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 ReturnStmt *ASTMaker::makeReturn(const Expr *RetVal) {
205   return ReturnStmt::Create(C, SourceLocation(), const_cast<Expr *>(RetVal),
206                             /* NRVOCandidate=*/nullptr);
207 }
208 
209 IntegerLiteral *ASTMaker::makeIntegerLiteral(uint64_t Value, QualType Ty) {
210   llvm::APInt APValue = llvm::APInt(C.getTypeSize(Ty), Value);
211   return IntegerLiteral::Create(C, APValue, Ty, SourceLocation());
212 }
213 
214 MemberExpr *ASTMaker::makeMemberExpression(Expr *base, ValueDecl *MemberDecl,
215                                            bool IsArrow,
216                                            ExprValueKind ValueKind) {
217 
218   DeclAccessPair FoundDecl = DeclAccessPair::make(MemberDecl, AS_public);
219   return MemberExpr::Create(
220       C, base, IsArrow, SourceLocation(), NestedNameSpecifierLoc(),
221       SourceLocation(), MemberDecl, FoundDecl,
222       DeclarationNameInfo(MemberDecl->getDeclName(), SourceLocation()),
223       /* TemplateArgumentListInfo=*/ nullptr, MemberDecl->getType(), ValueKind,
224       OK_Ordinary);
225 }
226 
227 ValueDecl *ASTMaker::findMemberField(const RecordDecl *RD, StringRef Name) {
228 
229   CXXBasePaths Paths(
230       /* FindAmbiguities=*/false,
231       /* RecordPaths=*/false,
232       /* DetectVirtual=*/ false);
233   const IdentifierInfo &II = C.Idents.get(Name);
234   DeclarationName DeclName = C.DeclarationNames.getIdentifier(&II);
235 
236   DeclContextLookupResult Decls = RD->lookup(DeclName);
237   for (NamedDecl *FoundDecl : Decls)
238     if (!FoundDecl->getDeclContext()->isFunctionOrMethod())
239       return cast<ValueDecl>(FoundDecl);
240 
241   return nullptr;
242 }
243 
244 //===----------------------------------------------------------------------===//
245 // Creation functions for faux ASTs.
246 //===----------------------------------------------------------------------===//
247 
248 typedef Stmt *(*FunctionFarmer)(ASTContext &C, const FunctionDecl *D);
249 
250 static CallExpr *create_call_once_funcptr_call(ASTContext &C, ASTMaker M,
251                                                const ParmVarDecl *Callback,
252                                                ArrayRef<Expr *> CallArgs) {
253 
254   QualType Ty = Callback->getType();
255   DeclRefExpr *Call = M.makeDeclRefExpr(Callback);
256   Expr *SubExpr;
257   if (Ty->isRValueReferenceType()) {
258     SubExpr = M.makeImplicitCast(
259         Call, Ty.getNonReferenceType(), CK_LValueToRValue);
260   } else if (Ty->isLValueReferenceType() &&
261              Call->getType()->isFunctionType()) {
262     Ty = C.getPointerType(Ty.getNonReferenceType());
263     SubExpr = M.makeImplicitCast(Call, Ty, CK_FunctionToPointerDecay);
264   } else if (Ty->isLValueReferenceType()
265              && Call->getType()->isPointerType()
266              && Call->getType()->getPointeeType()->isFunctionType()){
267     SubExpr = Call;
268   } else {
269     llvm_unreachable("Unexpected state");
270   }
271 
272   return new (C)
273       CallExpr(C, SubExpr, CallArgs, C.VoidTy, VK_RValue, SourceLocation());
274 }
275 
276 static CallExpr *create_call_once_lambda_call(ASTContext &C, ASTMaker M,
277                                               const ParmVarDecl *Callback,
278                                               CXXRecordDecl *CallbackDecl,
279                                               ArrayRef<Expr *> CallArgs) {
280   assert(CallbackDecl != nullptr);
281   assert(CallbackDecl->isLambda());
282   FunctionDecl *callOperatorDecl = CallbackDecl->getLambdaCallOperator();
283   assert(callOperatorDecl != nullptr);
284 
285   DeclRefExpr *callOperatorDeclRef =
286       DeclRefExpr::Create(/* Ctx =*/ C,
287                           /* QualifierLoc =*/ NestedNameSpecifierLoc(),
288                           /* TemplateKWLoc =*/ SourceLocation(),
289                           const_cast<FunctionDecl *>(callOperatorDecl),
290                           /* RefersToEnclosingVariableOrCapture=*/ false,
291                           /* NameLoc =*/ SourceLocation(),
292                           /* T =*/ callOperatorDecl->getType(),
293                           /* VK =*/ VK_LValue);
294 
295   return new (C)
296       CXXOperatorCallExpr(/*AstContext=*/C, OO_Call, callOperatorDeclRef,
297                           /*args=*/CallArgs,
298                           /*QualType=*/C.VoidTy,
299                           /*ExprValueType=*/VK_RValue,
300                           /*SourceLocation=*/SourceLocation(), FPOptions());
301 }
302 
303 /// Create a fake body for std::call_once.
