diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 22d6252..7d23cd0 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -329,9 +329,16 @@
     MachineInstr *CopyMI = NULL;
     unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
     if (mi->isExtractSubreg() || mi->isInsertSubreg() || mi->isSubregToReg() ||
-        tii_->isMoveInstr(*mi, SrcReg, DstReg, SrcSubReg, DstSubReg))
+        tii_->isMoveInstr(*mi, SrcReg, DstReg, SrcSubReg, DstSubReg)) {
       CopyMI = mi;
 
+      // Some of the REG_SEQUENCE lowering in TwoAddressInstrPass creates
+      // implicit defs without really knowing. It shows up as INSERT_SUBREG
+      // using an undefined register.
+      if (mi->isInsertSubreg())
+        mi->getOperand(1).setIsUndef();
+    }
+
     VNInfo *ValNo = interval.getNextValue(defIndex, CopyMI, true,
                                           VNInfoAllocator);
     assert(ValNo->id == 0 && "First value in interval is not 0?");