1 //===- SValBuilder.cpp - Basic class for all SValBuilder implementations --===//
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/ASTContext.h"
17 #include "clang/AST/Decl.h"
18 #include "clang/AST/DeclCXX.h"
19 #include "clang/AST/ExprCXX.h"
20 #include "clang/AST/ExprObjC.h"
21 #include "clang/AST/Stmt.h"
22 #include "clang/AST/Type.h"
23 #include "clang/Basic/LLVM.h"
24 #include "clang/Analysis/AnalysisDeclContext.h"
25 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
26 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
27 #include "clang/StaticAnalyzer/Core/PathSensitive/BasicValueFactory.h"
28 #include "clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h"
29 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
30 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState_Fwd.h"
31 #include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
32 #include "clang/StaticAnalyzer/Core/PathSensitive/Store.h"
33 #include "clang/StaticAnalyzer/Core/PathSensitive/SubEngine.h"
34 #include "clang/StaticAnalyzer/Core/PathSensitive/SymExpr.h"
35 #include "clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h"
36 #include "llvm/ADT/APSInt.h"
37 #include "llvm/ADT/None.h"
38 #include "llvm/ADT/Optional.h"
39 #include "llvm/Support/Casting.h"
40 #include "llvm/Support/Compiler.h"
41 #include <cassert>
42 #include <tuple>
43 
44 using namespace clang;
45 using namespace ento;
46 
47 //===----------------------------------------------------------------------===//
48 // Basic SVal creation.
49 //===----------------------------------------------------------------------===//
50 
51 void SValBuilder::anchor() {}
52 
53 DefinedOrUnknownSVal SValBuilder::makeZeroVal(QualType type) {
54   if (Loc::isLocType(type))
55     return makeNull();
56 
57   if (type->isIntegralOrEnumerationType())
58     return makeIntVal(0, type);
59 
60   if (type->isArrayType() || type->isRecordType() || type->isVectorType() ||
61       type->isAnyComplexType())
62     return makeCompoundVal(type, BasicVals.getEmptySValList());
63 
64   // FIXME: Handle floats.
65   return UnknownVal();
66 }
67 
68 NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
69                                 const llvm::APSInt& rhs, QualType type) {
70   // The Environment ensures we always get a persistent APSInt in
71   // BasicValueFactory, so we don't need to get the APSInt from
72   // BasicValueFactory again.
73   assert(lhs);
74   assert(!Loc::isLocType(type));
75   return nonloc::SymbolVal(SymMgr.getSymIntExpr(lhs, op, rhs, type));
76 }
77 
78 NonLoc SValBuilder::makeNonLoc(const llvm::APSInt& lhs,
79                                BinaryOperator::Opcode op, const SymExpr *rhs,
80                                QualType type) {
81   assert(rhs);
82   assert(!Loc::isLocType(type));
83   return nonloc::SymbolVal(SymMgr.getIntSymExpr(lhs, op, rhs, type));
84 }
85 
86 NonLoc SValBuilder::makeNonLoc(const SymExpr *lhs, BinaryOperator::Opcode op,
87                                const SymExpr *rhs, QualType type) {
88   assert(lhs && rhs);
89   assert(!Loc::isLocType(type));
90   return nonloc::SymbolVal(SymMgr.getSymSymExpr(lhs, op, rhs, type));
91 }
92 
93 NonLoc SValBuilder::makeNonLoc(const SymExpr *operand,
94                                QualType fromTy, QualType toTy) {
95   assert(operand);
96   assert(!Loc::isLocType(toTy));
97   return nonloc::SymbolVal(SymMgr.getCastSymbol(operand, fromTy, toTy));
98 }
99 
100 SVal SValBuilder::convertToArrayIndex(SVal val) {
101   if (val.isUnknownOrUndef())
102     return val;
103 
104   // Common case: we have an appropriately sized integer.