304 /// Emulates the following function body:
305 ///
306 /// \code
307 /// typedef struct once_flag_s {
308 ///   unsigned long __state = 0;
309 /// } once_flag;
310 /// template<class Callable>
311 /// void call_once(once_flag& o, Callable func) {
312 ///   if (!o.__state) {
313 ///     func();
314 ///   }
315 ///   o.__state = 1;
316 /// }
317 /// \endcode
318 static Stmt *create_call_once(ASTContext &C, const FunctionDecl *D) {
319   LLVM_DEBUG(llvm::dbgs() << "Generating body for call_once\n");
320 
321   // We need at least two parameters.
322   if (D->param_size() < 2)
323     return nullptr;
324 
325   ASTMaker M(C);
326 
327   const ParmVarDecl *Flag = D->getParamDecl(0);
328   const ParmVarDecl *Callback = D->getParamDecl(1);
329 
330   if (!Callback->getType()->isReferenceType()) {
331     llvm::dbgs() << "libcxx03 std::call_once implementation, skipping.\n";
332     return nullptr;
333   }
334   if (!Flag->getType()->isReferenceType()) {
335     llvm::dbgs() << "unknown std::call_once implementation, skipping.\n";
336     return nullptr;
337   }
338 
339   QualType CallbackType = Callback->getType().getNonReferenceType();
340 
341   // Nullable pointer, non-null iff function is a CXXRecordDecl.
342   CXXRecordDecl *CallbackRecordDecl = CallbackType->getAsCXXRecordDecl();
343   QualType FlagType = Flag->getType().getNonReferenceType();
344   auto *FlagRecordDecl = FlagType->getAsRecordDecl();
345 
346   if (!FlagRecordDecl) {
347     LLVM_DEBUG(llvm::dbgs() << "Flag field is not a record: "
348                             << "unknown std::call_once implementation, "
349                             << "ignoring the call.\n");
350     return nullptr;
351   }
352 
353   // We initially assume libc++ implementation of call_once,
354   // where the once_flag struct has a field `__state_`.
355   ValueDecl *FlagFieldDecl = M.findMemberField(FlagRecordDecl, "__state_");
356 
357   // Otherwise, try libstdc++ implementation, with a field
358   // `_M_once`
359   if (!FlagFieldDecl) {
360     FlagFieldDecl = M.findMemberField(FlagRecordDecl, "_M_once");
361   }
362 
363   if (!FlagFieldDecl) {
364     LLVM_DEBUG(llvm::dbgs() << "No field _M_once or __state_ found on "
365                             << "std::once_flag struct: unknown std::call_once "
366                             << "implementation, ignoring the call.");
367     return nullptr;
368   }
369 
370   bool isLambdaCall = CallbackRecordDecl && CallbackRecordDecl->isLambda();
371   if (CallbackRecordDecl && !isLambdaCall) {
372     LLVM_DEBUG(llvm::dbgs()
373                << "Not supported: synthesizing body for functors when "
374                << "body farming std::call_once, ignoring the call.");
375     return nullptr;
376   }
377 
378   SmallVector<Expr *, 5> CallArgs;
379   const FunctionProtoType *CallbackFunctionType;
380   if (isLambdaCall) {
381 
382     // Lambda requires callback itself inserted as a first parameter.
383     CallArgs.push_back(
384         M.makeDeclRefExpr(Callback,
385                           /* RefersToEnclosingVariableOrCapture=*/ true));
386     CallbackFunctionType = CallbackRecordDecl->getLambdaCallOperator()
387                                ->getType()
388                                ->getAs<FunctionProtoType>();
389   } else if (!CallbackType->getPointeeType().isNull()) {
390     CallbackFunctionType =
391         CallbackType->getPointeeType()->getAs<FunctionProtoType>();
392   } else {
393     CallbackFunctionType = CallbackType->getAs<FunctionProtoType>();
394   }
395 
396   if (!CallbackFunctionType)
397     return nullptr;
398 
399   // First two arguments are used for the flag and for the callback.
