lib/CodeGen/CGObjCRuntime.cpp - platform/external/clang - Gitiles

 //==- CGObjCRuntime.cpp - Interface to Shared Objective-C Runtime Features ==//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This abstract class defines the interface for Objective-C runtime-specific
 // code generation.  It provides some concrete helper methods for functionality
 // shared between all (or most) of the Objective-C runtimes supported by clang.
 //
 //===----------------------------------------------------------------------===//

 #include "CGObjCRuntime.h"

 #include "CGRecordLayout.h"
 #include "CodeGenModule.h"
 #include "CodeGenFunction.h"
 #include "CGCleanup.h"

 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtObjC.h"

 #include "llvm/Support/CallSite.h"

 using namespace clang;
 using namespace CodeGen;

 static uint64_t LookupFieldBitOffset(CodeGen::CodeGenModule &CGM,
                                      const ObjCInterfaceDecl *OID,
                                      const ObjCImplementationDecl *ID,
                                      const ObjCIvarDecl *Ivar) {
   const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();

   // FIXME: We should eliminate the need to have ObjCImplementationDecl passed
   // in here; it should never be necessary because that should be the lexical
   // decl context for the ivar.

   // If we know have an implementation (and the ivar is in it) then
   // look up in the implementation layout.
   const ASTRecordLayout *RL;
   if (ID && ID->getClassInterface() == Container)
     RL = &CGM.getContext().getASTObjCImplementationLayout(ID);
   else
     RL = &CGM.getContext().getASTObjCInterfaceLayout(Container);

   // Compute field index.
   //
   // FIXME: The index here is closely tied to how ASTContext::getObjCLayout is
   // implemented. This should be fixed to get the information from the layout
   // directly.
   unsigned Index = 0;

   for (const ObjCIvarDecl *IVD = Container->all_declared_ivar_begin();
        IVD; IVD = IVD->getNextIvar()) {
     if (Ivar == IVD)
       break;
     ++Index;
   }
   assert(Index < RL->getFieldCount() && "Ivar is not inside record layout!");

   return RL->getFieldOffset(Index);
 }

 uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                               const ObjCInterfaceDecl *OID,
                                               const ObjCIvarDecl *Ivar) {
   return LookupFieldBitOffset(CGM, OID, 0, Ivar) /
     CGM.getContext().getCharWidth();
 }

 uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
                                               const ObjCImplementationDecl *OID,
                                               const ObjCIvarDecl *Ivar) {
   return LookupFieldBitOffset(CGM, OID->getClassInterface(), OID, Ivar) /
     CGM.getContext().getCharWidth();
 }

 LValue CGObjCRuntime::EmitValueForIvarAtOffset(CodeGen::CodeGenFunction &CGF,
                                                const ObjCInterfaceDecl *OID,
                                                llvm::Value *BaseValue,
                                                const ObjCIvarDecl *Ivar,
                                                unsigned CVRQualifiers,
                                                llvm::Value *Offset) {
   // Compute (type*) ( (char *) BaseValue + Offset)
   llvm::Type *I8Ptr = llvm::Type::getInt8PtrTy(CGF.getLLVMContext());
   QualType IvarTy = Ivar->getType();
   llvm::Type *LTy = CGF.CGM.getTypes().ConvertTypeForMem(IvarTy);
   llvm::Value *V = CGF.Builder.CreateBitCast(BaseValue, I8Ptr);
   V = CGF.Builder.CreateInBoundsGEP(V, Offset, "add.ptr");
   V = CGF.Builder.CreateBitCast(V, llvm::PointerType::getUnqual(LTy));

   if (!Ivar->isBitField()) {
     LValue LV = CGF.MakeAddrLValue(V, IvarTy);
     LV.getQuals().addCVRQualifiers(CVRQualifiers);
     return LV;
   }

