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diff --git a/include/llvm/CodeGen/LiveRangeCalc.h b/include/llvm/CodeGen/LiveRangeCalc.h
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+//===- LiveRangeCalc.h - Calculate live ranges ------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// The LiveRangeCalc class can be used to compute live ranges from scratch.  It
+// caches information about values in the CFG to speed up repeated operations
+// on the same live range.  The cache can be shared by non-overlapping live
+// ranges.  SplitKit uses that when computing the live range of split products.
+//
+// A low-level interface is available to clients that know where a variable is
+// live, but don't know which value it has as every point.  LiveRangeCalc will
+// propagate values down the dominator tree, and even insert PHI-defs where
+// needed.  SplitKit uses this faster interface when possible.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_LIVERANGECALC_H
+#define LLVM_LIB_CODEGEN_LIVERANGECALC_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/IndexedMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/LiveInterval.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/SlotIndexes.h"
+#include "llvm/MC/LaneBitmask.h"
+#include <utility>
+
+namespace llvm {
+
+template <class NodeT> class DomTreeNodeBase;
+class MachineDominatorTree;
+class MachineFunction;
+class MachineRegisterInfo;
+
+using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
+
+class LiveRangeCalc {
+  const MachineFunction *MF = nullptr;
+  const MachineRegisterInfo *MRI = nullptr;
+  SlotIndexes *Indexes = nullptr;
+  MachineDominatorTree *DomTree = nullptr;
+  VNInfo::Allocator *Alloc = nullptr;
+
+  /// LiveOutPair - A value and the block that defined it.  The domtree node is
+  /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
+  using LiveOutPair = std::pair<VNInfo *, MachineDomTreeNode *>;
+
+  /// LiveOutMap - Map basic blocks to the value leaving the block.
+  using LiveOutMap = IndexedMap<LiveOutPair, MBB2NumberFunctor>;
+
+  /// Bit vector of active entries in LiveOut, also used as a visited set by
+  /// findReachingDefs.  One entry per basic block, indexed by block number.
+  /// This is kept as a separate bit vector because it can be cleared quickly
+  /// when switching live ranges.
+  BitVector Seen;
+
+  /// Map LiveRange to sets of blocks (represented by bit vectors) that
+  /// in the live range are defined on entry and undefined on entry.
+  /// A block is defined on entry if there is a path from at least one of
+  /// the defs in the live range to the entry of the block, and conversely,
+  /// a block is undefined on entry, if there is no such path (i.e. no
+  /// definition reaches the entry of the block). A single LiveRangeCalc
+  /// object is used to track live-out information for multiple registers
+  /// in live range splitting (which is ok, since the live ranges of these
+  /// registers do not overlap), but the defined/undefined information must
+  /// be kept separate for each individual range.
+  /// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
+  using EntryInfoMap = DenseMap<LiveRange *, std::pair<BitVector, BitVector>>;
+  EntryInfoMap EntryInfos;
+
+  /// Map each basic block where a live range is live out to the live-out value
+  /// and its defining block.
+  ///
+  /// For every basic block, MBB, one of these conditions shall be true:
+  ///
+  ///  1. !Seen.count(MBB->getNumber())
+  ///     Blocks without a Seen bit are ignored.
+  ///  2. LiveOut[MBB].second.getNode() == MBB
+  ///     The live-out value is defined in MBB.
+  ///  3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
+  ///     The live-out value passses through MBB. All predecessors must carry
+  ///     the same value.
+  ///
+  /// The domtree node may be null, it can be computed.
+  ///
+  /// The map can be shared by multiple live ranges as long as no two are
+  /// live-out of the same block.
+  LiveOutMap Map;
+
+  /// LiveInBlock - Information about a basic block where a live range is known
+  /// to be live-in, but the value has not yet been determined.
+  struct LiveInBlock {
+    // The live range set that is live-in to this block.  The algorithms can
+    // handle multiple non-overlapping live ranges simultaneously.
+    LiveRange &LR;
+
+    // DomNode - Dominator tree node for the block.
