diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 5a6aa1a..4caf16c 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -483,7 +483,8 @@
 /// specified record (struct/union/class), which indicates its size and field
 /// position information.
 const ASTRecordLayout &ASTContext::getASTRecordLayout(const RecordDecl *D) {
-  assert(D->isDefinition() && "Cannot get layout of forward declarations!");
+  D = D->getDefinition(*this);
+  assert(D && "Cannot get layout of forward declarations!");
 
   // Look up this layout, if already laid out, return what we have.
   const ASTRecordLayout *&Entry = ASTRecordLayouts[D];
@@ -898,7 +899,7 @@
 
 /// getTypeDeclType - Return the unique reference to the type for the
 /// specified type declaration.
-QualType ASTContext::getTypeDeclType(TypeDecl *Decl) {
+QualType ASTContext::getTypeDeclType(TypeDecl *Decl, TypeDecl* PrevDecl) {
   if (Decl->TypeForDecl) return QualType(Decl->TypeForDecl, 0);
   
   if (TypedefDecl *Typedef = dyn_cast_or_null<TypedefDecl>(Decl))
@@ -907,19 +908,31 @@
              = dyn_cast_or_null<ObjCInterfaceDecl>(Decl))
     return getObjCInterfaceType(ObjCInterface);
 
-  if (CXXRecordDecl *CXXRecord = dyn_cast_or_null<CXXRecordDecl>(Decl))
-    Decl->TypeForDecl = new CXXRecordType(CXXRecord);
-  else if (RecordDecl *Record = dyn_cast_or_null<RecordDecl>(Decl))
-    Decl->TypeForDecl = new RecordType(Record);
+  if (CXXRecordDecl *CXXRecord = dyn_cast_or_null<CXXRecordDecl>(Decl)) {
+    Decl->TypeForDecl = PrevDecl ? PrevDecl->TypeForDecl
+                                 : new CXXRecordType(CXXRecord);
+  }
+  else if (RecordDecl *Record = dyn_cast_or_null<RecordDecl>(Decl)) {
+    Decl->TypeForDecl = PrevDecl ? PrevDecl->TypeForDecl
+                                 : new RecordType(Record);
+  }
   else if (EnumDecl *Enum = dyn_cast_or_null<EnumDecl>(Decl))
     Decl->TypeForDecl = new EnumType(Enum);
   else
     assert(false && "TypeDecl without a type?");
 
-  Types.push_back(Decl->TypeForDecl);
+  if (!PrevDecl) Types.push_back(Decl->TypeForDecl);
   return QualType(Decl->TypeForDecl, 0);
 }
 
+/// setTagDefinition - Used by RecordDecl::defineBody to inform ASTContext
+///  about which RecordDecl serves as the definition of a particular
+///  struct/union/class.  This will eventually be used by enums as well.
+void ASTContext::setTagDefinition(TagDecl* D) {
+  assert (D->isDefinition());
+  cast<TagType>(D->TypeForDecl)->decl = D;  
+}
+
 /// getTypedefType - Return the unique reference to the type for the
 /// specified typename decl.
 QualType ASTContext::getTypedefType(TypedefDecl *Decl) {
@@ -1366,7 +1379,7 @@
       FieldDecls[i] = FieldDecl::Create(*this, SourceLocation(), 0,
                                         FieldTypes[i]);
   
-    CFConstantStringTypeDecl->defineBody(FieldDecls, 4);
+    CFConstantStringTypeDecl->defineBody(*this, FieldDecls, 4);
   }
   
   return getTagDeclType(CFConstantStringTypeDecl);
@@ -1392,7 +1405,7 @@
       RecordDecl::Create(*this, TagDecl::TK_struct, TUDecl, SourceLocation(),
                          &Idents.get("__objcFastEnumerationState"));
     
-    ObjCFastEnumerationStateTypeDecl->defineBody(FieldDecls, 4);
+    ObjCFastEnumerationStateTypeDecl->defineBody(*this, FieldDecls, 4);
   }
   
   return getTagDeclType(ObjCFastEnumerationStateTypeDecl);
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index eb9d0ef..8bc212d 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -200,6 +200,16 @@
 }
 
 //===----------------------------------------------------------------------===//
+// TagdDecl Implementation
+//===----------------------------------------------------------------------===//
+
+TagDecl* TagDecl::getDefinition(ASTContext& C) const {
+  QualType T = C.getTypeDeclType(const_cast<TagDecl*>(this));
+  TagDecl* D = cast<TagDecl>(cast<TagType>(T)->getDecl());  
+  return D->isDefinition() ? D : 0;
+}
+
+//===----------------------------------------------------------------------===//
 // RecordDecl Implementation
 //===----------------------------------------------------------------------===//
 
