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diff --git a/contrib/llvm/tools/clang/include/clang/AST/Redeclarable.h b/contrib/llvm/tools/clang/include/clang/AST/Redeclarable.h
new file mode 100644
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--- /dev/null
+++ b/contrib/llvm/tools/clang/include/clang/AST/Redeclarable.h
@@ -0,0 +1,179 @@
+//===-- Redeclarable.h - Base for Decls that can be redeclared -*- 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 Redeclarable interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_REDECLARABLE_H
+#define LLVM_CLANG_AST_REDECLARABLE_H
+
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/Support/Casting.h"
+#include <iterator>
+
+namespace clang {
+
+/// \brief Provides common interface for the Decls that can be redeclared.
+template<typename decl_type>
+class Redeclarable {
+
+protected:
+  // FIXME: PointerIntPair is a value class that should not be inherited from.
+  // This should change to using containment.
+  struct DeclLink : public llvm::PointerIntPair<decl_type *, 1, bool> {
+    DeclLink(decl_type *D, bool isLatest)
+      : llvm::PointerIntPair<decl_type *, 1, bool>(D, isLatest) { }
+
+    typedef llvm::PointerIntPair<decl_type *, 1, bool> base_type;
+
+    bool NextIsPrevious() const { return base_type::getInt() == false; }
+    bool NextIsLatest() const { return base_type::getInt() == true; }
+    decl_type *getNext() const { return base_type::getPointer(); }
+  };
+
+  struct PreviousDeclLink : public DeclLink {
+    PreviousDeclLink(decl_type *D) : DeclLink(D, false) { }
+  };
+
+  struct LatestDeclLink : public DeclLink {
+    LatestDeclLink(decl_type *D) : DeclLink(D, true) { }
+  };
+
+  /// \brief Points to the next redeclaration in the chain.
+  ///
+  /// If NextIsPrevious() is true, this is a link to the previous declaration
+  /// of this same Decl. If NextIsLatest() is true, this is the first
+  /// declaration and Link points to the latest declaration. For example:
+  ///
+  ///  #1 int f(int x, int y = 1); // <pointer to #3, true>
+  ///  #2 int f(int x = 0, int y); // <pointer to #1, false>
+  ///  #3 int f(int x, int y) { return x + y; } // <pointer to #2, false>
+  ///
+  /// If there is only one declaration, it is <pointer to self, true>
+  DeclLink RedeclLink;
+
+public:
+  Redeclarable() : RedeclLink(LatestDeclLink(static_cast<decl_type*>(this))) { }
+
+  /// \brief Return the previous declaration of this declaration or NULL if this
+  /// is the first declaration.
+  decl_type *getPreviousDeclaration() {
+    if (RedeclLink.NextIsPrevious())
+      return RedeclLink.getNext();
+    return 0;
+  }
+  const decl_type *getPreviousDeclaration() const {
+    return const_cast<decl_type *>(
+                 static_cast<const decl_type*>(this))->getPreviousDeclaration();
+  }
+
+  /// \brief Return the first declaration of this declaration or itself if this
+  /// is the only declaration.
+  decl_type *getFirstDeclaration() {
+    decl_type *D = static_cast<decl_type*>(this);
+    while (D->getPreviousDeclaration())
+      D = D->getPreviousDeclaration();
+    return D;
+  }
+
+  /// \brief Return the first declaration of this declaration or itself if this
+  /// is the only declaration.
+  const decl_type *getFirstDeclaration() const {
+    const decl_type *D = static_cast<const decl_type*>(this);
+    while (D->getPreviousDeclaration())
+      D = D->getPreviousDeclaration();
+    return D;
+  }
+
+  /// \brief Returns the most recent (re)declaration of this declaration.
+  decl_type *getMostRecentDeclaration() {
+    return getFirstDeclaration()->RedeclLink.getNext();
+  }
+
+  /// \brief Returns the most recent (re)declaration of this declaration.
+  const decl_type *getMostRecentDeclaration() const {
+    return getFirstDeclaration()->RedeclLink.getNext();
+  }
+  
+  /// \brief Set the previous declaration. If PrevDecl is NULL, set this as the
+  /// first and only declaration.
+  void setPreviousDeclaration(decl_type *PrevDecl) {
+    decl_type *First;
+
+    if (PrevDecl) {
+      // Point to previous. Make sure that this is actually the most recent
+      // redeclaration, or we can build invalid chains. If the most recent
+      // redeclaration is invalid, it won't be PrevDecl, but we want it anyway.
+      RedeclLink = PreviousDeclLink(llvm::cast<decl_type>(
+                                      PrevDecl->getMostRecentDeclaration()));
+      First = PrevDecl->getFirstDeclaration();
+      assert(First->RedeclLink.NextIsLatest() && "Expected first");
+    } else {
+      // Make this first.
+      First = static_cast<decl_type*>(this);
+    }
+
+    // First one will point to this one as latest.
+    First->RedeclLink = LatestDeclLink(static_cast<decl_type*>(this));
+  }
+
+  /// \brief Iterates through all the redeclarations of the same decl.
+  class redecl_iterator {
+    /// Current - The current declaration.
+    decl_type *Current;
+    decl_type *Starter;
+
+  public:
+    typedef decl_type*                value_type;
+    typedef decl_type*                reference;
+    typedef decl_type*                pointer;
+    typedef std::forward_iterator_tag iterator_category;
+    typedef std::ptrdiff_t            difference_type;
+
+    redecl_iterator() : Current(0) { }
+    explicit redecl_iterator(decl_type *C) : Current(C), Starter(C) { }
+
+    reference operator*() const { return Current; }
+    pointer operator->() const { return Current; }
+
+    redecl_iterator& operator++() {
+      assert(Current && "Advancing while iterator has reached end");
+      // Get either previous decl or latest decl.
+      decl_type *Next = Current->RedeclLink.getNext();
+      Current = (Next != Starter ? Next : 0);
+      return *this;
+    }
+
+    redecl_iterator operator++(int) {
+      redecl_iterator tmp(*this);
+      ++(*this);
+      return tmp;
+    }
+
+    friend bool operator==(redecl_iterator x, redecl_iterator y) {
+      return x.Current == y.Current;
+    }
+    friend bool operator!=(redecl_iterator x, redecl_iterator y) {
+      return x.Current != y.Current;
+    }
+  };
+
+  /// \brief Returns iterator for all the redeclarations of the same decl.
+  /// It will iterate at least once (when this decl is the only one).
+  redecl_iterator redecls_begin() const {
+    return redecl_iterator(const_cast<decl_type*>(
+                                          static_cast<const decl_type*>(this)));
+  }
+  redecl_iterator redecls_end() const { return redecl_iterator(); }
+};
+
+}
+
+#endif