diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index c9001f1..cc57bdd 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5000,7 +5000,8 @@
       SearchDC = SearchDC->getEnclosingNamespaceContext();
     }
 
-    // In C++, look for a shadow friend decl.
+    // In C++, we need to do a redeclaration lookup to properly
+    // diagnose some problems.
     if (getLangOptions().CPlusPlus) {
       Previous.setRedeclarationKind(ForRedeclaration);
       LookupQualifiedName(Previous, SearchDC);
@@ -5009,6 +5010,30 @@
 
   if (!Previous.empty()) {
     NamedDecl *PrevDecl = (*Previous.begin())->getUnderlyingDecl();
+
+    // It's okay to have a tag decl in the same scope as a typedef
+    // which hides a tag decl in the same scope.  Finding this
+    // insanity with a redeclaration lookup can only actually happen
+    // in C++.
+    //
+    // This is also okay for elaborated-type-specifiers, which is
+    // technically forbidden by the current standard but which is
+    // okay according to the likely resolution of an open issue;
+    // see http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#407
+    if (getLangOptions().CPlusPlus) {
+      if (TypedefDecl *TD = dyn_cast<TypedefDecl>(PrevDecl)) {
+        if (const TagType *TT = TD->getUnderlyingType()->getAs<TagType>()) {
+          TagDecl *Tag = TT->getDecl();
+          if (Tag->getDeclName() == Name &&
+              Tag->getDeclContext()->Equals(TD->getDeclContext())) {
+            PrevDecl = Tag;
+            Previous.clear();
+            Previous.addDecl(Tag);
+          }
+        }
+      }
+    }
+
     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
@@ -5100,23 +5125,61 @@
       // If we get here, we're going to create a new Decl. If PrevDecl
       // is non-NULL, it's a definition of the tag declared by
       // PrevDecl. If it's NULL, we have a new definition.
+
+
+    // Otherwise, PrevDecl is not a tag, but was found with tag
+    // lookup.  This is only actually possible in C++, where a few
+    // things like templates still live in the tag namespace.
     } else {
-      // PrevDecl is a namespace, template, or anything else
-      // that lives in the IDNS_Tag identifier namespace.
-      if (TUK == TUK_Reference || TUK == TUK_Friend ||
-          isDeclInScope(PrevDecl, SearchDC, S)) {
-        // The tag name clashes with a namespace name, issue an error and
-        // recover by making this tag be anonymous.
+      assert(getLangOptions().CPlusPlus);
+
+      // Use a better diagnostic if an elaborated-type-specifier
+      // found the wrong kind of type on the first
+      // (non-redeclaration) lookup.
+      if ((TUK == TUK_Reference || TUK == TUK_Friend) &&
+          !Previous.isForRedeclaration()) {
+        unsigned Kind = 0;
+        if (isa<TypedefDecl>(PrevDecl)) Kind = 1;
+        else if (isa<ClassTemplateDecl>(PrevDecl)) Kind = 2;
+        Diag(NameLoc, diag::err_tag_reference_non_tag) << Kind;
+        Diag(PrevDecl->getLocation(), diag::note_declared_at);
+        Invalid = true;
+
+      // Otherwise, only diagnose if the declaration is in scope.
+      } else if (!isDeclInScope(PrevDecl, SearchDC, S)) {
+        // do nothing
+
+      // Diagnose implicit declarations introduced by elaborated types.
+      } else if (TUK == TUK_Reference || TUK == TUK_Friend) {
+        unsigned Kind = 0;
+        if (isa<TypedefDecl>(PrevDecl)) Kind = 1;
+        else if (isa<ClassTemplateDecl>(PrevDecl)) Kind = 2;
+        Diag(NameLoc, diag::err_tag_reference_conflict) << Kind;
+        Diag(PrevDecl->getLocation(), diag::note_previous_decl) << PrevDecl;
+        Invalid = true;
+
+      // Otherwise it's a declaration.  Call out a particularly common
+      // case here.
+      } else if (isa<TypedefDecl>(PrevDecl)) {
+        Diag(NameLoc, diag::err_tag_definition_of_typedef)
+          << Name
+          << cast<TypedefDecl>(PrevDecl)->getUnderlyingType();
+        Diag(PrevDecl->getLocation(), diag::note_previous_decl) << PrevDecl;
+        Invalid = true;
+
+      // Otherwise, diagnose.
+      } else {
+        // The tag name clashes with something else in the target scope,
+        // issue an error and recover by making this tag be anonymous.
         Diag(NameLoc, diag::err_redefinition_different_kind) << Name;
         Diag(PrevDecl->getLocation(), diag::note_previous_definition);
         Name = 0;
-        Previous.clear();
         Invalid = true;
-      } else {
-        // The existing declaration isn't relevant to us; we're in a
-        // new scope, so clear out the previous declaration.
-        Previous.clear();
       }
+
+      // The existing declaration isn't relevant to us; we're in a
+      // new scope, so clear out the previous declaration.
+      Previous.clear();
     }
   }
 
@@ -5187,28 +5250,6 @@
       New->addAttr(::new (Context) PragmaPackAttr(Alignment * 8));
   }
 
-  if (getLangOptions().CPlusPlus && SS.isEmpty() && Name && !Invalid) {
-    // C++ [dcl.typedef]p3:
-    //   [...] Similarly, in a given scope, a class or enumeration
-    //   shall not be declared with the same name as a typedef-name
-    //   that is declared in that scope and refers to a type other
-    //   than the class or enumeration itself.
-    LookupResult Lookup(*this, Name, NameLoc, LookupOrdinaryName,
-                        ForRedeclaration);
-    LookupName(Lookup, S);
-    TypedefDecl *PrevTypedef = Lookup.getAsSingle<TypedefDecl>();
-    NamedDecl *PrevTypedefNamed = PrevTypedef;
-    if (PrevTypedef && isDeclInScope(PrevTypedefNamed, SearchDC, S) &&
-        Context.getCanonicalType(Context.getTypeDeclType(PrevTypedef)) !=
-          Context.getCanonicalType(Context.getTypeDeclType(New))) {
-      Diag(Loc, diag::err_tag_definition_of_typedef)
-        << Context.getTypeDeclType(New)
-        << PrevTypedef->getUnderlyingType();
-      Diag(PrevTypedef->getLocation(), diag::note_previous_definition);
-      Invalid = true;
-    }
-  }
-
   // If this is a specialization of a member class (of a class template),
   // check the specialization.
   if (isExplicitSpecialization && CheckMemberSpecialization(New, Previous))