RFR: 8281467: Allow larger OptoLoopAlignment and CodeEntryAlignment

[Jie Fu]

On Tue, 15 Feb 2022 06:17:57 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> I am following up on the performance issue where the culprit seems to be the too low `OptoLoopAlignment`. To perform better experiments, I suggest allowing larger alignments.
>> 
>> Note that we cannot make `OptoLoopAlignment` larger than `CodeEntryAlignment`, because nmethod copy would break it, see assert in `MacroAssembler::align`. See [JDK-8273459](https://bugs.openjdk.java.net/browse/JDK-8273459) for latest discussion about it. So `CodeEntryAlignment` needs to be configurable as well.
>> 
>> The default values for options are different per platform, so tests are x86_64 specific.
>> 
>> No default value is changed, this only unblocks experiments.
>> 
>> Additional testing:
>>  - [x] New tests on Linux x86_64 fastdebug
>>  - [x] New tests on Linux x86_64 release
>
> Thank you!

Hi @shipilev ,

compiler/arguments/TestCodeEntryAlignment.java fails on AVX512 machines.
Please have a look: https://github.com/openjdk/jdk/pull/7485
Thanks.

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PR: https://git.openjdk.java.net/jdk/pull/7388