@@ -214,7 +224,8 @@
 }
 
 RecordDecl *RecordDecl::Create(ASTContext &C, TagKind TK, DeclContext *DC,
-                               SourceLocation L, IdentifierInfo *Id) {
+                               SourceLocation L, IdentifierInfo *Id,
+                               RecordDecl* PrevDecl) {
   
   void *Mem = C.getAllocator().Allocate<RecordDecl>();
   Kind DK;
@@ -225,7 +236,10 @@
     case TK_union:  DK = Union;  break;
     case TK_class:  DK = Class;  break;
   }
-  return new (Mem) RecordDecl(DK, DC, L, Id);
+  
+  RecordDecl* R = new (Mem) RecordDecl(DK, DC, L, Id);
+  C.getTypeDeclType(R, PrevDecl);
+  return R;
 }
 
 RecordDecl::~RecordDecl() {
@@ -243,7 +257,8 @@
 /// defineBody - When created, RecordDecl's correspond to a forward declared
 /// record.  This method is used to mark the decl as being defined, with the
 /// specified contents.
-void RecordDecl::defineBody(FieldDecl **members, unsigned numMembers) {
+void RecordDecl::defineBody(ASTContext& C, FieldDecl **members,
+                            unsigned numMembers) {
   assert(!isDefinition() && "Cannot redefine record!");
   setDefinition(true);
   NumMembers = numMembers;
@@ -251,8 +266,12 @@
     Members = new FieldDecl*[numMembers];
     memcpy(Members, members, numMembers*sizeof(Decl*));
   }
+  
+  // Let ASTContext know that this is the defining RecordDecl this type.
+  C.setTagDefinition(this);
 }
 
