RFR: 8257436: [aarch64] Regressions in ArrayCopyUnalignedDst.testByte/testChar for 65-78 bytes when UseSIMDForMemoryOps is on

[Evgeny Astigeevich]

On Wed, 2 Dec 2020 11:12:41 GMT, Evgeny Astigeevich <github.com+42899633+eastig at openjdk.org> wrote:

>>> @theRealAph could please check if it causes any issues on ThunderX 2?
>> 
>> Is there some script you use that generates the comparison? Otherwise it'll take some time.
>
>> > @theRealAph could please check if it causes any issues on ThunderX 2?
>> 
>> Is there some script you use that generates the comparison? Otherwise it'll take some time.
> 
> Unfortunately, no. I have scripts that do runs. Then I pull all results in Excel.
> BTW, I attached data comparing SIMD_OFF vs SIMD_ON(patch). JDK-8257436 has data showing regressions with SIMD three ldpq instructions. I'll attach data comparing SIMD_no_fix vs SIMD_fix later.

I updated the attached data. It now includes the following:
- UseSIMDForMemoryOps is off.
- UseSIMDForMemoryOps is on.
- UseSIMDForMemoryOps + fix is on.

The fix is narrowed to be used for byte and char arraycopies. They have the most problems with unaligned accesses. Int arraycopies are at least 4 byte aligned. Long arraycopies are always 8 byte aligned.

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PR: https://git.openjdk.java.net/jdk/pull/1558