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      1 // SValBuilder.cpp - Basic class for all SValBuilder implementations -*- C++ -*-
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 //  This file defines SValBuilder, the base class for all (complete) SValBuilder
     11 //  implementations.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
     16 #include "clang/AST/DeclCXX.h"
     17 #include "clang/AST/ExprCXX.h"
     18 #include "clang/StaticAnalyzer/Core/PathSensitive/BasicValueFactory.h"
     19 #include "clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h"
     20 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
     21 #include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
     22 
     23 using namespace clang;
     24 using namespace ento;
     25 
     26 //===----------------------------------------------------------------------===//
     27 // Basic SVal creation.
     28 //===----------------------------------------------------------------------===//
     29 
     30 void SValBuilder::anchor() { }
     31 
     32 DefinedOrUnknownSVal SValBuilder::makeZeroVal(QualType type) {
     33   if (Loc::isLocType(type))
     34     return makeNull();
     35 
     36   if (type->isIntegralOrEnumerationType())
     37     return makeIntVal(0, type);
     38 
     39   // FIXME: Handle floats.
     40   // FIXME: Handle structs.
     41   return UnknownVal();
     42 }
     43 
     44 NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
     45                                 const llvm::APSInt& rhs, QualType type) {
     46   // The Environment ensures we always get a persistent APSInt in
     47   // BasicValueFactory, so we don't need to get the APSInt from
     48   // BasicValueFactory again.
     49   assert(lhs);
     50   assert(!Loc::isLocType(type));
     51   return nonloc::SymbolVal(SymMgr.getSymIntExpr(lhs, op, rhs, type));
     52 }
     53 
     54 NonLoc SValBuilder::makeNonLoc(const llvm::APSInt& lhs,
     55                                BinaryOperator::Opcode op, const SymExpr *rhs,
     56                                QualType type) {
     57   assert(rhs);
     58   assert(!Loc::isLocType(type));
     59   return nonloc::SymbolVal(SymMgr.getIntSymExpr(lhs, op, rhs, type));
     60 }
     61 
     62 NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
     63                                const SymExpr *rhs, QualType type) {
     64   assert(lhs && rhs);
     65   assert(!Loc::isLocType(type));
     66   return nonloc::SymbolVal(SymMgr.getSymSymExpr(lhs, op, rhs, type));
     67 }
     68 
     69 NonLoc SValBuilder::makeNonLoc(const SymExpr *operand,
     70                                QualType fromTy, QualType toTy) {
     71   assert(operand);
     72   assert(!Loc::isLocType(toTy));
     73   return nonloc::SymbolVal(SymMgr.getCastSymbol(operand, fromTy, toTy));
     74 }
     75 
     76 SVal SValBuilder::convertToArrayIndex(SVal val) {
     77   if (val.isUnknownOrUndef())
     78     return val;
     79 
     80   // Common case: we have an appropriately sized integer.
     81   if (Optional<nonloc::ConcreteInt> CI = val.getAs<nonloc::ConcreteInt>()) {
     82     const llvm::APSInt& I = CI->getValue();
     83     if (I.getBitWidth() == ArrayIndexWidth && I.isSigned())
     84       return val;
     85   }
     86 
     87   return evalCastFromNonLoc(val.castAs<NonLoc>(), ArrayIndexTy);
     88 }
     89 
     90 nonloc::ConcreteInt SValBuilder::makeBoolVal(const CXXBoolLiteralExpr *boolean){
     91   return makeTruthVal(boolean->getValue());
     92 }
     93 
     94 DefinedOrUnknownSVal
     95 SValBuilder::getRegionValueSymbolVal(const TypedValueRegion* region) {
     96   QualType T = region->getValueType();
     97 
     98   if (T->isNullPtrType())
     99     return makeZeroVal(T);
    100 
    101   if (!SymbolManager::canSymbolicate(T))
    102     return UnknownVal();
    103 
    104   SymbolRef sym = SymMgr.getRegionValueSymbol(region);
    105 
    106   if (Loc::isLocType(T))
    107     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
    108 
    109   return nonloc::SymbolVal(sym);
    110 }
    111 
    112 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *SymbolTag,
    113                                                    const Expr *Ex,
    114                                                    const LocationContext *LCtx,
    115                                                    unsigned Count) {
    116   QualType T = Ex->getType();
    117 
    118   if (T->isNullPtrType())
    119     return makeZeroVal(T);
    120 
    121   // Compute the type of the result. If the expression is not an R-value, the
    122   // result should be a location.
