[IR] Reformulate LLVM's EH funclet IR

While we have successfully implemented a funclet-oriented EH scheme on
top of LLVM IR, our scheme has some notable deficiencies:
- catchendpad and cleanupendpad are necessary in the current design
  but they are difficult to explain to others, even to seasoned LLVM
  experts.
- catchendpad and cleanupendpad are optimization barriers.  They cannot
  be split and force all potentially throwing call-sites to be invokes.
  This has a noticable effect on the quality of our code generation.
- catchpad, while similar in some aspects to invoke, is fairly awkward.
  It is unsplittable, starts a funclet, and has control flow to other
  funclets.
- The nesting relationship between funclets is currently a property of
  control flow edges.  Because of this, we are forced to carefully
  analyze the flow graph to see if there might potentially exist illegal
  nesting among funclets.  While we have logic to clone funclets when
  they are illegally nested, it would be nicer if we had a
  representation which forbade them upfront.

Let's clean this up a bit by doing the following:
- Instead, make catchpad more like cleanuppad and landingpad: no control
  flow, just a bunch of simple operands;  catchpad would be splittable.
- Introduce catchswitch, a control flow instruction designed to model
  the constraints of funclet oriented EH.
- Make funclet scoping explicit by having funclet instructions consume
  the token produced by the funclet which contains them.
- Remove catchendpad and cleanupendpad.  Their presence can be inferred
  implicitly using coloring information.

N.B.  The state numbering code for the CLR has been updated but the
veracity of it's output cannot be spoken for.  An expert should take a
look to make sure the results are reasonable.

Reviewers: rnk, JosephTremoulet, andrew.w.kaylor

Differential Revision: http://reviews.llvm.org/D15139

llvm-svn: 255422

1 files changed, 137 insertions, 210 deletions

diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 11c55865135..82eb1e0f2f7 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -764,61 +764,6 @@ BasicBlock *ResumeInst::getSuccessorV(unsigned idx) const {
 }
 
 //===----------------------------------------------------------------------===//
-//                        CleanupEndPadInst Implementation
-//===----------------------------------------------------------------------===//
-
-CleanupEndPadInst::CleanupEndPadInst(const CleanupEndPadInst &CEPI)
-    : TerminatorInst(CEPI.getType(), Instruction::CleanupEndPad,
-                     OperandTraits<CleanupEndPadInst>::op_end(this) -
-                         CEPI.getNumOperands(),
-                     CEPI.getNumOperands()) {
-  setInstructionSubclassData(CEPI.getSubclassDataFromInstruction());
-  setCleanupPad(CEPI.getCleanupPad());
-  if (BasicBlock *UnwindDest = CEPI.getUnwindDest())
-    setUnwindDest(UnwindDest);
-}
-
-void CleanupEndPadInst::init(CleanupPadInst *CleanupPad, BasicBlock *UnwindBB) {
-  setCleanupPad(CleanupPad);
-  if (UnwindBB) {
-    setInstructionSubclassData(getSubclassDataFromInstruction() | 1);
-    setUnwindDest(UnwindBB);
-  }
-}
-
-CleanupEndPadInst::CleanupEndPadInst(CleanupPadInst *CleanupPad,
-                                     BasicBlock *UnwindBB, unsigned Values,
-                                     Instruction *InsertBefore)
-    : TerminatorInst(Type::getVoidTy(CleanupPad->getContext()),
-                     Instruction::CleanupEndPad,
-                     OperandTraits<CleanupEndPadInst>::op_end(this) - Values,
-                     Values, InsertBefore) {
-  init(CleanupPad, UnwindBB);
-}
-
-CleanupEndPadInst::CleanupEndPadInst(CleanupPadInst *CleanupPad,
-                                     BasicBlock *UnwindBB, unsigned Values,
-                                     BasicBlock *InsertAtEnd)
-    : TerminatorInst(Type::getVoidTy(CleanupPad->getContext()),
-                     Instruction::CleanupEndPad,
-                     OperandTraits<CleanupEndPadInst>::op_end(this) - Values,
-                     Values, InsertAtEnd) {
-  init(CleanupPad, UnwindBB);
-}
-
-BasicBlock *CleanupEndPadInst::getSuccessorV(unsigned Idx) const {
-  assert(Idx == 0);
-  return getUnwindDest();
-}
-unsigned CleanupEndPadInst::getNumSuccessorsV() const {
-  return getNumSuccessors();
-}
-void CleanupEndPadInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
-  assert(Idx == 0);
-  setUnwindDest(B);
-}
-
-//===----------------------------------------------------------------------===//
 //                        CleanupReturnInst Implementation
 //===----------------------------------------------------------------------===//
 
