1 //== BodyFarm.cpp  - Factory for conjuring up fake bodies ----------*- 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 // BodyFarm is a factory for creating faux implementations for functions/methods
11 // for analysis purposes.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "clang/Analysis/BodyFarm.h"
16 #include "clang/AST/ASTContext.h"
17 #include "clang/AST/CXXInheritance.h"
18 #include "clang/AST/Decl.h"
19 #include "clang/AST/Expr.h"
20 #include "clang/AST/ExprCXX.h"
21 #include "clang/AST/ExprObjC.h"
22 #include "clang/AST/NestedNameSpecifier.h"
23 #include "clang/Analysis/CodeInjector.h"
24 #include "clang/Basic/OperatorKinds.h"
25 #include "llvm/ADT/StringSwitch.h"
26 #include "llvm/Support/Debug.h"
27 
28 #define DEBUG_TYPE "body-farm"
29 
30 using namespace clang;
31 
32 //===----------------------------------------------------------------------===//
33 // Helper creation functions for constructing faux ASTs.
34 //===----------------------------------------------------------------------===//
35 
36 static bool isDispatchBlock(QualType Ty) {
37   // Is it a block pointer?
38   const BlockPointerType *BPT = Ty->getAs<BlockPointerType>();
39   if (!BPT)
40     return false;
41 
42   // Check if the block pointer type takes no arguments and
43   // returns void.
44   const FunctionProtoType *FT =
45   BPT->getPointeeType()->getAs<FunctionProtoType>();
46   return FT && FT->getReturnType()->isVoidType() && FT->getNumParams() == 0;
47 }
48 
49 namespace {
50 class ASTMaker {
51 public:
52   ASTMaker(ASTContext &C) : C(C) {}
53 
54   /// Create a new BinaryOperator representing a simple assignment.
55   BinaryOperator *makeAssignment(const Expr *LHS, const Expr *RHS, QualType Ty);
56 
57   /// Create a new BinaryOperator representing a comparison.
58   BinaryOperator *makeComparison(const Expr *LHS, const Expr *RHS,
59                                  BinaryOperator::Opcode Op);
60 
61   /// Create a new compound stmt using the provided statements.
62   CompoundStmt *makeCompound(ArrayRef<Stmt*>);
63 
64   /// Create a new DeclRefExpr for the referenced variable.
65   DeclRefExpr *makeDeclRefExpr(const VarDecl *D,
66                                bool RefersToEnclosingVariableOrCapture = false);
67 
68   /// Create a new UnaryOperator representing a dereference.
69   UnaryOperator *makeDereference(const Expr *Arg, QualType Ty);
70 
71   /// Create an implicit cast for an integer conversion.
72   Expr *makeIntegralCast(const Expr *Arg, QualType Ty);
73 
74   /// Create an implicit cast to a builtin boolean type.
75   ImplicitCastExpr *makeIntegralCastToBoolean(const Expr *Arg);
76 
77   /// Create an implicit cast for lvalue-to-rvaluate conversions.
78   ImplicitCastExpr *makeLvalueToRvalue(const Expr *Arg, QualType Ty);
79 
80   /// Make RValue out of variable declaration, creating a temporary
81   /// DeclRefExpr in the process.
82   ImplicitCastExpr *
83   makeLvalueToRvalue(const VarDecl *Decl,
84                      bool RefersToEnclosingVariableOrCapture = false);
85 
86   /// Create an implicit cast of the given type.
87   ImplicitCastExpr *makeImplicitCast(const Expr *Arg, QualType Ty,
88                                      CastKind CK = CK_LValueToRValue);
89 
90   /// Create an Objective-C bool literal.
91   ObjCBoolLiteralExpr *makeObjCBool(bool Val);
92 
93   /// Create an Objective-C ivar reference.
94   ObjCIvarRefExpr *makeObjCIvarRef(const Expr *Base, const ObjCIvarDecl *IVar);
95 
96   /// Create a Return statement.
97   ReturnStmt *makeReturn(const Expr *RetVal);
98 
99   /// Create an integer literal expression of the given type.
100   IntegerLiteral *makeIntegerLiteral(uint64_t Value, QualType Ty);
101 
102   /// Create a member expression.
103   MemberExpr *makeMemberExpression(Expr *base, ValueDecl *MemberDecl,
104                                    bool IsArrow = false,
105                                    ExprValueKind ValueKind = VK_LValue);
106 
107   /// Returns a *first* member field of a record declaration with a given name.
