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 //===- llvm/CodeGen/LiveInterval.h - Interval representation ----*- 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
 //
 //===----------------------------------------------------------------------===//
 //
 // 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/ArrayRef.h"
 #include "llvm/ADT/IntEqClasses.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/CodeGen/Register.h"
 #include "llvm/CodeGen/SlotIndexes.h"
 #include "llvm/MC/LaneBitmask.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <functional>
 #include <memory>
 #include <set>
 #include <tuple>
 #include <utility>
 
 namespace llvm {
 
   class CoalescerPair;
   class LiveIntervals;
   class MachineRegisterInfo;
   class raw_ostream;
 
   /// VNInfo - Value Number Information.
   /// This class holds information about a machine level values, including
   /// definition and use points.
   ///
   class VNInfo {
   public:
     using Allocator = BumpPtrAllocator;
 
     /// 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 = nullptr; // identifier for the value contained in this
                                // segment.
 
       Segment() = default;
 
       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;
       }
 
       bool operator!=(const Segment &Other) const {
         return !(*this == Other);
       }
 
       void dump() const;
     };
 
     using Segments = SmallVector<Segment, 2>;
     using VNInfoList = SmallVector<VNInfo *, 2>;
 
     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.
     using SegmentSet = std::set<Segment>;
     std::unique_ptr<SegmentSet> segmentSet;
 
     using iterator = Segments::iterator;
     using const_iterator = Segments::const_iterator;
 
     iterator begin() { return segments.begin(); }
     iterator end()   { return segments.end(); }
 
     const_iterator begin() const { return segments.begin(); }
     const_iterator end() const  { return segments.end(); }
 
     using vni_iterator = VNInfoList::iterator;
     using const_vni_iterator = VNInfoList::const_iterator;
 
     vni_iterator vni_begin() { return valnos.begin(); }
     vni_iterator vni_end()   { return valnos.end(); }
 
     const_vni_iterator vni_begin() const { return valnos.begin(); }
     const_vni_iterator vni_end() const   { return valnos.end(); }
 
     iterator_range<vni_iterator> vnis() {
       return make_range(vni_begin(), vni_end());
     }
 
     iterator_range<const_vni_iterator> vnis() const {
       return make_range(vni_begin(), vni_end());
     }
 
     /// Constructs a new LiveRange object.
     LiveRange(bool UseSegmentSet = false)
         : segmentSet(UseSegmentSet ? std::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.
     /// @p Def is the index of 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 &VNIAlloc);
 
     /// 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
     /// necessarily 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 StartPos) 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 Kill);
 
     /// 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 interval from this live range.
     /// Does nothing if interval is not part of this live range.
     /// Note that the interval must be within 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.
     iterator removeSegment(iterator I, bool RemoveDeadValNo = false);
 
     /// Mark \p ValNo for deletion if no segments in this range use it.
     void removeValNoIfDead(VNInfo *ValNo);
 
     /// 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 llvm::any_of(Undefs, [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();
 
     /// Stores indexes from the input index sequence R at which this LiveRange
     /// is live to the output O iterator.
     /// R is a range of _ascending sorted_ _random_ access iterators
     /// to the input indexes. Indexes stored at O are ascending sorted so it
     /// can be used directly in the subsequent search (for example for
     /// subranges). Returns true if found at least one index.
     template <typename Range, typename OutputIt>
     bool findIndexesLiveAt(Range &&R, OutputIt O) const {
       assert(llvm::is_sorted(R));
       auto Idx = R.begin(), EndIdx = R.end();
       auto Seg = segments.begin(), EndSeg = segments.end();
       bool Found = false;
       while (Idx != EndIdx && Seg != EndSeg) {
         // if the Seg is lower find first segment that is above Idx using binary
         // search
         if (Seg->end <= *Idx) {
           Seg =
               std::upper_bound(++Seg, EndSeg, *Idx, [=](auto V, const auto &S) {
                 return V < S.end;
               });
           if (Seg == EndSeg)
             break;
         }
         auto NotLessStart = std::lower_bound(Idx, EndIdx, Seg->start);
         if (NotLessStart == EndIdx)
           break;
         auto NotLessEnd = std::lower_bound(NotLessStart, EndIdx, Seg->end);
         if (NotLessEnd != NotLessStart) {
           Found = true;
           O = std::copy(NotLessStart, NotLessEnd, O);
         }
         Idx = NotLessEnd;
         ++Seg;
       }
       return Found;
     }
 
     void print(raw_ostream &OS) const;
     void dump() const;
 
     /// Walk the range and assert if any invariants fail to hold.
     ///
     /// Note that this is a no-op when asserts are disabled.
 #ifdef NDEBUG
     [[nodiscard]] bool verify() const { return true; }
 #else
     [[nodiscard]] bool 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:
     using super = LiveRange;
 
