Re: Popcount optimization using AVX512

On Thu, Mar 28, 2024 at 10:29:47PM +0000, Amonson, Paul D wrote:
> I see in the meson.build you added the new file twice?
> 
> @@ -7,6 +7,7 @@ pgport_sources = [
>    'noblock.c',
>    'path.c',
>    'pg_bitutils.c',
> +  'pg_popcount_avx512.c',
>    'pg_strong_random.c',
>    'pgcheckdir.c',
>    'pgmkdirp.c',
> @@ -84,6 +85,7 @@ replace_funcs_pos = [
>    ['pg_crc32c_sse42', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK', 'crc'],
>    ['pg_crc32c_sse42_choose', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK'],
>    ['pg_crc32c_sb8', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK'],
> +  ['pg_popcount_avx512', 'USE_AVX512_POPCNT_WITH_RUNTIME_CHECK', 'avx512_popcnt'],
> 
> I was putting the file with special flags ONLY in the second section and all seemed to work. :)

Ah, yes, I think that's a mistake, and without looking closely, might
explain the MSVC warnings [0]:

    [22:05:47.444] pg_popcount_avx512.c.obj : warning LNK4006: pg_popcount_avx512_available already defined in
pg_popcount_a...

It might be nice if we conditionally built pg_popcount_avx512.o in autoconf
builds, too, but AFAICT we still need to wrap most of that code with
macros, so I'm not sure it's worth the trouble.  I'll take another look at
this...

[0] http://commitfest.cputube.org/highlights/all.html#4883

-- 
Nathan Bossart
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