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diff --git a/include/llvm/Support/BinaryStreamArray.h b/include/llvm/Support/BinaryStreamArray.h
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+//===- BinaryStreamArray.h - Array backed by an arbitrary stream *- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_BINARYSTREAMARRAY_H
+#define LLVM_SUPPORT_BINARYSTREAMARRAY_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/iterator.h"
+#include "llvm/Support/BinaryStreamRef.h"
+#include "llvm/Support/Error.h"
+#include <cassert>
+#include <cstdint>
+
+/// Lightweight arrays that are backed by an arbitrary BinaryStream.  This file
+/// provides two different array implementations.
+///
+///     VarStreamArray - Arrays of variable length records.  The user specifies
+///       an Extractor type that can extract a record from a given offset and
+///       return the number of bytes consumed by the record.
+///
+///     FixedStreamArray - Arrays of fixed length records.  This is similar in
+///       spirit to ArrayRef<T>, but since it is backed by a BinaryStream, the
+///       elements of the array need not be laid out in contiguous memory.
+namespace llvm {
+
+/// VarStreamArrayExtractor is intended to be specialized to provide customized
+/// extraction logic.  On input it receives a BinaryStreamRef pointing to the
+/// beginning of the next record, but where the length of the record is not yet
+/// known.  Upon completion, it should return an appropriate Error instance if
+/// a record could not be extracted, or if one could be extracted it should
+/// return success and set Len to the number of bytes this record occupied in
+/// the underlying stream, and it should fill out the fields of the value type
+/// Item appropriately to represent the current record.
+///
+/// You can specialize this template for your own custom value types to avoid
+/// having to specify a second template argument to VarStreamArray (documented
+/// below).
+template <typename T> struct VarStreamArrayExtractor {
+  // Method intentionally deleted.  You must provide an explicit specialization
+  // with the following method implemented.
+  Error operator()(BinaryStreamRef Stream, uint32_t &Len,
+                   T &Item) const = delete;
+};
+
+/// VarStreamArray represents an array of variable length records backed by a
+/// stream.  This could be a contiguous sequence of bytes in memory, it could
+/// be a file on disk, or it could be a PDB stream where bytes are stored as
+/// discontiguous blocks in a file.  Usually it is desirable to treat arrays
+/// as contiguous blocks of memory, but doing so with large PDB files, for
+/// example, could mean allocating huge amounts of memory just to allow
+/// re-ordering of stream data to be contiguous before iterating over it.  By
+/// abstracting this out, we need not duplicate this memory, and we can
+/// iterate over arrays in arbitrarily formatted streams.  Elements are parsed
+/// lazily on iteration, so there is no upfront cost associated with building
+/// or copying a VarStreamArray, no matter how large it may be.
+///
+/// You create a VarStreamArray by specifying a ValueType and an Extractor type.
+/// If you do not specify an Extractor type, you are expected to specialize
+/// VarStreamArrayExtractor<T> for your ValueType.
+///
+/// By default an Extractor is default constructed in the class, but in some
+/// cases you might find it useful for an Extractor to maintain state across
+/// extractions.  In this case you can provide your own Extractor through a
+/// secondary constructor.  The following examples show various ways of
+/// creating a VarStreamArray.
+///
+///       // Will use VarStreamArrayExtractor<MyType> as the extractor.
+///       VarStreamArray<MyType> MyTypeArray;
+///
+///       // Will use a default-constructed MyExtractor as the extractor.
+///       VarStreamArray<MyType, MyExtractor> MyTypeArray2;
+///
+///       // Will use the specific instance of MyExtractor provided.
+///       // MyExtractor need not be default-constructible in this case.
