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diff --git a/llvm/lib/CodeGen/SpillPlacement.h b/llvm/lib/CodeGen/SpillPlacement.h
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+//===- SpillPlacement.h - Optimal Spill Code Placement ---------*- 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 analysis computes the optimal spill code placement between basic blocks.
+//
+// The runOnMachineFunction() method only precomputes some profiling information
+// about the CFG. The real work is done by prepare(), addConstraints(), and
+// finish() which are called by the register allocator.
+//
+// Given a variable that is live across multiple basic blocks, and given
+// constraints on the basic blocks where the variable is live, determine which
+// edge bundles should have the variable in a register and which edge bundles
+// should have the variable in a stack slot.
+//
+// The returned bit vector can be used to place optimal spill code at basic
+// block entries and exits. Spill code placement inside a basic block is not
+// considered.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_SPILLPLACEMENT_H
+#define LLVM_LIB_CODEGEN_SPILLPLACEMENT_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SparseSet.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Support/BlockFrequency.h"
+
+namespace llvm {
+
+class BitVector;
+class EdgeBundles;
+class MachineBlockFrequencyInfo;
+class MachineFunction;
+class MachineLoopInfo;
+
+class SpillPlacement : public MachineFunctionPass {
+  struct Node;
+  const MachineFunction *MF;
+  const EdgeBundles *bundles;
+  const MachineLoopInfo *loops;
+  const MachineBlockFrequencyInfo *MBFI;
+  Node *nodes = nullptr;
+
+  // Nodes that are active in the current computation. Owned by the prepare()
+  // caller.
+  BitVector *ActiveNodes;
+
+  // Nodes with active links. Populated by scanActiveBundles.
+  SmallVector<unsigned, 8> Linked;
+
+  // Nodes that went positive during the last call to scanActiveBundles or
+  // iterate.
+  SmallVector<unsigned, 8> RecentPositive;
+
+  // Block frequencies are computed once. Indexed by block number.
+  SmallVector<BlockFrequency, 8> BlockFrequencies;
+
+  /// Decision threshold. A node gets the output value 0 if the weighted sum of
+  /// its inputs falls in the open interval (-Threshold;Threshold).
+  BlockFrequency Threshold;
+
+  /// List of nodes that need to be updated in ::iterate.
+  SparseSet<unsigned> TodoList;
+
+public:
+  static char ID; // Pass identification, replacement for typeid.
+
+  SpillPlacement() : MachineFunctionPass(ID) {}
+  ~SpillPlacement() override { releaseMemory(); }
+
+  /// BorderConstraint - A basic block has separate constraints for entry and
+  /// exit.
+  enum BorderConstraint {
+    DontCare,  ///< Block doesn't care / variable not live.
+    PrefReg,   ///< Block entry/exit prefers a register.
+    PrefSpill, ///< Block entry/exit prefers a stack slot.
+    PrefBoth,  ///< Block entry prefers both register and stack.
+    MustSpill  ///< A register is impossible, variable must be spilled.
+  };
+
+  /// BlockConstraint - Entry and exit constraints for a basic block.
+  struct BlockConstraint {
+    unsigned Number;            ///< Basic block number (from MBB::getNumber()).
+    BorderConstraint Entry : 8; ///< Constraint on block entry.
+    BorderConstraint Exit : 8;  ///< Constraint on block exit.
+
+    /// True when this block changes the value of the live range. This means
+    /// the block has a non-PHI def.  When this is false, a live-in value on
+    /// the stack can be live-out on the stack without inserting a spill.
+    bool ChangesValue;
+  };
+
+  /// prepare - Reset state and prepare for a new spill placement computation.
+  /// @param RegBundles Bit vector to receive the edge bundles where the
+  ///                   variable should be kept in a register. Each bit
+  ///                   corresponds to an edge bundle, a set bit means the
+  ///                   variable should be kept in a register through the
+  ///                   bundle. A clear bit means the variable should be
+  ///                   spilled. This vector is retained.
+  void prepare(BitVector &RegBundles);
+
+  /// addConstraints - Add constraints and biases. This method may be called
+  /// more than once to accumulate constraints.
+  /// @param LiveBlocks Constraints for blocks that have the variable live in or
+  ///                   live out.
+  void addConstraints(ArrayRef<BlockConstraint> LiveBlocks);
+
+  /// addPrefSpill - Add PrefSpill constraints to all blocks listed.  This is
+  /// equivalent to calling addConstraint with identical BlockConstraints with
+  /// Entry = Exit = PrefSpill, and ChangesValue = false.
+  ///
+  /// @param Blocks Array of block numbers that prefer to spill in and out.
+  /// @param Strong When true, double the negative bias for these blocks.
+  void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
+
+  /// addLinks - Add transparent blocks with the given numbers.
+  void addLinks(ArrayRef<unsigned> Links);
+
+  /// scanActiveBundles - Perform an initial scan of all bundles activated by
+  /// addConstraints and addLinks, updating their state. Add all the bundles
+  /// that now prefer a register to RecentPositive.
+  /// Prepare internal data structures for iterate.
+  /// Return true is there are any positive nodes.
+  bool scanActiveBundles();
+
+  /// iterate - Update the network iteratively until convergence, or new bundles
+  /// are found.
+  void iterate();
+
+  /// getRecentPositive - Return an array of bundles that became positive during
+  /// the previous call to scanActiveBundles or iterate.
+  ArrayRef<unsigned> getRecentPositive() { return RecentPositive; }
+
+  /// finish - Compute the optimal spill code placement given the
+  /// constraints. No MustSpill constraints will be violated, and the smallest
+  /// possible number of PrefX constraints will be violated, weighted by
+  /// expected execution frequencies.
+  /// The selected bundles are returned in the bitvector passed to prepare().
+  /// @return True if a perfect solution was found, allowing the variable to be
+  ///         in a register through all relevant bundles.
+  bool finish();
+
+  /// getBlockFrequency - Return the estimated block execution frequency per
+  /// function invocation.
+  BlockFrequency getBlockFrequency(unsigned Number) const {
+    return BlockFrequencies[Number];
+  }
+
+private:
+  bool runOnMachineFunction(MachineFunction &mf) override;
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+  void releaseMemory() override;
+
+  void activate(unsigned n);
+  void setThreshold(const BlockFrequency &Entry);
+
+  bool update(unsigned n);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_CODEGEN_SPILLPLACEMENT_H