cling/patches/llvm-tools-clang-MultiplexExternalSemaSource.diff

Index: tools/clang/include/clang/Sema/Sema.h
===================================================================
--- tools/clang/include/clang/Sema/Sema.h	(revision 165095)
+++ tools/clang/include/clang/Sema/Sema.h	(working copy)
@@ -190,6 +190,13 @@
   Sema(const Sema &) LLVM_DELETED_FUNCTION;
   void operator=(const Sema &) LLVM_DELETED_FUNCTION;
   mutable const TargetAttributesSema* TheTargetAttributesSema;
+
+  ///\brief Source of additional semantic information.
+  ExternalSemaSource *ExternalSource;
+
+  ///\brief Whether Sema has generated a multiplexer and has to delete it.
+  bool isMultiplexExternalSource;
+
 public:
   typedef OpaquePtr<DeclGroupRef> DeclGroupPtrTy;
   typedef OpaquePtr<TemplateName> TemplateTy;
@@ -208,9 +215,6 @@
   /// \brief Flag indicating whether or not to collect detailed statistics.
   bool CollectStats;
 
-  /// \brief Source of additional semantic information.
-  ExternalSemaSource *ExternalSource;
-
   /// \brief Code-completion consumer.
   CodeCompleteConsumer *CodeCompleter;
 
@@ -770,7 +774,15 @@
   ASTContext &getASTContext() const { return Context; }
   ASTConsumer &getASTConsumer() const { return Consumer; }
   ASTMutationListener *getASTMutationListener() const;
+  ExternalSemaSource* getExternalSource() const { return ExternalSource; }
 
+  ///\brief Registers an external source. If an external source already exists,
+  /// creates a multiplex external source and appends to it.
+  ///
+  ///\param[in] E - A non-null external sema source.
+  ///
+  void addExternalSource(ExternalSemaSource *E);
+
   void PrintStats() const;
 
   /// \brief Helper class that creates diagnostics with optional
Index: tools/clang/include/clang/Sema/MultiplexExternalSemaSource.h
===================================================================
--- tools/clang/include/clang/Sema/MultiplexExternalSemaSource.h	(revision 0)
+++ tools/clang/include/clang/Sema/MultiplexExternalSemaSource.h	(revision 0)
@@ -0,0 +1,367 @@
+//===--- MultiplexExternalSemaSource.h - External Sema Interface-*- 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 ExternalSemaSource interface, dispatching to all clients
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_CLANG_SEMA_MULTIPLEX_EXTERNAL_SEMA_SOURCE_H
+#define LLVM_CLANG_SEMA_MULTIPLEX_EXTERNAL_SEMA_SOURCE_H
+
+#include "clang/Sema/ExternalSemaSource.h"
+#include "clang/Sema/Weak.h"
+
+#include "llvm/ADT/SmallVector.h"
+
+#include <utility>
+
+namespace clang {
+
+  class CXXConstructorDecl;
+  class CXXRecordDecl;
+  class DeclaratorDecl;
+  struct ExternalVTableUse;
+  class LookupResult;
+  class NamespaceDecl;
+  class Scope;
+  class Sema;
+  class TypedefNameDecl;
+  class ValueDecl;
+  class VarDecl;
+
+
+/// \brief An abstract interface that should be implemented by
+/// external AST sources that also provide information for semantic
+/// analysis.
+class MultiplexExternalSemaSource : public ExternalSemaSource {
+
+private:
+  llvm::SmallVector<ExternalSemaSource*, 2> Sources; // doesn't own them.
+
+public:
+  
+  ///\brief Constructs a new multiplexing external sema source and appends the
+  /// given element to it.
+  ///
+  ///\param[in] s1 - A non-null (old) ExternalSemaSource.
+  ///\param[in] s2 - A non-null (new) ExternalSemaSource.
+  ///
+  MultiplexExternalSemaSource(ExternalSemaSource& s1, ExternalSemaSource& s2);
+
+  ~MultiplexExternalSemaSource();
+
+  ///\brief Appends new source to the source list.
