On Tue, 19 Mar 2024 at 10:08, Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> On Tue, Mar 19, 2024 at 10:02:18AM +1300, David Rowley wrote:
> > The only thing I'd question in the patch is in pg_popcount_fast(). It
> > looks like you've opted to not do the 32-bit processing on 32-bit
> > machines. I think that's likely still worth coding in a similar way to
> > how pg_popcount_slow() works. i.e. use "#if SIZEOF_VOID_P >= 8".
> > Probably one day we'll remove that code, but it seems strange to have
> > pg_popcount_slow() do it and not pg_popcount_fast().
>
> The only reason I left it out was because I couldn't convince myself that
> it wasn't dead code, given we assume that popcntq is available in
> pg_popcount64_fast() today. But I don't see any harm in adding that just
> in case.
It's probably more of a case of using native instructions rather than
ones that might be implemented only via microcode. For the record, I
don't know if that would be the case for popcntq on x86 32-bit and I
don't have the hardware to test it. It just seems less risky just to
do it.
David
