//== BodyFarm.cpp  - Factory for conjuring up fake bodies ----------*- C++ -*-//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// BodyFarm is a factory for creating faux implementations for functions/methods

// for analysis purposes.

//

//===----------------------------------------------------------------------===//

#include "clang/Analysis/BodyFarm.h"

#include "clang/AST/ASTContext.h"

#include "clang/AST/CXXInheritance.h"

#include "clang/AST/Decl.h"

#include "clang/AST/Expr.h"

#include "clang/AST/ExprCXX.h"

#include "clang/AST/ExprObjC.h"

#include "clang/AST/NestedNameSpecifier.h"

#include "clang/Analysis/CodeInjector.h"

#include "clang/Basic/Builtins.h"

#include "clang/Basic/OperatorKinds.h"

#include "llvm/ADT/StringSwitch.h"

#include "llvm/Support/Debug.h"

#include <optional>

#define DEBUG_TYPE "body-farm"

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,

                               bool RefersToEnclosingVariableOrCapture = false);

  /// 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);

  /// Make RValue out of variable declaration, creating a temporary

  /// DeclRefExpr in the process.

  ImplicitCastExpr *

  makeLvalueToRvalue(const VarDecl *Decl,

                     bool RefersToEnclosingVariableOrCapture = false);

  /// Create an implicit cast of the given type.

  ImplicitCastExpr *makeImplicitCast(const Expr *Arg, QualType Ty,

                                     CastKind CK = CK_LValueToRValue);

  /// Create a cast to reference type.

  CastExpr *makeReferenceCast(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);

  /// Create an integer literal expression of the given type.

  IntegerLiteral *makeIntegerLiteral(uint64_t Value, QualType Ty);

  /// Create a member expression.

  MemberExpr *makeMemberExpression(Expr *base, ValueDecl *MemberDecl,

                                   bool IsArrow = false,

                                   ExprValueKind ValueKind = VK_LValue);

  /// Returns a *first* member field of a record declaration with a given name.

  /// \return an nullptr if no member with such a name exists.

  ValueDecl *findMemberField(const RecordDecl *RD, StringRef Name);

private:

  ASTContext &C;

};

}

BinaryOperator *ASTMaker::makeAssignment(const Expr *LHS, const Expr *RHS,

                                         QualType Ty) {

  return BinaryOperator::Create(

      C, const_cast<Expr *>(LHS), const_cast<Expr *>(RHS), BO_Assign, Ty,

      VK_PRValue, OK_Ordinary, SourceLocation(), FPOptionsOverride());

}

BinaryOperator *ASTMaker::makeComparison(const Expr *LHS, const Expr *RHS,

                                         BinaryOperator::Opcode Op) {

  assert(BinaryOperator::isLogicalOp(Op) ||

         BinaryOperator::isComparisonOp(Op));

  return BinaryOperator::Create(

      C, const_cast<Expr *>(LHS), const_cast<Expr *>(RHS), Op,

      C.getLogicalOperationType(), VK_PRValue, OK_Ordinary, SourceLocation(),

      FPOptionsOverride());

}

CompoundStmt *ASTMaker::makeCompound(ArrayRef<Stmt *> Stmts) {

  return CompoundStmt::Create(C, Stmts, FPOptionsOverride(), SourceLocation(),

                              SourceLocation());

}

DeclRefExpr *ASTMaker::makeDeclRefExpr(

    const VarDecl *D,

    bool RefersToEnclosingVariableOrCapture) {

  QualType Type = D->getType().getNonReferenceType();

  DeclRefExpr *DR = DeclRefExpr::Create(

      C, NestedNameSpecifierLoc(), SourceLocation(), const_cast<VarDecl *>(D),

      RefersToEnclosingVariableOrCapture, SourceLocation(), Type, VK_LValue);

  return DR;

}

UnaryOperator *ASTMaker::makeDereference(const Expr *Arg, QualType Ty) {

  return UnaryOperator::Create(C, const_cast<Expr *>(Arg), UO_Deref, Ty,

                               VK_LValue, OK_Ordinary, SourceLocation(),

                               /*CanOverflow*/ false, FPOptionsOverride());