@@ -828,23 +773,22 @@ CleanupReturnInst::CleanupReturnInst(const CleanupReturnInst &CRI)
                          CRI.getNumOperands(),
                      CRI.getNumOperands()) {
   setInstructionSubclassData(CRI.getSubclassDataFromInstruction());
-  Op<-1>() = CRI.Op<-1>();
+  Op<0>() = CRI.Op<0>();
   if (CRI.hasUnwindDest())
-    Op<-2>() = CRI.Op<-2>();
+    Op<1>() = CRI.Op<1>();
 }
 
-void CleanupReturnInst::init(CleanupPadInst *CleanupPad, BasicBlock *UnwindBB) {
+void CleanupReturnInst::init(Value *CleanupPad, BasicBlock *UnwindBB) {
   if (UnwindBB)
     setInstructionSubclassData(getSubclassDataFromInstruction() | 1);
 
-  Op<-1>() = CleanupPad;
+  Op<0>() = CleanupPad;
   if (UnwindBB)
-    Op<-2>() = UnwindBB;
+    Op<1>() = UnwindBB;
 }
 
-CleanupReturnInst::CleanupReturnInst(CleanupPadInst *CleanupPad,
-                                     BasicBlock *UnwindBB, unsigned Values,
-                                     Instruction *InsertBefore)
+CleanupReturnInst::CleanupReturnInst(Value *CleanupPad, BasicBlock *UnwindBB,
+                                     unsigned Values, Instruction *InsertBefore)
     : TerminatorInst(Type::getVoidTy(CleanupPad->getContext()),
                      Instruction::CleanupRet,
                      OperandTraits<CleanupReturnInst>::op_end(this) - Values,
@@ -852,9 +796,8 @@ CleanupReturnInst::CleanupReturnInst(CleanupPadInst *CleanupPad,
   init(CleanupPad, UnwindBB);
 }
 
-CleanupReturnInst::CleanupReturnInst(CleanupPadInst *CleanupPad,
-                                     BasicBlock *UnwindBB, unsigned Values,
-                                     BasicBlock *InsertAtEnd)
+CleanupReturnInst::CleanupReturnInst(Value *CleanupPad, BasicBlock *UnwindBB,
+                                     unsigned Values, BasicBlock *InsertAtEnd)
     : TerminatorInst(Type::getVoidTy(CleanupPad->getContext()),
                      Instruction::CleanupRet,
                      OperandTraits<CleanupReturnInst>::op_end(this) - Values,
@@ -875,58 +818,9 @@ void CleanupReturnInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
 }
 