108   /// \return an nullptr if no member with such a name exists.
109   ValueDecl *findMemberField(const RecordDecl *RD, StringRef Name);
110 
111 private:
112   ASTContext &C;
113 };
114 }
115 
116 BinaryOperator *ASTMaker::makeAssignment(const Expr *LHS, const Expr *RHS,
117                                          QualType Ty) {
118  return new (C) BinaryOperator(const_cast<Expr*>(LHS), const_cast<Expr*>(RHS),
119                                BO_Assign, Ty, VK_RValue,
120                                OK_Ordinary, SourceLocation(), FPOptions());
121 }
122 
123 BinaryOperator *ASTMaker::makeComparison(const Expr *LHS, const Expr *RHS,
124                                          BinaryOperator::Opcode Op) {
125   assert(BinaryOperator::isLogicalOp(Op) ||
126          BinaryOperator::isComparisonOp(Op));
127   return new (C) BinaryOperator(const_cast<Expr*>(LHS),
128                                 const_cast<Expr*>(RHS),
129                                 Op,
130                                 C.getLogicalOperationType(),
131                                 VK_RValue,
132                                 OK_Ordinary, SourceLocation(), FPOptions());
133 }
134 
135 CompoundStmt *ASTMaker::makeCompound(ArrayRef<Stmt *> Stmts) {
136   return CompoundStmt::Create(C, Stmts, SourceLocation(), SourceLocation());
137 }
138 
139 DeclRefExpr *ASTMaker::makeDeclRefExpr(
140     const VarDecl *D,
141     bool RefersToEnclosingVariableOrCapture) {
142   QualType Type = D->getType().getNonReferenceType();
143 
144   DeclRefExpr *DR = DeclRefExpr::Create(
145       C, NestedNameSpecifierLoc(), SourceLocation(), const_cast<VarDecl *>(D),
146       RefersToEnclosingVariableOrCapture, SourceLocation(), Type, VK_LValue);
147   return DR;
148 }
149 
150 UnaryOperator *ASTMaker::makeDereference(const Expr *Arg, QualType Ty) {
151   return new (C) UnaryOperator(const_cast<Expr*>(Arg), UO_Deref, Ty,
152                                VK_LValue, OK_Ordinary, SourceLocation(),
153                               /*CanOverflow*/ false);
154 }
155 
156 ImplicitCastExpr *ASTMaker::makeLvalueToRvalue(const Expr *Arg, QualType Ty) {
157   return makeImplicitCast(Arg, Ty, CK_LValueToRValue);
158 }
159 
160 ImplicitCastExpr *
161 ASTMaker::makeLvalueToRvalue(const VarDecl *Arg,
162                              bool RefersToEnclosingVariableOrCapture) {
163   QualType Type = Arg->getType().getNonReferenceType();
164   return makeLvalueToRvalue(makeDeclRefExpr(Arg,
165                                             RefersToEnclosingVariableOrCapture),
166                             Type);
167 }
168 
169 ImplicitCastExpr *ASTMaker::makeImplicitCast(const Expr *Arg, QualType Ty,
170                                              CastKind CK) {
171   return ImplicitCastExpr::Create(C, Ty,
172                                   /* CastKind=*/ CK,
173                                   /* Expr=*/ const_cast<Expr *>(Arg),
174                                   /* CXXCastPath=*/ nullptr,
175                                   /* ExprValueKind=*/ VK_RValue);
176 }
177 
178 Expr *ASTMaker::makeIntegralCast(const Expr *Arg, QualType Ty) {
179   if (Arg->getType() == Ty)
180     return const_cast<Expr*>(Arg);
181 
182   return ImplicitCastExpr::Create(C, Ty, CK_IntegralCast,
183                                   const_cast<Expr*>(Arg), nullptr, VK_RValue);
184 }
185 
186 ImplicitCastExpr *ASTMaker::makeIntegralCastToBoolean(const Expr *Arg) {
187   return ImplicitCastExpr::Create(C, C.BoolTy, CK_IntegralToBoolean,
188                                   const_cast<Expr*>(Arg), nullptr, VK_RValue);
189 }
190 
191 ObjCBoolLiteralExpr *ASTMaker::makeObjCBool(bool Val) {
192   QualType Ty = C.getBOOLDecl() ? C.getBOOLType() : C.ObjCBuiltinBoolTy;
193   return new (C) ObjCBoolLiteralExpr(Val, Ty, SourceLocation());
194 }
195 
196 ObjCIvarRefExpr *ASTMaker::makeObjCIvarRef(const Expr *Base,
197                                            const ObjCIvarDecl *IVar) {
198   return new (C) ObjCIvarRefExpr(const_cast<ObjCIvarDecl*>(IVar),
199                                  IVar->getType(), SourceLocation(),
200                                  SourceLocation(), const_cast<Expr*>(Base),
201                                  /*arrow=*/true, /*free=*/false);
202 }
203 
204 
205 ReturnStmt *ASTMaker::makeReturn(const Expr *RetVal) {
