diff --git a/llvm/include/llvm/Bitcode/BitcodeConvenience.h b/llvm/include/llvm/Bitcode/BitcodeConvenience.h
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@@ -0,0 +1,486 @@
+//===- llvm/Bitcode/BitcodeConvenience.h - Convenience Wrappers -*- 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file Convenience wrappers for the LLVM bitcode format and bitstream APIs.
+///
+/// This allows you to use a sort of DSL to declare and use bitcode
+/// abbreviations and records. Example:
+///
+/// \code
+///     using Metadata = BCRecordLayout<
+///       METADATA_ID,  // ID
+///       BCFixed<16>,  // Module format major version
+///       BCFixed<16>,  // Module format minor version
+///       BCBlob        // misc. version information
+///     >;
+///     Metadata metadata(Out);
+///     metadata.emit(ScratchRecord, VERSION_MAJOR, VERSION_MINOR, Data);
+/// \endcode
+///
+/// For details on the bitcode format, see
+///   http://llvm.org/docs/BitCodeFormat.html
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_BITCODE_BITCODECONVENIENCE_H
+#define LLVM_BITCODE_BITCODECONVENIENCE_H
+
+#include "llvm/Bitstream/BitCodes.h"
+#include "llvm/Bitstream/BitstreamWriter.h"
+#include <cstdint>
+
+namespace llvm {
+namespace detail {
+/// Convenience base for all kinds of bitcode abbreviation fields.
+///
+/// This just defines common properties queried by the metaprogramming.
+template <bool Compound = false> class BCField {
+public:
+  static const bool IsCompound = Compound;
+
+  /// Asserts that the given data is a valid value for this field.
+  template <typename T> static void assertValid(const T &data) {}
+
+  /// Converts a raw numeric representation of this value to its preferred
+  /// type.
+  template <typename T> static T convert(T rawValue) { return rawValue; }
+};
+} // namespace detail
+
+/// Represents a literal operand in a bitcode record.
+///
+/// The value of a literal operand is the same for all instances of the record,
+/// so it is only emitted in the abbreviation definition.
+///
+/// Note that because this uses a compile-time template, you cannot have a
+/// literal operand that is fixed at run-time without dropping down to the
+/// raw LLVM APIs.
+template <uint64_t Value> class BCLiteral : public detail::BCField<> {
+public:
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(Value));
+  }
+
+  template <typename T> static void assertValid(const T &data) {
+    assert(data == Value && "data value does not match declared literal value");
+  }
+};
+
+/// Represents a fixed-width value in a bitcode record.
+///
+/// Note that the LLVM bitcode format only supports unsigned values.
+template <unsigned Width> class BCFixed : public detail::BCField<> {
+public:
+  static_assert(Width <= 64, "fixed-width field is too large");
+
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::Fixed, Width));
+  }
+
+  static void assertValid(const bool &data) {
+    assert(llvm::isUInt<Width>(data) &&
+           "data value does not fit in the given bit width");
+  }
+
+  template <typename T> static void assertValid(const T &data) {
+    assert(data >= 0 && "cannot encode signed integers");
+    assert(llvm::isUInt<Width>(data) &&
+           "data value does not fit in the given bit width");
+  }
+};
+
+/// Represents a variable-width value in a bitcode record.
+///
+/// The \p Width parameter should include the continuation bit.
+///
+/// Note that the LLVM bitcode format only supports unsigned values.
+template <unsigned Width> class BCVBR : public detail::BCField<> {
+  static_assert(Width >= 2, "width does not have room for continuation bit");
+
+public:
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::VBR, Width));
+  }
+
+  template <typename T> static void assertValid(const T &data) {
+    assert(data >= 0 && "cannot encode signed integers");
+  }
+};
+
+/// Represents a character encoded in LLVM's Char6 encoding.
+///
+/// This format is suitable for encoding decimal numbers (without signs or
+/// exponents) and C identifiers (without dollar signs), but not much else.
+///
+/// \sa http://llvm.org/docs/BitCodeFormat.html#char6-encoded-value
+class BCChar6 : public detail::BCField<> {
+public:
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::Char6));
+  }
+
+  template <typename T> static void assertValid(const T &data) {
+    assert(llvm::BitCodeAbbrevOp::isChar6(data) && "invalid Char6 data");
+  }
+
+  template <typename T> char convert(T rawValue) {
+    return static_cast<char>(rawValue);
+  }
+};
+
+/// Represents an untyped blob of bytes.
+///
+/// If present, this must be the last field in a record.
