Horton

Re: refactor architecture-specific popcount code

John Naylor <johncnaylorls@gmail.com>

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From: John Naylor <johncnaylorls@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Greg Burd <greg@burd.me>, Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-02-12T04:58:37Z
Lists: pgsql-hackers 
On Thu, Feb 12, 2026 at 12:39 AM Nathan Bossart
<nathandbossart@gmail.com> wrote:
>
> On Wed, Feb 11, 2026 at 02:10:37PM +0700, John Naylor wrote:
> > I don't think we need to worry about this, but the attached looks
> > nicer to me. There might be a disadvantage of using macros here, but
> > I'm not sure what it would be.
>
> The only problem that I see with this is that a compiler that understands
> Neon intrinsics but not SVE ones will probably fail because we build
> external functions that call the Neon versions in that case.

Ah, right.

> But that's
> easy enough to work around by adding an extra #elif defined(USE_NEON)
> section, and it still saves a handful of lines of code.  Perhaps someday
> this situation will be rare enough that we can remove that hack and just
> point to the portable versions if the compiler doesn't understand both Neon
> and SVE, but I'm not sure we're there yet.

I have a better idea, but it depends on re-thinking feature detection
and compile-time vs run-time checks, and that's not quite ready to
share, so let's shelve this for now.

Anyway, I think 0001 and 0002 are ready for commit.

-- 
John Naylor
Amazon Web Services

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