RFR: 8325541: C2 SuperWord: refactor filter / split [v5]

[Christian Hagedorn]

On Sat, 10 Feb 2024 14:25:22 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> A few filter / split methods are currently bunched together. We should peal them apart so that moving / changing things becomes easier in the future.
>> 
>> 
>> combine_packs -> refactored into:
>>   combine_packs (now really only combines)
>>   split_packs_for_max_vector_size
>>   filter_packs_for_power_of_2_size
>>   filter_packs_for_mutual_independence
>> 
>> filter_packs -> refactored into:
>>   filter_packs_for_implemented
>>   filter_packs_for_profitable
>> 
>> 
>> Since we have so many "filter" passes, I created a dedicated `SuperWord::filter_packs` method, that takes a `FilterPredicate` lambda. This also allows me now to systematically debug dump any packs that are rejected .
>> 
>> I also took the liberty to enforce a new invariant between passes: there cannot be any `nullptr` in the packlist.
>> Before the "filter" passes just set some packs to `nullptr`. I now shift all surviving packs down, and truncate the packlist.
>
> Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8325541
>  - refactored filter_packs_for_alignment using filter_packs
>  - updates for Christian
>  - small bugfix
>  - small update
>  - 8325541

Thanks for the doing the updates. Otherwise, looks good!

src/hotspot/share/opto/superword.cpp line 526:

> 524: 
> 525:   // Split packs if they are too long
> 526:   split_packs_longer_than_max_vector_size();

I think you can now safely remove the comments as the method names already cover that information.

src/hotspot/share/opto/superword.cpp line 1704:

> 1702: 
> 1703:   filter_packs("SuperWord::filter_packs_for_alignment",
> 1704:                "rejected by AlignVector (strinct alignment requirement)",

Suggestion:

               "rejected by AlignVector (strict alignment requirement)",

-------------

Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17785#pullrequestreview-1874746223
PR Review Comment: https://git.openjdk.org/jdk/pull/17785#discussion_r1485874213
PR Review Comment: https://git.openjdk.org/jdk/pull/17785#discussion_r1485873731