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 "BodyFarm.h"
16#include "clang/AST/ASTContext.h"
17#include "clang/AST/Decl.h"
18#include "clang/AST/Expr.h"
19#include "clang/AST/ExprObjC.h"
20#include "llvm/ADT/StringSwitch.h"
21
22using namespace clang;
23
24//===----------------------------------------------------------------------===//
25// Helper creation functions for constructing faux ASTs.
26//===----------------------------------------------------------------------===//
27
28static bool isDispatchBlock(QualType Ty) {
29  // Is it a block pointer?
30  const BlockPointerType *BPT = Ty->getAs<BlockPointerType>();
31  if (!BPT)
32    return false;
33
34  // Check if the block pointer type takes no arguments and
35  // returns void.
36  const FunctionProtoType *FT =
37  BPT->getPointeeType()->getAs<FunctionProtoType>();
38  if (!FT || !FT->getReturnType()->isVoidType() || FT->getNumParams() != 0)
39    return false;
40
41  return true;
42}
43
44namespace {
45class ASTMaker {
46public:
47  ASTMaker(ASTContext &C) : C(C) {}
48
49  /// Create a new BinaryOperator representing a simple assignment.
50  BinaryOperator *makeAssignment(const Expr *LHS, const Expr *RHS, QualType Ty);
51
52  /// Create a new BinaryOperator representing a comparison.
53  BinaryOperator *makeComparison(const Expr *LHS, const Expr *RHS,
54                                 BinaryOperator::Opcode Op);
55
56  /// Create a new compound stmt using the provided statements.
57  CompoundStmt *makeCompound(ArrayRef<Stmt*>);
58
59  /// Create a new DeclRefExpr for the referenced variable.
60  DeclRefExpr *makeDeclRefExpr(const VarDecl *D);
61
62  /// Create a new UnaryOperator representing a dereference.
63  UnaryOperator *makeDereference(const Expr *Arg, QualType Ty);
64
65  /// Create an implicit cast for an integer conversion.
66  Expr *makeIntegralCast(const Expr *Arg, QualType Ty);
67
68  /// Create an implicit cast to a builtin boolean type.
69  ImplicitCastExpr *makeIntegralCastToBoolean(const Expr *Arg);
70
71  // Create an implicit cast for lvalue-to-rvaluate conversions.
72  ImplicitCastExpr *makeLvalueToRvalue(const Expr *Arg, QualType Ty);
73
74  /// Create an Objective-C bool literal.
75  ObjCBoolLiteralExpr *makeObjCBool(bool Val);
76
77  /// Create an Objective-C ivar reference.
78  ObjCIvarRefExpr *makeObjCIvarRef(const Expr *Base, const ObjCIvarDecl *IVar);
79
80  /// Create a Return statement.
81  ReturnStmt *makeReturn(const Expr *RetVal);
82
83private:
84  ASTContext &C;
85};
86}
87
88BinaryOperator *ASTMaker::makeAssignment(const Expr *LHS, const Expr *RHS,
89                                         QualType Ty) {
90 return new (C) BinaryOperator(const_cast<Expr*>(LHS), const_cast<Expr*>(RHS),
91                               BO_Assign, Ty, VK_RValue,
92                               OK_Ordinary, SourceLocation(), false);
93}
94
95BinaryOperator *ASTMaker::makeComparison(const Expr *LHS, const Expr *RHS,
96                                         BinaryOperator::Opcode Op) {
97  assert(BinaryOperator::isLogicalOp(Op) ||
98         BinaryOperator::isComparisonOp(Op));
99  return new (C) BinaryOperator(const_cast<Expr*>(LHS),
100                                const_cast<Expr*>(RHS),
101                                Op,
102                                C.getLogicalOperationType(),
103                                VK_RValue,
104                                OK_Ordinary, SourceLocation(), false);
105}
106
107CompoundStmt *ASTMaker::makeCompound(ArrayRef<Stmt *> Stmts) {
108  return new (C) CompoundStmt(C, Stmts, SourceLocation(), SourceLocation());
109}
110
111DeclRefExpr *ASTMaker::makeDeclRefExpr(const VarDecl *D) {
112  DeclRefExpr *DR =
113    DeclRefExpr::Create(/* Ctx = */ C,
114                        /* QualifierLoc = */ NestedNameSpecifierLoc(),
115                        /* TemplateKWLoc = */ SourceLocation(),
116                        /* D = */ const_cast<VarDecl*>(D),
117                        /* isEnclosingLocal = */ false,
118                        /* NameLoc = */ SourceLocation(),
119                        /* T = */ D->getType(),
120                        /* VK = */ VK_LValue);
121  return DR;
