Fix a bug in liveness analysis code and add more comments.

runtime/vm/bit_vector.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 "vm/bit_vector.h"
 
 #include "vm/os.h"
 
 namespace dart {
 
@@ skipping 15 matching lines @@
   }
   // Skip zero bits.
   while ((current_word_ & 0x1) == 0) {
     current_word_ >>= 1;
     ++bit_index_;
   }
   current_word_ = current_word_ >> 1;
 }
 
 
+bool BitVector::AddAll(BitVector* from) {
+  ASSERT(data_length_ == from->data_length_);
+  bool changed = false;
+  for (intptr_t i = 0; i < data_length_; i++) {
+    const uword before = data_[i];
+    const uword after = data_[i] | from->data_[i];
+    if (before != after) changed = true;
+    data_[i] = after;
+  }
+  return changed;
+}
+
+
+bool BitVector::KillAndAdd(BitVector* kill, BitVector* gen) {
+  ASSERT(data_length_ == kill->data_length_);
+  ASSERT(data_length_ == gen->data_length_);
+  bool changed = false;
+  for (intptr_t i = 0; i < data_length_; i++) {
+    const uword before = data_[i];
+    const uword after = data_[i] | (gen->data_[i] & ~kill->data_[i]);
+    if (before != after) changed = true;
+    data_[i] = after;
+  }
+  return changed;
+}
+
+
 }  // namespace dart