Horton

Re: refactor architecture-specific popcount code

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: John Naylor <johncnaylorls@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@postgresql.org
Date: 2026-01-29T17:06:03Z
Lists: pgsql-hackers

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On Thu, Jan 29, 2026 at 06:31:53PM +0700, John Naylor wrote:
> On Mon, Jan 26, 2026 at 10:41 PM Nathan Bossart
> <nathandbossart@gmail.com> wrote:
>> I added a 0003 that swaps that final popcount with pg_popcount().
> 
> I'm not sure either if this part matters much, but it makes more sense
> to me to continue using single word functions for that last part.
> Since they have very few call sites anymore, we can make them inline
> without bloating the binary on x86.

Okay, I abandoned that patch.

> Right, just the portable ones. Here, too, inlining them everywhere
> would mitigate any impact.

Done.

> +static inline int
> +pg_popcount64_neon(uint64 word)
> 
> ...if they were inlined from the header, I think we wouldn't need this
> separate neon function in this file at all. Currently, we rely on
> __builtin_popcountl for the portable function outside this file. We
> could either keep using that or switch to neon if there's a
> portability difference.

Done.

-- 
nathan

Commits

  1. Make use of pg_popcount() in more places.

  2. Remove uses of popcount builtins.

  3. Remove some unnecessary optimizations in popcount code.

  4. Remove specialized word-length popcount implementations.

  5. Move x86-64-specific popcount code to pg_popcount_x86.c.

  6. Refactor some SIMD and popcount macros.

  7. Rename "fast" and "slow" popcount functions.

  8. Rename pg_popcount_avx512.c to pg_popcount_x86.c.

  9. Remove trailing zero words from Bitmapsets

  10. Don't use _BitScanForward64/_BitScanReverse64 on 32-bit MSVC builds