Index: lib/CodeGen/MachineInstr.cpp
===================================================================
--- lib/CodeGen/MachineInstr.cpp
+++ lib/CodeGen/MachineInstr.cpp
@@ -1126,6 +1126,8 @@
     // For example, machine CSE pass only cares about finding common
     // subexpressions, so it's safe to ignore virtual register defs.
     if (MO.isDef()) {
+      if (!OMO.isDef())
+        return false;
       if (Check == IgnoreDefs)
         continue;
       else if (Check == IgnoreVRegDefs) {