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diff --git a/clang/lib/Sema/IdentifierResolver.cpp b/clang/lib/Sema/IdentifierResolver.cpp
new file mode 100644
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+++ b/clang/lib/Sema/IdentifierResolver.cpp
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+//===- IdentifierResolver.cpp - 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 implements the IdentifierResolver class, which is used for lexical
+// scoped lookup, based on declaration names.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Sema/IdentifierResolver.h"
+#include "clang/Sema/Scope.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclObjC.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Lex/ExternalPreprocessorSource.h"
+#include "clang/Lex/Preprocessor.h"
+
+using namespace clang;
+
+//===----------------------------------------------------------------------===//
+// IdDeclInfoMap class
+//===----------------------------------------------------------------------===//
+
+/// IdDeclInfoMap - Associates IdDeclInfos with declaration names.
+/// Allocates 'pools' (vectors of IdDeclInfos) to avoid allocating each
+/// individual IdDeclInfo to heap.
+class IdentifierResolver::IdDeclInfoMap {
+  static const unsigned int POOL_SIZE = 512;
+
+  /// We use our own linked-list implementation because it is sadly
+  /// impossible to add something to a pre-C++0x STL container without
+  /// a completely unnecessary copy.
+  struct IdDeclInfoPool {
+    IdDeclInfoPool(IdDeclInfoPool *Next) : Next(Next) {}
+    
+    IdDeclInfoPool *Next;
+    IdDeclInfo Pool[POOL_SIZE];
+  };
+  
+  IdDeclInfoPool *CurPool;
+  unsigned int CurIndex;
+
+public:
+  IdDeclInfoMap() : CurPool(0), CurIndex(POOL_SIZE) {}
+
+  ~IdDeclInfoMap() {
+    IdDeclInfoPool *Cur = CurPool;
+    while (IdDeclInfoPool *P = Cur) {
+      Cur = Cur->Next;
+      delete P;
+    }
+  }
+
+  /// Returns the IdDeclInfo associated to the DeclarationName.
+  /// It creates a new IdDeclInfo if one was not created before for this id.
+  IdDeclInfo &operator[](DeclarationName Name);
+};
+
+
+//===----------------------------------------------------------------------===//
+// IdDeclInfo Implementation
+//===----------------------------------------------------------------------===//
+
+/// RemoveDecl - Remove the decl from the scope chain.
+/// The decl must already be part of the decl chain.
+void IdentifierResolver::IdDeclInfo::RemoveDecl(NamedDecl *D) {
+  for (DeclsTy::iterator I = Decls.end(); I != Decls.begin(); --I) {
+    if (D == *(I-1)) {
+      Decls.erase(I-1);
+      return;
+    }
+  }
+
+  llvm_unreachable("Didn't find this decl on its identifier's chain!");
+}
+
+bool
+IdentifierResolver::IdDeclInfo::ReplaceDecl(NamedDecl *Old, NamedDecl *New) {
+  for (DeclsTy::iterator I = Decls.end(); I != Decls.begin(); --I) {
+    if (Old == *(I-1)) {
+      *(I - 1) = New;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+
+//===----------------------------------------------------------------------===//
+// IdentifierResolver Implementation
+//===----------------------------------------------------------------------===//
+
+IdentifierResolver::IdentifierResolver(Preprocessor &PP)
+  : LangOpt(PP.getLangOpts()), PP(PP),
+    IdDeclInfos(new IdDeclInfoMap) {
+}
+
+IdentifierResolver::~IdentifierResolver() {
+  delete IdDeclInfos;
+}
+
+/// 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 IdentifierResolver::isDeclInScope(Decl *D, DeclContext *Ctx,
+                                       ASTContext &Context, Scope *S,
+                             bool ExplicitInstantiationOrSpecialization) const {
+  Ctx = Ctx->getRedeclContext();
+
+  if (Ctx->isFunctionOrMethod() || S->isFunctionPrototypeScope()) {
+    // Ignore the scopes associated within transparent declaration contexts.
+    while (S->getEntity() &&
+           ((DeclContext *)S->getEntity())->isTransparentContext())
+      S = S->getParent();
+
+    if (S->isDeclScope(D))
+      return true;
+    if (LangOpt.CPlusPlus) {
+      // C++ 3.3.2p3:
+      // The name declared in a catch exception-declaration is local to the
+      // handler and shall not be redeclared in the outermost block of the
+      // handler.
+      // C++ 3.3.2p4:
+      // Names declared in the for-init-statement, and in the condition of if,
+      // while, for, and switch statements are local to the if, while, for, or
+      // switch statement (including the controlled statement), and shall not be
+      // redeclared in a subsequent condition of that statement nor in the
+      // outermost block (or, for the if statement, any of the outermost blocks)
+      // of the controlled statement.
+      //
+      assert(S->getParent() && "No TUScope?");
+      if (S->getParent()->getFlags() & Scope::ControlScope)
+        return S->getParent()->isDeclScope(D);
+    }
+    return false;
+  }
+
+  DeclContext *DCtx = D->getDeclContext()->getRedeclContext();
+  return ExplicitInstantiationOrSpecialization
+           ? Ctx->InEnclosingNamespaceSetOf(DCtx)
+           : Ctx->Equals(DCtx);
+}
+
+/// AddDecl - Link the decl to its shadowed decl chain.
