Re: refactor architecture-specific popcount code

On Fri, Jan 16, 2026 at 2:07 AM Nathan Bossart <nathandbossart(at)gmail(dot)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(at)gmail(dot)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