Improve redundant load elimination

runtime/vm/bit_vector_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 #include "vm/bit_vector.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
@@ skipping 84 matching lines @@
     EXPECT_EQ(true, a->Equals(*b));
   }
 
   { BitVector* a = new BitVector(2);
     BitVector* b = new BitVector(2);
     a->SetAll();
     a->Remove(0);
     a->Remove(1);
     EXPECT_EQ(true, a->Equals(*b));
   }
+
+  { BitVector* a = new BitVector(128);
+    BitVector* b = new BitVector(128);
+    b->Add(0);
+    b->Add(32);
+    b->Add(64);
+    a->Add(0);
+    a->Add(64);
+    b->RemoveAll(a);
+    EXPECT_EQ(false, b->Contains(0));
+    EXPECT_EQ(true, b->Contains(32));
+    EXPECT_EQ(false, b->Contains(64));
+  }
 }
 
 }  // namespace dart