text: //===-- llvm/CodeGen/LiveInterval.h - Interval representation ---*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the LiveRange and LiveInterval classes.  Given some
  // numbering of each the machine instructions an interval [i, j) is said to be a
  // live range for register v if there is no instruction with number j' >= j
  // such that v is live at j' and there is no instruction with number i' < i such
  // that v is live at i'. In this implementation ranges can have holes,
  // i.e. a range might look like [1,20), [50,65), [1000,1001).  Each
  // individual segment is represented as an instance of LiveRange::Segment,
  // and the whole range is represented as an instance of LiveRange.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_CODEGEN_LIVEINTERVAL_H
  #define LLVM_CODEGEN_LIVEINTERVAL_H
  
  #include "llvm/ADT/IntEqClasses.h"
  #include "llvm/CodeGen/SlotIndexes.h"
  #include "llvm/Support/Allocator.h"
  #include "llvm/Target/TargetRegisterInfo.h"
  #include <cassert>
  #include <climits>
  #include <set>
  
  namespace llvm {
    class CoalescerPair;
    class LiveIntervals;
    class MachineInstr;
    class MachineRegisterInfo;
    class TargetRegisterInfo;
    class raw_ostream;
    template <typename T, unsigned Small> class SmallPtrSet;
  
    /// VNInfo - Value Number Information.
    /// This class holds information about a machine level values, including
    /// definition and use points.
    ///
    class VNInfo {
    public:
      typedef BumpPtrAllocator Allocator;
  
      /// The ID number of this value.
      unsigned id;
  
      /// The index of the defining instruction.
      SlotIndex def;
  
      /// VNInfo constructor.
      VNInfo(unsigned i, SlotIndex d)
        : id(i), def(d)
      { }
  
      /// VNInfo constructor, copies values from orig, except for the value number.
      VNInfo(unsigned i, const VNInfo &orig)
        : id(i), def(orig.def)
      { }
  
      /// Copy from the parameter into this VNInfo.
      void copyFrom(VNInfo &src) {
        def = src.def;
      }
  
      /// Returns true if this value is defined by a PHI instruction (or was,
      /// PHI instructions may have been eliminated).
      /// PHI-defs begin at a block boundary, all other defs begin at register or
      /// EC slots.
      bool isPHIDef() const { return def.isBlock(); }
  
      /// Returns true if this value is unused.
      bool isUnused() const { return !def.isValid(); }
  
      /// Mark this value as unused.
      void markUnused() { def = SlotIndex(); }
    };
  
    /// Result of a LiveRange query. This class hides the implementation details
    /// of live ranges, and it should be used as the primary interface for
    /// examining live ranges around instructions.
    class LiveQueryResult {
      VNInfo *const EarlyVal;
      VNInfo *const LateVal;
      const SlotIndex EndPoint;
      const bool Kill;
  
    public:
      LiveQueryResult(VNInfo *EarlyVal, VNInfo *LateVal, SlotIndex EndPoint,
                      bool Kill)
        : EarlyVal(EarlyVal), LateVal(LateVal), EndPoint(EndPoint), Kill(Kill)
      {}
  
      /// Return the value that is live-in to the instruction. This is the value
      /// that will be read by the instruction's use operands. Return NULL if no
      /// value is live-in.
      VNInfo *valueIn() const {
        return EarlyVal;
      }
  
      /// Return true if the live-in value is killed by this instruction. This
      /// means that either the live range ends at the instruction, or it changes
      /// value.
      bool isKill() const {
        return Kill;
      }
  
      /// Return true if this instruction has a dead def.
      bool isDeadDef() const {
        return EndPoint.isDead();
      }
  
      /// Return the value leaving the instruction, if any. This can be a
      /// live-through value, or a live def. A dead def returns NULL.
      VNInfo *valueOut() const {
        return isDeadDef() ? nullptr : LateVal;
      }
  
      /// Returns the value alive at the end of the instruction, if any. This can
      /// be a live-through value, a live def or a dead def.
      VNInfo *valueOutOrDead() const {
        return LateVal;
      }
  
      /// Return the value defined by this instruction, if any. This includes
      /// dead defs, it is the value created by the instruction's def operands.
      VNInfo *valueDefined() const {
        return EarlyVal == LateVal ? nullptr : LateVal;
      }
  
