RFR: 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents [v3]

[David Holmes]

On Thu, 24 Sep 2020 16:59:03 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> Hi,
>> 
>> this is the continuation of the review of the implementation for:
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8227745
>> https://bugs.openjdk.java.net/browse/JDK-8233915
>> 
>> It allows for JIT optimizations based on escape analysis even if JVMTI agents acquire capabilities to access references
>> to objects that are subject to such optimizations, e.g. scalar replacement. The implementation reverts such
>> optimizations just before access very much as when switching from JIT compiled execution to the interpreter, aka
>> "deoptimization".  Webrev.8 was the last one before before the transition to Git/Github:
>> 
>> http://cr.openjdk.java.net/~rrich/webrevs/8227745/webrev.8/
>> 
>> Thanks, Richard.
>
> Richard Reingruber has updated the pull request with a new target base due to a merge or a rebase. The incremental
> webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional
> commits since the last revision:
>  - Merge branch 'master' into JDK-8227745
>  - Changes based on dholmes' feedback.
>    
>    EscapeBarrier::sync_and_suspend_all():
>    
>      - Set suspend flags before handshake because then the setting will be visible
>        after leaving the _thread_blocked state in JavaThread::wait_for_object_deoptimization()
>    
>    JavaThread::wait_for_object_deoptimization()
>    
>      - Reuse SpinYield instead of new custom spinning code.
>    
>      - Do safepoint check after the loop. This is possible because the
>        set_obj_deopt_flag is done before the handshake.
>    
>      - Don't set_suspend_equivalent() anymore for more simplicity. It's just an
>        optimization (that won't pay off here).
>    
>    Added/updated source code comments.
>    
>    Additional smaller enhancements.
>  - 8227745, 8233915: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents

The minor updates in response to my comments are fine.

The more major updates ... I can't really comment on.

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PR: https://git.openjdk.java.net/jdk/pull/119