206   return new (C) ReturnStmt(SourceLocation(), const_cast<Expr*>(RetVal),
207                             nullptr);
208 }
209 
210 IntegerLiteral *ASTMaker::makeIntegerLiteral(uint64_t Value, QualType Ty) {
211   llvm::APInt APValue = llvm::APInt(C.getTypeSize(Ty), Value);
212   return IntegerLiteral::Create(C, APValue, Ty, SourceLocation());
213 }
214 
215 MemberExpr *ASTMaker::makeMemberExpression(Expr *base, ValueDecl *MemberDecl,
216                                            bool IsArrow,
217                                            ExprValueKind ValueKind) {
218 
219   DeclAccessPair FoundDecl = DeclAccessPair::make(MemberDecl, AS_public);
220   return MemberExpr::Create(
221       C, base, IsArrow, SourceLocation(), NestedNameSpecifierLoc(),
222       SourceLocation(), MemberDecl, FoundDecl,
223       DeclarationNameInfo(MemberDecl->getDeclName(), SourceLocation()),
224       /* TemplateArgumentListInfo=*/ nullptr, MemberDecl->getType(), ValueKind,
225       OK_Ordinary);
226 }
227 
228 ValueDecl *ASTMaker::findMemberField(const RecordDecl *RD, StringRef Name) {
229 
230   CXXBasePaths Paths(
231       /* FindAmbiguities=*/false,
232       /* RecordPaths=*/false,
233       /* DetectVirtual=*/ false);
234   const IdentifierInfo &II = C.Idents.get(Name);
235   DeclarationName DeclName = C.DeclarationNames.getIdentifier(&II);
236 
237   DeclContextLookupResult Decls = RD->lookup(DeclName);
238   for (NamedDecl *FoundDecl : Decls)
239     if (!FoundDecl->getDeclContext()->isFunctionOrMethod())
240       return cast<ValueDecl>(FoundDecl);
241 
242   return nullptr;
243 }
244 
245 //===----------------------------------------------------------------------===//
246 // Creation functions for faux ASTs.
247 //===----------------------------------------------------------------------===//
248 
249 typedef Stmt *(*FunctionFarmer)(ASTContext &C, const FunctionDecl *D);
250 
251 static CallExpr *create_call_once_funcptr_call(ASTContext &C, ASTMaker M,
252                                                const ParmVarDecl *Callback,
253                                                ArrayRef<Expr *> CallArgs) {
254 
255   QualType Ty = Callback->getType();
256   DeclRefExpr *Call = M.makeDeclRefExpr(Callback);
257   CastKind CK;
258   if (Ty->isRValueReferenceType()) {
259     CK = CK_LValueToRValue;
260   } else {
261     assert(Ty->isLValueReferenceType());
262     CK = CK_FunctionToPointerDecay;
263     Ty = C.getPointerType(Ty.getNonReferenceType());
264   }
265 
266   return new (C)
267       CallExpr(C, M.makeImplicitCast(Call, Ty.getNonReferenceType(), CK),
268                /*args=*/CallArgs,
269                /*QualType=*/C.VoidTy,
270                /*ExprValueType=*/VK_RValue,
271                /*SourceLocation=*/SourceLocation());
272 }
273 
274 static CallExpr *create_call_once_lambda_call(ASTContext &C, ASTMaker M,
275                                               const ParmVarDecl *Callback,
276                                               CXXRecordDecl *CallbackDecl,
277                                               ArrayRef<Expr *> CallArgs) {
278   assert(CallbackDecl != nullptr);
279   assert(CallbackDecl->isLambda());
280   FunctionDecl *callOperatorDecl = CallbackDecl->getLambdaCallOperator();
281   assert(callOperatorDecl != nullptr);
282 
283   DeclRefExpr *callOperatorDeclRef =
284       DeclRefExpr::Create(/* Ctx =*/ C,
285                           /* QualifierLoc =*/ NestedNameSpecifierLoc(),
286                           /* TemplateKWLoc =*/ SourceLocation(),
287                           const_cast<FunctionDecl *>(callOperatorDecl),
288                           /* RefersToEnclosingVariableOrCapture=*/ false,
289                           /* NameLoc =*/ SourceLocation(),
290                           /* T =*/ callOperatorDecl->getType(),
291                           /* VK =*/ VK_LValue);
292 
293   return new (C)
294       CXXOperatorCallExpr(/*AstContext=*/C, OO_Call, callOperatorDeclRef,
295                           /*args=*/CallArgs,
296                           /*QualType=*/C.VoidTy,
297                           /*ExprValueType=*/VK_RValue,
298                           /*SourceLocation=*/SourceLocation(), FPOptions());
299 }
300 
301 /// Create a fake body for std::call_once.