    123   QualType ExType = Ex->getType();
    124   if (Ex->isGLValue())
    125     T = LCtx->getAnalysisDeclContext()->getASTContext().getPointerType(ExType);
    126 
    127   return conjureSymbolVal(SymbolTag, Ex, LCtx, T, Count);
    128 }
    129 
    130 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *symbolTag,
    131                                                    const Expr *expr,
    132                                                    const LocationContext *LCtx,
    133                                                    QualType type,
    134                                                    unsigned count) {
    135   if (type->isNullPtrType())
    136     return makeZeroVal(type);
    137 
    138   if (!SymbolManager::canSymbolicate(type))
    139     return UnknownVal();
    140 
    141   SymbolRef sym = SymMgr.conjureSymbol(expr, LCtx, type, count, symbolTag);
    142 
    143   if (Loc::isLocType(type))
    144     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
    145 
    146   return nonloc::SymbolVal(sym);
    147 }
    148 
    149 
    150 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const Stmt *stmt,
    151                                                    const LocationContext *LCtx,
    152                                                    QualType type,
    153                                                    unsigned visitCount) {
    154   if (type->isNullPtrType())
    155     return makeZeroVal(type);
    156 
    157   if (!SymbolManager::canSymbolicate(type))
    158     return UnknownVal();
    159 
    160   SymbolRef sym = SymMgr.conjureSymbol(stmt, LCtx, type, visitCount);
    161 
    162   if (Loc::isLocType(type))
    163     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
    164 
    165   return nonloc::SymbolVal(sym);
    166 }
    167 
    168 DefinedOrUnknownSVal
    169 SValBuilder::getConjuredHeapSymbolVal(const Expr *E,
    170                                       const LocationContext *LCtx,
    171                                       unsigned VisitCount) {
    172   QualType T = E->getType();
    173   assert(Loc::isLocType(T));
    174   assert(SymbolManager::canSymbolicate(T));
    175   if (T->isNullPtrType())
    176     return makeZeroVal(T);
    177 
    178   SymbolRef sym = SymMgr.conjureSymbol(E, LCtx, T, VisitCount);
    179   return loc::MemRegionVal(MemMgr.getSymbolicHeapRegion(sym));
    180 }
    181 
    182 DefinedSVal SValBuilder::getMetadataSymbolVal(const void *symbolTag,
    183                                               const MemRegion *region,
    184                                               const Expr *expr, QualType type,
    185                                               unsigned count) {
    186   assert(SymbolManager::canSymbolicate(type) && "Invalid metadata symbol type");
    187 
    188   SymbolRef sym =
    189       SymMgr.getMetadataSymbol(region, expr, type, count, symbolTag);
    190 
    191   if (Loc::isLocType(type))
    192     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
    193 
    194   return nonloc::SymbolVal(sym);
    195 }
    196 
    197 DefinedOrUnknownSVal
    198 SValBuilder::getDerivedRegionValueSymbolVal(SymbolRef parentSymbol,
    199                                              const TypedValueRegion *region) {
    200   QualType T = region->getValueType();
    201 
    202   if (T->isNullPtrType())
    203     return makeZeroVal(T);
    204 
    205   if (!SymbolManager::canSymbolicate(T))
    206     return UnknownVal();
    207 
    208   SymbolRef sym = SymMgr.getDerivedSymbol(parentSymbol, region);
    209 
    210   if (Loc::isLocType(T))
    211     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
    212 
    213   return nonloc::SymbolVal(sym);
    214 }
    215 
    216 DefinedSVal SValBuilder::getFunctionPointer(const FunctionDecl *func) {
    217   return loc::MemRegionVal(MemMgr.getFunctionCodeRegion(func));
    218 }
    219 
    220 DefinedSVal SValBuilder::getBlockPointer(const BlockDecl *block,
    221                                          CanQualType locTy,
    222                                          const LocationContext *locContext,
    223                                          unsigned blockCount) {
    224   const BlockCodeRegion *BC =
    225     MemMgr.getBlockCodeRegion(block, locTy, locContext->getAnalysisDeclContext());
    226   const BlockDataRegion *BD = MemMgr.getBlockDataRegion(BC, locContext,
    227                                                         blockCount);
    228   return loc::MemRegionVal(BD);
    229 }
    230 
    231 /// Return a memory region for the 'this' object reference.
