleanType() || 651 getContext().hasSameUnqualifiedType(symIntExpr->getType(), 652 getConditionType())); 653 // Negate the comparison and make a value. 654 opc = BinaryOperator::negateComparisonOp(opc); 655 return makeNonLoc(symIntExpr->getLHS(), opc, 656 symIntExpr->getRHS(), resultTy); 657 } 658 } 659 660 // For now, only handle expressions whose RHS is a constant. 661 if (const llvm::APSInt *RHSValue = getConstValue(state, rhs)) { 662 // If both the LHS and the current expression are additive, 663 // fold their constants and try again. 664 if (BinaryOperator::isAdditiveOp(op)) { 665 BinaryOperator::Opcode lop = symIntExpr->getOpcode(); 666 if (BinaryOperator::isAdditiveOp(lop)) { 667 // Convert the two constants to a common type, then combine them. 668 669 // resultTy may not be the best type to convert to, but it's 670 // probably the best choice in expressions with mixed type 671 // (such as x+1U+2LL). The rules for implicit conversions should 672 // choose a reasonable type to preserve the expression, and will 673 // at least match how the value is going to be used. 674 APSIntType IntType = BasicVals.getAPSIntType(resultTy); 675 const llvm::APSInt &first = IntType.convert(symIntExpr->getRHS()); 676 const llvm::APSInt &second = IntType.convert(*RHSValue); 677 678 // If the op and lop agrees, then we just need to 679 // sum the constants. Otherwise, we change to operation 680 // type if substraction would produce negative value 681 // (and cause overflow for unsigned integers), 682 // as consequence x+1U-10 produces x-9U, instead 683 // of x+4294967287U, that would be produced without this 684 // additional check. 685 const llvm::APSInt *newRHS; 686 if (lop == op) { 687 newRHS = BasicVals.evalAPSInt(BO_Add, first, second); 688 } else if (first >= second) { 689 newRHS = BasicVals.evalAPSInt(BO_Sub, first, second); 690 op = lop; 691 } else { 692 newRHS = BasicVals.evalAPSInt(BO_Sub, second, first); 693 } 694 695 assert(newRHS && "Invalid operation despite common type!"); 696 rhs = nonloc::ConcreteInt(*newRHS); 697 lhs = nonloc::SymbolVal(symIntExpr->getLHS()); 698 continue; 699 } 700 } 701 702 // Otherwise, make a SymIntExpr out of the expression. 703 return MakeSymIntVal(symIntExpr, op, *RHSValue, resultTy); 704 } 705 } 706 707 // Is the RHS a constant? 708 if (const llvm::APSInt *RHSValue = getConstValue(state, rhs)) 709 return MakeSymIntVal(Sym, op, *RHSValue, resultTy); 710 711 if (std::optional<NonLoc> V = tryRearrange(state, op, lhs, rhs, resultTy)) 712 return *V; 713 714 // Give up -- this is not a symbolic expression we can handle. 715 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy); 716 } 717 } 718 } 719 } 720 721 static SVal evalBinOpFieldRegionFieldRegion(const FieldRegion *LeftFR, 722 const FieldRegion *RightFR, 723 BinaryOperator::Opcode op, 724 QualType resultTy, 725 SimpleSValBuilder &SVB) { 726 // Only comparisons are meaningful here! 727 if (!BinaryOperator::isComparisonOp(op)) 728 return UnknownVal(); 729 730 // Next, see if the two FRs have the same super-region. 731 // FIXME: This doesn't handle casts yet, and simply stripping the casts 732 // doesn't help. 733 if (LeftFR->getSuperRegion() != RightFR->getSuperRegion()) 734 return UnknownVal(); 735 736 const FieldDecl *LeftFD = LeftFR->getDecl(); 737 const FieldDecl *RightFD = RightFR->getDecl(); 738 const RecordDecl *RD = LeftFD->getParent(); 739 740 // Make sure the two FRs are from the same kind of record. Just in case! 741 // FIXME: This is probably where inheritance would be a problem. 