+
 FieldDecl *RecordDecl::getMember(IdentifierInfo *II) {
   if (Members == 0 || NumMembers < 0)
     return 0;
diff --git a/lib/AST/DeclCXX.cpp b/lib/AST/DeclCXX.cpp
index 0cce7db..0a65ab3 100644
--- a/lib/AST/DeclCXX.cpp
+++ b/lib/AST/DeclCXX.cpp
@@ -1,65 +1,68 @@
-//===--- DeclCXX.cpp - C++ Declaration AST Node Implementation ------------===//
-//
-//                     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 C++ related Decl classes.
-//
-//===----------------------------------------------------------------------===//
-
-#include "clang/AST/DeclCXX.h"
-#include "clang/AST/ASTContext.h"
-using namespace clang;
-
-//===----------------------------------------------------------------------===//
-// Decl Allocation/Deallocation Method Implementations
-//===----------------------------------------------------------------------===//
- 
-CXXFieldDecl *CXXFieldDecl::Create(ASTContext &C, CXXRecordDecl *RD,
-                                   SourceLocation L, IdentifierInfo *Id,
-                                   QualType T, Expr *BW) {
-  void *Mem = C.getAllocator().Allocate<CXXFieldDecl>();
-  return new (Mem) CXXFieldDecl(RD, L, Id, T, BW);
-}
-
-CXXRecordDecl *CXXRecordDecl::Create(ASTContext &C, TagKind TK, DeclContext *DC,
-                                     SourceLocation L, IdentifierInfo *Id) {
-  Kind DK;
-  switch (TK) {
-    default: assert(0 && "Invalid TagKind!");
-    case TK_enum:   assert(0 && "Enum TagKind passed for Record!");
-    case TK_struct: DK = CXXStruct; break;
-    case TK_union:  DK = CXXUnion;  break;
-    case TK_class:  DK = CXXClass;  break;
-  }
-  void *Mem = C.getAllocator().Allocate<CXXRecordDecl>();
-  return new (Mem) CXXRecordDecl(DK, DC, L, Id);
-}
-
-CXXMethodDecl *
-CXXMethodDecl::Create(ASTContext &C, CXXRecordDecl *RD,
-                      SourceLocation L, IdentifierInfo *Id,
-                      QualType T, bool isStatic, bool isInline,
-                      ScopedDecl *PrevDecl) {
-  void *Mem = C.getAllocator().Allocate<CXXMethodDecl>();
-  return new (Mem) CXXMethodDecl(RD, L, Id, T, isStatic, isInline, PrevDecl);
-}
-
-QualType CXXMethodDecl::getThisType(ASTContext &C) const {
-  assert(isInstance() && "No 'this' for static methods!");
-  QualType ClassTy = C.getTagDeclType(cast<CXXRecordDecl>(getParent()));
-  QualType ThisTy = C.getPointerType(ClassTy);
-  ThisTy.addConst();
-  return ThisTy;
-}
-
-CXXClassVarDecl *CXXClassVarDecl::Create(ASTContext &C, CXXRecordDecl *RD,
-                                   SourceLocation L, IdentifierInfo *Id,
-                                   QualType T, ScopedDecl *PrevDecl) {
-  void *Mem = C.getAllocator().Allocate<CXXClassVarDecl>();
-  return new (Mem) CXXClassVarDecl(RD, L, Id, T, PrevDecl);
-}
+//===--- DeclCXX.cpp - C++ Declaration AST Node Implementation ------------===//
+//
+//                     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 C++ related Decl classes.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/DeclCXX.h"
+#include "clang/AST/ASTContext.h"
+using namespace clang;
+
+//===----------------------------------------------------------------------===//
+// Decl Allocation/Deallocation Method Implementations
+//===----------------------------------------------------------------------===//
+ 
+CXXFieldDecl *CXXFieldDecl::Create(ASTContext &C, CXXRecordDecl *RD,
+                                   SourceLocation L, IdentifierInfo *Id,
+                                   QualType T, Expr *BW) {
+  void *Mem = C.getAllocator().Allocate<CXXFieldDecl>();
+  return new (Mem) CXXFieldDecl(RD, L, Id, T, BW);
+}
+
+CXXRecordDecl *CXXRecordDecl::Create(ASTContext &C, TagKind TK, DeclContext *DC,
+                                     SourceLocation L, IdentifierInfo *Id,
+                                     CXXRecordDecl* PrevDecl) {
+  Kind DK;
+  switch (TK) {
+    default: assert(0 && "Invalid TagKind!");
+    case TK_enum:   assert(0 && "Enum TagKind passed for Record!");
+    case TK_struct: DK = CXXStruct; break;
+    case TK_union:  DK = CXXUnion;  break;
+    case TK_class:  DK = CXXClass;  break;
+  }
+  void *Mem = C.getAllocator().Allocate<CXXRecordDecl>();
+  CXXRecordDecl* R = new (Mem) CXXRecordDecl(DK, DC, L, Id);
+  C.getTypeDeclType(R, PrevDecl);  
+  return R;
+}
+
+CXXMethodDecl *
+CXXMethodDecl::Create(ASTContext &C, CXXRecordDecl *RD,
+                      SourceLocation L, IdentifierInfo *Id,
+                      QualType T, bool isStatic, bool isInline,
+                      ScopedDecl *PrevDecl) {
+  void *Mem = C.getAllocator().Allocate<CXXMethodDecl>();
+  return new (Mem) CXXMethodDecl(RD, L, Id, T, isStatic, isInline, PrevDecl);
+}
+
+QualType CXXMethodDecl::getThisType(ASTContext &C) const {
+  assert(isInstance() && "No 'this' for static methods!");
+  QualType ClassTy = C.getTagDeclType(cast<CXXRecordDecl>(getParent()));
+  QualType ThisTy = C.getPointerType(ClassTy);
+  ThisTy.addConst();
+  return ThisTy;
+}
+
+CXXClassVarDecl *CXXClassVarDecl::Create(ASTContext &C, CXXRecordDecl *RD,
+                                   SourceLocation L, IdentifierInfo *Id,
+                                   QualType T, ScopedDecl *PrevDecl) {
+  void *Mem = C.getAllocator().Allocate<CXXClassVarDecl>();
+  return new (Mem) CXXClassVarDecl(RD, L, Id, T, PrevDecl);
+}
diff --git a/lib/CodeGen/CGObjCMac.cpp b/lib/CodeGen/CGObjCMac.cpp
index a535ea2..3922ae6 100644
--- a/lib/CodeGen/CGObjCMac.cpp
+++ b/lib/CodeGen/CGObjCMac.cpp
@@ -1872,7 +1872,7 @@
                                     Ctx.getObjCIdType());
   FieldDecls[1] = FieldDecl::Create(Ctx, SourceLocation(), 0,
                                     Ctx.getObjCClassType());
-  RD->defineBody(FieldDecls, 2);
+  RD->defineBody(Ctx, FieldDecls, 2);
 
