Fix bogus assertion failures

llvm-svn: 4919
diff --git a/llvm/lib/Target/X86/Printer.cpp b/llvm/lib/Target/X86/Printer.cpp
index ae14e41..bfaa4bd 100644
--- a/llvm/lib/Target/X86/Printer.cpp
+++ b/llvm/lib/Target/X86/Printer.cpp
@@ -96,7 +96,7 @@
                     const MRegisterInfo &RI) {
   switch (MO.getType()) {
   case MachineOperand::MO_VirtualRegister:
-    if (Value *V = MO.getVRegValue()) {
+    if (Value *V = MO.getVRegValueOrNull()) {
       O << "<" << V->getName() << ">";
       return;
     }