30#define DEBUG_TYPE "ir"
31STATISTIC(NumInstrRenumberings,
"Number of renumberings across all blocks");
35 cl::desc(
"Enable communicating debuginfo positions "
36 "through iterators, eliminating intrinsics"),
41 "Tried to create a marker in a non new debug-info block!");
46 I->DbgMarker = Marker;
52 "Tried to create a marker in a non new debug-info block!");
75 assert(!
I.DbgMarker &&
"DbgMarker already set on old-format instrs?");
80 DVI->eraseFromParent();
103 for (
auto &Inst : *
this) {
109 InstList.
insert(Inst.getIterator(),
110 DPV.createDebugIntrinsic(
getModule(),
nullptr));
128 auto TestFailure = [Assert, Msg, &RetVal,
OS](
bool Val,
const char *Text) {
144 "Parent function doesn't have the same debug-info format");
152 for (
auto It =
begin(); It !=
end(); ++It) {
157 DPMarker *CurrentDebugMarker = It->DbgMarker;
160 TestFailure(CurrentDebugMarker->
MarkedInstr == &*It,
161 "Debug Marker points to incorrect instruction?");
166 TestFailure(DPV.getMarker() == CurrentDebugMarker,
167 "Not pointing at correct next marker!");
172 "DebugProgramValues must not appear before PHI nodes in a block!");
184 for (
auto &Inst : *
this) {
188 dbgs() <<
"@ " << Inst.DbgMarker <<
" ";
189 Inst.DbgMarker->dump();
203 return F->getValueSymbolTable();
223 IsNewDbgInfoFormat(
false), Parent(nullptr) {
226 insertInto(NewParent, InsertBefore);
229 "Cannot insert block before another block with no function!");
237 assert(NewParent &&
"Expected a parent");
238 assert(!Parent &&
"Already has a parent");
245 NewParent->
insert(NewParent->
end(),
this);
269 assert(
getParent() ==
nullptr &&
"BasicBlock still linked into the program!");
271 for (
auto &Inst : *
this) {
274 Inst.DbgMarker->eraseFromParent();
279void BasicBlock::setParent(
Function *parent) {
281 InstList.setSymTabObject(&Parent, parent);
288 return !isa<DbgInfoIntrinsic>(
I) &&
289 !(SkipPseudoOp && isa<PseudoProbeInst>(
I));
298 return !isa<DbgInfoIntrinsic>(
I) &&
299 !(SkipPseudoOp && isa<PseudoProbeInst>(
I));
333 if (InstList.empty())
335 const ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
336 if (!RI || RI == &InstList.front())
348 if (
auto *BI = dyn_cast<BitCastInst>(Prev)) {
351 if (!Prev || RV != Prev)
356 if (
auto *CI = dyn_cast<CallInst>(Prev)) {
357 if (CI->isMustTailCall())
364 if (InstList.empty())
366 auto *RI = dyn_cast<ReturnInst>(&InstList.back());
367 if (!RI || RI == &InstList.front())
370 if (
auto *CI = dyn_cast_or_null<CallInst>(RI->getPrevNode()))
371 if (
Function *
F = CI->getCalledFunction())
372 if (
F->getIntrinsicID() == Intrinsic::experimental_deoptimize)
383 if (!Visited.
