RFR: 8284563: AArch64: bitperm feature detection for SVE2 on Linux [v2]

[Eric Liu]

On Mon, 18 Apr 2022 08:08:00 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> OK. Then could you also update the usages of these two `features` with your new functions?
>
> `STXR_PREFETCH` is usually done unconditionally in non-JVM code. Does it ever hurt performance? If not, let's get rid of `STXR_PREFETCH` and do prefetching unconditionally.

@theRealAph 

TBH I don't know the history about this code. Considering that may impact the performance, I don't have too much confidence to dispose of  it in this patch.

Do you think it's fine to trace it in a separate JBS?

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PR: https://git.openjdk.java.net/jdk/pull/8258