 //===----------------------------------------------------------------------===//
-//                        CatchEndPadInst Implementation
-//===----------------------------------------------------------------------===//
-
-CatchEndPadInst::CatchEndPadInst(const CatchEndPadInst &CRI)
-    : TerminatorInst(CRI.getType(), Instruction::CatchEndPad,
-                     OperandTraits<CatchEndPadInst>::op_end(this) -
-                         CRI.getNumOperands(),
-                     CRI.getNumOperands()) {
-  setInstructionSubclassData(CRI.getSubclassDataFromInstruction());
-  if (BasicBlock *UnwindDest = CRI.getUnwindDest())
-    setUnwindDest(UnwindDest);
-}
-
-void CatchEndPadInst::init(BasicBlock *UnwindBB) {
-  if (UnwindBB) {
-    setInstructionSubclassData(getSubclassDataFromInstruction() | 1);
-    setUnwindDest(UnwindBB);
-  }
-}
-
-CatchEndPadInst::CatchEndPadInst(LLVMContext &C, BasicBlock *UnwindBB,
-                                 unsigned Values, Instruction *InsertBefore)
-    : TerminatorInst(Type::getVoidTy(C), Instruction::CatchEndPad,
-                     OperandTraits<CatchEndPadInst>::op_end(this) - Values,
-                     Values, InsertBefore) {
-  init(UnwindBB);
-}
-
-CatchEndPadInst::CatchEndPadInst(LLVMContext &C, BasicBlock *UnwindBB,
-                                 unsigned Values, BasicBlock *InsertAtEnd)
-    : TerminatorInst(Type::getVoidTy(C), Instruction::CatchEndPad,
-                     OperandTraits<CatchEndPadInst>::op_end(this) - Values,
-                     Values, InsertAtEnd) {
-  init(UnwindBB);
-}
-
-BasicBlock *CatchEndPadInst::getSuccessorV(unsigned Idx) const {
-  assert(Idx == 0);
-  return getUnwindDest();
-}
-unsigned CatchEndPadInst::getNumSuccessorsV() const {
-  return getNumSuccessors();
-}
-void CatchEndPadInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
-  assert(Idx == 0);
-  setUnwindDest(B);
-}
-
-//===----------------------------------------------------------------------===//
 //                        CatchReturnInst Implementation
 //===----------------------------------------------------------------------===//
-void CatchReturnInst::init(CatchPadInst *CatchPad, BasicBlock *BB) {
+void CatchReturnInst::init(Value *CatchPad, BasicBlock *BB) {
   Op<0>() = CatchPad;
   Op<1>() = BB;
 }
@@ -938,7 +832,7 @@ CatchReturnInst::CatchReturnInst(const CatchReturnInst &CRI)
   Op<1>() = CRI.Op<1>();
 }
 
-CatchReturnInst::CatchReturnInst(CatchPadInst *CatchPad, BasicBlock *BB,
+CatchReturnInst::CatchReturnInst(Value *CatchPad, BasicBlock *BB,
                                  Instruction *InsertBefore)
     : TerminatorInst(Type::getVoidTy(BB->getContext()), Instruction::CatchRet,
                      OperandTraits<CatchReturnInst>::op_begin(this), 2,
@@ -946,7 +840,7 @@ CatchReturnInst::CatchReturnInst(CatchPadInst *CatchPad, BasicBlock *BB,
   init(CatchPad, BB);
 }
 
-CatchReturnInst::CatchReturnInst(CatchPadInst *CatchPad, BasicBlock *BB,
+CatchReturnInst::CatchReturnInst(Value *CatchPad, BasicBlock *BB,
                                  BasicBlock *InsertAtEnd)
     : TerminatorInst(Type::getVoidTy(BB->getContext()), Instruction::CatchRet,
                      OperandTraits<CatchReturnInst>::op_begin(this), 2,
@@ -967,64 +861,136 @@ void CatchReturnInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
 }
 
 //===----------------------------------------------------------------------===//
-//                        CatchPadInst Implementation
+//                       CatchSwitchInst Implementation
 //===----------------------------------------------------------------------===//
-void CatchPadInst::init(BasicBlock *IfNormal, BasicBlock *IfException,
-                        ArrayRef<Value *> Args, const Twine &NameStr) {
-  assert(getNumOperands() == 2 + Args.size() && "NumOperands not set up?");
-  Op<-2>() = IfNormal;
-  Op<-1>() = IfException;
-  std::copy(Args.begin(), Args.end(), op_begin());
+
+CatchSwitchInst::CatchSwitchInst(Value *ParentPad, BasicBlock *UnwindDest,
+                                 unsigned NumReservedValues,
+                                 const Twine &NameStr,
+                                 Instruction *InsertBefore)
+    : TerminatorInst(ParentPad->getType(), Instruction::CatchSwitch, nullptr, 0,
+                     InsertBefore) {
+  if (UnwindDest)
+    ++NumReservedValues;
+  init(ParentPad, UnwindDest, NumReservedValues + 1);
   setName(NameStr);
 }
 