      /// Return the end point of the last live range segment to interact with
      /// the instruction, if any.
      ///
      /// The end point is an invalid SlotIndex only if the live range doesn't
      /// intersect the instruction at all.
      ///
      /// The end point may be at or past the end of the instruction's basic
      /// block. That means the value was live out of the block.
      SlotIndex endPoint() const {
        return EndPoint;
      }
    };
  
    /// This class represents the liveness of a register, stack slot, etc.
    /// It manages an ordered list of Segment objects.
    /// The Segments are organized in a static single assignment form: At places
    /// where a new value is defined or different values reach a CFG join a new
    /// segment with a new value number is used.
    class LiveRange {
    public:
  
      /// This represents a simple continuous liveness interval for a value.
      /// The start point is inclusive, the end point exclusive. These intervals
      /// are rendered as [start,end).
      struct Segment {
        SlotIndex start;  // Start point of the interval (inclusive)
        SlotIndex end;    // End point of the interval (exclusive)
        VNInfo *valno;    // identifier for the value contained in this segment.
  
        Segment() : valno(nullptr) {}
  
        Segment(SlotIndex S, SlotIndex E, VNInfo *V)
          : start(S), end(E), valno(V) {
          assert(S < E && "Cannot create empty or backwards segment");
        }
  
        /// Return true if the index is covered by this segment.
        bool contains(SlotIndex I) const {
          return start <= I && I < end;
        }
  
        /// Return true if the given interval, [S, E), is covered by this segment.
        bool containsInterval(SlotIndex S, SlotIndex E) const {
          assert((S < E) && "Backwards interval?");
          return (start <= S && S < end) && (start < E && E <= end);
        }
  
        bool operator<(const Segment &Other) const {
          return std::tie(start, end) < std::tie(Other.start, Other.end);
        }
        bool operator==(const Segment &Other) const {
          return start == Other.start && end == Other.end;
        }
  
        void dump() const;
      };
  
      typedef SmallVector<Segment, 2> Segments;
      typedef SmallVector<VNInfo *, 2> VNInfoList;
  
      Segments segments;   // the liveness segments
      VNInfoList valnos;   // value#'s
  
      // The segment set is used temporarily to accelerate initial computation
      // of live ranges of physical registers in computeRegUnitRange.
      // After that the set is flushed to the segment vector and deleted.
      typedef std::set<Segment> SegmentSet;
      std::unique_ptr<SegmentSet> segmentSet;
  
      typedef Segments::iterator iterator;
      iterator begin() { return segments.begin(); }
      iterator end()   { return segments.end(); }
  
      typedef Segments::const_iterator const_iterator;
      const_iterator begin() const { return segments.begin(); }
      const_iterator end() const  { return segments.end(); }
  
      typedef VNInfoList::iterator vni_iterator;
      vni_iterator vni_begin() { return valnos.begin(); }
      vni_iterator vni_end()   { return valnos.end(); }
  
      typedef VNInfoList::const_iterator const_vni_iterator;
      const_vni_iterator vni_begin() const { return valnos.begin(); }
      const_vni_iterator vni_end() const   { return valnos.end(); }
  
      /// Constructs a new LiveRange object.
      LiveRange(bool UseSegmentSet = false)
          : segmentSet(UseSegmentSet ? llvm::make_unique<SegmentSet>()
                                     : nullptr) {}
  
      /// Constructs a new LiveRange object by copying segments and valnos from
      /// another LiveRange.
      LiveRange(const LiveRange &Other, BumpPtrAllocator &Allocator) {
        assert(Other.segmentSet == nullptr &&
               "Copying of LiveRanges with active SegmentSets is not supported");
        assign(Other, Allocator);
      }
  
      /// Copies values numbers and live segments from \p Other into this range.
      void assign(const LiveRange &Other, BumpPtrAllocator &Allocator) {
        if (this == &Other)
          return;
  
        assert(Other.segmentSet == nullptr &&
               "Copying of LiveRanges with active SegmentSets is not supported");
        // Duplicate valnos.
        for (const VNInfo *VNI : Other.valnos)
          createValueCopy(VNI, Allocator);
        // Now we can copy segments and remap their valnos.
        for (const Segment &S : Other.segments)
          segments.push_back(Segment(S.start, S.end, valnos[S.valno->id]));
      }
  
