RFR: 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents [v2]

[Richard Reingruber]

> 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 incrementally with one additional commit since the last revision:

  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.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/119/files
  - new: https://git.openjdk.java.net/jdk/pull/119/files/79f5b823..18dd54b4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=119&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=119&range=00-01

  Stats: 109 lines in 6 files changed: 54 ins; 36 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/119.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/119/head:pull/119

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