diff --git a/llvm/lib/Support/FileOutputBuffer.cpp b/llvm/lib/Support/FileOutputBuffer.cpp
new file mode 100644
index 0000000..7dc9587
--- /dev/null
+++ b/llvm/lib/Support/FileOutputBuffer.cpp
@@ -0,0 +1,148 @@
+//===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Utility for creating a in-memory buffer that will be written to a file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/FileOutputBuffer.h"
+
+#include "llvm/ADT/OwningPtr.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/system_error.h"
+
+
+namespace llvm {
+
+
+FileOutputBuffer::FileOutputBuffer(uint8_t *Start, uint8_t *End, 
+                                  StringRef Path, StringRef TmpPath)
+  : BufferStart(Start), BufferEnd(End) {
+  FinalPath.assign(Path);
+  TempPath.assign(TmpPath);
+}
+
+
+FileOutputBuffer::~FileOutputBuffer() {
+  // If not already commited, delete buffer and remove temp file.
+  if ( BufferStart != NULL ) {
+    sys::fs::unmap_file_pages((void*)BufferStart, getBufferSize());
+    bool Existed;
+    sys::fs::remove(Twine(TempPath), Existed);
+  }
+}
+
+ 
+error_code FileOutputBuffer::create(StringRef FilePath, 
+                                    size_t Size,  
+                                    OwningPtr<FileOutputBuffer> &Result,
+                                    unsigned Flags) {
+  // If file already exists, it must be a regular file (to be mappable).
+  sys::fs::file_status Stat;
+  error_code EC = sys::fs::status(FilePath, Stat);
+  switch (Stat.type()) {
+    case sys::fs::file_type::file_not_found:
+      // If file does not exist, we'll create one.
+      break;
+    case sys::fs::file_type::regular_file: {
+        // If file is not currently writable, error out.
+        // FIXME: There is no sys::fs:: api for checking this.
+        // FIXME: In posix, you use the access() call to check this.
+      }
+      break;
+    default:
+      if (EC)
+        return EC;
+      else
+        return make_error_code(errc::operation_not_permitted);
+  }
+
+  // Delete target file.
+  bool Existed;
+  EC = sys::fs::remove(FilePath, Existed);
+  if (EC)
+    return EC;
+  
+  // Create new file in same directory but with random name.
+  SmallString<128> TempFilePath;
+  int FD;
+  EC = sys::fs::unique_file(Twine(FilePath) + ".tmp%%%%%%%",  
+                                                FD, TempFilePath, false, 0644);
+  if (EC)
+    return EC;
+  
+  // The unique_file() interface leaks lower layers and returns a file 
+  // descriptor.  There is no way to directly close it, so use this hack
+  // to hand it off to raw_fd_ostream to close for us.
+  {
+    raw_fd_ostream Dummy(FD, /*shouldClose=*/true);
+  }
+  
+  // Resize file to requested initial size
+  EC = sys::fs::resize_file(Twine(TempFilePath), Size);
+  if (EC)
+    return EC;
+  
+  // If requested, make the output file executable.
+  if ( Flags & F_executable ) {
+    sys::fs::file_status Stat2;
+    EC = sys::fs::status(Twine(TempFilePath), Stat2);
+    if (EC)
+      return EC;
+    
+    sys::fs::perms new_perms = Stat2.permissions();
+    if ( new_perms & sys::fs::owner_read )
+      new_perms |= sys::fs::owner_exe;
+    if ( new_perms & sys::fs::group_read )
+      new_perms |= sys::fs::group_exe;
+    if ( new_perms & sys::fs::others_read )
+      new_perms |= sys::fs::others_exe;
+    new_perms |= sys::fs::add_perms;
+    EC = sys::fs::permissions(Twine(TempFilePath), new_perms);
+    if (EC)
+      return EC;
+  }
+
+  // Memory map new file.
+  void *Base;
+  EC = sys::fs::map_file_pages(Twine(TempFilePath), 0, Size, true, Base);
+  if (EC)
+    return EC;
+  
+  // Create FileOutputBuffer object to own mapped range.
+  uint8_t *Start = reinterpret_cast<uint8_t*>(Base);
+  Result.reset(new FileOutputBuffer(Start, Start+Size, FilePath, TempFilePath));
+                     
+  return error_code::success();
+}                    
+
+
+error_code FileOutputBuffer::commit(int64_t NewSmallerSize) {
+  // Unmap buffer, letting OS flush dirty pages to file on disk.
+  void *Start = reinterpret_cast<void*>(BufferStart);
+  error_code EC = sys::fs::unmap_file_pages(Start, getBufferSize());
+  if (EC)
+    return EC;
+  
+  // If requested, resize file as part of commit.
+  if ( NewSmallerSize != -1 ) {
+    EC = sys::fs::resize_file(Twine(TempPath), NewSmallerSize);
+    if (EC)
+      return EC;
+  }
+  
+  // Rename file to final name.
+  return sys::fs::rename(Twine(TempPath), Twine(FinalPath));
+}
+
+
+} // namespace
+