   // We need to compute an access strategy for this bit-field. We are given the
   // offset to the first byte in the bit-field, the sub-byte offset is taken
   // from the original layout. We reuse the normal bit-field access strategy by
   // treating this as an access to a struct where the bit-field is in byte 0,
   // and adjust the containing type size as appropriate.
   //
   // FIXME: Note that currently we make a very conservative estimate of the
   // alignment of the bit-field, because (a) it is not clear what guarantees the
   // runtime makes us, and (b) we don't have a way to specify that the struct is
   // at an alignment plus offset.
   //
   // Note, there is a subtle invariant here: we can only call this routine on
   // non-synthesized ivars but we may be called for synthesized ivars.  However,
   // a synthesized ivar can never be a bit-field, so this is safe.
   const ASTRecordLayout &RL =
     CGF.CGM.getContext().getASTObjCInterfaceLayout(OID);
   uint64_t TypeSizeInBits = CGF.CGM.getContext().toBits(RL.getSize());
   uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar);
   uint64_t BitOffset = FieldBitOffset % CGF.CGM.getContext().getCharWidth();
   uint64_t ContainingTypeAlign = CGF.CGM.getContext().Target.getCharAlign();
   uint64_t ContainingTypeSize = TypeSizeInBits - (FieldBitOffset - BitOffset);
   uint64_t BitFieldSize =
     Ivar->getBitWidth()->EvaluateAsInt(CGF.getContext()).getZExtValue();

   // Allocate a new CGBitFieldInfo object to describe this access.
   //
   // FIXME: This is incredibly wasteful, these should be uniqued or part of some
   // layout object. However, this is blocked on other cleanups to the
   // Objective-C code, so for now we just live with allocating a bunch of these
   // objects.
   CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
     CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
                              ContainingTypeSize, ContainingTypeAlign));

   return LValue::MakeBitfield(V, *Info,
                               IvarTy.withCVRQualifiers(CVRQualifiers));
 }

 namespace {
   struct CatchHandler {
     const VarDecl *Variable;
     const Stmt *Body;
     llvm::BasicBlock *Block;
     llvm::Value *TypeInfo;
   };

   struct CallObjCEndCatch : EHScopeStack::Cleanup {
     CallObjCEndCatch(bool MightThrow, llvm::Value *Fn) :
       MightThrow(MightThrow), Fn(Fn) {}
     bool MightThrow;
     llvm::Value *Fn;

     void Emit(CodeGenFunction &CGF, Flags flags) {
       if (!MightThrow) {
         CGF.Builder.CreateCall(Fn)->setDoesNotThrow();
         return;
       }

       CGF.EmitCallOrInvoke(Fn);
     }
   };
 }


 void CGObjCRuntime::EmitTryCatchStmt(CodeGenFunction &CGF,
                                      const ObjCAtTryStmt &S,
                                      llvm::Constant *beginCatchFn,
                                      llvm::Constant *endCatchFn,
                                      llvm::Constant *exceptionRethrowFn) {
   // Jump destination for falling out of catch bodies.
   CodeGenFunction::JumpDest Cont;
   if (S.getNumCatchStmts())
     Cont = CGF.getJumpDestInCurrentScope("eh.cont");

   CodeGenFunction::FinallyInfo FinallyInfo;
   if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt())
     FinallyInfo.enter(CGF, Finally->getFinallyBody(),
                       beginCatchFn, endCatchFn, exceptionRethrowFn);

   llvm::SmallVector<CatchHandler, 8> Handlers;

   // Enter the catch, if there is one.
   if (S.getNumCatchStmts()) {
     for (unsigned I = 0, N = S.getNumCatchStmts(); I != N; ++I) {
       const ObjCAtCatchStmt *CatchStmt = S.getCatchStmt(I);
       const VarDecl *CatchDecl = CatchStmt->getCatchParamDecl();

       Handlers.push_back(CatchHandler());
       CatchHandler &Handler = Handlers.back();
       Handler.Variable = CatchDecl;
       Handler.Body = CatchStmt->getCatchBody();
       Handler.Block = CGF.createBasicBlock("catch");

       // @catch(...) always matches.
       if (!CatchDecl) {
         Handler.TypeInfo = 0; // catch-all
         // Don't consider any other catches.
         break;
       }

