RFR: 8354674: AArch64: Intrinsify Unsafe::setMemory [v6]

[Per Minborg]

On Wed, 14 May 2025 10:47:40 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> This intrinsic is generally faster than the current implementation for Panama segment operations for all writes larger than about 8 bytes in size, increasing to more than 2* the performance on larger memory blocks on Graviton 2, between "panama" (C2 generated, what we use now) and "unsafe" (this intrinsic).
>> 
>> 
>> Benchmark                       (aligned)  (size)  Mode  Cnt     Score    Error  Units
>> MemorySegmentFillUnsafe.panama       true  262143  avgt   10  7295.638 ±  0.422  ns/op
>> MemorySegmentFillUnsafe.panama      false  262143  avgt   10  8345.300 ± 80.161  ns/op
>> MemorySegmentFillUnsafe.unsafe       true  262143  avgt   10  2930.594 ±  0.180  ns/op
>> MemorySegmentFillUnsafe.unsafe      false  262143  avgt   10  3136.828 ±  0.232  ns/op
>
> Andrew Haley has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - AvoidUnalignedAccesses
>  - Temp
>  - The cherry on the cake

The changes in `SegmentBulkOperations` look good.

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PR Comment: https://git.openjdk.org/jdk/pull/25147#issuecomment-2880312073