text: //== BodyFarm.cpp  - Factory for conjuring up fake bodies ----------*- C++ -*-//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // BodyFarm is a factory for creating faux implementations for functions/methods
  // for analysis purposes.
  //
  //===----------------------------------------------------------------------===//
  
  #include "BodyFarm.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/Decl.h"
  #include "clang/AST/Expr.h"
  #include "clang/AST/ExprObjC.h"
  #include "clang/Analysis/CodeInjector.h"
  #include "llvm/ADT/StringSwitch.h"
  
  using namespace clang;
  
  //===----------------------------------------------------------------------===//
  // Helper creation functions for constructing faux ASTs.
  //===----------------------------------------------------------------------===//
  
  static bool isDispatchBlock(QualType Ty) {
    // Is it a block pointer?
    const BlockPointerType *BPT = Ty->getAs<BlockPointerType>();
    if (!BPT)
      return false;
  
    // Check if the block pointer type takes no arguments and
    // returns void.
    const FunctionProtoType *FT =
    BPT->getPointeeType()->getAs<FunctionProtoType>();
    return FT && FT->getReturnType()->isVoidType() && FT->getNumParams() == 0;
  }
  
  namespace {
  class ASTMaker {
  public:
    ASTMaker(ASTContext &C) : C(C) {}
    
    /// Create a new BinaryOperator representing a simple assignment.
    BinaryOperator *makeAssignment(const Expr *LHS, const Expr *RHS, QualType Ty);
    
    /// Create a new BinaryOperator representing a comparison.
    BinaryOperator *makeComparison(const Expr *LHS, const Expr *RHS,
                                   BinaryOperator::Opcode Op);
    
    /// Create a new compound stmt using the provided statements.
    CompoundStmt *makeCompound(ArrayRef<Stmt*>);
    
    /// Create a new DeclRefExpr for the referenced variable.
    DeclRefExpr *makeDeclRefExpr(const VarDecl *D);
    
    /// Create a new UnaryOperator representing a dereference.
    UnaryOperator *makeDereference(const Expr *Arg, QualType Ty);
    
    /// Create an implicit cast for an integer conversion.
    Expr *makeIntegralCast(const Expr *Arg, QualType Ty);
    
    /// Create an implicit cast to a builtin boolean type.
    ImplicitCastExpr *makeIntegralCastToBoolean(const Expr *Arg);
    
    // Create an implicit cast for lvalue-to-rvaluate conversions.
    ImplicitCastExpr *makeLvalueToRvalue(const Expr *Arg, QualType Ty);
    
    /// Create an Objective-C bool literal.
    ObjCBoolLiteralExpr *makeObjCBool(bool Val);
  
    /// Create an Objective-C ivar reference.
    ObjCIvarRefExpr *makeObjCIvarRef(const Expr *Base, const ObjCIvarDecl *IVar);
    
    /// Create a Return statement.
    ReturnStmt *makeReturn(const Expr *RetVal);
    
  private:
    ASTContext &C;
  };
  }
  
  BinaryOperator *ASTMaker::makeAssignment(const Expr *LHS, const Expr *RHS,
                                           QualType Ty) {
   return new (C) BinaryOperator(const_cast<Expr*>(LHS), const_cast<Expr*>(RHS),
                                 BO_Assign, Ty, VK_RValue,
                                 OK_Ordinary, SourceLocation(), false);
  }
  
  BinaryOperator *ASTMaker::makeComparison(const Expr *LHS, const Expr *RHS,
                                           BinaryOperator::Opcode Op) {
    assert(BinaryOperator::isLogicalOp(Op) ||
           BinaryOperator::isComparisonOp(Op));
    return new (C) BinaryOperator(const_cast<Expr*>(LHS),
                                  const_cast<Expr*>(RHS),
                                  Op,
                                  C.getLogicalOperationType(),
                                  VK_RValue,
                                  OK_Ordinary, SourceLocation(), false);
  }
  
  CompoundStmt *ASTMaker::makeCompound(ArrayRef<Stmt *> Stmts) {
    return new (C) CompoundStmt(C, Stmts, SourceLocation(), SourceLocation());
  }
  