+  ///
+  ///\param[in] source - An ExternalSemaSource.
+  ///
+  void addSource(ExternalSemaSource &source);
+
+  //===--------------------------------------------------------------------===//
+  // ExternalASTSource.
+  //===--------------------------------------------------------------------===//
+
+  /// \brief Resolve a declaration ID into a declaration, potentially
+  /// building a new declaration.
+  ///
+  /// This method only needs to be implemented if the AST source ever
+  /// passes back decl sets as VisibleDeclaration objects.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual Decl *GetExternalDecl(uint32_t ID);
+
+  /// \brief Resolve a selector ID into a selector.
+  ///
+  /// This operation only needs to be implemented if the AST source
+  /// returns non-zero for GetNumKnownSelectors().
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual Selector GetExternalSelector(uint32_t ID);
+
+  /// \brief Returns the number of selectors known to the external AST
+  /// source.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual uint32_t GetNumExternalSelectors();
+
+  /// \brief Resolve the offset of a statement in the decl stream into
+  /// a statement.
+  ///
+  /// This operation is meant to be used via a LazyOffsetPtr.  It only
+  /// needs to be implemented if the AST source uses methods like
+  /// FunctionDecl::setLazyBody when building decls.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual Stmt *GetExternalDeclStmt(uint64_t Offset);
+
+  /// \brief Resolve the offset of a set of C++ base specifiers in the decl
+  /// stream into an array of specifiers.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual CXXBaseSpecifier *GetExternalCXXBaseSpecifiers(uint64_t Offset);
+
+  /// \brief Finds all declarations with the given name in the
+  /// given context.
+  ///
+  /// Generally the final step of this method is either to call
+  /// SetExternalVisibleDeclsForName or to recursively call lookup on
+  /// the DeclContext after calling SetExternalVisibleDecls.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual DeclContextLookupResult
+  FindExternalVisibleDeclsByName(const DeclContext *DC, DeclarationName Name);
+
+  /// \brief Ensures that the table of all visible declarations inside this
+  /// context is up to date.
+  ///
+  /// The default implementation of this functino is a no-op.
+  virtual void completeVisibleDeclsMap(const DeclContext *DC);
+
+  /// \brief Finds all declarations lexically contained within the given
+  /// DeclContext, after applying an optional filter predicate.
+  ///
+  /// \param isKindWeWant a predicate function that returns true if the passed
+  /// declaration kind is one we are looking for. If NULL, all declarations
+  /// are returned.
+  ///
+  /// \return an indication of whether the load succeeded or failed.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual ExternalLoadResult FindExternalLexicalDecls(const DeclContext *DC,
+                                        bool (*isKindWeWant)(Decl::Kind),
+                                        SmallVectorImpl<Decl*> &Result);
+
+  /// \brief Finds all declarations lexically contained within the given
+  /// DeclContext.
+  ///
+  /// \return true if an error occurred
+  ExternalLoadResult FindExternalLexicalDecls(const DeclContext *DC,
+                                SmallVectorImpl<Decl*> &Result) {
+    return FindExternalLexicalDecls(DC, 0, Result);
+  }
+
+  template <typename DeclTy>
+  ExternalLoadResult FindExternalLexicalDeclsBy(const DeclContext *DC,
+                                  SmallVectorImpl<Decl*> &Result) {
+    return FindExternalLexicalDecls(DC, DeclTy::classofKind, Result);
+  }
+
+  /// \brief Get the decls that are contained in a file in the Offset/Length
+  /// range. \p Length can be 0 to indicate a point at \p Offset instead of
+  /// a range. 
+  virtual void FindFileRegionDecls(FileID File, unsigned Offset,unsigned Length,
+                                   SmallVectorImpl<Decl *> &Decls);
+
+  /// \brief Gives the external AST source an opportunity to complete
+  /// an incomplete type.
+  virtual void CompleteType(TagDecl *Tag);
+
+  /// \brief Gives the external AST source an opportunity to complete an
+  /// incomplete Objective-C class.
