Add an AVX512 enabled SDOT function

written in C intrinsics for best readability.
(the same C code works for Haswell as well)

For logistical reasons the code falls back to the existing
haswell AVX2 implementation if the GCC or LLVM compiler is not new enough

kernel/x86_64/sdot.c

@@ -34,8 +34,10 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "sdot_microk_steamroller-2.c"
 #elif defined(NEHALEM)
 #include "sdot_microk_nehalem-2.c"
-#elif defined(HASWELL) || defined(ZEN) || defined (SKYLAKEX)
+#elif defined(HASWELL) || defined(ZEN)
 #include "sdot_microk_haswell-2.c"
+#elif  defined (SKYLAKEX)
+#include "sdot_microk_skylakex-2.c"
 #elif defined(SANDYBRIDGE)
 #include "sdot_microk_sandy-2.c"
 #endif

kernel/x86_64/sdot_microk_skylakex-2.c

@@ -0,0 +1,98 @@
+/***************************************************************************
+Copyright (c) 2014, The OpenBLAS Project
+All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+1. Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in
+the documentation and/or other materials provided with the
+distribution.
+3. Neither the name of the OpenBLAS project nor the names of
+its contributors may be used to endorse or promote products
+derived from this software without specific prior written permission.
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE OPENBLAS PROJECT OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*****************************************************************************/
+
+/* need a new enough GCC for avx512 support */
+#if (( defined(__GNUC__)  && __GNUC__   > 6 && defined(__AVX2__)) || (defined(__clang__) && __clang_major__ >= 6))
+
+#define HAVE_KERNEL_16 1
+
+#include <immintrin.h>
+
+static void sdot_kernel_16( BLASLONG n, FLOAT *x, FLOAT *y, FLOAT *dot)
+
+{
+	int i = 0;
+	__m256 accum_0, accum_1, accum_2, accum_3;
+
+	accum_0 = _mm256_setzero_ps();
+	accum_1 = _mm256_setzero_ps();
+	accum_2 = _mm256_setzero_ps();
+	accum_3 = _mm256_setzero_ps();
+
+#ifdef __AVX512CD__
+	__m512 accum_05, accum_15, accum_25, accum_35;
+	int n64;
+	n64 = n & (~63);
+
+	accum_05 = _mm512_setzero_ps();
+	accum_15 = _mm512_setzero_ps();
+	accum_25 = _mm512_setzero_ps();
+	accum_35 = _mm512_setzero_ps();
+
+	for (; i < n64; i += 64) {
+		accum_05 += _mm512_loadu_ps(&x[i+ 0]) * _mm512_loadu_ps(&y[i+ 0]);
+		accum_15 += _mm512_loadu_ps(&x[i+16]) * _mm512_loadu_ps(&y[i+16]);
+		accum_25 += _mm512_loadu_ps(&x[i+32]) * _mm512_loadu_ps(&y[i+32]);
+		accum_35 += _mm512_loadu_ps(&x[i+48]) * _mm512_loadu_ps(&y[i+48]);
+	}
+
+	/*
+	 * 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 = _mm512_extractf32x8_ps(accum_05, 0) + _mm512_extractf32x8_ps(accum_05, 1);
+	accum_1 = _mm512_extractf32x8_ps(accum_15, 0) + _mm512_extractf32x8_ps(accum_15, 1);
+	accum_2 = _mm512_extractf32x8_ps(accum_25, 0) + _mm512_extractf32x8_ps(accum_25, 1);
+	accum_3 = _mm512_extractf32x8_ps(accum_35, 0) + _mm512_extractf32x8_ps(accum_35, 1))
+
+#endif
+	for (; i < n; i += 32) {
+		accum_0 += _mm256_loadu_ps(&x[i+ 0]) * _mm256_loadu_ps(&y[i+ 0]);
+		accum_1 += _mm256_loadu_ps(&x[i+ 8]) * _mm256_loadu_ps(&y[i+ 8]);
+		accum_2 += _mm256_loadu_ps(&x[i+16]) * _mm256_loadu_ps(&y[i+16]);
+		accum_3 += _mm256_loadu_ps(&x[i+24]) * _mm256_loadu_ps(&y[i+24]);
+	}
+
+	/* we now have the partial sums of the dot product in the 4 accumulation vectors, time to consolidate */
+
+	accum_0 = accum_0 + accum_1 + accum_2 + accum_3;
+
+	__m128 half_accum0;
+
+	/* Add upper half to lower half of each of the 256 bit vector to get a 128 bit vector */
+	half_accum0 = _mm256_extractf128_ps(accum_0, 0) + _mm256_extractf128_ps(accum_0, 1);
+
+	/* in 128 bit land there is a hadd operation to do the rest of the element-wise sum in one go */
+	half_accum0 = _mm_hadd_ps(half_accum0, half_accum0);
+	half_accum0 = _mm_hadd_ps(half_accum0, half_accum0);
+
+	*dot = half_accum0[0];
+}
+
+#else
+#include "sdot_microk_haswell-2.c"
+#endif