reg0 references are not real registers.  This fixes a crash on the 
attached testcase.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68712 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index 965c2a2..ade8683 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -739,7 +739,7 @@
 bool MachineInstr::isRegTiedToDefOperand(unsigned UseOpIdx, unsigned *DefOpIdx){
   if (getOpcode() == TargetInstrInfo::INLINEASM) {
     const MachineOperand &MO = getOperand(UseOpIdx);
-    if (!MO.isReg() || !MO.isUse())
+    if (!MO.isReg() || !MO.isUse() || MO.getReg() == 0)
       return false;
     assert(UseOpIdx > 0);
     const MachineOperand &UFMO = getOperand(UseOpIdx-1);