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: 2026-02-07T08:54:31Z
Lists: pgsql-hackers 
On Fri, Feb 6, 2026 at 11:13 PM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> On Thu, Feb 05, 2026 at 02:48:44PM +0700, John Naylor wrote:
> > On Thu, Feb 5, 2026 at 4:43 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
> >> Sure.  I'm tempted to suggest that we only use the plain C version here,
> >> too.  The SSE4.2 bms_num_members() test I did yesterday used it and showed
> >> improvement at one word.  If we do that, we can rip out even more code
> >> since we no longer need the popcount built-ins.
> >
> > Unlike the 32-bit case, people do run production on 64-bit platforms
> > that are not Arm/x86, so that would require effort to see if the
> > builtins are worth it for them. That seems like a separate effort. I
> > can help with that, but let's get the tested stuff in first.
>
> Alright.  I moved that to a new 0004 patch that we can consider separately
> once 0001-0003 have been committed.

Okay, this is looking good. I have just one more suggestion: For 0002,
just copy the word-wise functions verbatim. That way, it's a pure
refactoring commit and the exception doesn't need explaining. With
that, I'd say go ahead and commit 0001/2.

Then after a bit more research, the final form of the inline functions
can be visible in a single commit. I've tested S390X already and hope
to test one other platform.

-- 
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