RFR: 8344306: RISC-V: Add zicond [v2]

[Robbin Ehn]

On Tue, 26 Nov 2024 14:43:52 GMT, Hamlin Li <mli at openjdk.org> wrote:

>>> Seems the critical path when `+UseZicond` is longer than `-UseZicond`, I'm not sure how much impact the branch code will bring when `-UseZicond`.
>> 
>> As I said, those 4 instructions saves ~1 cycle compared branch in out-order cpu models.
>
> Thanks for the discussion!
> Overall speaking, I think the new patch with cmov is more promising in terms of performance (in terms of pipeline), although we can not enumerate all the use cases.

Yes, exactly, a branch is always more 'intrusive' in the pipeline than plain scalar ops.
As we discussed, there are cases where czero perform in pair with branch, but in general it's a win.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22386#discussion_r1860491415