Re: [PATCH 0/5] Reinstate ability to use Qemu on pre-SSE4.1 x86 hosts

[Alexander Monakov]

On Wed, 12 Jun 2024, Paolo Bonzini wrote:

> Ahah, nice. :) I'm pretty sure that, when I tested "pf =
> (__builtin_popcount(x) & 1) * 4;", it was generating a call to
> __builtin_popcountsi2.

Why write '__builtin_popcount(x) & 1' when you can write
'__builtin_parity(x)' in the first place? 

> Still - for something that has a code generator, there _is_ a cost in
> supporting old CPUs, so I'd rather avoid reverting this. The glibc bug
> that you linked is very different not just because it affected 32-bit
> installation media, but also because it was a bug rather than
> intentional.
> 
> Since you are reporting this issue, how did you find out / what broke for you?

I found out from the mailing list. My Core2-based desktop would be affected.

Last but not the least, I'm sympathetic to the efforts of my distro maintainers,
who I imagine would be put in an uncomfortable position by this change.

Alexander