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diff --git a/llvm/lib/CodeGen/AllocationOrder.h b/llvm/lib/CodeGen/AllocationOrder.h
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+++ b/llvm/lib/CodeGen/AllocationOrder.h
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+//===-- llvm/CodeGen/AllocationOrder.h - Allocation Order -*- 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 an allocation order for virtual registers.
+//
+// The preferred allocation order for a virtual register depends on allocation
+// hints and target hooks. The AllocationOrder class encapsulates all of that.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_ALLOCATIONORDER_H
+#define LLVM_LIB_CODEGEN_ALLOCATIONORDER_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/MC/MCRegisterInfo.h"
+
+namespace llvm {
+
+class RegisterClassInfo;
+class VirtRegMap;
+class LiveRegMatrix;
+
+class LLVM_LIBRARY_VISIBILITY AllocationOrder {
+  SmallVector<MCPhysReg, 16> Hints;
+  ArrayRef<MCPhysReg> Order;
+  int Pos;
+
+  // If HardHints is true, *only* Hints will be returned.
+  bool HardHints;
+
+public:
+
+  /// Create a new AllocationOrder for VirtReg.
+  /// @param VirtReg      Virtual register to allocate for.
+  /// @param VRM          Virtual register map for function.
+  /// @param RegClassInfo Information about reserved and allocatable registers.
+  AllocationOrder(unsigned VirtReg,
+                  const VirtRegMap &VRM,
+                  const RegisterClassInfo &RegClassInfo,
+                  const LiveRegMatrix *Matrix);
+
+  /// Get the allocation order without reordered hints.
+  ArrayRef<MCPhysReg> getOrder() const { return Order; }
+
+  /// Return the next physical register in the allocation order, or 0.
+  /// It is safe to call next() again after it returned 0, it will keep
+  /// returning 0 until rewind() is called.
+  unsigned next(unsigned Limit = 0) {
+    if (Pos < 0)
+      return Hints.end()[Pos++];
+    if (HardHints)
+      return 0;
+    if (!Limit)
+      Limit = Order.size();
+    while (Pos < int(Limit)) {
+      unsigned Reg = Order[Pos++];
+      if (!isHint(Reg))
+        return Reg;
+    }
+    return 0;
+  }
+
+  /// As next(), but allow duplicates to be returned, and stop before the
+  /// Limit'th register in the RegisterClassInfo allocation order.
+  ///
+  /// This can produce more than Limit registers if there are hints.
+  unsigned nextWithDups(unsigned Limit) {
+    if (Pos < 0)
+      return Hints.end()[Pos++];
+    if (HardHints)
+      return 0;
+    if (Pos < int(Limit))
+      return Order[Pos++];
+    return 0;
+  }
+
+  /// Start over from the beginning.
+  void rewind() { Pos = -int(Hints.size()); }
+
+  /// Return true if the last register returned from next() was a preferred register.
+  bool isHint() const { return Pos <= 0; }
+
+  /// Return true if PhysReg is a preferred register.
+  bool isHint(unsigned PhysReg) const { return is_contained(Hints, PhysReg); }
+};
+
+} // end namespace llvm
+
+#endif