400   if (D->getNumParams() != CallbackFunctionType->getNumParams() + 2) {
401     LLVM_DEBUG(llvm::dbgs() << "Types of params of the callback do not match "
402                             << "params passed to std::call_once, "
403                             << "ignoring the call\n");
404     return nullptr;
405   }
406 
407   // All arguments past first two ones are passed to the callback,
408   // and we turn lvalues into rvalues if the argument is not passed by
409   // reference.
410   for (unsigned int ParamIdx = 2; ParamIdx < D->getNumParams(); ParamIdx++) {
411     const ParmVarDecl *PDecl = D->getParamDecl(ParamIdx);
412     if (PDecl &&
413         CallbackFunctionType->getParamType(ParamIdx - 2)
414                 .getNonReferenceType()
415                 .getCanonicalType() !=
416             PDecl->getType().getNonReferenceType().getCanonicalType()) {
417       LLVM_DEBUG(llvm::dbgs() << "Types of params of the callback do not match "
418                               << "params passed to std::call_once, "
419                               << "ignoring the call\n");
420       return nullptr;
421     }
422     Expr *ParamExpr = M.makeDeclRefExpr(PDecl);
423     if (!CallbackFunctionType->getParamType(ParamIdx - 2)->isReferenceType()) {
424       QualType PTy = PDecl->getType().getNonReferenceType();
425       ParamExpr = M.makeLvalueToRvalue(ParamExpr, PTy);
426     }
427     CallArgs.push_back(ParamExpr);
428   }
429 
430   CallExpr *CallbackCall;
431   if (isLambdaCall) {
432 
433     CallbackCall = create_call_once_lambda_call(C, M, Callback,
434                                                 CallbackRecordDecl, CallArgs);
435   } else {
436 
437     // Function pointer case.
438     CallbackCall = create_call_once_funcptr_call(C, M, Callback, CallArgs);
439   }
440 
441   DeclRefExpr *FlagDecl =
442       M.makeDeclRefExpr(Flag,
443                         /* RefersToEnclosingVariableOrCapture=*/true);
444 
445 
446   MemberExpr *Deref = M.makeMemberExpression(FlagDecl, FlagFieldDecl);
447   assert(Deref->isLValue());
448   QualType DerefType = Deref->getType();
449 
450   // Negation predicate.
451   UnaryOperator *FlagCheck = new (C) UnaryOperator(
452       /* input=*/
453       M.makeImplicitCast(M.makeLvalueToRvalue(Deref, DerefType), DerefType,
454                          CK_IntegralToBoolean),
455       /* opc=*/ UO_LNot,
456       /* QualType=*/ C.IntTy,
457       /* ExprValueKind=*/ VK_RValue,
458       /* ExprObjectKind=*/ OK_Ordinary, SourceLocation(),
459       /* CanOverflow*/ false);
460 
461   // Create assignment.
462   BinaryOperator *FlagAssignment = M.makeAssignment(
463       Deref, M.makeIntegralCast(M.makeIntegerLiteral(1, C.IntTy), DerefType),
464       DerefType);
465 
466   auto *Out =
467       IfStmt::Create(C, SourceLocation(),
468                      /* IsConstexpr=*/false,
469                      /* init=*/nullptr,
470                      /* var=*/nullptr,
471                      /* cond=*/FlagCheck,
472                      /* then=*/M.makeCompound({CallbackCall, FlagAssignment}));
473 
474   return Out;
475 }
476 
477 /// Create a fake body for dispatch_once.
478 static Stmt *create_dispatch_once(ASTContext &C, const FunctionDecl *D) {
479   // Check if we have at least two parameters.
480   if (D->param_size() != 2)
481     return nullptr;
482 
483   // Check if the first parameter is a pointer to integer type.
484   const ParmVarDecl *Predicate = D->getParamDecl(0);
485   QualType PredicateQPtrTy = Predicate->getType();
486   const PointerType *PredicatePtrTy = PredicateQPtrTy->getAs<PointerType>();
487   if (!PredicatePtrTy)
488     return nullptr;
489   QualType PredicateTy = PredicatePtrTy->getPointeeType();
490   if (!PredicateTy->isIntegerType())
491     return nullptr;
492 
493   // Check if the second parameter is the proper block type.
