Feedback-ID: i675e48f3:Fastmail
Date: Tue, 3 Feb 2026 14:38:11 -0500
From: Greg Burd <greg@burd.me>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: John Naylor <johncnaylorls@gmail.com>, Heikki Linnakangas
 <hlinnaka@iki.fi>, pgsql-hackers <pgsql-hackers@postgresql.org>
Message-ID: <E22D691E-A655-44B7-9C1B-C7A86735FE15@greg.burd.me>
In-Reply-To: <aYIzS4-IJOOgpIql@nathan>
References: <aYIzS4-IJOOgpIql@nathan>
Subject: Re: refactor architecture-specific popcount code
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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