Revamp our representation of C++ nested-name-specifiers. We now have a

uniqued representation that should both save some memory and make it
far easier to properly build canonical types for types involving
dependent nested-name-specifiers, e.g., "typename T::Nested::type".

This approach will greatly simplify the representation of
CXXScopeSpec. That'll be next.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67799 91177308-0d34-0410-b5e6-96231b3b80d8

17 files changed, 470 insertions, 348 deletions

diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index 36bf12b787..3cf48b4994 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -18,6 +18,7 @@
 #include "clang/Basic/LangOptions.h"
 #include "clang/AST/Builtins.h"
 #include "clang/AST/Decl.h"
+#include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/SourceLocation.h"
 #include "llvm/ADT/DenseMap.h"
@@ -74,6 +75,14 @@ class ASTContext {
   llvm::FoldingSet<QualifiedNameType> QualifiedNameTypes;
   llvm::FoldingSet<ObjCQualifiedInterfaceType> ObjCQualifiedInterfaceTypes;
   llvm::FoldingSet<ObjCQualifiedIdType> ObjCQualifiedIdTypes;
+
+  /// \brief The set of nested name specifiers.
+  ///
+  /// This set is managed by the NestedNameSpecifier class.
+  llvm::FoldingSet<NestedNameSpecifier> NestedNameSpecifiers;
+  NestedNameSpecifier *GlobalNestedNameSpecifier;
+  friend class NestedNameSpecifier;
+
   /// ASTRecordLayouts - A cache mapping from RecordDecls to ASTRecordLayouts.
   ///  This is lazily created.  This is intentionally not serialized.
   llvm::DenseMap<const RecordDecl*, const ASTRecordLayout*> ASTRecordLayouts;
@@ -284,8 +293,7 @@ public:
                                               unsigned NumArgs,
                                               QualType Canon = QualType());
 
-  QualType getQualifiedNameType(const NestedNameSpecifier *Components,
-                                unsigned NumComponents,
+  QualType getQualifiedNameType(NestedNameSpecifier *NNS,
                                 QualType NamedType);
 
   /// getObjCQualifiedInterfaceType - Return a 
diff --git a/include/clang/AST/ExprCXX.h b/include/clang/AST/ExprCXX.h
index 1292eaf2d2..366f860c50 100644
--- a/include/clang/AST/ExprCXX.h
+++ b/include/clang/AST/ExprCXX.h
@@ -856,34 +856,22 @@ class QualifiedDeclRefExpr : public DeclRefExpr {
   /// nested-name-specifier.
   SourceRange QualifierRange;
 
-  /// The number of components in the complete nested-name-specifier.
-  unsigned NumComponents;
-
-  QualifiedDeclRefExpr(NamedDecl *d, QualType t, SourceLocation l, bool TD, 
-                       bool VD, SourceRange R,
-                       const NestedNameSpecifier *Components,
-                       unsigned NumComponents);
+  /// \brief The nested-name-specifier that qualifies this declaration
+  /// name.
+  NestedNameSpecifier *NNS;
 
 public:
-  static QualifiedDeclRefExpr *Create(ASTContext &Context, NamedDecl *d, 
-                                      QualType t, SourceLocation l, bool TD, 
-                                      bool VD, SourceRange R,
-                                      const NestedNameSpecifier *Components,
-                                      unsigned NumComponents);
+  QualifiedDeclRefExpr(NamedDecl *d, QualType t, SourceLocation l, bool TD, 
+                       bool VD, SourceRange R, NestedNameSpecifier *NNS)
+    : DeclRefExpr(QualifiedDeclRefExprClass, d, t, l, TD, VD), 
+      QualifierRange(R), NNS(NNS) { }
 
   /// \brief Retrieve the source range of the nested-name-specifier.
   SourceRange getQualifierRange() const { return QualifierRange; }
 
-  // Iteration over of the parts of the nested-name-specifier.
-  typedef const NestedNameSpecifier * iterator;
-
-  iterator begin() const { 
-    return reinterpret_cast<const NestedNameSpecifier *>(this + 1); 
-  }
-
-  iterator end() const { return begin() + NumComponents; }
-
-  unsigned size() const { return NumComponents; }
+  /// \brief Retrieve the nested-name-specifier that qualifies this
+  /// declaration.
+  NestedNameSpecifier *getQualifier() const { return NNS; }
 
