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diff --git a/include/clang/Sema/IdentifierResolver.h b/include/clang/Sema/IdentifierResolver.h
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+++ b/include/clang/Sema/IdentifierResolver.h
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+//===- IdentifierResolver.h - Lexical Scope Name lookup ---------*- 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 IdentifierResolver class, which is used for lexical
+// scoped lookup, based on declaration names.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_SEMA_IDENTIFIERRESOLVER_H
+#define LLVM_CLANG_AST_SEMA_IDENTIFIERRESOLVER_H
+
+#include "clang/Basic/IdentifierTable.h"
+
+namespace clang {
+
+class ASTContext;
+class Decl;
+class DeclContext;
+class DeclarationName;
+class NamedDecl;
+class Scope;
+
+/// IdentifierResolver - Keeps track of shadowed decls on enclosing
+/// scopes.  It manages the shadowing chains of declaration names and
+/// implements efficent decl lookup based on a declaration name.
+class IdentifierResolver {
+
+  /// IdDeclInfo - Keeps track of information about decls associated
+  /// to a particular declaration name. IdDeclInfos are lazily
+  /// constructed and assigned to a declaration name the first time a
+  /// decl with that declaration name is shadowed in some scope.
+  class IdDeclInfo {
+  public:
+    typedef llvm::SmallVector<NamedDecl*, 2> DeclsTy;
+
+    inline DeclsTy::iterator decls_begin() { return Decls.begin(); }
+    inline DeclsTy::iterator decls_end() { return Decls.end(); }
+
+    void AddDecl(NamedDecl *D) { Decls.push_back(D); }
+
+    /// RemoveDecl - Remove the decl from the scope chain.
+    /// The decl must already be part of the decl chain.
+    void RemoveDecl(NamedDecl *D);
+
+    /// Replaces the Old declaration with the New declaration. If the
+    /// replacement is successful, returns true. If the old
+    /// declaration was not found, returns false.
+    bool ReplaceDecl(NamedDecl *Old, NamedDecl *New);
+
+  private:
+    DeclsTy Decls;
+  };
+
+public:
+
+  /// iterator - Iterate over the decls of a specified declaration name.
+  /// It will walk or not the parent declaration contexts depending on how
+  /// it was instantiated.
+  class iterator {
+  public:
+    typedef NamedDecl *             value_type;
+    typedef NamedDecl *             reference;
+    typedef NamedDecl *             pointer;
+    typedef std::input_iterator_tag iterator_category;
+    typedef std::ptrdiff_t          difference_type;
+
+    /// Ptr - There are 3 forms that 'Ptr' represents:
+    /// 1) A single NamedDecl. (Ptr & 0x1 == 0)
+    /// 2) A IdDeclInfo::DeclsTy::iterator that traverses only the decls of the
+    ///    same declaration context. (Ptr & 0x3 == 0x1)
+    /// 3) A IdDeclInfo::DeclsTy::iterator that traverses the decls of parent
+    ///    declaration contexts too. (Ptr & 0x3 == 0x3)
+    uintptr_t Ptr;
+    typedef IdDeclInfo::DeclsTy::iterator BaseIter;
+
+    /// A single NamedDecl. (Ptr & 0x1 == 0)
+    iterator(NamedDecl *D) {
+      Ptr = reinterpret_cast<uintptr_t>(D);
+      assert((Ptr & 0x1) == 0 && "Invalid Ptr!");
+    }
+    /// A IdDeclInfo::DeclsTy::iterator that walks or not the parent declaration
+    /// contexts depending on 'LookInParentCtx'.
+    iterator(BaseIter I) {
+      Ptr = reinterpret_cast<uintptr_t>(I) | 0x1;
+    }
+
+    bool isIterator() const { return (Ptr & 0x1); }
+
+    BaseIter getIterator() const {
+      assert(isIterator() && "Ptr not an iterator!");
+      return reinterpret_cast<BaseIter>(Ptr & ~0x3);
+    }
+
+    friend class IdentifierResolver;
+
+    void incrementSlowCase();
+  public:
+    iterator() : Ptr(0) {}
+
+    NamedDecl *operator*() const {
+      if (isIterator())
+        return *getIterator();
+      else
+        return reinterpret_cast<NamedDecl*>(Ptr);
+    }
+
+    bool operator==(const iterator &RHS) const {
+      return Ptr == RHS.Ptr;
+    }
+    bool operator!=(const iterator &RHS) const {
+      return Ptr != RHS.Ptr;
+    }
+
+    // Preincrement.
+    iterator& operator++() {
+      if (!isIterator()) // common case.
+        Ptr = 0;
+      else
+        incrementSlowCase();
+      return *this;
+    }
+
+    uintptr_t getAsOpaqueValue() const { return Ptr; }
+
+    static iterator getFromOpaqueValue(uintptr_t P) {
+      iterator Result;
+      Result.Ptr = P;
+      return Result;
+    }
+  };
+
+  /// begin - Returns an iterator for decls with the name 'Name'.
+  static iterator begin(DeclarationName Name);
+
+  /// end - Returns an iterator that has 'finished'.
+  static iterator end() {
+    return iterator();
+  }
+
+  /// isDeclInScope - If 'Ctx' is a function/method, isDeclInScope returns true
+  /// if 'D' is in Scope 'S', otherwise 'S' is ignored and isDeclInScope returns
+  /// true if 'D' belongs to the given declaration context.
+  bool isDeclInScope(Decl *D, DeclContext *Ctx, ASTContext &Context,
+                     Scope *S = 0) const;
+
+  /// AddDecl - Link the decl to its shadowed decl chain.
+  void AddDecl(NamedDecl *D);
+
+  /// RemoveDecl - Unlink the decl from its shadowed decl chain.
+  /// The decl must already be part of the decl chain.
+  void RemoveDecl(NamedDecl *D);
+
+  /// Replace the decl Old with the new declaration New on its
+  /// identifier chain. Returns true if the old declaration was found
+  /// (and, therefore, replaced).
+  bool ReplaceDecl(NamedDecl *Old, NamedDecl *New);
+
+  /// \brief Link the declaration into the chain of declarations for
+  /// the given identifier.
+  ///
+  /// This is a lower-level routine used by the AST reader to link a
+  /// declaration into a specific IdentifierInfo before the
+  /// declaration actually has a name.
+  void AddDeclToIdentifierChain(IdentifierInfo *II, NamedDecl *D);
+
+  explicit IdentifierResolver(const LangOptions &LangOpt);
+  ~IdentifierResolver();
+
+private:
+  const LangOptions &LangOpt;
+
+  class IdDeclInfoMap;
+  IdDeclInfoMap *IdDeclInfos;
+
+  /// FETokenInfo contains a Decl pointer if lower bit == 0.
+  static inline bool isDeclPtr(void *Ptr) {
+    return (reinterpret_cast<uintptr_t>(Ptr) & 0x1) == 0;
+  }
+
+  /// FETokenInfo contains a IdDeclInfo pointer if lower bit == 1.
+  static inline IdDeclInfo *toIdDeclInfo(void *Ptr) {
+    assert((reinterpret_cast<uintptr_t>(Ptr) & 0x1) == 1
+          && "Ptr not a IdDeclInfo* !");
+    return reinterpret_cast<IdDeclInfo*>(
+                    reinterpret_cast<uintptr_t>(Ptr) & ~0x1
+                                                            );
+  }
+};
+
+} // end namespace clang
+
+#endif