insert(Succ).second)
391 if (InstList.empty())
394 if (isa<LoadInst>(
I) || isa<StoreInst>(
I) || isa<CallBase>(
I))
401 if (!isa<PHINode>(
I))
418 if (isa<PHINode>(
I) || isa<DbgInfoIntrinsic>(
I))
421 if (SkipPseudoOp && isa<PseudoProbeInst>(
I))
432 if (isa<PHINode>(
I) || isa<DbgInfoIntrinsic>(
I))
435 if (
I.isLifetimeStartOrEnd())
438 if (SkipPseudoOp && isa<PseudoProbeInst>(
I))
452 if (InsertPt->isEHPad()) ++InsertPt;
456 InsertPt.setHeadBit(
true);
466 if (InsertPt->isEHPad())
471 while (InsertPt !=
End &&
472 (isa<AllocaInst>(*InsertPt) || isa<DbgInfoIntrinsic>(*InsertPt) ||
473 isa<PseudoProbeInst>(*InsertPt))) {
474 if (
const AllocaInst *AI = dyn_cast<AllocaInst>(&*InsertPt)) {
475 if (!AI->isStaticAlloca())
486 I.dropAllReferences();
491 if (PI ==
E)
return nullptr;
494 return (PI ==
E) ? ThePred :
nullptr ;
499 if (PI ==
E)
return nullptr;
502 for (;PI !=
E; ++PI) {
521 if (SI ==
E)
return nullptr;
524 return (SI ==
E) ? TheSucc :
nullptr ;
529 if (SI ==
E)
return nullptr;
532 for (;SI !=
E; ++SI) {
543 return make_range<phi_iterator>(
P,
nullptr);
547 bool KeepOneInputPHIs) {
550 "Pred is not a predecessor!");
556 unsigned NumPreds = cast<PHINode>(
front()).getNumIncomingValues();
558 Phi.removeIncomingValue(Pred, !KeepOneInputPHIs);
559 if (KeepOneInputPHIs)
568 if (
Value *PhiConstant = Phi.hasConstantValue()) {
569 Phi.replaceAllUsesWith(PhiConstant);
570 Phi.eraseFromParent();
577 if (isa<LandingPadInst>(FirstNonPHI))
594 assert(Term->getNumSuccessors() > 0);
598 return !Term->isSpecialTerminator();
603 assert(
F &&
"Block must have a parent function to use this API");
604 return this == &
F->getEntryBlock();
614 "Trying to get me to create degenerate basic block!");
623 New->splice(New->end(),
this,
I,
end());
634 New->replaceSuccessorsPhiUsesWith(
this, New);
640 "Can't use splitBasicBlockBefore on degenerate BB!");
642 "Trying to get me to create degenerate basic block!");
645 "cannot split on multi incoming phis");
652 New->splice(New->end(),
this,
begin(),
I);
678 return InstList.
erase(FromIt, ToIt);
685 PHINode *PN = dyn_cast<PHINode>(&
I);
700 Succ->replacePhiUsesWith(Old, New);
717 if (
MDNode *MDIrrLoopHeader =
719 MDString *MDName = cast<MDString>(MDIrrLoopHeader->getOperand(0));
721 auto *CI = mdconst::extract<ConstantInt>(MDIrrLoopHeader->getOperand(1));
722 return std::optional<uint64_t>(CI->getValue().getZExtValue());
729 while (isa<DbgInfoIntrinsic>(It))
740 BasicBlockBits Bits = getBasicBlockBits();
741 Bits.InstrOrderValid =
true;
742 setBasicBlockBits(Bits);
744 NumInstrRenumberings++;
768 if (!TrailingDPValues)
772 Term->DbgMarker->absorbDebugValues(*TrailingDPValues,
false);
801 bool InsertAtHead = Dest.getHeadBit();
802 bool ReadFromHead =
First.getHeadBit();
810 "Transferring trailing DPValues to another trailing position");
811 DPMarker *SrcTrailingDPValues = Src->getTrailingDPValues();
812 if (!SrcTrailingDPValues)
816 M->absorbDebugValues(*SrcTrailingDPValues, InsertAtHead);
818 Src->deleteTrailingDPValues();
825 if (!Src->empty() &&
First == Src->begin() && ReadFromHead)
826 Dest->DbgMarker->absorbDebugValues(*
First->DbgMarker, InsertAtHead);
868 DPMarker *MoreDanglingDPValues =
nullptr;
870 if (Dest ==
end() && !Dest.getHeadBit() && OurTrailingDPValues) {
873 if (!
