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

[Emanuel Peter]

On Fri, 23 Jun 2023 12:07:55 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/vmaskloop.hpp line 97:
> 
>> 95:   }
>> 96: 
>> 97:   bool is_memory_phi(Node* n) {
> 
> Looks like a helper method that could live in `node.hpp` or `cfgnode.hpp`.

SuperWord also makes similar checks, you could refactor those too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14581#discussion_r1239739568