Re: Popcount optimization using AVX512

On Mon, Mar 25, 2024 at 03:05:51PM -0500, Nathan Bossart wrote:
> On Mon, Mar 25, 2024 at 06:42:36PM +0000, Amonson, Paul D wrote:
>> Ok, CI turned green after my re-post of the patches. Can this please get
>> merged?
>
> Thanks for the new patches. I intend to take another look soon.

Thanks for your patience. I spent most of my afternoon looking into the
latest patch set, but I needed to do a CHECKPOINT and take a break. I am
in the middle of doing some rather heavy editorialization, but the core of
your changes will remain the same (and so I still intend to give you
authorship credit). I've attached what I have so far, which is still
missing the configuration checks and the changes to make sure the extra
compiler flags make it to the right places.

Unless something pops up while I work on the remainder of this patch, I
think we'll end up going with a simpler approach. I originally set out to
make this look like the CRC32C stuff (e.g., a file per implementation), but
that seemed primarily useful if we can choose which files need to be
compiled at configure-time. However, the TRY_POPCNT_FAST macro is defined
at compile-time (AFAICT for good reason [0]), so we end up having to
compile all the files in many cases anyway, and we continue to need to
surround lots of code with "#ifdef TRY_POPCNT_FAST" or similar. So, my
current thinking is that we should only move the AVX512 stuff to its own
file for the purposes of compiling it with special flags when possible. (I
realize that I'm essentially recanting much of my previous feedback, which
I apologize for.)

[0] https://postgr.es/m/CAApHDvrONNcYxGV6C0O3ZmaL0BvXBWY%2BrBOCBuYcQVUOURwhkA%40mail.gmail.com

--
Nathan Bossart
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