  DeclRefExpr *ASTMaker::makeDeclRefExpr(const VarDecl *D) {
    DeclRefExpr *DR =
      DeclRefExpr::Create(/* Ctx = */ C,
                          /* QualifierLoc = */ NestedNameSpecifierLoc(),
                          /* TemplateKWLoc = */ SourceLocation(),
                          /* D = */ const_cast<VarDecl*>(D),
                          /* RefersToEnclosingVariableOrCapture = */ false,
                          /* NameLoc = */ SourceLocation(),
                          /* T = */ D->getType(),
                          /* VK = */ VK_LValue);
    return DR;
  }
  
  UnaryOperator *ASTMaker::makeDereference(const Expr *Arg, QualType Ty) {
    return new (C) UnaryOperator(const_cast<Expr*>(Arg), UO_Deref, Ty,
                                 VK_LValue, OK_Ordinary, SourceLocation());
  }
  
  ImplicitCastExpr *ASTMaker::makeLvalueToRvalue(const Expr *Arg, QualType Ty) {
    return ImplicitCastExpr::Create(C, Ty, CK_LValueToRValue,
                                    const_cast<Expr*>(Arg), nullptr, VK_RValue);
  }
  
  Expr *ASTMaker::makeIntegralCast(const Expr *Arg, QualType Ty) {
    if (Arg->getType() == Ty)
      return const_cast<Expr*>(Arg);
  
    return ImplicitCastExpr::Create(C, Ty, CK_IntegralCast,
                                    const_cast<Expr*>(Arg), nullptr, VK_RValue);
  }
  
  ImplicitCastExpr *ASTMaker::makeIntegralCastToBoolean(const Expr *Arg) {
    return ImplicitCastExpr::Create(C, C.BoolTy, CK_IntegralToBoolean,
                                    const_cast<Expr*>(Arg), nullptr, VK_RValue);
  }
  
  ObjCBoolLiteralExpr *ASTMaker::makeObjCBool(bool Val) {
    QualType Ty = C.getBOOLDecl() ? C.getBOOLType() : C.ObjCBuiltinBoolTy;
    return new (C) ObjCBoolLiteralExpr(Val, Ty, SourceLocation());
  }
  
  ObjCIvarRefExpr *ASTMaker::makeObjCIvarRef(const Expr *Base,
                                             const ObjCIvarDecl *IVar) {
    return new (C) ObjCIvarRefExpr(const_cast<ObjCIvarDecl*>(IVar),
                                   IVar->getType(), SourceLocation(),
                                   SourceLocation(), const_cast<Expr*>(Base),
                                   /*arrow=*/true, /*free=*/false);
  }
  
  
  ReturnStmt *ASTMaker::makeReturn(const Expr *RetVal) {
    return new (C) ReturnStmt(SourceLocation(), const_cast<Expr*>(RetVal),
                              nullptr);
  }
  
  //===----------------------------------------------------------------------===//
  // Creation functions for faux ASTs.
  //===----------------------------------------------------------------------===//
  
  typedef Stmt *(*FunctionFarmer)(ASTContext &C, const FunctionDecl *D);
  
  /// Create a fake body for dispatch_once.
  static Stmt *create_dispatch_once(ASTContext &C, const FunctionDecl *D) {
    // Check if we have at least two parameters.
    if (D->param_size() != 2)
      return nullptr;
  
    // Check if the first parameter is a pointer to integer type.
    const ParmVarDecl *Predicate = D->getParamDecl(0);
    QualType PredicateQPtrTy = Predicate->getType();
    const PointerType *PredicatePtrTy = PredicateQPtrTy->getAs<PointerType>();
    if (!PredicatePtrTy)
      return nullptr;
    QualType PredicateTy = PredicatePtrTy->getPointeeType();
    if (!PredicateTy->isIntegerType())
      return nullptr;
  
    // Check if the second parameter is the proper block type.
    const ParmVarDecl *Block = D->getParamDecl(1);
    QualType Ty = Block->getType();
    if (!isDispatchBlock(Ty))
      return nullptr;
  