       Handler.TypeInfo = GetEHType(CatchDecl->getType());
     }

     EHCatchScope *Catch = CGF.EHStack.pushCatch(Handlers.size());
     for (unsigned I = 0, E = Handlers.size(); I != E; ++I)
       Catch->setHandler(I, Handlers[I].TypeInfo, Handlers[I].Block);
   }

   // Emit the try body.
   CGF.EmitStmt(S.getTryBody());

   // Leave the try.
   if (S.getNumCatchStmts())
     CGF.EHStack.popCatch();

   // Remember where we were.
   CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();

   // Emit the handlers.
   for (unsigned I = 0, E = Handlers.size(); I != E; ++I) {
     CatchHandler &Handler = Handlers[I];

     CGF.EmitBlock(Handler.Block);
     llvm::Value *RawExn = CGF.Builder.CreateLoad(CGF.getExceptionSlot());

     // Enter the catch.
     llvm::Value *Exn = RawExn;
     if (beginCatchFn) {
       Exn = CGF.Builder.CreateCall(beginCatchFn, RawExn, "exn.adjusted");
       cast<llvm::CallInst>(Exn)->setDoesNotThrow();
     }

     CodeGenFunction::RunCleanupsScope cleanups(CGF);

     if (endCatchFn) {
       // Add a cleanup to leave the catch.
       bool EndCatchMightThrow = (Handler.Variable == 0);

       CGF.EHStack.pushCleanup<CallObjCEndCatch>(NormalAndEHCleanup,
                                                 EndCatchMightThrow,
                                                 endCatchFn);
     }

     // Bind the catch parameter if it exists.
     if (const VarDecl *CatchParam = Handler.Variable) {
       llvm::Type *CatchType = CGF.ConvertType(CatchParam->getType());
       llvm::Value *CastExn = CGF.Builder.CreateBitCast(Exn, CatchType);

       CGF.EmitAutoVarDecl(*CatchParam);
       CGF.Builder.CreateStore(CastExn, CGF.GetAddrOfLocalVar(CatchParam));
     }

     CGF.ObjCEHValueStack.push_back(Exn);
     CGF.EmitStmt(Handler.Body);
     CGF.ObjCEHValueStack.pop_back();

     // Leave any cleanups associated with the catch.
     cleanups.ForceCleanup();

     CGF.EmitBranchThroughCleanup(Cont);
   }

   // Go back to the try-statement fallthrough.
   CGF.Builder.restoreIP(SavedIP);

   // Pop out of the finally.
   if (S.getFinallyStmt())
     FinallyInfo.exit(CGF);

   if (Cont.isValid())
     CGF.EmitBlock(Cont.getBlock());
 }

 namespace {
   struct CallSyncExit : EHScopeStack::Cleanup {
     llvm::Value *SyncExitFn;
     llvm::Value *SyncArg;
     CallSyncExit(llvm::Value *SyncExitFn, llvm::Value *SyncArg)
       : SyncExitFn(SyncExitFn), SyncArg(SyncArg) {}

     void Emit(CodeGenFunction &CGF, Flags flags) {
       CGF.Builder.CreateCall(SyncExitFn, SyncArg)->setDoesNotThrow();
     }
   };
 }

 void CGObjCRuntime::EmitAtSynchronizedStmt(CodeGenFunction &CGF,
                                            const ObjCAtSynchronizedStmt &S,
                                            llvm::Function *syncEnterFn,
                                            llvm::Function *syncExitFn) {
   // Evaluate the lock operand.  This should dominate the cleanup.
   llvm::Value *SyncArg =
     CGF.EmitScalarExpr(S.getSynchExpr());

   // Acquire the lock.
   SyncArg = CGF.Builder.CreateBitCast(SyncArg, syncEnterFn->getFunctionType()->getParamType(0));
   CGF.Builder.CreateCall(syncEnterFn, SyncArg);

   // Register an all-paths cleanup to release the lock.
   CGF.EHStack.pushCleanup<CallSyncExit>(NormalAndEHCleanup, syncExitFn,
       SyncArg);

   // Emit the body of the statement.
   CGF.EmitStmt(S.getSynchBody());