+void IdentifierResolver::AddDecl(NamedDecl *D) {
+  DeclarationName Name = D->getDeclName();
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    updatingIdentifier(*II);
+
+  void *Ptr = Name.getFETokenInfo<void>();
+
+  if (!Ptr) {
+    Name.setFETokenInfo(D);
+    return;
+  }
+
+  IdDeclInfo *IDI;
+
+  if (isDeclPtr(Ptr)) {
+    Name.setFETokenInfo(NULL);
+    IDI = &(*IdDeclInfos)[Name];
+    NamedDecl *PrevD = static_cast<NamedDecl*>(Ptr);
+    IDI->AddDecl(PrevD);
+  } else
+    IDI = toIdDeclInfo(Ptr);
+
+  IDI->AddDecl(D);
+}
+
+void IdentifierResolver::InsertDeclAfter(iterator Pos, NamedDecl *D) {
+  DeclarationName Name = D->getDeclName();
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    updatingIdentifier(*II);
+  
+  void *Ptr = Name.getFETokenInfo<void>();
+  
+  if (!Ptr) {
+    AddDecl(D);
+    return;
+  }
+
+  if (isDeclPtr(Ptr)) {
+    // We only have a single declaration: insert before or after it,
+    // as appropriate.
+    if (Pos == iterator()) {
+      // Add the new declaration before the existing declaration.
+      NamedDecl *PrevD = static_cast<NamedDecl*>(Ptr);
+      RemoveDecl(PrevD);
+      AddDecl(D);
+      AddDecl(PrevD);
+    } else {
+      // Add new declaration after the existing declaration.
+      AddDecl(D);
+    }
+
+    return;
+  }
+
+  // General case: insert the declaration at the appropriate point in the 
+  // list, which already has at least two elements.
+  IdDeclInfo *IDI = toIdDeclInfo(Ptr);
+  if (Pos.isIterator()) {
+    IDI->InsertDecl(Pos.getIterator() + 1, D);
+  } else
+    IDI->InsertDecl(IDI->decls_begin(), D);
+}
+
+/// RemoveDecl - Unlink the decl from its shadowed decl chain.
+/// The decl must already be part of the decl chain.
+void IdentifierResolver::RemoveDecl(NamedDecl *D) {
+  assert(D && "null param passed");
+  DeclarationName Name = D->getDeclName();
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    updatingIdentifier(*II);
+
+  void *Ptr = Name.getFETokenInfo<void>();
+
+  assert(Ptr && "Didn't find this decl on its identifier's chain!");
+
+  if (isDeclPtr(Ptr)) {
+    assert(D == Ptr && "Didn't find this decl on its identifier's chain!");
+    Name.setFETokenInfo(NULL);
+    return;
+  }
+
+  return toIdDeclInfo(Ptr)->RemoveDecl(D);
+}
+
+bool IdentifierResolver::ReplaceDecl(NamedDecl *Old, NamedDecl *New) {
+  assert(Old->getDeclName() == New->getDeclName() &&
+         "Cannot replace a decl with another decl of a different name");
+
+  DeclarationName Name = Old->getDeclName();
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    updatingIdentifier(*II);
+
+  void *Ptr = Name.getFETokenInfo<void>();
+
+  if (!Ptr)
+    return false;
+
+  if (isDeclPtr(Ptr)) {
+    if (Ptr == Old) {
+      Name.setFETokenInfo(New);
+      return true;
+    }
+    return false;
+  }
+
+  return toIdDeclInfo(Ptr)->ReplaceDecl(Old, New);
+}
+
+/// begin - Returns an iterator for decls with name 'Name'.
+IdentifierResolver::iterator
+IdentifierResolver::begin(DeclarationName Name) {
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    readingIdentifier(*II);
+    
+  void *Ptr = Name.getFETokenInfo<void>();
+  if (!Ptr) return end();
+
+  if (isDeclPtr(Ptr))
+    return iterator(static_cast<NamedDecl*>(Ptr));
+
+  IdDeclInfo *IDI = toIdDeclInfo(Ptr);
+
+  IdDeclInfo::DeclsTy::iterator I = IDI->decls_end();
+  if (I != IDI->decls_begin())
+    return iterator(I-1);
+  // No decls found.
+  return end();
+}
+
+namespace {
+  enum DeclMatchKind {
+    DMK_Different,
+    DMK_Replace,
+    DMK_Ignore
+  };
+}
+
+/// \brief Compare two declarations to see whether they are different or,
+/// if they are the same, whether the new declaration should replace the 
+/// existing declaration.
+static DeclMatchKind compareDeclarations(NamedDecl *Existing, NamedDecl *New) {
+  // If the declarations are identical, ignore the new one.
+  if (Existing == New)
+    return DMK_Ignore;
+
+  // If the declarations have different kinds, they're obviously different.
+  if (Existing->getKind() != New->getKind())
+    return DMK_Different;
+
+  // If the declarations are redeclarations of each other, keep the newest one.
