Optimizing: Reduce memory usage of HInstructions.

Pack narrow fields and flags into a single 32-bit field.

Change-Id: Ib2f7abf987caee0339018d21f0d498f8db63542d
diff --git a/compiler/dex/compiler_enums.h b/compiler/dex/compiler_enums.h
index b78b3d7..8800e4b 100644
--- a/compiler/dex/compiler_enums.h
+++ b/compiler/dex/compiler_enums.h
@@ -569,6 +569,7 @@
   kStoreStore,
   kAnyAny,
   kNTStoreStore,
+  kLastBarrierKind = kNTStoreStore
 };
 std::ostream& operator<<(std::ostream& os, const MemBarrierKind& kind);