From: Douglas Gregor <dgregor@apple.com>
Date: Sat, 17 Dec 2011 23:38:30 +0000 (+0000)
Subject: Completely re-implement (de-)serialization of declaration
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a1be278c4f3a234ff61f04018d26c6beecde1654;p=clang

Completely re-implement (de-)serialization of declaration
chains. The previous implementation relied heavily on the declaration
chain being stored as a (circular) linked list on disk, as it is in
memory. However, when deserializing from multiple modules, the
different chains could get mixed up, leading to broken declaration chains.

The new solution keeps track of the first and last declarations in the
chain for each module file. When we load a declaration, we search all
of the module files for redeclarations of that declaration, then
splice together all of the lists into a coherent whole (along with any
redeclarations that were actually parsed).

As a drive-by fix, (de-)serialize the redeclaration chains of
TypedefNameDecls, which had somehow gotten missed previously. Add a
test of this serialization.

This new scheme creates a redeclaration table that is fairly large in
the PCH file (on the order of 400k for Cocoa.h's 12MB PCH file). The
table is mmap'd in and searched via a binary search, but it's still
quite large. A future tweak will eliminate entries for declarations
that have no redeclarations anywhere, and should
drastically reduce the size of this table.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146841 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Serialization/ASTBitCodes.h b/include/clang/Serialization/ASTBitCodes.h
index 41ef74ee0a..cce6916b4e 100644
--- a/include/clang/Serialization/ASTBitCodes.h
+++ b/include/clang/Serialization/ASTBitCodes.h
@@ -452,7 +452,11 @@ namespace clang {
       
       /// \brief Record code for an array of all of the (sub)modules that were
       /// imported by the AST file.
-      IMPORTED_MODULES
+      IMPORTED_MODULES,
+      
+      /// \brief Record code for the array describing the first/last local
+      /// redeclarations of each entity.
+      LOCAL_REDECLARATIONS
     };
 
     /// \brief Record types used within a source manager block.
@@ -1190,6 +1194,33 @@ namespace clang {
       CTOR_INITIALIZER_INDIRECT_MEMBER
     };
 
+    /// \brief Describes the redeclarations of a declaration.
+    struct LocalRedeclarationsInfo {
+      DeclID FirstID;      // The ID of the first declaration
+      DeclID FirstLocalID; // The ID of the first local declaration
+      DeclID LastLocalID;  // The ID of the last local declaration
+      
+      friend bool operator<(const LocalRedeclarationsInfo &X,
+                            const LocalRedeclarationsInfo &Y) {
+        return X.FirstID < Y.FirstID;
+      }
+      
+      friend bool operator>(const LocalRedeclarationsInfo &X,
+                            const LocalRedeclarationsInfo &Y) {
+        return X.FirstID > Y.FirstID;
+      }
+      
+      friend bool operator<=(const LocalRedeclarationsInfo &X,
+                             const LocalRedeclarationsInfo &Y) {
+        return X.FirstID <= Y.FirstID;
+      }
+      
+      friend bool operator>=(const LocalRedeclarationsInfo &X,
+                             const LocalRedeclarationsInfo &Y) {
+        return X.FirstID >= Y.FirstID;
+      }
+    };
+
     /// @}
   }
 } // end namespace clang
diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index 0947dfc4eb..10ed5dceea 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -674,6 +674,17 @@ private:
   /// deeply nested calls when there are many redeclarations.
   std::deque<std::pair<Decl *, serialization::DeclID> > PendingPreviousDecls;
 
+  /// \brief The list of redeclaration chains that still need to be 
+  /// reconstructed.
+  ///
+  /// Each element is the global declaration ID of the first declaration in
+  /// the chain. Elements in this vector should be unique; use 
+  /// PendingDeclChainsKnown to ensure uniqueness.
+  llvm::SmallVector<serialization::DeclID, 16> PendingDeclChains;
+
+  /// \brief Keeps track of the elements added to PendingDeclChains.
+  llvm::SmallSet<serialization::DeclID, 16> PendingDeclChainsKnown;
+
   /// \brief We delay loading the chain of objc categories after recursive
   /// loading of declarations is finished.
   std::vector<std::pair<ObjCInterfaceDecl *, serialization::DeclID> >
@@ -759,6 +770,7 @@ private:
   RecordLocation DeclCursorForID(serialization::DeclID ID,
                                  unsigned &RawLocation);
   void loadDeclUpdateRecords(serialization::DeclID ID, Decl *D);
+  void loadPendingDeclChain(serialization::GlobalDeclID ID);
   void loadObjCChainedCategories(serialization::GlobalDeclID ID,
                                  ObjCInterfaceDecl *D);
 
@@ -1028,6 +1040,15 @@ public:
     return cast_or_null<T>(GetLocalDecl(F, LocalID));
   }
 