742 if (RD != RightFD->getParent()) 743 return UnknownVal(); 744 745 // We know for sure that the two fields are not the same, since that 746 // would have given us the same SVal. 747 if (op == BO_EQ) 748 return SVB.makeTruthVal(false, resultTy); 749 if (op == BO_NE) 750 return SVB.makeTruthVal(true, resultTy); 751 752 // Iterate through the fields and see which one comes first. 753 // [C99 6.7.2.1.13] "Within a structure object, the non-bit-field 754 // members and the units in which bit-fields reside have addresses that 755 // increase in the order in which they are declared." 756 bool leftFirst = (op == BO_LT || op == BO_LE); 757 for (const auto *I : RD->fields()) { 758 if (I == LeftFD) 759 return SVB.makeTruthVal(leftFirst, resultTy); 760 if (I == RightFD) 761 return SVB.makeTruthVal(!leftFirst, resultTy); 762 } 763 764 llvm_unreachable("Fields not found in parent record's definition"); 765 } 766 767 // This is used in debug builds only for now because some downstream users 768 // may hit this assert in their subsequent merges. 769 // There are still places in the analyzer where equal bitwidth Locs 770 // are compared, and need to be found and corrected. Recent previous fixes have 771 // addressed the known problems of making NULLs with specific bitwidths 772 // for Loc comparisons along with deprecation of APIs for the same purpose. 773 // 774 static void assertEqualBitWidths(ProgramStateRef State, Loc RhsLoc, 775 Loc LhsLoc) { 776 // Implements a "best effort" check for RhsLoc and LhsLoc bit widths 777 ASTContext &Ctx = State->getStateManager().getContext(); 778 uint64_t RhsBitwidth = 779 RhsLoc.getType(Ctx).isNull() ? 0 : Ctx.getTypeSize(RhsLoc.getType(Ctx)); 780 uint64_t LhsBitwidth = 781 LhsLoc.getType(Ctx).isNull() ? 0 : Ctx.getTypeSize(LhsLoc.getType(Ctx)); 782 if (RhsBitwidth && LhsBitwidth && (LhsLoc.getKind() == RhsLoc.getKind())) { 783 assert(RhsBitwidth == LhsBitwidth && 784 "RhsLoc and LhsLoc bitwidth must be same!"); 785 } 786 } 787 788 // FIXME: all this logic will change if/when we have MemRegion::getLocation(). 789 SVal SimpleSValBuilder::evalBinOpLL(ProgramStateRef state, 790 BinaryOperator::Opcode op, 791 Loc lhs, Loc rhs, 792 QualType resultTy) { 793 794 // Assert that bitwidth of lhs and rhs are the same. 795 // This can happen if two different address spaces are used, 796 // and the bitwidths of the address spaces are different. 797 // See LIT case clang/test/Analysis/cstring-checker-addressspace.c 798 // FIXME: See comment above in the function assertEqualBitWidths 799 assertEqualBitWidths(state, rhs, lhs); 800 801 // Only comparisons and subtractions are valid operations on two pointers. 802 // See [C99 6.5.5 through 6.5.14] or [C++0x 5.6 through 5.15]. 803 // However, if a pointer is casted to an integer, evalBinOpNN may end up 804 // calling this function with another operation (PR7527). We don't attempt to 805 // model this for now, but it could be useful, particularly when the 806 // "location" is actually an integer value that's been passed through a void*. 807 if (!(BinaryOperator::isComparisonOp(op) || op == BO_Sub)) 808 return UnknownVal(); 809 810 // Special cases for when both sides are identical. 