   virtual SourceRange getSourceRange() const { 
     return SourceRange(QualifierRange.getBegin(), getLocation()); 
@@ -908,7 +896,10 @@ public:
 /// the qualification (e.g., X<T>::) refers to a dependent type. In
 /// this case, X<T>::value cannot resolve to a declaration because the
 /// declaration will differ from on instantiation of X<T> to the
-/// next. Therefore, UnresolvedDeclRefExpr keeps track of the qualifier (X<T>::) and the name of the entity being referenced ("value"). Such expressions will instantiate to QualifiedDeclRefExprs.
+/// next. Therefore, UnresolvedDeclRefExpr keeps track of the
+/// qualifier (X<T>::) and the name of the entity being referenced
+/// ("value"). Such expressions will instantiate to
+/// QualifiedDeclRefExprs.
 class UnresolvedDeclRefExpr : public Expr {
   /// The name of the entity we will be referencing.
   DeclarationName Name;
@@ -920,18 +911,15 @@ class UnresolvedDeclRefExpr : public Expr {
   /// nested-name-specifier.
   SourceRange QualifierRange;
 
-  /// The number of components in the complete nested-name-specifier.
-  unsigned NumComponents;
-
-  UnresolvedDeclRefExpr(DeclarationName N, QualType T, SourceLocation L,
-                        SourceRange R, const NestedNameSpecifier *Components,
-                        unsigned NumComponents);
+  /// \brief The nested-name-specifier that qualifies this unresolved
+  /// declaration name.
+  NestedNameSpecifier *NNS;
 
 public:
-  static UnresolvedDeclRefExpr *Create(ASTContext &Context, DeclarationName N,
-                                       SourceLocation L, SourceRange R,
-                                       const NestedNameSpecifier *Components,
-                                       unsigned NumComponents);
+  UnresolvedDeclRefExpr(DeclarationName N, QualType T, SourceLocation L,
+                        SourceRange R, NestedNameSpecifier *NNS)
+    : Expr(UnresolvedDeclRefExprClass, T, true, true), 
+      Name(N), Loc(L), QualifierRange(R), NNS(NNS) { }
 
   /// \brief Retrieve the name that this expression refers to.
   DeclarationName getDeclName() const { return Name; }
@@ -942,16 +930,9 @@ public:
   /// \brief Retrieve the source range of the nested-name-specifier.
   SourceRange getQualifierRange() const { return QualifierRange; }
 
-  // Iteration over of the parts of the nested-name-specifier.
-  typedef const NestedNameSpecifier * iterator;
-
-  iterator begin() const { 
-    return reinterpret_cast<const NestedNameSpecifier *>(this + 1); 
-  }
-
-  iterator end() const { return begin() + NumComponents; }
-
-  unsigned size() const { return NumComponents; }
+  /// \brief Retrieve the nested-name-specifier that qualifies this
+  /// declaration.
+  NestedNameSpecifier *getQualifier() const { return NNS; }
 
   virtual SourceRange getSourceRange() const { 
     return SourceRange(QualifierRange.getBegin(), getLocation()); 
diff --git a/include/clang/AST/NestedNameSpecifier.h b/include/clang/AST/NestedNameSpecifier.h
index a371e89638..a740efbe09 100644
--- a/include/clang/AST/NestedNameSpecifier.h
+++ b/include/clang/AST/NestedNameSpecifier.h
@@ -14,8 +14,8 @@
 #ifndef LLVM_CLANG_AST_NESTEDNAMESPECIFIER_H
 #define LLVM_CLANG_AST_NESTEDNAMESPECIFIER_H
 
-#include "llvm/Support/DataTypes.h"
-#include <cassert>
+#include "llvm/ADT/FoldingSet.h"
+#include "llvm/ADT/PointerIntPair.h"
 
 namespace llvm {
   class raw_ostream;
@@ -24,93 +24,151 @@ namespace llvm {
 namespace clang {
 
 class ASTContext;
-class DeclContext;
+class DeclContext; // FIXME: die die die
+class NamespaceDecl;
+class IdentifierInfo;
 class Type;
 
