RFR: 8256820: AArch64: Optimize vector rotate (immediate) with shift and insert instructions

[Andrew Haley]

On 14/12/2020 06:02, Dong Bo wrote:
> The JMH micro `test/micro/org/openjdk/bench/java/lang/RotateBenchmark.java` is used for performance test.
> Witnessed ~15.4% performance improvements on Kunpeng920 (CPU tsv110), but ~15.8% regression on Kunpeng916 (CPU A72).
> So a switch `UseSIMDShiftInsertForRotation` is introduced on aarch64 with default value `false`, and set `true` for Kunpeng920.

I am seriously wondering if this change is worth doing. To find out,
we'd have to test on all of the different AArch64 systems in use.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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