Index: lib/CodeGen/TargetSchedule.cpp
===================================================================
--- lib/CodeGen/TargetSchedule.cpp
+++ lib/CodeGen/TargetSchedule.cpp
@@ -212,7 +212,7 @@
       && !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
       && SchedModel.isComplete()) {
     errs() << "DefIdx " << DefIdx << " exceeds machine model writes for "
-           << *DefMI;
+           << *DefMI << " (Try with MCSchedModel.CompleteModel set to false)";
     llvm_unreachable("incomplete machine model");
   }
 #endif