First.getHeadBit() &&
First->hasDbgValues()) {
874 MoreDanglingDPValues = Src->getMarker(
First);
878 if (
First->hasDbgValues()) {
897 First.setHeadBit(
true);
901 spliceDebugInfoImpl(Dest, Src,
First,
Last);
905 if (!MoreDanglingDPValues)
920 bool InsertAtHead = Dest.getHeadBit();
921 bool ReadFromHead =
First.getHeadBit();
924 bool ReadFromTail = !
Last.getTailBit();
925 bool LastIsEnd = (
Last == Src->end());
997 if (ReadFromTail && Src->getMarker(
Last)) {
1003 Src->deleteTrailingDPValues();
1010 if (!ReadFromHead &&
First->hasDbgValues()) {
1031 }
else if (Dest ==
end() && !InsertAtHead) {
1038 if (TrailingDPValues) {
1050#ifdef EXPENSIVE_CHECKS
1052 auto FromBBEnd = Src->end();
1054 assert(It != FromBBEnd &&
"FromBeginIt not before FromEndIt!");
1060 spliceDebugInfoEmptyBlock(Dest, Src,
First,
Last);
1066 spliceDebugInfo(Dest, Src,
First,
Last);
1076 assert(
I->getParent() ==
this);
1078 iterator NextIt = std::next(
I->getIterator());
1090 assert(Where->getParent() ==
this);
1091 bool InsertAtHead = Where.getHeadBit();
1092 Where->DbgMarker->insertDPValue(DPV, InsertAtHead);
1096 return getMarker(std::next(
I->getIterator()));
1104 return It->DbgMarker;
1108 Instruction *
I, std::optional<DPValue::self_iterator> Pos) {
1148 DPMarker *DPM = (*Pos)->getMarker();
1150 if (Range.begin() == Range.end())
1168 "cached instruction ordering is incorrect");
cl::opt< bool > UseNewDbgInfoFormat("experimental-debuginfo-iterators", cl::desc("Enable communicating debuginfo positions " "through iterators, eliminating intrinsics"), cl::init(false))
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
llvm::cl::opt< bool > UseNewDbgInfoFormat
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
an instruction to allocate memory on the stack
LLVM Basic Block Representation.
BasicBlock::iterator erase(BasicBlock::iterator FromIt, BasicBlock::iterator ToIt)
Erases a range of instructions from FromIt to (not including) ToIt.
void replaceSuccessorsPhiUsesWith(BasicBlock *Old, BasicBlock *New)
Update all phi nodes in this basic block's successors to refer to basic block New instead of basic bl...
DPMarker * getMarker(InstListType::iterator It)
Return the DPMarker for the position given by It, so that DPValues can be inserted there.
iterator begin()
Instruction iterator methods.
iterator_range< const_phi_iterator > phis() const
Returns a range that iterates over the phis in the basic block.
const LandingPadInst * getLandingPadInst() const
Return the landingpad instruction associated with the landing pad.
const_iterator getFirstInsertionPt() const
Returns an iterator to the first instruction in this block that is suitable for inserting a non-PHI i...
void renumberInstructions()
Renumber instructions and mark the ordering as valid.
iterator_range< filter_iterator< BasicBlock::const_iterator, std::function< bool(const Instruction &)> > > instructionsWithoutDebug(bool SkipPseudoOp=true) const
Return a const iterator range over the instructions in the block, skipping any debug instructions.
BasicBlock * splitBasicBlockBefore(iterator I, const Twine &BBName="")
Split the basic block into two basic blocks at the specified instruction and insert the new basic blo...
bool hasAddressTaken() const
Returns true if there are any uses of this basic block other than direct branches,...
InstListType::const_iterator getFirstNonPHIIt() const
Iterator returning form of getFirstNonPHI.
void invalidateOrders()
Mark instruction ordering invalid. Done on every instruction insert.
friend void Instruction::removeFromParent()
void convertToNewDbgValues()
Convert variable location debugging information stored in dbg.value intrinsics into DPMarker / DPValu...
