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//===- LiveIntervalUnion.h - Live interval union data struct ---*- 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

//

//===----------------------------------------------------------------------===//

//

// LiveIntervalUnion is a union of live segments across multiple live virtual

// registers. This may be used during coalescing to represent a congruence

// class, or during register allocation to model liveness of a physical

// register.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_LIVEINTERVALUNION_H

#define LLVM_CODEGEN_LIVEINTERVALUNION_H

#include "llvm/ADT/IntervalMap.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/CodeGen/LiveInterval.h"

#include "llvm/CodeGen/SlotIndexes.h"

#include <cassert>

#include <limits>

namespace llvm {

class raw_ostream;

class TargetRegisterInfo;

#ifndef NDEBUG

// forward declaration

template <unsigned Element> class SparseBitVector;

using LiveVirtRegBitSet = SparseBitVector<128>;

#endif

/// Union of live intervals that are strong candidates for coalescing into a

/// single register (either physical or virtual depending on the context).  We

/// expect the constituent live intervals to be disjoint, although we may

/// eventually make exceptions to handle value-based interference.

class LiveIntervalUnion {

  // A set of live virtual register segments that supports fast insertion,

  // intersection, and removal.

  // Mapping SlotIndex intervals to virtual register numbers.

  using LiveSegments = IntervalMap<SlotIndex, const LiveInterval *>;

public:

  // SegmentIter can advance to the next segment ordered by starting position

  // which may belong to a different live virtual register. We also must be able

  // to reach the current segment's containing virtual register.

  using SegmentIter = LiveSegments::iterator;

  /// Const version of SegmentIter.

  using ConstSegmentIter = LiveSegments::const_iterator;

  // LiveIntervalUnions share an external allocator.

  using Allocator = LiveSegments::Allocator;

private:

  unsigned Tag = 0;       // unique tag for current contents.

  LiveSegments Segments;  // union of virtual reg segments

public:

  explicit LiveIntervalUnion(Allocator &a) : Segments(a) {}

  // Iterate over all segments in the union of live virtual registers ordered

  // by their starting position.

  SegmentIter begin() { return Segments.begin(); }

  SegmentIter end() { return Segments.end(); }

  SegmentIter find(SlotIndex x) { return Segments.find(x); }

  ConstSegmentIter begin() const { return Segments.begin(); }

  ConstSegmentIter end() const { return Segments.end(); }

  ConstSegmentIter find(SlotIndex x) const { return Segments.find(x); }

  bool empty() const { return Segments.empty(); }

  SlotIndex startIndex() const { return Segments.start(); }

  SlotIndex endIndex() const { return Segments.stop(); }

  // Provide public access to the underlying map to allow overlap iteration.

  using Map = LiveSegments;

  const Map &getMap() const { return Segments; }

  /// getTag - Return an opaque tag representing the current state of the union.

  unsigned getTag() const { return Tag; }

  /// changedSince - Return true if the union change since getTag returned tag.

  bool changedSince(unsigned tag) const { return tag != Tag; }

  // Add a live virtual register to this union and merge its segments.

  void unify(const LiveInterval &VirtReg, const LiveRange &Range);

  // Remove a live virtual register's segments from this union.

  void extract(const LiveInterval &VirtReg, const LiveRange &Range);

  // Remove all inserted virtual registers.

  void clear() { Segments.clear(); ++Tag; }

  // Print union, using TRI to translate register names

  void print(raw_ostream &OS, const TargetRegisterInfo *TRI) const;

#ifndef NDEBUG

  // Verify the live intervals in this union and add them to the visited set.

  void verify(LiveVirtRegBitSet& VisitedVRegs);

#endif

  // Get any virtual register that is assign to this physical unit

  const LiveInterval *getOneVReg() const;

  /// Query interferences between a single live virtual register and a live

  /// interval union.

  class Query {

    const LiveIntervalUnion *LiveUnion = nullptr;

    const LiveRange *LR = nullptr;

    LiveRange::const_iterator LRI;  ///< current position in LR

    ConstSegmentIter LiveUnionI;    ///< current position in LiveUnion

    SmallVector<const LiveInterval *, 4> InterferingVRegs;

    bool CheckedFirstInterference = false;

    bool SeenAllInterferences = false;

    unsigned Tag = 0;

    unsigned UserTag = 0;

    // Count the virtual registers in this union that interfere with this

    // query's live virtual register, up to maxInterferingRegs.

    unsigned collectInterferingVRegs(unsigned MaxInterferingRegs);

    // Was this virtual register visited during collectInterferingVRegs?

    bool isSeenInterference(const LiveInterval *VirtReg) const;

  public:

    Query() = default;

    Query(const LiveRange &LR, const LiveIntervalUnion &LIU)

        : LiveUnion(&LIU), LR(&LR) {}

    Query(const Query &) = delete;

    Query &operator=(const Query &) = delete;

    void reset(unsigned NewUserTag, const LiveRange &NewLR,

               const LiveIntervalUnion &NewLiveUnion) {

      LiveUnion = &NewLiveUnion;

      LR = &NewLR;

      InterferingVRegs.clear();

      CheckedFirstInterference = false;

      SeenAllInterferences = false;

      Tag = NewLiveUnion.getTag();

      UserTag = NewUserTag;

    }

    void init(unsigned NewUserTag, const LiveRange &NewLR,

              const LiveIntervalUnion &NewLiveUnion) {

      if (UserTag == NewUserTag && LR == &NewLR && LiveUnion == &NewLiveUnion &&

          !NewLiveUnion.changedSince(Tag)) {

        // Retain cached results, e.g. firstInterference.

        return;

      }

      reset(NewUserTag, NewLR, NewLiveUnion);

    }

    // Does this live virtual register interfere with the union?

    bool checkInterference() { return collectInterferingVRegs(1); }

    // Vector generated by collectInterferingVRegs.

    const SmallVectorImpl<const LiveInterval *> &interferingVRegs(

        unsigned MaxInterferingRegs = std::numeric_limits<unsigned>::max()) {

      if (!SeenAllInterferences || MaxInterferingRegs < InterferingVRegs.size())

        collectInterferingVRegs(MaxInterferingRegs);

      return InterferingVRegs;

    }

  };

  // Array of LiveIntervalUnions.

  class Array {

    unsigned Size = 0;

    LiveIntervalUnion *LIUs = nullptr;

  public:

    Array() = default;

    ~Array() { clear(); }

    // Initialize the array to have Size entries.

    // Reuse an existing allocation if the size matches.

    void init(LiveIntervalUnion::Allocator&, unsigned Size);

    unsigned size() const { return Size; }

    void clear();

    LiveIntervalUnion& operator[](unsigned idx) {

      assert(idx <  Size && "idx out of bounds");

      return LIUs[idx];

    }

    const LiveIntervalUnion& operator[](unsigned Idx) const {

      assert(Idx < Size && "Idx out of bounds");

      return LIUs[Idx];

    }

  };

};

} // end namespace llvm

#endif // LLVM_CODEGEN_LIVEINTERVALUNION_H