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

[Volker Simonis]

On Wed, 18 Nov 2020 14:10:48 GMT, Eugene Astigeevich <github.com+42899633+eastig at openjdk.org> wrote:

> This patch fixes 27%-48% performance regressions of small arraycopies on Graviton2 (Neoverse N1) when UseSIMDForMemoryOps is enabled. For such copies ldpq/stpq are used instead of ld4/st4.
> This follows what the Arm Optimization Guide, including for Neoverse N1, recommends: Use discrete, non-writeback forms of load and store instructions while interleaving them.
> 
> The patch passed jtreg tier1-2 and all gtest tests with linux-aarch64-server-release build and UseSIMDForMemoryOps enabled.

Thanks for the detailed performance numbers.
Looks good to me.

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Marked as reviewed by simonis (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1293