RFR: 8291600: [vectorapi] vector cast op check is not always needed for vector mask cast [v7]

[Xiaohong Gong]

On Thu, 15 Sep 2022 08:06:35 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Yes, it is. Just want to double check in the compiler side, or it maybe confusing if someone is not familiar with the vector api java codes.
>
> I see, may be we can just add a comment/assert instead.

Yeah, agree to you. Or maybe as assert under `if(num_elem_from < num_elem_to)` and `if(num_elem_from > num_elem_to)` ?  I'm sorry that I didn't find a better place to add the comment. Any suggestions? For me, it's better to add the comment inside the `if(is_cast)` block since it has different paths based on the `num_elem_from` and `num_elem_to`.

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PR: https://git.openjdk.org/jdk/pull/9737