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

[Emanuel Peter]

On Fri, 23 Jun 2023 14:53:59 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.cpp line 317:
> 
>> 315: 
>> 316: // Find element basic type for each vectorization candidate node
>> 317: bool VectorMaskedLoop::find_vector_element_types() {
> 
> This is very similar to `SuperWord::compute_vector_element_type`. It would be nice to extract it from both and have some shared utility, right?

Or is there a clear reason why the two are too different?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14581#discussion_r1239921855