-CatchPadInst::CatchPadInst(const CatchPadInst &CPI)
-    : TerminatorInst(CPI.getType(), Instruction::CatchPad,
-                     OperandTraits<CatchPadInst>::op_end(this) -
-                         CPI.getNumOperands(),
-                     CPI.getNumOperands()) {
-  std::copy(CPI.op_begin(), CPI.op_end(), op_begin());
+CatchSwitchInst::CatchSwitchInst(Value *ParentPad, BasicBlock *UnwindDest,
+                                 unsigned NumReservedValues,
+                                 const Twine &NameStr, BasicBlock *InsertAtEnd)
+    : TerminatorInst(ParentPad->getType(), Instruction::CatchSwitch, nullptr, 0,
+                     InsertAtEnd) {
+  if (UnwindDest)
+    ++NumReservedValues;
+  init(ParentPad, UnwindDest, NumReservedValues + 1);
+  setName(NameStr);
 }
 
-CatchPadInst::CatchPadInst(BasicBlock *IfNormal, BasicBlock *IfException,
-                           ArrayRef<Value *> Args, unsigned Values,
-                           const Twine &NameStr, Instruction *InsertBefore)
-    : TerminatorInst(Type::getTokenTy(IfNormal->getContext()),
-                     Instruction::CatchPad,
-                     OperandTraits<CatchPadInst>::op_end(this) - Values, Values,
-                     InsertBefore) {
-  init(IfNormal, IfException, Args, NameStr);
+CatchSwitchInst::CatchSwitchInst(const CatchSwitchInst &CSI)
+    : TerminatorInst(CSI.getType(), Instruction::CatchSwitch, nullptr,
+                     CSI.getNumOperands()) {
+  init(CSI.getParentPad(), CSI.getUnwindDest(), CSI.getNumOperands());
+  setNumHungOffUseOperands(ReservedSpace);
+  Use *OL = getOperandList();
+  const Use *InOL = CSI.getOperandList();
+  for (unsigned I = 1, E = ReservedSpace; I != E; ++I)
+    OL[I] = InOL[I];
 }
 
-CatchPadInst::CatchPadInst(BasicBlock *IfNormal, BasicBlock *IfException,
-                           ArrayRef<Value *> Args, unsigned Values,
-                           const Twine &NameStr, BasicBlock *InsertAtEnd)
-    : TerminatorInst(Type::getTokenTy(IfNormal->getContext()),
-                     Instruction::CatchPad,
-                     OperandTraits<CatchPadInst>::op_end(this) - Values, Values,
-                     InsertAtEnd) {
-  init(IfNormal, IfException, Args, NameStr);
+void CatchSwitchInst::init(Value *ParentPad, BasicBlock *UnwindDest,
+                           unsigned NumReservedValues) {
+  assert(ParentPad && NumReservedValues);
+
+  ReservedSpace = NumReservedValues;
+  setNumHungOffUseOperands(UnwindDest ? 2 : 1);
+  allocHungoffUses(ReservedSpace);
+
+  Op<0>() = ParentPad;
+  if (UnwindDest) {
+    setInstructionSubclassData(getSubclassDataFromInstruction() | 1);
+    setUnwindDest(UnwindDest);
+  }
 }
 