+class BCBlob : public detail::BCField<true> {
+public:
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::Blob));
+  }
+};
+
+/// Represents an array of some other type.
+///
+/// If present, this must be the last field in a record.
+template <typename ElementTy> class BCArray : public detail::BCField<true> {
+  static_assert(!ElementTy::IsCompound, "arrays can only contain scalar types");
+
+public:
+  static void emitOp(llvm::BitCodeAbbrev &abbrev) {
+    abbrev.Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::Array));
+    ElementTy::emitOp(abbrev);
+  }
+};
+
+namespace detail {
+/// Attaches the last field to an abbreviation.
+///
+/// This is the base case for \c emitOps.
+///
+/// \sa BCRecordLayout::emitAbbrev
+template <typename FieldTy> static void emitOps(llvm::BitCodeAbbrev &abbrev) {
+  FieldTy::emitOp(abbrev);
+}
+
+/// Attaches fields to an abbreviation.
+///
+/// This is the recursive case for \c emitOps.
+///
+/// \sa BCRecordLayout::emitAbbrev
+template <typename FieldTy, typename Next, typename... Rest>
+static void emitOps(llvm::BitCodeAbbrev &abbrev) {
+  static_assert(!FieldTy::IsCompound,
+                "arrays and blobs may not appear in the middle of a record");
+  FieldTy::emitOp(abbrev);
+  emitOps<Next, Rest...>(abbrev);
+}
+
+/// Helper class for dealing with a scalar element in the middle of a record.
+///
+/// \sa BCRecordLayout
+template <typename ElementTy, typename... Fields> class BCRecordCoding {
+public:
+  template <typename BufferTy, typename ElementDataTy, typename... DataTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, ElementDataTy element, DataTy &&...data) {
+    static_assert(!ElementTy::IsCompound,
+                  "arrays and blobs may not appear in the middle of a record");
+    ElementTy::assertValid(element);
+    buffer.push_back(element);
+    BCRecordCoding<Fields...>::emit(Stream, buffer, code,
+                                    std::forward<DataTy>(data)...);
+  }
+
+  template <typename T, typename ElementDataTy, typename... DataTy>
+  static void read(ArrayRef<T> buffer, ElementDataTy &element,
+                   DataTy &&...data) {
+    assert(!buffer.empty() && "too few elements in buffer");
+    element = ElementTy::convert(buffer.front());
+    BCRecordCoding<Fields...>::read(buffer.slice(1),
+                                    std::forward<DataTy>(data)...);
+  }
+
+  template <typename T, typename... DataTy>
+  static void read(ArrayRef<T> buffer, NoneType, DataTy &&...data) {
+    assert(!buffer.empty() && "too few elements in buffer");
+    BCRecordCoding<Fields...>::read(buffer.slice(1),
+                                    std::forward<DataTy>(data)...);
+  }
+};
+
+/// Helper class for dealing with a scalar element at the end of a record.
+///
+/// This has a separate implementation because up until now we've only been
+/// \em building the record (into a data buffer), and now we need to hand it
+/// off to the BitstreamWriter to be emitted.
+///
+/// \sa BCRecordLayout
+template <typename ElementTy> class BCRecordCoding<ElementTy> {
+public:
+  template <typename BufferTy, typename DataTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, const DataTy &data) {
+    static_assert(!ElementTy::IsCompound,
+                  "arrays and blobs need special handling");
+    ElementTy::assertValid(data);
+    buffer.push_back(data);
+    Stream.EmitRecordWithAbbrev(code, buffer);
+  }
+
+  template <typename T, typename DataTy>
+  static void read(ArrayRef<T> buffer, DataTy &data) {
+    assert(buffer.size() == 1 && "record data does not match layout");
+    data = ElementTy::convert(buffer.front());
+  }
+
+  template <typename T> static void read(ArrayRef<T> buffer, NoneType) {
+    assert(buffer.size() == 1 && "record data does not match layout");
+    (void)buffer;
+  }
+
+  template <typename T> static void read(ArrayRef<T> buffer) = delete;
+};
+
+/// Helper class for dealing with an array at the end of a record.
+///
+/// \sa BCRecordLayout::emitRecord
+template <typename ElementTy> class BCRecordCoding<BCArray<ElementTy>> {
+public:
+  template <typename BufferTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, StringRef data) {
+    // TODO: validate array data.
