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diff --git a/include/llvm/DebugInfo/GSYM/GsymReader.h b/include/llvm/DebugInfo/GSYM/GsymReader.h
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+++ b/include/llvm/DebugInfo/GSYM/GsymReader.h
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+//===- GsymReader.h ---------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_DEBUGINFO_GSYM_GSYMREADER_H
+#define LLVM_DEBUGINFO_GSYM_GSYMREADER_H
+
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/DebugInfo/GSYM/FileEntry.h"
+#include "llvm/DebugInfo/GSYM/FunctionInfo.h"
+#include "llvm/DebugInfo/GSYM/Header.h"
+#include "llvm/DebugInfo/GSYM/LineEntry.h"
+#include "llvm/DebugInfo/GSYM/StringTable.h"
+#include "llvm/Support/DataExtractor.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/ErrorOr.h"
+
+#include <inttypes.h>
+#include <memory>
+#include <stdint.h>
+#include <string>
+#include <vector>
+
+namespace llvm {
+class MemoryBuffer;
+class raw_ostream;
+
+namespace gsym {
+
+/// GsymReader is used to read GSYM data from a file or buffer.
+///
+/// This class is optimized for very quick lookups when the endianness matches
+/// the host system. The Header, address table, address info offsets, and file
+/// table is designed to be mmap'ed as read only into memory and used without
+/// any parsing needed. If the endianness doesn't match, we swap these objects
+/// and tables into GsymReader::SwappedData and then point our header and
+/// ArrayRefs to this swapped internal data.
+///
+/// GsymReader objects must use one of the static functions to create an
+/// instance: GsymReader::openFile(...) and GsymReader::copyBuffer(...).
+
+class GsymReader {
+  GsymReader(std::unique_ptr<MemoryBuffer> Buffer);
+  llvm::Error parse();
+
+  std::unique_ptr<MemoryBuffer> MemBuffer;
+  StringRef GsymBytes;
+  llvm::support::endianness Endian;
+  const Header *Hdr = nullptr;
+  ArrayRef<uint8_t> AddrOffsets;
+  ArrayRef<uint32_t> AddrInfoOffsets;
+  ArrayRef<FileEntry> Files;
+  StringTable StrTab;
+  /// When the GSYM file's endianness doesn't match the host system then
+  /// we must decode all data structures that need to be swapped into
+  /// local storage and set point the ArrayRef objects above to these swapped
+  /// copies.
+  struct SwappedData {
+    Header Hdr;
+    std::vector<uint8_t> AddrOffsets;
+    std::vector<uint32_t> AddrInfoOffsets;
+    std::vector<FileEntry> Files;
+  };
+  std::unique_ptr<SwappedData> Swap;
+
+public:
+  GsymReader(GsymReader &&RHS);
+  ~GsymReader();
+
+  /// Construct a GsymReader from a file on disk.
+  ///
+  /// \param Path The file path the GSYM file to read.
+  /// \returns An expected GsymReader that contains the object or an error
+  /// object that indicates reason for failing to read the GSYM.
+  static llvm::Expected<GsymReader> openFile(StringRef Path);
+
+  /// Construct a GsymReader from a buffer.
+  ///
+  /// \param Bytes A set of bytes that will be copied and owned by the
+  /// returned object on success.
+  /// \returns An expected GsymReader that contains the object or an error
+  /// object that indicates reason for failing to read the GSYM.
+  static llvm::Expected<GsymReader> copyBuffer(StringRef Bytes);
+
+  /// Access the GSYM header.
+  /// \returns A native endian version of the GSYM header.
+  const Header &getHeader() const;
+
+  /// Get the full function info for an address.
+  ///
+  /// \param Addr A virtual address from the orignal object file to lookup.
+  /// \returns An expected FunctionInfo that contains the function info object
+  /// or an error object that indicates reason for failing to lookup the
+  /// address,
+  llvm::Expected<FunctionInfo> getFunctionInfo(uint64_t Addr) const;
+
+  /// Get a string from the string table.
+  ///
+  /// \param Offset The string table offset for the string to retrieve.
+  /// \returns The string from the strin table.
+  StringRef getString(uint32_t Offset) const { return StrTab[Offset]; }
+
+protected:
+  /// Gets an address from the address table.
+  ///
+  /// Addresses are stored as offsets frrom the gsym::Header::BaseAddress.
+  ///
+  /// \param Index A index into the address table.
+  /// \returns A resolved virtual address for adddress in the address table
+  /// or llvm::None if Index is out of bounds.
+  Optional<uint64_t> getAddress(size_t Index) const;
+
+  /// Get the a file entry for the suppplied file index.
+  ///
+  /// Used to convert any file indexes in the FunctionInfo data back into
+  /// files. This function can be used for iteration, but is more commonly used
+  /// for random access when doing lookups.