   // Pop the lock-release cleanup.
   CGF.PopCleanupBlock();
 }
	//==- CGObjCRuntime.cpp - Interface to Shared Objective-C Runtime Features ==//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This abstract class defines the interface for Objective-C runtime-specific
	// code generation. It provides some concrete helper methods for functionality
	// shared between all (or most) of the Objective-C runtimes supported by clang.
	//
	//===----------------------------------------------------------------------===//

	#include "CGObjCRuntime.h"

	#include "CGRecordLayout.h"
	#include "CodeGenModule.h"
	#include "CodeGenFunction.h"
	#include "CGCleanup.h"

	#include "clang/AST/RecordLayout.h"
	#include "clang/AST/StmtObjC.h"

	#include "llvm/Support/CallSite.h"

	using namespace clang;
	using namespace CodeGen;

	static uint64_t LookupFieldBitOffset(CodeGen::CodeGenModule &CGM,
	const ObjCInterfaceDecl *OID,
	const ObjCImplementationDecl *ID,
	const ObjCIvarDecl *Ivar) {
	const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();

	// FIXME: We should eliminate the need to have ObjCImplementationDecl passed
	// in here; it should never be necessary because that should be the lexical
	// decl context for the ivar.

	// If we know have an implementation (and the ivar is in it) then
	// look up in the implementation layout.
	const ASTRecordLayout *RL;
	if (ID && ID->getClassInterface() == Container)
	RL = &CGM.getContext().getASTObjCImplementationLayout(ID);
	else
	RL = &CGM.getContext().getASTObjCInterfaceLayout(Container);

	// Compute field index.
	//
	// FIXME: The index here is closely tied to how ASTContext::getObjCLayout is
	// implemented. This should be fixed to get the information from the layout
	// directly.
	unsigned Index = 0;

	for (const ObjCIvarDecl *IVD = Container->all_declared_ivar_begin();
	IVD; IVD = IVD->getNextIvar()) {
	if (Ivar == IVD)
	break;
	++Index;
	}
	assert(Index < RL->getFieldCount() && "Ivar is not inside record layout!");

	return RL->getFieldOffset(Index);
	}

	uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
	const ObjCInterfaceDecl *OID,
	const ObjCIvarDecl *Ivar) {
	return LookupFieldBitOffset(CGM, OID, 0, Ivar) /
	CGM.getContext().getCharWidth();
	}

	uint64_t CGObjCRuntime::ComputeIvarBaseOffset(CodeGen::CodeGenModule &CGM,
	const ObjCImplementationDecl *OID,
	const ObjCIvarDecl *Ivar) {
	return LookupFieldBitOffset(CGM, OID->getClassInterface(), OID, Ivar) /
	CGM.getContext().getCharWidth();
	}

	LValue CGObjCRuntime::EmitValueForIvarAtOffset(CodeGen::CodeGenFunction &CGF,
	const ObjCInterfaceDecl *OID,
	llvm::Value *BaseValue,
	const ObjCIvarDecl *Ivar,
	unsigned CVRQualifiers,
	llvm::Value *Offset) {
	// Compute (type) ( (char ) BaseValue + Offset)
	llvm::Type *I8Ptr = llvm::Type::getInt8PtrTy(CGF.getLLVMContext());
	QualType IvarTy = Ivar->getType();
	llvm::Type *LTy = CGF.CGM.getTypes().ConvertTypeForMem(IvarTy);
	llvm::Value *V = CGF.Builder.CreateBitCast(BaseValue, I8Ptr);
	V = CGF.Builder.CreateInBoundsGEP(V, Offset, "add.ptr");
	V = CGF.Builder.CreateBitCast(V, llvm::PointerType::getUnqual(LTy));

	if (!Ivar->isBitField()) {
	LValue LV = CGF.MakeAddrLValue(V, IvarTy);
	LV.getQuals().addCVRQualifiers(CVRQualifiers);
	return LV;
	}

