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

[Xiaohong Gong]

On Sat, 26 Mar 2022 01:48:34 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Summary of changes:
>> 
>> - Patch re-uses existing C2 IR nodes and re-organizes LUT based JIT code sequence of VectorOperations.BIT_COUNT operation 
>>   for sub-word type (BYTE, SHORT) vectors over X86 targets supporting AVA2 and AVX512 features.
>> - Efficient single instruction POPCOUNT instruction is emitted for applicable targets. 
>> 
>> Kindly review and share you feedback.
>> 
>> Best Regards,
>> Jatin
>
> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8283709: Adding new CPU feature AVX512_BITALG to JVMCI feature set.

src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 4537:

> 4535:     ShouldNotReachHere();
> 4536:   }
> 4537:   if (rbt == T_INT) {

So the SLP and the VectorAPI uses the same `PopCountVL` with different basic type?

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