Add AVX512 support to DDOT

now that it's written in C + intrinsics it's easy to add AVX512 support
for DDOT

kernel/x86_64/ddot_microk_haswell-2.c

@@ -26,7 +26,8 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *****************************************************************************/
 
 /* Ensure that the compiler knows how to generate AVX2 instructions if it doesn't already */
-#ifndef __AVX512CD_
+
+#ifndef __AVX512CD__
 #pragma GCC target("avx2,fma")
 #endif
 
@@ -35,7 +36,6 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define HAVE_KERNEL_8 1
 
 #include <immintrin.h>
-static void ddot_kernel_8( BLASLONG n, FLOAT *x, FLOAT *y , FLOAT *dot) __attribute__ ((noinline));
 
 static void ddot_kernel_8( BLASLONG n, FLOAT *x, FLOAT *y, FLOAT *dot)
 {
@@ -47,10 +47,37 @@ static void ddot_kernel_8( BLASLONG n, FLOAT *x, FLOAT *y, FLOAT *dot)
 	accum_2 = _mm256_setzero_pd();
 	accum_3 = _mm256_setzero_pd();
 
+#ifdef __AVX512CD__
+	__m512d accum_05, accum_15, accum_25, accum_35;
+	int n32;
+	n32 = n & (~31);
+
+	accum_05 = _mm512_setzero_pd();
+	accum_15 = _mm512_setzero_pd();
+	accum_25 = _mm512_setzero_pd();
+	accum_35 = _mm512_setzero_pd();
+
+	for (; i < n32; i += 32) {
+		accum_05 += _mm512_loadu_pd(&x[i+ 0]) * _mm512_loadu_pd(&y[i+ 0]);
+		accum_15 += _mm512_loadu_pd(&x[i+ 8]) * _mm512_loadu_pd(&y[i+ 8]);
+		accum_25 += _mm512_loadu_pd(&x[i+16]) * _mm512_loadu_pd(&y[i+16]);
+		accum_35 += _mm512_loadu_pd(&x[i+24]) * _mm512_loadu_pd(&y[i+24]);
+	}
+
+	/*
+	 * we need to fold our 512 bit wide accumulator vectors into 256 bit wide vectors so that the AVX2 code
+	 * below can continue using the intermediate results in its loop
+	 */
+	accum_0 = _mm256_add_pd(_mm512_extractf64x4_pd(accum_05, 0), _mm512_extractf64x4_pd(accum_05, 1));
+	accum_1 = _mm256_add_pd(_mm512_extractf64x4_pd(accum_15, 0), _mm512_extractf64x4_pd(accum_15, 1));
+	accum_2 = _mm256_add_pd(_mm512_extractf64x4_pd(accum_25, 0), _mm512_extractf64x4_pd(accum_25, 1));
+	accum_3 = _mm256_add_pd(_mm512_extractf64x4_pd(accum_35, 0), _mm512_extractf64x4_pd(accum_35, 1));
+
+#endif
 	for (; i < n; i += 16) {
-		accum_0 += _mm256_loadu_pd(&x[i+ 0]) * _mm256_loadu_pd(&y[i+0]);
-		accum_1 += _mm256_loadu_pd(&x[i+ 4]) * _mm256_loadu_pd(&y[i+4]);
-		accum_2 += _mm256_loadu_pd(&x[i+ 8]) * _mm256_loadu_pd(&y[i+8]);
+		accum_0 += _mm256_loadu_pd(&x[i+ 0]) * _mm256_loadu_pd(&y[i+ 0]);
+		accum_1 += _mm256_loadu_pd(&x[i+ 4]) * _mm256_loadu_pd(&y[i+ 4]);
+		accum_2 += _mm256_loadu_pd(&x[i+ 8]) * _mm256_loadu_pd(&y[i+ 8]);
 		accum_3 += _mm256_loadu_pd(&x[i+12]) * _mm256_loadu_pd(&y[i+12]);
 	}