[vectorIntrinsics] RFR: 8281562:[vectorapi] Add support for popcount operation

[Paul Sandoz]

On Thu, 10 Feb 2022 00:56:40 GMT, Smita Kamath <svkamath at openjdk.org> wrote:

>> src/jdk.incubator.vector/share/classes/jdk/incubator/vector/LongVector.java line 449:
>> 
>>> 447:     /*package-private*/
>>> 448:     @ForceInline
>>> 449:     static int popcount(long a) {
>> 
>> Method is unnecessary.
>
> @PaulSandoz Byte and Short types don't have a bitCount method. I will need this supporting method when I implement popcount for them. Do you think it's alright to keep this method? Do let me know. Thank you.

I see. My recommendation is to only add them for byte/short, then as a separate PR to jdk add those methods directly to `Byte` and `Short`.

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PR: https://git.openjdk.java.net/panama-vector/pull/173