diff --git a/lib/Target/X86/AsmPrinter/X86MCInstLower.cpp b/lib/Target/X86/AsmPrinter/X86MCInstLower.cpp
index 5ede37b..d498c57 100644
--- a/lib/Target/X86/AsmPrinter/X86MCInstLower.cpp
+++ b/lib/Target/X86/AsmPrinter/X86MCInstLower.cpp
@@ -306,6 +306,8 @@
       MI->dump();
       llvm_unreachable("unknown operand type");
     case MachineOperand::MO_Register:
+      // Ignore all implicit register operands.
+      if (MO.isImplicit()) continue;
       MCOp = MCOperand::CreateReg(MO.getReg());
       break;
     case MachineOperand::MO_Immediate: