RFR: 8324969: C2: prevent elimination of unbalanced coarsened locking regions [v6]

[Vladimir Kozlov]

On Fri, 16 Feb 2024 07:07:47 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add verivication for unbalanced BoxLock marking
>
> src/hotspot/share/opto/compile.cpp line 4991:
> 
>> 4989:           }
>> 4990:         }
>> 4991:         assert(box->is_unbalanced() == box->is_marked_unbalanced(),"inconsistency");
> 
> Could you even move this a scope out, i.e. a line down, so this check is even run with `alock->is_coarsened() == false`?

Right. It will verify that we did not miss `is_unbalanced()` check when do EA or nested elimination to avoid them.

I will also move the assert at line 4984 under `(box != this_box)` to avoid duplication of check when `box` is the same.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17697#discussion_r1492787405