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: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@postgresql.org
Date: 2026-01-16T05:51:59Z
Lists: pgsql-hackers 
On Fri, Jan 16, 2026 at 2:07 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> Here is a new patch set. Notably, I've added a 0004 that does the
> following:
>
> * Removes TRY_POPCNT_X86_64.  We now assume that the required CPUID
> intrinsics are available, as we have long done in some of the CRC-32C code.
>
> * Moves the MSVC check for HAVE_X86_64_POPCNTQ to configuration-time.  This
> way, we set it for all relevant platforms in one place.

LGTM.

> * Moves the #defines for USE_SSE2 and USE_NEON to c.h so that they can be
> used elsewhere without simd.h.  Consequently, we can remove POPCNT_AARCH64.

Seems reasonable.

> * Moves the #includes for pg_bitutils.h to below the system headers in
> pg_popcount_{aarch64,x86}.c (since we no longer depend on macros defined in
> pg_bitutils.h).

Good.

v2-0003

+ * XXX Technically, POPCNT is not part of SSE4.2, and isn't even a vector
+ * operation, but in practice this is close enough, and "sse42" seems easier to
+ * follow than "popcnt" for these names.

Quibble -- XXX is a bit loud for a side note.

On Thu, Jan 15, 2026 at 11:08 PM Nathan Bossart
<nathandbossart@gmail.com> wrote:
>
> On Thu, Jan 15, 2026 at 11:42:14AM +0200, Heikki Linnakangas wrote:

> > "fallback", or "portable" ?
>
> I've no strong opinions, but "portable" seems reasonable to me.

I have a mild preference for "fallback" since it's a noun and we
already have comments in src/(include/)port referring to fallbacks. No
objection to "portable", though.

--
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