-/// \brief Represents a single component in a C++ nested-name-specifier.
+/// \brief Represents a C++ nested name specifier, such as
+/// "::std::vector<int>::".
 ///
-/// C++ nested-name-specifiers are the prefixes to qualified
-/// namespaces. For example, "foo::" in "foo::x" is a
-/// nested-name-specifier. Multiple nested-name-specifiers can be
-/// strung together to build qualified names, e.g., "foo::bar::" in
-/// "foo::bar::x". Each NestedNameSpecifier class contains one of the
-/// terms, e.g., "foo::" or "bar::", which may be represented either
-/// as a type or as a DeclContext.
-class NestedNameSpecifier {
-  /// \brief A DeclContext or Type pointer, depending on whether the
-  /// low bit is set.
-  uintptr_t Data;
+/// C++ nested name specifiers are the prefixes to qualified
+/// namespaces. For example, "foo::" in "foo::x" is a nested name
+/// specifier. Nested name specifiers are made up of a sequence of
+/// specifiers, each of which can be a namespace, type, identifier
+/// (for dependent names), or the global specifier ('::', must be the
+/// first specifier).
+class NestedNameSpecifier : public llvm::FoldingSetNode {
+  /// \brief The nested name specifier that precedes this nested name
+  /// specifier.
+  NestedNameSpecifier *Prefix;
+
+  /// \brief The last component in the nested name specifier, which
+  /// can be an identifier, a declaration, or a type.
+  ///
+  /// When the pointer is NULL, this specifier represents the global
+  /// specifier '::'. Otherwise, the pointer is one of
+  /// IdentifierInfo*, Namespace*, or Type*, depending on the kind of
+  /// specifier. The integer stores one ofthe first four values of
+  /// type SpecifierKind.
+  llvm::PointerIntPair<void*, 2> Specifier;
 
 public:
-  NestedNameSpecifier() : Data(0) { }
-
-  /// \brief Construct a nested name specifier that refers to a type.
-  NestedNameSpecifier(const Type *T) { 
-    Data = reinterpret_cast<uintptr_t>(T);
-    assert((Data & 0x01) == 0 && "cv-qualified type in nested-name-specifier");
-    Data |= 0x01;
+  /// \brief The kind of specifier that completes this nested name
+  /// specifier.
+  enum SpecifierKind {
+    /// \brief An identifier, stored as an IdentifierInfo*.
+    Identifier = 0,
+    /// \brief A namespace, stored as a Namespace*.
+    Namespace = 1,
+    /// \brief A type, stored as a Type*.
+    TypeSpec = 2,
+    /// \brief A type that was preceded by the 'template' keyword,
+    /// stored as a Type*.
+    TypeSpecWithTemplate = 3,
+    /// \brief The global specifier '::'. There is no stored value.
+    Global = 4
+  };
+
+private:
+  /// \brief Builds the global specifier.
+  NestedNameSpecifier() : Prefix(0), Specifier(0, 0) { }
+
+  /// \brief Copy constructor used internally to clone nested name
+  /// specifiers.
+  NestedNameSpecifier(const NestedNameSpecifier &Other) 
+    : llvm::FoldingSetNode(Other), Prefix(Other.Prefix), 
+      Specifier(Other.Specifier) {
   }
 
-  /// \brief Construct nested name specifier that refers to a
-  /// DeclContext.
-  NestedNameSpecifier(const DeclContext *DC) {
-    Data = reinterpret_cast<uintptr_t>(DC);
-    assert((Data & 0x01) == 0 && "Badly aligned DeclContext pointer");
-  }
+  NestedNameSpecifier &operator=(const NestedNameSpecifier &); // do not implement
 
-  /// \brief Determines whether this nested-name-specifier refers to a
-  /// type. Otherwise, it refers to a DeclContext.
-  bool isType() const { return Data & 0x01; }
+  /// \brief Either find or insert the given nested name specifier
+  /// mockup in the given context.
+  static NestedNameSpecifier *FindOrInsert(ASTContext &Context, const NestedNameSpecifier &Mockup);
 
-  /// \brief Compute the declaration context to which this
-  /// nested-name-specifier refers.
+public:
+  /// \brief Builds a specifier combining a prefix and an identifier.
   ///
-  /// This routine computes the declaration context referenced by this
-  /// nested-name-specifier. The nested-name-specifier may store
-  /// either a DeclContext (the trivial case) or a non-dependent type
-  /// (which will have an associated DeclContext). It is an error to
-  /// invoke this routine when the nested-name-specifier refers to a
-  /// dependent type.
+  /// The prefix must be dependent, since nested name specifiers
+  /// referencing an identifier are only permitted when the identifier
+  /// cannot be resolved.
+  static NestedNameSpecifier *Create(ASTContext &Context, 
+                                     NestedNameSpecifier *Prefix, 
+                                     IdentifierInfo *II);
+
+  /// \brief Builds a nested name specifier that names a namespace.
+  static NestedNameSpecifier *Create(ASTContext &Context, 
+                                     NestedNameSpecifier *Prefix, 
+                                     NamespaceDecl *NS);
+
+  /// \brief Builds a nested name specifier that names a type.
+  static NestedNameSpecifier *Create(ASTContext &Context, 
+                                     NestedNameSpecifier *Prefix, 
+                                     bool Template, Type *T);
+
+  /// \brief Returns the nested name specifier representing the global
+  /// scope.
+  static NestedNameSpecifier *GlobalSpecifier(ASTContext &Context);
+
+  /// \brief Return the prefix of this nested name specifier.
   ///
-  /// \returns The stored DeclContext, if the nested-name-specifier
-  /// stores a DeclContext. If the nested-name-specifier stores a
-  /// non-dependent type, returns the DeclContext associated with that
-  /// type.
-  DeclContext *computeDeclContext(ASTContext &Context) const;
+  /// The prefix contains all of the parts of the nested name
+  /// specifier that preced this current specifier. For example, for a
+  /// nested name specifier that represents "foo::bar::", the current
+  /// specifier will contain "bar::" and the prefix will contain
+  /// "foo::".
+  NestedNameSpecifier *getPrefix() const { return Prefix; }
+
+  /// \brief Determine what kind of nested name specifier is stored.
+  SpecifierKind getKind() const { 
+    if (Specifier.getPointer() == 0)
+      return Global;
+    return (SpecifierKind)Specifier.getInt(); 
+  }
 
