[TII] Do not fold undef copies

Change-Id: I0d76cc98d2368f4f929bee032c22714560f273cc

Author: jrbyrnes

llvm/lib/CodeGen/InlineSpiller.cpp

@@ -946,9 +946,6 @@ foldMemoryOperand(ArrayRef<std::pair<MachineInstr *, unsigned>> Ops,
     if (MO.isUse() && !MO.readsReg() && !MO.isTied())
       continue;
 
-    if (MI->isCopy() && MI->getOperand(1).isUndef())
-      continue;
-
     if (MO.isImplicit()) {
       ImpReg = MO.getReg();
       continue;

llvm/lib/CodeGen/TargetInstrInfo.cpp

@@ -476,6 +476,9 @@ static const TargetRegisterClass *canFoldCopy(const MachineInstr &MI,
   if (FoldOp.getSubReg() || LiveOp.getSubReg())
     return nullptr;
 
+  if (LiveOp.isUndef())
+    return nullptr;
+
   Register FoldReg = FoldOp.getReg();
   Register LiveReg = LiveOp.getReg();