+  ///
+  /// This routine will only be invoked if the "externally completed" bit is
+  /// set on the ObjCInterfaceDecl via the function 
+  /// \c ObjCInterfaceDecl::setExternallyCompleted().
+  virtual void CompleteType(ObjCInterfaceDecl *Class);
+
+  /// \brief Loads comment ranges.
+  virtual void ReadComments();
+
+  /// \brief Notify ExternalASTSource that we started deserialization of
+  /// a decl or type so until FinishedDeserializing is called there may be
+  /// decls that are initializing. Must be paired with FinishedDeserializing.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual void StartedDeserializing();
+
+  /// \brief Notify ExternalASTSource that we finished the deserialization of
+  /// a decl or type. Must be paired with StartedDeserializing.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual void FinishedDeserializing();
+
+  /// \brief Function that will be invoked when we begin parsing a new
+  /// translation unit involving this external AST source.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual void StartTranslationUnit(ASTConsumer *Consumer);
+
+  /// \brief Print any statistics that have been gathered regarding
+  /// the external AST source.
+  ///
+  /// The default implementation of this method is a no-op.
+  virtual void PrintStats();
+  
+  
+  /// \brief Perform layout on the given record.
+  ///
+  /// This routine allows the external AST source to provide an specific 
+  /// layout for a record, overriding the layout that would normally be
+  /// constructed. It is intended for clients who receive specific layout
+  /// details rather than source code (such as LLDB). The client is expected
+  /// to fill in the field offsets, base offsets, virtual base offsets, and
+  /// complete object size.
+  ///
+  /// \param Record The record whose layout is being requested.
+  ///
+  /// \param Size The final size of the record, in bits.
+  ///
+  /// \param Alignment The final alignment of the record, in bits.
+  ///
+  /// \param FieldOffsets The offset of each of the fields within the record,
+  /// expressed in bits. All of the fields must be provided with offsets.
+  ///
+  /// \param BaseOffsets The offset of each of the direct, non-virtual base
+  /// classes. If any bases are not given offsets, the bases will be laid 
+  /// out according to the ABI.
+  ///
+  /// \param VirtualBaseOffsets The offset of each of the virtual base classes
+  /// (either direct or not). If any bases are not given offsets, the bases will 
+  /// be laid out according to the ABI.
+  /// 
+  /// \returns true if the record layout was provided, false otherwise.
+  virtual bool 
+  layoutRecordType(const RecordDecl *Record,
+                   uint64_t &Size, uint64_t &Alignment,
+                   llvm::DenseMap<const FieldDecl *, uint64_t> &FieldOffsets,
+                 llvm::DenseMap<const CXXRecordDecl *, CharUnits> &BaseOffsets,
+          llvm::DenseMap<const CXXRecordDecl *, CharUnits> &VirtualBaseOffsets);
+
+  /// Return the amount of memory used by memory buffers, breaking down
+  /// by heap-backed versus mmap'ed memory.
+  virtual void getMemoryBufferSizes(MemoryBufferSizes &sizes) const;
+
+  //===--------------------------------------------------------------------===//
+  // ExternalSemaSource.
+  //===--------------------------------------------------------------------===//
+
+  /// \brief Initialize the semantic source with the Sema instance
+  /// being used to perform semantic analysis on the abstract syntax
+  /// tree.
+  virtual void InitializeSema(Sema &S);
+
+  /// \brief Inform the semantic consumer that Sema is no longer available.
+  virtual void ForgetSema();
+
+  /// \brief Load the contents of the global method pool for a given
+  /// selector.
+  virtual void ReadMethodPool(Selector Sel);
+
+  /// \brief Load the set of namespaces that are known to the external source,
+  /// which will be used during typo correction.
+  virtual void ReadKnownNamespaces(SmallVectorImpl<NamespaceDecl*> &Namespaces);
+  
+  /// \brief Do last resort, unqualified lookup on a LookupResult that
+  /// Sema cannot find.
+  ///
+  /// \param R a LookupResult that is being recovered.