-  /// \brief Retrieve the nested-name-specifier as a type. 
-  ///
-  /// \returns The stored type. If the nested-name-specifier does not
-  /// store a type, returns NULL.
-  Type *getAsType() const {
-    if (Data & 0x01)
-      return reinterpret_cast<Type *>(Data & ~0x01);
+  /// \brief Retrieve the identifier stored in this nested name
+  /// specifier.
+  IdentifierInfo *getAsIdentifier() const {
+    if (Specifier.getInt() == Identifier)
+      return (IdentifierInfo *)Specifier.getPointer();
 
     return 0;
   }
+  
+  /// \brief Retrieve the namespace stored in this nested name
+  /// specifier.
+  NamespaceDecl *getAsNamespace() const {
+    if (Specifier.getInt() == Namespace)
+      return (NamespaceDecl *)Specifier.getPointer();
 
-  /// \brief Retrieves the nested-name-specifier as a DeclContext.
-  ///
-  /// \returns The stored DeclContext. If the nested-name-specifier
-  /// does not store a DeclContext, returns NULL.
-  DeclContext *getAsDeclContext() const {
-    if (Data & 0x01)
-      return 0;
-    return reinterpret_cast<DeclContext *>(Data);
+    return 0;
   }
 
-  /// \brief Retrieve nested name specifier as an opaque pointer.
-  void *getAsOpaquePtr() const { return reinterpret_cast<void *>(Data); }
+  /// \brief Retrieve the type stored in this nested name specifier.
+  Type *getAsType() const {
+    if (Specifier.getInt() == TypeSpec || 
+        Specifier.getInt() == TypeSpecWithTemplate)
+      return (Type *)Specifier.getPointer();
+
+    return 0;
+  }
+
+  /// \brief Whether this nested name specifier refers to a dependent
+  /// type or not.
+  bool isDependent() const;
+
+  /// \brief Print this nested name specifier to the given output
+  /// stream.
+  void Print(llvm::raw_ostream &OS) const;
 
-  /// \brief Reconstruct a nested name specifier from an opaque pointer.
-  static NestedNameSpecifier getFromOpaquePtr(void *Ptr) {
-    NestedNameSpecifier NS;
-    NS.Data = reinterpret_cast<uintptr_t>(Ptr);
-    return NS;
+  void Profile(llvm::FoldingSetNodeID &ID) const {
+    ID.AddPointer(Prefix);
+    ID.AddPointer(Specifier.getPointer());
+    ID.AddInteger(Specifier.getInt());
   }
 
-  static void Print(llvm::raw_ostream &OS, const NestedNameSpecifier *First,
-                    const NestedNameSpecifier *Last);
+  void Destroy(ASTContext &Context);
 };
 
 }
diff --git a/include/clang/AST/Type.h b/include/clang/AST/Type.h
index 3453cb09df..e37b186871 100644
--- a/include/clang/AST/Type.h
+++ b/include/clang/AST/Type.h
@@ -1564,32 +1564,22 @@ protected:
 /// This type is used to keep track of a type name as written in the
 /// source code, including any nested-name-specifiers.
 class QualifiedNameType : public Type, public llvm::FoldingSetNode {
-  /// \brief The number of components in the qualified name, not
-  /// counting the final type.
-  unsigned NumComponents;
+  /// \brief The nested name specifier containing the qualifier.
+  NestedNameSpecifier *NNS;
 
   /// \brief The type that this qualified name refers to.
   QualType NamedType;
 
