Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -15573,6 +15573,10 @@
     if (!Completed)
       Record->completeDefinition();
 
+    // Handle attributes before checking for alignas underalignment.
+    if (Attr)
+      ProcessDeclAttributeList(S, Record, Attr);
+
     // We may have deferred checking for a deleted destructor. Check now.
     if (CXXRecordDecl *CXXRecord = dyn_cast<CXXRecordDecl>(Record)) {
       auto *Dtor = CXXRecord->getDestructor();
@@ -15703,9 +15707,6 @@
       CDecl->setIvarRBraceLoc(RBrac);
     }
   }
-
-  if (Attr)
-    ProcessDeclAttributeList(S, Record, Attr);
 }
 
 /// \brief Determine whether the given integral value is representable within