RFR: 8316186: RISC-V: Remove PlatformCmpxchg<4> [v3]

[Fei Yang]

On Thu, 28 Sep 2023 11:07:10 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hi, please consider.
>> 
>> I don't know the history behind the Cmpxhg<4>, but it is not needed anymore.
>> Using compiler as in 8 byte case is just fine.
>> 
>> Passes hotspot-tier (qemu, vf2 still running), some manual extra testing via gtest, looked at compiler: output, e.g. https://godbolt.org/z/a31Gdqn8q
>> 
>> If you know the history please share, and if you have a reason why we should keep it please speak up!
>
> Robbin Ehn 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:
> 
>  - Merge branch 'master' into 8316186-4cmpxchg
>  - Remove redudant local
>  - Removed

Looks good. So far my local regression tests with release build from GCC-11 are fine.

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15715#pullrequestreview-1649070518