RFR: JDK-8308994: C2: Re-implement experimental post loop vectorization

[Emanuel Peter]

On Fri, 23 Jun 2023 10:55:17 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> ## TL;DR
>> 
>> This patch completely re-implements C2's experimental post loop vectorization for better stability, maintainability and performance. Compared with the original implementation, this new implementation adds a standalone loop phase in C2's ideal loop phases and can vectorize more post loops. The original implementation and all code related to multi-versioned post loops are deleted in this patch. More details about this patch can be found in the document replied in this pull request.
>
> src/hotspot/share/opto/superword.cpp line 3881:
> 
>> 3879: }
>> 3880: 
>> 3881: // Following is used outside superword optimization
> 
> Could we move the whole SWPointer outside of SuperWord, into some "autovectorization.hpp" maybe? Because the SW of SWPointer means SuperWord, maybe a renaming could be good too?

If you are going to do that, I'd suggest doing this refactoring in a separate RFE. It would help in general with any future extension to auto-vectorization.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14581#discussion_r1239677815