302 /// Emulates the following function body:
303 ///
304 /// \code
305 /// typedef struct once_flag_s {
306 ///   unsigned long __state = 0;
307 /// } once_flag;
308 /// template<class Callable>
309 /// void call_once(once_flag& o, Callable func) {
310 ///   if (!o.__state) {
311 ///     func();
312 ///   }
313 ///   o.__state = 1;
314 /// }
315 /// \endcode
316 static Stmt *create_call_once(ASTContext &C, const FunctionDecl *D) {
317   DEBUG(llvm::dbgs() << "Generating body for call_once\n");
318 
319   // We need at least two parameters.
320   if (D->param_size() < 2)
321     return nullptr;
322 
323   ASTMaker M(C);
324 
325   const ParmVarDecl *Flag = D->getParamDecl(0);
326   const ParmVarDecl *Callback = D->getParamDecl(1);
327 
328   if (!Callback->getType()->isReferenceType()) {
329     llvm::dbgs() << "libcxx03 std::call_once implementation, skipping.\n";
330     return nullptr;
331   }
332   if (!Flag->getType()->isReferenceType()) {
333     llvm::dbgs() << "unknown std::call_once implementation, skipping.\n";
334     return nullptr;
335   }
336 
337   QualType CallbackType = Callback->getType().getNonReferenceType();
338 
339   // Nullable pointer, non-null iff function is a CXXRecordDecl.
340   CXXRecordDecl *CallbackRecordDecl = CallbackType->getAsCXXRecordDecl();
341   QualType FlagType = Flag->getType().getNonReferenceType();
342   auto *FlagRecordDecl = dyn_cast_or_null<RecordDecl>(FlagType->getAsTagDecl());
343 
344   if (!FlagRecordDecl) {
345     DEBUG(llvm::dbgs() << "Flag field is not a record: "
346                        << "unknown std::call_once implementation, "
347                        << "ignoring the call.\n");
348     return nullptr;
349   }
350 
351   // We initially assume libc++ implementation of call_once,
352   // where the once_flag struct has a field `__state_`.
353   ValueDecl *FlagFieldDecl = M.findMemberField(FlagRecordDecl, "__state_");
354 
355   // Otherwise, try libstdc++ implementation, with a field
356   // `_M_once`
357   if (!FlagFieldDecl) {
358     FlagFieldDecl = M.findMemberField(FlagRecordDecl, "_M_once");
359   }
360 
361   if (!FlagFieldDecl) {
362     DEBUG(llvm::dbgs() << "No field _M_once or __state_ found on "
363                        << "std::once_flag struct: unknown std::call_once "
364                        << "implementation, ignoring the call.");
365     return nullptr;
366   }
367 
368   bool isLambdaCall = CallbackRecordDecl && CallbackRecordDecl->isLambda();
369   if (CallbackRecordDecl && !isLambdaCall) {
370     DEBUG(llvm::dbgs() << "Not supported: synthesizing body for functors when "
371                        << "body farming std::call_once, ignoring the call.");
372     return nullptr;
373   }
374 
375   SmallVector<Expr *, 5> CallArgs;
376   const FunctionProtoType *CallbackFunctionType;
377   if (isLambdaCall) {
378 
379     // Lambda requires callback itself inserted as a first parameter.
