Index: include/clang/Parse/Parser.h
===================================================================
--- include/clang/Parse/Parser.h	(revision 89660)
+++ include/clang/Parse/Parser.h	(working copy)
@@ -83,6 +83,7 @@
   llvm::OwningPtr<PragmaHandler> PackHandler;
   llvm::OwningPtr<PragmaHandler> UnusedHandler;
   llvm::OwningPtr<PragmaHandler> WeakHandler;
+  llvm::OwningPtr<PragmaHandler> RedefineExtnameHandler;
   llvm::OwningPtr<clang::CommentHandler> CommentHandler;

   /// Whether the '>' token acts as an operator or not. This will be
Index: include/clang/Parse/Action.h
===================================================================
--- include/clang/Parse/Action.h	(revision 89660)
+++ include/clang/Parse/Action.h	(working copy)
@@ -2212,6 +2212,15 @@
                                     SourceLocation AliasNameLoc) {
     return;
   }
+
+  /// ActOnPragmaRedefineExtnameAlias - Called on well formed #pragma redefine_extname oldname newname.
+  virtual void ActOnPragmaRedefineExtnameAlias(IdentifierInfo* RedefineExtnameName,
+                                    IdentifierInfo* AliasName,
+                                    SourceLocation PragmaLoc,
+                                    SourceLocation RedefineExtnameNameLoc,
+                                    SourceLocation AliasNameLoc) {
+    return;
+  }

   /// \name Code completion actions
   ///
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp	(revision 89660)
+++ lib/Sema/SemaDeclAttr.cpp	(working copy)
@@ -890,6 +890,18 @@
   D->addAttr(::new (S.Context) WeakImportAttr());
 }

+static void HandleRedefineExtnameAttr(Decl *D, const AttributeList &Attr, Sema &S) {
+  // check the attribute arguments.
+  if (Attr.getNumArgs() != 0) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 0;
+    return;
+  }
+
+  // FIXME: missing stuff?
+
+  D->addAttr(::new (S.Context) RedefineExtnameAttr());
+}
+
 static void HandleDLLImportAttr(Decl *D, const AttributeList &Attr, Sema &S) {
   // check the attribute arguments.
   if (Attr.getNumArgs() != 0) {
@@ -1942,6 +1954,7 @@
     break;
   case AttributeList::AT_weak:        HandleWeakAttr      (D, Attr, S); break;
   case AttributeList::AT_weak_import: HandleWeakImportAttr(D, Attr, S); break;
+  case AttributeList::AT_redefine_extname:        HandleRedefineExtnameAttr(D, Attr, S); break;
   case AttributeList::AT_transparent_union:
     HandleTransparentUnionAttr(D, Attr, S);
     break;
Index: lib/Parse/ParsePragma.cpp
===================================================================
--- lib/Parse/ParsePragma.cpp	(revision 89660)
+++ lib/Parse/ParsePragma.cpp	(working copy)
@@ -218,3 +218,45 @@
     Actions.ActOnPragmaWeakID(WeakName, WeakLoc, WeakNameLoc);
   }
 }
+
+// #pragma redefine_extname oldname newname
+void PragmaRedefineExtnameHandler::HandlePragma(Preprocessor &PP, Token &RedefineExtnameTok) {
+
+// FIXME: ALL MY LOGIC IS WRONG... fix this function!
+
+  // FIXME: Should we be expanding macros here? My guess is no.
+  SourceLocation RedefineExtnameLoc = RedefineExtnameTok.getLocation();
+
+  Token Tok;
+  PP.Lex(Tok);
+  if (Tok.isNot(tok::identifier)) {
+    PP.Diag(Tok.getLocation(), diag::warn_pragma_expected_identifier) << "redefine_extname";
+    return;
+  }
+
+  IdentifierInfo *RedefineExtnameName = Tok.getIdentifierInfo(), *AliasName = 0;
+  SourceLocation RedefineExtnameNameLoc = Tok.getLocation(), AliasNameLoc;
+
+  PP.Lex(Tok);
+  if (Tok.is(tok::equal)) { // FIXME: space not a =
+    PP.Lex(Tok);
+    if (Tok.isNot(tok::identifier)) {
+      PP.Diag(Tok.getLocation(), diag::warn_pragma_expected_identifier)
+          << "redefine_extname";
+      return;
+    }
+    AliasName = Tok.getIdentifierInfo();
+    AliasNameLoc = Tok.getLocation();
+    PP.Lex(Tok);
+  }
+
+  if (Tok.isNot(tok::eom)) {
+    PP.Diag(Tok.getLocation(), diag::warn_pragma_extra_tokens_at_eol) << "redefine_extname";
+    return;
+  }
+
+  if (AliasName) {
+    Actions.ActOnPragmaRedefineExtname(RedefineExtnameName,
+                                 AliasName, RedefineExtnameLoc, RedefineExtnameNameLoc, AliasNameLoc);
+  }
+}
Index: lib/Parse/ParsePragma.h
===================================================================
--- lib/Parse/ParsePragma.h	(revision 89660)
+++ lib/Parse/ParsePragma.h	(working copy)
@@ -48,6 +48,15 @@
   virtual void HandlePragma(Preprocessor &PP, Token &FirstToken);
 };

+class PragmaRedefineExtnameHandler : public PragmaHandler {
+  Action &Actions;
+public:
+  PragmaRedefineExtnameHandler(const IdentifierInfo *N, Action &A)
+    : PragmaHandler(N), Actions(A) {}
+
+  virtual void HandlePragma(Preprocessor &PP, Token &FirstToken);
+};
+
 }  // end namespace clang

 #endif
Index: lib/Parse/Parser.cpp
===================================================================
--- lib/Parse/Parser.cpp	(revision 89660)
+++ lib/Parse/Parser.cpp	(working copy)
@@ -58,6 +58,10 @@
           PragmaWeakHandler(&PP.getIdentifierTable().get("weak"), actions));
   PP.AddPragmaHandler(0, WeakHandler.get());

+  RedefineExtnameHandler.reset(new
+          PragmaRedefineExtnameHandler(&PP.getIdentifierTable().get("redefine_extname"), actions));
+  PP.AddPragmaHandler(0, RedefineExtnameHandler.get());
+
   CommentHandler.reset(new ActionCommentHandler(actions));
   PP.AddCommentHandler(CommentHandler.get());
 }
@@ -314,6 +318,8 @@
   UnusedHandler.reset();
   PP.RemovePragmaHandler(0, WeakHandler.get());
   WeakHandler.reset();
+  PP.RemovePragmaHandler(0, RedefineExtnameHandler.get());
+  RedefineExtnameHandler.reset();
   PP.RemoveCommentHandler(CommentHandler.get());
 }