RFR: 8282664: Unroll by hand StringUTF16 and StringLatin1 polynomial hash loops [v13]

[Ludovic Henry]

On Sun, 13 Nov 2022 21:08:53 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> Also, I'd like to note that C2 auto-vectorization support is not too far away from being able to optimize hash code computations. At some point, I was able to achieve some promising results with modest tweaking of SuperWord pass:
https://github.com/iwanowww/jdk/blob/superword/notes.txt
http://cr.openjdk.java.net/~vlivanov/superword.reduction/webrev.00/

That would be extremely helpful not just for this case but for many other cases that today require the Vector API or handrolled intrinsics. For cases that would be great to support, a good guide is the [gcc autovectorization support](https://gcc.gnu.org/projects/tree-ssa/vectorization.html) given they use SLP as well.

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PR: https://git.openjdk.org/jdk/pull/10847