[vectorIntrinsics] RFR: 8283709: Add x86 back-end implementation for bit BIT_COUNT operation [v3]

[Xiaohong Gong]

On Tue, 29 Mar 2022 08:54:42 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Yeah, so if the `ConvL2I` is supported to be auto-vectorized after then, the `PopCountL` is better to be auto-vectorized to "PopCountVL + VectorCastL2X" ? Do you have any plan on it? Thanks so much！
>
>> Yeah, so if the `ConvL2I` is supported to be auto-vectorized after then, the `PopCountL` is better to be auto-vectorized to "PopCountVL + VectorCastL2X" ? Do you have any plan on it? Thanks so much！
> 
> Agree to your proposal, once we have auto-vectorization for ConvL2I n place we can change the IR.

OK, thanks!

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PR: https://git.openjdk.java.net/panama-vector/pull/185