Re: Popcount optimization using AVX512

On Tue, Apr 02, 2024 at 12:11:59AM +0300, Ants Aasma wrote:
> What about using the masking capabilities of AVX-512 to handle the
> tail in the same code path? Masked out portions of a load instruction
> will not generate an exception. To allow byte level granularity
> masking, -mavx512bw is needed. Based on wikipedia this will only
> disable this fast path on Knights Mill (Xeon Phi), in all other cases
> VPOPCNTQ implies availability of BW.

Sounds promising.  IMHO we should really be sure that these kinds of loads
won't generate segfaults and the like due to the masked-out portions.  I
searched around a little bit but haven't found anything that seemed
definitive.

-- 
Nathan Bossart
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