RFR: JDK-8314890: Reduce number of loads for Klass decoding in static code [v2]

[Thomas Stuefe]

On Thu, 24 Aug 2023 08:58:35 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix -UseCCP case
>
> I see a few other places where `UseCompressedClassPointers` is used: `oopDesc::load_klass_raw` and `oopDesc::has_klass_gap`. Both seem to be only used from the diagnostic code, so their performance might not be relevant. Should those keep being omitted?
> 
> All other uses I see are in either compiler code (where we can afford reading the flag directly) or non-perf-critical parts of runtime.

@shipilev , @theRealAph how to continue? Should I scrap this? The improvements are there, albeit bit hard to measure.

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PR Comment: https://git.openjdk.org/jdk/pull/15389#issuecomment-1780954266