122}
123
124UnaryOperator *ASTMaker::makeDereference(const Expr *Arg, QualType Ty) {
125  return new (C) UnaryOperator(const_cast<Expr*>(Arg), UO_Deref, Ty,
126                               VK_LValue, OK_Ordinary, SourceLocation());
127}
128
129ImplicitCastExpr *ASTMaker::makeLvalueToRvalue(const Expr *Arg, QualType Ty) {
130  return ImplicitCastExpr::Create(C, Ty, CK_LValueToRValue,
131                                  const_cast<Expr*>(Arg), nullptr, VK_RValue);
132}
133
134Expr *ASTMaker::makeIntegralCast(const Expr *Arg, QualType Ty) {
135  if (Arg->getType() == Ty)
136    return const_cast<Expr*>(Arg);
137
138  return ImplicitCastExpr::Create(C, Ty, CK_IntegralCast,
139                                  const_cast<Expr*>(Arg), nullptr, VK_RValue);
140}
141
142ImplicitCastExpr *ASTMaker::makeIntegralCastToBoolean(const Expr *Arg) {
143  return ImplicitCastExpr::Create(C, C.BoolTy, CK_IntegralToBoolean,
144                                  const_cast<Expr*>(Arg), nullptr, VK_RValue);
145}
146
147ObjCBoolLiteralExpr *ASTMaker::makeObjCBool(bool Val) {
148  QualType Ty = C.getBOOLDecl() ? C.getBOOLType() : C.ObjCBuiltinBoolTy;
149  return new (C) ObjCBoolLiteralExpr(Val, Ty, SourceLocation());
150}
151
152ObjCIvarRefExpr *ASTMaker::makeObjCIvarRef(const Expr *Base,
153                                           const ObjCIvarDecl *IVar) {
154  return new (C) ObjCIvarRefExpr(const_cast<ObjCIvarDecl*>(IVar),
155                                 IVar->getType(), SourceLocation(),
156                                 SourceLocation(), const_cast<Expr*>(Base),
157                                 /*arrow=*/true, /*free=*/false);
158}
159
160
161ReturnStmt *ASTMaker::makeReturn(const Expr *RetVal) {
162  return new (C) ReturnStmt(SourceLocation(), const_cast<Expr*>(RetVal),
163                            nullptr);
164}
165
166//===----------------------------------------------------------------------===//
167// Creation functions for faux ASTs.
168//===----------------------------------------------------------------------===//
169
170typedef Stmt *(*FunctionFarmer)(ASTContext &C, const FunctionDecl *D);
171
172/// Create a fake body for dispatch_once.
173static Stmt *create_dispatch_once(ASTContext &C, const FunctionDecl *D) {
174  // Check if we have at least two parameters.
175  if (D->param_size() != 2)
176    return nullptr;
177
178  // Check if the first parameter is a pointer to integer type.
179  const ParmVarDecl *Predicate = D->getParamDecl(0);
180  QualType PredicateQPtrTy = Predicate->getType();
181  const PointerType *PredicatePtrTy = PredicateQPtrTy->getAs<PointerType>();
182  if (!PredicatePtrTy)
183    return nullptr;
184  QualType PredicateTy = PredicatePtrTy->getPointeeType();
185  if (!PredicateTy->isIntegerType())
186    return nullptr;
187
188  // Check if the second parameter is the proper block type.
189  const ParmVarDecl *Block = D->getParamDecl(1);
190  QualType Ty = Block->getType();
191  if (!isDispatchBlock(Ty))
192    return nullptr;
193
194  // Everything checks out.  Create a fakse body that checks the predicate,
195  // sets it, and calls the block.  Basically, an AST dump of:
196  //
197  // void dispatch_once(dispatch_once_t *predicate, dispatch_block_t block) {
198  //  if (!*predicate) {
199  //    *predicate = 1;
200  //    block();
201  //  }
202  // }
203
204  ASTMaker M(C);
205
206  // (1) Create the call.
207  DeclRefExpr *DR = M.makeDeclRefExpr(Block);
208  ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
209  CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
210                                  SourceLocation());
211
212  // (2) Create the assignment to the predicate.
213  IntegerLiteral *IL =
214    IntegerLiteral::Create(C, llvm::APInt(C.getTypeSize(C.IntTy), (uint64_t) 1),
215                           C.IntTy, SourceLocation());
216  BinaryOperator *B =
217    M.makeAssignment(
218       M.makeDereference(
219          M.makeLvalueToRvalue(
220            M.makeDeclRefExpr(Predicate), PredicateQPtrTy),
221            PredicateTy),
222       M.makeIntegralCast(IL, PredicateTy),
223       PredicateTy);
224
225  // (3) Create the compound statement.