105   if (Optional<nonloc::ConcreteInt> CI = val.getAs<nonloc::ConcreteInt>()) {
106     const llvm::APSInt& I = CI->getValue();
107     if (I.getBitWidth() == ArrayIndexWidth && I.isSigned())
108       return val;
109   }
110 
111   return evalCastFromNonLoc(val.castAs<NonLoc>(), ArrayIndexTy);
112 }
113 
114 nonloc::ConcreteInt SValBuilder::makeBoolVal(const CXXBoolLiteralExpr *boolean){
115   return makeTruthVal(boolean->getValue());
116 }
117 
118 DefinedOrUnknownSVal
119 SValBuilder::getRegionValueSymbolVal(const TypedValueRegion *region) {
120   QualType T = region->getValueType();
121 
122   if (T->isNullPtrType())
123     return makeZeroVal(T);
124 
125   if (!SymbolManager::canSymbolicate(T))
126     return UnknownVal();
127 
128   SymbolRef sym = SymMgr.getRegionValueSymbol(region);
129 
130   if (Loc::isLocType(T))
131     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
132 
133   return nonloc::SymbolVal(sym);
134 }
135 
136 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *SymbolTag,
137                                                    const Expr *Ex,
138                                                    const LocationContext *LCtx,
139                                                    unsigned Count) {
140   QualType T = Ex->getType();
141 
142   if (T->isNullPtrType())
143     return makeZeroVal(T);
144 
145   // Compute the type of the result. If the expression is not an R-value, the
146   // result should be a location.
147   QualType ExType = Ex->getType();
148   if (Ex->isGLValue())
149     T = LCtx->getAnalysisDeclContext()->getASTContext().getPointerType(ExType);
150 
151   return conjureSymbolVal(SymbolTag, Ex, LCtx, T, Count);
152 }
153 
154 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const void *symbolTag,
155                                                    const Expr *expr,
156                                                    const LocationContext *LCtx,
157                                                    QualType type,
158                                                    unsigned count) {
159   if (type->isNullPtrType())
160     return makeZeroVal(type);
161 
162   if (!SymbolManager::canSymbolicate(type))
163     return UnknownVal();
164 
165   SymbolRef sym = SymMgr.conjureSymbol(expr, LCtx, type, count, symbolTag);
166 
167   if (Loc::isLocType(type))
168     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
169 
170   return nonloc::SymbolVal(sym);
171 }
172 
173 DefinedOrUnknownSVal SValBuilder::conjureSymbolVal(const Stmt *stmt,
174                                                    const LocationContext *LCtx,
175                                                    QualType type,
176                                                    unsigned visitCount) {
177   if (type->isNullPtrType())
178     return makeZeroVal(type);
179 
180   if (!SymbolManager::canSymbolicate(type))
181     return UnknownVal();
182 
183   SymbolRef sym = SymMgr.conjureSymbol(stmt, LCtx, type, visitCount);
184 
185   if (Loc::isLocType(type))
186     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
187 
188   return nonloc::SymbolVal(sym);
189 }
190 
191 DefinedOrUnknownSVal
192 SValBuilder::getConjuredHeapSymbolVal(const Expr *E,
193                                       const LocationContext *LCtx,
194                                       unsigned VisitCount) {
195   QualType T = E->getType();
196   assert(Loc::isLocType(T));
197   assert(SymbolManager::canSymbolicate(T));
198   if (T->isNullPtrType())
199     return makeZeroVal(T);
200 
201   SymbolRef sym = SymMgr.conjureSymbol(E, LCtx, T, VisitCount);
202   return loc::MemRegionVal(MemMgr.getSymbolicHeapRegion(sym));
203 }
204 