+  /// \brief Map a global declaration ID into the declaration ID used to 
+  /// refer to this declaration within the given module fule.
+  ///
+  /// \returns the global ID of the given declaration as known in the given
+  /// module file.
+  serialization::DeclID 
+  mapGlobalIDToModuleFileGlobalID(ModuleFile &M,
+                                  serialization::DeclID GlobalID);
+  
   /// \brief Reads a declaration ID from the given position in a record in the
   /// given module.
   ///
diff --git a/include/clang/Serialization/ASTWriter.h b/include/clang/Serialization/ASTWriter.h
index ab0d1ef3d9..fd581bc452 100644
--- a/include/clang/Serialization/ASTWriter.h
+++ b/include/clang/Serialization/ASTWriter.h
@@ -312,7 +312,11 @@ private:
   /// serialized again. In this case, it is registered here, so that the reader
   /// knows to read the updated version.
   SmallVector<ReplacedDeclInfo, 16> ReplacedDecls;
-
+                    
+  /// \brief The list of local redeclarations of entities that were
+  /// first declared non-locally.
+  SmallVector<serialization::LocalRedeclarationsInfo, 2> LocalRedeclarations;
+                  
   /// \brief Statements that we've encountered while serializing a
   /// declaration or type.
   SmallVector<Stmt *, 16> StmtsToEmit;
diff --git a/include/clang/Serialization/Module.h b/include/clang/Serialization/Module.h
index 16d9779e04..cbac5cd148 100644
--- a/include/clang/Serialization/Module.h
+++ b/include/clang/Serialization/Module.h
@@ -260,6 +260,15 @@ public:
   /// \brief Remapping table for declaration IDs in this module.
   ContinuousRangeMap<uint32_t, int, 2> DeclRemap;
 
+  /// \brief Mapping from the module files that this module file depends on
+  /// to the base declaration ID for that module as it is understood within this
+  /// module.
+  ///
+  /// This is effectively a reverse global-to-local mapping for declaration
+  /// IDs, so that we can interpret a true global ID (for this translation unit)
+  /// as a local ID (for this module file).
+  llvm::DenseMap<ModuleFile *, serialization::DeclID> GlobalToLocalDeclIDs;
+
   /// \brief The number of C++ base specifier sets in this AST file.
   unsigned LocalNumCXXBaseSpecifiers;
 
@@ -286,6 +295,13 @@ public:
   /// \brief Array of file-level DeclIDs sorted by file.
   const serialization::DeclID *FileSortedDecls;
 
+  /// \brief Array of redeclaration information within this module file,
+  /// sorted by the first declaration ID.
+  const serialization::LocalRedeclarationsInfo *RedeclarationsInfo;
+
+  /// \brief The number of redeclaration info entries in RedeclarationsInfo.
+  unsigned LocalNumRedeclarationsInfos;
+  
   // === Types ===
 
   /// \brief The number of types in this AST file.
diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index a1713ee685..bc1cb3fca6 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -1063,6 +1063,8 @@ static NamedDecl *getPreviousDeclaration(NamedDecl *D) {
     return FD->getPreviousDeclaration();
   if (RedeclarableTemplateDecl *RTD = dyn_cast<RedeclarableTemplateDecl>(D))
     return RTD->getPreviousDeclaration();
+  if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D))
+    return TD->getPreviousDeclaration();
   if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D))
     return ID->getPreviousDeclaration();
   
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 3af04c2bc8..64414c9167 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -1846,6 +1846,10 @@ ASTReader::ReadASTBlock(ModuleFile &F) {
         F.DeclRemap.insert(std::make_pair(LocalBaseDeclID, 
                                           F.BaseDeclID - LocalBaseDeclID));
         
+        // Introduce the global -> local mapping for declarations within this
+        // module.
+        F.GlobalToLocalDeclIDs[&F] = LocalBaseDeclID;
+        
         DeclsLoaded.resize(DeclsLoaded.size() + F.LocalNumDecls);
       }
       break;
@@ -2125,6 +2129,9 @@ ASTReader::ReadASTBlock(ModuleFile &F) {
         
         TypeRemap.insert(std::make_pair(TypeIndexOffset, 
                                     OM->BaseTypeIndex - TypeIndexOffset));
+
+        // Global -> local mappings.
+        F.GlobalToLocalDeclIDs[OM] = DeclIDOffset;
       }
       break;
     }
@@ -2396,7 +2403,17 @@ ASTReader::ReadASTBlock(ModuleFile &F) {
         }
       }
       break;
+    }
+        
+    case LOCAL_REDECLARATIONS: {
+      if (F.LocalNumRedeclarationsInfos != 0) {
+        Error("duplicate LOCAL_REDECLARATIONS record in AST file");
+        return Failure;
+      }
       
+      F.LocalNumRedeclarationsInfos = Record[0];
+      F.RedeclarationsInfo = (const LocalRedeclarationsInfo *)BlobStart;
+      break;
     }
     }
   }
@@ -4568,6 +4585,23 @@ Decl *ASTReader::GetDecl(DeclID ID) {
   return DeclsLoaded[Index];
 }
 