+  ///
+  /// \param S the Scope of the identifier occurrence.
+  ///
+  /// \return true to tell Sema to recover using the LookupResult.
+  virtual bool LookupUnqualified(LookupResult &R, Scope *S);
+
+  /// \brief Read the set of tentative definitions known to the external Sema
+  /// source.
+  ///
+  /// The external source should append its own tentative definitions to the
+  /// given vector of tentative definitions. Note that this routine may be
+  /// invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadTentativeDefinitions(SmallVectorImpl<VarDecl*> &Defs);
+  
+  /// \brief Read the set of unused file-scope declarations known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own unused, filed-scope to the
+  /// given vector of declarations. Note that this routine may be
+  /// invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadUnusedFileScopedDecls(
+                                 SmallVectorImpl<const DeclaratorDecl*> &Decls);
+  
+  /// \brief Read the set of delegating constructors known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own delegating constructors to the
+  /// given vector of declarations. Note that this routine may be
+  /// invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadDelegatingConstructors(
+                                   SmallVectorImpl<CXXConstructorDecl*> &Decls);
+
+  /// \brief Read the set of ext_vector type declarations known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own ext_vector type declarations to
+  /// the given vector of declarations. Note that this routine may be
+  /// invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadExtVectorDecls(SmallVectorImpl<TypedefNameDecl*> &Decls);
+
+  /// \brief Read the set of dynamic classes known to the external Sema source.
+  ///
+  /// The external source should append its own dynamic classes to
+  /// the given vector of declarations. Note that this routine may be
+  /// invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadDynamicClasses(SmallVectorImpl<CXXRecordDecl*> &Decls);
+
+  /// \brief Read the set of locally-scoped external declarations known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own locally-scoped external
+  /// declarations to the given vector of declarations. Note that this routine 
+  /// may be invoked multiple times; the external source should take care not 
+  /// to introduce the same declarations repeatedly.
+  virtual void ReadLocallyScopedExternalDecls(SmallVectorImpl<NamedDecl*>&Decls);
+
+  /// \brief Read the set of referenced selectors known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own referenced selectors to the 
+  /// given vector of selectors. Note that this routine 
+  /// may be invoked multiple times; the external source should take care not 
+  /// to introduce the same selectors repeatedly.
+  virtual void ReadReferencedSelectors(SmallVectorImpl<std::pair<Selector, 
+                                                       SourceLocation> > &Sels);
+
+  /// \brief Read the set of weak, undeclared identifiers known to the
+  /// external Sema source.
+  ///
+  /// The external source should append its own weak, undeclared identifiers to
+  /// the given vector. Note that this routine may be invoked multiple times; 
+  /// the external source should take care not to introduce the same identifiers
+  /// repeatedly.
+  virtual void ReadWeakUndeclaredIdentifiers(
+                    SmallVectorImpl<std::pair<IdentifierInfo*, WeakInfo> > &WI);
+
+  /// \brief Read the set of used vtables known to the external Sema source.
+  ///
+  /// The external source should append its own used vtables to the given
+  /// vector. Note that this routine may be invoked multiple times; the external
+  /// source should take care not to introduce the same vtables repeatedly.
+  virtual void ReadUsedVTables(SmallVectorImpl<ExternalVTableUse> &VTables);
+
+  /// \brief Read the set of pending instantiations known to the external
+  /// Sema source.
+  ///
+  /// The external source should append its own pending instantiations to the
+  /// given vector. Note that this routine may be invoked multiple times; the
+  /// external source should take care not to introduce the same instantiations
+  /// repeatedly.