+    Stream.EmitRecordWithArray(code, buffer, data);
+  }
+
+  template <typename BufferTy, typename ArrayTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, const ArrayTy &array) {
+#ifndef NDEBUG
+    for (auto &element : array)
+      ElementTy::assertValid(element);
+#endif
+    buffer.reserve(buffer.size() + std::distance(array.begin(), array.end()));
+    std::copy(array.begin(), array.end(), std::back_inserter(buffer));
+    Stream.EmitRecordWithAbbrev(code, buffer);
+  }
+
+  template <typename BufferTy, typename ElementDataTy, typename... DataTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, ElementDataTy element, DataTy... data) {
+    std::array<ElementDataTy, 1 + sizeof...(data)> array{{element, data...}};
+    emit(Stream, buffer, code, array);
+  }
+
+  template <typename BufferTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &Buffer,
+                   unsigned code, NoneType) {
+    Stream.EmitRecordWithAbbrev(code, Buffer);
+  }
+
+  template <typename T>
+  static void read(ArrayRef<T> Buffer, ArrayRef<T> &rawData) {
+    rawData = Buffer;
+  }
+
+  template <typename T, typename ArrayTy>
+  static void read(ArrayRef<T> buffer, ArrayTy &array) {
+    array.append(llvm::map_iterator(buffer.begin(), T::convert),
+                 llvm::map_iterator(buffer.end(), T::convert));
+  }
+
+  template <typename T> static void read(ArrayRef<T> buffer, NoneType) {
+    (void)buffer;
+  }
+
+  template <typename T> static void read(ArrayRef<T> buffer) = delete;
+};
+
+/// Helper class for dealing with a blob at the end of a record.
+///
+/// \sa BCRecordLayout
+template <> class BCRecordCoding<BCBlob> {
+public:
+  template <typename BufferTy>
+  static void emit(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                   unsigned code, StringRef data) {
+    Stream.EmitRecordWithBlob(code, buffer, data);
+  }
+
+  template <typename T> static void read(ArrayRef<T> buffer) { (void)buffer; }
+
+  /// Blob data is not stored in the buffer if you are using the correct
+  /// accessor; this method should not be used.
+  template <typename T, typename DataTy>
+  static void read(ArrayRef<T> buffer, DataTy &data) = delete;
+};
+
+/// A type trait whose \c type field is the last of its template parameters.
+template <typename Head, typename... Tail> struct last_type {
+  using type = typename last_type<Tail...>::type;
+};
+
+template <typename Head> struct last_type<Head> { using type = Head; };
+
+/// A type trait whose \c value field is \c true if the last type is BCBlob.
+template <typename... Types>
+using has_blob = std::is_same<BCBlob, typename last_type<int, Types...>::type>;
+
+/// A type trait whose \c value field is \c true if the given type is a
+/// BCArray (of any element kind).
+template <typename T> struct is_array {
+private:
+  template <typename E> static bool check(BCArray<E> *);
+  static int check(...);
+
+public:
+  typedef bool value_type;
+  static constexpr bool value = !std::is_same<decltype(check((T *)nullptr)),
+                                              decltype(check(false))>::value;
+};
+
+/// A type trait whose \c value field is \c true if the last type is a
+/// BCArray (of any element kind).
+template <typename... Types>
+using has_array = is_array<typename last_type<int, Types...>::type>;
+} // namespace detail
+
+/// Represents a single bitcode record type.
+///
+/// This class template is meant to be instantiated and then given a name,
+/// so that from then on that name can be used.
+template <typename IDField, typename... Fields> class BCGenericRecordLayout {
+  llvm::BitstreamWriter &Stream;
+
+public:
+  /// The abbreviation code used for this record in the current block.
+  ///
+  /// Note that this is not the same as the semantic record code, which is the
+  /// first field of the record.
+  const unsigned AbbrevCode;
+
+  /// Create a layout and register it with the given bitstream writer.
+  explicit BCGenericRecordLayout(llvm::BitstreamWriter &Stream)
+      : Stream(Stream), AbbrevCode(emitAbbrev(Stream)) {}
+
+  /// Emit a record to the bitstream writer, using the given buffer for scratch
+  /// space.
+  ///
+  /// Note that even fixed arguments must be specified here.
+  template <typename BufferTy, typename... Data>
+  void emit(BufferTy &buffer, unsigned id, Data &&...data) const {
+    emitRecord(Stream, buffer, AbbrevCode, id, std::forward<Data>(data)...);
+  }
+
+  /// Registers this record's layout with the bitstream reader.
+  ///
+  /// eturns The abbreviation code for the newly-registered record type.