    // Everything checks out.  Create a fakse body that checks the predicate,
    // sets it, and calls the block.  Basically, an AST dump of:
    //
    // void dispatch_once(dispatch_once_t *predicate, dispatch_block_t block) {
    //  if (!*predicate) {
    //    *predicate = 1;
    //    block();
    //  }
    // }
    
    ASTMaker M(C);
    
    // (1) Create the call.
    DeclRefExpr *DR = M.makeDeclRefExpr(Block);
    ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
    CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
                                    SourceLocation());
  
    // (2) Create the assignment to the predicate.
    IntegerLiteral *IL =
      IntegerLiteral::Create(C, llvm::APInt(C.getTypeSize(C.IntTy), (uint64_t) 1),
                             C.IntTy, SourceLocation());
    BinaryOperator *B =
      M.makeAssignment(
         M.makeDereference(
            M.makeLvalueToRvalue(
              M.makeDeclRefExpr(Predicate), PredicateQPtrTy),
              PredicateTy),
         M.makeIntegralCast(IL, PredicateTy),
         PredicateTy);
    
    // (3) Create the compound statement.
    Stmt *Stmts[] = { B, CE };
    CompoundStmt *CS = M.makeCompound(Stmts);
    
    // (4) Create the 'if' condition.
    ImplicitCastExpr *LValToRval =
      M.makeLvalueToRvalue(
        M.makeDereference(
          M.makeLvalueToRvalue(
            M.makeDeclRefExpr(Predicate),
            PredicateQPtrTy),
          PredicateTy),
      PredicateTy);
    
    UnaryOperator *UO = new (C) UnaryOperator(LValToRval, UO_LNot, C.IntTy,
                                             VK_RValue, OK_Ordinary,
                                             SourceLocation());
    
    // (5) Create the 'if' statement.
    IfStmt *If = new (C) IfStmt(C, SourceLocation(), false, nullptr, nullptr,
                                UO, CS);
    return If;
  }
  
  /// Create a fake body for dispatch_sync.
  static Stmt *create_dispatch_sync(ASTContext &C, const FunctionDecl *D) {
    // Check if we have at least two parameters.
    if (D->param_size() != 2)
      return nullptr;
  
    // Check if the second parameter is a block.
    const ParmVarDecl *PV = D->getParamDecl(1);
    QualType Ty = PV->getType();
    if (!isDispatchBlock(Ty))
      return nullptr;
  
    // Everything checks out.  Create a fake body that just calls the block.
    // This is basically just an AST dump of:
    //
    // void dispatch_sync(dispatch_queue_t queue, void (^block)(void)) {
    //   block();
    // }
    //  
    ASTMaker M(C);
    DeclRefExpr *DR = M.makeDeclRefExpr(PV);
    ImplicitCastExpr *ICE = M.makeLvalueToRvalue(DR, Ty);
    CallExpr *CE = new (C) CallExpr(C, ICE, None, C.VoidTy, VK_RValue,
                                    SourceLocation());
    return CE;
  }
  
  static Stmt *create_OSAtomicCompareAndSwap(ASTContext &C, const FunctionDecl *D)
  {
    // There are exactly 3 arguments.
    if (D->param_size() != 3)
      return nullptr;
  
    // Signature:
    // _Bool OSAtomicCompareAndSwapPtr(void *__oldValue,
    //                                 void *__newValue,
    //                                 void * volatile *__theValue)
    // Generate body:
    //   if (oldValue == *theValue) {
    //    *theValue = newValue;
    //    return YES;
    //   }
    //   else return NO;
  