+  virtual void ReadPendingInstantiations(
+              SmallVectorImpl<std::pair<ValueDecl*, SourceLocation> >& Pending);
+
+  // isa/cast/dyn_cast support
+  static bool classof(const MultiplexExternalSemaSource*) { return true; }
+  //static bool classof(const ExternalSemaSource*) { return true; }
+}; 
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_SEMA_MULTIPLEX_EXTERNAL_SEMA_SOURCE_H
Index: tools/clang/lib/Sema/SemaCodeComplete.cpp
===================================================================
--- tools/clang/lib/Sema/SemaCodeComplete.cpp	(revision 165095)
+++ tools/clang/lib/Sema/SemaCodeComplete.cpp	(working copy)
@@ -5339,11 +5339,11 @@
     
     // If we have an external source, load the entire class method
     // pool from the AST file.
-    if (SemaRef.ExternalSource) {
+    if (SemaRef.getExternalSource()) {
       for (uint32_t I = 0, 
-                    N = SemaRef.ExternalSource->GetNumExternalSelectors();
+                    N = SemaRef.getExternalSource()->GetNumExternalSelectors();
            I != N; ++I) {
-        Selector Sel = SemaRef.ExternalSource->GetExternalSelector(I);
+        Selector Sel = SemaRef.getExternalSource()->GetExternalSelector(I);
         if (Sel.isNull() || SemaRef.MethodPool.count(Sel))
           continue;
         
Index: tools/clang/lib/Sema/SemaDeclObjC.cpp
===================================================================
--- tools/clang/lib/Sema/SemaDeclObjC.cpp	(revision 165095)
+++ tools/clang/lib/Sema/SemaDeclObjC.cpp	(working copy)
@@ -2582,7 +2582,7 @@
     // with this selector before.
     Sema::GlobalMethodPool::iterator it = S.MethodPool.find(selector);
     if (it == S.MethodPool.end()) {
-      if (!S.ExternalSource) return;
+      if (!S.getExternalSource()) return;
       S.ReadMethodPool(selector);
       
       it = S.MethodPool.find(selector);
Index: tools/clang/lib/Sema/MultiplexExternalSemaSource.cpp
===================================================================
--- tools/clang/lib/Sema/MultiplexExternalSemaSource.cpp	(revision 0)
+++ tools/clang/lib/Sema/MultiplexExternalSemaSource.cpp	(revision 0)
@@ -0,0 +1,271 @@
+//===--- MultiplexExternalSemaSource.cpp  ---------------------------------===//
+//
+//                     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 event dispatching to the subscribed clients.
+//
+//===----------------------------------------------------------------------===//
+#include "clang/Sema/MultiplexExternalSemaSource.h"
+
+#include "clang/AST/DeclContextInternals.h"
+#include "clang/Sema/Lookup.h"
+
+using namespace clang;
+
+///\brief Constructs a new multiplexing external sema source and appends the
+/// given element to it.
+///
+///\param[in] source - An ExternalSemaSource.
+///
+MultiplexExternalSemaSource::MultiplexExternalSemaSource(ExternalSemaSource &s1,
+                                                        ExternalSemaSource &s2){
+  Sources.push_back(&s1);
+  Sources.push_back(&s2);
+}
+
+// pin the vtable here.
+MultiplexExternalSemaSource::~MultiplexExternalSemaSource() {}
+
+///\brief Appends new source to the source list.
+///
+///\param[in] source - An ExternalSemaSource.
+///
+void MultiplexExternalSemaSource::addSource(ExternalSemaSource &source) {
+  Sources.push_back(&source);
+}
+
+//===----------------------------------------------------------------------===//
+// ExternalASTSource.