+DeclID ASTReader::mapGlobalIDToModuleFileGlobalID(ModuleFile &M, 
+                                                  DeclID GlobalID) {
+  if (GlobalID < NUM_PREDEF_DECL_IDS)
+    return GlobalID;
+  
+  GlobalDeclMapType::const_iterator I = GlobalDeclMap.find(GlobalID);
+  assert(I != GlobalDeclMap.end() && "Corrupted global declaration map");
+  ModuleFile *Owner = I->second;
+
+  llvm::DenseMap<ModuleFile *, serialization::DeclID>::iterator Pos
+    = M.GlobalToLocalDeclIDs.find(Owner);
+  if (Pos == M.GlobalToLocalDeclIDs.end())
+    return 0;
+      
+  return GlobalID - Owner->BaseDeclID + Pos->second;
+}
+
 serialization::DeclID ASTReader::ReadDeclID(ModuleFile &F, 
                                             const RecordData &Record,
                                             unsigned &Idx) {
@@ -6027,6 +6061,7 @@ void ASTReader::ClearSwitchCaseIDs() {
 void ASTReader::finishPendingActions() {
   while (!PendingIdentifierInfos.empty() ||
          !PendingPreviousDecls.empty() ||
+         !PendingDeclChains.empty() ||
          !PendingChainedObjCCategories.empty()) {
 
     // If any identifiers with corresponding top-level declarations have
@@ -6044,6 +6079,12 @@ void ASTReader::finishPendingActions() {
       PendingPreviousDecls.pop_front();
     }
   
+    // Load pending declaration chains.
+    for (unsigned I = 0; I != PendingDeclChains.size(); ++I) {
+      loadPendingDeclChain(PendingDeclChains[I]);
+    }
+    PendingDeclChains.clear();
+
     for (std::vector<std::pair<ObjCInterfaceDecl *,
                                serialization::DeclID> >::iterator
            I = PendingChainedObjCCategories.begin(),
@@ -6082,6 +6123,7 @@ void ASTReader::FinishedDeserializing() {
     }
 
     finishPendingActions();
+    PendingDeclChainsKnown.clear();
 
     assert(PendingForwardRefs.size() == 0 &&
            "Some forward refs did not get linked to the definition!");
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 5e5f1cb6fe..69f309aef0 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -114,6 +114,7 @@ namespace clang {
         TypeIDForTypeDecl(0) { }
 
     static void attachPreviousDecl(Decl *D, Decl *previous);
+    static void attachLatestDecl(Decl *D, Decl *latest);
 
     void Visit(Decl *D);
 
@@ -307,11 +308,13 @@ void ASTDeclReader::VisitTypeDecl(TypeDecl *TD) {
 }
 
 void ASTDeclReader::VisitTypedefDecl(TypedefDecl *TD) {
+  VisitRedeclarable(TD);
   VisitTypeDecl(TD);
   TD->setTypeSourceInfo(GetTypeSourceInfo(Record, Idx));
 }
 
 void ASTDeclReader::VisitTypeAliasDecl(TypeAliasDecl *TD) {
+  VisitRedeclarable(TD);
   VisitTypeDecl(TD);
   TD->setTypeSourceInfo(GetTypeSourceInfo(Record, Idx));
 }
@@ -1398,73 +1401,39 @@ ASTDeclReader::VisitDeclContext(DeclContext *DC) {
 
 template <typename T>
 void ASTDeclReader::VisitRedeclarable(Redeclarable<T> *D) {
-  enum RedeclKind { NoRedeclaration = 0, PointsToPrevious, PointsToLatest };
+  enum RedeclKind { FirstInFile, PointsToPrevious };
   RedeclKind Kind = (RedeclKind)Record[Idx++];
+  
+  // Read the first declaration ID, and note that we need to reconstruct
+  // the redeclaration chain once we hit the top level.
+  DeclID FirstDeclID = ReadDeclID(Record, Idx);
+  if (Reader.PendingDeclChainsKnown.insert(FirstDeclID))
+    Reader.PendingDeclChains.push_back(FirstDeclID);
+
+  T *FirstDecl = cast_or_null<T>(Reader.GetDecl(FirstDeclID));
+
   switch (Kind) {
-  default:
-    llvm_unreachable("Out of sync with ASTDeclWriter::VisitRedeclarable or"
-                     " messed up reading");
-  case NoRedeclaration:
+  case FirstInFile:
+    if (FirstDecl != D)
+      D->RedeclLink = typename Redeclarable<T>::PreviousDeclLink(FirstDecl);
     break;
+      
   case PointsToPrevious: {
     DeclID PreviousDeclID = ReadDeclID(Record, Idx);
-    DeclID FirstDeclID = ReadDeclID(Record, Idx);
+    
     // We delay loading of the redeclaration chain to avoid deeply nested calls.
     // We temporarily set the first (canonical) declaration as the previous one
     // which is the one that matters and mark the real previous DeclID to be
     // loaded & attached later on.
-    T *FirstDecl = cast_or_null<T>(Reader.GetDecl(FirstDeclID));
     D->RedeclLink = typename Redeclarable<T>::PreviousDeclLink(FirstDecl);
-    if (PreviousDeclID != FirstDeclID)
-      Reader.PendingPreviousDecls.push_back(std::make_pair(static_cast<T*>(D),
-                                                           PreviousDeclID));
-
-    // If the first declaration in the chain is in an inconsistent
-    // state where it thinks that it is the only declaration, fix its
-    // redeclaration link now to point at this declaration, so that we have a 
-    // proper redeclaration chain.
-    if (FirstDecl->RedeclLink.getPointer() == FirstDecl) {
-      FirstDecl->RedeclLink
-        = typename Redeclarable<T>::LatestDeclLink(static_cast<T*>(D));
-    }
-    break;
-  }
-  case PointsToLatest: {
-    T *LatestDecl = ReadDeclAs<T>(Record, Idx);
-    D->RedeclLink = typename Redeclarable<T>::LatestDeclLink(LatestDecl);
     