380     CallArgs.push_back(
381         M.makeDeclRefExpr(Callback,
382                           /* RefersToEnclosingVariableOrCapture=*/ true));
383     CallbackFunctionType = CallbackRecordDecl->getLambdaCallOperator()
384                                ->getType()
385                                ->getAs<FunctionProtoType>();
386   } else if (!CallbackType->getPointeeType().isNull()) {
387     CallbackFunctionType =
388         CallbackType->getPointeeType()->getAs<FunctionProtoType>();
389   } else {
390     CallbackFunctionType = CallbackType->getAs<FunctionProtoType>();
391   }
392 
393   if (!CallbackFunctionType)
394     return nullptr;
395 
396   // First two arguments are used for the flag and for the callback.
397   if (D->getNumParams() != CallbackFunctionType->getNumParams() + 2) {
398     DEBUG(llvm::dbgs() << "Types of params of the callback do not match "
399                        << "params passed to std::call_once, "
400                        << "ignoring the call\n");
401     return nullptr;
402   }
403 
404   // All arguments past first two ones are passed to the callback,
405   // and we turn lvalues into rvalues if the argument is not passed by
406   // reference.
407   for (unsigned int ParamIdx = 2; ParamIdx < D->getNumParams(); ParamIdx++) {
408     const ParmVarDecl *PDecl = D->getParamDecl(ParamIdx);
409     Expr *ParamExpr = M.makeDeclRefExpr(PDecl);
410     if (!CallbackFunctionType->getParamType(ParamIdx - 2)->isReferenceType()) {
411       QualType PTy = PDecl->getType().getNonReferenceType();
412       ParamExpr = M.makeLvalueToRvalue(ParamExpr, PTy);
413     }
414     CallArgs.push_back(ParamExpr);
415   }
416 
417   CallExpr *CallbackCall;
418   if (isLambdaCall) {
419 
420     CallbackCall = create_call_once_lambda_call(C, M, Callback,
421                                                 CallbackRecordDecl, CallArgs);
422   } else {
423 
424     // Function pointer case.
425     CallbackCall = create_call_once_funcptr_call(C, M, Callback, CallArgs);
426   }
427 
428   DeclRefExpr *FlagDecl =
429       M.makeDeclRefExpr(Flag,
430                         /* RefersToEnclosingVariableOrCapture=*/true);
431 
432 
433   MemberExpr *Deref = M.makeMemberExpression(FlagDecl, FlagFieldDecl);
434   assert(Deref->isLValue());
435   QualType DerefType = Deref->getType();
436 
437   // Negation predicate.
438   UnaryOperator *FlagCheck = new (C) UnaryOperator(
439       /* input=*/
440       M.makeImplicitCast(M.makeLvalueToRvalue(Deref, DerefType), DerefType,
441                          CK_IntegralToBoolean),
442       /* opc=*/ UO_LNot,
443       /* QualType=*/ C.IntTy,
444       /* ExprValueKind=*/ VK_RValue,
445       /* ExprObjectKind=*/ OK_Ordinary, SourceLocation(),
446       /* CanOverflow*/ false);
447 
448   // Create assignment.
449   BinaryOperator *FlagAssignment = M.makeAssignment(
450       Deref, M.makeIntegralCast(M.makeIntegerLiteral(1, C.IntTy), DerefType),
451       DerefType);
452 
453   IfStmt *Out = new (C)
454       IfStmt(C, SourceLocation(),
455              /* IsConstexpr=*/ false,
456              /* init=*/ nullptr,
457              /* var=*/ nullptr,
458              /* cond=*/ FlagCheck,
459              /* then=*/ M.makeCompound({CallbackCall, FlagAssignment}));
460 
461   return Out;
462 }
463 
464 /// Create a fake body for dispatch_once.
465 static Stmt *create_dispatch_once(ASTContext &C, const FunctionDecl *D) {
466   // Check if we have at least two parameters.
467   if (D->param_size() != 2)
468     return nullptr;
469 
470   // Check if the first parameter is a pointer to integer type.
471   const ParmVarDecl *Predicate = D->getParamDecl(0);
472   QualType PredicateQPtrTy = Predicate->getType();
473   const PointerType *PredicatePtrTy = PredicateQPtrTy->getAs<PointerType>();
474   if (!PredicatePtrTy)
475     return nullptr;
476   QualType PredicateTy = PredicatePtrTy->getPointeeType();
477   if (!PredicateTy->isIntegerType())
478     return nullptr;
479 
480   // Check if the second parameter is the proper block type.