+    // Cleared when the final value has been determined and LI has been updated.
+    MachineDomTreeNode *DomNode;
+
+    // Position in block where the live-in range ends, or SlotIndex() if the
+    // range passes through the block.  When the final value has been
+    // determined, the range from the block start to Kill will be added to LI.
+    SlotIndex Kill;
+
+    // Live-in value filled in by updateSSA once it is known.
+    VNInfo *Value = nullptr;
+
+    LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
+        : LR(LR), DomNode(node), Kill(kill) {}
+  };
+
+  /// LiveIn - Work list of blocks where the live-in value has yet to be
+  /// determined.  This list is typically computed by findReachingDefs() and
+  /// used as a work list by updateSSA().  The low-level interface may also be
+  /// used to add entries directly.
+  SmallVector<LiveInBlock, 16> LiveIn;
+
+  /// Check if the entry to block @p MBB can be reached by any of the defs
+  /// in @p LR. Return true if none of the defs reach the entry to @p MBB.
+  bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
+                    MachineBasicBlock &MBB, BitVector &DefOnEntry,
+                    BitVector &UndefOnEntry);
+
+  /// Find the set of defs that can reach @p Kill. @p Kill must belong to
+  /// @p UseMBB.
+  ///
+  /// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
+  /// all paths from the def to @p UseMBB are added to @p LR, and the function
+  /// returns true.
+  ///
+  /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
+  /// live in are added to the LiveIn array, and the function returns false.
+  ///
+  /// The array @p Undef provides the locations where the range @p LR becomes
+  /// undefined by <def,read-undef> operands on other subranges. If @p Undef
+  /// is non-empty and @p Kill is jointly dominated only by the entries of
+  /// @p Undef, the function returns false.
+  ///
+  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
+  bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB, SlotIndex Use,
+                        unsigned PhysReg, ArrayRef<SlotIndex> Undefs);
+
+  /// updateSSA - Compute the values that will be live in to all requested
+  /// blocks in LiveIn.  Create PHI-def values as required to preserve SSA form.
+  ///
+  /// Every live-in block must be jointly dominated by the added live-out
+  /// blocks.  No values are read from the live ranges.
+  void updateSSA();
+
+  /// Transfer information from the LiveIn vector to the live ranges and update
+  /// the given @p LiveOuts.
+  void updateFromLiveIns();
+
+  /// Extend the live range of @p LR to reach all uses of Reg.
+  ///
+  /// If @p LR is a main range, or if @p LI is null, then all uses must be
+  /// jointly dominated by the definitions from @p LR. If @p LR is a subrange
+  /// of the live interval @p LI, corresponding to lane mask @p LaneMask,
+  /// all uses must be jointly dominated by the definitions from @p LR
+  /// together with definitions of other lanes where @p LR becomes undefined
+  /// (via <def,read-undef> operands).
+  /// If @p LR is a main range, the @p LaneMask should be set to ~0, i.e.
+  /// LaneBitmask::getAll().
+  void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask,
+                    LiveInterval *LI = nullptr);
+
+  /// Reset Map and Seen fields.
+  void resetLiveOutMap();
+
+public:
+  LiveRangeCalc() = default;
+
+  //===--------------------------------------------------------------------===//
+  // High-level interface.
+  //===--------------------------------------------------------------------===//
+  //
+  // Calculate live ranges from scratch.
+  //
+
+  /// reset - Prepare caches for a new set of non-overlapping live ranges.  The
+  /// caches must be reset before attempting calculations with a live range
+  /// that may overlap a previously computed live range, and before the first
+  /// live range in a function.  If live ranges are not known to be
+  /// non-overlapping, call reset before each.
+  void reset(const MachineFunction *mf, SlotIndexes *SI,
+             MachineDominatorTree *MDT, VNInfo::Allocator *VNIA);
+
+  //===--------------------------------------------------------------------===//
+  // Mid-level interface.
+  //===--------------------------------------------------------------------===//
+  //
+  // Modify existing live ranges.
