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

[Claes Redestad]

On Sat, 29 Oct 2022 15:11:56 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

> I am planning to submit that patch after finishing with the current under-reviewed PRs. That patch was stalled because there was no node for vectorised unsigned cast and constant values. The first one has been added and the second one may be worked around as in the PR. I also thought of using masked loads for tail processing instead of falling back to scalar implementation.

Ok, then I think we might as well move forward with this enhancement first. It'd establish some new tests, microbenchmarks as well as unifying the polynomial hash loops into a single intrinsic endpoint - while also putting back something that would be straightforward to backport (less dependencies on other recent enhancements). Then once the vector IR nodes have matured we can easily rip out the `VectorizedHashCodeNode` and replace it with such an implementation. WDYT?

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