-  QualifiedNameType(const NestedNameSpecifier *Components,
-                    unsigned NumComponents, QualType NamedType,
-                    QualType CanonType);
+  QualifiedNameType(NestedNameSpecifier *NNS, QualType NamedType,
+                    QualType CanonType)
+    : Type(QualifiedName, CanonType, NamedType->isDependentType()),
+      NNS(NNS), NamedType(NamedType) { }
 
   friend class ASTContext;  // ASTContext creates these
 
 public:
-  typedef const NestedNameSpecifier * iterator;
-
-  iterator begin() const { return getComponents(); }
-  iterator end() const { return getComponents() + getNumComponents(); }
-
-  /// \brief Retrieve the array of nested-name-specifier components.
-  const NestedNameSpecifier *getComponents() const { 
-    return reinterpret_cast<const NestedNameSpecifier *>(this + 1);
-  }
-
-  /// \brief Retrieve the number of nested-name-specifier components.
-  unsigned getNumComponents() const { return NumComponents; }
+  /// \brief Retrieve the qualification on this type.
+  NestedNameSpecifier *getQualifier() const { return NNS; }
 
   /// \brief Retrieve the type named by the qualified-id.
   QualType getNamedType() const { return NamedType; }
@@ -1597,13 +1587,14 @@ public:
   virtual void getAsStringInternal(std::string &InnerString) const;
 
   void Profile(llvm::FoldingSetNodeID &ID) {
-    Profile(ID, getComponents(), NumComponents, NamedType);
+    Profile(ID, NNS, NamedType);
   }
 
-  static void Profile(llvm::FoldingSetNodeID &ID, 
-                      const NestedNameSpecifier *Components,
-                      unsigned NumComponents, 
-                      QualType NamedType);
+  static void Profile(llvm::FoldingSetNodeID &ID, NestedNameSpecifier *NNS,
+                      QualType NamedType) {
+    ID.AddPointer(NNS);
+    NamedType.Profile(ID);
+  }
 
   static bool classof(const Type *T) { 
     return T->getTypeClass() == QualifiedName; 
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index c656d966db..84976a0294 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -33,9 +33,9 @@ ASTContext::ASTContext(const LangOptions& LOpts, SourceManager &SM,
                        TargetInfo &t,
                        IdentifierTable &idents, SelectorTable &sels,
                        bool FreeMem, unsigned size_reserve) : 
-  CFConstantStringTypeDecl(0), ObjCFastEnumerationStateTypeDecl(0),
-  SourceMgr(SM), LangOpts(LOpts), FreeMemory(FreeMem), Target(t), 
-  Idents(idents), Selectors(sels)
+  GlobalNestedNameSpecifier(0), CFConstantStringTypeDecl(0), 
+  ObjCFastEnumerationStateTypeDecl(0), SourceMgr(SM), LangOpts(LOpts), 
+  FreeMemory(FreeMem), Target(t), Idents(idents), Selectors(sels)
 {  
   if (size_reserve > 0) Types.reserve(size_reserve);    
   InitBuiltinTypes();
@@ -77,7 +77,18 @@ ASTContext::~ASTContext() {
     }
   }
 
+  // Destroy nested-name-specifiers.
+  for (llvm::FoldingSet<NestedNameSpecifier>::iterator 
+         NNS = NestedNameSpecifiers.begin(),
+         NNSEnd = NestedNameSpecifiers.end(); 
+       NNS != NNSEnd; ++NNS)
+    NNS->Destroy(*this);
+
+  if (GlobalNestedNameSpecifier)
+    GlobalNestedNameSpecifier->Destroy(*this);
+
   TUDecl->Destroy(*this);
+
 }
 
 void ASTContext::PrintStats() const {
@@ -1376,11 +1387,10 @@ ASTContext::getClassTemplateSpecializationType(TemplateDecl *Template,
 }
 
 QualType 
-ASTContext::getQualifiedNameType(const NestedNameSpecifier *Components,
-                                 unsigned NumComponents,
+ASTContext::getQualifiedNameType(NestedNameSpecifier *NNS,
                                  QualType NamedType) {
   llvm::FoldingSetNodeID ID;
-  QualifiedNameType::Profile(ID, Components, NumComponents, NamedType);
+  QualifiedNameType::Profile(ID, NNS, NamedType);
 
   void *InsertPos = 0;
   QualifiedNameType *T 
@@ -1388,11 +1398,8 @@ ASTContext::getQualifiedNameType(const NestedNameSpecifier *Components,
   if (T)
     return QualType(T, 0);
 
