InstrRefBasedImpl.h

  /// Attempt to eliminate un-necessary PHIs on entry to a block. Examines the
  /// live-in values coming from predecessors live-outs, and replaces any PHIs
  /// already present in this blocks live-ins with a live-through value if the
  /// PHI isn't needed.
  /// \p LiveIn Old live-in value, overwritten with new one if live-in changes.
  /// \returns true if any live-ins change value, either from value propagation
  ///          or PHI elimination.
  bool vlocJoin(MachineBasicBlock &MBB, LiveIdxT &VLOCOutLocs,
                SmallPtrSet<const MachineBasicBlock *, 8> &BlocksToExplore,
                DbgValue &LiveIn);

  /// For the given block and live-outs feeding into it, try to find a
  /// machine location where all the variable values join together.
  /// \returns Value ID of a machine PHI if an appropriate one is available.
  Optional<ValueIDNum>
  pickVPHILoc(const MachineBasicBlock &MBB, const DebugVariable &Var,
              const LiveIdxT &LiveOuts, ValueIDNum **MOutLocs,
              const SmallVectorImpl<const MachineBasicBlock *> &BlockOrders);

  /// Given the solutions to the two dataflow problems, machine value locations
  /// in \p MInLocs and live-in variable values in \p SavedLiveIns, runs the
  /// TransferTracker class over the function to produce live-in and transfer
  /// DBG_VALUEs, then inserts them. Groups of DBG_VALUEs are inserted in the
  /// order given by AllVarsNumbering -- this could be any stable order, but
  /// right now "order of appearence in function, when explored in RPO", so
  /// that we can compare explictly against VarLocBasedImpl.
  void emitLocations(MachineFunction &MF, LiveInsT SavedLiveIns,
                     ValueIDNum **MOutLocs, ValueIDNum **MInLocs,
                     DenseMap<DebugVariable, unsigned> &AllVarsNumbering,
                     const TargetPassConfig &TPC);

  /// Boilerplate computation of some initial sets, artifical blocks and
  /// RPOT block ordering.
  void initialSetup(MachineFunction &MF);

  bool ExtendRanges(MachineFunction &MF, MachineDominatorTree *DomTree,
                    TargetPassConfig *TPC, unsigned InputBBLimit,
                    unsigned InputDbgValLimit) override;

public:
  /// Default construct and initialize the pass.
  InstrRefBasedLDV();

  LLVM_DUMP_METHOD
  void dump_mloc_transfer(const MLocTransferMap &mloc_transfer) const;

  bool isCalleeSaved(LocIdx L) const;

  bool hasFoldedStackStore(const MachineInstr &MI) {
    // Instruction must have a memory operand that's a stack slot, and isn't
    // aliased, meaning it's a spill from regalloc instead of a variable.
    // If it's aliased, we can't guarantee its value.
    if (!MI.hasOneMemOperand())
      return false;
    auto *MemOperand = *MI.memoperands_begin();
    return MemOperand->isStore() &&
           MemOperand->getPseudoValue() &&
           MemOperand->getPseudoValue()->kind() == PseudoSourceValue::FixedStack
           && !MemOperand->getPseudoValue()->isAliased(MFI);
  }

  Optional<LocIdx> findLocationForMemOperand(const MachineInstr &MI);
};

} // namespace LiveDebugValues

namespace llvm {
using namespace LiveDebugValues;

template <> struct DenseMapInfo<LocIdx> {
  static inline LocIdx getEmptyKey() { return LocIdx::MakeIllegalLoc(); }
  static inline LocIdx getTombstoneKey() { return LocIdx::MakeTombstoneLoc(); }

  static unsigned getHashValue(const LocIdx &Loc) { return Loc.asU64(); }

  static bool isEqual(const LocIdx &A, const LocIdx &B) { return A == B; }
};

template <> struct DenseMapInfo<ValueIDNum> {
  static inline ValueIDNum getEmptyKey() { return ValueIDNum::EmptyValue; }
  static inline ValueIDNum getTombstoneKey() {
    return ValueIDNum::TombstoneValue;
  }

  static unsigned getHashValue(const ValueIDNum &Val) { return Val.asU64(); }

  static bool isEqual(const ValueIDNum &A, const ValueIDNum &B) {
    return A == B;
  }
};

} // end namespace llvm

#endif /* LLVM_LIB_CODEGEN_LIVEDEBUGVALUES_INSTRREFBASEDLDV_H */