+///       MyExtractor E(SomeContext);
+///       VarStreamArray<MyType, MyExtractor> MyTypeArray3(E);
+///
+template <typename ValueType, typename Extractor> class VarStreamArrayIterator;
+
+template <typename ValueType,
+          typename Extractor = VarStreamArrayExtractor<ValueType>>
+
+class VarStreamArray {
+  friend class VarStreamArrayIterator<ValueType, Extractor>;
+
+public:
+  typedef VarStreamArrayIterator<ValueType, Extractor> Iterator;
+
+  VarStreamArray() = default;
+  explicit VarStreamArray(const Extractor &E) : E(E) {}
+
+  explicit VarStreamArray(BinaryStreamRef Stream) : Stream(Stream) {}
+  VarStreamArray(BinaryStreamRef Stream, const Extractor &E)
+      : Stream(Stream), E(E) {}
+
+  VarStreamArray(const VarStreamArray<ValueType, Extractor> &Other)
+      : Stream(Other.Stream), E(Other.E) {}
+
+  Iterator begin(bool *HadError = nullptr) const {
+    return Iterator(*this, E, HadError);
+  }
+
+  Iterator end() const { return Iterator(E); }
+
+  const Extractor &getExtractor() const { return E; }
+
+  BinaryStreamRef getUnderlyingStream() const { return Stream; }
+
+private:
+  BinaryStreamRef Stream;
+  Extractor E;
+};
+
+template <typename ValueType, typename Extractor>
+class VarStreamArrayIterator
+    : public iterator_facade_base<VarStreamArrayIterator<ValueType, Extractor>,
+                                  std::forward_iterator_tag, ValueType> {
+  typedef VarStreamArrayIterator<ValueType, Extractor> IterType;
+  typedef VarStreamArray<ValueType, Extractor> ArrayType;
+
+public:
+  VarStreamArrayIterator(const ArrayType &Array, const Extractor &E,
+                         bool *HadError = nullptr)
+      : IterRef(Array.Stream), Array(&Array), HadError(HadError), Extract(E) {
+    if (IterRef.getLength() == 0)
+      moveToEnd();
+    else {
+      auto EC = Extract(IterRef, ThisLen, ThisValue);
+      if (EC) {
+        consumeError(std::move(EC));
+        markError();
+      }
+    }
+  }
+  VarStreamArrayIterator() = default;
+  explicit VarStreamArrayIterator(const Extractor &E) : Extract(E) {}
+  ~VarStreamArrayIterator() = default;
+
+  bool operator==(const IterType &R) const {
+    if (Array && R.Array) {
+      // Both have a valid array, make sure they're same.
+      assert(Array == R.Array);
+      return IterRef == R.IterRef;
+    }
+
+    // Both iterators are at the end.
+    if (!Array && !R.Array)
+      return true;
+
+    // One is not at the end and one is.
+    return false;
+  }
+
+  const ValueType &operator*() const {
+    assert(Array && !HasError);
+    return ThisValue;
+  }
+
+  IterType &operator+=(unsigned N) {
+    for (unsigned I = 0; I < N; ++I) {
+      // We are done with the current record, discard it so that we are
+      // positioned at the next record.
+      IterRef = IterRef.drop_front(ThisLen);
+      if (IterRef.getLength() == 0) {
+        // There is nothing after the current record, we must make this an end
+        // iterator.
+        moveToEnd();
+      } else {
+        // There is some data after the current record.
+        auto EC = Extract(IterRef, ThisLen, ThisValue);
+        if (EC) {
+          consumeError(std::move(EC));
+          markError();
+        } else if (ThisLen == 0) {
+          // An empty record? Make this an end iterator.
+          moveToEnd();
+        }
+      }
+    }
+    return *this;
+  }
+
+private:
+  void moveToEnd() {
+    Array = nullptr;
+    ThisLen = 0;
+  }
+  void markError() {
+    moveToEnd();
+    HasError = true;
+    if (HadError != nullptr)
+      *HadError = true;
+  }
+
+  ValueType ThisValue;
+  BinaryStreamRef IterRef;
+  const ArrayType *Array{nullptr};
+  uint32_t ThisLen{0};
+  bool HasError{false};
+  bool *HadError{nullptr};
+  Extractor Extract;
+};
+
+template <typename T> class FixedStreamArrayIterator;
+
+/// FixedStreamArray is similar to VarStreamArray, except with each record
+/// having a fixed-length.  As with VarStreamArray, there is no upfront
+/// cost associated with building or copying a FixedStreamArray, as the
+/// memory for each element is not read from the backing stream until that
+/// element is iterated.