-    // If the latest declaration in the chain is in an inconsistent
-    // state where it thinks that it is the only declaration, fix its
-    // redeclaration link now to point at this declaration, so that we have a 
-    // proper redeclaration chain.
-    if (LatestDecl->RedeclLink.getPointer() == LatestDecl) {
-      LatestDecl->RedeclLink
-        = typename Redeclarable<T>::PreviousDeclLink(static_cast<T*>(D));
-    }
+    // Make a note that we need to wire up this declaration to its
+    // previous declaration, later.
+    Reader.PendingPreviousDecls.push_back(std::make_pair(static_cast<T*>(D),
+                                                         PreviousDeclID));
     break;
   }
   }
-
-  assert(!(Kind == PointsToPrevious &&
-           Reader.FirstLatestDeclIDs.find(ThisDeclID) !=
-               Reader.FirstLatestDeclIDs.end()) &&
-         "This decl is not first, it should not be in the map");
-  if (Kind == PointsToPrevious)
-    return;
-
-  // This decl is a first one and the latest declaration that it points to is in
-  // the same AST file. However, if this actually needs to point to a
-  // redeclaration in another AST file, we need to update it by checking the
-  // FirstLatestDeclIDs map which tracks this kind of decls.
-  assert(Reader.GetDecl(ThisDeclID) == static_cast<T*>(D) &&
-         "Invalid ThisDeclID ?");
-  ASTReader::FirstLatestDeclIDMap::iterator I
-      = Reader.FirstLatestDeclIDs.find(ThisDeclID);
-  if (I != Reader.FirstLatestDeclIDs.end()) {
-    Decl *NewLatest = Reader.GetDecl(I->second);
-    D->RedeclLink
-        = typename Redeclarable<T>::LatestDeclLink(cast_or_null<T>(NewLatest));
-  }
 }
 
 //===----------------------------------------------------------------------===//
@@ -1564,7 +1533,9 @@ void ASTDeclReader::attachPreviousDecl(Decl *D, Decl *previous) {
     FD->RedeclLink.setPointer(cast<FunctionDecl>(previous));
   } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
     VD->RedeclLink.setPointer(cast<VarDecl>(previous));
-  } else if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(previous)) {
+  } else if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D)) {
+    TD->RedeclLink.setPointer(cast<TypedefNameDecl>(previous));
+  } else if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D)) {
     ID->RedeclLink.setPointer(cast<ObjCInterfaceDecl>(previous));
   } else {
     RedeclarableTemplateDecl *TD = cast<RedeclarableTemplateDecl>(D);
@@ -1572,6 +1543,31 @@ void ASTDeclReader::attachPreviousDecl(Decl *D, Decl *previous) {
   }
 }
 
+void ASTDeclReader::attachLatestDecl(Decl *D, Decl *Latest) {
+  assert(D && Latest);
+  if (TagDecl *TD = dyn_cast<TagDecl>(D)) {
+    TD->RedeclLink
+      = Redeclarable<TagDecl>::LatestDeclLink(cast<TagDecl>(Latest));
+  } else if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    FD->RedeclLink 
+      = Redeclarable<FunctionDecl>::LatestDeclLink(cast<FunctionDecl>(Latest));
+  } else if (VarDecl *VD = dyn_cast<VarDecl>(D)) {
+    VD->RedeclLink
+      = Redeclarable<VarDecl>::LatestDeclLink(cast<VarDecl>(Latest));
+  } else if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D)) {
+    TD->RedeclLink
+      = Redeclarable<TypedefNameDecl>::LatestDeclLink(
+                                                cast<TypedefNameDecl>(Latest));
+  } else if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D)) {
+    ID->RedeclLink
+      = Redeclarable<ObjCInterfaceDecl>::LatestDeclLink(
+                                              cast<ObjCInterfaceDecl>(Latest));
+  } else {
+    RedeclarableTemplateDecl *TD = cast<RedeclarableTemplateDecl>(D);
+    TD->getCommonPtr()->Latest = cast<RedeclarableTemplateDecl>(Latest);
+  }
+}
+
 void ASTReader::loadAndAttachPreviousDecl(Decl *D, serialization::DeclID ID) {
   Decl *previous = GetDecl(ID);
   ASTDeclReader::attachPreviousDecl(D, previous);
@@ -1903,6 +1899,152 @@ void ASTReader::loadDeclUpdateRecords(serialization::DeclID ID, Decl *D) {
   }
 }
 