	// We need to compute an access strategy for this bit-field. We are given the
	// offset to the first byte in the bit-field, the sub-byte offset is taken
	// from the original layout. We reuse the normal bit-field access strategy by
	// treating this as an access to a struct where the bit-field is in byte 0,
	// and adjust the containing type size as appropriate.
	//
	// FIXME: Note that currently we make a very conservative estimate of the
	// alignment of the bit-field, because (a) it is not clear what guarantees the
	// runtime makes us, and (b) we don't have a way to specify that the struct is
	// at an alignment plus offset.
	//
	// Note, there is a subtle invariant here: we can only call this routine on
	// non-synthesized ivars but we may be called for synthesized ivars. However,
	// a synthesized ivar can never be a bit-field, so this is safe.
	const ASTRecordLayout &RL =
	CGF.CGM.getContext().getASTObjCInterfaceLayout(OID);
	uint64_t TypeSizeInBits = CGF.CGM.getContext().toBits(RL.getSize());
	uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar);
	uint64_t BitOffset = FieldBitOffset % CGF.CGM.getContext().getCharWidth();
	uint64_t ContainingTypeAlign = CGF.CGM.getContext().Target.getCharAlign();
	uint64_t ContainingTypeSize = TypeSizeInBits - (FieldBitOffset - BitOffset);
	uint64_t BitFieldSize =
	Ivar->getBitWidth()->EvaluateAsInt(CGF.getContext()).getZExtValue();

	// Allocate a new CGBitFieldInfo object to describe this access.
	//
	// FIXME: This is incredibly wasteful, these should be uniqued or part of some
	// layout object. However, this is blocked on other cleanups to the
	// Objective-C code, so for now we just live with allocating a bunch of these
	// objects.
	CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
	CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
	ContainingTypeSize, ContainingTypeAlign));

	return LValue::MakeBitfield(V, *Info,
	IvarTy.withCVRQualifiers(CVRQualifiers));
	}

	namespace {
	struct CatchHandler {
	const VarDecl *Variable;
	const Stmt *Body;
	llvm::BasicBlock *Block;
	llvm::Value *TypeInfo;
	};

	struct CallObjCEndCatch : EHScopeStack::Cleanup {
	CallObjCEndCatch(bool MightThrow, llvm::Value *Fn) :
	MightThrow(MightThrow), Fn(Fn) {}
	bool MightThrow;
	llvm::Value *Fn;

	void Emit(CodeGenFunction &CGF, Flags flags) {
	if (!MightThrow) {
	CGF.Builder.CreateCall(Fn)->setDoesNotThrow();
	return;
	}

	CGF.EmitCallOrInvoke(Fn);
	}
	};
	}


	void CGObjCRuntime::EmitTryCatchStmt(CodeGenFunction &CGF,
	const ObjCAtTryStmt &S,
	llvm::Constant *beginCatchFn,
	llvm::Constant *endCatchFn,
	llvm::Constant *exceptionRethrowFn) {
	// Jump destination for falling out of catch bodies.
	CodeGenFunction::JumpDest Cont;
	if (S.getNumCatchStmts())
	Cont = CGF.getJumpDestInCurrentScope("eh.cont");

	CodeGenFunction::FinallyInfo FinallyInfo;
	if (const ObjCAtFinallyStmt *Finally = S.getFinallyStmt())
	FinallyInfo.enter(CGF, Finally->getFinallyBody(),
	beginCatchFn, endCatchFn, exceptionRethrowFn);

	llvm::SmallVector<CatchHandler, 8> Handlers;

	// Enter the catch, if there is one.
	if (S.getNumCatchStmts()) {
	for (unsigned I = 0, N = S.getNumCatchStmts(); I != N; ++I) {
	const ObjCAtCatchStmt *CatchStmt = S.getCatchStmt(I);
	const VarDecl *CatchDecl = CatchStmt->getCatchParamDecl();

	Handlers.push_back(CatchHandler());
	CatchHandler &Handler = Handlers.back();
	Handler.Variable = CatchDecl;
	Handler.Body = CatchStmt->getCatchBody();
	Handler.Block = CGF.createBasicBlock("catch");

	// @catch(...) always matches.
	if (!CatchDecl) {
	Handler.TypeInfo = 0; // catch-all
	// Don't consider any other catches.
	break;
	}