-  void *Mem = Allocate((sizeof(QualifiedNameType) +
-                        sizeof(NestedNameSpecifier) * NumComponents), 
-                       8);
-  T = new (Mem) QualifiedNameType(Components, NumComponents, NamedType,
-                                  getCanonicalType(NamedType));
+  T = new (*this) QualifiedNameType(NNS, NamedType, 
+                                    getCanonicalType(NamedType));
   Types.push_back(T);
   QualifiedNameTypes.InsertNode(T, InsertPos);
   return QualType(T, 0);
diff --git a/lib/AST/ExprCXX.cpp b/lib/AST/ExprCXX.cpp
index 5a9de19254..c2fcc5f9ee 100644
--- a/lib/AST/ExprCXX.cpp
+++ b/lib/AST/ExprCXX.cpp
@@ -24,54 +24,6 @@ void CXXConditionDeclExpr::Destroy(ASTContext& C) {
   C.Deallocate(this);
 }
 
-QualifiedDeclRefExpr::QualifiedDeclRefExpr(NamedDecl *d, QualType t, 
-                                           SourceLocation l, bool TD, 
-                                           bool VD, SourceRange R,
-                                       const NestedNameSpecifier *Components,
-                                           unsigned NumComponents)
-  : DeclRefExpr(QualifiedDeclRefExprClass, d, t, l, TD, VD), 
-    QualifierRange(R), NumComponents(NumComponents) {
-  NestedNameSpecifier *Data 
-    = reinterpret_cast<NestedNameSpecifier *>(this + 1);
-  for (unsigned I = 0; I < NumComponents; ++I)
-    Data[I] = Components[I];
-}
-
-QualifiedDeclRefExpr *
-QualifiedDeclRefExpr::Create(ASTContext &Context, NamedDecl *d, QualType t, 
-                             SourceLocation l, bool TD, 
-                             bool VD, SourceRange R,
-                             const NestedNameSpecifier *Components,
-                             unsigned NumComponents) {
-  void *Mem = Context.Allocate((sizeof(QualifiedDeclRefExpr) +
-                                sizeof(NestedNameSpecifier) * NumComponents));
-  return new (Mem) QualifiedDeclRefExpr(d, t, l, TD, VD, R, Components, 
-                                        NumComponents);
-}
-
-UnresolvedDeclRefExpr::UnresolvedDeclRefExpr(DeclarationName N, QualType T,
-                                             SourceLocation L, SourceRange R,
-                                       const NestedNameSpecifier *Components,
-                                             unsigned NumComponents)
-  : Expr(UnresolvedDeclRefExprClass, T, true, true), 
-    Name(N), Loc(L), QualifierRange(R), NumComponents(NumComponents) {
-  NestedNameSpecifier *Data 
-    = reinterpret_cast<NestedNameSpecifier *>(this + 1);
-  for (unsigned I = 0; I < NumComponents; ++I)
-    Data[I] = Components[I];
-}
-
-UnresolvedDeclRefExpr *
-UnresolvedDeclRefExpr::Create(ASTContext &Context, DeclarationName N,
-                              SourceLocation L, SourceRange R,
-                              const NestedNameSpecifier *Components,
-                              unsigned NumComponents) {
-  void *Mem = Context.Allocate((sizeof(UnresolvedDeclRefExpr) +
-                                sizeof(NestedNameSpecifier) * NumComponents));
-  return new (Mem) UnresolvedDeclRefExpr(N, Context.DependentTy, L, R, 
-                                         Components, NumComponents);
-}
-
 //===----------------------------------------------------------------------===//
 //  Child Iterators for iterating over subexpressions/substatements
 //===----------------------------------------------------------------------===//
diff --git a/lib/AST/NestedNameSpecifier.cpp b/lib/AST/NestedNameSpecifier.cpp
index ea4b506e64..62e972efd5 100644
--- a/lib/AST/NestedNameSpecifier.cpp
+++ b/lib/AST/NestedNameSpecifier.cpp
@@ -16,46 +16,137 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/Type.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cassert>
 
 using namespace clang;
 
