On Fri, Mar 29, 2024 at 10:59:40AM -0500, Nathan Bossart wrote: > It might be nice if we conditionally built pg_popcount_avx512.o in autoconf > builds, too, but AFAICT we still need to wrap most of that code with > macros, so I'm not sure it's worth the trouble. I'll take another look at > this...
If we assumed that TRY_POPCNT_FAST would be set and either HAVE__GET_CPUID_COUNT or HAVE__CPUIDEX would be set whenever USE_AVX512_POPCNT_WITH_RUNTIME_CHECK is set, we could probably remove the surrounding macros and just compile pg_popcount_avx512.c conditionally based on USE_AVX512_POPCNT_WITH_RUNTIME_CHECK. However, the surrounding code seems to be pretty cautious about these assumptions (e.g., the CPUID macros are checked before setting TRY_POPCNT_FAST), so this would stray from the nearby precedent a bit. A counterexample is the CRC32C code. AFAICT we assume the presence of CPUID in that code (and #error otherwise). I imagine its probably safe to assume the compiler understands CPUID if it understands AVX512 intrinsics, but that is still mostly a guess. -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
