RFR: 8316186: RISC-V: Remove PlatformCmpxchg<4> [v2]

[Robbin Ehn]

On Tue, 26 Sep 2023 11:48:57 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 incrementally with one additional commit since the last revision:
> 
>   Remove redudant local

Merge with master, retested the problematic tests, we are all green now.
Please consider :)

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PR Comment: https://git.openjdk.org/jdk/pull/15715#issuecomment-1738931554