+namespace {
+  struct CompareLocalRedeclarationsInfoToID {
+    bool operator()(const LocalRedeclarationsInfo &X, DeclID Y) {
+      return X.FirstID < Y;
+    }
+
+    bool operator()(DeclID X, const LocalRedeclarationsInfo &Y) {
+      return X < Y.FirstID;
+    }
+
+    bool operator()(const LocalRedeclarationsInfo &X, 
+                    const LocalRedeclarationsInfo &Y) {
+      return X.FirstID < Y.FirstID;
+    }
+    bool operator()(DeclID X, DeclID Y) {
+      return X < Y;
+    }
+  };
+  
+  class RedeclChainVisitor {
+    ASTReader &Reader;
+    DeclID GlobalFirstID;
+    llvm::SmallVector<std::pair<Decl *, Decl *>, 4> Chains;
+    
+  public:
+    RedeclChainVisitor(ASTReader &Reader, DeclID GlobalFirstID)
+      : Reader(Reader), GlobalFirstID(GlobalFirstID) { }
+    
+    static bool visit(ModuleFile &M, bool Preorder, void *UserData) {
+      if (Preorder)
+        return false;
+      
+      return static_cast<RedeclChainVisitor *>(UserData)->visit(M);
+    }
+    
+    bool visit(ModuleFile &M) {
+      // Map global ID of the first declaration down to the local ID
+      // used in this module file.
+      DeclID FirstID = Reader.mapGlobalIDToModuleFileGlobalID(M, GlobalFirstID);
+      if (!FirstID)
+        return false;
+      
+      // Perform a binary search to find the local redeclarations for this
+      // declaration (if any).
+      const LocalRedeclarationsInfo *Result
+        = std::lower_bound(M.RedeclarationsInfo,
+                           M.RedeclarationsInfo + M.LocalNumRedeclarationsInfos, 
+                           FirstID, CompareLocalRedeclarationsInfoToID());
+      if (Result == M.RedeclarationsInfo + M.LocalNumRedeclarationsInfos ||
+          Result->FirstID != FirstID)
+        return false;
+
+      // Dig out the starting/ending declarations.
+      Decl *FirstLocalDecl = Reader.GetLocalDecl(M, Result->FirstLocalID);
+      Decl *LastLocalDecl = Reader.GetLocalDecl(M, Result->LastLocalID);
+      if (!FirstLocalDecl || !LastLocalDecl)
+        return false;
+      
+      // Append this redeclaration chain to the list.
+      Chains.push_back(std::make_pair(FirstLocalDecl, LastLocalDecl));
+      return false;
+    }
+    
+    ArrayRef<std::pair<Decl *, Decl *> > getChains() const {
+      return Chains;
+    }
+    
+    void addParsed(Decl *FirstParsedDecl, Decl *LastParsedDecl) {
+      Chains.push_back(std::make_pair(FirstParsedDecl, LastParsedDecl));
+    }
+  };
+}
+
+/// \brief Retrieve the previous declaration to D.
+static Decl *getPreviousDecl(Decl *D) {
+  if (TagDecl *TD = dyn_cast<TagDecl>(D))
+    return TD->getPreviousDeclaration();
+  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
+    return FD->getPreviousDeclaration();
+  if (VarDecl *VD = dyn_cast<VarDecl>(D))
+    return VD->getPreviousDeclaration();
+  if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D))
+    return TD->getPreviousDeclaration();
+  if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D))
+    return ID->getPreviousDeclaration();
+  
+  return cast<RedeclarableTemplateDecl>(D)->getPreviousDeclaration();
+}
+
+/// \brief Retrieve the most recent declaration of D.
+static Decl *getMostRecentDecl(Decl *D) {
+  if (TagDecl *TD = dyn_cast<TagDecl>(D))
+    return TD->getMostRecentDeclaration();
+  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
+    return FD->getMostRecentDeclaration();
+  if (VarDecl *VD = dyn_cast<VarDecl>(D))
+    return VD->getMostRecentDeclaration();
+  if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D))
+    return TD->getMostRecentDeclaration();
+  if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D))
+    return ID->getMostRecentDeclaration();
+  
+  return cast<RedeclarableTemplateDecl>(D)->getMostRecentDeclaration();
+}
+
+void ASTReader::loadPendingDeclChain(serialization::GlobalDeclID ID) {
+  // Build up the list of redeclaration chains.
+  RedeclChainVisitor Visitor(*this, ID);
+  ModuleMgr.visitDepthFirst(&RedeclChainVisitor::visit, &Visitor);
+  
+  // Retrieve the chains.
+  ArrayRef<std::pair<Decl *, Decl *> > Chains = Visitor.getChains();
+  if (Chains.empty())
+    return;
+  
+  // FIXME: Splice local (not from AST file) declarations into the list,
+  // rather than always re-ordering them.
+  Decl *CanonDecl = GetDecl(ID);  
+  
+  // Capture all of the parsed declarations and put them at the end.
+  Decl *MostRecent = getMostRecentDecl(CanonDecl);
+  Decl *FirstParsed = MostRecent;
+  if (CanonDecl != MostRecent && !MostRecent->isFromASTFile()) {
+    Decl *Current = MostRecent;
+    while (Decl *Prev = getPreviousDecl(Current)) {
+      if (Prev->isFromASTFile()) {
+        Current = Prev;
+        continue;
+      }
+      
+      // Chain all of the parsed declarations together.
+      ASTDeclReader::attachPreviousDecl(FirstParsed, Prev);
+      FirstParsed = Prev;
+      Current = Prev;
+    }
+    
+    Visitor.addParsed(FirstParsed, MostRecent);
+  }
+  
+  // Hook up the separate chains.
+  Chains = Visitor.getChains();
+  for (unsigned I = 1, N = Chains.size(); I != N; ++I)
+    ASTDeclReader::attachPreviousDecl(Chains[I].first, Chains[I-1].second);    
+  ASTDeclReader::attachLatestDecl(CanonDecl, Chains.back().second);
+}
+
 namespace {
   /// \brief Given an ObjC interface, goes through the modules and links to the
   /// interface all the categories for it.
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index b3f76f7494..bb2b1cb5b0 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -798,7 +798,8 @@ void ASTWriter::WriteBlockInfoBlock() {
   RECORD(KNOWN_NAMESPACES);
   RECORD(MODULE_OFFSET_MAP);
   RECORD(SOURCE_MANAGER_LINE_TABLE);
-  
+  RECORD(LOCAL_REDECLARATIONS);
+         
   // SourceManager Block.
   BLOCK(SOURCE_MANAGER_BLOCK);
   RECORD(SM_SLOC_FILE_ENTRY);
@@ -3411,6 +3412,25 @@ void ASTWriter::WriteASTCore(Sema &SemaRef, MemorizeStatCalls *StatCalls,
   WriteDeclReplacementsBlock();
   WriteChainedObjCCategories();
 