   SuperCTy = Ctx.getTagDeclType(RD);
   SuperPtrCTy = Ctx.getPointerType(SuperCTy);
diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index f5a85a5..96f6e53 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -251,6 +251,11 @@
   virtual DeclTy *ActOnTag(Scope *S, unsigned TagType, TagKind TK,
                            SourceLocation KWLoc, IdentifierInfo *Name,
                            SourceLocation NameLoc, AttributeList *Attr);
+  
+  DeclTy* ActOnTagStruct(Scope *S, TagDecl::TagKind Kind, TagKind TK,
+                         SourceLocation KWLoc, IdentifierInfo *Name,
+                         SourceLocation NameLoc, AttributeList *Attr);  
+  
   virtual void ActOnDefs(Scope *S, SourceLocation DeclStart,
                          IdentifierInfo *ClassName,
                          llvm::SmallVectorImpl<DeclTy*> &Decls);
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 467da81..df91182 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1682,6 +1682,12 @@
   case DeclSpec::TST_enum:   Kind = TagDecl::TK_enum; break;
   }
   
+  // Two code paths: a new one for structs/unions/classes where we create
+  //   separate decls for forward declarations, and an old (eventually to
+  //   be removed) code path for enums.
+  if (Kind != TagDecl::TK_enum)
+    return ActOnTagStruct(S, Kind, TK, KWLoc, Name, NameLoc, Attr);
+  
   // If this is a named struct, check to see if there was a previous forward
   // declaration or definition.
   // Use ScopedDecl instead of TagDecl, because a NamespaceDecl may come up.
@@ -1781,6 +1787,121 @@
   return New;
 }
 