}

ImplicitCastExpr *ASTMaker::makeLvalueToRvalue(const Expr *Arg, QualType Ty) {

  return makeImplicitCast(Arg, Ty, CK_LValueToRValue);

}

ImplicitCastExpr *

ASTMaker::makeLvalueToRvalue(const VarDecl *Arg,

                             bool RefersToEnclosingVariableOrCapture) {

  QualType Type = Arg->getType().getNonReferenceType();

  return makeLvalueToRvalue(makeDeclRefExpr(Arg,

                                            RefersToEnclosingVariableOrCapture),

                            Type);

}

ImplicitCastExpr *ASTMaker::makeImplicitCast(const Expr *Arg, QualType Ty,

                                             CastKind CK) {

  return ImplicitCastExpr::Create(C, Ty,

                                  /* CastKind=*/CK,

                                  /* Expr=*/const_cast<Expr *>(Arg),

                                  /* CXXCastPath=*/nullptr,

                                  /* ExprValueKind=*/VK_PRValue,

                                  /* FPFeatures */ FPOptionsOverride());

}

CastExpr *ASTMaker::makeReferenceCast(const Expr *Arg, QualType Ty) {

  assert(Ty->isReferenceType());

  return CXXStaticCastExpr::Create(

      C, Ty.getNonReferenceType(),

      Ty->isLValueReferenceType() ? VK_LValue : VK_XValue, CK_NoOp,

      const_cast<Expr *>(Arg), /*CXXCastPath=*/nullptr,

      /*Written=*/C.getTrivialTypeSourceInfo(Ty), FPOptionsOverride(),

      SourceLocation(), SourceLocation(), SourceRange());

}

Expr *ASTMaker::makeIntegralCast(const Expr *Arg, QualType Ty) {

  if (Arg->getType() == Ty)

    return const_cast<Expr*>(Arg);

  return makeImplicitCast(Arg, Ty, CK_IntegralCast);

}

ImplicitCastExpr *ASTMaker::makeIntegralCastToBoolean(const Expr *Arg) {

  return makeImplicitCast(Arg, C.BoolTy, CK_IntegralToBoolean);

}

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 ReturnStmt::Create(C, SourceLocation(), const_cast<Expr *>(RetVal),

                            /* NRVOCandidate=*/nullptr);

}

IntegerLiteral *ASTMaker::makeIntegerLiteral(uint64_t Value, QualType Ty) {

  llvm::APInt APValue = llvm::APInt(C.getTypeSize(Ty), Value);

  return IntegerLiteral::Create(C, APValue, Ty, SourceLocation());

}

MemberExpr *ASTMaker::makeMemberExpression(Expr *base, ValueDecl *MemberDecl,

                                           bool IsArrow,

                                           ExprValueKind ValueKind) {

  DeclAccessPair FoundDecl = DeclAccessPair::make(MemberDecl, AS_public);

  return MemberExpr::Create(

      C, base, IsArrow, SourceLocation(), NestedNameSpecifierLoc(),

      SourceLocation(), MemberDecl, FoundDecl,

      DeclarationNameInfo(MemberDecl->getDeclName(), SourceLocation()),

      /* TemplateArgumentListInfo=*/ nullptr, MemberDecl->getType(), ValueKind,

      OK_Ordinary, NOUR_None);

}

ValueDecl *ASTMaker::findMemberField(const RecordDecl *RD, StringRef Name) {

  CXXBasePaths Paths(

      /* FindAmbiguities=*/false,

      /* RecordPaths=*/false,

      /* DetectVirtual=*/ false);

  const IdentifierInfo &II = C.Idents.get(Name);

  DeclarationName DeclName = C.DeclarationNames.getIdentifier(&II);

  DeclContextLookupResult Decls = RD->lookup(DeclName);

  for (NamedDecl *FoundDecl : Decls)

    if (!FoundDecl->getDeclContext()->isFunctionOrMethod())

      return cast<ValueDecl>(FoundDecl);

  return nullptr;

}

//===----------------------------------------------------------------------===//

// Creation functions for faux ASTs.

