RFR: 8256488: [aarch64] Use ldpq/stpq instead of ld4/st4 for small copies in StubGenerator::copy_memory

[Andrew Haley]

Hi,

On 11/27/20 6:26 AM, Jie He wrote:
>  I also have a patch to fix the unaligned copy small memory (< 16 bytes) when copy a big chunk of memory (> 96 bytes) in this function copy_memory_small(), but it couldn't impact the performance too much, I'm not sure if it is worth pushing to upstream. please refer to [1].
> 
> 1. [JBS-8149448](https://bugs.openjdk.java.net/browse/JDK-8149448)

Thank you.

>From what I remember, that was about optimizing for machines with poor
performance for misaligned loads. As far as I understand it, AArch64
manufacturers have seen the error of their ways, understand that if
they want to compete with Intel they have to fix unaligned memory
performance, and have mostly done so.

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