811 if (lhs == rhs) { 812 switch (op) { 813 default: 814 llvm_unreachable("Unimplemented operation for two identical values"); 815 case BO_Sub: 816 return makeZeroVal(resultTy); 817 case BO_EQ: 818 case BO_LE: 819 case BO_GE: 820 return makeTruthVal(true, resultTy); 821 case BO_NE: 822 case BO_LT: 823 case BO_GT: 824 return makeTruthVal(false, resultTy); 825 } 826 } 827 828 switch (lhs.getKind()) { 829 default: 830 llvm_unreachable("Ordering not implemented for this Loc."); 831 832 case loc::GotoLabelKind: 833 // The only thing we know about labels is that they're non-null. 834 if (rhs.isZeroConstant()) { 835 switch (op) { 836 default: 837 break; 838 case BO_Sub: 839 return evalCast(lhs, resultTy, QualType{}); 840 case BO_EQ: 841 case BO_LE: 842 case BO_LT: 843 return makeTruthVal(false, resultTy); 844 case BO_NE: 845 case BO_GT: 846 case BO_GE: 847 return makeTruthVal(true, resultTy); 848 } 849 } 850 // There may be two labels for the same location, and a function region may 851 // have the same address as a label at the start of the function (depending 852 // on the ABI). 853 // FIXME: we can probably do a comparison against other MemRegions, though. 854 // FIXME: is there a way to tell if two labels refer to the same location? 855 return UnknownVal(); 856 857 case loc::ConcreteIntKind: { 858 auto L = lhs.castAs<loc::ConcreteInt>(); 859 860 // If one of the operands is a symbol and the other is a constant, 861 // build an expression for use by the constraint manager. 862 if (SymbolRef rSym = rhs.getAsLocSymbol()) { 863 // We can only build expressions with symbols on the left, 864 // so we need a reversible operator. 865 if (!BinaryOperator::isComparisonOp(op) || op == BO_Cmp) 866 return UnknownVal(); 867 868 op = BinaryOperator::reverseComparisonOp(op); 869 return makeNonLoc(rSym, op, L.getValue(), resultTy); 870 } 871 872 // If both operands are constants, just perform the operation. 873 if (std::optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) { 874 assert(BinaryOperator::isComparisonOp(op) || op == BO_Sub); 875 876 if (const auto *ResultInt = 877 BasicVals.evalAPSInt(op, L.getValue(), rInt->getValue())) 878 return evalCast(nonloc::ConcreteInt(*ResultInt), resultTy, QualType{}); 879 return UnknownVal(); 880 } 881 882 // Special case comparisons against NULL. 883 // This must come after the test if the RHS is a symbol, which is used to 884 // build constraints. The address of any non-symbolic region is guaranteed 885 // to be non-NULL, as is any label. 886 assert((isa<loc::MemRegionVal, loc::GotoLabel>(rhs))); 887 if (lhs.isZeroConstant()) { 888 switch (op) { 889 default: 890 break; 891 case BO_EQ: 892 case BO_GT: 893 case BO_GE: 894 return makeTruthVal(false, resultTy); 895 case BO_NE: 896 case BO_LT: 897 case BO_LE: 898 return makeTruthVal(true, resultTy); 899 } 900 } 901 902 // Comparing an arbitrary integer to a region or label address is 903 // completely unknowable. 904 return UnknownVal(); 905 } 906 case loc::MemRegionValKind: { 907 if (std::optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) { 908 // If one of the operands is a symbol and the other is a constant, 909 // build an expression for use by the constraint manager. 910 if (SymbolRef lSym = lhs.getAsLocSymbol(true)) { 911 if (BinaryOperator::isComparisonOp(op)) 912 return MakeSymIntVal(lSym, op, rInt->getValue(), resultTy); 913 return UnknownVal(); 914 } 915 // Special case comparisons to NULL. 916 // This must come after the test if the LHS is a symbol, which is used to 917 // build constraints. The address of any non-symbolic region is guaranteed 918 // to be non-NULL. 919 if (rInt->isZeroConstant()) { 920 if (op == BO_Sub) 921 return evalCast(lhs, resultTy, QualType{}); 922 923 if (BinaryOperator::isComparisonOp(op)) { 924 QualType boolType = getContext().BoolTy; 925 NonLoc l = evalCast(lhs, boolType, QualType{}).castAs<NonLoc>(); 926 NonLoc r = makeTruthVal(false, boolType).castAs<NonLoc>(); 927 return evalBinOpNN(state, op, l, r, resultTy); 928 } 929 } 930 931 // Comparing a region to an arbitrary integer is completely unknowable. 