-BasicBlock *CatchPadInst::getSuccessorV(unsigned Idx) const {
-  return getSuccessor(Idx);
+/// growOperands - grow operands - This grows the operand list in response to a
+/// push_back style of operation. This grows the number of ops by 2 times.
+void CatchSwitchInst::growOperands(unsigned Size) {
+  unsigned NumOperands = getNumOperands();
+  assert(NumOperands >= 1);
+  if (ReservedSpace >= NumOperands + Size)
+    return;
+  ReservedSpace = (NumOperands + Size / 2) * 2;
+  growHungoffUses(ReservedSpace);
+}
+
+void CatchSwitchInst::addHandler(BasicBlock *Handler) {
+  unsigned OpNo = getNumOperands();
+  growOperands(1);
+  assert(OpNo < ReservedSpace && "Growing didn't work!");
+  setNumHungOffUseOperands(getNumOperands() + 1);
+  getOperandList()[OpNo] = Handler;
+}
+
+BasicBlock *CatchSwitchInst::getSuccessorV(unsigned idx) const {
+  return getSuccessor(idx);
 }
-unsigned CatchPadInst::getNumSuccessorsV() const {
+unsigned CatchSwitchInst::getNumSuccessorsV() const {
   return getNumSuccessors();
 }
-void CatchPadInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
-  return setSuccessor(Idx, B);
+void CatchSwitchInst::setSuccessorV(unsigned idx, BasicBlock *B) {
+  setSuccessor(idx, B);
+}
+
+//===----------------------------------------------------------------------===//
+//                        FuncletPadInst Implementation
+//===----------------------------------------------------------------------===//
+void FuncletPadInst::init(Value *ParentPad, ArrayRef<Value *> Args,
+                          const Twine &NameStr) {
+  assert(getNumOperands() == 1 + Args.size() && "NumOperands not set up?");
+  std::copy(Args.begin(), Args.end(), op_begin());
+  setParentPad(ParentPad);
+  setName(NameStr);
+}
+
+FuncletPadInst::FuncletPadInst(const FuncletPadInst &FPI)
+    : Instruction(FPI.getType(), FPI.getOpcode(),
+                  OperandTraits<FuncletPadInst>::op_end(this) -
+                      FPI.getNumOperands(),
+                  FPI.getNumOperands()) {
+  std::copy(FPI.op_begin(), FPI.op_end(), op_begin());
+  setParentPad(FPI.getParentPad());
+}
+
+FuncletPadInst::FuncletPadInst(Instruction::FuncletPadOps Op, Value *ParentPad,
+                               ArrayRef<Value *> Args, unsigned Values,
+                               const Twine &NameStr, Instruction *InsertBefore)
+    : Instruction(ParentPad->getType(), Op,
+                  OperandTraits<FuncletPadInst>::op_end(this) - Values, Values,
+                  InsertBefore) {
+  init(ParentPad, Args, NameStr);
+}
+
+FuncletPadInst::FuncletPadInst(Instruction::FuncletPadOps Op, Value *ParentPad,
+                               ArrayRef<Value *> Args, unsigned Values,
+                               const Twine &NameStr, BasicBlock *InsertAtEnd)
+    : Instruction(ParentPad->getType(), Op,
+                  OperandTraits<FuncletPadInst>::op_end(this) - Values, Values,
+                  InsertAtEnd) {
+  init(ParentPad, Args, NameStr);
 }
 
 //===----------------------------------------------------------------------===//
 //                        TerminatePadInst Implementation
 //===----------------------------------------------------------------------===//
-void TerminatePadInst::init(BasicBlock *BB, ArrayRef<Value *> Args) {
-  if (BB)
+void TerminatePadInst::init(Value *ParentPad, BasicBlock *BB,
+                            ArrayRef<Value *> Args) {
+  if (BB) {
     setInstructionSubclassData(getSubclassDataFromInstruction() | 1);
-  if (BB)
-    Op<-1>() = BB;
-  std::copy(Args.begin(), Args.end(), op_begin());
+    setUnwindDest(BB);
+  }
+  std::copy(Args.begin(), Args.end(), arg_begin());
+  setParentPad(ParentPad);
 }
 
 TerminatePadInst::TerminatePadInst(const TerminatePadInst &TPI)
@@ -1036,22 +1002,24 @@ TerminatePadInst::TerminatePadInst(const TerminatePadInst &TPI)
   std::copy(TPI.op_begin(), TPI.op_end(), op_begin());
 }
 
-TerminatePadInst::TerminatePadInst(LLVMContext &C, BasicBlock *BB,
+TerminatePadInst::TerminatePadInst(Value *ParentPad, BasicBlock *BB,
                                    ArrayRef<Value *> Args, unsigned Values,
                                    Instruction *InsertBefore)
-    : TerminatorInst(Type::getVoidTy(C), Instruction::TerminatePad,
+    : TerminatorInst(Type::getVoidTy(ParentPad->getContext()),
+                     Instruction::TerminatePad,
                      OperandTraits<TerminatePadInst>::op_end(this) - Values,
                      Values, InsertBefore) {
-  init(BB, Args);
+  init(ParentPad, BB, Args);
 }
 