494   const ParmVarDecl *Block = D->getParamDecl(1);
495   QualType Ty = Block->getType();
496   if (!isDispatchBlock(Ty))
497     return nullptr;
498 
499   // Everything checks out.  Create a fakse body that checks the predicate,
500   // sets it, and calls the block.  Basically, an AST dump of:
501   //
502   // void dispatch_once(dispatch_once_t *predicate, dispatch_block_t block) {
503   //  if (*predicate != ~0l) {
504   //    *predicate = ~0l;
505   //    block();
506   //  }
507   // }
508 
509   ASTMaker M(C);
510 
511   // (1) Create the call.
512   CallExpr *CE = new (C) CallExpr(
513       /*ASTContext=*/C,
514       /*StmtClass=*/M.makeLvalueToRvalue(/*Expr=*/Block),
515       /*args=*/None,
516       /*QualType=*/C.VoidTy,
517       /*ExprValueType=*/VK_RValue,
518       /*SourceLocation=*/SourceLocation());
519 
520   // (2) Create the assignment to the predicate.
521   Expr *DoneValue =
522       new (C) UnaryOperator(M.makeIntegerLiteral(0, C.LongTy), UO_Not, C.LongTy,
523                             VK_RValue, OK_Ordinary, SourceLocation(),
524                             /*CanOverflow*/false);
525 
526   BinaryOperator *B =
527     M.makeAssignment(
528        M.makeDereference(
529           M.makeLvalueToRvalue(
530             M.makeDeclRefExpr(Predicate), PredicateQPtrTy),
531             PredicateTy),
532        M.makeIntegralCast(DoneValue, PredicateTy),
533        PredicateTy);
534 
535   // (3) Create the compound statement.
536   Stmt *Stmts[] = { B, CE };
537   CompoundStmt *CS = M.makeCompound(Stmts);
538 
539   // (4) Create the 'if' condition.
540   ImplicitCastExpr *LValToRval =
541     M.makeLvalueToRvalue(
542       M.makeDereference(
543         M.makeLvalueToRvalue(
544           M.makeDeclRefExpr(Predicate),
545           PredicateQPtrTy),
546         PredicateTy),
547     PredicateTy);
548 
549   Expr *GuardCondition = M.makeComparison(LValToRval, DoneValue, BO_NE);
550   // (5) Create the 'if' statement.
551   auto *If = IfStmt::Create(C, SourceLocation(),
552                             /* IsConstexpr=*/false,
553                             /* init=*/nullptr,
554                             /* var=*/nullptr,
555                             /* cond=*/GuardCondition,
556                             /* then=*/CS);
557   return If;
558 }
559 
560 /// Create a fake body for dispatch_sync.
561 static Stmt *create_dispatch_sync(ASTContext &C, const FunctionDecl *D) {
562   // Check if we have at least two parameters.
563   if (D->param_size() != 2)
564     return nullptr;
565 
566   // Check if the second parameter is a block.
567   const ParmVarDecl *PV = D->getParamDecl(1);
568   QualType Ty = PV->getType();
569   if (!isDispatchBlock(Ty))
570     return nullptr;
571 
572   // Everything checks out.  Create a fake body that just calls the block.
573   // This is basically just an AST dump of:
574   //
575   // void dispatch_sync(dispatch_queue_t queue, void (^block)(void)) {
576   //   block();
577   // }
578   //
579   ASTMaker M(C);
580   DeclRefExpr *DR = M.makeDeclRefExpr(PV);
581   ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
582   CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
583                                   SourceLocation());
584   return CE;
585 }
586 
587 static Stmt *create_OSAtomicCompareAndSwap(ASTContext &C, const FunctionDecl *D)
588 {
589   // There are exactly 3 arguments.
