Fix mishandling of deletedness for assignment operators of classes with
indirect virtual bases. We don't need to be able to invoke such an assignment
operator from the derived class, and we shouldn't delete the derived assignment
op if we can't do so.

llvm-svn: 280288
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 585cd04..eb8c3d2 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -6765,13 +6765,14 @@
   SpecialMemberDeletionInfo SMI(*this, MD, CSM, ICI, Diagnose);
 
   for (auto &BI : RD->bases())
-    if (!BI.isVirtual() &&
+    if ((SMI.IsAssignment || !BI.isVirtual()) &&
         SMI.shouldDeleteForBase(&BI))
       return true;
 
   // Per DR1611, do not consider virtual bases of constructors of abstract
-  // classes, since we are not going to construct them.
-  if (!RD->isAbstract() || !SMI.IsConstructor) {
+  // classes, since we are not going to construct them. For assignment
+  // operators, we only assign (and thus only consider) direct bases.
+  if ((!RD->isAbstract() || !SMI.IsConstructor) && !SMI.IsAssignment) {
     for (auto &BI : RD->vbases())
       if (SMI.shouldDeleteForBase(&BI))
         return true;