On Wed, Feb 12, 2025 at 10:12:20PM +0000, Devulapalli, Raghuveer wrote: >> Well, I suspect the AVX-512 version will pretty much always need the runtime >> check given that its not available on a lot of newer hardware and requires a >> bunch of extra runtime checks (see pg_popcount_avx512.c). But it might be >> worth doing for PCLMUL. Otherwise, I think we'd have to leave out the PCLMUL >> optimizations if built with -msse4.2 -mpclmul because we don't want to >> regress >> existing -msse4.2 users with a runtime check. > > Sounds good to me. Although, users building with just -msse4.2 will now > encounter an > an additional pclmul runtime check. That would be a regression unless they > update to > building with both -msse4.2 and -mpclmul.
My thinking was that building with just -msse4.2 would cause the existing SSE 4.2 implementation to be used (without the function pointer). That's admittedly a bit goofy because they'd miss out on the PCLMUL optimization, but things at least don't get any worse for them. -- nathan