      /// advanceTo - Advance the specified iterator to point to the Segment
      /// containing the specified position, or end() if the position is past the
      /// end of the range.  If no Segment contains this position, but the
      /// position is in a hole, this method returns an iterator pointing to the
      /// Segment immediately after the hole.
      iterator advanceTo(iterator I, SlotIndex Pos) {
        assert(I != end());
        if (Pos >= endIndex())
          return end();
        while (I->end <= Pos) ++I;
        return I;
      }
  
      const_iterator advanceTo(const_iterator I, SlotIndex Pos) const {
        assert(I != end());
        if (Pos >= endIndex())
          return end();
        while (I->end <= Pos) ++I;
        return I;
      }
  
      /// find - Return an iterator pointing to the first segment that ends after
      /// Pos, or end(). This is the same as advanceTo(begin(), Pos), but faster
      /// when searching large ranges.
      ///
      /// If Pos is contained in a Segment, that segment is returned.
      /// If Pos is in a hole, the following Segment is returned.
      /// If Pos is beyond endIndex, end() is returned.
      iterator find(SlotIndex Pos);
  
      const_iterator find(SlotIndex Pos) const {
        return const_cast<LiveRange*>(this)->find(Pos);
      }
  
      void clear() {
        valnos.clear();
        segments.clear();
      }
  
      size_t size() const {
        return segments.size();
      }
  
      bool hasAtLeastOneValue() const { return !valnos.empty(); }
  
      bool containsOneValue() const { return valnos.size() == 1; }
  
      unsigned getNumValNums() const { return (unsigned)valnos.size(); }
  
      /// getValNumInfo - Returns pointer to the specified val#.
      ///
      inline VNInfo *getValNumInfo(unsigned ValNo) {
        return valnos[ValNo];
      }
      inline const VNInfo *getValNumInfo(unsigned ValNo) const {
        return valnos[ValNo];
      }
  
      /// containsValue - Returns true if VNI belongs to this range.
      bool containsValue(const VNInfo *VNI) const {
        return VNI && VNI->id < getNumValNums() && VNI == getValNumInfo(VNI->id);
      }
  
      /// getNextValue - Create a new value number and return it.  MIIdx specifies
      /// the instruction that defines the value number.
      VNInfo *getNextValue(SlotIndex def, VNInfo::Allocator &VNInfoAllocator) {
        VNInfo *VNI =
          new (VNInfoAllocator) VNInfo((unsigned)valnos.size(), def);
        valnos.push_back(VNI);
        return VNI;
      }
  
      /// createDeadDef - Make sure the range has a value defined at Def.
      /// If one already exists, return it. Otherwise allocate a new value and
      /// add liveness for a dead def.
      VNInfo *createDeadDef(SlotIndex Def, VNInfo::Allocator &VNInfoAllocator);
  
      /// Create a def of value @p VNI. Return @p VNI. If there already exists
      /// a definition at VNI->def, the value defined there must be @p VNI.
      VNInfo *createDeadDef(VNInfo *VNI);
  
      /// Create a copy of the given value. The new value will be identical except
      /// for the Value number.
      VNInfo *createValueCopy(const VNInfo *orig,
                              VNInfo::Allocator &VNInfoAllocator) {
        VNInfo *VNI =
          new (VNInfoAllocator) VNInfo((unsigned)valnos.size(), *orig);
        valnos.push_back(VNI);
        return VNI;
      }
  
      /// RenumberValues - Renumber all values in order of appearance and remove
      /// unused values.
      void RenumberValues();
  
      /// MergeValueNumberInto - This method is called when two value numbers
      /// are found to be equivalent.  This eliminates V1, replacing all
      /// segments with the V1 value number with the V2 value number.  This can
      /// cause merging of V1/V2 values numbers and compaction of the value space.
      VNInfo* MergeValueNumberInto(VNInfo *V1, VNInfo *V2);
  
      /// Merge all of the live segments of a specific val# in RHS into this live
      /// range as the specified value number. The segments in RHS are allowed
      /// to overlap with segments in the current range, it will replace the
      /// value numbers of the overlaped live segments with the specified value
      /// number.
      void MergeSegmentsInAsValue(const LiveRange &RHS, VNInfo *LHSValNo);
  
