Re: pgsql: Fix compiler builtin usage in new pg_bitutils.c

On 2019-Feb-15, Tom Lane wrote:

> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > I'm done with this stuff. Anybody feel free to run with it, but for a
> > barely noticeable performance improvement it's not going to be me.
>
> Sure, I'll pick it up. I agree it's probably a marginal performance
> change, but it seems a shame to give up when we were 80% of the way
> there.

(BTW, my reading of the articles I cited, as well as my own runs of the
test programs therein, suggest that in order to get a really good
performance improvement you need to hand-code calls to the POPCNT
instruction in assembly rather than rely on the compiler intrinsics. I
think there is^Wwas almost enough infrastructure to do that. I'm not
sure that the operations being optimized by these changes are
interesting enough, in the grand scheme of things.)

--
Álvaro Herrera https://www.2ndQuadrant.com/
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