RFR: 8281467: Allow larger OptoLoopAlignment and CodeEntryAlignment

[Harold Seigel]

On Tue, 8 Feb 2022 18:19:00 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

src/hotspot/share/runtime/globals.hpp line 1539:

> 1537:           range(1, 128)                                                     \
> 1538:           constraint(OptoLoopAlignmentConstraintFunc, AfterErgo)            \
> 1539:                                                                             \

Should OptoLoopAlignment be an int, instead of an intx, since its range is small?

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