    232 loc::MemRegionVal SValBuilder::getCXXThis(const CXXMethodDecl *D,
    233                                           const StackFrameContext *SFC) {
    234   return loc::MemRegionVal(getRegionManager().
    235                            getCXXThisRegion(D->getThisType(getContext()), SFC));
    236 }
    237 
    238 /// Return a memory region for the 'this' object reference.
    239 loc::MemRegionVal SValBuilder::getCXXThis(const CXXRecordDecl *D,
    240                                           const StackFrameContext *SFC) {
    241   const Type *T = D->getTypeForDecl();
    242   QualType PT = getContext().getPointerType(QualType(T, 0));
    243   return loc::MemRegionVal(getRegionManager().getCXXThisRegion(PT, SFC));
    244 }
    245 
    246 Optional<SVal> SValBuilder::getConstantVal(const Expr *E) {
    247   E = E->IgnoreParens();
    248 
    249   switch (E->getStmtClass()) {
    250   // Handle expressions that we treat differently from the AST's constant
    251   // evaluator.
    252   case Stmt::AddrLabelExprClass:
    253     return makeLoc(cast<AddrLabelExpr>(E));
    254 
    255   case Stmt::CXXScalarValueInitExprClass:
    256   case Stmt::ImplicitValueInitExprClass:
    257     return makeZeroVal(E->getType());
    258 
    259   case Stmt::ObjCStringLiteralClass: {
    260     const ObjCStringLiteral *SL = cast<ObjCStringLiteral>(E);
    261     return makeLoc(getRegionManager().getObjCStringRegion(SL));
    262   }
    263 
    264   case Stmt::StringLiteralClass: {
    265     const StringLiteral *SL = cast<StringLiteral>(E);
    266     return makeLoc(getRegionManager().getStringRegion(SL));
    267   }
    268 
    269   // Fast-path some expressions to avoid the overhead of going through the AST's
    270   // constant evaluator
    271   case Stmt::CharacterLiteralClass: {
    272     const CharacterLiteral *C = cast<CharacterLiteral>(E);
    273     return makeIntVal(C->getValue(), C->getType());
    274   }
    275 
    276   case Stmt::CXXBoolLiteralExprClass:
    277     return makeBoolVal(cast<CXXBoolLiteralExpr>(E));
    278 
    279   case Stmt::TypeTraitExprClass: {
    280     const TypeTraitExpr *TE = cast<TypeTraitExpr>(E);
    281     return makeTruthVal(TE->getValue(), TE->getType());
    282   }
    283 
    284   case Stmt::IntegerLiteralClass:
    285     return makeIntVal(cast<IntegerLiteral>(E));
    286 
    287   case Stmt::ObjCBoolLiteralExprClass:
    288     return makeBoolVal(cast<ObjCBoolLiteralExpr>(E));
    289 
    290   case Stmt::CXXNullPtrLiteralExprClass:
    291     return makeNull();
    292 
    293   case Stmt::ImplicitCastExprClass: {
    294     const CastExpr *CE = cast<CastExpr>(E);
    295     switch (CE->getCastKind()) {
    296     default:
    297       break;
    298     case CK_ArrayToPointerDecay:
    299     case CK_BitCast: {
    300       const Expr *SE = CE->getSubExpr();
    301       Optional<SVal> Val = getConstantVal(SE);
    302       if (!Val)
    303         return None;
    304       return evalCast(*Val, CE->getType(), SE->getType());
    305     }
    306     }
    307     // FALLTHROUGH
    308   }
    309 
    310   // If we don't have a special case, fall back to the AST's constant evaluator.
    311   default: {
    312     // Don't try to come up with a value for materialized temporaries.
