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.

src/hotspot/share/opto/vmaskloop.cpp line 337:

> 335:           // For load node, check if it has the same vector element size with
> 336:           // the bottom type of the statement
> 337:           if (!same_element_size(mem_type, stmt_bottom_type)) {

Can this limitation be removed in the future?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14581#discussion_r1239917583