     /// 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 = nullptr;
       LaneBitmask LaneMask;
 
       /// Constructs a new SubRange object.
       SubRange(LaneBitmask LaneMask) : LaneMask(LaneMask) {}
 
       /// Constructs a new SubRange object by copying liveness from @p Other.
       SubRange(LaneBitmask LaneMask, const LiveRange &Other,
                BumpPtrAllocator &Allocator)
         : LiveRange(Other, Allocator), LaneMask(LaneMask) {}
 
       void print(raw_ostream &OS) const;
       void dump() const;
     };
 
   private:
     SubRange *SubRanges = nullptr; ///< Single linked list of subregister live
                                    /// ranges.
     const Register Reg; // the register or stack slot of this interval.
     float Weight = 0.0; // weight of this interval
 
   public:
     Register reg() const { return Reg; }
     float weight() const { return Weight; }
     void incrementWeight(float Inc) { Weight += Inc; }
     void setWeight(float Value) { Weight = Value; }
 
     LiveInterval(unsigned Reg, float Weight) : Reg(Reg), Weight(Weight) {}
 
     ~LiveInterval() {
       clearSubRanges();
     }
 
     template<typename T>
     class SingleLinkedListIterator {
       T *P;
 
     public:
       using difference_type = ptrdiff_t;
       using value_type = T;
       using pointer = T *;
       using reference = T &;
       using iterator_category = std::forward_iterator_tag;
 
       SingleLinkedListIterator(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) const {
         return P != Other.operator->();
       }
       bool operator==(const SingleLinkedListIterator<T> &Other) const {
         return P == Other.operator->();
       }
       T &operator*() const {
         return *P;
       }
       T *operator->() const {
         return P;
       }
     };
 
     using subrange_iterator = SingleLinkedListIterator<SubRange>;
     using const_subrange_iterator = SingleLinkedListIterator<const SubRange>;
 
     subrange_iterator subrange_begin() {
       return subrange_iterator(SubRanges);
     }
     subrange_iterator subrange_end() {
       return subrange_iterator(nullptr);
     }
 
     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 != huge_valf; }
 
     /// markNotSpillable - Mark interval as not spillable
     void markNotSpillable() { Weight = 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.
     ///
     /// \p Indexes and \p TRI are required to clean up the VNIs that
     /// don't define the related lane masks after they get shrunk. E.g.,
     /// when L000F gets split into L0007 and L0008 maybe only a subset
     /// of the VNIs that defined L000F defines L0007.
     ///
     /// The clean up of the VNIs need to look at the actual instructions
     /// to decide what is or is not live at a definition point. If the
     /// update of the subranges occurs while the IR does not reflect these
     /// changes, \p ComposeSubRegIdx can be used to specify how the
     /// definition are going to be rewritten.
     /// E.g., let say we want to merge:
     ///     V1.sub1:<2 x s32> = COPY V2.sub3:<4 x s32>
     /// We do that by choosing a class where sub1:<2 x s32> and sub3:<4 x s32>
     /// overlap, i.e., by choosing a class where we can find "offset + 1 == 3".
     /// Put differently we align V2's sub3 with V1's sub1:
     /// V2: sub0 sub1 sub2 sub3
     /// V1: <offset>  sub0 sub1
     ///
     /// This offset will look like a composed subregidx in the class:
     ///     V1.(composed sub2 with sub1):<4 x s32> = COPY V2.sub3:<4 x s32>
     /// =>  V1.(composed sub2 with sub1):<4 x s32> = COPY V2.sub3:<4 x s32>
     ///
     /// Now if we didn't rewrite the uses and def of V1, all the checks for V1
     /// need to account for this offset.
     /// This happens during coalescing where we update the live-ranges while
     /// still having the old IR around because updating the IR on-the-fly
     /// would actually clobber some information on how the live-ranges that
     /// are being updated look like.
     void refineSubRanges(BumpPtrAllocator &Allocator, LaneBitmask LaneMask,
                          std::function<void(LiveInterval::SubRange &)> Apply,
                          const SlotIndexes &Indexes,
                          const TargetRegisterInfo &TRI,
                          unsigned ComposeSubRegIdx = 0);
 
     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;
 
     /// Walks the interval and assert if any invariants fail to hold.
     ///
     /// Note that this is a no-op when asserts are disabled.
 #ifdef NDEBUG
     [[nodiscard]] bool verify(const MachineRegisterInfo *MRI = nullptr) const {
       return true;
     }
 #else
     [[nodiscard]] bool 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);
   };
 
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_LIVEINTERVAL_H

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