+/// ActOnTagStruct - New "ActOnTag" logic for structs/unions/classes.  Unlike
+///  the logic for enums, we create separate decls for forward declarations.
+///  This is called by ActOnTag, but eventually will replace its logic.
+Sema::DeclTy *Sema::ActOnTagStruct(Scope *S, TagDecl::TagKind Kind, TagKind TK,
+                             SourceLocation KWLoc, IdentifierInfo *Name,
+                             SourceLocation NameLoc, AttributeList *Attr) {
+  
+  // If this is a named struct, check to see if there was a previous forward
+  // declaration or definition.
+  // Use ScopedDecl instead of TagDecl, because a NamespaceDecl may come up.
+  ScopedDecl *PrevDecl = 
+    dyn_cast_or_null<ScopedDecl>(LookupDecl(Name, Decl::IDNS_Tag, S));
+  
+  if (PrevDecl) {    
+    assert((isa<TagDecl>(PrevDecl) || isa<NamespaceDecl>(PrevDecl)) &&
+           "unexpected Decl type");
+    
+    if (TagDecl *PrevTagDecl = dyn_cast<TagDecl>(PrevDecl)) {
+      // If this is a use of a previous tag, or if the tag is already declared
+      // in the same scope (so that the definition/declaration completes or
+      // rementions the tag), reuse the decl.
+      if (TK == TK_Reference ||
+          IdResolver.isDeclInScope(PrevDecl, CurContext, S)) {
+        // Make sure that this wasn't declared as an enum and now used as a
+        // struct or something similar.
+        if (PrevTagDecl->getTagKind() != Kind) {
+          Diag(KWLoc, diag::err_use_with_wrong_tag, Name->getName());
+          Diag(PrevDecl->getLocation(), diag::err_previous_use);
+          // Recover by making this an anonymous redefinition.
+          Name = 0;
+          PrevDecl = 0;
+        } else {
+          // If this is a use, return the original decl.
+          
+          // FIXME: In the future, return a variant or some other clue
+          //  for the consumer of this Decl to know it doesn't own it.
+          //  For our current ASTs this shouldn't be a problem, but will
+          //  need to be changed with DeclGroups.
+          if (TK == TK_Reference)
+            return PrevDecl;
+          
+          // The new decl is a definition?
+          if (TK == TK_Definition) {
+            // Diagnose attempts to redefine a tag.
+            if (RecordDecl* DefRecord =
+                cast<RecordDecl>(PrevTagDecl)->getDefinition(Context)) {
+              Diag(NameLoc, diag::err_redefinition, Name->getName());
+              Diag(DefRecord->getLocation(), diag::err_previous_definition);
+              // If this is a redefinition, recover by making this struct be
+              // anonymous, which will make any later references get the previous
+              // definition.
+              Name = 0;
+              PrevDecl = 0;
+            }
+            // Okay, this is definition of a previously declared or referenced
+            // tag.  We're going to create a new Decl.
+          }
+        }
+        // If we get here we have (another) forward declaration.  Just create
+        // a new decl.        
+      }
+      else {
+        // If we get here, this is a definition of a new struct type in a nested
+        // scope, e.g. "struct foo; void bar() { struct foo; }", just create a 
+        // new decl/type.  We set PrevDecl to NULL so that the Records
+        // have distinct types.
+        PrevDecl = 0;
+      }
+    } else {
+      // PrevDecl is a namespace.
+      if (IdResolver.isDeclInScope(PrevDecl, CurContext, S)) {
+        // The tag name clashes with a namespace name, issue an error and
+        // recover by making this tag be anonymous.
+        Diag(NameLoc, diag::err_redefinition_different_kind, Name->getName());
+        Diag(PrevDecl->getLocation(), diag::err_previous_definition);
+        Name = 0;
+      }
+    }
+  }
+  
+  // If there is an identifier, use the location of the identifier as the
+  // location of the decl, otherwise use the location of the struct/union
+  // keyword.
+  SourceLocation Loc = NameLoc.isValid() ? NameLoc : KWLoc;
+  
+  // Otherwise, if this is the first time we've seen this tag, create the decl.
+  TagDecl *New;
+    
+  // FIXME: Tag decls should be chained to any simultaneous vardecls, e.g.:
+  // struct X { int A; } D;    D should chain to X.
+  if (getLangOptions().CPlusPlus)
+    New = CXXRecordDecl::Create(Context, Kind, CurContext, Loc, Name,
+                                dyn_cast_or_null<CXXRecordDecl>(PrevDecl));
+  else
+    New = RecordDecl::Create(Context, Kind, CurContext, Loc, Name,
+                             dyn_cast_or_null<RecordDecl>(PrevDecl));
+  
+  // If this has an identifier, add it to the scope stack.
+  if ((TK == TK_Definition || !PrevDecl) && Name) {
+    // The scope passed in may not be a decl scope.  Zip up the scope tree until
+    // we find one that is.
+    while ((S->getFlags() & Scope::DeclScope) == 0)
+      S = S->getParent();
+    
+    // Add it to the decl chain.
+    PushOnScopeChains(New, S);
+  }
+  
+  if (Attr)
+    ProcessDeclAttributeList(New, Attr);
+
+  return New;
+}
+
+
 /// Collect the instance variables declared in an Objective-C object.  Used in
 /// the creation of structures from objects using the @defs directive.
 static void CollectIvars(ObjCInterfaceDecl *Class, ASTContext& Ctx,
@@ -1977,17 +2098,19 @@
   assert(EnclosingDecl && "missing record or interface decl");
   RecordDecl *Record = dyn_cast<RecordDecl>(EnclosingDecl);
   
-  if (Record && Record->isDefinition()) {
-    // Diagnose code like:
-    //     struct S { struct S {} X; };
-    // We discover this when we complete the outer S.  Reject and ignore the
-    // outer S.
-    Diag(Record->getLocation(), diag::err_nested_redefinition,
-         Record->getKindName());
-    Diag(RecLoc, diag::err_previous_definition);
-    Record->setInvalidDecl();
-    return;
-  }
+  if (Record)
+    if (RecordDecl* DefRecord = Record->getDefinition(Context)) {
+      // Diagnose code like:
+      //     struct S { struct S {} X; };
+      // We discover this when we complete the outer S.  Reject and ignore the
+      // outer S.
+      Diag(DefRecord->getLocation(), diag::err_nested_redefinition,
+           DefRecord->getKindName());
+      Diag(RecLoc, diag::err_previous_definition);
+      Record->setInvalidDecl();
+      return;
+    }
+  
   // Verify that all the fields are okay.
   unsigned NumNamedMembers = 0;
   llvm::SmallVector<FieldDecl*, 32> RecFields;
@@ -2099,7 +2222,7 @@
  
   // Okay, we successfully defined 'Record'.
   if (Record) {
-    Record->defineBody(&RecFields[0], RecFields.size());
+    Record->defineBody(Context, &RecFields[0], RecFields.size());
     // If this is a C++ record, HandleTagDeclDefinition will be invoked in
     // Sema::ActOnFinishCXXClassDef.
     if (!isa<CXXRecordDecl>(Record))