-DeclContext *
-NestedNameSpecifier::computeDeclContext(ASTContext &Context) const {
-  // The simple case: we're storing a DeclContext
-  if ((Data & 0x01) == 0)
-    return reinterpret_cast<DeclContext *>(Data);
-
-  Type *T = getAsType();
-  if (!T)
-    return 0;
-
-  // Retrieve the DeclContext associated with this type.
-  const TagType *TagT = T->getAsTagType();
-  assert(TagT && "No DeclContext from a non-tag type");
-  return TagT->getDecl();
-}
-
-void NestedNameSpecifier::Print(llvm::raw_ostream &OS, 
-                                const NestedNameSpecifier *First,
-                                const NestedNameSpecifier *Last) {
-  for (; First != Last; ++First) {
-    if (Type *T = First->getAsType()) {
-      std::string TypeStr;
-
-      // If this is a qualified name type, suppress the qualification:
-      // it's part of our nested-name-specifier sequence anyway.
-      if (const QualifiedNameType *QualT = dyn_cast<QualifiedNameType>(T))
-        T = QualT->getNamedType().getTypePtr();
-
-      if (const TagType *TagT = dyn_cast<TagType>(T))
-        TagT->getAsStringInternal(TypeStr, true);
-      else
-        T->getAsStringInternal(TypeStr);
-      OS << TypeStr;
-    } else if (NamedDecl *NamedDC 
-                 = dyn_cast_or_null<NamedDecl>(First->getAsDeclContext()))
-      OS << NamedDC->getNameAsString();
+NestedNameSpecifier *
+NestedNameSpecifier::FindOrInsert(ASTContext &Context, 
+                                  const NestedNameSpecifier &Mockup) {
+  llvm::FoldingSetNodeID ID;
+  Mockup.Profile(ID);
+
+  void *InsertPos = 0;
+  NestedNameSpecifier *NNS 
+    = Context.NestedNameSpecifiers.FindNodeOrInsertPos(ID, InsertPos);
+  if (!NNS) {
+    NNS = new (Context) NestedNameSpecifier(Mockup);
+    Context.NestedNameSpecifiers.InsertNode(NNS, InsertPos);
+  }
+
+  return NNS;
+}
+
+NestedNameSpecifier *
+NestedNameSpecifier::Create(ASTContext &Context, NestedNameSpecifier *Prefix, 
+                            IdentifierInfo *II) {
+  assert(II && "Identifier cannot be NULL");
+  assert(Prefix && Prefix->isDependent() && "Prefix must be dependent");
+
+  NestedNameSpecifier Mockup;
+  Mockup.Prefix = Prefix;
+  Mockup.Specifier.setPointer(II);
+  Mockup.Specifier.setInt(Identifier);
+  return FindOrInsert(Context, Mockup);
+}
+
+NestedNameSpecifier *
+NestedNameSpecifier::Create(ASTContext &Context, NestedNameSpecifier *Prefix, 
+                            NamespaceDecl *NS) {
+  assert(NS && "Namespace cannot be NULL");
+  assert((!Prefix || 
+          (Prefix->getAsType() == 0 && Prefix->getAsIdentifier() == 0)) &&
+         "Broken nested name specifier");
+  NestedNameSpecifier Mockup;
+  Mockup.Prefix = Prefix;
+  Mockup.Specifier.setPointer(NS);
+  Mockup.Specifier.setInt(Namespace);
+  return FindOrInsert(Context, Mockup);
+}
+
+NestedNameSpecifier *
+NestedNameSpecifier::Create(ASTContext &Context, NestedNameSpecifier *Prefix,
+                            bool Template, Type *T) {
+  assert(T && "Type cannot be NULL");
+  NestedNameSpecifier Mockup;
+  Mockup.Prefix = Prefix;
+  Mockup.Specifier.setPointer(T);
+  Mockup.Specifier.setInt(Template? TypeSpecWithTemplate : TypeSpec);
+  return FindOrInsert(Context, Mockup);
+}
   
