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

[Jatin Bhateja]

On Thu, 15 Sep 2022 07:51:34 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> src/hotspot/share/opto/vectorIntrinsics.cpp line 2554:
>> 
>>> 2552:       op = gvn().transform(new VectorReinterpretNode(op, src_type, resize_type));
>>> 2553:       op = gvn().transform(VectorCastNode::make(cast_vopc, op, elem_bt_to, num_elem_to));
>>> 2554:     } else { // num_elem_from == num_elem_to
>> 
>> There is one comment unrelated to this patch but since your patch touches this function may be we can address it.
>> Call to VectorMaskCastNode::makeCastNode in else block at following line
>> https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/vectorIntrinsics.cpp#L2555
>> should be able to handle the true block. 
>> But, newly created IR node on following location https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/vectornode.cpp#L1761 should be passed through gvn transform before returning.
>
> Yes, you are right. That's also what is the first version of this PR (please see: https://openjdk.github.io/cr/?repo=jdk&pr=9737&range=00).  And since @merykitty  suggested to unify the whole vector mask cast operations with `VectorMaskCastNode`, I prepare a follow-up patch to specifically do this refactorization (please see: https://github.com/openjdk/jdk/pull/10192). And as suggested by @DamonFool , we only fix the `FIRST_NONZERO` performance issue in this PR.

Yes, I just noticed that #10192 is addressing above two comments

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