InstListType::const_iterator const_iterator
void setIsNewDbgInfoFormat(bool NewFlag)
Ensure the block is in "old" dbg.value format (NewFlag == false) or in the new format (NewFlag == tru...
const Instruction * getFirstNonPHI() const
Returns a pointer to the first instruction in this block that is not a PHINode instruction.
const Instruction & front() const
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
friend BasicBlock::iterator Instruction::eraseFromParent()
bool isEntryBlock() const
Return true if this is the entry block of the containing function.
ValueSymbolTable * getValueSymbolTable()
Returns a pointer to the symbol table if one exists.
void moveAfter(BasicBlock *MovePos)
Unlink this basic block from its current function and insert it right after MovePos in the function M...
bool hasNPredecessors(unsigned N) const
Return true if this block has exactly N predecessors.
BasicBlock * splitBasicBlock(iterator I, const Twine &BBName="", bool Before=false)
Split the basic block into two basic blocks at the specified instruction.
DPMarker * getTrailingDPValues()
Fetch the collection of DPValues that "trail" after the last instruction of this block,...
void convertFromNewDbgValues()
Convert variable location debugging information stored in DPMarkers and DPValues into the dbg....
const BasicBlock * getUniqueSuccessor() const
Return the successor of this block if it has a unique successor.
const BasicBlock * getSinglePredecessor() const
Return the predecessor of this block if it has a single predecessor block.
DPMarker * createMarker(Instruction *I)
Attach a DPMarker to the given instruction.
std::optional< uint64_t > getIrrLoopHeaderWeight() const
void dumpDbgValues() const
bool validateDbgValues(bool Assert=true, bool Msg=false, raw_ostream *OS=nullptr)
Validate any DPMarkers / DPValues attached to instructions in this block, and block-level stored data...
const CallInst * getTerminatingDeoptimizeCall() const
Returns the call instruction calling @llvm.experimental.deoptimize prior to the terminating return in...
void replacePhiUsesWith(BasicBlock *Old, BasicBlock *New)
Update all phi nodes in this basic block to refer to basic block New instead of basic block Old.
const Instruction * getFirstNonPHIOrDbgOrLifetime(bool SkipPseudoOp=true) const
Returns a pointer to the first instruction in this block that is not a PHINode, a debug intrinsic,...
const BasicBlock * getUniquePredecessor() const
Return the predecessor of this block if it has a unique predecessor block.
const BasicBlock * getSingleSuccessor() const
Return the successor of this block if it has a single successor.
const Function * getParent() const
Return the enclosing method, or null if none.
void setTrailingDPValues(DPMarker *M)
Record that the collection of DPValues in M "trails" after the last instruction of this block.
void validateInstrOrdering() const
Asserts that instruction order numbers are marked invalid, or that they are in ascending order.
const Instruction * getFirstNonPHIOrDbg(bool SkipPseudoOp=true) const
Returns a pointer to the first instruction in this block that is not a PHINode or a debug intrinsic,...
filter_iterator< BasicBlock::const_iterator, std::function< bool(constInstruction &)> >::difference_type sizeWithoutDebug() const
Return the size of the basic block ignoring debug instructions.
InstListType::iterator iterator
Instruction iterators...
LLVMContext & getContext() const
Get the context in which this basic block lives.
const_iterator getFirstNonPHIOrDbgOrAlloca() const
Returns an iterator to the first instruction in this block that is not a PHINode, a debug intrinsic,...
bool IsNewDbgInfoFormat
Flag recording whether or not this block stores debug-info in the form of intrinsic instructions (fal...
void dropAllReferences()
Cause all subinstructions to "let go" of all the references that said subinstructions are maintaining...
void reinsertInstInDPValues(Instruction *I, std::optional< DPValue::self_iterator > Pos)
In rare circumstances instructions can be speculatively removed from blocks, and then be re-inserted ...
void moveBefore(BasicBlock *MovePos)
Unlink this basic block from its current function and insert it into the function that MovePos lives ...
bool isLandingPad() const
Return true if this basic block is a landing pad.