932 return UnknownVal(); 933 } 934 935 // Get both values as regions, if possible. 936 const MemRegion *LeftMR = lhs.getAsRegion(); 937 assert(LeftMR && "MemRegionValKind SVal doesn't have a region!"); 938 939 const MemRegion *RightMR = rhs.getAsRegion(); 940 if (!RightMR) 941 // The RHS is probably a label, which in theory could address a region. 942 // FIXME: we can probably make a more useful statement about non-code 943 // regions, though. 944 return UnknownVal(); 945 946 const MemRegion *LeftBase = LeftMR->getBaseRegion(); 947 const MemRegion *RightBase = RightMR->getBaseRegion(); 948 const MemSpaceRegion *LeftMS = LeftBase->getMemorySpace(); 949 const MemSpaceRegion *RightMS = RightBase->getMemorySpace(); 950 const MemSpaceRegion *UnknownMS = MemMgr.getUnknownRegion(); 951 952 // If the two regions are from different known memory spaces they cannot be 953 // equal. Also, assume that no symbolic region (whose memory space is 954 // unknown) is on the stack. 955 if (LeftMS != RightMS && 956 ((LeftMS != UnknownMS && RightMS != UnknownMS) || 957 (isa<StackSpaceRegion>(LeftMS) || isa<StackSpaceRegion>(RightMS)))) { 958 switch (op) { 959 default: 960 return UnknownVal(); 961 case BO_EQ: 962 return makeTruthVal(false, resultTy); 963 case BO_NE: 964 return makeTruthVal(true, resultTy); 965 } 966 } 967 968 // If both values wrap regions, see if they're from different base regions. 969 // Note, heap base symbolic regions are assumed to not alias with 970 // each other; for example, we assume that malloc returns different address 971 // on each invocation. 972 // FIXME: ObjC object pointers always reside on the heap, but currently 973 // we treat their memory space as unknown, because symbolic pointers 974 // to ObjC objects may alias. There should be a way to construct 975 // possibly-aliasing heap-based regions. For instance, MacOSXApiChecker 976 // guesses memory space for ObjC object pointers manually instead of 977 // relying on us. 978 if (LeftBase != RightBase && 979 ((!isa<SymbolicRegion>(LeftBase) && !isa<SymbolicRegion>(RightBase)) || 980 (isa<HeapSpaceRegion>(LeftMS) || isa<HeapSpaceRegion>(RightMS))) ){ 981 switch (op) { 982 default: 983 return UnknownVal(); 984 case BO_EQ: 985 return makeTruthVal(false, resultTy); 986 case BO_NE: 987 return makeTruthVal(true, resultTy); 988 } 989 } 990 991 // Handle special cases for when both regions are element regions. 992 const ElementRegion *RightER = dyn_cast<ElementRegion>(RightMR); 993 const ElementRegion *LeftER = dyn_cast<ElementRegion>(LeftMR); 994 if (RightER && LeftER) { 995 // Next, see if the two ERs have the same super-region and matching types. 996 // FIXME: This should do something useful even if the types don't match, 997 // though if both indexes are constant the RegionRawOffset path will 998 // give the correct answer. 999 if (LeftER->getSuperRegion() == RightER->getSuperRegion() && 1000 LeftER->getElementType() == RightER->getElementType()) { 1001 // Get the left index and cast it to the correct type. 1002 // If the index is unknown or undefined, bail out here. 1003 SVal LeftIndexVal = LeftER->getIndex(); 1004 std::optional<NonLoc> LeftIndex = LeftIndexVal.getAs<NonLoc>(); 1005 if (!LeftIndex) 1006 return UnknownVal(); 1007 LeftIndexVal = evalCast(*LeftIndex, ArrayIndexTy, QualType{}); 1008 LeftIndex = LeftIndexVal.getAs<NonLoc>(); 1009 if (!LeftIndex) 1010 return UnknownVal(); 1011 1012 // Do the same for the right index. 