RFR: 8355094: Performance drop in auto-vectorized kernel due to split store [v2]

[Emanuel Peter]

On Thu, 15 May 2025 21:25:08 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update src/hotspot/share/opto/superword.cpp
>>   
>>   Co-authored-by: Manuel Hässig <manuel at haessig.org>
>
> Impressive analysis, Emanuel! Very deep, thorough, and insightful.
> 
> Looks good.
> 
> Speaking of Vector API, we experimented with getting access alignment under control.  Unfortunately, when it comes to on-heap accesses it boils down to hyper-aligned objects support which is not there yet.
> 
> PS: yay, you found a way to turn PRs into blog posts! :-)

@iwanowww Thanks for your kind words 😊 

Indeed: on-heap access would profit from hyper-aligned objects. Are there any ideas on how to do that? I wonder if it is worth it, or if it is good enough to just use off-heap (native) MemorySegments to guarantee alignment for very performance critical cases?

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PR Comment: https://git.openjdk.org/jdk/pull/25065#issuecomment-2885883207