+  //
+
+  /// Extend the live range of @p LR to reach @p Use.
+  ///
+  /// The existing values in @p LR must be live so they jointly dominate @p Use.
+  /// If @p Use is not dominated by a single existing value, PHI-defs are
+  /// inserted as required to preserve SSA form.
+  ///
+  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
+  void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
+              ArrayRef<SlotIndex> Undefs);
+
+  /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
+  /// Each instruction defining Reg gets a new VNInfo with a corresponding
+  /// minimal live range.
+  void createDeadDefs(LiveRange &LR, unsigned Reg);
+
+  /// Extend the live range of @p LR to reach all uses of Reg.
+  ///
+  /// All uses must be jointly dominated by existing liveness.  PHI-defs are
+  /// inserted as needed to preserve SSA form.
+  void extendToUses(LiveRange &LR, unsigned PhysReg) {
+    extendToUses(LR, PhysReg, LaneBitmask::getAll());
+  }
+
+  /// Calculates liveness for the register specified in live interval @p LI.
+  /// Creates subregister live ranges as needed if subreg liveness tracking is
+  /// enabled.
+  void calculate(LiveInterval &LI, bool TrackSubRegs);
+
+  /// For live interval \p LI with correct SubRanges construct matching
+  /// information for the main live range. Expects the main live range to not
+  /// have any segments or value numbers.
+  void constructMainRangeFromSubranges(LiveInterval &LI);
+
+  //===--------------------------------------------------------------------===//
+  // Low-level interface.
+  //===--------------------------------------------------------------------===//
+  //
+  // These functions can be used to compute live ranges where the live-in and
+  // live-out blocks are already known, but the SSA value in each block is
+  // unknown.
+  //
+  // After calling reset(), add known live-out values and known live-in blocks.
+  // Then call calculateValues() to compute the actual value that is
+  // live-in to each block, and add liveness to the live ranges.
+  //
+
+  /// setLiveOutValue - Indicate that VNI is live out from MBB.  The
+  /// calculateValues() function will not add liveness for MBB, the caller
+  /// should take care of that.
+  ///
+  /// VNI may be null only if MBB is a live-through block also passed to
+  /// addLiveInBlock().
+  void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
+    Seen.set(MBB->getNumber());
+    Map[MBB] = LiveOutPair(VNI, nullptr);
+  }
+
+  /// addLiveInBlock - Add a block with an unknown live-in value.  This
+  /// function can only be called once per basic block.  Once the live-in value
+  /// has been determined, calculateValues() will add liveness to LI.
+  ///
+  /// @param LR      The live range that is live-in to the block.
+  /// @param DomNode The domtree node for the block.
+  /// @param Kill    Index in block where LI is killed.  If the value is
+  ///                live-through, set Kill = SLotIndex() and also call
+  ///                setLiveOutValue(MBB, 0).
+  void addLiveInBlock(LiveRange &LR, MachineDomTreeNode *DomNode,
+                      SlotIndex Kill = SlotIndex()) {
+    LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
+  }
+
+  /// calculateValues - Calculate the value that will be live-in to each block
+  /// added with addLiveInBlock.  Add PHI-def values as needed to preserve SSA
+  /// form.  Add liveness to all live-in blocks up to the Kill point, or the
+  /// whole block for live-through blocks.
+  ///
+  /// Every predecessor of a live-in block must have been given a value with
+  /// setLiveOutValue, the value may be null for live-trough blocks.
+  void calculateValues();
+
+  /// A diagnostic function to check if the end of the block @p MBB is
+  /// jointly dominated by the blocks corresponding to the slot indices
+  /// in @p Defs. This function is mainly for use in self-verification
+  /// checks.
+  LLVM_ATTRIBUTE_UNUSED
+  static bool isJointlyDominated(const MachineBasicBlock *MBB,
+                                 ArrayRef<SlotIndex> Defs,
+                                 const SlotIndexes &Indexes);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_CODEGEN_LIVERANGECALC_H