205 DefinedSVal SValBuilder::getMetadataSymbolVal(const void *symbolTag,
206                                               const MemRegion *region,
207                                               const Expr *expr, QualType type,
208                                               const LocationContext *LCtx,
209                                               unsigned count) {
210   assert(SymbolManager::canSymbolicate(type) && "Invalid metadata symbol type");
211 
212   SymbolRef sym =
213       SymMgr.getMetadataSymbol(region, expr, type, LCtx, count, symbolTag);
214 
215   if (Loc::isLocType(type))
216     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
217 
218   return nonloc::SymbolVal(sym);
219 }
220 
221 DefinedOrUnknownSVal
222 SValBuilder::getDerivedRegionValueSymbolVal(SymbolRef parentSymbol,
223                                              const TypedValueRegion *region) {
224   QualType T = region->getValueType();
225 
226   if (T->isNullPtrType())
227     return makeZeroVal(T);
228 
229   if (!SymbolManager::canSymbolicate(T))
230     return UnknownVal();
231 
232   SymbolRef sym = SymMgr.getDerivedSymbol(parentSymbol, region);
233 
234   if (Loc::isLocType(T))
235     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));
236 
237   return nonloc::SymbolVal(sym);
238 }
239 
240 DefinedSVal SValBuilder::getMemberPointer(const DeclaratorDecl *DD) {
241   assert(!DD || isa<CXXMethodDecl>(DD) || isa<FieldDecl>(DD));
242 
243   if (const auto *MD = dyn_cast_or_null<CXXMethodDecl>(DD)) {
244     // Sema treats pointers to static member functions as have function pointer
245     // type, so return a function pointer for the method.
246     // We don't need to play a similar trick for static member fields
247     // because these are represented as plain VarDecls and not FieldDecls
248     // in the AST.
249     if (MD->isStatic())
250       return getFunctionPointer(MD);
251   }
252 
253   return nonloc::PointerToMember(DD);
254 }
255 
256 DefinedSVal SValBuilder::getFunctionPointer(const FunctionDecl *func) {
257   return loc::MemRegionVal(MemMgr.getFunctionCodeRegion(func));
258 }
259 
260 DefinedSVal SValBuilder::getBlockPointer(const BlockDecl *block,
261                                          CanQualType locTy,
262                                          const LocationContext *locContext,
263                                          unsigned blockCount) {
264   const BlockCodeRegion *BC =
265     MemMgr.getBlockCodeRegion(block, locTy, locContext->getAnalysisDeclContext());
266   const BlockDataRegion *BD = MemMgr.getBlockDataRegion(BC, locContext,
267                                                         blockCount);
268   return loc::MemRegionVal(BD);
269 }
270 
271 /// Return a memory region for the 'this' object reference.
272 loc::MemRegionVal SValBuilder::getCXXThis(const CXXMethodDecl *D,
273                                           const StackFrameContext *SFC) {
274   return loc::MemRegionVal(getRegionManager().
275                            getCXXThisRegion(D->getThisType(getContext()), SFC));
276 }
277 
278 /// Return a memory region for the 'this' object reference.
279 loc::MemRegionVal SValBuilder::getCXXThis(const CXXRecordDecl *D,
280                                           const StackFrameContext *SFC) {
281   const Type *T = D->getTypeForDecl();
282   QualType PT = getContext().getPointerType(QualType(T, 0));
283   return loc::MemRegionVal(getRegionManager().getCXXThisRegion(PT, SFC));
284 }
285 
286 Optional<SVal> SValBuilder::getConstantVal(const Expr *E) {
287   E = E->IgnoreParens();
288 
289   switch (E->getStmtClass()) {
290   // Handle expressions that we treat differently from the AST's constant
291   // evaluator.
