Index: lib/CodeGen/VirtRegMap.cpp
===================================================================
--- lib/CodeGen/VirtRegMap.cpp
+++ lib/CodeGen/VirtRegMap.cpp
@@ -441,10 +441,25 @@
       if (MI->isIdentityCopy()) {
         ++NumIdCopies;
         DEBUG(dbgs() << "Deleting identity copy.\n");
-        if (Indexes)
-          Indexes->removeMachineInstrFromMaps(*MI);
-        // It's safe to erase MI because MII has already been incremented.
-        MI->eraseFromParent();
+
+        // A COPY which has an implicit def of a super register must
+        // become an IMPLICIT_DEF of that register.
+        if (MI->getNumOperands() > 2) {
+          MachineOperand &MO = MI->getOperand(2);
+          if (MO.isDef() && MO.isImplicit()) {
+            MI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
+            MI->RemoveOperand(0);
+            MI->RemoveOperand(0);
+            MI->getOperand(0).setImplicit(false);
+            assert (MI->getNumOperands() == 1 && "Not a single super reg implicit def?");
+          }
+        }
+        else {
+          if (Indexes)
+            Indexes->removeMachineInstrFromMaps(*MI);
+          // It's safe to erase MI because MII has already been incremented.
+          MI->eraseFromParent();
+        }
       }
     }
   }