481   const ParmVarDecl *Block = D->getParamDecl(1);
482   QualType Ty = Block->getType();
483   if (!isDispatchBlock(Ty))
484     return nullptr;
485 
486   // Everything checks out.  Create a fakse body that checks the predicate,
487   // sets it, and calls the block.  Basically, an AST dump of:
488   //
489   // void dispatch_once(dispatch_once_t *predicate, dispatch_block_t block) {
490   //  if (*predicate != ~0l) {
491   //    *predicate = ~0l;
492   //    block();
493   //  }
494   // }
495 
496   ASTMaker M(C);
497 
498   // (1) Create the call.
499   CallExpr *CE = new (C) CallExpr(
500       /*ASTContext=*/C,
501       /*StmtClass=*/M.makeLvalueToRvalue(/*Expr=*/Block),
502       /*args=*/None,
503       /*QualType=*/C.VoidTy,
504       /*ExprValueType=*/VK_RValue,
505       /*SourceLocation=*/SourceLocation());
506 
507   // (2) Create the assignment to the predicate.
508   Expr *DoneValue =
509       new (C) UnaryOperator(M.makeIntegerLiteral(0, C.LongTy), UO_Not, C.LongTy,
510                             VK_RValue, OK_Ordinary, SourceLocation(),
511                             /*CanOverflow*/false);
512 
513   BinaryOperator *B =
514     M.makeAssignment(
515        M.makeDereference(
516           M.makeLvalueToRvalue(
517             M.makeDeclRefExpr(Predicate), PredicateQPtrTy),
518             PredicateTy),
519        M.makeIntegralCast(DoneValue, PredicateTy),
520        PredicateTy);
521 
522   // (3) Create the compound statement.
523   Stmt *Stmts[] = { B, CE };
524   CompoundStmt *CS = M.makeCompound(Stmts);
525 
526   // (4) Create the 'if' condition.
527   ImplicitCastExpr *LValToRval =
528     M.makeLvalueToRvalue(
529       M.makeDereference(
530         M.makeLvalueToRvalue(
531           M.makeDeclRefExpr(Predicate),
532           PredicateQPtrTy),
533         PredicateTy),
534     PredicateTy);
535 
536   Expr *GuardCondition = M.makeComparison(LValToRval, DoneValue, BO_NE);
537   // (5) Create the 'if' statement.
538   IfStmt *If = new (C) IfStmt(C, SourceLocation(),
539                               /* IsConstexpr=*/ false,
540                               /* init=*/ nullptr,
541                               /* var=*/ nullptr,
542                               /* cond=*/ GuardCondition,
543                               /* then=*/ CS);
544   return If;
545 }
546 
547 /// Create a fake body for dispatch_sync.
548 static Stmt *create_dispatch_sync(ASTContext &C, const FunctionDecl *D) {
549   // Check if we have at least two parameters.
550   if (D->param_size() != 2)
551     return nullptr;
552 
553   // Check if the second parameter is a block.
554   const ParmVarDecl *PV = D->getParamDecl(1);
555   QualType Ty = PV->getType();
556   if (!isDispatchBlock(Ty))
557     return nullptr;
558 
559   // Everything checks out.  Create a fake body that just calls the block.
560   // This is basically just an AST dump of:
561   //
562   // void dispatch_sync(dispatch_queue_t queue, void (^block)(void)) {
563   //   block();
564   // }
565   //
566   ASTMaker M(C);
567   DeclRefExpr *DR = M.makeDeclRefExpr(PV);
568   ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
569   CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
570                                   SourceLocation());
571   return CE;
572 }
573 
574 static Stmt *create_OSAtomicCompareAndSwap(ASTContext &C, const FunctionDecl *D)
575 {
576   // There are exactly 3 arguments.
