Re: refactor architecture-specific popcount code

On Feb 3 2026, at 12:41 pm, Nathan Bossart <nathandbossart@gmail.com> wrote:

> On Tue, Feb 03, 2026 at 12:19:48PM -0500, Greg Burd wrote:
>> Thanks for the focus on this area of the code.  I've been looking into
>> what to do with popcnt when building Win11/ARM64/MSVC.  I know that when
>> _MSC_VER and _M_ARM64 are defined we can make use of the
>> __popcnt(unsigned int) and __popcnt64(unsigned __int64) intrinsics which
>> have been available since VS 2022 17.11+.  I thought I'd check that combo
>> out and it turns out that it is identical to clang/gcc on that platform
>> [0].
>> 
>> I'll wait for your work to land before proposing a patch to add these
>> unless it is really easy to fit it and you feel like giving it a go. :)
> 
> We should probably just add something like
> 
>     #ifdef _MSC_VER
>         return __popcnt(word);

Right, it seemed to me after reviewing the patch to fit right in.

> for the new inlined versions of pg_popcount{32,64}.  We're already doing
> that today for x86-64, and the AArch64-specific versions use intrinsics
> that in theory compile to the same thing.  Plus, popcnt is required for
> Windows these days.
> 
> I'm working on polishing/benchmarking these patches at the moment, so I
> will work this change in.  Thanks!

Not a problem, thank you!

> -- 
> nathan

-greg