	Handler.TypeInfo = GetEHType(CatchDecl->getType());
	}

	EHCatchScope *Catch = CGF.EHStack.pushCatch(Handlers.size());
	for (unsigned I = 0, E = Handlers.size(); I != E; ++I)
	Catch->setHandler(I, Handlers[I].TypeInfo, Handlers[I].Block);
	}

	// Emit the try body.
	CGF.EmitStmt(S.getTryBody());

	// Leave the try.
	if (S.getNumCatchStmts())
	CGF.EHStack.popCatch();

	// Remember where we were.
	CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP();

	// Emit the handlers.
	for (unsigned I = 0, E = Handlers.size(); I != E; ++I) {
	CatchHandler &Handler = Handlers[I];

	CGF.EmitBlock(Handler.Block);
	llvm::Value *RawExn = CGF.Builder.CreateLoad(CGF.getExceptionSlot());

	// Enter the catch.
	llvm::Value *Exn = RawExn;
	if (beginCatchFn) {
	Exn = CGF.Builder.CreateCall(beginCatchFn, RawExn, "exn.adjusted");
	cast<llvm::CallInst>(Exn)->setDoesNotThrow();
	}

	CodeGenFunction::RunCleanupsScope cleanups(CGF);

	if (endCatchFn) {
	// Add a cleanup to leave the catch.
	bool EndCatchMightThrow = (Handler.Variable == 0);

	CGF.EHStack.pushCleanup<CallObjCEndCatch>(NormalAndEHCleanup,
	EndCatchMightThrow,
	endCatchFn);
	}

	// Bind the catch parameter if it exists.
	if (const VarDecl *CatchParam = Handler.Variable) {
	llvm::Type *CatchType = CGF.ConvertType(CatchParam->getType());
	llvm::Value *CastExn = CGF.Builder.CreateBitCast(Exn, CatchType);

	CGF.EmitAutoVarDecl(*CatchParam);
	CGF.Builder.CreateStore(CastExn, CGF.GetAddrOfLocalVar(CatchParam));
	}

	CGF.ObjCEHValueStack.push_back(Exn);
	CGF.EmitStmt(Handler.Body);
	CGF.ObjCEHValueStack.pop_back();

	// Leave any cleanups associated with the catch.
	cleanups.ForceCleanup();

	CGF.EmitBranchThroughCleanup(Cont);
	}

	// Go back to the try-statement fallthrough.
	CGF.Builder.restoreIP(SavedIP);

	// Pop out of the finally.
	if (S.getFinallyStmt())
	FinallyInfo.exit(CGF);

	if (Cont.isValid())
	CGF.EmitBlock(Cont.getBlock());
	}

	namespace {
	struct CallSyncExit : EHScopeStack::Cleanup {
	llvm::Value *SyncExitFn;
	llvm::Value *SyncArg;
	CallSyncExit(llvm::Value SyncExitFn, llvm::Value SyncArg)
	: SyncExitFn(SyncExitFn), SyncArg(SyncArg) {}

	void Emit(CodeGenFunction &CGF, Flags flags) {
	CGF.Builder.CreateCall(SyncExitFn, SyncArg)->setDoesNotThrow();
	}
	};
	}

	void CGObjCRuntime::EmitAtSynchronizedStmt(CodeGenFunction &CGF,
	const ObjCAtSynchronizedStmt &S,
	llvm::Function *syncEnterFn,
	llvm::Function *syncExitFn) {
	// Evaluate the lock operand. This should dominate the cleanup.
	llvm::Value *SyncArg =
	CGF.EmitScalarExpr(S.getSynchExpr());

	// Acquire the lock.
	SyncArg = CGF.Builder.CreateBitCast(SyncArg, syncEnterFn->getFunctionType()->getParamType(0));
	CGF.Builder.CreateCall(syncEnterFn, SyncArg);

	// Register an all-paths cleanup to release the lock.
	CGF.EHStack.pushCleanup<CallSyncExit>(NormalAndEHCleanup, syncExitFn,
	SyncArg);

	// Emit the body of the statement.
	CGF.EmitStmt(S.getSynchBody());

	// Pop the lock-release cleanup.
	CGF.PopCleanupBlock();
	}