[vectorIntrinsics] RFR: 8283709: Add x86 back-end implementation for bit BIT_COUNT operation [v9]

[Jatin Bhateja]

On Mon, 11 Apr 2022 21:20:26 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8283709: Review comments resolved.
>
> src/hotspot/cpu/x86/vm_version_x86.cpp line 1705:
> 
>> 1703: 
>> 1704:   // Use population count instruction if available.
>> 1705:   if (supports_popcnt() || supports_avx512_vpopcntdq() || supports_avx512_bitalg()) {
> 
> The UsePopCountInstruction is only for scalar popcont. Extending it to Vector popcount is causing lot of confustion. Let us keep it for scalar only as below:
> if (supports_popcnt()) {
>  ...
> }

UsePopcountInstruction implies generating direct popcount instruction for targets which support it. A bit count operation can also be implemented without popcount as depicted by this patch.

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