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diff --git a/llvm/lib/CodeGen/AntiDepBreaker.h b/llvm/lib/CodeGen/AntiDepBreaker.h
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+//===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- 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 AntiDepBreaker class, which implements
+// anti-dependence breaking heuristics for post-register-allocation scheduling.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
+#define LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
+
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/Support/Compiler.h"
+#include <cassert>
+#include <utility>
+#include <vector>
+
+namespace llvm {
+
+/// This class works in conjunction with the post-RA scheduler to rename
+/// registers to break register anti-dependencies (WAR hazards).
+class LLVM_LIBRARY_VISIBILITY AntiDepBreaker {
+public:
+  using DbgValueVector =
+      std::vector<std::pair<MachineInstr *, MachineInstr *>>;
+
+  virtual ~AntiDepBreaker();
+
+  /// Initialize anti-dep breaking for a new basic block.
+  virtual void StartBlock(MachineBasicBlock *BB) = 0;
+
+  /// Identifiy anti-dependencies within a basic-block region and break them by
+  /// renaming registers. Return the number of anti-dependencies broken.
+  virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
+                                         MachineBasicBlock::iterator Begin,
+                                         MachineBasicBlock::iterator End,
+                                         unsigned InsertPosIndex,
+                                         DbgValueVector &DbgValues) = 0;
+
+  /// Update liveness information to account for the current
+  /// instruction, which will not be scheduled.
+  virtual void Observe(MachineInstr &MI, unsigned Count,
+                       unsigned InsertPosIndex) = 0;
+
+  /// Finish anti-dep breaking for a basic block.
+  virtual void FinishBlock() = 0;
+
+  /// Update DBG_VALUE if dependency breaker is updating
+  /// other machine instruction to use NewReg.
+  void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) {
+    assert(MI.isDebugValue() && "MI is not DBG_VALUE!");
+    if (MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == OldReg)
+      MI.getOperand(0).setReg(NewReg);
+  }
+
+  /// Update all DBG_VALUE instructions that may be affected by the dependency
+  /// breaker's update of ParentMI to use NewReg.
+  void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
+                       unsigned OldReg, unsigned NewReg) {
+    // The following code is dependent on the order in which the DbgValues are
+    // constructed in ScheduleDAGInstrs::buildSchedGraph.
+    MachineInstr *PrevDbgMI = nullptr;
+    for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
+      MachineInstr *PrevMI = DV.second;
+      if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
+        MachineInstr *DbgMI = DV.first;
+        UpdateDbgValue(*DbgMI, OldReg, NewReg);
+        PrevDbgMI = DbgMI;
+      } else if (PrevDbgMI) {
+        break; // If no match and already found a DBG_VALUE, we're done.
+      }
+    }
+  }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H