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
bool canSplitPredecessors() const
void deleteTrailingDPValues()
Delete any trailing DPValues at the end of this block, see setTrailingDPValues.
const CallInst * getTerminatingMustTailCall() const
Returns the call instruction marked 'musttail' prior to the terminating return instruction of this ba...
friend BasicBlock::iterator Instruction::insertInto(BasicBlock *BB, BasicBlock::iterator It)
void insertDPValueAfter(DPValue *DPV, Instruction *I)
Insert a DPValue into a block at the position given by I.
bool isLegalToHoistInto() const
Return true if it is legal to hoist instructions into this block.
DPMarker * getNextMarker(Instruction *I)
Return the DPMarker for the position that comes after I.
bool hasNPredecessorsOrMore(unsigned N) const
Return true if this block has N predecessors or more.
bool isInstrOrderValid() const
Returns true if the Order field of child Instructions is valid.
const CallInst * getPostdominatingDeoptimizeCall() const
Returns the call instruction calling @llvm.experimental.deoptimize that is present either in current ...
const Instruction * getFirstMayFaultInst() const
Returns the first potential AsynchEH faulty instruction currently it checks for loads/stores (which m...
void splice(BasicBlock::iterator ToIt, BasicBlock *FromBB)
Transfer all instructions from FromBB to this basic block at ToIt.
void insertDPValueBefore(DPValue *DPV, InstListType::iterator Here)
Insert a DPValue into a block at the position given by Here.
void flushTerminatorDbgValues()
Eject any debug-info trailing at the end of a block.
const Module * getModule() const
Return the module owning the function this basic block belongs to, or nullptr if the function does no...
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs=false)
Update PHI nodes in this BasicBlock before removal of predecessor Pred.
The address of a basic block.
Conditional or Unconditional Branch instruction.
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
This class represents a function call, abstracting a target machine's calling convention.
static Constant * getIntToPtr(Constant *C, Type *Ty, bool OnlyIfReduced=false)
static Constant * get(Type *Ty, uint64_t V, bool IsSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
This is an important base class in LLVM.
void destroyConstant()
Called if some element of this constant is no longer valid.
Per-instruction record of debug-info.
iterator_range< simple_ilist< DPValue >::iterator > getDbgValueRange()
Produce a range over all the DPValues in this Marker.
simple_ilist< DPValue > StoredDPValues
List of DPValues, each recording a single variable assignment, the equivalent of a dbg....
Instruction * MarkedInstr
Link back to the Instruction that owns this marker.
void absorbDebugValues(DPMarker &Src, bool InsertAtHead)
Transfer any DPValues from Src into this DPMarker.
void insertDPValue(DPValue *New, bool InsertAtHead)
Insert a DPValue into this DPMarker, at the end of the list.
Record of a variable value-assignment, aka a non instruction representation of the dbg....
This represents the llvm.dbg.value instruction.
void splice(Function::iterator ToIt, Function *FromF)
Transfer all blocks from FromF to this function at ToIt.
bool IsNewDbgInfoFormat
Is this function using intrinsics to record the position of debugging information,...
Function::iterator insert(Function::iterator Position, BasicBlock *BB)
Insert BB in the basic block list at Position.
Module * getParent()
Get the module that this global value is contained inside of...
bool isEHPad() const
Return true if the instruction is a variety of EH-block.
void replaceSuccessorWith(BasicBlock *OldBB, BasicBlock *NewBB)
Replace specified successor OldBB to point at the provided block.
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
bool comesBefore(const Instruction *Other) const
Given an instruction Other in the same basic block as this instruction, return true if this instructi...
