Request for review: 7168280: Eliminate the generic signature index slot from field array for field without generic signature

[Dean Long]

How about using a typeArrayOop as your temporary storage in 
parse_fields() instead of a u2 array?  That way you can use the existing 
from_field_array() that does a bounds check.

It is unfortunate that FieldInfo can't get generic signature information 
anymore, forcing you to move more logic into the callers.

Some of the code that iterates through all the fields could be more 
efficient if you still had all_fields_count() so you could easily find 
the generic signature information at the end.  One way to do that is to 
store the total fields count at the end of the array only if the array 
contains generic signature information.  You can tell if the array 
contains generic signature information by the length.  If the length % 
FieldInfo::field_slots == 0, then there is no generic signature 
information, and all_fields_count() is computed like before.  If length 
% FieldInfo::field_slots != 0 then get the fields count from the end of 
the array.  You would need to pad the array with an extra slot if the 
number of generic signature slots happened to be a multiple of 
FieldInfo::field_slots.

dl

On 5/11/2012 2:43 PM, Jiangli Zhou wrote:
> Hi Dean,
>
> Here is the updated webrev 
> http://cr.openjdk.java.net/~jiangli/7168280/webrev.01/. In 
> init_generic_signature_start_slot(), it first scans from f[0] to 
> f[_index - 1] so the generic signature slots for those fields can be 
> skipped while scanning from f[_index] to the end.
>
> Thanks again,
>
> Jiangli
>
> On 05/11/2012 01:53 PM, Jiangli Zhou wrote:
>> Hi Dean,
>>
>> Good catch! Thanks for the comments.
>>
>> Jiangli
>>
>> On 05/11/2012 01:38 PM, Dean Long wrote:
>>> I think this breaks InternalFieldStream. The loop in 
>>> init_generic_signature_start_slot() will start at 
>>> java_fields_count() instead of 0, so it won't decrement "length" for 
>>> any Java fields with a generic signature, resulting in scanning too 
>>> many elements.
>>>
>>> dl
>>>
>>> On 5/11/2012 12:02 PM, Jiangli Zhou wrote:
>>>> Hi,
>>>>
>>>> The field array is an array of 7-shorts [access, name index, sig 
>>>> index, initval index, low offset, high offset, generic signature 
>>>> index]. Most fields don't have generic signature attribute, in that 
>>>> case the generic signature index in the field array is 0 and 
>>>> unused. For all classes in rt.jar, there are total about 28973 
>>>> fields. From which 27466 fields do not have generic signature and 
>>>> only 1507 fields have generic signature.
>>>>
>>>> Following is a webrev that eliminates the unused generic signature 
>>>> index slot from field array. For field without generic signature, 
>>>> the field data is 6-shorts. For field with generic signature, it is 
>>>> still 7-shorts of data. A new flag is added in the field access 
>>>> flag to indicate if the field has the extra short for generic 
>>>> signature index.
>>>>
>>>>   http://cr.openjdk.java.net/~jiangli/7168280/webrev.00/
>>>>
>>>> Thanks,
>>>>
>>>> Jiangli
>>
>