+//===----------------------------------------------------------------------===//
+
+Decl *MultiplexExternalSemaSource::GetExternalDecl(uint32_t ID) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    if (Decl *Result = Sources[i]->GetExternalDecl(ID))
+      return Result;
+  return 0;
+}
+
+Selector MultiplexExternalSemaSource::GetExternalSelector(uint32_t ID) {
+  Selector Sel;
+  for(size_t i = 0; i < Sources.size(); ++i) {
+    Sel = Sources[i]->GetExternalSelector(ID);
+    if (!Sel.isNull())
+      return Sel;
+  }
+  return Sel;
+}
+
+uint32_t MultiplexExternalSemaSource::GetNumExternalSelectors() {
+  uint32_t total = 0;
+  for(size_t i = 0; i < Sources.size(); ++i)
+    total += Sources[i]->GetNumExternalSelectors();
+  return total;
+}
+
+Stmt *MultiplexExternalSemaSource::GetExternalDeclStmt(uint64_t Offset) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    if (Stmt *Result = Sources[i]->GetExternalDeclStmt(Offset))
+      return Result;
+  return 0;
+}
+
+CXXBaseSpecifier *MultiplexExternalSemaSource::GetExternalCXXBaseSpecifiers(
+                                                               uint64_t Offset){
+  for(size_t i = 0; i < Sources.size(); ++i)
+    if (CXXBaseSpecifier *R = Sources[i]->GetExternalCXXBaseSpecifiers(Offset))
+      return R;
+  return 0; 
+}
+
+DeclContextLookupResult MultiplexExternalSemaSource::
+FindExternalVisibleDeclsByName(const DeclContext *DC, DeclarationName Name) {
+  StoredDeclsList DeclsFound;
+  DeclContextLookupResult lookup;
+  for(size_t i = 0; i < Sources.size(); ++i) {
+    lookup = Sources[i]->FindExternalVisibleDeclsByName(DC, Name);
+    while(lookup.first != lookup.second) {
+      if (!DeclsFound.HandleRedeclaration(*lookup.first))
+        DeclsFound.AddSubsequentDecl(*lookup.first);
+      lookup.first++;
+    }
+  }
+  return DeclsFound.getLookupResult(); 
+}
+
+void MultiplexExternalSemaSource::completeVisibleDeclsMap(const DeclContext *DC){
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->completeVisibleDeclsMap(DC);
+}
+
+ExternalLoadResult MultiplexExternalSemaSource::
+FindExternalLexicalDecls(const DeclContext *DC,
+                         bool (*isKindWeWant)(Decl::Kind),
+                         SmallVectorImpl<Decl*> &Result) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    // FIXME: The semantics of the return result is unclear to me...
+    Sources[i]->FindExternalLexicalDecls(DC, isKindWeWant, Result);
+
+  return ELR_Success;
+}
+
+void MultiplexExternalSemaSource::FindFileRegionDecls(FileID File, 
+                                                      unsigned Offset,
+                                                      unsigned Length,
+                                                SmallVectorImpl<Decl *> &Decls){
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->FindFileRegionDecls(File, Offset, Length, Decls);
+}
+
+void MultiplexExternalSemaSource::CompleteType(TagDecl *Tag) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->CompleteType(Tag);
+}
+
+void MultiplexExternalSemaSource::CompleteType(ObjCInterfaceDecl *Class) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->CompleteType(Class);
+}
+
+void MultiplexExternalSemaSource::ReadComments() {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadComments();
+}
+
+void MultiplexExternalSemaSource::StartedDeserializing() {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->StartedDeserializing();
+}
+
+void MultiplexExternalSemaSource::FinishedDeserializing() {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->FinishedDeserializing();
+}
+
+void MultiplexExternalSemaSource::StartTranslationUnit(ASTConsumer *Consumer) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->StartTranslationUnit(Consumer);
+}
+
+void MultiplexExternalSemaSource::PrintStats() {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->PrintStats();
+}
+
+bool MultiplexExternalSemaSource::layoutRecordType(const RecordDecl *Record,
+                                                   uint64_t &Size, 
+                                                   uint64_t &Alignment,
+                      llvm::DenseMap<const FieldDecl *, uint64_t> &FieldOffsets,
+                  llvm::DenseMap<const CXXRecordDecl *, CharUnits> &BaseOffsets,
+          llvm::DenseMap<const CXXRecordDecl *, CharUnits> &VirtualBaseOffsets){
+  for(size_t i = 0; i < Sources.size(); ++i)
+    if (Sources[i]->layoutRecordType(Record, Size, Alignment, FieldOffsets, 
+                                     BaseOffsets, VirtualBaseOffsets))
+      return true;
+  return false;
+}
+
+void MultiplexExternalSemaSource::
+getMemoryBufferSizes(MemoryBufferSizes &sizes) const {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->getMemoryBufferSizes(sizes);
+
+}
+
+//===----------------------------------------------------------------------===//
+// ExternalSemaSource.