226  Stmt *Stmts[2];
227  Stmts[0] = B;
228  Stmts[1] = CE;
229  CompoundStmt *CS = M.makeCompound(ArrayRef<Stmt*>(Stmts, 2));
230
231  // (4) Create the 'if' condition.
232  ImplicitCastExpr *LValToRval =
233    M.makeLvalueToRvalue(
234      M.makeDereference(
235        M.makeLvalueToRvalue(
236          M.makeDeclRefExpr(Predicate),
237          PredicateQPtrTy),
238        PredicateTy),
239    PredicateTy);
240
241  UnaryOperator *UO = new (C) UnaryOperator(LValToRval, UO_LNot, C.IntTy,
242                                           VK_RValue, OK_Ordinary,
243                                           SourceLocation());
244
245  // (5) Create the 'if' statement.
246  IfStmt *If = new (C) IfStmt(C, SourceLocation(), nullptr, UO, CS);
247  return If;
248}
249
250/// Create a fake body for dispatch_sync.
251static Stmt *create_dispatch_sync(ASTContext &C, const FunctionDecl *D) {
252  // Check if we have at least two parameters.
253  if (D->param_size() != 2)
254    return nullptr;
255
256  // Check if the second parameter is a block.
257  const ParmVarDecl *PV = D->getParamDecl(1);
258  QualType Ty = PV->getType();
259  if (!isDispatchBlock(Ty))
260    return nullptr;
261
262  // Everything checks out.  Create a fake body that just calls the block.
263  // This is basically just an AST dump of:
264  //
265  // void dispatch_sync(dispatch_queue_t queue, void (^block)(void)) {
266  //   block();
267  // }
268  //
269  ASTMaker M(C);
270  DeclRefExpr *DR = M.makeDeclRefExpr(PV);
271  ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
272  CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
273                                  SourceLocation());
274  return CE;
275}
276
277static Stmt *create_OSAtomicCompareAndSwap(ASTContext &C, const FunctionDecl *D)
278{
279  // There are exactly 3 arguments.
280  if (D->param_size() != 3)
281    return nullptr;
282
283  // Signature:
284  // _Bool OSAtomicCompareAndSwapPtr(void *__oldValue,
285  //                                 void *__newValue,
286  //                                 void * volatile *__theValue)
287  // Generate body:
288  //   if (oldValue == *theValue) {
289  //    *theValue = newValue;
290  //    return YES;
291  //   }
292  //   else return NO;
293
294  QualType ResultTy = D->getReturnType();
295  bool isBoolean = ResultTy->isBooleanType();
296  if (!isBoolean && !ResultTy->isIntegralType(C))
297    return nullptr;
298
299  const ParmVarDecl *OldValue = D->getParamDecl(0);
300  QualType OldValueTy = OldValue->getType();
301
302  const ParmVarDecl *NewValue = D->getParamDecl(1);
303  QualType NewValueTy = NewValue->getType();
304
305  assert(OldValueTy == NewValueTy);
306
307  const ParmVarDecl *TheValue = D->getParamDecl(2);
308  QualType TheValueTy = TheValue->getType();
309  const PointerType *PT = TheValueTy->getAs<PointerType>();
310  if (!PT)
311    return nullptr;
312  QualType PointeeTy = PT->getPointeeType();
313
314  ASTMaker M(C);
315  // Construct the comparison.
316  Expr *Comparison =
317    M.makeComparison(
318      M.makeLvalueToRvalue(M.makeDeclRefExpr(OldValue), OldValueTy),
319      M.makeLvalueToRvalue(
320        M.makeDereference(
321          M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
322          PointeeTy),
323        PointeeTy),
324      BO_EQ);
325
326  // Construct the body of the IfStmt.
327  Stmt *Stmts[2];
328  Stmts[0] =
329    M.makeAssignment(
330      M.makeDereference(
331        M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
332        PointeeTy),
333      M.makeLvalueToRvalue(M.makeDeclRefExpr(NewValue), NewValueTy),
334      NewValueTy);
335
336  Expr *BoolVal = M.makeObjCBool(true);
337  Expr *RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
338                           : M.makeIntegralCast(BoolVal, ResultTy);
339  Stmts[1] = M.makeReturn(RetVal);
340  CompoundStmt *Body = M.makeCompound(ArrayRef<Stmt*>(Stmts, 2));
341
342  // Construct the else clause.
