4 files changed, 46 insertions, 11 deletions
diff --git a/include/clang/AST/DeclBase.h b/include/clang/AST/DeclBase.h
index 8a07475800..3ff38dc0d5 100644
--- a/include/clang/AST/DeclBase.h
+++ b/include/clang/AST/DeclBase.h
@@ -222,11 +222,14 @@ protected:
   // NOTE: VC++ treats enums as signed, avoid using the AccessSpecifier enum
   unsigned Access : 2;
   friend class CXXClassMemberWrapper;
-  
-  // PCHLevel - the "level" of precompiled header/AST file from which this
-  // declaration was built.
-  unsigned PCHLevel : 3;
-  
+
+  /// PCHLevel - the "level" of precompiled header/AST file from which this
+  /// declaration was built.
+  unsigned PCHLevel : 2;
+
+  /// PCHChanged - if this declaration has changed since being deserialized
+  bool PCHChanged : 1;
+
   /// IdentifierNamespace - This specifies what IDNS_* namespace this lives in.
   unsigned IdentifierNamespace : 15;
 
@@ -243,7 +246,7 @@ protected:
     : NextDeclInContext(0), DeclCtx(DC),
       Loc(L), DeclKind(DK), InvalidDecl(0),
       HasAttrs(false), Implicit(false), Used(false),
-      Access(AS_none), PCHLevel(0),
+      Access(AS_none), PCHLevel(0), PCHChanged(false),
       IdentifierNamespace(getIdentifierNamespaceForKind(DK)) {
     if (Decl::CollectingStats()) add(DK);
   }
@@ -251,7 +254,7 @@ protected:
   Decl(Kind DK, EmptyShell Empty)
     : NextDeclInContext(0), DeclKind(DK), InvalidDecl(0),
       HasAttrs(false), Implicit(false), Used(false),
-      Access(AS_none), PCHLevel(0),
+      Access(AS_none), PCHLevel(0), PCHChanged(false),
       IdentifierNamespace(getIdentifierNamespaceForKind(DK)) {
     if (Decl::CollectingStats()) add(DK);
   }
@@ -358,7 +361,7 @@ public:
   unsigned getPCHLevel() const { return PCHLevel; }
 
   /// \brief The maximum PCH level that any declaration may have.
-  static const unsigned MaxPCHLevel = 7;
+  static const unsigned MaxPCHLevel = 3;
 
   /// \brief Set the PCH level of this declaration.
   void setPCHLevel(unsigned Level) { 
@@ -366,6 +369,17 @@ public:
     PCHLevel = Level;
   }
 
+  /// \brief Query whether this declaration was changed in a significant way
+  /// since being loaded from a PCH file.
+  ///
+  /// In an epic violation of layering, what is "significant" is entirely
+  /// up to the PCH system, but implemented in AST and Sema.
+  bool isChangedSinceDeserialization() const { return PCHChanged; }
+
+  /// \brief Mark this declaration as having changed since deserialization, or
+  /// reset the flag.
+  void setChangedSinceDeserialization(bool Changed) { PCHChanged = Changed; }
+
   unsigned getIdentifierNamespace() const {
     return IdentifierNamespace;
   }
diff --git a/include/clang/Frontend/PCHBitCodes.h b/include/clang/Frontend/PCHBitCodes.h
index 7605670f0e..bce5c287e7 100644
--- a/include/clang/Frontend/PCHBitCodes.h
+++ b/include/clang/Frontend/PCHBitCodes.h
@@ -256,7 +256,14 @@ namespace clang {
       WEAK_UNDECLARED_IDENTIFIERS = 31,
 
       /// \brief Record code for pending implicit instantiations.
-      PENDING_IMPLICIT_INSTANTIATIONS = 32
+      PENDING_IMPLICIT_INSTANTIATIONS = 32,
+
+      /// \brief Record code for a decl replacement block.
+      ///
+      /// If a declaration is modified after having been deserialized, and then
+      /// written to a dependent PCH file, its ID and offset must be added to
+      /// the replacement block.
+      DECL_REPLACEMENTS = 33
     };
 
     /// \brief Record types used within a source manager block.
diff --git a/include/clang/Frontend/PCHReader.h b/include/clang/Frontend/PCHReader.h
index 7be86050ab..906e3e1b22 100644
--- a/include/clang/Frontend/PCHReader.h
+++ b/include/clang/Frontend/PCHReader.h
@@ -321,6 +321,11 @@ private:
   /// = I + 1 has already been loaded.
   std::vector<Decl *> DeclsLoaded;
 
+  typedef llvm::DenseMap<pch::DeclID, std::pair<PerFileData *, uint64_t> >
+      DeclReplacementMap;
+  /// \brief Declarations that have been replaced in a later file in the chain.
+  DeclReplacementMap ReplacedDecls;
+
   /// \brief Information about the contents of a DeclContext.
   struct DeclContextInfo {
     llvm::BitstreamCursor *Stream;
@@ -577,7 +582,7 @@ private:
   RecordLocation TypeCursorForIndex(unsigned Index);
   void LoadedDecl(unsigned Index, Decl *D);
   Decl *ReadDeclRecord(unsigned Index, pch::DeclID ID);
-  RecordLocation DeclCursorForIndex(unsigned Index);
+  RecordLocation DeclCursorForIndex(unsigned Index, pch::DeclID ID);
 
   void PassInterestingDeclsToConsumer();
 
diff --git a/include/clang/Frontend/PCHWriter.h b/include/clang/Frontend/PCHWriter.h
index 11422b4ba2..bb083eaf8f 100644
--- a/include/clang/Frontend/PCHWriter.h
+++ b/include/clang/Frontend/PCHWriter.h
@@ -227,10 +227,18 @@ private:
   /// to this set, so that we can write out lexical content updates for it.
   llvm::SmallPtrSet<const NamespaceDecl *, 16> UpdatedNamespaces;
 
+  /// \brief Decls that have been replaced in the current dependent PCH.
+  ///
+  /// When a decl changes fundamentally after being deserialized (this shouldn't
+  /// happen, but the ObjC AST nodes are designed this way), it will be
+  /// serialized again. In this case, it is registered here, so that the reader
+  /// knows to read the updated version.
+  llvm::SmallVector<std::pair<pch::DeclID, uint64_t>, 16> ReplacedDecls;
+
   /// \brief Statements that we've encountered while serializing a
   /// declaration or type.
   llvm::SmallVector<Stmt *, 16> StmtsToEmit;
-  
+
   /// \brief Statements collection to use for PCHWriter::AddStmt().
   /// It will point to StmtsToEmit unless it is overriden. 
   llvm::SmallVector<Stmt *, 16> *CollectedStmts;
@@ -274,6 +282,7 @@ private:
   void WriteReferencedSelectorsPool(Sema &SemaRef);
   void WriteIdentifierTable(Preprocessor &PP);
   void WriteAttributeRecord(const Attr *Attr);
+  void WriteDeclUpdateBlock();
 
   unsigned ParmVarDeclAbbrev;
   unsigned DeclContextLexicalAbbrev;