+//===----------------------------------------------------------------------===//
+
+
+void MultiplexExternalSemaSource::InitializeSema(Sema &S) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->InitializeSema(S);
+}
+
+void MultiplexExternalSemaSource::ForgetSema() {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ForgetSema();
+}
+
+void MultiplexExternalSemaSource::ReadMethodPool(Selector Sel) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadMethodPool(Sel);
+}
+
+void MultiplexExternalSemaSource::ReadKnownNamespaces(
+                                   SmallVectorImpl<NamespaceDecl*> &Namespaces){
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadKnownNamespaces(Namespaces);
+}
+  
+bool MultiplexExternalSemaSource::LookupUnqualified(LookupResult &R, Scope *S){ 
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->LookupUnqualified(R, S);
+  
+  return !R.empty();
+}
+
+void MultiplexExternalSemaSource::ReadTentativeDefinitions(
+                                     SmallVectorImpl<VarDecl*> &TentativeDefs) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadTentativeDefinitions(TentativeDefs);
+}
+  
+void MultiplexExternalSemaSource::ReadUnusedFileScopedDecls(
+                                SmallVectorImpl<const DeclaratorDecl*> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadUnusedFileScopedDecls(Decls);
+}
+  
+void MultiplexExternalSemaSource::ReadDelegatingConstructors(
+                                  SmallVectorImpl<CXXConstructorDecl*> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadDelegatingConstructors(Decls);
+}
+
+void MultiplexExternalSemaSource::ReadExtVectorDecls(
+                                     SmallVectorImpl<TypedefNameDecl*> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadExtVectorDecls(Decls);
+}
+
+void MultiplexExternalSemaSource::ReadDynamicClasses(
+                                       SmallVectorImpl<CXXRecordDecl*> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadDynamicClasses(Decls);
+}
+
+void MultiplexExternalSemaSource::ReadLocallyScopedExternalDecls(
+                                           SmallVectorImpl<NamedDecl*> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadLocallyScopedExternalDecls(Decls);
+}
+
+void MultiplexExternalSemaSource::ReadReferencedSelectors(
+                  SmallVectorImpl<std::pair<Selector, SourceLocation> > &Sels) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadReferencedSelectors(Sels);
+}
+
+void MultiplexExternalSemaSource::ReadWeakUndeclaredIdentifiers(
+                   SmallVectorImpl<std::pair<IdentifierInfo*, WeakInfo> > &WI) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadWeakUndeclaredIdentifiers(WI);
+}
+
+void MultiplexExternalSemaSource::ReadUsedVTables(
+                                  SmallVectorImpl<ExternalVTableUse> &VTables) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadUsedVTables(VTables);
+}
+
+void MultiplexExternalSemaSource::ReadPendingInstantiations(
+                                           SmallVectorImpl<std::pair<ValueDecl*,
+                                                   SourceLocation> > &Pending) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadPendingInstantiations(Pending);
+}
Index: tools/clang/lib/Sema/CMakeLists.txt
===================================================================
--- tools/clang/lib/Sema/CMakeLists.txt	(revision 165095)
+++ tools/clang/lib/Sema/CMakeLists.txt	(working copy)
@@ -13,6 +13,7 @@
   DelayedDiagnostic.cpp
   IdentifierResolver.cpp
   JumpDiagnostics.cpp
+  MultiplexExternalSemaSource.cpp
   Scope.cpp
   ScopeInfo.cpp
   Sema.cpp
Index: tools/clang/lib/Sema/SemaExprMember.cpp
===================================================================
--- tools/clang/lib/Sema/SemaExprMember.cpp	(revision 165095)
+++ tools/clang/lib/Sema/SemaExprMember.cpp	(working copy)
@@ -354,7 +354,7 @@
   // Now look up the TypeDefDecl from the vector type. Without this,
   // diagostics look bad. We want extended vector types to appear built-in.