+template <typename T> class FixedStreamArray {
+  friend class FixedStreamArrayIterator<T>;
+
+public:
+  FixedStreamArray() = default;
+  explicit FixedStreamArray(BinaryStreamRef Stream) : Stream(Stream) {
+    assert(Stream.getLength() % sizeof(T) == 0);
+  }
+
+  bool operator==(const FixedStreamArray<T> &Other) const {
+    return Stream == Other.Stream;
+  }
+
+  bool operator!=(const FixedStreamArray<T> &Other) const {
+    return !(*this == Other);
+  }
+
+  FixedStreamArray &operator=(const FixedStreamArray &) = default;
+
+  const T &operator[](uint32_t Index) const {
+    assert(Index < size());
+    uint32_t Off = Index * sizeof(T);
+    ArrayRef<uint8_t> Data;
+    if (auto EC = Stream.readBytes(Off, sizeof(T), Data)) {
+      assert(false && "Unexpected failure reading from stream");
+      // This should never happen since we asserted that the stream length was
+      // an exact multiple of the element size.
+      consumeError(std::move(EC));
+    }
+    assert(llvm::alignmentAdjustment(Data.data(), alignof(T)) == 0);
+    return *reinterpret_cast<const T *>(Data.data());
+  }
+
+  uint32_t size() const { return Stream.getLength() / sizeof(T); }
+
+  bool empty() const { return size() == 0; }
+
+  FixedStreamArrayIterator<T> begin() const {
+    return FixedStreamArrayIterator<T>(*this, 0);
+  }
+
+  FixedStreamArrayIterator<T> end() const {
+    return FixedStreamArrayIterator<T>(*this, size());
+  }
+
+  BinaryStreamRef getUnderlyingStream() const { return Stream; }
+
+private:
+  BinaryStreamRef Stream;
+};
+
+template <typename T>
+class FixedStreamArrayIterator
+    : public iterator_facade_base<FixedStreamArrayIterator<T>,
+                                  std::random_access_iterator_tag, T> {
+
+public:
+  FixedStreamArrayIterator(const FixedStreamArray<T> &Array, uint32_t Index)
+      : Array(Array), Index(Index) {}
+
+  FixedStreamArrayIterator<T> &
+  operator=(const FixedStreamArrayIterator<T> &Other) {
+    Array = Other.Array;
+    Index = Other.Index;
+    return *this;
+  }
+
+  const T &operator*() const { return Array[Index]; }
+
+  bool operator==(const FixedStreamArrayIterator<T> &R) const {
+    assert(Array == R.Array);
+    return (Index == R.Index) && (Array == R.Array);
+  }
+
+  FixedStreamArrayIterator<T> &operator+=(std::ptrdiff_t N) {
+    Index += N;
+    return *this;
+  }
+
+  FixedStreamArrayIterator<T> &operator-=(std::ptrdiff_t N) {
+    assert(Index >= N);
+    Index -= N;
+    return *this;
+  }
+
+  std::ptrdiff_t operator-(const FixedStreamArrayIterator<T> &R) const {
+    assert(Array == R.Array);
+    assert(Index >= R.Index);
+    return Index - R.Index;
+  }
+
+  bool operator<(const FixedStreamArrayIterator<T> &RHS) const {
+    assert(Array == RHS.Array);
+    return Index < RHS.Index;
+  }
+
+private:
+  FixedStreamArray<T> Array;
+  uint32_t Index;
+};
+
+} // namespace llvm
+
+#endif // LLVM_SUPPORT_BINARYSTREAMARRAY_H