-TerminatePadInst::TerminatePadInst(LLVMContext &C, BasicBlock *BB,
+TerminatePadInst::TerminatePadInst(Value *ParentPad, BasicBlock *BB,
                                    ArrayRef<Value *> Args, unsigned Values,
                                    BasicBlock *InsertAtEnd)
-    : TerminatorInst(Type::getVoidTy(C), Instruction::TerminatePad,
+    : TerminatorInst(Type::getVoidTy(ParentPad->getContext()),
+                     Instruction::TerminatePad,
                      OperandTraits<TerminatePadInst>::op_end(this) - Values,
                      Values, InsertAtEnd) {
-  init(BB, Args);
+  init(ParentPad, BB, Args);
 }
 
 BasicBlock *TerminatePadInst::getSuccessorV(unsigned Idx) const {
@@ -1067,39 +1035,6 @@ void TerminatePadInst::setSuccessorV(unsigned Idx, BasicBlock *B) {
 }
 
 //===----------------------------------------------------------------------===//
-//                        CleanupPadInst Implementation
-//===----------------------------------------------------------------------===//
-void CleanupPadInst::init(ArrayRef<Value *> Args, const Twine &NameStr) {
-  assert(getNumOperands() == Args.size() && "NumOperands not set up?");
-  std::copy(Args.begin(), Args.end(), op_begin());
-  setName(NameStr);
-}
-
-CleanupPadInst::CleanupPadInst(const CleanupPadInst &CPI)
-    : Instruction(CPI.getType(), Instruction::CleanupPad,
-                  OperandTraits<CleanupPadInst>::op_end(this) -
-                      CPI.getNumOperands(),
-                  CPI.getNumOperands()) {
-  std::copy(CPI.op_begin(), CPI.op_end(), op_begin());
-}
-
-CleanupPadInst::CleanupPadInst(LLVMContext &C, ArrayRef<Value *> Args,
-                               const Twine &NameStr, Instruction *InsertBefore)
-    : Instruction(Type::getTokenTy(C), Instruction::CleanupPad,
-                  OperandTraits<CleanupPadInst>::op_end(this) - Args.size(),
-                  Args.size(), InsertBefore) {
-  init(Args, NameStr);
-}
-
-CleanupPadInst::CleanupPadInst(LLVMContext &C, ArrayRef<Value *> Args,
-                               const Twine &NameStr, BasicBlock *InsertAtEnd)
-    : Instruction(Type::getTokenTy(C), Instruction::CleanupPad,
-                  OperandTraits<CleanupPadInst>::op_end(this) - Args.size(),
-                  Args.size(), InsertAtEnd) {
-  init(Args, NameStr);
-}
-
-//===----------------------------------------------------------------------===//
 //                      UnreachableInst Implementation
 //===----------------------------------------------------------------------===//
 
@@ -4074,32 +4009,24 @@ InvokeInst *InvokeInst::cloneImpl() const {
 
 ResumeInst *ResumeInst::cloneImpl() const { return new (1) ResumeInst(*this); }
 
-CleanupEndPadInst *CleanupEndPadInst::cloneImpl() const {
-  return new (getNumOperands()) CleanupEndPadInst(*this);
-}
-
 CleanupReturnInst *CleanupReturnInst::cloneImpl() const {
   return new (getNumOperands()) CleanupReturnInst(*this);
 }
 
-CatchEndPadInst *CatchEndPadInst::cloneImpl() const {
-  return new (getNumOperands()) CatchEndPadInst(*this);
-}
-
 CatchReturnInst *CatchReturnInst::cloneImpl() const {
   return new (getNumOperands()) CatchReturnInst(*this);
 }
 
-CatchPadInst *CatchPadInst::cloneImpl() const {
-  return new (getNumOperands()) CatchPadInst(*this);
+CatchSwitchInst *CatchSwitchInst::cloneImpl() const {
+  return new CatchSwitchInst(*this);
 }
 
-TerminatePadInst *TerminatePadInst::cloneImpl() const {
-  return new (getNumOperands()) TerminatePadInst(*this);
+FuncletPadInst *FuncletPadInst::cloneImpl() const {
+  return new (getNumOperands()) FuncletPadInst(*this);
 }
 
-CleanupPadInst *CleanupPadInst::cloneImpl() const {
-  return new (getNumOperands()) CleanupPadInst(*this);
+TerminatePadInst *TerminatePadInst::cloneImpl() const {
+  return new (getNumOperands()) TerminatePadInst(*this);
 }
 
 UnreachableInst *UnreachableInst::cloneImpl() const {