llvm/IR/DebugProgramInstruction.h

//===-- llvm/DebugProgramInstruction.h - Stream of debug info ---*- 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
//
//===----------------------------------------------------------------------===//
//
// Data structures for storing variable assignment information in LLVM. In the
// dbg.value design, a dbg.value intrinsic specifies the position in a block
// a source variable take on an LLVM Value:
//
//    %foo = add i32 1, %0
//    dbg.value(metadata i32 %foo, ...)
//    %bar = void call @ext(%foo);
//
// and all information is stored in the Value / Metadata hierachy defined
// elsewhere in LLVM. In the "DbgRecord" design, each instruction /may/ have a
// connection with a DPMarker, which identifies a position immediately before
// the instruction, and each DPMarker /may/ then have connections to DbgRecords
// which record the variable assignment information. To illustrate:
//
//    %foo = add i32 1, %0
//       ; foo->DbgMarker == nullptr
//       ;; There are no variable assignments / debug records "in front" of
//       ;; the instruction for %foo, therefore it has no DbgMarker.
//    %bar = void call @ext(%foo)
//       ; bar->DbgMarker = {
//       ;   StoredDbgRecords = {
//       ;     DPValue(metadata i32 %foo, ...)
//       ;   }
//       ; }
//       ;; There is a debug-info record in front of the %bar instruction,
//       ;; thus it points at a DPMarker object. That DPMarker contains a
//       ;; DPValue in it's ilist, storing the equivalent information to the
//       ;; dbg.value above: the Value, DILocalVariable, etc.
//
// This structure separates the two concerns of the position of the debug-info
// in the function, and the Value that it refers to. It also creates a new
// "place" in-between the Value / Metadata hierachy where we can customise
// storage and allocation techniques to better suite debug-info workloads.
// NB: as of the initial prototype, none of that has actually been attempted
// yet.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_DEBUGPROGRAMINSTRUCTION_H
#define LLVM_IR_DEBUGPROGRAMINSTRUCTION_H

#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/ADT/iterator.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/SymbolTableListTraits.h"
#include "llvm/Support/Casting.h"

namespace llvm {

class Instruction;
class BasicBlock;
class MDNode;
class Module;
class DbgVariableIntrinsic;
class DbgInfoIntrinsic;
class DbgLabelInst;
class DIAssignID;
class DPMarker;
class DPValue;
class raw_ostream;

/// A typed tracking MDNode reference that does not require a definition for its
/// parameter type. Necessary to avoid including DebugInfoMetadata.h, which has
/// a significant impact on compile times if included in this file.
template <typename T> class DbgRecordParamRef {
  TrackingMDNodeRef Ref;

public:
public:
  DbgRecordParamRef() = default;

  /// Construct from the templated type.
  DbgRecordParamRef(const T *Param);

  /// Construct from an \a MDNode.
  ///
  /// Note: if \c Param does not have the template type, a verifier check will
  /// fail, and accessors will crash.  However, construction from other nodes
  /// is supported in order to handle forward references when reading textual
  /// IR.
  explicit DbgRecordParamRef(const MDNode *Param);

  /// Get the underlying type.
  ///
  /// \pre !*this or \c isa<T>(getAsMDNode()).
  /// @{
  T *get() const;
  operator T *() const { return get(); }
  T *operator->() const { return get(); }
  T &operator*() const { return *get(); }
  /// @}

  /// Check for null.
  ///
  /// Check for null in a way that is safe with broken debug info.
  explicit operator bool() const { return Ref; }

  /// Return \c this as a \a MDNode.
  MDNode *getAsMDNode() const { return Ref; }

  bool operator==(const DbgRecordParamRef &Other) const {
    return Ref == Other.Ref;
  }
  bool operator!=(const DbgRecordParamRef &Other) const {
    return Ref != Other.Ref;
  }
};

