Index: llvm/trunk/include/llvm/Support/FileSystem.h
===================================================================
--- llvm/trunk/include/llvm/Support/FileSystem.h
+++ llvm/trunk/include/llvm/Support/FileSystem.h
@@ -817,9 +817,38 @@
   return A;
 }
 
+/// @brief Opens the file with the given name in a write-only or read-write
+/// mode, returning its open file descriptor. If the file does not exist, it
+/// is created.
+///
+/// The caller is responsible for closing the file descriptor once they are
+/// finished with it.
+///
+/// @param Name The path of the file to open, relative or absolute.
+/// @param ResultFD If the file could be opened successfully, its descriptor
+///                 is stored in this location. Otherwise, this is set to -1.
+/// @param Flags Additional flags used to determine whether the file should be
+///              opened in, for example, read-write or in write-only mode.
+/// @param Mode The access permissions of the file, represented in octal.
+/// @returns errc::success if \a Name has been opened, otherwise a
+///          platform-specific error_code.
 std::error_code openFileForWrite(const Twine &Name, int &ResultFD,
                                  OpenFlags Flags, unsigned Mode = 0666);
 
+/// @brief Opens the file with the given name in a read-only mode, returning
+/// its open file descriptor.
+///
+/// The caller is responsible for closing the file descriptor once they are
+/// finished with it.
+///
+/// @param Name The path of the file to open, relative or absolute.
+/// @param ResultFD If the file could be opened successfully, its descriptor
+///                 is stored in this location. Otherwise, this is set to -1.
+/// @param RealPath If nonnull, extra work is done to determine the real path
+///                 of the opened file, and that path is stored in this
+///                 location.
+/// @returns errc::success if \a Name has been opened, otherwise a
+///          platform-specific error_code.
 std::error_code openFileForRead(const Twine &Name, int &ResultFD,
                                 SmallVectorImpl<char> *RealPath = nullptr);
 
Index: llvm/trunk/lib/Support/Windows/Path.inc
===================================================================
--- llvm/trunk/lib/Support/Windows/Path.inc
+++ llvm/trunk/lib/Support/Windows/Path.inc
@@ -1052,6 +1052,7 @@
 
 std::error_code openFileForRead(const Twine &Name, int &ResultFD,
                                 SmallVectorImpl<char> *RealPath) {
+  ResultFD = -1;
   SmallVector<wchar_t, 128> PathUTF16;
 
   if (std::error_code EC = widenPath(Name, PathUTF16))
@@ -1074,8 +1075,8 @@
     return EC;
   }
 
-  int FD = ::_open_osfhandle(intptr_t(H), 0);
-  if (FD == -1) {
+  ResultFD = ::_open_osfhandle(intptr_t(H), 0);
+  if (ResultFD == -1) {
     ::CloseHandle(H);
     return mapWindowsError(ERROR_INVALID_HANDLE);
   }
@@ -1084,7 +1085,6 @@
   if (RealPath)
     realPathFromHandle(H, *RealPath);
 
-  ResultFD = FD;
   return std::error_code();
 }
 
@@ -1094,6 +1094,7 @@
   assert((!(Flags & sys::fs::F_Excl) || !(Flags & sys::fs::F_Append)) &&
          "Cannot specify both 'excl' and 'append' file creation flags!");
 
+  ResultFD = -1;
   SmallVector<wchar_t, 128> PathUTF16;
 
   if (std::error_code EC = widenPath(Name, PathUTF16))
@@ -1141,13 +1142,12 @@
   if (Flags & F_Text)
     OpenFlags |= _O_TEXT;
 
-  int FD = ::_open_osfhandle(intptr_t(H), OpenFlags);
-  if (FD == -1) {
+  ResultFD = ::_open_osfhandle(intptr_t(H), OpenFlags);
+  if (ResultFD == -1) {
     ::CloseHandle(H);
     return mapWindowsError(ERROR_INVALID_HANDLE);
   }
 
-  ResultFD = FD;
   return std::error_code();
 }