577   if (D->param_size() != 3)
578     return nullptr;
579 
580   // Signature:
581   // _Bool OSAtomicCompareAndSwapPtr(void *__oldValue,
582   //                                 void *__newValue,
583   //                                 void * volatile *__theValue)
584   // Generate body:
585   //   if (oldValue == *theValue) {
586   //    *theValue = newValue;
587   //    return YES;
588   //   }
589   //   else return NO;
590 
591   QualType ResultTy = D->getReturnType();
592   bool isBoolean = ResultTy->isBooleanType();
593   if (!isBoolean && !ResultTy->isIntegralType(C))
594     return nullptr;
595 
596   const ParmVarDecl *OldValue = D->getParamDecl(0);
597   QualType OldValueTy = OldValue->getType();
598 
599   const ParmVarDecl *NewValue = D->getParamDecl(1);
600   QualType NewValueTy = NewValue->getType();
601 
602   assert(OldValueTy == NewValueTy);
603 
604   const ParmVarDecl *TheValue = D->getParamDecl(2);
605   QualType TheValueTy = TheValue->getType();
606   const PointerType *PT = TheValueTy->getAs<PointerType>();
607   if (!PT)
608     return nullptr;
609   QualType PointeeTy = PT->getPointeeType();
610 
611   ASTMaker M(C);
612   // Construct the comparison.
613   Expr *Comparison =
614     M.makeComparison(
615       M.makeLvalueToRvalue(M.makeDeclRefExpr(OldValue), OldValueTy),
616       M.makeLvalueToRvalue(
617         M.makeDereference(
618           M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
619           PointeeTy),
620         PointeeTy),
621       BO_EQ);
622 
623   // Construct the body of the IfStmt.
624   Stmt *Stmts[2];
625   Stmts[0] =
626     M.makeAssignment(
627       M.makeDereference(
628         M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
629         PointeeTy),
630       M.makeLvalueToRvalue(M.makeDeclRefExpr(NewValue), NewValueTy),
631       NewValueTy);
632 
633   Expr *BoolVal = M.makeObjCBool(true);
634   Expr *RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
635                            : M.makeIntegralCast(BoolVal, ResultTy);
636   Stmts[1] = M.makeReturn(RetVal);
637   CompoundStmt *Body = M.makeCompound(Stmts);
638 
639   // Construct the else clause.
640   BoolVal = M.makeObjCBool(false);
641   RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
642                      : M.makeIntegralCast(BoolVal, ResultTy);
643   Stmt *Else = M.makeReturn(RetVal);
644 
645   /// Construct the If.
646   Stmt *If = new (C) IfStmt(C, SourceLocation(), false, nullptr, nullptr,
647                             Comparison, Body, SourceLocation(), Else);
648 
649   return If;
650 }
651 
652 Stmt *BodyFarm::getBody(const FunctionDecl *D) {
653   D = D->getCanonicalDecl();
654 
655   Optional<Stmt *> &Val = Bodies[D];
656   if (Val.hasValue())
657     return Val.getValue();
658 
659   Val = nullptr;
660 
661   if (D->getIdentifier() == nullptr)
662     return nullptr;
663 
664   StringRef Name = D->getName();
665   if (Name.empty())
666     return nullptr;
667 
668   FunctionFarmer FF;
669 
670   if (Name.startswith("OSAtomicCompareAndSwap") ||
671       Name.startswith("objc_atomicCompareAndSwap")) {
672     FF = create_OSAtomicCompareAndSwap;
673   } else if (Name == "call_once" && D->getDeclContext()->isStdNamespace()) {
674     FF = create_call_once;
675   } else {
676     FF = llvm::StringSwitch<FunctionFarmer>(Name)
677           .Case("dispatch_sync", create_dispatch_sync)
678           .Case("dispatch_once", create_dispatch_once)
679           .Default(nullptr);
680   }
681 
682   if (FF) { Val = FF(C, D); }
683   else if (Injector) { Val = Injector->getBody(D); }
684   return Val.getValue();
685 }
686 
687 static const ObjCIvarDecl *findBackingIvar(const ObjCPropertyDecl *Prop) {
688   const ObjCIvarDecl *IVar = Prop->getPropertyIvarDecl();
689 
690   if (IVar)
691     return IVar;
692 
693   // When a readonly property is shadowed in a class extensions with a
694   // a readwrite property, the instance variable belongs to the shadowing
695   // property rather than the shadowed property. If there is no instance
696   // variable on a readonly property, check to see whether the property is
697   // shadowed and if so try to get the instance variable from shadowing
698   // property.
