Date: Thu, 15 Jan 2026 10:08:16 -0600
From: Nathan Bossart <nathandbossart@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: John Naylor <johncnaylorls@gmail.com>, pgsql-hackers@postgresql.org
Subject: Re: refactor architecture-specific popcount code
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On Thu, Jan 15, 2026 at 11:42:14AM +0200, Heikki Linnakangas wrote:
> On 15/01/2026 11:07, John Naylor wrote:
>> s/slow/generic/:
>> 
>> I'm ambivalent about this. The "slow" designation is flat-out wrong
>> since at least Power and aarch64 can emit a single instruction here
>> without prodding the compiler. On the other hand, "generic" seems
>> wrong too, since e.g. pg_popcount64_slow() has three configure symbols
>> and two compiler builtins. :-D
> 
> "fallback", or "portable" ?

I've no strong opinions, but "portable" seems reasonable to me.

> Yeah, I noticed that on x86_64, pg_popcount_optimized is always a function
> pointer with runtime check, even if you use compiler flags to target a CPU
> where the special instructions are available unconditionally.

I wonder how close we are to being able to just require SSE4.2/POPCNT for
x86-64 builds.  I suppose there's always a chance that someone will try to
run Postgres 19 on a CPU from the aughts...  In any case, avoiding the
function pointer when possible seems like a good follow-up.

-- 
nathan