+  if (!LocalRedeclarations.empty()) {
+    // Sort the local redeclarations info by the first declaration ID,
+    // since the reader will be perforing binary searches on this information.
+    llvm::array_pod_sort(LocalRedeclarations.begin(),LocalRedeclarations.end());
+    
+    llvm::BitCodeAbbrev *Abbrev = new BitCodeAbbrev();
+    Abbrev->Add(BitCodeAbbrevOp(LOCAL_REDECLARATIONS));
+    Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // # of entries
+    Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
+    unsigned AbbrevID = Stream.EmitAbbrev(Abbrev);
+
+    Record.clear();
+    Record.push_back(LOCAL_REDECLARATIONS);
+    Record.push_back(LocalRedeclarations.size());
+    Stream.EmitRecordWithBlob(AbbrevID, Record, 
+      reinterpret_cast<char*>(LocalRedeclarations.data()),
+      LocalRedeclarations.size() * sizeof(LocalRedeclarationsInfo));
+  }
+  
   // Some simple statistics
   Record.clear();
   Record.push_back(NumStatements);
diff --git a/lib/Serialization/ASTWriterDecl.cpp b/lib/Serialization/ASTWriterDecl.cpp
index 9b74aaeae4..6c6428d55a 100644
--- a/lib/Serialization/ASTWriterDecl.cpp
+++ b/lib/Serialization/ASTWriterDecl.cpp
@@ -125,6 +125,30 @@ namespace clang {
   };
 }
 
+static bool isFirstDeclInFile(Decl *D) {
+  // FIXME: There must be a better way to abstract Redeclarable<T> into a 
+  // more-general "redeclarable type".
+  if (TagDecl *Tag = dyn_cast<TagDecl>(D))
+    return !Tag->getPreviousDeclaration() ||
+           Tag->getPreviousDeclaration()->isFromASTFile();
+  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
+    return !FD->getPreviousDeclaration() ||
+           FD->getPreviousDeclaration()->isFromASTFile();
+  if (VarDecl *VD = dyn_cast<VarDecl>(D))
+    return !VD->getPreviousDeclaration() ||
+           VD->getPreviousDeclaration()->isFromASTFile();
+  if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D))
+    return !TD->getPreviousDeclaration() ||
+           TD->getPreviousDeclaration()->isFromASTFile();
+  if (ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D))
+    return !ID->getPreviousDeclaration() ||
+            ID->getPreviousDeclaration()->isFromASTFile();
+  
+  RedeclarableTemplateDecl *RTD = cast<RedeclarableTemplateDecl>(D);
+  return !RTD->getPreviousDeclaration() ||
+          RTD->getPreviousDeclaration()->isFromASTFile();  
+}
+
 void ASTDeclWriter::Visit(Decl *D) {
   DeclVisitor<ASTDeclWriter>::Visit(D);
 
@@ -177,13 +201,14 @@ void ASTDeclWriter::VisitTypeDecl(TypeDecl *D) {
 }
 
 void ASTDeclWriter::VisitTypedefDecl(TypedefDecl *D) {
+  VisitRedeclarable(D);
   VisitTypeDecl(D);
   Writer.AddTypeSourceInfo(D->getTypeSourceInfo(), Record);
 
   if (!D->hasAttrs() &&
       !D->isImplicit() &&
       !D->isUsed(false) &&
-      D->RedeclLink.getNext() == D &&
+      isFirstDeclInFile(D) &&
       !D->isInvalidDecl() &&
       !D->isReferenced() &&
       !D->isTopLevelDeclInObjCContainer() &&
@@ -196,6 +221,7 @@ void ASTDeclWriter::VisitTypedefDecl(TypedefDecl *D) {
 }
 