590   if (D->param_size() != 3)
591     return nullptr;
592 
593   // Signature:
594   // _Bool OSAtomicCompareAndSwapPtr(void *__oldValue,
595   //                                 void *__newValue,
596   //                                 void * volatile *__theValue)
597   // Generate body:
598   //   if (oldValue == *theValue) {
599   //    *theValue = newValue;
600   //    return YES;
601   //   }
602   //   else return NO;
603 
604   QualType ResultTy = D->getReturnType();
605   bool isBoolean = ResultTy->isBooleanType();
606   if (!isBoolean && !ResultTy->isIntegralType(C))
607     return nullptr;
608 
609   const ParmVarDecl *OldValue = D->getParamDecl(0);
610   QualType OldValueTy = OldValue->getType();
611 
612   const ParmVarDecl *NewValue = D->getParamDecl(1);
613   QualType NewValueTy = NewValue->getType();
614 
615   assert(OldValueTy == NewValueTy);
616 
617   const ParmVarDecl *TheValue = D->getParamDecl(2);
618   QualType TheValueTy = TheValue->getType();
619   const PointerType *PT = TheValueTy->getAs<PointerType>();
620   if (!PT)
621     return nullptr;
622   QualType PointeeTy = PT->getPointeeType();
623 
624   ASTMaker M(C);
625   // Construct the comparison.
626   Expr *Comparison =
627     M.makeComparison(
628       M.makeLvalueToRvalue(M.makeDeclRefExpr(OldValue), OldValueTy),
629       M.makeLvalueToRvalue(
630         M.makeDereference(
631           M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
632           PointeeTy),
633         PointeeTy),
634       BO_EQ);
635 
636   // Construct the body of the IfStmt.
637   Stmt *Stmts[2];
638   Stmts[0] =
639     M.makeAssignment(
640       M.makeDereference(
641         M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
642         PointeeTy),
643       M.makeLvalueToRvalue(M.makeDeclRefExpr(NewValue), NewValueTy),
644       NewValueTy);
645 
646   Expr *BoolVal = M.makeObjCBool(true);
647   Expr *RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
648                            : M.makeIntegralCast(BoolVal, ResultTy);
649   Stmts[1] = M.makeReturn(RetVal);
650   CompoundStmt *Body = M.makeCompound(Stmts);
651 
652   // Construct the else clause.
653   BoolVal = M.makeObjCBool(false);
654   RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
655                      : M.makeIntegralCast(BoolVal, ResultTy);
656   Stmt *Else = M.makeReturn(RetVal);
657 
658   /// Construct the If.
659   auto *If = IfStmt::Create(C, SourceLocation(),
660                             /* IsConstexpr=*/false,
661                             /* init=*/nullptr,
662                             /* var=*/nullptr, Comparison, Body,
663                             SourceLocation(), Else);
664 
665   return If;
666 }
667 
668 Stmt *BodyFarm::getBody(const FunctionDecl *D) {
669   D = D->getCanonicalDecl();
670 
671   Optional<Stmt *> &Val = Bodies[D];
672   if (Val.hasValue())
673     return Val.getValue();
674 
675   Val = nullptr;
676 
677   if (D->getIdentifier() == nullptr)
678     return nullptr;
679 
680   StringRef Name = D->getName();
681   if (Name.empty())
682     return nullptr;
683 
684   FunctionFarmer FF;
685 
686   if (Name.startswith("OSAtomicCompareAndSwap") ||
687       Name.startswith("objc_atomicCompareAndSwap")) {
688     FF = create_OSAtomicCompareAndSwap;
689   } else if (Name == "call_once" && D->getDeclContext()->isStdNamespace()) {
690     FF = create_call_once;
691   } else {
692     FF = llvm::StringSwitch<FunctionFarmer>(Name)
693           .Case("dispatch_sync", create_dispatch_sync)
694           .Case("dispatch_once", create_dispatch_once)
695           .Default(nullptr);
696   }
697 
698   if (FF) { Val = FF(C, D); }
699   else if (Injector) { Val = Injector->getBody(D); }
700   return Val.getValue();
701 }
702 
703 static const ObjCIvarDecl *findBackingIvar(const ObjCPropertyDecl *Prop) {
704   const ObjCIvarDecl *IVar = Prop->getPropertyIvarDecl();
705 
706   if (IVar)
707     return IVar;
708 
709   // When a readonly property is shadowed in a class extensions with a
710   // a readwrite property, the instance variable belongs to the shadowing
711   // property rather than the shadowed property. If there is no instance
712   // variable on a readonly property, check to see whether the property is
713   // shadowed and if so try to get the instance variable from shadowing
714   // property.