    QualType ResultTy = D->getReturnType();
    bool isBoolean = ResultTy->isBooleanType();
    if (!isBoolean && !ResultTy->isIntegralType(C))
      return nullptr;
  
    const ParmVarDecl *OldValue = D->getParamDecl(0);
    QualType OldValueTy = OldValue->getType();
  
    const ParmVarDecl *NewValue = D->getParamDecl(1);
    QualType NewValueTy = NewValue->getType();
    
    assert(OldValueTy == NewValueTy);
    
    const ParmVarDecl *TheValue = D->getParamDecl(2);
    QualType TheValueTy = TheValue->getType();
    const PointerType *PT = TheValueTy->getAs<PointerType>();
    if (!PT)
      return nullptr;
    QualType PointeeTy = PT->getPointeeType();
    
    ASTMaker M(C);
    // Construct the comparison.
    Expr *Comparison =
      M.makeComparison(
        M.makeLvalueToRvalue(M.makeDeclRefExpr(OldValue), OldValueTy),
        M.makeLvalueToRvalue(
          M.makeDereference(
            M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
            PointeeTy),
          PointeeTy),
        BO_EQ);
  
    // Construct the body of the IfStmt.
    Stmt *Stmts[2];
    Stmts[0] =
      M.makeAssignment(
        M.makeDereference(
          M.makeLvalueToRvalue(M.makeDeclRefExpr(TheValue), TheValueTy),
          PointeeTy),
        M.makeLvalueToRvalue(M.makeDeclRefExpr(NewValue), NewValueTy),
        NewValueTy);
    
    Expr *BoolVal = M.makeObjCBool(true);
    Expr *RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
                             : M.makeIntegralCast(BoolVal, ResultTy);
    Stmts[1] = M.makeReturn(RetVal);
    CompoundStmt *Body = M.makeCompound(Stmts);
    
    // Construct the else clause.
    BoolVal = M.makeObjCBool(false);
    RetVal = isBoolean ? M.makeIntegralCastToBoolean(BoolVal)
                       : M.makeIntegralCast(BoolVal, ResultTy);
    Stmt *Else = M.makeReturn(RetVal);
    
    /// Construct the If.
    Stmt *If = new (C) IfStmt(C, SourceLocation(), false, nullptr, nullptr,
                              Comparison, Body, SourceLocation(), Else);
  
    return If;  
  }
  
  Stmt *BodyFarm::getBody(const FunctionDecl *D) {
    D = D->getCanonicalDecl();
    
    Optional<Stmt *> &Val = Bodies[D];
    if (Val.hasValue())
      return Val.getValue();
  
    Val = nullptr;
  
    if (D->getIdentifier() == nullptr)
      return nullptr;
  
    StringRef Name = D->getName();
    if (Name.empty())
      return nullptr;
  
    FunctionFarmer FF;
  
    if (Name.startswith("OSAtomicCompareAndSwap") ||
        Name.startswith("objc_atomicCompareAndSwap")) {
      FF = create_OSAtomicCompareAndSwap;
    }
    else {
      FF = llvm::StringSwitch<FunctionFarmer>(Name)
            .Case("dispatch_sync", create_dispatch_sync)
            .Case("dispatch_once", create_dispatch_once)
            .Default(nullptr);
    }
    
    if (FF) { Val = FF(C, D); }
    else if (Injector) { Val = Injector->getBody(D); }
    return Val.getValue();
  }
  
  static const ObjCIvarDecl *findBackingIvar(const ObjCPropertyDecl *Prop) {
    const ObjCIvarDecl *IVar = Prop->getPropertyIvarDecl();
  
    if (IVar)
      return IVar;
  
    // When a readonly property is shadowed in a class extensions with a
    // a readwrite property, the instance variable belongs to the shadowing
    // property rather than the shadowed property. If there is no instance
    // variable on a readonly property, check to see whether the property is
    // shadowed and if so try to get the instance variable from shadowing
    // property.
    if (!Prop->isReadOnly())
      return nullptr;
  
    auto *Container = cast<ObjCContainerDecl>(Prop->getDeclContext());
    const ObjCInterfaceDecl *PrimaryInterface = nullptr;
    if (auto *InterfaceDecl = dyn_cast<ObjCInterfaceDecl>(Container)) {
      PrimaryInterface = InterfaceDecl;
    } else if (auto *CategoryDecl = dyn_cast<ObjCCategoryDecl>(Container)) {
      PrimaryInterface = CategoryDecl->getClassInterface();
    } else if (auto *ImplDecl = dyn_cast<ObjCImplDecl>(Container)) {
      PrimaryInterface = ImplDecl->getClassInterface();
    } else {
      return nullptr;
    }
  