//===----------------------------------------------------------------------===//

typedef Stmt *(*FunctionFarmer)(ASTContext &C, const FunctionDecl *D);

static CallExpr *create_call_once_funcptr_call(ASTContext &C, ASTMaker M,

                                               const ParmVarDecl *Callback,

                                               ArrayRef<Expr *> CallArgs) {

  QualType Ty = Callback->getType();

  DeclRefExpr *Call = M.makeDeclRefExpr(Callback);

  Expr *SubExpr;

  if (Ty->isRValueReferenceType()) {

    SubExpr = M.makeImplicitCast(

        Call, Ty.getNonReferenceType(), CK_LValueToRValue);

  } else if (Ty->isLValueReferenceType() &&

             Call->getType()->isFunctionType()) {

    Ty = C.getPointerType(Ty.getNonReferenceType());

    SubExpr = M.makeImplicitCast(Call, Ty, CK_FunctionToPointerDecay);

  } else if (Ty->isLValueReferenceType()

             && Call->getType()->isPointerType()

             && Call->getType()->getPointeeType()->isFunctionType()){

    SubExpr = Call;

  } else {

    llvm_unreachable("Unexpected state");

  }

  return CallExpr::Create(C, SubExpr, CallArgs, C.VoidTy, VK_PRValue,

                          SourceLocation(), FPOptionsOverride());

}

static CallExpr *create_call_once_lambda_call(ASTContext &C, ASTMaker M,

                                              const ParmVarDecl *Callback,

                                              CXXRecordDecl *CallbackDecl,

                                              ArrayRef<Expr *> CallArgs) {

  assert(CallbackDecl != nullptr);

  assert(CallbackDecl->isLambda());

  FunctionDecl *callOperatorDecl = CallbackDecl->getLambdaCallOperator();

  assert(callOperatorDecl != nullptr);

  DeclRefExpr *callOperatorDeclRef =

      DeclRefExpr::Create(/* Ctx =*/ C,

                          /* QualifierLoc =*/ NestedNameSpecifierLoc(),

                          /* TemplateKWLoc =*/ SourceLocation(),

                          const_cast<FunctionDecl *>(callOperatorDecl),

                          /* RefersToEnclosingVariableOrCapture=*/ false,

                          /* NameLoc =*/ SourceLocation(),

                          /* T =*/ callOperatorDecl->getType(),

                          /* VK =*/ VK_LValue);

  return CXXOperatorCallExpr::Create(

      /*AstContext=*/C, OO_Call, callOperatorDeclRef,

      /*Args=*/CallArgs,

      /*QualType=*/C.VoidTy,

      /*ExprValueType=*/VK_PRValue,

      /*SourceLocation=*/SourceLocation(),

      /*FPFeatures=*/FPOptionsOverride());

}

/// Create a fake body for 'std::move' or 'std::forward'. This is just:

///

/// \code

/// return static_cast<return_type>(param);

/// \endcode

static Stmt *create_std_move_forward(ASTContext &C, const FunctionDecl *D) {

  LLVM_DEBUG(llvm::dbgs() << "Generating body for std::move / std::forward\n");

  ASTMaker M(C);

  QualType ReturnType = D->getType()->castAs<FunctionType>()->getReturnType();

  Expr *Param = M.makeDeclRefExpr(D->getParamDecl(0));

  Expr *Cast = M.makeReferenceCast(Param, ReturnType);

  return M.makeReturn(Cast);

}

/// Create a fake body for std::call_once.

