diff --git a/lib/CodeGen/CGBlocks.cpp b/lib/CodeGen/CGBlocks.cpp
index 94ba269..a2ab883 100644
--- a/lib/CodeGen/CGBlocks.cpp
+++ b/lib/CodeGen/CGBlocks.cpp
@@ -24,36 +24,6 @@
 using namespace clang;
 using namespace CodeGen;
 
-/// CGBlockInfo - Information to generate a block literal.
-class clang::CodeGen::CGBlockInfo {
-public:
-  /// Name - The name of the block, kindof.
-  const char *Name;
-
-  /// DeclRefs - Variables from parent scopes that have been
-  /// imported into this block.
-  llvm::SmallVector<const BlockDeclRefExpr *, 8> DeclRefs;
-
-  /// InnerBlocks - This block and the blocks it encloses.
-  llvm::SmallPtrSet<const DeclContext *, 4> InnerBlocks;
-
-  /// CXXThisRef - Non-null if 'this' was required somewhere, in
-  /// which case this is that expression.
-  const CXXThisExpr *CXXThisRef;
-
-  /// NeedsObjCSelf - True if something in this block has an implicit
-  /// reference to 'self'.
-  bool NeedsObjCSelf;
-
-  /// These are initialized by GenerateBlockFunction.
-  bool BlockHasCopyDispose;
-  CharUnits BlockSize;
-  CharUnits BlockAlign;
-  llvm::SmallVector<const Expr*, 8> BlockLayout;
-
-  CGBlockInfo(const char *Name);
-};
-
 CGBlockInfo::CGBlockInfo(const char *N)
   : Name(N), CXXThisRef(0), NeedsObjCSelf(false) {
     
@@ -64,9 +34,11 @@
 
 
 llvm::Constant *CodeGenFunction::
-BuildDescriptorBlockDecl(const BlockExpr *BE, bool BlockHasCopyDispose, CharUnits Size,
+BuildDescriptorBlockDecl(const BlockExpr *BE, const CGBlockInfo &Info,
                          const llvm::StructType* Ty,
                          std::vector<HelperInfo> *NoteForHelper) {
+  bool BlockHasCopyDispose = Info.BlockHasCopyDispose;
+  CharUnits Size = Info.BlockSize;
   const llvm::Type *UnsignedLongTy
     = CGM.getTypes().ConvertType(getContext().UnsignedLongTy);
   llvm::Constant *C;
@@ -100,7 +72,11 @@
           CGM.GetAddrOfConstantCString(BlockTypeEncoding), PtrToInt8Ty));
   
   // Layout.
-  C = llvm::ConstantInt::get(UnsignedLongTy, 0);
+  if (CGM.getContext().getLangOptions().ObjC1)
+    C = CGM.getObjCRuntime().GCBlockLayout(*this, Info.DeclRefs);
+  else
+    C = llvm::Constant::getNullValue(PtrToInt8Ty);
+  
   Elts.push_back(C);
 
   C = llvm::ConstantStruct::get(VMContext, Elts, false);
@@ -257,8 +233,7 @@
 
     if (Info.BlockLayout.empty()) {
       // __descriptor
-      Elts[4] = BuildDescriptorBlockDecl(BE, Info.BlockHasCopyDispose,
-                                         Info.BlockSize, 0, 0);
+      Elts[4] = BuildDescriptorBlockDecl(BE, Info, 0, 0);
 
       // Optimize to being a global block.
       Elts[0] = CGM.getNSConcreteGlobalBlock();
@@ -412,9 +387,7 @@
     NoteForHelper.resize(NumHelpers);
 
     // __descriptor
-    llvm::Value *Descriptor = BuildDescriptorBlockDecl(BE,
-                                                       Info.BlockHasCopyDispose,
-                                                       Info.BlockSize, Ty,
+    llvm::Value *Descriptor = BuildDescriptorBlockDecl(BE, Info, Ty,
                                                        &NoteForHelper);
     Descriptor = Builder.CreateBitCast(Descriptor, PtrToInt8Ty);
     Builder.CreateStore(Descriptor, Builder.CreateStructGEP(V, 4, "block.tmp"));
diff --git a/lib/CodeGen/CGObjCGNU.cpp b/lib/CodeGen/CGObjCGNU.cpp
index a9519ed..fdee1de 100644
--- a/lib/CodeGen/CGObjCGNU.cpp
+++ b/lib/CodeGen/CGObjCGNU.cpp
@@ -212,6 +212,10 @@
   virtual llvm::Value *EmitIvarOffset(CodeGen::CodeGenFunction &CGF,
                                       const ObjCInterfaceDecl *Interface,
                                       const ObjCIvarDecl *Ivar);
+  virtual llvm::Constant *GCBlockLayout(CodeGen::CodeGenFunction &CGF,
+              const llvm::SmallVectorImpl<const BlockDeclRefExpr *> &) {
+    return NULLPtr;
+  }
 };
 } // end anonymous namespace
 