    // FindPropertyVisibleInPrimaryClass() looks first in class extensions, so it
    // is guaranteed to find the shadowing property, if it exists, rather than
    // the shadowed property.
    auto *ShadowingProp = PrimaryInterface->FindPropertyVisibleInPrimaryClass(
        Prop->getIdentifier(), Prop->getQueryKind());
    if (ShadowingProp && ShadowingProp != Prop) {
      IVar = ShadowingProp->getPropertyIvarDecl();
    }
  
    return IVar;
  }
  
  static Stmt *createObjCPropertyGetter(ASTContext &Ctx,
                                        const ObjCPropertyDecl *Prop) {
    // First, find the backing ivar.
    const ObjCIvarDecl *IVar = findBackingIvar(Prop);
    if (!IVar)
      return nullptr;
  
    // Ignore weak variables, which have special behavior.
    if (Prop->getPropertyAttributes() & ObjCPropertyDecl::OBJC_PR_weak)
      return nullptr;
  
    // Look to see if Sema has synthesized a body for us. This happens in
    // Objective-C++ because the return value may be a C++ class type with a
    // non-trivial copy constructor. We can only do this if we can find the
    // @synthesize for this property, though (or if we know it's been auto-
    // synthesized).
    const ObjCImplementationDecl *ImplDecl =
      IVar->getContainingInterface()->getImplementation();
    if (ImplDecl) {
      for (const auto *I : ImplDecl->property_impls()) {
        if (I->getPropertyDecl() != Prop)
          continue;
  
        if (I->getGetterCXXConstructor()) {
          ASTMaker M(Ctx);
          return M.makeReturn(I->getGetterCXXConstructor());
        }
      }
    }
  
    // Sanity check that the property is the same type as the ivar, or a
    // reference to it, and that it is either an object pointer or trivially
    // copyable.
    if (!Ctx.hasSameUnqualifiedType(IVar->getType(),
                                    Prop->getType().getNonReferenceType()))
      return nullptr;
    if (!IVar->getType()->isObjCLifetimeType() &&
        !IVar->getType().isTriviallyCopyableType(Ctx))
      return nullptr;
  
    // Generate our body:
    //   return self->_ivar;
    ASTMaker M(Ctx);
  
    const VarDecl *selfVar = Prop->getGetterMethodDecl()->getSelfDecl();
  
    Expr *loadedIVar =
      M.makeObjCIvarRef(
        M.makeLvalueToRvalue(
          M.makeDeclRefExpr(selfVar),
          selfVar->getType()),
        IVar);
  
    if (!Prop->getType()->isReferenceType())
      loadedIVar = M.makeLvalueToRvalue(loadedIVar, IVar->getType());
  
    return M.makeReturn(loadedIVar);
  }
  
  Stmt *BodyFarm::getBody(const ObjCMethodDecl *D) {
    // We currently only know how to synthesize property accessors.
    if (!D->isPropertyAccessor())
      return nullptr;
  
    D = D->getCanonicalDecl();
  
    Optional<Stmt *> &Val = Bodies[D];
    if (Val.hasValue())
      return Val.getValue();
    Val = nullptr;
  
    const ObjCPropertyDecl *Prop = D->findPropertyDecl();
    if (!Prop)
      return nullptr;
  
    // For now, we only synthesize getters.
    // Synthesizing setters would cause false negatives in the
    // RetainCountChecker because the method body would bind the parameter
    // to an instance variable, causing it to escape. This would prevent
    // warning in the following common scenario:
    //
    //  id foo = [[NSObject alloc] init];
    //  self.foo = foo; // We should warn that foo leaks here.
    //
    if (D->param_size() != 0)
      return nullptr;
  
    Val = createObjCPropertyGetter(C, Prop);
  
    return Val.getValue();
  }
  
  