292   case Stmt::AddrLabelExprClass:
293     return makeLoc(cast<AddrLabelExpr>(E));
294 
295   case Stmt::CXXScalarValueInitExprClass:
296   case Stmt::ImplicitValueInitExprClass:
297     return makeZeroVal(E->getType());
298 
299   case Stmt::ObjCStringLiteralClass: {
300     const auto *SL = cast<ObjCStringLiteral>(E);
301     return makeLoc(getRegionManager().getObjCStringRegion(SL));
302   }
303 
304   case Stmt::StringLiteralClass: {
305     const auto *SL = cast<StringLiteral>(E);
306     return makeLoc(getRegionManager().getStringRegion(SL));
307   }
308 
309   // Fast-path some expressions to avoid the overhead of going through the AST's
310   // constant evaluator
311   case Stmt::CharacterLiteralClass: {
312     const auto *C = cast<CharacterLiteral>(E);
313     return makeIntVal(C->getValue(), C->getType());
314   }
315 
316   case Stmt::CXXBoolLiteralExprClass:
317     return makeBoolVal(cast<CXXBoolLiteralExpr>(E));
318 
319   case Stmt::TypeTraitExprClass: {
320     const auto *TE = cast<TypeTraitExpr>(E);
321     return makeTruthVal(TE->getValue(), TE->getType());
322   }
323 
324   case Stmt::IntegerLiteralClass:
325     return makeIntVal(cast<IntegerLiteral>(E));
326 
327   case Stmt::ObjCBoolLiteralExprClass:
328     return makeBoolVal(cast<ObjCBoolLiteralExpr>(E));
329 
330   case Stmt::CXXNullPtrLiteralExprClass:
331     return makeNull();
332 
333   case Stmt::CStyleCastExprClass:
334   case Stmt::CXXFunctionalCastExprClass:
335   case Stmt::CXXConstCastExprClass:
336   case Stmt::CXXReinterpretCastExprClass:
337   case Stmt::CXXStaticCastExprClass:
338   case Stmt::ImplicitCastExprClass: {
339     const auto *CE = cast<CastExpr>(E);
340     switch (CE->getCastKind()) {
341     default:
342       break;
343     case CK_ArrayToPointerDecay:
344     case CK_IntegralToPointer:
345     case CK_NoOp:
346     case CK_BitCast: {
347       const Expr *SE = CE->getSubExpr();
348       Optional<SVal> Val = getConstantVal(SE);
349       if (!Val)
350         return None;
351       return evalCast(*Val, CE->getType(), SE->getType());
352     }
353     }
354     // FALLTHROUGH
355     LLVM_FALLTHROUGH;
356   }
357 
358   // If we don't have a special case, fall back to the AST's constant evaluator.
359   default: {
360     // Don't try to come up with a value for materialized temporaries.
361     if (E->isGLValue())
362       return None;
363 
364     ASTContext &Ctx = getContext();
365     llvm::APSInt Result;
366     if (E->EvaluateAsInt(Result, Ctx))
367       return makeIntVal(Result);
368 
369     if (Loc::isLocType(E->getType()))
370       if (E->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNotNull))
371         return makeNull();
372 
373     return None;
374   }
375   }
376 }
377 
378 SVal SValBuilder::makeSymExprValNN(BinaryOperator::Opcode Op,
379                                    NonLoc LHS, NonLoc RHS,
380                                    QualType ResultTy) {
381   const SymExpr *symLHS = LHS.getAsSymExpr();
382   const SymExpr *symRHS = RHS.getAsSymExpr();
383 
384   // TODO: When the Max Complexity is reached, we should conjure a symbol
385   // instead of generating an Unknown value and propagate the taint info to it.