    313     if (E->isGLValue())
    314       return None;
    315 
    316     ASTContext &Ctx = getContext();
    317     llvm::APSInt Result;
    318     if (E->EvaluateAsInt(Result, Ctx))
    319       return makeIntVal(Result);
    320 
    321     if (Loc::isLocType(E->getType()))
    322       if (E->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNotNull))
    323         return makeNull();
    324 
    325     return None;
    326   }
    327   }
    328 }
    329 
    330 //===----------------------------------------------------------------------===//
    331 
    332 SVal SValBuilder::makeSymExprValNN(ProgramStateRef State,
    333                                    BinaryOperator::Opcode Op,
    334                                    NonLoc LHS, NonLoc RHS,
    335                                    QualType ResultTy) {
    336   if (!State->isTainted(RHS) && !State->isTainted(LHS))
    337     return UnknownVal();
    338 
    339   const SymExpr *symLHS = LHS.getAsSymExpr();
    340   const SymExpr *symRHS = RHS.getAsSymExpr();
    341   // TODO: When the Max Complexity is reached, we should conjure a symbol
    342   // instead of generating an Unknown value and propagate the taint info to it.
    343   const unsigned MaxComp = 10000; // 100000 28X
    344 
    345   if (symLHS && symRHS &&
    346       (symLHS->computeComplexity() + symRHS->computeComplexity()) <  MaxComp)
    347     return makeNonLoc(symLHS, Op, symRHS, ResultTy);
    348 
    349   if (symLHS && symLHS->computeComplexity() < MaxComp)
    350     if (Optional<nonloc::ConcreteInt> rInt = RHS.getAs<nonloc::ConcreteInt>())
    351       return makeNonLoc(symLHS, Op, rInt->getValue(), ResultTy);
    352 
    353   if (symRHS && symRHS->computeComplexity() < MaxComp)
    354     if (Optional<nonloc::ConcreteInt> lInt = LHS.getAs<nonloc::ConcreteInt>())
    355       return makeNonLoc(lInt->getValue(), Op, symRHS, ResultTy);
    356 
    357   return UnknownVal();
    358 }
    359 
    360 
    361 SVal SValBuilder::evalBinOp(ProgramStateRef state, BinaryOperator::Opcode op,
    362                             SVal lhs, SVal rhs, QualType type) {
    363 
    364   if (lhs.isUndef() || rhs.isUndef())
    365     return UndefinedVal();
    366 
    367   if (lhs.isUnknown() || rhs.isUnknown())
    368     return UnknownVal();
    369 
    370   if (lhs.getAs<nonloc::LazyCompoundVal>() ||
    371       rhs.getAs<nonloc::LazyCompoundVal>()) {
    372     return UnknownVal();
    373   }
    374 
    375   if (Optional<Loc> LV = lhs.getAs<Loc>()) {
    376     if (Optional<Loc> RV = rhs.getAs<Loc>())
    377       return evalBinOpLL(state, op, *LV, *RV, type);
    378 
    379     return evalBinOpLN(state, op, *LV, rhs.castAs<NonLoc>(), type);
    380   }
    381 
    382   if (Optional<Loc> RV = rhs.getAs<Loc>()) {
    383     // Support pointer arithmetic where the addend is on the left
    384     // and the pointer on the right.
    385     assert(op == BO_Add);
    386 
    387     // Commute the operands.
    388     return evalBinOpLN(state, op, *RV, lhs.castAs<NonLoc>(), type);
    389   }
    390 
    391   return evalBinOpNN(state, op, lhs.castAs<NonLoc>(), rhs.castAs<NonLoc>(),
    392                      type);
    393 }
    394 
    395 DefinedOrUnknownSVal SValBuilder::evalEQ(ProgramStateRef state,
    396                                          DefinedOrUnknownSVal lhs,
    397                                          DefinedOrUnknownSVal rhs) {
    398   return evalBinOp(state, BO_EQ, lhs, rhs, getConditionType())
    399       .castAs<DefinedOrUnknownSVal>();
    400 }
    401 
    402 /// Recursively check if the pointer types are equal modulo const, volatile,
    403 /// and restrict qualifiers. Also, assume that all types are similar to 'void'.
    404 /// Assumes the input types are canonical.
    405 static bool shouldBeModeledWithNoOp(ASTContext &Context, QualType ToTy,
    406                                                          QualType FromTy) {
    407   while (Context.UnwrapSimilarPointerTypes(ToTy, FromTy)) {
    408     Qualifiers Quals1, Quals2;
    409     ToTy = Context.getUnqualifiedArrayType(ToTy, Quals1);
    410     FromTy = Context.getUnqualifiedArrayType(FromTy, Quals2);
    411 
    412     // Make sure that non-cvr-qualifiers the other qualifiers (e.g., address
    413     // spaces) are identical.
