diff --git a/lib/common/xxhash.h b/lib/common/xxhash.h index e5ed3dc0443..d95bad19166 100644 --- a/lib/common/xxhash.h +++ b/lib/common/xxhash.h @@ -3317,6 +3317,23 @@ static xxh_u64 XXH64_round(xxh_u64 acc, xxh_u64 input) acc += input * XXH_PRIME64_2; acc = XXH_rotl64(acc, 31); acc *= XXH_PRIME64_1; +#if (defined(__AVX512F__)) && !defined(XXH_ENABLE_AUTOVECTORIZE) + /* + * DISABLE AUTOVECTORIZATION: + * A compiler fence is used to prevent GCC and Clang from + * autovectorizing the XXH64 loop (pragmas and attributes don't work for some + * reason) without globally disabling AVX512. + * + * Autovectorization of XXH64 tends to be detrimental, + * though the exact outcome may change depending on exact cpu and compiler version. + * For information, it has been reported as detrimental for Skylake-X, + * but possibly beneficial for Zen4. + * + * The default is to disable auto-vectorization, + * but you can select to enable it instead using `XXH_ENABLE_AUTOVECTORIZE` build variable. + */ + XXH_COMPILER_GUARD(acc); +#endif return acc; }