   for (Sema::ExtVectorDeclsType::iterator 
-         I = S.ExtVectorDecls.begin(S.ExternalSource),
+         I = S.ExtVectorDecls.begin(S.getExternalSource()),
          E = S.ExtVectorDecls.end(); 
        I != E; ++I) {
     if ((*I)->getUnderlyingType() == VT)
Index: tools/clang/lib/Sema/Sema.cpp
===================================================================
--- tools/clang/lib/Sema/Sema.cpp	(revision 165095)
+++ tools/clang/lib/Sema/Sema.cpp	(working copy)
@@ -22,6 +22,7 @@
 #include "clang/Sema/CXXFieldCollector.h"
 #include "clang/Sema/TemplateDeduction.h"
 #include "clang/Sema/ExternalSemaSource.h"
+#include "clang/Sema/MultiplexExternalSemaSource.h"
 #include "clang/Sema/ObjCMethodList.h"
 #include "clang/Sema/PrettyDeclStackTrace.h"
 #include "clang/Sema/Scope.h"
@@ -68,10 +69,11 @@
 Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
            TranslationUnitKind TUKind,
            CodeCompleteConsumer *CodeCompleter)
-  : TheTargetAttributesSema(0), FPFeatures(pp.getLangOpts()),
+  : TheTargetAttributesSema(0), ExternalSource(0), 
+    isMultiplexExternalSource(false), FPFeatures(pp.getLangOpts()),
     LangOpts(pp.getLangOpts()), PP(pp), Context(ctxt), Consumer(consumer),
     Diags(PP.getDiagnostics()), SourceMgr(PP.getSourceManager()),
-    CollectStats(false), ExternalSource(0), CodeCompleter(CodeCompleter),
+    CollectStats(false), CodeCompleter(CodeCompleter),
     CurContext(0), OriginalLexicalContext(0),
     PackContext(0), MSStructPragmaOn(false), VisContext(0),
     IsBuildingRecoveryCallExpr(false),
@@ -188,6 +190,10 @@
   if (ExternalSemaSource *ExternalSema
         = dyn_cast_or_null<ExternalSemaSource>(Context.getExternalSource()))
     ExternalSema->ForgetSema();
+
+  // If Sema's ExternalSource is the multiplexer - we own it.
+  if (isMultiplexExternalSource)
+    delete ExternalSource;
 }
 
 /// makeUnavailableInSystemHeader - There is an error in the current
@@ -219,6 +225,27 @@
   return getASTConsumer().GetASTMutationListener();
 }
 
+///\brief Registers an external source. If an external source already exists,
+/// creates a multiplex external source and appends to it.
+///
+///\param[in] E - A non-null external sema source.
+///
+void Sema::addExternalSource(ExternalSemaSource *E) {
+  assert(E && "Cannot use with NULL ptr");
+
+  if (!ExternalSource) {
+    ExternalSource = E;
+    return;
+  }
+
+  if (isMultiplexExternalSource)
+    static_cast<MultiplexExternalSemaSource*>(ExternalSource)->addSource(*E);
+  else {
+    ExternalSource = new MultiplexExternalSemaSource(*ExternalSource, *E);
+    isMultiplexExternalSource = true;
+  }
+}
+
 /// \brief Print out statistics about the semantic analysis.
 void Sema::PrintStats() const {
   llvm::errs() << "\n*** Semantic Analysis Stats:\n";
Index: tools/clang/lib/Serialization/ASTReader.cpp
===================================================================
--- tools/clang/lib/Serialization/ASTReader.cpp	(revision 165095)
+++ tools/clang/lib/Serialization/ASTReader.cpp	(working copy)
@@ -5289,7 +5289,7 @@
 
 void ASTReader::InitializeSema(Sema &S) {
   SemaObj = &S;
-  S.ExternalSource = this;
+  S.addExternalSource(this);
 
   // Makes sure any declarations that were deserialized "too early"
   // still get added to the identifier's declaration chains.