RFR: 8315716: RISC-V: implement ChaCha20 intrinsic

[Hamlin Li]

On Wed, 27 Sep 2023 13:46:52 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Thanks for discussion. Yes, I see your point.
>> What I mean above is that the java heap can only be touched when store back to memory, but store `only access memory or raise exceptions for active elements.`, that seems mean that a vectore operation might touch tail elements in vector group register, but a vector store will not touch the memory corresponding to the tail elements.
>> Am I understanding the spec correctly?
>
> I don't see that the specs guarantees that under no circumstance tail memory will not be touched.
> So I don't know, for now it's better to be safe than sorry.

Sure, in fact vsetvli was already modifed to use default arguments as you suggested.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15899#discussion_r1338662157