    414     Quals1.removeCVRQualifiers();
    415     Quals2.removeCVRQualifiers();
    416     if (Quals1 != Quals2)
    417       return false;
    418   }
    419 
    420   // If we are casting to void, the 'From' value can be used to represent the
    421   // 'To' value.
    422   if (ToTy->isVoidType())
    423     return true;
    424 
    425   if (ToTy != FromTy)
    426     return false;
    427 
    428   return true;
    429 }
    430 
    431 // Handles casts of type CK_IntegralCast.
    432 // At the moment, this function will redirect to evalCast, except when the range
    433 // of the original value is known to be greater than the max of the target type.
    434 SVal SValBuilder::evalIntegralCast(ProgramStateRef state, SVal val,
    435                                    QualType castTy, QualType originalTy) {
    436 
    437   // No truncations if target type is big enough.
    438   if (getContext().getTypeSize(castTy) >= getContext().getTypeSize(originalTy))
    439     return evalCast(val, castTy, originalTy);
    440 
    441   const SymExpr *se = val.getAsSymbolicExpression();
    442   if (!se) // Let evalCast handle non symbolic expressions.
    443     return evalCast(val, castTy, originalTy);
    444 
    445   // Find the maximum value of the target type.
    446   APSIntType ToType(getContext().getTypeSize(castTy),
    447                     castTy->isUnsignedIntegerType());
    448   llvm::APSInt ToTypeMax = ToType.getMaxValue();
    449   NonLoc ToTypeMaxVal =
    450       makeIntVal(ToTypeMax.isUnsigned() ? ToTypeMax.getZExtValue()
    451                                         : ToTypeMax.getSExtValue(),
    452                  castTy)
    453           .castAs<NonLoc>();
    454   // Check the range of the symbol being casted against the maximum value of the
    455   // target type.
    456   NonLoc FromVal = val.castAs<NonLoc>();
    457   QualType CmpTy = getConditionType();
    458   NonLoc CompVal =
    459       evalBinOpNN(state, BO_LE, FromVal, ToTypeMaxVal, CmpTy).castAs<NonLoc>();
    460   ProgramStateRef IsNotTruncated, IsTruncated;
    461   std::tie(IsNotTruncated, IsTruncated) = state->assume(CompVal);
    462   if (!IsNotTruncated && IsTruncated) {
    463     // Symbol is truncated so we evaluate it as a cast.
    464     NonLoc CastVal = makeNonLoc(se, originalTy, castTy);
    465     return CastVal;
    466   }
    467   return evalCast(val, castTy, originalTy);
    468 }
    469 
    470 // FIXME: should rewrite according to the cast kind.
    471 SVal SValBuilder::evalCast(SVal val, QualType castTy, QualType originalTy) {
    472   castTy = Context.getCanonicalType(castTy);
    473   originalTy = Context.getCanonicalType(originalTy);
    474   if (val.isUnknownOrUndef() || castTy == originalTy)
    475     return val;
    476 
    477   if (castTy->isBooleanType()) {
    478     if (val.isUnknownOrUndef())
    479       return val;
    480     if (val.isConstant())
    481       return makeTruthVal(!val.isZeroConstant(), castTy);
    482     if (!Loc::isLocType(originalTy) &&
    483         !originalTy->isIntegralOrEnumerationType() &&
    484         !originalTy->isMemberPointerType())
    485       return UnknownVal();
    486     if (SymbolRef Sym = val.getAsSymbol(true)) {
    487       BasicValueFactory &BVF = getBasicValueFactory();
    488       // FIXME: If we had a state here, we could see if the symbol is known to
    489       // be zero, but we don't.
    490       return makeNonLoc(Sym, BO_NE, BVF.getValue(0, Sym->getType()), castTy);
    491     }
    492     // Loc values are not always true, they could be weakly linked functions.
    493     if (Optional<Loc> L = val.getAs<Loc>())
    494       return evalCastFromLoc(*L, castTy);
    495 
    496     Loc L = val.castAs<nonloc::LocAsInteger>().getLoc();
    497     return evalCastFromLoc(L, castTy);
    498   }
    499 
    500   // For const casts, casts to void, just propagate the value.
    501   if (!castTy->isVariableArrayType() && !originalTy->isVariableArrayType())
    502     if (shouldBeModeledWithNoOp(Context, Context.getPointerType(castTy),
    503                                          Context.getPointerType(originalTy)))
    504       return val;
    505 
    506   // Check for casts from pointers to integers.