+  ///
+  /// \param Index An index into the file table.
+  /// \returns An optional FileInfo that will be valid if the file index is
+  /// valid, or llvm::None if the file index is out of bounds,
+  Optional<FileEntry> getFile(uint32_t Index) const {
+    if (Index < Files.size())
+      return Files[Index];
+    return llvm::None;
+  }
+
+  /// Get an appropriate address info offsets array.
+  ///
+  /// The address table in the GSYM file is stored as array of 1, 2, 4 or 8
+  /// byte offsets from the The gsym::Header::BaseAddress. The table is stored
+  /// internally as a array of bytes that are in the correct endianness. When
+  /// we access this table we must get an array that matches those sizes. This
+  /// templatized helper function is used when accessing address offsets in the
+  /// AddrOffsets member variable.
+  ///
+  /// \returns An ArrayRef of an appropriate address offset size.
+  template <class T> ArrayRef<T>
+  getAddrOffsets() const {
+    return ArrayRef<T>(reinterpret_cast<const T *>(AddrOffsets.data()),
+                       AddrOffsets.size()/sizeof(T));
+  }
+
+  /// Get an appropriate address from the address table.
+  ///
+  /// The address table in the GSYM file is stored as array of 1, 2, 4 or 8
+  /// byte address offsets from the The gsym::Header::BaseAddress. The table is
+  /// stored internally as a array of bytes that are in the correct endianness.
+  /// In order to extract an address from the address table we must access the
+  /// address offset using the correct size and then add it to the BaseAddress
+  /// in the header.
+  ///
+  /// \param Index An index into the AddrOffsets array.
+  /// \returns An virtual address that matches the original object file for the
+  /// address as the specified index, or llvm::None if Index is out of bounds.
+  template <class T> Optional<uint64_t>
+  addressForIndex(size_t Index) const {
+    ArrayRef<T> AIO = getAddrOffsets<T>();
+    if (Index < AIO.size())
+      return AIO[Index] + Hdr->BaseAddress;
+    return llvm::None;
+  }
+  /// Lookup an address offset in the AddrOffsets table.
+  ///
+  /// Given an address offset, look it up using a binary search of the
+  /// AddrOffsets table.
+  ///
+  /// \param AddrOffset An address offset, that has already been computed by
+  /// subtracting the gsym::Header::BaseAddress.
+  /// \returns The matching address offset index. This index will be used to
+  /// extract the FunctionInfo data's offset from the AddrInfoOffsets array.
+  template <class T>
+  uint64_t getAddressOffsetIndex(const uint64_t AddrOffset) const {
+    ArrayRef<T> AIO = getAddrOffsets<T>();
+    const auto Begin = AIO.begin();
+    const auto End = AIO.end();
+    auto Iter = std::lower_bound(Begin, End, AddrOffset);
+    if (Iter == End || AddrOffset < *Iter)
+      --Iter;
+    return std::distance(Begin, Iter);
+  }
+
+  /// Create a GSYM from a memory buffer.
+  ///
+  /// Called by both openFile() and copyBuffer(), this function does all of the
+  /// work of parsing the GSYM file and returning an error.
+  ///
+  /// \param MemBuffer A memory buffer that will transfer ownership into the
+  /// GsymReader.
+  /// \returns An expected GsymReader that contains the object or an error
+  /// object that indicates reason for failing to read the GSYM.
+  static llvm::Expected<llvm::gsym::GsymReader>
+  create(std::unique_ptr<MemoryBuffer> &MemBuffer);
+
+
+  /// Given an address, find the address index.
+  ///
+  /// Binary search the address table and find the matching address index.
+  ///
+  /// \param Addr A virtual address that matches the original object file
+  /// to lookup.
+  /// \returns An index into the address table. This index can be used to
+  /// extract the FunctionInfo data's offset from the AddrInfoOffsets array.
+  /// Returns an error if the address isn't in the GSYM with details of why.
+  Expected<uint64_t> getAddressIndex(const uint64_t Addr) const;
+
+  /// Given an address index, get the offset for the FunctionInfo.
+  ///
+  /// Looking up an address is done by finding the corresponding address
+  /// index for the address. This index is then used to get the offset of the
+  /// FunctionInfo data that we will decode using this function.
+  ///
+  /// \param Index An index into the address table.
+  /// \returns An optional GSYM data offset for the offset of the FunctionInfo
+  /// that needs to be decoded.
+  Optional<uint64_t> getAddressInfoOffset(size_t Index) const;
+};
+
+} // namespace gsym
+} // namespace llvm
+
+#endif // #ifndef LLVM_DEBUGINFO_GSYM_GSYMREADER_H