RFR: 8278241: Implement JVM SpinPause on linux-aarch64 [v3]

[Evgeny Astigeevich]

On Tue, 14 Dec 2021 10:20:59 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Check if StubRoutines::aarch64::spin_wait() is not null
>
> src/hotspot/os_cpu/linux_aarch64/os_linux_aarch64.cpp line 389:
> 
>> 387:     if (func == nullptr) {
>> 388:       return 0;
>> 389:     }
> 
> It's better simply to give `_spin_wait` a default value that points to a `ret` instruction.

Done

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PR: https://git.openjdk.java.net/jdk/pull/6803