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

[Emanuel Peter]

On Wed, 21 Jun 2023 08:24:19 GMT, Pengfei Li <pli 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.

I'm in the middle of reviewing, but have to end it here for the week now 😊 

For now it's a lot of detail-feedback. I'll give a more overall-feedback once I'm done reading through, and reflecting on it.

Still: this is good work. We will have to discuss the performance benefits vs the code complexity. And maybe we first need to refactor some things to reduce code duplication. But this looks much better than the previous post-loop vectorization.

Have a great weekend,
Emanuel

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PR Comment: https://git.openjdk.org/jdk/pull/14581#issuecomment-1604429147