RFR: 8273380: ARM32: Default to {ldrexd, strexd} in StubRoutines::atomic_{load|store}_long [v2]

[Aleksey Shipilev]

On Thu, 23 Sep 2021 11:17:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Current ARM32 is one of few remaining uses of `os::is_MP`, the rest is removed by JDK-8188764. There are some interesting bugs in OS/libc that might give incorrect `os::is_MP` sometimes, e.g. in containers. Instead of risking it, we can default to {ldrexd,strexd} for ARMv7 (which always have them), and leave the `os::is_MP` path for ARMv6 (for which this is the only remaining way to load the 64-bit long). 
>> 
>> @mychris, you might want to take a look and do light performance testing for it?
>> 
>> Additional testing:
>>  - [x] Linux ARM32 cross-compiled build completes
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Move out bx
>  - Merge branch 'master' into JDK-8273380-arm32-default-to-ldrex
>  - First attempt

Thank you!

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PR: https://git.openjdk.java.net/jdk/pull/5379