Re: Popcount optimization using AVX512

On Thu, Apr 18, 2024 at 09:29:55PM +0000, Devulapalli, Raghuveer wrote:
> (1) Shouldn't it be: return (_xgetbv(0) & 0xe6) == 0xe6; ? Otherwise
> zmm_regs_available() will return false..

Yes, that's a mistake.  I fixed that in v3.

> (2) Nitpick: avx512_popcnt_available and avx512_bw_available() run the
> same cpuid leaf. You could combine them into one to avoid running cpuid
> twice. My apologies, I should have mentioned this before..

Good call.  The byte-and-word instructions were a late addition to the
patch, so I missed this originally.

On that note, is it necessary to also check for avx512f?  At the moment, we
are assuming that's supported if the other AVX-512 instructions are
available.

-- 
Nathan Bossart
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