RFR: 8290700: Optimize AArch64 nmethod entry barriers [v3]

[Erik Österlund]

On Fri, 22 Jul 2022 20:06:30 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Erik Österlund has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:
>> 
>>  - Merge branch 'master' into 8290700_faster_aarch64_entry_barriers
>>  - 8290700: Optimize AArch64 nmethod entry barriers
>>  - fixing 32 bit build again
>>  - fix 32 bit build again
>>  - 32 bit build fix
>>  - Optimize x86 nmethod entry barriers
>
> Marked as reviewed by dlong (Reviewer).

Thanks for the review @dean-long!

> src/hotspot/cpu/aarch64/gc/shared/barrierSetNMethod_aarch64.cpp line 85:
> 
>> 83:       }
>> 84:       ShouldNotReachHere();
>> 85:     }
> 
> I'm guessing this function is not performance-critical.  If it was, then we could consider adding a new field to the nmethod to keep track of the offset for the guard.

Yeah I thought about adding a new entry to CodeOffsets, but it seemed like this C2-only AArch64-only detail seemed a bit noisy in the shared code then. And it didn't seem warranted, given how cold this path is by design.

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PR: https://git.openjdk.org/jdk/pull/9574