Use the BitField class for Code::Flags.

src/lithium.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 147 matching lines @@
         policy() == FIXED_SLOT;
   }
   bool HasRegisterPolicy() const {
     return policy() == WRITABLE_REGISTER || policy() == MUST_HAVE_REGISTER;
   }
   bool HasSameAsInputPolicy() const {
     return policy() == SAME_AS_FIRST_INPUT;
   }
   Policy policy() const { return PolicyField::decode(value_); }
   void set_policy(Policy policy) {
-    value_ &= ~PolicyField::mask();
-    value_ |= PolicyField::encode(policy);
+    value_ = PolicyField::update(value_, policy);
   }
   int fixed_index() const {
     return static_cast<int>(value_) >> kFixedIndexShift;
   }
 
   unsigned virtual_register() const {
     return VirtualRegisterField::decode(value_);
   }
 
   void set_virtual_register(unsigned id) {
-    value_ &= ~VirtualRegisterField::mask();
-    value_ |= VirtualRegisterField::encode(id);
+    value_ = VirtualRegisterField::update(value_, id);
   }
 
   LUnallocated* CopyUnconstrained() {
     LUnallocated* result = new LUnallocated(ANY);
     result->set_virtual_register(virtual_register());
     return result;
   }
 
   static LUnallocated* cast(LOperand* op) {
     ASSERT(op->IsUnallocated());
@@ skipping 393 matching lines @@
   ShallowIterator current_iterator_;
 };
 
 
 int ElementsKindToShiftSize(ElementsKind elements_kind);
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LITHIUM_H_