/// Emulates the following function body:

///

/// \code

/// typedef struct once_flag_s {

///   unsigned long __state = 0;

/// } once_flag;

/// template<class Callable>

/// void call_once(once_flag& o, Callable func) {

///   if (!o.__state) {

///     func();

///   }

///   o.__state = 1;

/// }

/// \endcode

static Stmt *create_call_once(ASTContext &C, const FunctionDecl *D) {

  LLVM_DEBUG(llvm::dbgs() << "Generating body for call_once\n");

  // We need at least two parameters.

  if (D->param_size() < 2)

    return nullptr;

  ASTMaker M(C);

  const ParmVarDecl *Flag = D->getParamDecl(0);

  const ParmVarDecl *Callback = D->getParamDecl(1);

  if (!Callback->getType()->isReferenceType()) {

    llvm::dbgs() << "libcxx03 std::call_once implementation, skipping.\n";

    return nullptr;

  }

  if (!Flag->getType()->isReferenceType()) {

    llvm::dbgs() << "unknown std::call_once implementation, skipping.\n";

    return nullptr;

  }

  QualType CallbackType = Callback->getType().getNonReferenceType();

  // Nullable pointer, non-null iff function is a CXXRecordDecl.

  CXXRecordDecl *CallbackRecordDecl = CallbackType->getAsCXXRecordDecl();

  QualType FlagType = Flag->getType().getNonReferenceType();

  auto *FlagRecordDecl = FlagType->getAsRecordDecl();

  if (!FlagRecordDecl) {

    LLVM_DEBUG(llvm::dbgs() << "Flag field is not a record: "

                            << "unknown std::call_once implementation, "

                            << "ignoring the call.\n");

    return nullptr;

  }

  // We initially assume libc++ implementation of call_once,

  // where the once_flag struct has a field `__state_`.

  ValueDecl *FlagFieldDecl = M.findMemberField(FlagRecordDecl, "__state_");

  // Otherwise, try libstdc++ implementation, with a field

  // `_M_once`

  if (!FlagFieldDecl) {

    FlagFieldDecl = M.findMemberField(FlagRecordDecl, "_M_once");

  }

  if (!FlagFieldDecl) {

    LLVM_DEBUG(llvm::dbgs() << "No field _M_once or __state_ found on "

                            << "std::once_flag struct: unknown std::call_once "

                            << "implementation, ignoring the call.");

    return nullptr;

  }

  bool isLambdaCall = CallbackRecordDecl && CallbackRecordDecl->isLambda();

  if (CallbackRecordDecl && !isLambdaCall) {

    LLVM_DEBUG(llvm::dbgs()

               << "Not supported: synthesizing body for functors when "

               << "body farming std::call_once, ignoring the call.");

    return nullptr;

  }

  SmallVector<Expr *, 5> CallArgs;

  const FunctionProtoType *CallbackFunctionType;

  if (isLambdaCall) {

    // Lambda requires callback itself inserted as a first parameter.

    CallArgs.push_back(

        M.makeDeclRefExpr(Callback,

                          /* RefersToEnclosingVariableOrCapture=*/ true));

    CallbackFunctionType = CallbackRecordDecl->getLambdaCallOperator()

                               ->getType()

                               ->getAs<FunctionProtoType>();

  } else if (!CallbackType->getPointeeType().isNull()) {

    CallbackFunctionType =

        CallbackType->getPointeeType()->getAs<FunctionProtoType>();

  } else {

    CallbackFunctionType = CallbackType->getAs<FunctionProtoType>();

  }

  if (!CallbackFunctionType)

    return nullptr;

  // First two arguments are used for the flag and for the callback.

  if (D->getNumParams() != CallbackFunctionType->getNumParams() + 2) {

    LLVM_DEBUG(llvm::dbgs() << "Types of params of the callback do not match "

                            << "params passed to std::call_once, "

                            << "ignoring the call\n");

    return nullptr;

  }

  // All arguments past first two ones are passed to the callback,

  // and we turn lvalues into rvalues if the argument is not passed by

  // reference.

  for (unsigned int ParamIdx = 2; ParamIdx < D->getNumParams(); ParamIdx++) {

    const ParmVarDecl *PDecl = D->getParamDecl(ParamIdx);

    assert(PDecl);

    if (CallbackFunctionType->getParamType(ParamIdx - 2)

                .getNonReferenceType()

                .getCanonicalType() !=

            PDecl->getType().getNonReferenceType().getCanonicalType()) {

      LLVM_DEBUG(llvm::dbgs() << "Types of params of the callback do not match "