715   if (!Prop->isReadOnly())
716     return nullptr;
717 
718   auto *Container = cast<ObjCContainerDecl>(Prop->getDeclContext());
719   const ObjCInterfaceDecl *PrimaryInterface = nullptr;
720   if (auto *InterfaceDecl = dyn_cast<ObjCInterfaceDecl>(Container)) {
721     PrimaryInterface = InterfaceDecl;
722   } else if (auto *CategoryDecl = dyn_cast<ObjCCategoryDecl>(Container)) {
723     PrimaryInterface = CategoryDecl->getClassInterface();
724   } else if (auto *ImplDecl = dyn_cast<ObjCImplDecl>(Container)) {
725     PrimaryInterface = ImplDecl->getClassInterface();
726   } else {
727     return nullptr;
728   }
729 
730   // FindPropertyVisibleInPrimaryClass() looks first in class extensions, so it
731   // is guaranteed to find the shadowing property, if it exists, rather than
732   // the shadowed property.
733   auto *ShadowingProp = PrimaryInterface->FindPropertyVisibleInPrimaryClass(
734       Prop->getIdentifier(), Prop->getQueryKind());
735   if (ShadowingProp && ShadowingProp != Prop) {
736     IVar = ShadowingProp->getPropertyIvarDecl();
737   }
738 
739   return IVar;
740 }
741 
742 static Stmt *createObjCPropertyGetter(ASTContext &Ctx,
743                                       const ObjCPropertyDecl *Prop) {
744   // First, find the backing ivar.
745   const ObjCIvarDecl *IVar = findBackingIvar(Prop);
746   if (!IVar)
747     return nullptr;
748 
749   // Ignore weak variables, which have special behavior.
750   if (Prop->getPropertyAttributes() & ObjCPropertyDecl::OBJC_PR_weak)
751     return nullptr;
752 
753   // Look to see if Sema has synthesized a body for us. This happens in
754   // Objective-C++ because the return value may be a C++ class type with a
755   // non-trivial copy constructor. We can only do this if we can find the
756   // @synthesize for this property, though (or if we know it's been auto-
757   // synthesized).
758   const ObjCImplementationDecl *ImplDecl =
759     IVar->getContainingInterface()->getImplementation();
760   if (ImplDecl) {
761     for (const auto *I : ImplDecl->property_impls()) {
762       if (I->getPropertyDecl() != Prop)
763         continue;
764 
765       if (I->getGetterCXXConstructor()) {
766         ASTMaker M(Ctx);
767         return M.makeReturn(I->getGetterCXXConstructor());
768       }
769     }
770   }
771 
772   // Sanity check that the property is the same type as the ivar, or a
773   // reference to it, and that it is either an object pointer or trivially
774   // copyable.
775   if (!Ctx.hasSameUnqualifiedType(IVar->getType(),
776                                   Prop->getType().getNonReferenceType()))
777     return nullptr;
778   if (!IVar->getType()->isObjCLifetimeType() &&
779       !IVar->getType().isTriviallyCopyableType(Ctx))
780     return nullptr;
781 
782   // Generate our body:
783   //   return self->_ivar;
784   ASTMaker M(Ctx);
785 
786   const VarDecl *selfVar = Prop->getGetterMethodDecl()->getSelfDecl();
787   if (!selfVar)
788     return nullptr;
789 
790   Expr *loadedIVar =
791     M.makeObjCIvarRef(
792       M.makeLvalueToRvalue(
793         M.makeDeclRefExpr(selfVar),
794         selfVar->getType()),
795       IVar);
796 
797   if (!Prop->getType()->isReferenceType())
798     loadedIVar = M.makeLvalueToRvalue(loadedIVar, IVar->getType());
799 
800   return M.makeReturn(loadedIVar);
801 }
802 
803 Stmt *BodyFarm::getBody(const ObjCMethodDecl *D) {
804   // We currently only know how to synthesize property accessors.
805   if (!D->isPropertyAccessor())
806     return nullptr;
807 
808   D = D->getCanonicalDecl();
809 
810   Optional<Stmt *> &Val = Bodies[D];
811   if (Val.hasValue())
812     return Val.getValue();
813   Val = nullptr;
814 
815   const ObjCPropertyDecl *Prop = D->findPropertyDecl();
816   if (!Prop)
817     return nullptr;
818 
819   // For now, we only synthesize getters.
820   // Synthesizing setters would cause false negatives in the
821   // RetainCountChecker because the method body would bind the parameter
822   // to an instance variable, causing it to escape. This would prevent
823   // warning in the following common scenario:
824   //
825   //  id foo = [[NSObject alloc] init];
826   //  self.foo = foo; // We should warn that foo leaks here.
827   //
828   if (D->param_size() != 0)
829     return nullptr;
830 
831   Val = createObjCPropertyGetter(C, Prop);
832 
833   return Val.getValue();
834 }
835