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diff --git a/clang/include/clang/Lex/MultipleIncludeOpt.h b/clang/include/clang/Lex/MultipleIncludeOpt.h
new file mode 100644
index 0000000..95b00df
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+++ b/clang/include/clang/Lex/MultipleIncludeOpt.h
@@ -0,0 +1,130 @@
+//===--- MultipleIncludeOpt.h - Header Multiple-Include Optzn ---*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the MultipleIncludeOpt interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_MULTIPLEINCLUDEOPT_H
+#define LLVM_CLANG_MULTIPLEINCLUDEOPT_H
+
+namespace clang {
+class IdentifierInfo;
+
+/// MultipleIncludeOpt - This class implements the simple state machine that the
+/// Lexer class uses to detect files subject to the 'multiple-include'
+/// optimization.  The public methods in this class are triggered by various
+/// events that occur when a file is lexed, and after the entire file is lexed,
+/// information about which macro (if any) controls the header is returned.
+class MultipleIncludeOpt {
+  /// ReadAnyTokens - This is set to false when a file is first opened and true
+  /// any time a token is returned to the client or a (non-multiple-include)
+  /// directive is parsed.  When the final #endif is parsed this is reset back
+  /// to false, that way any tokens before the first #ifdef or after the last
+  /// #endif can be easily detected.
+  bool ReadAnyTokens;
+
+  /// ReadAnyTokens - This is set to false when a file is first opened and true
+  /// any time a token is returned to the client or a (non-multiple-include)
+  /// directive is parsed.  When the final #endif is parsed this is reset back
+  /// to false, that way any tokens before the first #ifdef or after the last
+  /// #endif can be easily detected.
+  bool DidMacroExpansion;
+
+  /// TheMacro - The controlling macro for a file, if valid.
+  ///
+  const IdentifierInfo *TheMacro;
+public:
+  MultipleIncludeOpt() {
+    ReadAnyTokens = false;
+    DidMacroExpansion = false;
+    TheMacro = 0;
+  }
+
+  /// Invalidate - Permanently mark this file as not being suitable for the
+  /// include-file optimization.
+  void Invalidate() {
+    // If we have read tokens but have no controlling macro, the state-machine
+    // below can never "accept".
+    ReadAnyTokens = true;
+    TheMacro = 0;
+  }
+
+  /// getHasReadAnyTokensVal - This is used for the #ifndef hande-shake at the
+  /// top of the file when reading preprocessor directives.  Otherwise, reading
+  /// the "ifndef x" would count as reading tokens.
+  bool getHasReadAnyTokensVal() const { return ReadAnyTokens; }
+
+  // If a token is read, remember that we have seen a side-effect in this file.
+  void ReadToken() { ReadAnyTokens = true; }
+
+  /// ExpandedMacro - When a macro is expanded with this lexer as the current
+  /// buffer, this method is called to disable the MIOpt if needed.
+  void ExpandedMacro() { DidMacroExpansion = true; }
+
+  /// EnterTopLevelIFNDEF - When entering a top-level #ifndef directive (or the
+  /// "#if !defined" equivalent) without any preceding tokens, this method is
+  /// called.
+  ///
+  /// Note, we don't care about the input value of 'ReadAnyTokens'.  The caller
+  /// ensures that this is only called if there are no tokens read before the
+  /// #ifndef.  The caller is required to do this, because reading the #if line
+  /// obviously reads in in tokens.
+  void EnterTopLevelIFNDEF(const IdentifierInfo *M) {
+    // If the macro is already set, this is after the top-level #endif.
+    if (TheMacro)
+      return Invalidate();
+
+    // If we have already expanded a macro by the end of the #ifndef line, then
+    // there is a macro expansion *in* the #ifndef line.  This means that the
+    // condition could evaluate differently when subsequently #included.  Reject
+    // this.
+    if (DidMacroExpansion)
+      return Invalidate();
+
+    // Remember that we're in the #if and that we have the macro.
+    ReadAnyTokens = true;
+    TheMacro = M;
+  }
+
+  /// EnterTopLevelConditional - This is invoked when a top level conditional
+  /// (except #ifndef) is found.
+  void EnterTopLevelConditional() {
+    /// If a conditional directive (except #ifndef) is found at the top level,
+    /// there is a chunk of the file not guarded by the controlling macro.
+    Invalidate();
+  }
+
+  /// ExitTopLevelConditional - This method is called when the lexer exits the
+  /// top-level conditional.
+  void ExitTopLevelConditional() {
+    // If we have a macro, that means the top of the file was ok.  Set our state
+    // back to "not having read any tokens" so we can detect anything after the
+    // #endif.
+    if (!TheMacro) return Invalidate();
+
+    // At this point, we haven't "read any tokens" but we do have a controlling
+    // macro.
+    ReadAnyTokens = false;
+  }
+
+  /// GetControllingMacroAtEndOfFile - Once the entire file has been lexed, if
+  /// there is a controlling macro, return it.
+  const IdentifierInfo *GetControllingMacroAtEndOfFile() const {
+    // If we haven't read any tokens after the #endif, return the controlling
+    // macro if it's valid (if it isn't, it will be null).
+    if (!ReadAnyTokens)
+      return TheMacro;
+    return 0;
+  }
+};
+
+}  // end namespace clang
+
+#endif