-    OS <<  "::";
+NestedNameSpecifier *NestedNameSpecifier::GlobalSpecifier(ASTContext &Context) {
+  if (!Context.GlobalNestedNameSpecifier)
+    Context.GlobalNestedNameSpecifier = new (Context) NestedNameSpecifier();
+  return Context.GlobalNestedNameSpecifier;
+}
+
+/// \brief Whether this nested name specifier refers to a dependent
+/// type or not.
+bool NestedNameSpecifier::isDependent() const {
+  switch (getKind()) {
+  case Identifier:
+    // Identifier specifiers always represent dependent types
+    return true;
+
+  case Namespace:
+  case Global:
+    return false;
+
+  case TypeSpec:
+  case TypeSpecWithTemplate:
+    return getAsType()->isDependentType();
   }
+
+  // Necessary to suppress a GCC warning.
+  return false;
+}
+
+/// \brief Print this nested name specifier to the given output
+/// stream.
+void NestedNameSpecifier::Print(llvm::raw_ostream &OS) const {
+  if (Prefix)
+    Prefix->Print(OS);
+
+  switch (getKind()) {
+  case Identifier:
+    OS << getAsIdentifier()->getName();
+    break;
+
+  case Namespace:
+    OS << getAsNamespace()->getIdentifier()->getName();
+    break;
+
+  case Global:
+    break;
+
+  case TypeSpecWithTemplate:
+    OS << "template ";
+    // Fall through to print the type.
+
+  case TypeSpec: {
+    std::string TypeStr;
+    Type *T = getAsType();
+
+    // If this is a qualified name type, suppress the qualification:
+    // it's part of our nested-name-specifier sequence anyway.  FIXME:
+    // We should be able to assert that this doesn't happen.
+    if (const QualifiedNameType *QualT = dyn_cast<QualifiedNameType>(T))
+      T = QualT->getNamedType().getTypePtr();
+    
+    if (const TagType *TagT = dyn_cast<TagType>(T))
+      TagT->getAsStringInternal(TypeStr, true);
+    else
+      T->getAsStringInternal(TypeStr);
+    OS << TypeStr;
+    break;
+  }
+  }
+
+  OS << "::";
+}
+
+void NestedNameSpecifier::Destroy(ASTContext &Context) {
+  this->~NestedNameSpecifier();
+  Context.Deallocate((void *)this);
 }
diff --git a/lib/AST/StmtPrinter.cpp b/lib/AST/StmtPrinter.cpp
index 60300ba04e..bd5e22491e 100644
--- a/lib/AST/StmtPrinter.cpp
+++ b/lib/AST/StmtPrinter.cpp
@@ -533,12 +533,12 @@ void StmtPrinter::VisitDeclRefExpr(DeclRefExpr *Node) {
 void StmtPrinter::VisitQualifiedDeclRefExpr(QualifiedDeclRefExpr *Node) {  
   NamedDecl *D = Node->getDecl();
 
-  NestedNameSpecifier::Print(OS, Node->begin(), Node->end());
+  Node->getQualifier()->Print(OS);
   OS << D->getNameAsString();
 }
 
 void StmtPrinter::VisitUnresolvedDeclRefExpr(UnresolvedDeclRefExpr *Node) {  
-  NestedNameSpecifier::Print(OS, Node->begin(), Node->end());
+  Node->getQualifier()->Print(OS);
   OS << Node->getDeclName().getAsString();
 }
 
diff --git a/lib/AST/Type.cpp b/lib/AST/Type.cpp
index 19a3f14423..103c0a9134 100644
--- a/lib/AST/Type.cpp
+++ b/lib/AST/Type.cpp
@@ -1047,28 +1047,6 @@ ClassTemplateSpecializationType::Profile(llvm::FoldingSetNodeID &ID,
     Args[Idx].Profile(ID);
 }
 
-QualifiedNameType::QualifiedNameType(const NestedNameSpecifier *Components,
-                                     unsigned NumComponents, 
-                                     QualType NamedType,
-                                     QualType CanonType)
-  : Type(QualifiedName, CanonType, NamedType->isDependentType()),
-    NumComponents(NumComponents), NamedType(NamedType) {
-  NestedNameSpecifier *InitComponents 
-    = reinterpret_cast<NestedNameSpecifier *>(this + 1);
-  for (unsigned I = 0; I < NumComponents; ++I)
-    new (InitComponents + I) NestedNameSpecifier(Components[I]);
-}
-
-void QualifiedNameType::Profile(llvm::FoldingSetNodeID &ID, 
-                                const NestedNameSpecifier *Components,
-                                unsigned NumComponents, 
-                                QualType NamedType) {
-  ID.AddInteger(NumComponents);
-  for (unsigned I = 0; I < NumComponents; ++I)
-    ID.AddPointer(Components[I].getAsOpaquePtr());
-  NamedType.Profile(ID);
-}
-
 //===----------------------------------------------------------------------===//
 // Type Printing
 //===----------------------------------------------------------------------===//
@@ -1440,7 +1418,7 @@ void QualifiedNameType::getAsStringInternal(std::string &InnerString) const {
 
   {
     llvm::raw_string_ostream OS(MyString);
-    NestedNameSpecifier::Print(OS, begin(), end());
+    NNS->Print(OS);
   }
   
   std::string TypeStr;
diff --git a/lib/AST/TypeSerialization.cpp b/lib/AST/TypeSerialization.cpp
index 6f93a1859f..4490847a56 100644
--- a/lib/AST/TypeSerialization.cpp
+++ b/lib/AST/TypeSerialization.cpp
@@ -421,9 +421,7 @@ CreateImpl(ASTCon