After PostRA scheduling, don't set kill flags on undef operands.

This should fix the ATOM buildbot failing on break-avx-dep.ll.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192824 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/PostRASchedulerList.cpp b/lib/CodeGen/PostRASchedulerList.cpp
index b8747b9..1afc1ec 100644
--- a/lib/CodeGen/PostRASchedulerList.cpp
+++ b/lib/CodeGen/PostRASchedulerList.cpp
@@ -515,11 +515,11 @@
 
     // Examine all used registers and set/clear kill flag. When a
     // register is used multiple times we only set the kill flag on
-    // the first use.
+    // the first use. Don't set kill flags on undef operands.
     killedRegs.reset();
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       MachineOperand &MO = MI->getOperand(i);
-      if (!MO.isReg() || !MO.isUse()) continue;
+      if (!MO.isReg() || !MO.isUse() || MO.isUndef()) continue;
       unsigned Reg = MO.getReg();
       if ((Reg == 0) || MRI.isReserved(Reg)) continue;