/// Base class for non-instruction debug metadata records that have positions
/// within IR. Features various methods copied across from the Instruction
/// class to aid ease-of-use. DbgRecords should always be linked into a
/// DPMarker's StoredDbgRecords list. The marker connects a DbgRecord back to
/// it's position in the BasicBlock.
///
/// We need a discriminator for dyn/isa casts. In order to avoid paying for a
/// vtable for "virtual" functions too, subclasses must add a new discriminator
/// value (RecordKind) and cases to a few functions in the base class:
///   deleteRecord
///   clone
///   isIdenticalToWhenDefined
///   both print methods
///   createDebugIntrinsic
class DbgRecord : public ilist_node<DbgRecord> {
public:
  /// Marker that this DbgRecord is linked into.
  DPMarker *Marker = nullptr;
  /// Subclass discriminator.
  enum Kind : uint8_t { ValueKind, LabelKind };

protected:
  DebugLoc DbgLoc;
  Kind RecordKind; ///< Subclass discriminator.

public:
  DbgRecord(Kind RecordKind, DebugLoc DL)
      : DbgLoc(DL), RecordKind(RecordKind) {}

  /// Methods that dispatch to subclass implementations. These need to be
  /// manually updated when a new subclass is added.
  ///@{
  void deleteRecord();
  DbgRecord *clone() const;
  void print(raw_ostream &O, bool IsForDebug = false) const;
  void print(raw_ostream &O, ModuleSlotTracker &MST, bool IsForDebug) const;
  bool isIdenticalToWhenDefined(const DbgRecord &R) const;
  /// Convert this DbgRecord back into an appropriate llvm.dbg.* intrinsic.
  /// \p InsertBefore Optional position to insert this intrinsic.
  /// \returns A new llvm.dbg.* intrinsic representiung this DbgRecord.
  DbgInfoIntrinsic *createDebugIntrinsic(Module *M,
                                         Instruction *InsertBefore) const;
  ///@}

  /// Same as isIdenticalToWhenDefined but checks DebugLoc too.
  bool isEquivalentTo(const DbgRecord &R) const;

  Kind getRecordKind() const { return RecordKind; }

  void setMarker(DPMarker *M) { Marker = M; }

  DPMarker *getMarker() { return Marker; }
  const DPMarker *getMarker() const { return Marker; }

  BasicBlock *getBlock();
  const BasicBlock *getBlock() const;

  Function *getFunction();
  const Function *getFunction() const;

  Module *getModule();
  const Module *getModule() const;

  LLVMContext &getContext();
  const LLVMContext &getContext() const;

  const Instruction *getInstruction() const;
  const BasicBlock *getParent() const;
  BasicBlock *getParent();

  void removeFromParent();
  void eraseFromParent();

  DbgRecord *getNextNode() { return &*std::next(getIterator()); }
  DbgRecord *getPrevNode() { return &*std::prev(getIterator()); }
  void insertBefore(DbgRecord *InsertBefore);
  void insertAfter(DbgRecord *InsertAfter);
  void moveBefore(DbgRecord *MoveBefore);
  void moveAfter(DbgRecord *MoveAfter);

  DebugLoc getDebugLoc() const { return DbgLoc; }
  void setDebugLoc(DebugLoc Loc) { DbgLoc = std::move(Loc); }

  void dump() const;

  using self_iterator = simple_ilist<DbgRecord>::iterator;
  using const_self_iterator = simple_ilist<DbgRecord>::const_iterator;

protected:
  /// Similarly to Value, we avoid paying the cost of a vtable
  /// by protecting the dtor and having deleteRecord dispatch
  /// cleanup.
  /// Use deleteRecord to delete a generic record.
  ~DbgRecord() = default;
};

inline raw_ostream &operator<<(raw_ostream &OS, const DbgRecord &R) {
  R.print(OS);
  return OS;
}