1013 SVal RightIndexVal = RightER->getIndex(); 1014 std::optional<NonLoc> RightIndex = RightIndexVal.getAs<NonLoc>(); 1015 if (!RightIndex) 1016 return UnknownVal(); 1017 RightIndexVal = evalCast(*RightIndex, ArrayIndexTy, QualType{}); 1018 RightIndex = RightIndexVal.getAs<NonLoc>(); 1019 if (!RightIndex) 1020 return UnknownVal(); 1021 1022 // Actually perform the operation. 1023 // evalBinOpNN expects the two indexes to already be the right type. 1024 return evalBinOpNN(state, op, *LeftIndex, *RightIndex, resultTy); 1025 } 1026 } 1027 1028 // Special handling of the FieldRegions, even with symbolic offsets. 1029 const FieldRegion *RightFR = dyn_cast<FieldRegion>(RightMR); 1030 const FieldRegion *LeftFR = dyn_cast<FieldRegion>(LeftMR); 1031 if (RightFR && LeftFR) { 1032 SVal R = evalBinOpFieldRegionFieldRegion(LeftFR, RightFR, op, resultTy, 1033 *this); 1034 if (!R.isUnknown()) 1035 return R; 1036 } 1037 1038 // Compare the regions using the raw offsets. 1039 RegionOffset LeftOffset = LeftMR->getAsOffset(); 1040 RegionOffset RightOffset = RightMR->getAsOffset(); 1041 1042 if (LeftOffset.getRegion() != nullptr && 1043 LeftOffset.getRegion() == RightOffset.getRegion() && 1044 !LeftOffset.hasSymbolicOffset() && !RightOffset.hasSymbolicOffset()) { 1045 int64_t left = LeftOffset.getOffset(); 1046 int64_t right = RightOffset.getOffset(); 1047 1048 switch (op) { 1049 default: 1050 return UnknownVal(); 1051 case BO_LT: 1052 return makeTruthVal(left < right, resultTy); 1053 case BO_GT: 1054 return makeTruthVal(left > right, resultTy); 1055 case BO_LE: 1056 return makeTruthVal(left <= right, resultTy); 1057 case BO_GE: 1058 return makeTruthVal(left >= right, resultTy); 1059 case BO_EQ: 1060 return makeTruthVal(left == right, resultTy); 1061 case BO_NE: 1062 return makeTruthVal(left != right, resultTy); 1063 } 1064 } 1065 1066 // At this point we're not going to get a good answer, but we can try 1067 // conjuring an expression instead. 1068 SymbolRef LHSSym = lhs.getAsLocSymbol(); 1069 SymbolRef RHSSym = rhs.getAsLocSymbol(); 1070 if (LHSSym && RHSSym) 1071 return makeNonLoc(LHSSym, op, RHSSym, resultTy); 1072 1073 // If we get here, we have no way of comparing the regions. 1074 return UnknownVal(); 1075 } 1076 } 1077 } 1078 1079 SVal SimpleSValBuilder::evalBinOpLN(ProgramStateRef state, 1080 BinaryOperator::Opcode op, Loc lhs, 1081 NonLoc rhs, QualType resultTy) { 1082 if (op >= BO_PtrMemD && op <= BO_PtrMemI) { 1083 if (auto PTMSV = rhs.getAs<nonloc::PointerToMember>()) { 1084 if (PTMSV->isNullMemberPointer()) 1085 return UndefinedVal(); 1086 1087 auto getFieldLValue = [&](const auto *FD) -> SVal { 1088 SVal Result = lhs; 1089 1090 for (const auto &I : *PTMSV) 1091 Result = StateMgr.getStoreManager().evalDerivedToBase( 1092 Result, I->getType(), I->isVirtual()); 1093 1094 return state->getLValue(FD, Result); 1095 }; 1096 1097 if (const auto *FD = PTMSV->getDeclAs<FieldDecl>()) { 1098 return getFieldLValue(FD); 1099 } 1100 if (const auto *FD = PTMSV->getDeclAs<IndirectFieldDecl>()) { 1101 return getFieldLValue(FD); 1102 } 1103 } 1104 1105 return rhs; 1106 } 1107 1108 assert(!BinaryOperator::isComparisonOp(op) && 1109 "arguments to comparison ops must be of the same type"); 1110 1111 // Special case: rhs is a zero constant. 1112 if (rhs.isZeroConstant()) 1113 return lhs; 1114 1115 // Perserve the null pointer so that it can be found by the DerefChecker. 1116 if (lhs.isZeroConstant()) 1117 return lhs; 1118 1119 // We are dealing with pointer arithmetic. 