On Wed, Feb 12, 2025 at 09:48:57PM +0000, Devulapalli, Raghuveer wrote: >> I think the idea behind USE_SSE42_CRC32C is to avoid the function pointer >> overhead if possible. I looked at switching to always using runtime checks >> for this >> stuff, and we concluded that we'd better not [0]. > > Does that mean we want this feature for the new PCLMUL (and AVX-512) crc32c > implementations too? The code for that will look a little ugly, I might need > to think about a cleaner way to do this.
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. -- nathan