/// Records a position in IR for a source label (DILabel). Corresponds to the
/// llvm.dbg.label intrinsic.
/// FIXME: Rename DbgLabelRecord when DPValue is renamed to DbgVariableRecord.
class DPLabel : public DbgRecord {
  DbgRecordParamRef<DILabel> Label;

  /// This constructor intentionally left private, so that it is only called via
  /// "createUnresolvedDPLabel", which clearly expresses that it is for parsing
  /// only.
  DPLabel(MDNode *Label, MDNode *DL);

public:
  DPLabel(DILabel *Label, DebugLoc DL);

  /// For use during parsing; creates a DPLabel from as-of-yet unresolved
  /// MDNodes. Trying to access the resulting DPLabel's fields before they are
  /// resolved, or if they resolve to the wrong type, will result in a crash.
  static DPLabel *createUnresolvedDPLabel(MDNode *Label, MDNode *DL);

  DPLabel *clone() const;
  void print(raw_ostream &O, bool IsForDebug = false) const;
  void print(raw_ostream &ROS, ModuleSlotTracker &MST, bool IsForDebug) const;
  DbgLabelInst *createDebugIntrinsic(Module *M,
                                     Instruction *InsertBefore) const;

  void setLabel(DILabel *NewLabel) { Label = NewLabel; }
  DILabel *getLabel() const { return Label.get(); }
  MDNode *getRawLabel() const { return Label.getAsMDNode(); };

  /// Support type inquiry through isa, cast, and dyn_cast.
  static bool classof(const DbgRecord *E) {
    return E->getRecordKind() == LabelKind;
  }
};

/// Record of a variable value-assignment, aka a non instruction representation
/// of the dbg.value intrinsic.
///
/// This class inherits from DebugValueUser to allow LLVM's metadata facilities
/// to update our references to metadata beneath our feet.
class DPValue : public DbgRecord, protected DebugValueUser {
  friend class DebugValueUser;

public:
  enum class LocationType : uint8_t {
    Declare,
    Value,
    Assign,

    End, ///< Marks the end of the concrete types.
    Any, ///< To indicate all LocationTypes in searches.
  };
  /// Classification of the debug-info record that this DPValue represents.
  /// Essentially, "is this a dbg.value or dbg.declare?". dbg.declares are not
  /// currently supported, but it would be trivial to do so.
  /// FIXME: We could use spare padding bits from DbgRecord for this.
  LocationType Type;

  // NB: there is no explicit "Value" field in this class, it's effectively the
  // DebugValueUser superclass instead. The referred to Value can either be a
  // ValueAsMetadata or a DIArgList.

  DbgRecordParamRef<DILocalVariable> Variable;
  DbgRecordParamRef<DIExpression> Expression;
  DbgRecordParamRef<DIExpression> AddressExpression;

public:
  /// Create a new DPValue representing the intrinsic \p DVI, for example the
  /// assignment represented by a dbg.value.
  DPValue(const DbgVariableIntrinsic *DVI);
  DPValue(const DPValue &DPV);
  /// Directly construct a new DPValue representing a dbg.value intrinsic
  /// assigning \p Location to the DV / Expr / DI variable.
  DPValue(Metadata *Location, DILocalVariable *DV, DIExpression *Expr,
          const DILocation *DI, LocationType Type = LocationType::Value);
  DPValue(Metadata *Value, DILocalVariable *Variable, DIExpression *Expression,
          DIAssignID *AssignID, Metadata *Address,
          DIExpression *AddressExpression, const DILocation *DI);

private:
  /// Private constructor for creating new instances during parsing only. Only
  /// called through `createUnresolvedDPValue` below, which makes clear that
  /// this is used for parsing only, and will later return a subclass depending
  /// on which Type is passed.
  DPValue(LocationType Type, Metadata *Val, MDNode *Variable,
          MDNode *Expression, MDNode *AssignID, Metadata *Address,
          MDNode *AddressExpression, MDNode *DI);

