Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -2346,7 +2346,7 @@
     success = getAArch64MicroArchFeaturesFromMcpu(D, getAArch64TargetCPU(Args),
                                                   Args, Features);
 
-  if (!success)
+  if (!success && A)
     D.Diag(diag::err_drv_clang_unsupported) << A->getAsString(Args);
 
   if (Args.getLastArg(options::OPT_mgeneral_regs_only)) {