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

[Emanuel Peter]

On Thu, 15 May 2025 08:15:24 GMT, Manuel Hässig <mhaessig 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>
>
> src/hotspot/share/opto/superword.cpp line 2676:
> 
>> 2674:     // it is worse if a store is split, and less bad if a load is split.
>> 2675:     // By default, we have SuperWordAutomaticAlignment=1, i.e. we align with a
>> 2676:     // load if possible, to avoid splitting that load.
> 
> Suggestion:
> 
>     // By default, we have SuperWordAutomaticAlignment=1, i.e. we align with a
>     // store if possible, to avoid splitting that store.
> 
> That conflicts with what the documentation in `c2_globals.hpp` says.

Yikes! Thanks for the catch!

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PR Review Comment: https://git.openjdk.org/jdk/pull/25065#discussion_r2090697049