public:
  /// Used to create DPValues during parsing, where some metadata references may
  /// still be unresolved. Although for some fields a generic `Metadata*`
  /// argument is accepted for forward type-references, the verifier and
  /// accessors will reject incorrect types later on. The function is used for
  /// all types of DPValues for simplicity while parsing, but asserts if any
  /// necessary fields are empty or unused fields are not empty, i.e. if the
  /// #dbg_assign fields are used for a non-dbg-assign type.
  static DPValue *createUnresolvedDPValue(LocationType Type, Metadata *Val,
                                          MDNode *Variable, MDNode *Expression,
                                          MDNode *AssignID, Metadata *Address,
                                          MDNode *AddressExpression,
                                          MDNode *DI);

  static DPValue *createDPVAssign(Value *Val, DILocalVariable *Variable,
                                  DIExpression *Expression,
                                  DIAssignID *AssignID, Value *Address,
                                  DIExpression *AddressExpression,
                                  const DILocation *DI);
  static DPValue *createLinkedDPVAssign(Instruction *LinkedInstr, Value *Val,
                                        DILocalVariable *Variable,
                                        DIExpression *Expression,
                                        Value *Address,
                                        DIExpression *AddressExpression,
                                        const DILocation *DI);

  static DPValue *createDPValue(Value *Location, DILocalVariable *DV,
                                DIExpression *Expr, const DILocation *DI);
  static DPValue *createDPValue(Value *Location, DILocalVariable *DV,
                                DIExpression *Expr, const DILocation *DI,
                                DPValue &InsertBefore);
  static DPValue *createDPVDeclare(Value *Address, DILocalVariable *DV,
                                   DIExpression *Expr, const DILocation *DI);
  static DPValue *createDPVDeclare(Value *Address, DILocalVariable *DV,
                                   DIExpression *Expr, const DILocation *DI,
                                   DPValue &InsertBefore);

  /// Iterator for ValueAsMetadata that internally uses direct pointer iteration
  /// over either a ValueAsMetadata* or a ValueAsMetadata**, dereferencing to the
  /// ValueAsMetadata .
  class location_op_iterator
      : public iterator_facade_base<location_op_iterator,
                                    std::bidirectional_iterator_tag, Value *> {
    PointerUnion<ValueAsMetadata *, ValueAsMetadata **> I;

  public:
    location_op_iterator(ValueAsMetadata *SingleIter) : I(SingleIter) {}
    location_op_iterator(ValueAsMetadata **MultiIter) : I(MultiIter) {}

    location_op_iterator(const location_op_iterator &R) : I(R.I) {}
    location_op_iterator &operator=(const location_op_iterator &R) {
      I = R.I;
      return *this;
    }
    bool operator==(const location_op_iterator &RHS) const {
      return I == RHS.I;
    }
    const Value *operator*() const {
      ValueAsMetadata *VAM = I.is<ValueAsMetadata *>()
                                 ? I.get<ValueAsMetadata *>()
                                 : *I.get<ValueAsMetadata **>();
      return VAM->getValue();
    };
    Value *operator*() {
      ValueAsMetadata *VAM = I.is<ValueAsMetadata *>()
                                 ? I.get<ValueAsMetadata *>()
                                 : *I.get<ValueAsMetadata **>();
      return VAM->getValue();
    }
    location_op_iterator &operator++() {
      if (I.is<ValueAsMetadata *>())
        I = I.get<ValueAsMetadata *>() + 1;
      else
        I = I.get<ValueAsMetadata **>() + 1;
      return *this;
    }
    location_op_iterator &operator--() {
      if (I.is<ValueAsMetadata *>())
        I = I.get<ValueAsMetadata *>() - 1;
      else
        I = I.get<ValueAsMetadata **>() - 1;
      return *this;
    }
  };

  bool isDbgDeclare() { return Type == LocationType::Declare; }
  bool isDbgValue() { return Type == LocationType::Value; }