386   const unsigned MaxComp = StateMgr.getOwningEngine()
387                                ->getAnalysisManager()
388                                .options.getMaxSymbolComplexity();
389 
390   if (symLHS && symRHS &&
391       (symLHS->computeComplexity() + symRHS->computeComplexity()) <  MaxComp)
392     return makeNonLoc(symLHS, Op, symRHS, ResultTy);
393 
394   if (symLHS && symLHS->computeComplexity() < MaxComp)
395     if (Optional<nonloc::ConcreteInt> rInt = RHS.getAs<nonloc::ConcreteInt>())
396       return makeNonLoc(symLHS, Op, rInt->getValue(), ResultTy);
397 
398   if (symRHS && symRHS->computeComplexity() < MaxComp)
399     if (Optional<nonloc::ConcreteInt> lInt = LHS.getAs<nonloc::ConcreteInt>())
400       return makeNonLoc(lInt->getValue(), Op, symRHS, ResultTy);
401 
402   return UnknownVal();
403 }
404 
405 SVal SValBuilder::evalBinOp(ProgramStateRef state, BinaryOperator::Opcode op,
406                             SVal lhs, SVal rhs, QualType type) {
407   if (lhs.isUndef() || rhs.isUndef())
408     return UndefinedVal();
409 
410   if (lhs.isUnknown() || rhs.isUnknown())
411     return UnknownVal();
412 
413   if (lhs.getAs<nonloc::LazyCompoundVal>() ||
414       rhs.getAs<nonloc::LazyCompoundVal>()) {
415     return UnknownVal();
416   }
417 
418   if (Optional<Loc> LV = lhs.getAs<Loc>()) {
419     if (Optional<Loc> RV = rhs.getAs<Loc>())
420       return evalBinOpLL(state, op, *LV, *RV, type);
421 
422     return evalBinOpLN(state, op, *LV, rhs.castAs<NonLoc>(), type);
423   }
424 
425   if (Optional<Loc> RV = rhs.getAs<Loc>()) {
426     // Support pointer arithmetic where the addend is on the left
427     // and the pointer on the right.
428     assert(op == BO_Add);
429 
430     // Commute the operands.
431     return evalBinOpLN(state, op, *RV, lhs.castAs<NonLoc>(), type);
432   }
433 
434   return evalBinOpNN(state, op, lhs.castAs<NonLoc>(), rhs.castAs<NonLoc>(),
435                      type);
436 }
437 
438 ConditionTruthVal SValBuilder::areEqual(ProgramStateRef state, SVal lhs,
439                                         SVal rhs) {
440   return state->isNonNull(evalEQ(state, lhs, rhs));
441 }
442 
443 SVal SValBuilder::evalEQ(ProgramStateRef state, SVal lhs, SVal rhs) {
444   return evalBinOp(state, BO_EQ, lhs, rhs, getConditionType());
445 }
446 
447 DefinedOrUnknownSVal SValBuilder::evalEQ(ProgramStateRef state,
448                                          DefinedOrUnknownSVal lhs,
449                                          DefinedOrUnknownSVal rhs) {
450   return evalEQ(state, static_cast<SVal>(lhs), static_cast<SVal>(rhs))
451       .castAs<DefinedOrUnknownSVal>();
452 }
453 
454 /// Recursively check if the pointer types are equal modulo const, volatile,
455 /// and restrict qualifiers. Also, assume that all types are similar to 'void'.
456 /// Assumes the input types are canonical.
457 static bool shouldBeModeledWithNoOp(ASTContext &Context, QualType ToTy,
458                                                          QualType FromTy) {
459   while (Context.UnwrapSimilarTypes(ToTy, FromTy)) {
460     Qualifiers Quals1, Quals2;
461     ToTy = Context.getUnqualifiedArrayType(ToTy, Quals1);
462     FromTy = Context.getUnqualifiedArrayType(FromTy, Quals2);
463 
464     // Make sure that non-cvr-qualifiers the other qualifiers (e.g., address
465     // spaces) are identical.
466     Quals1.removeCVRQualifiers();
467     Quals2.removeCVRQualifiers();
468     if (Quals1 != Quals2)
469       return false;
470   }
471 
472   // If we are casting to void, the 'From' value can be used to represent the
473   // 'To' value.
474   //
475   // FIXME: Doing this after unwrapping the types doesn't make any sense. A
476   // cast from 'int**' to 'void**' is not special in the way that a cast from
477   // 'int*' to 'void*' is.
478   if (ToTy->isVoidType())
479     return true;
480 
481   if (ToTy != FromTy)
482     return false;
483 
484   return true;
485 }
486 
487 // Handles casts of type CK_IntegralCast.