      /// MergeValueInAsValue - Merge all of the segments of a specific val#
      /// in RHS into this live range as the specified value number.
      /// The segments in RHS are allowed to overlap with segments in the
      /// current range, but only if the overlapping segments have the
      /// specified value number.
      void MergeValueInAsValue(const LiveRange &RHS,
                               const VNInfo *RHSValNo, VNInfo *LHSValNo);
  
      bool empty() const { return segments.empty(); }
  
      /// beginIndex - Return the lowest numbered slot covered.
      SlotIndex beginIndex() const {
        assert(!empty() && "Call to beginIndex() on empty range.");
        return segments.front().start;
      }
  
      /// endNumber - return the maximum point of the range of the whole,
      /// exclusive.
      SlotIndex endIndex() const {
        assert(!empty() && "Call to endIndex() on empty range.");
        return segments.back().end;
      }
  
      bool expiredAt(SlotIndex index) const {
        return index >= endIndex();
      }
  
      bool liveAt(SlotIndex index) const {
        const_iterator r = find(index);
        return r != end() && r->start <= index;
      }
  
      /// Return the segment that contains the specified index, or null if there
      /// is none.
      const Segment *getSegmentContaining(SlotIndex Idx) const {
        const_iterator I = FindSegmentContaining(Idx);
        return I == end() ? nullptr : &*I;
      }
  
      /// Return the live segment that contains the specified index, or null if
      /// there is none.
      Segment *getSegmentContaining(SlotIndex Idx) {
        iterator I = FindSegmentContaining(Idx);
        return I == end() ? nullptr : &*I;
      }
  
      /// getVNInfoAt - Return the VNInfo that is live at Idx, or NULL.
      VNInfo *getVNInfoAt(SlotIndex Idx) const {
        const_iterator I = FindSegmentContaining(Idx);
        return I == end() ? nullptr : I->valno;
      }
  
      /// getVNInfoBefore - Return the VNInfo that is live up to but not
      /// necessarilly including Idx, or NULL. Use this to find the reaching def
      /// used by an instruction at this SlotIndex position.
      VNInfo *getVNInfoBefore(SlotIndex Idx) const {
        const_iterator I = FindSegmentContaining(Idx.getPrevSlot());
        return I == end() ? nullptr : I->valno;
      }
  
      /// Return an iterator to the segment that contains the specified index, or
      /// end() if there is none.
      iterator FindSegmentContaining(SlotIndex Idx) {
        iterator I = find(Idx);
        return I != end() && I->start <= Idx ? I : end();
      }
  
      const_iterator FindSegmentContaining(SlotIndex Idx) const {
        const_iterator I = find(Idx);
        return I != end() && I->start <= Idx ? I : end();
      }
  
      /// overlaps - Return true if the intersection of the two live ranges is
      /// not empty.
      bool overlaps(const LiveRange &other) const {
        if (other.empty())
          return false;
        return overlapsFrom(other, other.begin());
      }
  
      /// overlaps - Return true if the two ranges have overlapping segments
      /// that are not coalescable according to CP.
      ///
      /// Overlapping segments where one range is defined by a coalescable
      /// copy are allowed.
      bool overlaps(const LiveRange &Other, const CoalescerPair &CP,
                    const SlotIndexes&) const;
  
      /// overlaps - Return true if the live range overlaps an interval specified
      /// by [Start, End).
      bool overlaps(SlotIndex Start, SlotIndex End) const;
  
      /// overlapsFrom - Return true if the intersection of the two live ranges
      /// is not empty.  The specified iterator is a hint that we can begin
      /// scanning the Other range starting at I.
      bool overlapsFrom(const LiveRange &Other, const_iterator I) const;
  
      /// Returns true if all segments of the @p Other live range are completely
      /// covered by this live range.
      /// Adjacent live ranges do not affect the covering:the liverange
      /// [1,5](5,10] covers (3,7].
      bool covers(const LiveRange &Other) const;
  
      /// Add the specified Segment to this range, merging segments as
      /// appropriate.  This returns an iterator to the inserted segment (which
      /// may have grown since it was inserted).
      iterator addSegment(Segment S);
  