  /// Get the locations corresponding to the variable referenced by the debug
  /// info intrinsic.  Depending on the intrinsic, this could be the
  /// variable's value or its address.
  iterator_range<location_op_iterator> location_ops() const;

  Value *getVariableLocationOp(unsigned OpIdx) const;

  void replaceVariableLocationOp(Value *OldValue, Value *NewValue,
                                 bool AllowEmpty = false);
  void replaceVariableLocationOp(unsigned OpIdx, Value *NewValue);
  /// Adding a new location operand will always result in this intrinsic using
  /// an ArgList, and must always be accompanied by a new expression that uses
  /// the new operand.
  void addVariableLocationOps(ArrayRef<Value *> NewValues,
                              DIExpression *NewExpr);

  unsigned getNumVariableLocationOps() const;

  bool hasArgList() const { return isa<DIArgList>(getRawLocation()); }
  /// Returns true if this DPValue has no empty MDNodes in its location list.
  bool hasValidLocation() const { return getVariableLocationOp(0) != nullptr; }

  /// Does this describe the address of a local variable. True for dbg.addr
  /// and dbg.declare, but not dbg.value, which describes its value.
  bool isAddressOfVariable() const { return Type == LocationType::Declare; }
  LocationType getType() const { return Type; }

  void setKillLocation();
  bool isKillLocation() const;

  void setVariable(DILocalVariable *NewVar) { Variable = NewVar; }
  DILocalVariable *getVariable() const { return Variable.get(); };
  MDNode *getRawVariable() const { return Variable.getAsMDNode(); }

  void setExpression(DIExpression *NewExpr) { Expression = NewExpr; }
  DIExpression *getExpression() const { return Expression.get(); }
  MDNode *getRawExpression() const { return Expression.getAsMDNode(); }

  /// Returns the metadata operand for the first location description. i.e.,
  /// dbg intrinsic dbg.value,declare operand and dbg.assign 1st location
  /// operand (the "value componenet"). Note the operand (singular) may be
  /// a DIArgList which is a list of values.
  Metadata *getRawLocation() const { return DebugValues[0]; }

  Value *getValue(unsigned OpIdx = 0) const {
    return getVariableLocationOp(OpIdx);
  }

  /// Use of this should generally be avoided; instead,
  /// replaceVariableLocationOp and addVariableLocationOps should be used where
  /// possible to avoid creating invalid state.
  void setRawLocation(Metadata *NewLocation) {
    assert(
        (isa<ValueAsMetadata>(NewLocation) || isa<DIArgList>(NewLocation) ||
         isa<MDNode>(NewLocation)) &&
        "Location for a DPValue must be either ValueAsMetadata or DIArgList");
    resetDebugValue(0, NewLocation);
  }

  /// Get the size (in bits) of the variable, or fragment of the variable that
  /// is described.
  std::optional<uint64_t> getFragmentSizeInBits() const;

  bool isEquivalentTo(const DPValue &Other) const {
    return DbgLoc == Other.DbgLoc && isIdenticalToWhenDefined(Other);
  }
  // Matches the definition of the Instruction version, equivalent to above but
  // without checking DbgLoc.
  bool isIdenticalToWhenDefined(const DPValue &Other) const {
    return std::tie(Type, DebugValues, Variable, Expression,
                    AddressExpression) ==
           std::tie(Other.Type, Other.DebugValues, Other.Variable,
                    Other.Expression, Other.AddressExpression);
  }

  /// @name DbgAssign Methods
  /// @{
  bool isDbgAssign() const { return getType() == LocationType::Assign; }

