On Mon, Nov 06, 2023 at 09:52:58PM -0500, Tom Lane wrote: > Nathan Bossart <nathandboss...@gmail.com> writes: > > Like I said, I don't have any proposals yet, but assuming we do want to > > support newer intrinsics, either open-coded or via auto-vectorization, I > > suspect we'll need to gather consensus for a new policy/strategy. > > Yeah. The function-pointer solution kind of sucks, because for the > sort of operation we're considering here, adding a call and return > is probably order-of-100% overhead. Worse, it adds similar overhead > for everyone who doesn't get the benefit of the optimization.
The glibc/gcc "ifunc" mechanism was designed to solve this problem of choosing a function implementation based on the runtime CPU, without incurring function pointer overhead. I would not attempt to use AVX512 on non-glibc systems, and I would use ifunc to select the desired popcount implementation on glibc: https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/Function-Attributes.html