      /// Attempt to extend a value defined after @p StartIdx to include @p Use.
      /// Both @p StartIdx and @p Use should be in the same basic block. In case
      /// of subranges, an extension could be prevented by an explicit "undef"
      /// caused by a <def,read-undef> on a non-overlapping lane. The list of
      /// location of such "undefs" should be provided in @p Undefs.
      /// The return value is a pair: the first element is VNInfo of the value
      /// that was extended (possibly nullptr), the second is a boolean value
      /// indicating whether an "undef" was encountered.
      /// If this range is live before @p Use in the basic block that starts at
      /// @p StartIdx, and there is no intervening "undef", extend it to be live
      /// up to @p Use, and return the pair {value, false}. If there is no
      /// segment before @p Use and there is no "undef" between @p StartIdx and
      /// @p Use, return {nullptr, false}. If there is an "undef" before @p Use,
      /// return {nullptr, true}.
      std::pair<VNInfo*,bool> extendInBlock(ArrayRef<SlotIndex> Undefs,
          SlotIndex StartIdx, SlotIndex Use);
  
      /// Simplified version of the above "extendInBlock", which assumes that
      /// no register lanes are undefined by <def,read-undef> operands.
      /// If this range is live before @p Use in the basic block that starts
      /// at @p StartIdx, extend it to be live up to @p Use, and return the
      /// value. If there is no segment before @p Use, return nullptr.
      VNInfo *extendInBlock(SlotIndex StartIdx, SlotIndex Kill);
  
      /// join - Join two live ranges (this, and other) together.  This applies
      /// mappings to the value numbers in the LHS/RHS ranges as specified.  If
      /// the ranges are not joinable, this aborts.
      void join(LiveRange &Other,
                const int *ValNoAssignments,
                const int *RHSValNoAssignments,
                SmallVectorImpl<VNInfo *> &NewVNInfo);
  
      /// True iff this segment is a single segment that lies between the
      /// specified boundaries, exclusively. Vregs live across a backedge are not
      /// considered local. The boundaries are expected to lie within an extended
      /// basic block, so vregs that are not live out should contain no holes.
      bool isLocal(SlotIndex Start, SlotIndex End) const {
        return beginIndex() > Start.getBaseIndex() &&
          endIndex() < End.getBoundaryIndex();
      }
  
      /// Remove the specified segment from this range.  Note that the segment
      /// must be a single Segment in its entirety.
      void removeSegment(SlotIndex Start, SlotIndex End,
                         bool RemoveDeadValNo = false);
  
      void removeSegment(Segment S, bool RemoveDeadValNo = false) {
        removeSegment(S.start, S.end, RemoveDeadValNo);
      }
  
      /// Remove segment pointed to by iterator @p I from this range.  This does
      /// not remove dead value numbers.
      iterator removeSegment(iterator I) {
        return segments.erase(I);
      }
  
      /// Query Liveness at Idx.
      /// The sub-instruction slot of Idx doesn't matter, only the instruction
      /// it refers to is considered.
      LiveQueryResult Query(SlotIndex Idx) const {
        // Find the segment that enters the instruction.
        const_iterator I = find(Idx.getBaseIndex());
        const_iterator E = end();
        if (I == E)
          return LiveQueryResult(nullptr, nullptr, SlotIndex(), false);
  
        // Is this an instruction live-in segment?
        // If Idx is the start index of a basic block, include live-in segments
        // that start at Idx.getBaseIndex().
        VNInfo *EarlyVal = nullptr;
        VNInfo *LateVal  = nullptr;
        SlotIndex EndPoint;
        bool Kill = false;
        if (I->start <= Idx.getBaseIndex()) {
          EarlyVal = I->valno;
          EndPoint = I->end;
          // Move to the potentially live-out segment.
          if (SlotIndex::isSameInstr(Idx, I->end)) {
            Kill = true;
            if (++I == E)
              return LiveQueryResult(EarlyVal, LateVal, EndPoint, Kill);
          }
          // Special case: A PHIDef value can have its def in the middle of a
          // segment if the value happens to be live out of the layout
          // predecessor.
          // Such a value is not live-in.
          if (EarlyVal->def == Idx.getBaseIndex())
            EarlyVal = nullptr;
        }
        // I now points to the segment that may be live-through, or defined by
        // this instr. Ignore segments starting after the current instr.
        if (!SlotIndex::isEarlierInstr(Idx, I->start)) {
          LateVal = I->valno;
          EndPoint = I->end;
        }
        return LiveQueryResult(EarlyVal, LateVal, EndPoint, Kill);
      }
  
