Improve redundant load elimination

runtime/vm/bit_vector.h

Index: runtime/vm/bit_vector.h
diff --git a/runtime/vm/bit_vector.h b/runtime/vm/bit_vector.h
index 1b4828069fcee4c442e3ad12bde6996686554aba..3dcd11824dd4d1b2546f3f3124a219c74f3ed9b6 100644
--- a/runtime/vm/bit_vector.h
+++ b/runtime/vm/bit_vector.h
@@ -76,6 +76,9 @@ class BitVector: public ZoneAllocated {
   // Add all elements that are in the bitvector from.
   bool AddAll(const BitVector* from);
 
+  // Remove all elements that are in the bitvector from.
+  bool RemoveAll(const BitVector* from);
+
   // From the bitvector gen add those elements that are not in the
   // bitvector kill.
   bool KillAndAdd(BitVector* kill, BitVector* gen);