RFR: 8291600: [vectorapi] vector cast op check is not always needed for vector mask cast [v3]

[Jie Fu]

On Thu, 25 Aug 2022 03:50:19 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> Thanks for the advice! Yes, this patch firstly fix the performance issue for FIRST_NONZERO and together with some clean up for the related codes. I considered to split the changes before. However, to think more, if the patch only fixes the performance issue, the final codes will look mess and we need to add the additional complex IR checks for the vector mask cast (please see the initial fixing changes here https://openjdk.github.io/cr/?repo=jdk&pr=9737&range=00). Unifying the usage to `VectorMaskCast` IR makes the final code clean. So I prefer to make the whole changes together.


I'm not sure if there would be some side effect about the vector unbox code change.

Since the original goal of this pr is optimizing `FIRST_NONZERO`, it might be better to do the others (code cleanup, unifying the usage of VectorMaskCast) in a separate pr to lower the risk.
Thanks.

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