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diff --git a/llvm/lib/CodeGen/CriticalAntiDepBreaker.h b/llvm/lib/CodeGen/CriticalAntiDepBreaker.h
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+//===- llvm/CodeGen/CriticalAntiDepBreaker.h - Anti-Dep Support -*- 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 CriticalAntiDepBreaker class, which
+// implements register anti-dependence breaking along a blocks
+// critical path during post-RA scheduler.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H
+#define LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H
+
+#include "AntiDepBreaker.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/Support/Compiler.h"
+#include <map>
+#include <vector>
+
+namespace llvm {
+
+class MachineBasicBlock;
+class MachineFunction;
+class MachineInstr;
+class MachineOperand;
+class MachineRegisterInfo;
+class RegisterClassInfo;
+class TargetInstrInfo;
+class TargetRegisterClass;
+class TargetRegisterInfo;
+
+class LLVM_LIBRARY_VISIBILITY CriticalAntiDepBreaker : public AntiDepBreaker {
+    MachineFunction& MF;
+    MachineRegisterInfo &MRI;
+    const TargetInstrInfo *TII;
+    const TargetRegisterInfo *TRI;
+    const RegisterClassInfo &RegClassInfo;
+
+    /// The set of allocatable registers.
+    /// We'll be ignoring anti-dependencies on non-allocatable registers,
+    /// because they may not be safe to break.
+    const BitVector AllocatableSet;
+
+    /// For live regs that are only used in one register class in a
+    /// live range, the register class. If the register is not live, the
+    /// corresponding value is null. If the register is live but used in
+    /// multiple register classes, the corresponding value is -1 casted to a
+    /// pointer.
+    std::vector<const TargetRegisterClass *> Classes;
+
+    /// Map registers to all their references within a live range.
+    std::multimap<unsigned, MachineOperand *> RegRefs;
+
+    using RegRefIter =
+        std::multimap<unsigned, MachineOperand *>::const_iterator;
+
+    /// The index of the most recent kill (proceeding bottom-up),
+    /// or ~0u if the register is not live.
+    std::vector<unsigned> KillIndices;
+
+    /// The index of the most recent complete def (proceeding
+    /// bottom up), or ~0u if the register is live.
+    std::vector<unsigned> DefIndices;
+
+    /// A set of registers which are live and cannot be changed to
+    /// break anti-dependencies.
+    BitVector KeepRegs;
+
+  public:
+    CriticalAntiDepBreaker(MachineFunction& MFi, const RegisterClassInfo &RCI);
+    ~CriticalAntiDepBreaker() override;
+
+    /// Initialize anti-dep breaking for a new basic block.
+    void StartBlock(MachineBasicBlock *BB) override;
+
+    /// Identifiy anti-dependencies along the critical path
+    /// of the ScheduleDAG and break them by renaming registers.
+    unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
+                                   MachineBasicBlock::iterator Begin,
+                                   MachineBasicBlock::iterator End,
+                                   unsigned InsertPosIndex,
+                                   DbgValueVector &DbgValues) override;
+
+    /// Update liveness information to account for the current
+    /// instruction, which will not be scheduled.
+    void Observe(MachineInstr &MI, unsigned Count,
+                 unsigned InsertPosIndex) override;
+
+    /// Finish anti-dep breaking for a basic block.
+    void FinishBlock() override;
+
+  private:
+    void PrescanInstruction(MachineInstr &MI);
+    void ScanInstruction(MachineInstr &MI, unsigned Count);
+    bool isNewRegClobberedByRefs(RegRefIter RegRefBegin,
+                                 RegRefIter RegRefEnd,
+                                 unsigned NewReg);
+    unsigned findSuitableFreeRegister(RegRefIter RegRefBegin,
+                                      RegRefIter RegRefEnd,
+                                      unsigned AntiDepReg,
+                                      unsigned LastNewReg,
+                                      const TargetRegisterClass *RC,
+                                      SmallVectorImpl<unsigned> &Forbid);
+  };
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H