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diff --git a/third_party/llvm-project/include/llvm/MC/MCRegister.h b/third_party/llvm-project/include/llvm/MC/MCRegister.h
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+++ b/third_party/llvm-project/include/llvm/MC/MCRegister.h
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+//===-- llvm/MC/Register.h --------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_REGISTER_H
+#define LLVM_MC_REGISTER_H
+
+#include "llvm/ADT/DenseMapInfo.h"
+#include <cassert>
+
+namespace llvm {
+
+/// An unsigned integer type large enough to represent all physical registers,
+/// but not necessarily virtual registers.
+using MCPhysReg = uint16_t;
+
+/// Wrapper class representing physical registers. Should be passed by value.
+class MCRegister {
+  unsigned Reg;
+
+public:
+  MCRegister(unsigned Val = 0): Reg(Val) {}
+
+  // Register numbers can represent physical registers, virtual registers, and
+  // sometimes stack slots. The unsigned values are divided into these ranges:
+  //
+  //   0           Not a register, can be used as a sentinel.
+  //   [1;2^30)    Physical registers assigned by TableGen.
+  //   [2^30;2^31) Stack slots. (Rarely used.)
+  //   [2^31;2^32) Virtual registers assigned by MachineRegisterInfo.
+  //
+  // Further sentinels can be allocated from the small negative integers.
+  // DenseMapInfo<unsigned> uses -1u and -2u.
+
+  /// This is the portion of the positive number space that is not a physical
+  /// register. StackSlot values do not exist in the MC layer, see
+  /// Register::isStackSlot() for the more information on them.
+  ///
+  /// Note that isVirtualRegister() and isPhysicalRegister() cannot handle stack
+  /// slots, so if a variable may contains a stack slot, always check
+  /// isStackSlot() first.
+  static bool isStackSlot(unsigned Reg) {
+    return int(Reg) >= (1 << 30);
+  }
+
+  /// Return true if the specified register number is in
+  /// the physical register namespace.
+  static bool isPhysicalRegister(unsigned Reg) {
+    assert(!isStackSlot(Reg) && "Not a register! Check isStackSlot() first.");
+    return int(Reg) > 0;
+  }
+
+  /// Return true if the specified register number is in the physical register
+  /// namespace.
+  bool isPhysical() const {
+    return isPhysicalRegister(Reg);
+  }
+
+  operator unsigned() const {
+    return Reg;
+  }
+
+  unsigned id() const {
+    return Reg;
+  }
+
+  bool isValid() const {
+    return Reg != 0;
+  }
+
+  /// Comparisons between register objects
+  bool operator==(const MCRegister &Other) const { return Reg == Other.Reg; }
+  bool operator!=(const MCRegister &Other) const { return Reg != Other.Reg; }
+
+  /// Comparisons against register constants. E.g.
+  /// * R == AArch64::WZR
+  /// * R == 0
+  /// * R == VirtRegMap::NO_PHYS_REG
+  bool operator==(unsigned Other) const { return Reg == Other; }
+  bool operator!=(unsigned Other) const { return Reg != Other; }
+  bool operator==(int Other) const { return Reg == unsigned(Other); }
+  bool operator!=(int Other) const { return Reg != unsigned(Other); }
+  // MSVC requires that we explicitly declare these two as well.
+  bool operator==(MCPhysReg Other) const { return Reg == unsigned(Other); }
+  bool operator!=(MCPhysReg Other) const { return Reg != unsigned(Other); }
+};
+
+// Provide DenseMapInfo for MCRegister
+template<> struct DenseMapInfo<MCRegister> {
+  static inline unsigned getEmptyKey() {
+    return DenseMapInfo<unsigned>::getEmptyKey();
+  }
+  static inline unsigned getTombstoneKey() {
+    return DenseMapInfo<unsigned>::getTombstoneKey();
+  }
+  static unsigned getHashValue(const MCRegister &Val) {
+    return DenseMapInfo<unsigned>::getHashValue(Val.id());
+  }
+  static bool isEqual(const MCRegister &LHS, const MCRegister &RHS) {
+    return DenseMapInfo<unsigned>::isEqual(LHS.id(), RHS.id());
+  }
+};
+
+}
+
+#endif // ifndef LLVM_MC_REGISTER_H