+  static unsigned emitAbbrev(llvm::BitstreamWriter &Stream) {
+    auto Abbrev = std::make_shared<llvm::BitCodeAbbrev>();
+    detail::emitOps<IDField, Fields...>(*Abbrev);
+    return Stream.EmitAbbrev(std::move(Abbrev));
+  }
+
+  /// Emit a record identified by \p abbrCode to bitstream reader \p Stream,
+  /// using \p buffer for scratch space.
+  ///
+  /// Note that even fixed arguments must be specified here. Blobs are passed
+  /// as StringRefs, while arrays can be passed inline, as aggregates, or as
+  /// pre-encoded StringRef data. Skipped values and empty arrays should use
+  /// the special Nothing value.
+  template <typename BufferTy, typename... Data>
+  static void emitRecord(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                         unsigned abbrCode, unsigned recordID, Data &&...data) {
+    static_assert(sizeof...(data) <= sizeof...(Fields) ||
+                      detail::has_array<Fields...>::value,
+                  "Too many record elements");
+    static_assert(sizeof...(data) >= sizeof...(Fields),
+                  "Too few record elements");
+    buffer.clear();
+    detail::BCRecordCoding<IDField, Fields...>::emit(
+        Stream, buffer, abbrCode, recordID, std::forward<Data>(data)...);
+  }
+
+  /// Extract record data from \p buffer into the given data fields.
+  ///
+  /// Note that even fixed arguments must be specified here. Pass \c Nothing
+  /// if you don't care about a particular parameter. Blob data is not included
+  /// in the buffer and should be handled separately by the caller.
+  template <typename ElementTy, typename... Data>
+  static void readRecord(ArrayRef<ElementTy> buffer, Data &&...data) {
+    static_assert(sizeof...(data) <= sizeof...(Fields),
+                  "Too many record elements");
+    static_assert(sizeof...(Fields) <=
+                      sizeof...(data) + detail::has_blob<Fields...>::value,
+                  "Too few record elements");
+    return detail::BCRecordCoding<Fields...>::read(buffer,
+                                                   std::forward<Data>(data)...);
+  }
+
+  /// Extract record data from \p buffer into the given data fields.
+  ///
+  /// Note that even fixed arguments must be specified here. Pass \c Nothing
+  /// if you don't care about a particular parameter. Blob data is not included
+  /// in the buffer and should be handled separately by the caller.
+  template <typename BufferTy, typename... Data>
+  static void readRecord(BufferTy &buffer, Data &&...data) {
+    return readRecord(llvm::makeArrayRef(buffer), std::forward<Data>(data)...);
+  }
+};
+
+/// A record with a fixed record code.
+template <unsigned RecordCode, typename... Fields>
+class BCRecordLayout
+    : public BCGenericRecordLayout<BCLiteral<RecordCode>, Fields...> {
+  using Base = BCGenericRecordLayout<BCLiteral<RecordCode>, Fields...>;
+
+public:
+  enum : unsigned {
+    /// The record code associated with this layout.
+    Code = RecordCode
+  };
+
+  /// Create a layout and register it with the given bitstream writer.
+  explicit BCRecordLayout(llvm::BitstreamWriter &Stream) : Base(Stream) {}
+
+  /// Emit a record to the bitstream writer, using the given buffer for scratch
+  /// space.
+  ///
+  /// Note that even fixed arguments must be specified here.
+  template <typename BufferTy, typename... Data>
+  void emit(BufferTy &buffer, Data &&...data) const {
+    Base::emit(buffer, RecordCode, std::forward<Data>(data)...);
+  }
+
+  /// Emit a record identified by \p abbrCode to bitstream reader \p Stream,
+  /// using \p buffer for scratch space.
+  ///
+  /// Note that even fixed arguments must be specified here. Currently, arrays
+  /// and blobs can only be passed as StringRefs.
+  template <typename BufferTy, typename... Data>
+  static void emitRecord(llvm::BitstreamWriter &Stream, BufferTy &buffer,
+                         unsigned abbrCode, Data &&...data) {
+    Base::emitRecord(Stream, buffer, abbrCode, RecordCode,
+                     std::forward<Data>(data)...);
+  }
+};
+
+/// RAII object to pair entering and exiting a sub-block.
+class BCBlockRAII {
+  llvm::BitstreamWriter &Stream;
+
+public:
+  BCBlockRAII(llvm::BitstreamWriter &Stream, unsigned block, unsigned abbrev)
+      : Stream(Stream) {
+    Stream.EnterSubblock(block, abbrev);
+  }
+
+  ~BCBlockRAII() { Stream.ExitBlock(); }
+};
+} // namespace llvm
+
+#endif