1120 1121 // Handle pointer arithmetic on constant values. 1122 if (std::optional<nonloc::ConcreteInt> rhsInt = 1123 rhs.getAs<nonloc::ConcreteInt>()) { 1124 if (std::optional<loc::ConcreteInt> lhsInt = 1125 lhs.getAs<loc::ConcreteInt>()) { 1126 const llvm::APSInt &leftI = lhsInt->getValue(); 1127 assert(leftI.isUnsigned()); 1128 llvm::APSInt rightI(rhsInt->getValue(), /* isUnsigned */ true); 1129 1130 // Convert the bitwidth of rightI. This should deal with overflow 1131 // since we are dealing with concrete values. 1132 rightI = rightI.extOrTrunc(leftI.getBitWidth()); 1133 1134 // Offset the increment by the pointer size. 1135 llvm::APSInt Multiplicand(rightI.getBitWidth(), /* isUnsigned */ true); 1136 QualType pointeeType = resultTy->getPointeeType(); 1137 Multiplicand = getContext().getTypeSizeInChars(pointeeType).getQuantity(); 1138 rightI *= Multiplicand; 1139 1140 // Compute the adjusted pointer. 1141 switch (op) { 1142 case BO_Add: 1143 rightI = leftI + rightI; 1144 break; 1145 case BO_Sub: 1146 rightI = leftI - rightI; 1147 break; 1148 default: 1149 llvm_unreachable("Invalid pointer arithmetic operation"); 1150 } 1151 return loc::ConcreteInt(getBasicValueFactory().getValue(rightI)); 1152 } 1153 } 1154 1155 // Handle cases where 'lhs' is a region. 1156 if (const MemRegion *region = lhs.getAsRegion()) { 1157 rhs = convertToArrayIndex(rhs).castAs<NonLoc>(); 1158 SVal index = UnknownVal(); 1159 const SubRegion *superR = nullptr; 1160 // We need to know the type of the pointer in order to add an integer to it. 1161 // Depending on the type, different amount of bytes is added. 1162 QualType elementType; 1163 1164 if (const ElementRegion *elemReg = dyn_cast<ElementRegion>(region)) { 1165 assert(op == BO_Add || op == BO_Sub); 1166 index = evalBinOpNN(state, op, elemReg->getIndex(), rhs, 1167 getArrayIndexType()); 1168 superR = cast<SubRegion>(elemReg->getSuperRegion()); 1169 elementType = elemReg->getElementType(); 1170 } 1171 else if (isa<SubRegion>(region)) { 1172 assert(op == BO_Add || op == BO_Sub); 1173 index = (op == BO_Add) ? rhs : evalMinus(rhs); 1174 superR = cast<SubRegion>(region); 1175 // TODO: Is this actually reliable? Maybe improving our MemRegion 1176 // hierarchy to provide typed regions for all non-void pointers would be 1177 // better. For instance, we cannot extend this towards LocAsInteger 1178 // operations, where result type of the expression is integer. 1179 if (resultTy->isAnyPointerType()) 1180 elementType = resultTy->getPointeeType(); 1181 } 1182 1183 // Represent arithmetic on void pointers as arithmetic on char pointers. 1184 // It is fine when a TypedValueRegion of char value type represents 1185 // a void pointer. Note that arithmetic on void pointers is a GCC extension. 1186 if (elementType->isVoidType()) 1187 elementType = getContext().CharTy; 1188 1189 if (std::optional<NonLoc> indexV = index.getAs<NonLoc>()) { 1190 return loc::MemRegionVal(MemMgr.getElementRegion(elementType, *indexV, 1191 superR, getContext())); 1192 } 1193 } 1194 return UnknownVal(); 1195 } 1196 1197 const llvm::APSInt *SimpleSValBuilder::getConstValue(ProgramStateRef state, 1198 SVal V) { 1199 if (const llvm::APSInt *Res = getConcreteValue(V)) 1200 return Res; 1201 1202 if (SymbolRef Sym = V.getAsSymbol()) 1203 return state->getConstraintManager().getSymVal(state, Sym); 1204 1205 return nullptr; 1206 } 1207 1208 const llvm::APSInt *SimpleSValBuilder::getConcreteValue(SVal V) { 1209 if (std::optional<loc::ConcreteInt> X = V.getAs<loc::ConcreteInt>()) 1210 return &X->getValue(); 1211 1212 if (std::optional<nonloc::ConcreteInt> X = V.getAs<nonloc::ConcreteInt>()) 1213 return &X->getValue(); 1214 1215 return nullptr; 1216 } 1217 1218 const llvm::APSInt *SimpleSValBuilder::getKnownValue(ProgramStateRef state, 1219 SVal V) { 1220 return getConstValue(state, simplifySVal(state, V)); 1221 } 1222 1223 const llvm::APSInt *SimpleSValBuilder::getMinValue(ProgramStateRef state, 1224 SVal V) { 1225 V = simplifySVal(state, V); 1226 1227 if (const llvm::APSInt *Res = getConcreteValue(V)) 1228 return Res; 1229 1230 if (SymbolRef Sym = V.getAsSymbol()) 1231 return state->getConstraintManager().getSymMinVal(state, Sym); 1232 1233 return nullptr; 1234 } 1235 1236 const llvm::APSInt *SimpleSValBuilder::getMaxValue(ProgramStateRef state, 1237 SVal V) { 1238 V = simplifySVal(state, V); 1239 1240 if (const llvm::APSInt *Res = getConcreteValue(V)) 1241 return Res; 1242 1243 if (SymbolRef Sym = V.getAsSymbol()) 1244 return state->getConstraintManager().getSymMaxVal(state, Sym); 1245 1246 return nullptr; 1247 } 1248 1249 SVal SimpleSValBuilder::simplifyUntilFixpoint(ProgramStateRef State, SVal Val) { 1250 SVal SimplifiedVal = simplifySValOnce(State, Val); 1251 while (SimplifiedVal != Val) { 1252 Val = SimplifiedVal; 1253 SimplifiedVal = simplifySValOnce(State, Val); 1254 } 1255 return SimplifiedVal; 1256 } 1257 1258 SVal SimpleSValBuilder::simplifySVal(ProgramStateRef State, SVal V) { 1259 return simplifyUntilFixpoint(State, V); 1260 } 1261 1262 SVal SimpleSValBuilder::simplifySValOnce(ProgramStateRef State, SVal V) { 1263 // For now, this function tries to constant-fold symbols inside a 1264 // nonloc::SymbolVal, and does nothing else. More simplifications should 1265 // be possible, such as constant-folding an index in an ElementRegion. 1266 1267 class Simplifier : public FullSValVisitor<Simplifier, SVal> { 1268 ProgramStateRef State; 1269 SValBuilder &SVB; 1270 1271 // Cache results for the lifetime of the Simplifier. Results change every 1272 // time new constraints are added to the program state, which is the whole 1273 // point of simplifying, and for that very reason it's pointless to maintain 1274 // the same cache for the duration of the whole analysis. 1275 llvm::DenseMap<SymbolRef, SVal> Cached; 1276 1277 static bool isUnchanged(SymbolRef Sym, SVal Val) { 1278 return Sym == Val.getAsSymbol(); 1279 } 1280 1281 SVal cache(SymbolRef Sym, SVal V) { 1282 Cached[Sym] = V; 1283 return V; 1284 } 1285 1286 SVal skip(SymbolRef Sym) { 1287 return cache(Sym, SVB.makeSymbolVal(Sym)); 1288 } 1289 1290 // Return the known const value for the Sym if available, or return Undef 1291 // otherwise. 1292 SVal getConst(SymbolRef Sym) { 1293 const llvm::APSInt *Const = 1294 State->getConstraintManager().getSymVal(State, Sym); 1295 if (Const) 1296 return Loc::isLocType(Sym->getType()) ? (SVal)SVB.makeIntLocVal(*Const) 1297 : (SVal)SVB.makeIntVal(*Const); 1298 return UndefinedVal(); 1299 } 1300 1301 SVal getConstOrVisit(SymbolRef Sym) { 1302 const SVal Ret = getConst(Sym); 1303 if (Ret.isUndef()) 1304 return Visit(Sym); 1305 return Ret; 1306 } 1307 1308 public: 1309 Simplifier(ProgramStateRef State) 1310 : State(State), SVB(State->getStateManager().getSValBuilder()) {} 1311 1312 SVal VisitSymbolData(const SymbolData *S) { 1313 // No cache here. 1314 if (const llvm::APSInt *I = 1315 State->getConstraintManager().getSymVal(State, S)) 1316 return Loc::isLocType(S->getType()) ? (SVal)SVB.makeIntLocVal(*I) 1317 : (SVal)SVB.makeIntVal(*I); 1318 return SVB.makeSymbolVal(S); 1319 } 1320 1321 SVal VisitSymIntExpr(const SymIntExpr *S) { 1322 auto I = Cached.find(S); 1323 if (I != Cached.end()) 1324 return I->second; 1325 1326 SVal LHS = getConstOrVisit(S->getLHS()); 1327 if (isUnchanged(S->getLHS(), LHS)) 1328 return skip(S); 1329 1330 SVal RHS; 1331 // By looking at the APSInt in the right-hand side of S, we cannot 1332 // figure out if it should be treated as a Loc or as a NonLoc. 