RFR: 8292898: [vectorapi] Unify vector mask cast operation [v4]

[Xiaohong Gong]

On Tue, 27 Sep 2022 03:42:19 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Do you mean the mask is using k register when `UseAVX > 2` ?
>
> UseAVX > 2 signifies AVX512 target where carrier of all currently valid mask IR nodes is an opmask register.

I see, thanks! I will change this later.

>> Thanks for pointing out this limitation! So the original `VectorCast` pattern also has the similar issue, right? Further thinking about this limitation, since almost all the mask generation/using API will check the `VectorLoadMask`, this rule may not be useful. But keeping it is fine to me in case `VectorMaskCast` is used for other cases or the limitation is relaxed in future. WDYT?
>
> Correct it's an existing limitation, but in general any newly added code should be reachable in some execution path of a valid testcase. WDYT ?

Make sense to me! So we need to add the same limitation to `VectorMaskCast`?

-------------

PR: https://git.openjdk.org/jdk/pull/10192