diff --git a/lib/CodeGen/CGObjCMac.cpp b/lib/CodeGen/CGObjCMac.cpp
index 4db7ec5..b30b44b 100644
--- a/lib/CodeGen/CGObjCMac.cpp
+++ b/lib/CodeGen/CGObjCMac.cpp
@@ -1033,6 +1033,9 @@
   /// forward references will be filled in with empty bodies if no
   /// definition is seen. The return value has type ProtocolPtrTy.
   virtual llvm::Constant *GetOrEmitProtocolRef(const ObjCProtocolDecl *PD)=0;
+  virtual llvm::Constant *GCBlockLayout(CodeGen::CodeGenFunction &CGF,
+                      const llvm::SmallVectorImpl<const BlockDeclRefExpr *> &);
+  
 };
 
 class CGObjCMac : public CGObjCCommonMac {
@@ -1686,6 +1689,11 @@
   return CGF.EmitCall(FnInfo, Fn, Return, ActualArgs);
 }
 
+llvm::Constant *CGObjCCommonMac::GCBlockLayout(CodeGen::CodeGenFunction &CGF,
+              const llvm::SmallVectorImpl<const BlockDeclRefExpr *> &BDRE) {
+  return llvm::Constant::getNullValue(llvm::Type::getInt8PtrTy(VMContext));
+}
+
 llvm::Value *CGObjCMac::GenerateProtocolRef(CGBuilderTy &Builder,
                                             const ObjCProtocolDecl *PD) {
   // FIXME: I don't understand why gcc generates this, or where it is
diff --git a/lib/CodeGen/CGObjCRuntime.h b/lib/CodeGen/CGObjCRuntime.h
index bf172f9..584760f 100644
--- a/lib/CodeGen/CGObjCRuntime.h
+++ b/lib/CodeGen/CGObjCRuntime.h
@@ -52,6 +52,7 @@
   class Selector;
   class ObjCIvarDecl;
   class ObjCStringLiteral;
+  class BlockDeclRefExpr;
 
 namespace CodeGen {
   class CodeGenModule;
@@ -218,6 +219,9 @@
                                         llvm::Value *DestPtr,
                                         llvm::Value *SrcPtr,
                                         llvm::Value *Size) = 0;
+  virtual llvm::Constant *GCBlockLayout(CodeGen::CodeGenFunction &CGF,
+                  const llvm::SmallVectorImpl<const BlockDeclRefExpr *> &) = 0;
+                                        
 };
 
 /// Creates an instance of an Objective-C runtime class.
diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index 7874570..b9abe14 100644
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -759,8 +759,7 @@
 
   llvm::Value *BuildBlockLiteralTmp(const BlockExpr *);
   llvm::Constant *BuildDescriptorBlockDecl(const BlockExpr *,
-                                           bool BlockHasCopyDispose,
-                                           CharUnits Size,
+                                           const CGBlockInfo &Info,
                                            const llvm::StructType *,
                                            std::vector<HelperInfo> *);
 
@@ -1677,7 +1676,36 @@
   void EmitDeclMetadata();
 };
 
-
+/// CGBlockInfo - Information to generate a block literal.
+class CGBlockInfo {
+public:
+  /// Name - The name of the block, kindof.
+  const char *Name;
+    
+  /// DeclRefs - Variables from parent scopes that have been
+  /// imported into this block.
+  llvm::SmallVector<const BlockDeclRefExpr *, 8> DeclRefs;
+    
+  /// InnerBlocks - This block and the blocks it encloses.
+  llvm::SmallPtrSet<const DeclContext *, 4> InnerBlocks;
+    
+  /// CXXThisRef - Non-null if 'this' was required somewhere, in
+  /// which case this is that expression.
+  const CXXThisExpr *CXXThisRef;
+    
+  /// NeedsObjCSelf - True if something in this block has an implicit
+  /// reference to 'self'.
+  bool NeedsObjCSelf;
+    
+  /// These are initialized by GenerateBlockFunction.
+  bool BlockHasCopyDispose;
+  CharUnits BlockSize;
+  CharUnits BlockAlign;
+  llvm::SmallVector<const Expr*, 8> BlockLayout;
+    
+  CGBlockInfo(const char *Name);
+};
+  
 }  // end namespace CodeGen
 }  // end namespace clang