Use a special EnumLength field to indicate number of valid enum cache values.

src/utils.h

 // Copyright 2012 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 230 matching lines @@
 // ----------------------------------------------------------------------------
 // BitField is a help template for encoding and decode bitfield with
 // unsigned content.
 template<class T, int shift, int size>
 class BitField {
  public:
   // A uint32_t mask of bit field.  To use all bits of a uint32 in a
   // bitfield without compiler warnings we have to compute 2^32 without
   // using a shift count of 32.
   static const uint32_t kMask = ((1U << shift) << size) - (1U << shift);
+  static const uint32_t kShift = shift;
 
   // Value for the field with all bits set.
   static const T kMax = static_cast<T>((1U << size) - 1);
 
   // Tells whether the provided value fits into the bit field.
   static bool is_valid(T value) {
     return (static_cast<uint32_t>(value) & ~static_cast<uint32_t>(kMax)) == 0;
   }
 
   // Returns a uint32_t with the bit field value encoded.
@@ skipping 715 matching lines @@
     ASSERT(element < static_cast<int>(sizeof(T) * CHAR_BIT));
     return 1 << element;
   }
 
   T bits_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_UTILS_H_