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/LiveInterval.cpp b/lib/CodeGen/LiveInterval.cpp
index db00d2e..0a795e6 100644
--- a/lib/CodeGen/LiveInterval.cpp
+++ b/lib/CodeGen/LiveInterval.cpp
@@ -160,7 +160,7 @@
       valnos.pop_back();
     } while (!valnos.empty() && valnos.back()->isUnused());
   } else {
-    ValNo->setIsUnused(true);
+    ValNo->markUnused();
   }
 }
 
@@ -667,9 +667,6 @@
     }
   }
 
-  // Merge the relevant flags.
-  V2->mergeFlags(V1);
-
   // Now that V1 is dead, remove it.
   markValNoForDeletion(V1);