                              << "params passed to std::call_once, "

                              << "ignoring the call\n");

      return nullptr;

    }

    Expr *ParamExpr = M.makeDeclRefExpr(PDecl);

    if (!CallbackFunctionType->getParamType(ParamIdx - 2)->isReferenceType()) {

      QualType PTy = PDecl->getType().getNonReferenceType();

      ParamExpr = M.makeLvalueToRvalue(ParamExpr, PTy);

    }

    CallArgs.push_back(ParamExpr);

  }

  CallExpr *CallbackCall;

  if (isLambdaCall) {

    CallbackCall = create_call_once_lambda_call(C, M, Callback,

                                                CallbackRecordDecl, CallArgs);

  } else {

    // Function pointer case.

    CallbackCall = create_call_once_funcptr_call(C, M, Callback, CallArgs);

  }

  DeclRefExpr *FlagDecl =

      M.makeDeclRefExpr(Flag,

                        /* RefersToEnclosingVariableOrCapture=*/true);

  MemberExpr *Deref = M.makeMemberExpression(FlagDecl, FlagFieldDecl);

  assert(Deref->isLValue());

  QualType DerefType = Deref->getType();

  // Negation predicate.

  UnaryOperator *FlagCheck = UnaryOperator::Create(

      C,

      /* input=*/

      M.makeImplicitCast(M.makeLvalueToRvalue(Deref, DerefType), DerefType,

                         CK_IntegralToBoolean),

      /* opc=*/UO_LNot,

      /* QualType=*/C.IntTy,

      /* ExprValueKind=*/VK_PRValue,

      /* ExprObjectKind=*/OK_Ordinary, SourceLocation(),

      /* CanOverflow*/ false, FPOptionsOverride());

  // Create assignment.

  BinaryOperator *FlagAssignment = M.makeAssignment(

      Deref, M.makeIntegralCast(M.makeIntegerLiteral(1, C.IntTy), DerefType),

      DerefType);

  auto *Out =

      IfStmt::Create(C, SourceLocation(), IfStatementKind::Ordinary,

                     /* Init=*/nullptr,

                     /* Var=*/nullptr,

                     /* Cond=*/FlagCheck,

                     /* LPL=*/SourceLocation(),

                     /* RPL=*/SourceLocation(),

                     /* Then=*/M.makeCompound({CallbackCall, FlagAssignment}));

  return Out;

}

/// 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 != ~0l) {

  //    *predicate = ~0l;

  //    block();

  //  }

  // }

  ASTMaker M(C);

  // (1) Create the call.

  CallExpr *CE = CallExpr::Create(

      /*ASTContext=*/C,

      /*StmtClass=*/M.makeLvalueToRvalue(/*Expr=*/Block),

      /*Args=*/std::nullopt,

      /*QualType=*/C.VoidTy,

      /*ExprValueType=*/VK_PRValue,

      /*SourceLocation=*/SourceLocation(), FPOptionsOverride());

  // (2) Create the assignment to the predicate.

  Expr *DoneValue =

      UnaryOperator::Create(C, M.makeIntegerLiteral(0, C.LongTy), UO_Not,

                            C.LongTy, VK_PRValue, OK_Ordinary, SourceLocation(),

                            /*CanOverflow*/ false, FPOptionsOverride());

  BinaryOperator *B =

    M.makeAssignment(

       M.makeDereference(

          M.makeLvalueToRvalue(

            M.makeDeclRefExpr(Predicate), PredicateQPtrTy),

            PredicateTy),

       M.makeIntegralCast(DoneValue, 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);

  Expr *GuardCondition = M.makeComparison(LValToRval, DoneValue, BO_NE);

  // (5) Create the 'if' statement.

  auto *If = IfStmt::Create(C, SourceLocation(), IfStatementKind::Ordinary,

                            /* Init=*/nullptr,

                            /* Var=*/nullptr,

                            /* Cond=*/GuardCondition,

                            /* LPL=*/SourceLocation(),

                            /* RPL=*/SourceLocation(),

                            /* Then=*/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 = CallExpr::Create(C, ICE, std::nullopt, C.VoidTy, VK_PRValue,