488 // At the moment, this function will redirect to evalCast, except when the range
489 // of the original value is known to be greater than the max of the target type.
490 SVal SValBuilder::evalIntegralCast(ProgramStateRef state, SVal val,
491                                    QualType castTy, QualType originalTy) {
492   // No truncations if target type is big enough.
493   if (getContext().getTypeSize(castTy) >= getContext().getTypeSize(originalTy))
494     return evalCast(val, castTy, originalTy);
495 
496   const SymExpr *se = val.getAsSymbolicExpression();
497   if (!se) // Let evalCast handle non symbolic expressions.
498     return evalCast(val, castTy, originalTy);
499 
500   // Find the maximum value of the target type.
501   APSIntType ToType(getContext().getTypeSize(castTy),
502                     castTy->isUnsignedIntegerType());
503   llvm::APSInt ToTypeMax = ToType.getMaxValue();
504   NonLoc ToTypeMaxVal =
505       makeIntVal(ToTypeMax.isUnsigned() ? ToTypeMax.getZExtValue()
506                                         : ToTypeMax.getSExtValue(),
507                  castTy)
508           .castAs<NonLoc>();
509   // Check the range of the symbol being casted against the maximum value of the
510   // target type.
511   NonLoc FromVal = val.castAs<NonLoc>();
512   QualType CmpTy = getConditionType();
513   NonLoc CompVal =
514       evalBinOpNN(state, BO_LE, FromVal, ToTypeMaxVal, CmpTy).castAs<NonLoc>();
515   ProgramStateRef IsNotTruncated, IsTruncated;
516   std::tie(IsNotTruncated, IsTruncated) = state->assume(CompVal);
517   if (!IsNotTruncated && IsTruncated) {
518     // Symbol is truncated so we evaluate it as a cast.
519     NonLoc CastVal = makeNonLoc(se, originalTy, castTy);
520     return CastVal;
521   }
522   return evalCast(val, castTy, originalTy);
523 }
524 
525 // FIXME: should rewrite according to the cast kind.
526 SVal SValBuilder::evalCast(SVal val, QualType castTy, QualType originalTy) {
527   castTy = Context.getCanonicalType(castTy);
528   originalTy = Context.getCanonicalType(originalTy);
529   if (val.isUnknownOrUndef() || castTy == originalTy)
530     return val;
531 
532   if (castTy->isBooleanType()) {
533     if (val.isUnknownOrUndef())
534       return val;
535     if (val.isConstant())
536       return makeTruthVal(!val.isZeroConstant(), castTy);
537     if (!Loc::isLocType(originalTy) &&
538         !originalTy->isIntegralOrEnumerationType() &&
539         !originalTy->isMemberPointerType())
540       return UnknownVal();
541     if (SymbolRef Sym = val.getAsSymbol(true)) {
542       BasicValueFactory &BVF = getBasicValueFactory();
543       // FIXME: If we had a state here, we could see if the symbol is known to
544       // be zero, but we don't.
545       return makeNonLoc(Sym, BO_NE, BVF.getValue(0, Sym->getType()), castTy);
546     }
547     // Loc values are not always true, they could be weakly linked functions.
548     if (Optional<Loc> L = val.getAs<Loc>())
549       return evalCastFromLoc(*L, castTy);
550 
551     Loc L = val.castAs<nonloc::LocAsInteger>().getLoc();
552     return evalCastFromLoc(L, castTy);
553   }
554 
555   // For const casts, casts to void, just propagate the value.
556   if (!castTy->isVariableArrayType() && !originalTy->isVariableArrayType())
557     if (shouldBeModeledWithNoOp(Context, Context.getPointerType(castTy),
558                                          Context.getPointerType(originalTy)))
559       return val;
560 
561   // Check for casts from pointers to integers.
562   if (castTy->isIntegralOrEnumerationType() && Loc::isLocType(originalTy))
563     return evalCastFromLoc(val.castAs<Loc>(), castTy);
564 
565   // Check for casts from integers to pointers.
