Is this a missed optimization for popcount implementation?

[andre maute]

On 12/7/20 11:03 PM, Jim Wilson wrote:
> On Sat, Dec 5, 2020 at 11:48 AM andre maute <andre.maute@gmx.de> wrote:
>
>> I'm wondering why is there a special optimization
>> for the "trick" code, and why isn't there one for the "naive" code?
>>
> Because a bug report was submitted for the example that you are calling
> trick code.
>       https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82479
> and a patch was written to fix that.  The bug report says this code is
> present in spec2017, which is why they wanted it optimized., and why a
> volunteer was willing to write the complicated code necessary to perform
> this optimization.
>
> Anyways, yes, I'd call this a missing optimization, though likely of
> limited interest, unless you can point at a benchmark or important program
> that really needs it.  You are welcome to submit a bug report, and maybe
> point back at bug 82479.
>
> But in general, you are better off calling __builtin_popcount.
>
> Jim
>
Thank you Jim for the pointer.
I was triggered watching a youtube video with Matt Godbolt
	https://www.youtube.com/watch?v=w0sz5WbS5AM
about how amazing compilers are.

Wouldn't it be nice if you could tell your colleagues
that you don't have to remember those bit hacking "tricks" anymore.

This might become relevant, if you still have to additionally support
old pre C++11 multiplatform sources.

With your pointer and
https://graphics.stanford.edu/~seander/bithacks.html
this could be a nice beginner project.

Regards Andre