      /// removeValNo - Remove all the segments defined by the specified value#.
      /// Also remove the value# from value# list.
      void removeValNo(VNInfo *ValNo);
  
      /// Returns true if the live range is zero length, i.e. no live segments
      /// span instructions. It doesn't pay to spill such a range.
      bool isZeroLength(SlotIndexes *Indexes) const {
        for (const Segment &S : segments)
          if (Indexes->getNextNonNullIndex(S.start).getBaseIndex() <
              S.end.getBaseIndex())
            return false;
        return true;
      }
  
      // Returns true if any segment in the live range contains any of the
      // provided slot indexes.  Slots which occur in holes between
      // segments will not cause the function to return true.
      bool isLiveAtIndexes(ArrayRef<SlotIndex> Slots) const;
  
      bool operator<(const LiveRange& other) const {
        const SlotIndex &thisIndex = beginIndex();
        const SlotIndex &otherIndex = other.beginIndex();
        return thisIndex < otherIndex;
      }
  
      /// Returns true if there is an explicit "undef" between @p Begin
      /// @p End.
      bool isUndefIn(ArrayRef<SlotIndex> Undefs, SlotIndex Begin,
                     SlotIndex End) const {
        return std::any_of(Undefs.begin(), Undefs.end(),
                  [Begin,End] (SlotIndex Idx) -> bool {
                    return Begin <= Idx && Idx < End;
                  });
      }
  
      /// Flush segment set into the regular segment vector.
      /// The method is to be called after the live range
      /// has been created, if use of the segment set was
      /// activated in the constructor of the live range.
      void flushSegmentSet();
  
      void print(raw_ostream &OS) const;
      void dump() const;
  
      /// \brief Walk the range and assert if any invariants fail to hold.
      ///
      /// Note that this is a no-op when asserts are disabled.
  #ifdef NDEBUG
      void verify() const {}
  #else
      void verify() const;
  #endif
  
    protected:
      /// Append a segment to the list of segments.
      void append(const LiveRange::Segment S);
  
    private:
      friend class LiveRangeUpdater;
      void addSegmentToSet(Segment S);
      void markValNoForDeletion(VNInfo *V);
    };
  
    inline raw_ostream &operator<<(raw_ostream &OS, const LiveRange &LR) {
      LR.print(OS);
      return OS;
    }
  
    /// LiveInterval - This class represents the liveness of a register,
    /// or stack slot.
    class LiveInterval : public LiveRange {
    public:
      typedef LiveRange super;
  
      /// A live range for subregisters. The LaneMask specifies which parts of the
      /// super register are covered by the interval.
      /// (@sa TargetRegisterInfo::getSubRegIndexLaneMask()).
      class SubRange : public LiveRange {
      public:
        SubRange *Next;
        LaneBitmask LaneMask;
  
        /// Constructs a new SubRange object.
        SubRange(LaneBitmask LaneMask)
          : Next(nullptr), LaneMask(LaneMask) {
        }
  
        /// Constructs a new SubRange object by copying liveness from @p Other.
        SubRange(LaneBitmask LaneMask, const LiveRange &Other,
                 BumpPtrAllocator &Allocator)
          : LiveRange(Other, Allocator), Next(nullptr), LaneMask(LaneMask) {
        }
  
        void print(raw_ostream &OS) const;
        void dump() const;
      };
  
    private:
      SubRange *SubRanges; ///< Single linked list of subregister live ranges.
  
    public:
      const unsigned reg;  // the register or stack slot of this interval.
      float weight;        // weight of this interval
  
      LiveInterval(unsigned Reg, float Weight)
        : SubRanges(nullptr), reg(Reg), weight(Weight) {}
  
      ~LiveInterval() {
        clearSubRanges();
      }
  
      template<typename T>
      class SingleLinkedListIterator {
        T *P;
      public:
        SingleLinkedListIterator<T>(T *P) : P(P) {}
        SingleLinkedListIterator<T> &operator++() {
          P = P->Next;
          return *this;
        }
        SingleLinkedListIterator<T> operator++(int) {
          SingleLinkedListIterator res = *this;
          ++*this;
          return res;
        }
        bool operator!=(const SingleLinkedListIterator<T> &Other) {
          return P != Other.operator->();
        }
        bool operator==(const SingleLinkedListIterator<T> &Other) {
          return P == Other.operator->();
        }
        T &operator*() const {
          return *P;
        }
        T *operator->() const {
          return P;
        }
      };
  
