OpenBLAS/kernel/x86_64/ddot_microk_skylakex-2.c

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/* need a new enough GCC for avx512 support */
#ifdef __NVCOMPILER
#define NVCOMPVERS ( __NVCOMPILER_MAJOR__ * 100 + __NVCOMPILER_MINOR__ )
#endif
#if (( defined(__GNUC__)  && __GNUC__   > 6 && defined(__AVX2__)) || (defined(__clang__) && __clang_major__ >= 6)) || ( defined(__NVCOMPILER) && NVCOMPVERS >= 2203 )

#define HAVE_KERNEL_8 1

#include <immintrin.h>

static void ddot_kernel_8( BLASLONG n, FLOAT *x, FLOAT *y, FLOAT *dot)
{
	int i = 0;
	__m256d accum_0, accum_1, accum_2, accum_3;
	
	accum_0 = _mm256_setzero_pd();
	accum_1 = _mm256_setzero_pd();
	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 = _mm512_extractf64x4_pd(accum_05, 0) + _mm512_extractf64x4_pd(accum_05, 1);
	accum_1 = _mm512_extractf64x4_pd(accum_15, 0) + _mm512_extractf64x4_pd(accum_15, 1);
	accum_2 = _mm512_extractf64x4_pd(accum_25, 0) + _mm512_extractf64x4_pd(accum_25, 1);
	accum_3 = _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_3 += _mm256_loadu_pd(&x[i+12]) * _mm256_loadu_pd(&y[i+12]);
	}

	/* 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;

	__m128d half_accum0;

	/* Add upper half to lower half of each of the 256 bit vector to get a 128 bit vector */
	half_accum0 = _mm_add_pd(_mm256_extractf128_pd(accum_0, 0), _mm256_extractf128_pd(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_pd(half_accum0, half_accum0);

	*dot = half_accum0[0];
}

#else
#include "ddot_microk_haswell-2.c"
#endif