  Value *getAddress() const;
  Metadata *getRawAddress() const {
    return isDbgAssign() ? DebugValues[1] : DebugValues[0];
  }
  Metadata *getRawAssignID() const { return DebugValues[2]; }
  DIAssignID *getAssignID() const;
  DIExpression *getAddressExpression() const { return AddressExpression.get(); }
  MDNode *getRawAddressExpression() const {
    return AddressExpression.getAsMDNode();
  }
  void setAddressExpression(DIExpression *NewExpr) {
    AddressExpression = NewExpr;
  }
  void setAssignId(DIAssignID *New);
  void setAddress(Value *V) { resetDebugValue(1, ValueAsMetadata::get(V)); }
  /// Kill the address component.
  void setKillAddress();
  /// Check whether this kills the address component. This doesn't take into
  /// account the position of the intrinsic, therefore a returned value of false
  /// does not guarentee the address is a valid location for the variable at the
  /// intrinsic's position in IR.
  bool isKillAddress() const;

  /// @}

  DPValue *clone() const;
  /// Convert this DPValue back into a dbg.value intrinsic.
  /// \p InsertBefore Optional position to insert this intrinsic.
  /// \returns A new dbg.value intrinsic representiung this DPValue.
  DbgVariableIntrinsic *createDebugIntrinsic(Module *M,
                                             Instruction *InsertBefore) const;

  /// Handle changes to the location of the Value(s) that we refer to happening
  /// "under our feet".
  void handleChangedLocation(Metadata *NewLocation);

  void print(raw_ostream &O, bool IsForDebug = false) const;
  void print(raw_ostream &ROS, ModuleSlotTracker &MST, bool IsForDebug) const;

  /// Filter the DbgRecord range to DPValue types only and downcast.
  static inline auto
  filter(iterator_range<simple_ilist<DbgRecord>::iterator> R) {
    return map_range(
        make_filter_range(R, [](DbgRecord &E) { return isa<DPValue>(E); }),
        [](DbgRecord &E) { return std::ref(cast<DPValue>(E)); });
  }

  /// Support type inquiry through isa, cast, and dyn_cast.
  static bool classof(const DbgRecord *E) {
    return E->getRecordKind() == ValueKind;
  }
};

/// Per-instruction record of debug-info. If an Instruction is the position of
/// some debugging information, it points at a DPMarker storing that info. Each
/// marker points back at the instruction that owns it. Various utilities are
/// provided for manipulating the DbgRecords contained within this marker.
///
/// This class has a rough surface area, because it's needed to preserve the
/// one arefact that we can't yet eliminate from the intrinsic / dbg.value
/// debug-info design: the order of records is significant, and duplicates can
/// exist. Thus, if one has a run of debug-info records such as:
///    dbg.value(...
///    %foo = barinst
///    dbg.value(...
/// and remove barinst, then the dbg.values must be preserved in the correct
/// order. Hence, the use of iterators to select positions to insert things
/// into, or the occasional InsertAtHead parameter indicating that new records
/// should go at the start of the list.
///
/// There are only five or six places in LLVM that truly rely on this ordering,
/// which we can improve in the future. Additionally, many improvements in the
/// way that debug-info is stored can be achieved in this class, at a future
/// date.
class DPMarker {
public:
  DPMarker() {}
  /// Link back to the Instruction that owns this marker. Can be null during
  /// operations that move a marker from one instruction to another.
  Instruction *MarkedInstr = nullptr;

  /// List of DbgRecords, the non-instruction equivalent of llvm.dbg.*
  /// intrinsics. There is a one-to-one relationship between each debug
  /// intrinsic in a block and each DbgRecord once the representation has been
  /// converted, and the ordering is meaningful in the same way.
  simple_ilist<DbgRecord> StoredDbgRecords;
  bool empty() const { return StoredDbgRecords.empty(); }

  const BasicBlock *getParent() const;
  BasicBlock *getParent();

  /// Handle the removal of a marker: the position of debug-info has gone away,
  /// but the stored debug records should not. Drop them onto the next
  /// instruction, or otherwise work out what to do with them.
  void removeMarker();
  void dump() const;

  void removeFromParent();
  void eraseFromParent();

  /// Implement operator<< on DPMarker.
  void print(raw_ostream &O, bool IsForDebug = false) const;
  void print(raw_ostream &ROS, ModuleSlotTracker &MST, bool IsForDebug) const;