1333 // So make our guess by recalling that we cannot multiply pointers 1334 // or compare a pointer to an integer. 1335 if (Loc::isLocType(S->getLHS()->getType()) && 1336 BinaryOperator::isComparisonOp(S->getOpcode())) { 1337 // The usual conversion of $sym to &SymRegion{$sym}, as they have 1338 // the same meaning for Loc-type symbols, but the latter form 1339 // is preferred in SVal computations for being Loc itself. 1340 if (SymbolRef Sym = LHS.getAsSymbol()) { 1341 assert(Loc::isLocType(Sym->getType())); 1342 LHS = SVB.makeLoc(Sym); 1343 } 1344 RHS = SVB.makeIntLocVal(S->getRHS()); 1345 } else { 1346 RHS = SVB.makeIntVal(S->getRHS()); 1347 } 1348 1349 return cache( 1350 S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType())); 1351 } 1352 1353 SVal VisitIntSymExpr(const IntSymExpr *S) { 1354 auto I = Cached.find(S); 1355 if (I != Cached.end()) 1356 return I->second; 1357 1358 SVal RHS = getConstOrVisit(S->getRHS()); 1359 if (isUnchanged(S->getRHS(), RHS)) 1360 return skip(S); 1361 1362 SVal LHS = SVB.makeIntVal(S->getLHS()); 1363 return cache( 1364 S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType())); 1365 } 1366 1367 SVal VisitSymSymExpr(const SymSymExpr *S) { 1368 auto I = Cached.find(S); 1369 if (I != Cached.end()) 1370 return I->second; 1371 1372 // For now don't try to simplify mixed Loc/NonLoc expressions 1373 // because they often appear from LocAsInteger operations 1374 // and we don't know how to combine a LocAsInteger 1375 // with a concrete value. 1376 if (Loc::isLocType(S->getLHS()->getType()) != 1377 Loc::isLocType(S->getRHS()->getType())) 1378 return skip(S); 1379 1380 SVal LHS = getConstOrVisit(S->getLHS()); 1381 SVal RHS = getConstOrVisit(S->getRHS()); 1382 1383 if (isUnchanged(S->getLHS(), LHS) && isUnchanged(S->getRHS(), RHS)) 1384 return skip(S); 1385 1386 return cache( 1387 S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType())); 1388 } 1389 1390 SVal VisitSymbolCast(const SymbolCast *S) { 1391 auto I = Cached.find(S); 1392 if (I != Cached.end()) 1393 return I->second; 1394 const SymExpr *OpSym = S->getOperand(); 1395 SVal OpVal = getConstOrVisit(OpSym); 1396 if (isUnchanged(OpSym, OpVal)) 1397 return skip(S); 1398 1399 return cache(S, SVB.evalCast(OpVal, S->getType(), OpSym->getType())); 1400 } 1401 1402 SVal VisitUnarySymExpr(const UnarySymExpr *S) { 1403 auto I = Cached.find(S); 1404 if (I != Cached.end()) 1405 return I->second; 1406 SVal Op = getConstOrVisit(S->getOperand()); 1407 if (isUnchanged(S->getOperand(), Op)) 1408 return skip(S); 1409 1410 return cache( 1411 S, SVB.evalUnaryOp(State, S->getOpcode(), Op, S->getType())); 1412 } 1413 1414 SVal VisitSymExpr(SymbolRef S) { return nonloc::SymbolVal(S); } 1415 1416 SVal VisitMemRegion(const MemRegion *R) { return loc::MemRegionVal(R); } 1417 1418 SVal VisitSymbolVal(nonloc::SymbolVal V) { 1419 // Simplification is much more costly than computing complexity. 1420 // For high complexity, it may be not worth it. 1421 return Visit(V.getSymbol()); 1422 } 1423 1424 SVal VisitSVal(SVal V) { return V; } 1425 }; 1426 1427 SVal SimplifiedV = Simplifier(State).Visit(V); 1428 return SimplifiedV; 1429 } 1430