A better mul_sum_i8_pairs_float implementation using AVX512

Author: MeouSker77

ggml.c

@@ -505,13 +505,19 @@ static inline __m256 sum_i16_pairs_float(const __m256i x) {
 
 // multiply int8_t, add results pairwise twice and return as float vector
 static inline __m256 mul_sum_i8_pairs_float(const __m256i x, const __m256i y) {
+#if __AVXVNNIINT8__
+    const __m256i zero = _mm256_setzero_si256();
+    const __m256i summed_pairs = _mm256_dpbssd_epi32(zero, x, y);
+    return _mm256_cvtepi32_ps(summed_pairs);
+#else
     // Get absolute values of x vectors
     const __m256i ax = _mm256_sign_epi8(x, x);
     // Sign the values of the y vectors
     const __m256i sy = _mm256_sign_epi8(y, x);
     // Perform multiplication and create 16-bit values
     const __m256i dot = _mm256_maddubs_epi16(ax, sy);
     return sum_i16_pairs_float(dot);
+#endif
 }
 
 static inline __m128i packNibbles( __m256i bytes )