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
void setTrailingDPValues(BasicBlock *B, DPMarker *M)
void deleteTrailingDPValues(BasicBlock *B)
DPMarker * getTrailingDPValues(BasicBlock *B)
This is an important class for using LLVM in a threaded context.
LLVMContextImpl *const pImpl
The landingpad instruction holds all of the information necessary to generate correct exception handl...
StringRef getString() const
A Module instance is used to store all the information related to an LLVM module.
void replaceIncomingBlockWith(const BasicBlock *Old, BasicBlock *New)
Replace every incoming basic block Old to basic block New.
Return a value (possibly void), from a function.
Value * getReturnValue() const
Convenience accessor. Returns null if there is no return value.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
void push_back(const T &Elt)
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
bool equals(StringRef RHS) const
equals - Check for string equality, this is more efficient than compare() when the relative ordering ...
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
The instances of the Type class are immutable: once they are created, they are never changed.
LLVMContext & getContext() const
Return the LLVMContext in which this type was uniqued.
static IntegerType * getInt32Ty(LLVMContext &C)
Value * getOperand(unsigned i) const
This class provides a symbol table of name/value pairs.
LLVM Value Representation.
Type * getType() const
All values are typed, get the type of this value.
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
bool hasNUsesOrMore(unsigned N) const
Return true if this value has N uses or more.
Specialization of filter_iterator_base for forward iteration only.
self_iterator getIterator()
BasicBlock * getNextNode()
Get the next node, or nullptr for the list tail.
void splice(iterator where, iplist_impl &L2)
base_list_type::iterator iterator
iterator erase(iterator where)
pointer remove(iterator &IT)
iterator insert(iterator where, pointer New)
A range adaptor for a pair of iterators.
This class implements an extremely fast bulk output stream that can only output to a stream.
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
@ C
The default llvm calling convention, compatible with C.
initializer< Ty > init(const Ty &Val)
This is an optimization pass for GlobalISel generic memory operations.
Interval::succ_iterator succ_end(Interval *I)
auto successors(const MachineBasicBlock *BB)
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
iterator_range< early_inc_iterator_impl< detail::IterOfRange< RangeT > > > make_early_inc_range(RangeT &&Range)
Make a range that does early increment to allow mutation of the underlying range without disrupting i...
bool hasNItemsOrMore(IterTy &&Begin, IterTy &&End, unsigned N, Pred &&ShouldBeCounted=[](const decltype(*std::declval< IterTy >()) &) { return true;}, std::enable_if_t< !std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< std::remove_reference_t< decltype(Begin)> >::iterator_category >::value, void > *=nullptr)
Return true if the sequence [Begin, End) has N or more items.
Interval::pred_iterator pred_end(Interval *I)
BasicBlock::iterator skipDebugIntrinsics(BasicBlock::iterator It)
Advance It while it points to a debug instruction and return the result.
bool hasNItems(IterTy &&Begin, IterTy &&End, unsigned N, Pred &&ShouldBeCounted=[](const decltype(*std::declval< IterTy >()) &) { return true;}, std::enable_if_t< !std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< std::remove_reference_t< decltype(Begin)> >::iterator_category >::value, void > *=nullptr)
Return true if the sequence [Begin, End) has exactly N items.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
iterator_range< filter_iterator< detail::IterOfRange< RangeT >, PredicateT > > make_filter_range(RangeT &&Range, PredicateT Pred)
Convenience function that takes a range of elements and a predicate, and return a new filter_iterator...
raw_fd_ostream & errs()
This returns a reference to a raw_ostream for standard error.
@ First
Helpers to iterate all locations in the MemoryEffectsBase class.
void invalidateParentIListOrdering(ParentClass *Parent)
Notify basic blocks when an instruction is inserted.
auto predecessors(const MachineBasicBlock *BB)
bool is_contained(R &&Range, const E &Element)
Returns true if Element is found in Range.
Option to add extra bits to the ilist_iterator.