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