699   if (!Prop->isReadOnly())
700     return nullptr;
701 
702   auto *Container = cast<ObjCContainerDecl>(Prop->getDeclContext());
703   const ObjCInterfaceDecl *PrimaryInterface = nullptr;
704   if (auto *InterfaceDecl = dyn_cast<ObjCInterfaceDecl>(Container)) {
705     PrimaryInterface = InterfaceDecl;
706   } else if (auto *CategoryDecl = dyn_cast<ObjCCategoryDecl>(Container)) {
707     PrimaryInterface = CategoryDecl->getClassInterface();
708   } else if (auto *ImplDecl = dyn_cast<ObjCImplDecl>(Container)) {
709     PrimaryInterface = ImplDecl->getClassInterface();
710   } else {
711     return nullptr;
712   }
713 
714   // FindPropertyVisibleInPrimaryClass() looks first in class extensions, so it
715   // is guaranteed to find the shadowing property, if it exists, rather than
716   // the shadowed property.
717   auto *ShadowingProp = PrimaryInterface->FindPropertyVisibleInPrimaryClass(
718       Prop->getIdentifier(), Prop->getQueryKind());
719   if (ShadowingProp && ShadowingProp != Prop) {
720     IVar = ShadowingProp->getPropertyIvarDecl();
721   }
722 
723   return IVar;
724 }
725 
726 static Stmt *createObjCPropertyGetter(ASTContext &Ctx,
727                                       const ObjCPropertyDecl *Prop) {
728   // First, find the backing ivar.
729   const ObjCIvarDecl *IVar = findBackingIvar(Prop);
730   if (!IVar)
731     return nullptr;
732 
733   // Ignore weak variables, which have special behavior.
734   if (Prop->getPropertyAttributes() & ObjCPropertyDecl::OBJC_PR_weak)
735     return nullptr;
736 
737   // Look to see if Sema has synthesized a body for us. This happens in
738   // Objective-C++ because the return value may be a C++ class type with a
739   // non-trivial copy constructor. We can only do this if we can find the
740   // @synthesize for this property, though (or if we know it's been auto-
741   // synthesized).
742   const ObjCImplementationDecl *ImplDecl =
743     IVar->getContainingInterface()->getImplementation();
744   if (ImplDecl) {
745     for (const auto *I : ImplDecl->property_impls()) {
746       if (I->getPropertyDecl() != Prop)
747         continue;
748 
749       if (I->getGetterCXXConstructor()) {
750         ASTMaker M(Ctx);
751         return M.makeReturn(I->getGetterCXXConstructor());
752       }
753     }
754   }
755 
756   // Sanity check that the property is the same type as the ivar, or a
757   // reference to it, and that it is either an object pointer or trivially
758   // copyable.
759   if (!Ctx.hasSameUnqualifiedType(IVar->getType(),
760                                   Prop->getType().getNonReferenceType()))
761     return nullptr;
762   if (!IVar->getType()->isObjCLifetimeType() &&
763       !IVar->getType().isTriviallyCopyableType(Ctx))
764     return nullptr;
765 
766   // Generate our body:
767   //   return self->_ivar;
768   ASTMaker M(Ctx);
769 
770   const VarDecl *selfVar = Prop->getGetterMethodDecl()->getSelfDecl();
771   if (!selfVar)
772     return nullptr;
773 
774   Expr *loadedIVar =
775     M.makeObjCIvarRef(
776       M.makeLvalueToRvalue(
777         M.makeDeclRefExpr(selfVar),
778         selfVar->getType()),
779       IVar);
780 
781   if (!Prop->getType()->isReferenceType())
782     loadedIVar = M.makeLvalueToRvalue(loadedIVar, IVar->getType());
783 
784   return M.makeReturn(loadedIVar);
785 }
786 
787 Stmt *BodyFarm::getBody(const ObjCMethodDecl *D) {
788   // We currently only know how to synthesize property accessors.
789   if (!D->isPropertyAccessor())
790     return nullptr;
791 
792   D = D->getCanonicalDecl();
793 
794   Optional<Stmt *> &Val = Bodies[D];
795   if (Val.hasValue())
796     return Val.getValue();
797   Val = nullptr;
798 
799   const ObjCPropertyDecl *Prop = D->findPropertyDecl();
800   if (!Prop)
801     return nullptr;
802 
803   // For now, we only synthesize getters.
804   // Synthesizing setters would cause false negatives in the
805   // RetainCountChecker because the method body would bind the parameter
806   // to an instance variable, causing it to escape. This would prevent
807   // warning in the following common scenario:
808   //
809   //  id foo = [[NSObject alloc] init];
810   //  self.foo = foo; // We should warn that foo leaks here.
811   //
812   if (D->param_size() != 0)
813     return nullptr;
814 
815   Val = createObjCPropertyGetter(C, Prop);
816 
817   return Val.getValue();
818 }
819 
820