      typedef SingleLinkedListIterator<SubRange> subrange_iterator;
      subrange_iterator subrange_begin() {
        return subrange_iterator(SubRanges);
      }
      subrange_iterator subrange_end() {
        return subrange_iterator(nullptr);
      }
  
      typedef SingleLinkedListIterator<const SubRange> const_subrange_iterator;
      const_subrange_iterator subrange_begin() const {
        return const_subrange_iterator(SubRanges);
      }
      const_subrange_iterator subrange_end() const {
        return const_subrange_iterator(nullptr);
      }
  
      iterator_range<subrange_iterator> subranges() {
        return make_range(subrange_begin(), subrange_end());
      }
  
      iterator_range<const_subrange_iterator> subranges() const {
        return make_range(subrange_begin(), subrange_end());
      }
  
      /// Creates a new empty subregister live range. The range is added at the
      /// beginning of the subrange list; subrange iterators stay valid.
      SubRange *createSubRange(BumpPtrAllocator &Allocator,
                               LaneBitmask LaneMask) {
        SubRange *Range = new (Allocator) SubRange(LaneMask);
        appendSubRange(Range);
        return Range;
      }
  
      /// Like createSubRange() but the new range is filled with a copy of the
      /// liveness information in @p CopyFrom.
      SubRange *createSubRangeFrom(BumpPtrAllocator &Allocator,
                                   LaneBitmask LaneMask,
                                   const LiveRange &CopyFrom) {
        SubRange *Range = new (Allocator) SubRange(LaneMask, CopyFrom, Allocator);
        appendSubRange(Range);
        return Range;
      }
  
      /// Returns true if subregister liveness information is available.
      bool hasSubRanges() const {
        return SubRanges != nullptr;
      }
  
      /// Removes all subregister liveness information.
      void clearSubRanges();
  
      /// Removes all subranges without any segments (subranges without segments
      /// are not considered valid and should only exist temporarily).
      void removeEmptySubRanges();
  
      /// getSize - Returns the sum of sizes of all the LiveRange's.
      ///
      unsigned getSize() const;
  
      /// isSpillable - Can this interval be spilled?
      bool isSpillable() const {
        return weight != llvm::huge_valf;
      }
  
      /// markNotSpillable - Mark interval as not spillable
      void markNotSpillable() {
        weight = llvm::huge_valf;
      }
  
      /// For a given lane mask @p LaneMask, compute indexes at which the
      /// lane is marked undefined by subregister <def,read-undef> definitions.
      void computeSubRangeUndefs(SmallVectorImpl<SlotIndex> &Undefs,
                                 LaneBitmask LaneMask,
                                 const MachineRegisterInfo &MRI,
                                 const SlotIndexes &Indexes) const;
  
      /// Refines the subranges to support \p LaneMask. This may only be called
      /// for LI.hasSubrange()==true. Subregister ranges are split or created
      /// until \p LaneMask can be matched exactly. \p Mod is executed on the
      /// matching subranges.
      ///
      /// Example:
      ///    Given an interval with subranges with lanemasks L0F00, L00F0 and
      ///    L000F, refining for mask L0018. Will split the L00F0 lane into
      ///    L00E0 and L0010 and the L000F lane into L0007 and L0008. The Mod
      ///    function will be applied to the L0010 and L0008 subranges.
      void refineSubRanges(BumpPtrAllocator &Allocator, LaneBitmask LaneMask,
                           std::function<void(LiveInterval::SubRange&)> Mod);
  
      bool operator<(const LiveInterval& other) const {
        const SlotIndex &thisIndex = beginIndex();
        const SlotIndex &otherIndex = other.beginIndex();
        return std::tie(thisIndex, reg) < std::tie(otherIndex, other.reg);
      }
  
      void print(raw_ostream &OS) const;
      void dump() const;
  
      /// \brief Walks the interval and assert if any invariants fail to hold.
      ///
      /// Note that this is a no-op when asserts are disabled.
  #ifdef NDEBUG
      void verify(const MachineRegisterInfo *MRI = nullptr) const {}
  #else
      void verify(const MachineRegisterInfo *MRI = nullptr) const;
  #endif
  
    private:
      /// Appends @p Range to SubRanges list.
      void appendSubRange(SubRange *Range) {
        Range->Next = SubRanges;
        SubRanges = Range;
      }
  