 void ASTDeclWriter::VisitTypeAliasDecl(TypeAliasDecl *D) {
+  VisitRedeclarable(D);
   VisitTypeDecl(D);
   Writer.AddTypeSourceInfo(D->getTypeSourceInfo(), Record);
   Code = serialization::DECL_TYPEALIAS;
@@ -234,7 +260,7 @@ void ASTDeclWriter::VisitEnumDecl(EnumDecl *D) {
       !D->isImplicit() &&
       !D->isUsed(false) &&
       !D->hasExtInfo() &&
-      D->RedeclLink.getNext() == D &&
+      isFirstDeclInFile(D) &&
       !D->isInvalidDecl() &&
       !D->isReferenced() &&
       !D->isTopLevelDeclInObjCContainer() &&
@@ -258,7 +284,7 @@ void ASTDeclWriter::VisitRecordDecl(RecordDecl *D) {
       !D->isImplicit() &&
       !D->isUsed(false) &&
       !D->hasExtInfo() &&
-      D->RedeclLink.getNext() == D &&
+      isFirstDeclInFile(D) &&
       !D->isInvalidDecl() &&
       !D->isReferenced() &&
       !D->isTopLevelDeclInObjCContainer() &&
@@ -701,7 +727,7 @@ void ASTDeclWriter::VisitVarDecl(VarDecl *D) {
       !D->isModulePrivate() &&
       D->getDeclName().getNameKind() == DeclarationName::Identifier &&
       !D->hasExtInfo() &&
-      D->RedeclLink.getNext() == D &&
+      isFirstDeclInFile(D) &&
       !D->hasCXXDirectInitializer() &&
       D->getInit() == 0 &&
       !isa<ParmVarDecl>(D) &&
@@ -1267,30 +1293,24 @@ void ASTDeclWriter::VisitDeclContext(DeclContext *DC, uint64_t LexicalOffset,
 
 template <typename T>
 void ASTDeclWriter::VisitRedeclarable(Redeclarable<T> *D) {
-  enum { NoRedeclaration = 0, PointsToPrevious, PointsToLatest };
-  if (D->RedeclLink.getNext() == D) {
-    Record.push_back(NoRedeclaration);
-  } else {
-    if (D->RedeclLink.NextIsPrevious()) {
-      Record.push_back(PointsToPrevious);
-      Writer.AddDeclRef(D->getPreviousDeclaration(), Record);
-      Writer.AddDeclRef(D->getFirstDeclaration(), Record);
-    } else {
-      Record.push_back(PointsToLatest);
-      Writer.AddDeclRef(D->RedeclLink.getPointer(), Record);
-    }
-  }
-
+  enum { FirstInFile, PointsToPrevious };
   T *First = D->getFirstDeclaration();
-  T *ThisDecl = static_cast<T*>(D);
-  // If this is a most recent redeclaration that is pointed to by a first decl
-  // in a chained PCH, keep track of the association with the map so we can
-  // update the first decl during AST reading.
-  if (ThisDecl != First && First->getMostRecentDeclaration() == ThisDecl &&
-      First->isFromASTFile() && !ThisDecl->isFromASTFile()) {
-    assert(Writer.FirstLatestDecls.find(First) == Writer.FirstLatestDecls.end()
-           && "The latest is already set");
-    Writer.FirstLatestDecls[First] = ThisDecl;
+  if (!D->getPreviousDeclaration() ||
+      D->getPreviousDeclaration()->isFromASTFile()) {
+    Record.push_back(FirstInFile);
+    Writer.AddDeclRef(First, Record);
+
+    // Capture the set of redeclarations in this file.
+    LocalRedeclarationsInfo LocalInfo = {
+      Writer.GetDeclRef(First),
+      Writer.GetDeclRef(static_cast<T*>(D)),
+      Writer.GetDeclRef(D->getMostRecentDeclaration())
+    };
+    Writer.LocalRedeclarations.push_back(LocalInfo);    
+  } else {
+    Record.push_back(PointsToPrevious);
+    Writer.AddDeclRef(First, Record);
+    Writer.AddDeclRef(D->getPreviousDeclaration(), Record);
   }
 }
 
@@ -1374,7 +1394,8 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv = new BitCodeAbbrev();
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_ENUM));
   // Redeclarable
-  Abv->Add(BitCodeAbbrevOp(0));                         // No redeclaration
+  Abv->Add(BitCodeAbbrevOp(0));                       // First in file
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // First ID
   // Decl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
@@ -1421,7 +1442,8 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv = new BitCodeAbbrev();
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_RECORD));
   // Redeclarable
-  Abv->Add(BitCodeAbbrevOp(0));                         // No redeclaration
+  Abv->Add(BitCodeAbbrevOp(0));                       // First in file
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // First ID
   // Decl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
@@ -1462,7 +1484,8 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv = new BitCodeAbbrev();
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_PARM_VAR));
   // Redeclarable
-  Abv->Add(BitCodeAbbrevOp(0));                       // No redeclaration
+  Abv->Add(BitCodeAbbrevOp(0));                       // First in file
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // First ID
   // Decl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
@@ -1511,6 +1534,9 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   // Abbreviation for DECL_TYPEDEF
   Abv = new BitCodeAbbrev();
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_TYPEDEF));
+  // Redeclarable
+  Abv->Add(BitCodeAbbrevOp(0));                       // First in file
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // First ID
   // Decl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
@@ -1538,7 +1564,8 @@ void ASTWriter::WriteDeclsBlockAbbrevs() {
   Abv = new BitCodeAbbrev();
   Abv->Add(BitCodeAbbrevOp(serialization::DECL_VAR));
   // Redeclarable
-  Abv->Add(BitCodeAbbrevOp(0));                       // No redeclaration
+  Abv->Add(BitCodeAbbrevOp(0));                       // First in file
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // First ID
   // Decl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // DeclContext
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LexicalDeclContext
diff --git a/lib/Serialization/Module.cpp b/lib/Serialization/Module.cpp
index 11e7243cd5..1298714dd0 100644
--- a/lib/Serialization/Module.cpp
+++ b/lib/Serialization/Module.cpp
@@ -35,7 +35,7 @@ ModuleFile::ModuleFile(ModuleKind Kind)
     SelectorLookupTableData(0), SelectorLookupTable(0), LocalNumDecls(0),
     DeclOffsets(0), BaseDeclID(0),
     LocalNumCXXBaseSpecifiers(0), CXXBaseSpecifiersOffsets(0),
-    FileSortedDecls(0),
+    FileSortedDecls(0), RedeclarationsInfo(0), LocalNumRedeclarationsInfos(0),
     LocalNumTypes(0), TypeOffsets(0), BaseTypeIndex(0), StatCache(0)
 {}
 