343  BoolVal = M.makeObjCBool(false);
344  RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
345                     : M.makeIntegralCast(BoolVal, ResultTy);
346  Stmt *Else = M.makeReturn(RetVal);
347
348  /// Construct the If.
349  Stmt *If =
350    new (C) IfStmt(C, SourceLocation(), nullptr, Comparison, Body,
351                   SourceLocation(), Else);
352
353  return If;
354}
355
356Stmt *BodyFarm::getBody(const FunctionDecl *D) {
357  D = D->getCanonicalDecl();
358
359  Optional<Stmt *> &Val = Bodies[D];
360  if (Val.hasValue())
361    return Val.getValue();
362
363  Val = nullptr;
364
365  if (D->getIdentifier() == nullptr)
366    return nullptr;
367
368  StringRef Name = D->getName();
369  if (Name.empty())
370    return nullptr;
371
372  FunctionFarmer FF;
373
374  if (Name.startswith("OSAtomicCompareAndSwap") ||
375      Name.startswith("objc_atomicCompareAndSwap")) {
376    FF = create_OSAtomicCompareAndSwap;
377  }
378  else {
379    FF = llvm::StringSwitch<FunctionFarmer>(Name)
380          .Case("dispatch_sync", create_dispatch_sync)
381          .Case("dispatch_once", create_dispatch_once)
382          .Default(nullptr);
383  }
384
385  if (FF) { Val = FF(C, D); }
386  return Val.getValue();
387}
388
389static Stmt *createObjCPropertyGetter(ASTContext &Ctx,
390                                      const ObjCPropertyDecl *Prop) {
391  // First, find the backing ivar.
392  const ObjCIvarDecl *IVar = Prop->getPropertyIvarDecl();
393  if (!IVar)
394    return nullptr;
395
396  // Ignore weak variables, which have special behavior.
397  if (Prop->getPropertyAttributes() & ObjCPropertyDecl::OBJC_PR_weak)
398    return nullptr;
399
400  // Look to see if Sema has synthesized a body for us. This happens in
401  // Objective-C++ because the return value may be a C++ class type with a
402  // non-trivial copy constructor. We can only do this if we can find the
403  // @synthesize for this property, though (or if we know it's been auto-
404  // synthesized).
405  const ObjCImplementationDecl *ImplDecl =
406    IVar->getContainingInterface()->getImplementation();
407  if (ImplDecl) {
408    for (const auto *I : ImplDecl->property_impls()) {
409      if (I->getPropertyDecl() != Prop)
410        continue;
411
412      if (I->getGetterCXXConstructor()) {
413        ASTMaker M(Ctx);
414        return M.makeReturn(I->getGetterCXXConstructor());
415      }
416    }
417  }
418
419  // Sanity check that the property is the same type as the ivar, or a
420  // reference to it, and that it is either an object pointer or trivially
421  // copyable.
422  if (!Ctx.hasSameUnqualifiedType(IVar->getType(),
423                                  Prop->getType().getNonReferenceType()))
424    return nullptr;
425  if (!IVar->getType()->isObjCLifetimeType() &&
426      !IVar->getType().isTriviallyCopyableType(Ctx))
427    return nullptr;
428
429  // Generate our body:
430  //   return self->_ivar;
431  ASTMaker M(Ctx);
432
433  const VarDecl *selfVar = Prop->getGetterMethodDecl()->getSelfDecl();
434
435  Expr *loadedIVar =
436    M.makeObjCIvarRef(
437      M.makeLvalueToRvalue(
438        M.makeDeclRefExpr(selfVar),
439        selfVar->getType()),
440      IVar);
441
442  if (!Prop->getType()->isReferenceType())
443    loadedIVar = M.makeLvalueToRvalue(loadedIVar, IVar->getType());
444
445  return M.makeReturn(loadedIVar);
446}
447
448Stmt *BodyFarm::getBody(const ObjCMethodDecl *D) {
449  // We currently only know how to synthesize property accessors.
450  if (!D->isPropertyAccessor())
451    return nullptr;
452
453  D = D->getCanonicalDecl();
454
455  Optional<Stmt *> &Val = Bodies[D];
456  if (Val.hasValue())
457    return Val.getValue();
458  Val = nullptr;
459
460  const ObjCPropertyDecl *Prop = D->findPropertyDecl();
461  if (!Prop)
462    return nullptr;
463
464  // For now, we only synthesize getters.
465  if (D->param_size() != 0)
466    return nullptr;
467
468  Val = createObjCPropertyGetter(C, Prop);
469
470  return Val.getValue();
471}
472
473