Re: refactor architecture-specific popcount code

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