566   if (Loc::isLocType(castTy) && originalTy->isIntegralOrEnumerationType()) {
567     if (Optional<nonloc::LocAsInteger> LV = val.getAs<nonloc::LocAsInteger>()) {
568       if (const MemRegion *R = LV->getLoc().getAsRegion()) {
569         StoreManager &storeMgr = StateMgr.getStoreManager();
570         R = storeMgr.castRegion(R, castTy);
571         return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
572       }
573       return LV->getLoc();
574     }
575     return dispatchCast(val, castTy);
576   }
577 
578   // Just pass through function and block pointers.
579   if (originalTy->isBlockPointerType() || originalTy->isFunctionPointerType()) {
580     assert(Loc::isLocType(castTy));
581     return val;
582   }
583 
584   // Check for casts from array type to another type.
585   if (const auto *arrayT =
586           dyn_cast<ArrayType>(originalTy.getCanonicalType())) {
587     // We will always decay to a pointer.
588     QualType elemTy = arrayT->getElementType();
589     val = StateMgr.ArrayToPointer(val.castAs<Loc>(), elemTy);
590 
591     // Are we casting from an array to a pointer?  If so just pass on
592     // the decayed value.
593     if (castTy->isPointerType() || castTy->isReferenceType())
594       return val;
595 
596     // Are we casting from an array to an integer?  If so, cast the decayed
597     // pointer value to an integer.
598     assert(castTy->isIntegralOrEnumerationType());
599 
600     // FIXME: Keep these here for now in case we decide soon that we
601     // need the original decayed type.
602     //    QualType elemTy = cast<ArrayType>(originalTy)->getElementType();
603     //    QualType pointerTy = C.getPointerType(elemTy);
604     return evalCastFromLoc(val.castAs<Loc>(), castTy);
605   }
606 
607   // Check for casts from a region to a specific type.
608   if (const MemRegion *R = val.getAsRegion()) {
609     // Handle other casts of locations to integers.
610     if (castTy->isIntegralOrEnumerationType())
611       return evalCastFromLoc(loc::MemRegionVal(R), castTy);
612 
613     // FIXME: We should handle the case where we strip off view layers to get
614     //  to a desugared type.
615     if (!Loc::isLocType(castTy)) {
616       // FIXME: There can be gross cases where one casts the result of a function
617       // (that returns a pointer) to some other value that happens to fit
618       // within that pointer value.  We currently have no good way to
619       // model such operations.  When this happens, the underlying operation
620       // is that the caller is reasoning about bits.  Conceptually we are
621       // layering a "view" of a location on top of those bits.  Perhaps
622       // we need to be more lazy about mutual possible views, even on an
623       // SVal?  This may be necessary for bit-level reasoning as well.
624       return UnknownVal();
625     }
626 
627     // We get a symbolic function pointer for a dereference of a function
628     // pointer, but it is of function type. Example:
629 
630     //  struct FPRec {
631     //    void (*my_func)(int * x);
632     //  };
633     //
634     //  int bar(int x);
635     //
636     //  int f1_a(struct FPRec* foo) {
637     //    int x;
638     //    (*foo->my_func)(&x);
639     //    return bar(x)+1; // no-warning
640     //  }
641 
642     assert(Loc::isLocType(originalTy) || originalTy->isFunctionType() ||
643            originalTy->isBlockPointerType() || castTy->isReferenceType());
644 
645     StoreManager &storeMgr = StateMgr.getStoreManager();
646 
647     // Delegate to store manager to get the result of casting a region to a
648     // different type.  If the MemRegion* returned is NULL, this expression
649     // Evaluates to UnknownVal.
650     R = storeMgr.castRegion(R, castTy);
651     return R ? SVal(loc::MemRegionVal(R)) : UnknownVal();
652   }
653 
654   return dispatchCast(val, castTy);
655 }
656