diff --git a/test/Modules/Inputs/module.map b/test/Modules/Inputs/module.map
index f7cc7d4b51..b101c01567 100644
--- a/test/Modules/Inputs/module.map
+++ b/test/Modules/Inputs/module.map
@@ -41,4 +41,20 @@ module decldef {
   explicit module Decl { header "decl.h" }
   explicit module Decl2 { header "decl2.h" }
   explicit module Def { header "def.h" }
-}
\ No newline at end of file
+}
+
+module redecl_merge_top { 
+  header "redecl-merge-top.h" 
+}
+module redecl_merge_left { 
+  header "redecl-merge-left.h" 
+  export *
+}
+module redecl_merge_right { 
+  header "redecl-merge-right.h" 
+  export *
+}
+module redecl_merge_bottom { 
+  header "redecl-merge-bottom.h" 
+  export *
+}
diff --git a/test/Modules/Inputs/redecl-merge-bottom.h b/test/Modules/Inputs/redecl-merge-bottom.h
new file mode 100644
index 0000000000..e45e0dea04
--- /dev/null
+++ b/test/Modules/Inputs/redecl-merge-bottom.h
@@ -0,0 +1,4 @@
+__import_module__ redecl_merge_left;
+__import_module__ redecl_merge_right;
+
+@class A;
diff --git a/test/Modules/Inputs/redecl-merge-left.h b/test/Modules/Inputs/redecl-merge-left.h
new file mode 100644
index 0000000000..0858922348
--- /dev/null
+++ b/test/Modules/Inputs/redecl-merge-left.h
@@ -0,0 +1,7 @@
+__import_module__ redecl_merge_top;
+
+@class A;
+
+@class A;
+
+@class A;
diff --git a/test/Modules/Inputs/redecl-merge-right.h b/test/Modules/Inputs/redecl-merge-right.h
new file mode 100644
index 0000000000..266146c995
--- /dev/null
+++ b/test/Modules/Inputs/redecl-merge-right.h
@@ -0,0 +1,9 @@
+__import_module__ redecl_merge_top;
+
+@interface Super
+@end
+
+@interface A : Super
+- (Super*)init;
+@end
+
diff --git a/test/Modules/Inputs/redecl-merge-top.h b/test/Modules/Inputs/redecl-merge-top.h
new file mode 100644
index 0000000000..886436cdda
--- /dev/null
+++ b/test/Modules/Inputs/redecl-merge-top.h
@@ -0,0 +1,5 @@
+@class A;
+
+@class A;
+
+@class A;
diff --git a/test/Modules/redecl-merge.m b/test/Modules/redecl-merge.m
new file mode 100644
index 0000000000..40c6aaf0ff
--- /dev/null
+++ b/test/Modules/redecl-merge.m
@@ -0,0 +1,20 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodule-cache-path %t -I %S/Inputs %s -verify
+__import_module__ redecl_merge_left;
+__import_module__ redecl_merge_right;
+
+@implementation A
+- (Super*)init { return self; }
+@end
+
+void f(A *a) {
+  [a init];
+}
+
+@class A;
+
+__import_module__ redecl_merge_bottom;
+
+void g(A *a) {
+  [a init];
+}
diff --git a/test/PCH/chain-cxx.cpp b/test/PCH/chain-cxx.cpp
index af0a23afea..c42ee7d39e 100644
--- a/test/PCH/chain-cxx.cpp
+++ b/test/PCH/chain-cxx.cpp
@@ -44,6 +44,8 @@ const int TS3<T>::value;
 // Instantiate struct, but not value.
 struct instantiate : TS3<int> {};
 
+// Typedef
+typedef int Integer;
 
 //===----------------------------------------------------------------------===//
 #elif not defined(HEADER2)
@@ -97,6 +99,9 @@ struct B : A { };
 // Instantiate TS3's member.
 static const int ts3m1 = TS3<int>::value;
 
+// Redefinition of typedef
+typedef int Integer;
+
 //===----------------------------------------------------------------------===//
 #else
 //===----------------------------------------------------------------------===//
@@ -122,6 +127,7 @@ void test() {
   TS2int ts2;
 
   B b;
+  Integer i = 17;
 }
 
 // Should have remembered that there is a definition.