Completely eliminate VNInfo flags.

The 'unused' state of a value number can be represented as an invalid
def SlotIndex. This also exposed code that shouldn't have been looking
at unused value VNInfos.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161258 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index bbc8c52..b488e8f 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -706,7 +706,7 @@
       continue;
     if (VNI->isPHIDef()) {
       // This is a dead PHI. Remove it.
-      VNI->setIsUnused(true);
+      VNI->markUnused();
       NewLI.removeRange(*LII);
       DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
       CanSeparate = true;