[9] RFR (X): 8163880: Constant pool caching of fields inhibited/delayed unnecessarily

[Vladimir Kozlov]

Okay I think I understand what you are trying to say but it was not my 
point. I was questioning why put_code is set when bytecode could be get 
instruction. Reading comments and code around I think I understand now.
We set both get_code and put_code marking that the field is resolved. 
But in some cases we delay marking to force field's reresolution.

In next code you can use is_static:

     bool uninitialized_static = ((bytecode == Bytecodes::_getstatic || 
bytecode == Bytecodes::_putstatic) &&
                                  !klass->is_initialized());

Code could be rearranged to be more compact (similar to original code):

     Bytecodes::Code put_code = (Bytecodes::Code)0;
     Bytecodes::Code get_code = (Bytecodes::Code)0;
     if (!uninitialized_static) {
       get_code = ((is_static) ? Bytecodes::_getstatic : 
Bytecodes::_getfield);
       if ((is_put && !has_initialized_final_update) || 
!info.access_flags().is_final()) {
         put_code = ((is_static) ? Bytecodes::_putstatic : 
Bytecodes::_putfield);
       }
     }

Thanks,
Vladimir

On 8/23/16 5:31 AM, Zoltán Majó wrote:
> Hi Vladimir,
>
>
> thank you for the feedback! Please see details below.
>
> On 08/22/2016 08:20 PM, Vladimir Kozlov wrote:
>> Typo (double 'not'):
>> +   // and the required IllegalAccessError would not not be thrown.
>
> OK, I've corrected that.
>
>>
>> I think has_initialized_final_update should be part of assert to see
>> it in hs_err:
>>
>> +   if (has_initialized_final_update) {
>> +     assert(info.access_flags().is_final(), "Fields with initialized
>> final updates must be final");
>> +   }
>
> Yes, I've updated that as well.
>
>>
>> Why is_put check is not done in outer check? It is missing for
>> is_final():
>>
>> +   if (!uninitialized_static) {
>> +     if ((is_put && !has_initialized_final_update) ||
>> !info.access_flags().is_final()) {
>
> I think it's an optimization to do it this way: For non-final-fields, we
> want to set up CP caching faster (i.e., we want to reduce the number of
> times we call into the runtime to
> LinkResolver::resolve_field_access()).We had that optimization in place
> before JDK-8160527, but not afterwards, which caused a performance
> regression.  Please see some details below.
>
> The CP cache does caching for get and put bytecodes individually.
> Normally, the caching for put (in 'put_code') should be set up by put
> instructions, the caching for get (in 'get_code') should be set up by
> get instruction.  The optimization is to let get instructions set up
> caching for put bytecodes in some select cases.  Here is the way that
> (not) workedbefore/after JDK-8160527.
>
>
> 1) The table below describes the way resolution worked before
> JDK-8160527.  The table shows if put_code was set (S) or not set (NS)
> after InterpreterRuntime::resolve_get_put().
>
>                | Instruction triggering resolution
>                |===================================
> Field type     | get          | put
> ===================================================
> final          | NS           |S
> non-final      | S            | S
>
> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/29ed49c42486#l1.38
>
>
> 2) Unfortunately, JDK-8160527 changed the table to:
>
>                | Instruction triggering resolution
>                |===================================
> Field type     | get          | put
> ===================================================
> final          | NS           |*NS*
> non-final      | *NS*         | S
>
> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/29ed49c42486#l1.30
>
> So the VM does not set up caching in *2additional cases*, which causes a
> performance regression.
>
>
> 3) The current webrev proposes the following:
>
>                | Instruction triggering resolution
>                |===================================
> Field type     | get          | put
> ===================================================
> final          | NS           |*S (unless has_initialized_final_update
> is true for the field)*
> non-final      | S            | S
>
> That table looks the same as what we had before JDK-8160527, except for
> fields with initialized final updates. For those fields we need to defer
> setting up CP caching so that the appropriate exception can be thrown at
> the right place (by LinkResolver::resolve_field_access()).
>
>
> 4) If we would do what you suggested (I hope I understood your
> suggestion correctly)thenwe'd move the is_put condition to the outer check:
>
> +   if (!uninitialized_static && is_put) {
> +     if (!has_initialized_final_update ||
> !info.access_flags().is_final()) {
>
> Then the table would look:
>
>                | Instruction triggering resolution
>                |===================================
> Field type     | get          | put
> ===================================================
> final          | NS           |S(unless has_initialized_final_update is
> true for the field)
> non-final      | *NS*         | S
>
> So we would have *still one case* where CP caching is not set up and
> that would most likely result in some performance regression (relative
> to pre-JDK-8160527).
>
>
> I hope I have not overlooked anythingabove.
>
> Here is the updated webrev:
> http://cr.openjdk.java.net/~zmajo/8163880/webrev.01/
>
> JPRT testing is running.
>
> Thank you!
>
> Best regards,
>
>
> Zoltan
>
>
>>
>> Thanks,
>> Vladimir
>>
>> On 8/22/16 4:20 AM, Zoltán Majó wrote:
>>> Hi,
>>>
>>>
>>> please review the fix for JDK-8163880.
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8163880
>>>
>>> Problem & solution: The performance regression reported by the bug is
>>> caused by unnecessary delay (or even inhibition) of constant pool
>>> caching for fields targeted by put instructions. For a more
>>> detailed description of the problem and possible solutions, please
>>> see the following comment in the bug report [1].
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~zmajo/8163880/webrev.00/
>>>
>>> Testing:
>>> - performance evaluation with the affected benchmark shows that fix
>>> above solves the performance regression;
>>> - all hotspot test with -Xmixed and -Xcomp (running).
>>>
>>> Thank you!
>>>
>>> Best regards,
>>>
>>>
>>> Zoltan
>>>
>>> [1]
>>> https://bugs.openjdk.java.net/browse/JDK-8163880?focusedCommentId=13990030&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13990030
>>>
>>>
>