                                  SourceLocation(), FPOptionsOverride());

  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.

  auto *If =

      IfStmt::Create(C, SourceLocation(), IfStatementKind::Ordinary,

                     /* Init=*/nullptr,

                     /* Var=*/nullptr, Comparison,

                     /* LPL=*/SourceLocation(),

                     /* RPL=*/SourceLocation(), Body, SourceLocation(), Else);

  return If;

}

Stmt *BodyFarm::getBody(const FunctionDecl *D) {

  std::optional<Stmt *> &Val = Bodies[D];

  if (Val)

    return *Val;

  Val = nullptr;

  if (D->getIdentifier() == nullptr)

    return nullptr;

  StringRef Name = D->getName();

  if (Name.empty())

    return nullptr;

  FunctionFarmer FF;

  if (unsigned BuiltinID = D->getBuiltinID()) {

    switch (BuiltinID) {

    case Builtin::BIas_const:

    case Builtin::BIforward:

    case Builtin::BIforward_like:

    case Builtin::BImove:

    case Builtin::BImove_if_noexcept:

      FF = create_std_move_forward;

      break;

    default:

      FF = nullptr;

      break;

    }

  } else if (Name.starts_with("OSAtomicCompareAndSwap") ||

             Name.starts_with("objc_atomicCompareAndSwap")) {

    FF = create_OSAtomicCompareAndSwap;

  } else if (Name == "call_once" && D->getDeclContext()->isStdNamespace()) {

    FF = create_call_once;

  } 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;

}

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 ObjCMethodDecl *MD) {

  // First, find the backing ivar.

  const ObjCIvarDecl *IVar = nullptr;

  const ObjCPropertyDecl *Prop = nullptr;

  // Property accessor stubs sometimes do not correspond to any property decl

  // in the current interface (but in a superclass). They still have a

  // corresponding property impl decl in this case.

  if (MD->isSynthesizedAccessorStub()) {

    const ObjCInterfaceDecl *IntD = MD->getClassInterface();

    const ObjCImplementationDecl *ImpD = IntD->getImplementation();

    for (const auto *PI : ImpD->property_impls()) {

      if (const ObjCPropertyDecl *Candidate = PI->getPropertyDecl()) {

        if (Candidate->getGetterName() == MD->getSelector()) {

          Prop = Candidate;

          IVar = Prop->getPropertyIvarDecl();

        }

      }

    }

  }

  if (!IVar) {

    Prop = MD->findPropertyDecl();

    IVar = Prop ? findBackingIvar(Prop) : nullptr;

  }

  if (!IVar || !Prop)

    return nullptr;

  // Ignore weak variables, which have special behavior.

  if (Prop->getPropertyAttributes() & ObjCPropertyAttribute::kind_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());

      }

    }

  }

  // We expect 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 = MD->getSelfDecl();

  if (!selfVar)

    return nullptr;

  Expr *loadedIVar = M.makeObjCIvarRef(

      M.makeLvalueToRvalue(M.makeDeclRefExpr(selfVar), selfVar->getType()),

      IVar);

  if (!MD->getReturnType()->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();

  // We should not try to synthesize explicitly redefined accessors.

  // We do not know for sure how they behave.

  if (!D->isImplicit())

    return nullptr;

  std::optional<Stmt *> &Val = Bodies[D];

  if (Val)

    return *Val;

  Val = 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;

  // If the property was defined in an extension, search the extensions for

  // overrides.

  const ObjCInterfaceDecl *OID = D->getClassInterface();

  if (dyn_cast<ObjCInterfaceDecl>(D->getParent()) != OID)

    for (auto *Ext : OID->known_extensions()) {

      auto *OMD = Ext->getInstanceMethod(D->getSelector());

      if (OMD && !OMD->isImplicit())

        return nullptr;

    }

  Val = createObjCPropertyGetter(C, D);

  return *Val;

}