+  if (Existing->getCanonicalDecl() == New->getCanonicalDecl()) {
+    // If the existing declaration is somewhere in the previous declaration
+    // chain of the new declaration, then prefer the new declaration.
+    for (Decl::redecl_iterator RD = New->redecls_begin(), 
+                            RDEnd = New->redecls_end();
+         RD != RDEnd; ++RD) {
+      if (*RD == Existing)
+        return DMK_Replace;
+        
+      if (RD->isCanonicalDecl())
+        break;
+    }
+    
+    return DMK_Ignore;
+  }
+  
+  return DMK_Different;
+}
+
+bool IdentifierResolver::tryAddTopLevelDecl(NamedDecl *D, DeclarationName Name){
+  if (IdentifierInfo *II = Name.getAsIdentifierInfo())
+    readingIdentifier(*II);
+  
+  void *Ptr = Name.getFETokenInfo<void>();
+    
+  if (!Ptr) {
+    Name.setFETokenInfo(D);
+    return true;
+  }
+  
+  IdDeclInfo *IDI;
+  
+  if (isDeclPtr(Ptr)) {
+    NamedDecl *PrevD = static_cast<NamedDecl*>(Ptr);
+    
+    switch (compareDeclarations(PrevD, D)) {
+    case DMK_Different:
+      break;
+      
+    case DMK_Ignore:
+      return false;
+      
+    case DMK_Replace:
+      Name.setFETokenInfo(D);
+      return true;
+    }
+    
+    Name.setFETokenInfo(NULL);
+    IDI = &(*IdDeclInfos)[Name];
+    
+    // If the existing declaration is not visible in translation unit scope,
+    // then add the new top-level declaration first.
+    if (!PrevD->getDeclContext()->getRedeclContext()->isTranslationUnit()) {
+      IDI->AddDecl(D);
+      IDI->AddDecl(PrevD);
+    } else {
+      IDI->AddDecl(PrevD);
+      IDI->AddDecl(D);
+    }
+    return true;
+  } 
+  
+  IDI = toIdDeclInfo(Ptr);
+
+  // See whether this declaration is identical to any existing declarations.
+  // If not, find the right place to insert it.
+  for (IdDeclInfo::DeclsTy::iterator I = IDI->decls_begin(), 
+                                  IEnd = IDI->decls_end();
+       I != IEnd; ++I) {
+    
+    switch (compareDeclarations(*I, D)) {
+    case DMK_Different:
+      break;
+      
+    case DMK_Ignore:
+      return false;
+      
+    case DMK_Replace:
+      *I = D;
+      return true;
+    }
+    
+    if (!(*I)->getDeclContext()->getRedeclContext()->isTranslationUnit()) {
+      // We've found a declaration that is not visible from the translation
+      // unit (it's in an inner scope). Insert our declaration here.
+      IDI->InsertDecl(I, D);
+      return true;
+    }
+  }
+  
+  // Add the declaration to the end.
+  IDI->AddDecl(D);
+  return true;
+}
+
+void IdentifierResolver::readingIdentifier(IdentifierInfo &II) {
+  if (II.isOutOfDate())
+    PP.getExternalSource()->updateOutOfDateIdentifier(II);  
+}
+
+void IdentifierResolver::updatingIdentifier(IdentifierInfo &II) {
+  if (II.isOutOfDate())
+    PP.getExternalSource()->updateOutOfDateIdentifier(II);
+  
+  if (II.isFromAST())
+    II.setChangedSinceDeserialization();
+}
+
+//===----------------------------------------------------------------------===//
+// IdDeclInfoMap Implementation
+//===----------------------------------------------------------------------===//
+
+/// Returns the IdDeclInfo associated to the DeclarationName.
+/// It creates a new IdDeclInfo if one was not created before for this id.
+IdentifierResolver::IdDeclInfo &
+IdentifierResolver::IdDeclInfoMap::operator[](DeclarationName Name) {
+  void *Ptr = Name.getFETokenInfo<void>();
+
+  if (Ptr) return *toIdDeclInfo(Ptr);
+
+  if (CurIndex == POOL_SIZE) {
+    CurPool = new IdDeclInfoPool(CurPool);
+    CurIndex = 0;
+  }
+  IdDeclInfo *IDI = &CurPool->Pool[CurIndex];
+  Name.setFETokenInfo(reinterpret_cast<void*>(
+                              reinterpret_cast<uintptr_t>(IDI) | 0x1)
+                                                                     );
+  ++CurIndex;
+  return *IDI;
+}
+
+void IdentifierResolver::iterator::incrementSlowCase() {
+  NamedDecl *D = **this;
+  void *InfoPtr = D->getDeclName().getFETokenInfo<void>();
+  assert(!isDeclPtr(InfoPtr) && "Decl with wrong id ?");
+  IdDeclInfo *Info = toIdDeclInfo(InfoPtr);
+
+  BaseIter I = getIterator();
+  if (I != Info->decls_begin())
+    *this = iterator(I-1);
+  else // No more decls.
+    *this = iterator();
+}