  /// Produce a range over all the DbgRecords in this Marker.
  iterator_range<simple_ilist<DbgRecord>::iterator> getDbgRecordRange();
  iterator_range<simple_ilist<DbgRecord>::const_iterator>
  getDbgRecordRange() const;
  /// Transfer any DbgRecords from \p Src into this DPMarker. If \p InsertAtHead
  /// is true, place them before existing DbgRecords, otherwise afterwards.
  void absorbDebugValues(DPMarker &Src, bool InsertAtHead);
  /// Transfer the DbgRecords in \p Range from \p Src into this DPMarker. If
  /// \p InsertAtHead is true, place them before existing DbgRecords, otherwise
  // afterwards.
  void absorbDebugValues(iterator_range<DbgRecord::self_iterator> Range,
                         DPMarker &Src, bool InsertAtHead);
  /// Insert a DbgRecord into this DPMarker, at the end of the list. If
  /// \p InsertAtHead is true, at the start.
  void insertDbgRecord(DbgRecord *New, bool InsertAtHead);
  /// Insert a DbgRecord prior to a DbgRecord contained within this marker.
  void insertDbgRecord(DbgRecord *New, DbgRecord *InsertBefore);
  /// Insert a DbgRecord after a DbgRecord contained within this marker.
  void insertDbgRecordAfter(DbgRecord *New, DbgRecord *InsertAfter);
  /// Clone all DPMarkers from \p From into this marker. There are numerous
  /// options to customise the source/destination, due to gnarliness, see class
  /// comment.
  /// \p FromHere If non-null, copy from FromHere to the end of From's
  /// DbgRecords
  /// \p InsertAtHead Place the cloned DbgRecords at the start of
  /// StoredDbgRecords
  /// \returns Range over all the newly cloned DbgRecords
  iterator_range<simple_ilist<DbgRecord>::iterator>
  cloneDebugInfoFrom(DPMarker *From,
                     std::optional<simple_ilist<DbgRecord>::iterator> FromHere,
                     bool InsertAtHead = false);
  /// Erase all DbgRecords in this DPMarker.
  void dropDbgRecords();
  /// Erase a single DbgRecord from this marker. In an ideal future, we would
  /// never erase an assignment in this way, but it's the equivalent to
  /// erasing a debug intrinsic from a block.
  void dropOneDbgRecord(DbgRecord *DR);

  /// We generally act like all llvm Instructions have a range of DbgRecords
  /// attached to them, but in reality sometimes we don't allocate the DPMarker
  /// to save time and memory, but still have to return ranges of DbgRecords.
  /// When we need to describe such an unallocated DbgRecord range, use this
  /// static markers range instead. This will bite us if someone tries to insert
  /// a DbgRecord in that range, but they should be using the Official (TM) API
  /// for that.
  static DPMarker EmptyDPMarker;
  static iterator_range<simple_ilist<DbgRecord>::iterator>
  getEmptyDbgRecordRange() {
    return make_range(EmptyDPMarker.StoredDbgRecords.end(),
                      EmptyDPMarker.StoredDbgRecords.end());
  }
};

inline raw_ostream &operator<<(raw_ostream &OS, const DPMarker &Marker) {
  Marker.print(OS);
  return OS;
}

/// Inline helper to return a range of DbgRecords attached to a marker. It needs
/// to be inlined as it's frequently called, but also come after the declaration
/// of DPMarker. Thus: it's pre-declared by users like Instruction, then an
/// inlineable body defined here.
inline iterator_range<simple_ilist<DbgRecord>::iterator>
getDbgRecordRange(DPMarker *DbgMarker) {
  if (!DbgMarker)
    return DPMarker::getEmptyDbgRecordRange();
  return DbgMarker->getDbgRecordRange();
}

} // namespace llvm

#endif // LLVM_IR_DEBUGPROGRAMINSTRUCTION_H