RFR: 8330266: RISC-V: Restore frm to RoundingMode::rne after JNI [v2]

[Ludovic Henry]

On Tue, 16 Apr 2024 10:09:27 GMT, Vladimir Kempik <vkempik at openjdk.org> wrote:

>> @VladimirKempik https://riscv-optimization-guide.riseproject.dev/#_controlling_rounding_behavior_scalar is written by multiple industry player who know how their hardware is going to behave, and it is confirmed that it will be more performant to have this `frrm`+`beq` than always doing `fsrm`. If you disagree with the wording in that guide, you're welcome to open a discussion on https://gitlab.com/riseproject/riscv-optimization-guide.
>
> @luhenry I've already saw a big criticism of that document. So it makes me take it with a grain of salt. It was written by a limited group of vendors ( not all of them participated) and basically shows  u-arch peculiarities of limited hw group.
> 
> I'm gonna check few version of this patch in jni_blank jmh microtest

@VladimirKempik again, happy to get input from more people on that document! :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/18785#discussion_r1567103936