    507   if (castTy->isIntegralOrEnumerationType() && Loc::isLocType(originalTy))
    508     return evalCastFromLoc(val.castAs<Loc>(), castTy);
    509 
    510   // Check for casts from integers to pointers.
    511   if (Loc::isLocType(castTy) && originalTy->isIntegralOrEnumerationType()) {
    512     if (Optional<nonloc::LocAsInteger> LV = val.getAs<nonloc::LocAsInteger>()) {
    513       if (const MemRegion *R = LV->getLoc().getAsRegion()) {
    514         StoreManager &storeMgr = StateMgr.getStoreManager();
    515         R = storeMgr.castRegion(R, castTy);
    516         return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
    517       }
    518       return LV->getLoc();
    519     }
    520     return dispatchCast(val, castTy);
    521   }
    522 
    523   // Just pass through function and block pointers.
    524   if (originalTy->isBlockPointerType() || originalTy->isFunctionPointerType()) {
    525     assert(Loc::isLocType(castTy));
    526     return val;
    527   }
    528 
    529   // Check for casts from array type to another type.
    530   if (const ArrayType *arrayT =
    531                       dyn_cast<ArrayType>(originalTy.getCanonicalType())) {
    532     // We will always decay to a pointer.
    533     QualType elemTy = arrayT->getElementType();
    534     val = StateMgr.ArrayToPointer(val.castAs<Loc>(), elemTy);
    535 
    536     // Are we casting from an array to a pointer?  If so just pass on
    537     // the decayed value.
    538     if (castTy->isPointerType() || castTy->isReferenceType())
    539       return val;
    540 
    541     // Are we casting from an array to an integer?  If so, cast the decayed
    542     // pointer value to an integer.
    543     assert(castTy->isIntegralOrEnumerationType());
    544 
    545     // FIXME: Keep these here for now in case we decide soon that we
    546     // need the original decayed type.
    547     //    QualType elemTy = cast<ArrayType>(originalTy)->getElementType();
    548     //    QualType pointerTy = C.getPointerType(elemTy);
    549     return evalCastFromLoc(val.castAs<Loc>(), castTy);
    550   }
    551 
    552   // Check for casts from a region to a specific type.
    553   if (const MemRegion *R = val.getAsRegion()) {
    554     // Handle other casts of locations to integers.
    555     if (castTy->isIntegralOrEnumerationType())
    556       return evalCastFromLoc(loc::MemRegionVal(R), castTy);
    557 
    558     // FIXME: We should handle the case where we strip off view layers to get
    559     //  to a desugared type.
    560     if (!Loc::isLocType(castTy)) {
    561       // FIXME: There can be gross cases where one casts the result of a function
    562       // (that returns a pointer) to some other value that happens to fit
    563       // within that pointer value.  We currently have no good way to
    564       // model such operations.  When this happens, the underlying operation
    565       // is that the caller is reasoning about bits.  Conceptually we are
    566       // layering a "view" of a location on top of those bits.  Perhaps
    567       // we need to be more lazy about mutual possible views, even on an
    568       // SVal?  This may be necessary for bit-level reasoning as well.
    569       return UnknownVal();
    570     }
    571 
    572     // We get a symbolic function pointer for a dereference of a function
    573     // pointer, but it is of function type. Example:
    574 
    575     //  struct FPRec {
    576     //    void (*my_func)(int * x);
    577     //  };
    578     //
    579     //  int bar(int x);
    580     //
    581     //  int f1_a(struct FPRec* foo) {
    582     //    int x;
    583     //    (*foo->my_func)(&x);
    584     //    return bar(x)+1; // no-warning
    585     //  }
    586 
    587     assert(Loc::isLocType(originalTy) || originalTy->isFunctionType() ||
    588            originalTy->isBlockPointerType() || castTy->isReferenceType());
    589 
    590     StoreManager &storeMgr = StateMgr.getStoreManager();
    591 
    592     // Delegate to store manager to get the result of casting a region to a
    593     // different type.  If the MemRegion* returned is NULL, this expression
    594     // Evaluates to UnknownVal.
    595     R = storeMgr.castRegion(R, castTy);
    596     return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
    597   }
    598 
    599   return dispatchCast(val, castTy);
    600 }
    601