      /// Free memory held by SubRange.
      void freeSubRange(SubRange *S);
    };
  
    inline raw_ostream &operator<<(raw_ostream &OS,
                                   const LiveInterval::SubRange &SR) {
      SR.print(OS);
      return OS;
    }
  
    inline raw_ostream &operator<<(raw_ostream &OS, const LiveInterval &LI) {
      LI.print(OS);
      return OS;
    }
  
    raw_ostream &operator<<(raw_ostream &OS, const LiveRange::Segment &S);
  
    inline bool operator<(SlotIndex V, const LiveRange::Segment &S) {
      return V < S.start;
    }
  
    inline bool operator<(const LiveRange::Segment &S, SlotIndex V) {
      return S.start < V;
    }
  
    /// Helper class for performant LiveRange bulk updates.
    ///
    /// Calling LiveRange::addSegment() repeatedly can be expensive on large
    /// live ranges because segments after the insertion point may need to be
    /// shifted. The LiveRangeUpdater class can defer the shifting when adding
    /// many segments in order.
    ///
    /// The LiveRange will be in an invalid state until flush() is called.
    class LiveRangeUpdater {
      LiveRange *LR;
      SlotIndex LastStart;
      LiveRange::iterator WriteI;
      LiveRange::iterator ReadI;
      SmallVector<LiveRange::Segment, 16> Spills;
      void mergeSpills();
  
    public:
      /// Create a LiveRangeUpdater for adding segments to LR.
      /// LR will temporarily be in an invalid state until flush() is called.
      LiveRangeUpdater(LiveRange *lr = nullptr) : LR(lr) {}
  
      ~LiveRangeUpdater() { flush(); }
  
      /// Add a segment to LR and coalesce when possible, just like
      /// LR.addSegment(). Segments should be added in increasing start order for
      /// best performance.
      void add(LiveRange::Segment);
  
      void add(SlotIndex Start, SlotIndex End, VNInfo *VNI) {
        add(LiveRange::Segment(Start, End, VNI));
      }
  
      /// Return true if the LR is currently in an invalid state, and flush()
      /// needs to be called.
      bool isDirty() const { return LastStart.isValid(); }
  
      /// Flush the updater state to LR so it is valid and contains all added
      /// segments.
      void flush();
  
      /// Select a different destination live range.
      void setDest(LiveRange *lr) {
        if (LR != lr && isDirty())
          flush();
        LR = lr;
      }
  
      /// Get the current destination live range.
      LiveRange *getDest() const { return LR; }
  
      void dump() const;
      void print(raw_ostream&) const;
    };
  
    inline raw_ostream &operator<<(raw_ostream &OS, const LiveRangeUpdater &X) {
      X.print(OS);
      return OS;
    }
  
    /// ConnectedVNInfoEqClasses - Helper class that can divide VNInfos in a
    /// LiveInterval into equivalence clases of connected components. A
    /// LiveInterval that has multiple connected components can be broken into
    /// multiple LiveIntervals.
    ///
    /// Given a LiveInterval that may have multiple connected components, run:
    ///
    ///   unsigned numComps = ConEQ.Classify(LI);
    ///   if (numComps > 1) {
    ///     // allocate numComps-1 new LiveIntervals into LIS[1..]
    ///     ConEQ.Distribute(LIS);
    /// }
  
    class ConnectedVNInfoEqClasses {
      LiveIntervals &LIS;
      IntEqClasses EqClass;
  
    public:
      explicit ConnectedVNInfoEqClasses(LiveIntervals &lis) : LIS(lis) {}
  
      /// Classify the values in \p LR into connected components.
      /// Returns the number of connected components.
      unsigned Classify(const LiveRange &LR);
  
      /// getEqClass - Classify creates equivalence classes numbered 0..N. Return
      /// the equivalence class assigned the VNI.
      unsigned getEqClass(const VNInfo *VNI) const { return EqClass[VNI->id]; }
  
      /// Distribute values in \p LI into a separate LiveIntervals
      /// for each connected component. LIV must have an empty LiveInterval for
      /// each additional connected component. The first connected component is
      /// left in \p LI.
      void Distribute(LiveInterval &LI, LiveInterval *LIV[],
                      MachineRegisterInfo &MRI);
    };
  }
  #endif
  