diff --git a/lib/CodeGen/VirtRegRewriter.cpp b/lib/CodeGen/VirtRegRewriter.cpp
index d988e10..240d28c 100644
--- a/lib/CodeGen/VirtRegRewriter.cpp
+++ b/lib/CodeGen/VirtRegRewriter.cpp
@@ -67,23 +67,16 @@
 /// Note that operands may be added, so the MO reference is no longer valid.
 static void substitutePhysReg(MachineOperand &MO, unsigned Reg,
                               const TargetRegisterInfo &TRI) {
-  if (unsigned SubIdx = MO.getSubReg()) {
-    // Insert the physical subreg and reset the subreg field.
-    MO.setReg(TRI.getSubReg(Reg, SubIdx));
-    MO.setSubReg(0);
+  if (MO.getSubReg()) {
+    MO.substPhysReg(Reg, TRI);
 
-    // Any def, dead, and kill flags apply to the full virtual register, so they
-    // also apply to the full physical register. Add imp-def/dead and imp-kill
-    // as needed.
+    // Any kill flags apply to the full virtual register, so they also apply to
+    // the full physical register.
+    // We assume that partial defs have already been decorated with a super-reg
+    // <imp-def> operand by LiveIntervals.
     MachineInstr &MI = *MO.getParent();
-    if (MO.isDef())
-      if (MO.isDead())
-        MI.addRegisterDead(Reg, &TRI, /*AddIfNotFound=*/ true);
-      else
-        MI.addRegisterDefined(Reg, &TRI);
-    else if (!MO.isUndef() &&
-             (MO.isKill() ||
-              MI.isRegTiedToDefOperand(&MO-&MI.getOperand(0))))
+    if (MO.isUse() && !MO.isUndef() &&
+        (MO.isKill() || MI.isRegTiedToDefOperand(&MO-&MI.getOperand(0))))
       MI.addRegisterKilled(Reg, &TRI, /*AddIfNotFound=*/ true);
   } else {
     MO.setReg(Reg);