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diff --git a/include/llvm/MC/MCDisassembler/MCDisassembler.h b/include/llvm/MC/MCDisassembler/MCDisassembler.h
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+++ b/include/llvm/MC/MCDisassembler/MCDisassembler.h
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+//===-- llvm/MC/MCDisassembler.h - Disassembler interface -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_MC_MCDISASSEMBLER_MCDISASSEMBLER_H
+#define LLVM_MC_MCDISASSEMBLER_MCDISASSEMBLER_H
+
+#include "llvm-c/Disassembler.h"
+#include "llvm/MC/MCDisassembler/MCSymbolizer.h"
+#include "llvm/Support/DataTypes.h"
+
+namespace llvm {
+
+template <typename T> class ArrayRef;
+class MCInst;
+class MCSubtargetInfo;
+class raw_ostream;
+class MCContext;
+
+/// Superclass for all disassemblers. Consumes a memory region and provides an
+/// array of assembly instructions.
+class MCDisassembler {
+public:
+  /// Ternary decode status. Most backends will just use Fail and
+  /// Success, however some have a concept of an instruction with
+  /// understandable semantics but which is architecturally
+  /// incorrect. An example of this is ARM UNPREDICTABLE instructions
+  /// which are disassemblable but cause undefined behaviour.
+  ///
+  /// Because it makes sense to disassemble these instructions, there
+  /// is a "soft fail" failure mode that indicates the MCInst& is
+  /// valid but architecturally incorrect.
+  ///
+  /// The enum numbers are deliberately chosen such that reduction
+  /// from Success->SoftFail ->Fail can be done with a simple
+  /// bitwise-AND:
+  ///
+  ///   LEFT & TOP =  | Success       Unpredictable   Fail
+  ///   --------------+-----------------------------------
+  ///   Success       | Success       Unpredictable   Fail
+  ///   Unpredictable | Unpredictable Unpredictable   Fail
+  ///   Fail          | Fail          Fail            Fail
+  ///
+  /// An easy way of encoding this is as 0b11, 0b01, 0b00 for
+  /// Success, SoftFail, Fail respectively.
+  enum DecodeStatus {
+    Fail = 0,
+    SoftFail = 1,
+    Success = 3
+  };
+
+  MCDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx)
+    : Ctx(Ctx), STI(STI), Symbolizer(), CommentStream(nullptr) {}
+
+  virtual ~MCDisassembler();
+
+  /// Returns the disassembly of a single instruction.
+  ///
+  /// \param Instr    - An MCInst to populate with the contents of the
+  ///                   instruction.
+  /// \param Size     - A value to populate with the size of the instruction, or
+  ///                   the number of bytes consumed while attempting to decode
+  ///                   an invalid instruction.
+  /// \param Address  - The address, in the memory space of region, of the first
+  ///                   byte of the instruction.
+  /// \param VStream  - The stream to print warnings and diagnostic messages on.
+  /// \param CStream  - The stream to print comments and annotations on.
+  /// \return         - MCDisassembler::Success if the instruction is valid,
+  ///                   MCDisassembler::SoftFail if the instruction was
+  ///                                            disassemblable but invalid,
+  ///                   MCDisassembler::Fail if the instruction was invalid.
+  virtual DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
+                                      ArrayRef<uint8_t> Bytes, uint64_t Address,
+                                      raw_ostream &VStream,
+                                      raw_ostream &CStream) const = 0;
+
+private:
+  MCContext &Ctx;
+
+protected:
+  // Subtarget information, for instruction decoding predicates if required.
+  const MCSubtargetInfo &STI;
+  std::unique_ptr<MCSymbolizer> Symbolizer;
+
+public:
+  // Helpers around MCSymbolizer
+  bool tryAddingSymbolicOperand(MCInst &Inst,
+                                int64_t Value,
+                                uint64_t Address, bool IsBranch,
+                                uint64_t Offset, uint64_t InstSize) const;
+
+  void tryAddingPcLoadReferenceComment(int64_t Value, uint64_t Address) const;
+
+  /// Set \p Symzer as the current symbolizer.
+  /// This takes ownership of \p Symzer, and deletes the previously set one.
+  void setSymbolizer(std::unique_ptr<MCSymbolizer> Symzer);
+
+  MCContext& getContext() const { return Ctx; }
+
+  const MCSubtargetInfo& getSubtargetInfo() const { return STI; }
+
+  // Marked mutable because we cache it inside the disassembler, rather than
+  // having to pass it around as an argument through all the autogenerated code.
+  mutable raw_ostream *CommentStream;
+};
+
+} // namespace llvm
+
+#endif