Merge pull request #10468 from fenrus75:avx512-2

* Add a 512 bit codepath to the AVX512 fastConv function

this patch adds a 512 wide codepath to the fastConv() function for
AVX512 use.
The basic idea is to process the first N * 16 elements of the vector
with avx512, and then run the rest of the vector using the traditional
AVX2 codepath.

* dnn: use unaligned AVX512 load (OpenCV aligns data on 32-byte boundary)

* dnn: change "vecsize" condition for AVX512

* dnn: fix indentation

modules/dnn/src/layers/layers_common.simd.hpp

@@ -112,6 +112,7 @@ void fastConv( const float* weights, size_t wstep, const float* bias,
         int j = 0;
         for( ; j <= blockSize - 4; j += 4 )
         {
+            int k = 0;
             const float* rptr = rowbuf + j*vecsize_aligned;
 
             __m256 vs00 = _mm256_setzero_ps(), vs01 = _mm256_setzero_ps(),
@@ -121,7 +122,65 @@ void fastConv( const float* weights, size_t wstep, const float* bias,
                    vs20 = _mm256_setzero_ps(), vs21 = _mm256_setzero_ps(),
                    vs22 = _mm256_setzero_ps(), vs23 = _mm256_setzero_ps();
 
-            for( int k = 0; k < vecsize; k += 8, rptr += 8 )
+#if CV_AVX512_SKX // AVX512VL is necessary to avoid register spilling
+            if (vecsize >= 32)
+            {
+                __m512 vs00_5 = _mm512_setzero_ps(), vs01_5 = _mm512_setzero_ps(),
+                       vs02_5 = _mm512_setzero_ps(), vs03_5 = _mm512_setzero_ps(),
+                       vs10_5 = _mm512_setzero_ps(), vs11_5 = _mm512_setzero_ps(),
+                       vs12_5 = _mm512_setzero_ps(), vs13_5 = _mm512_setzero_ps(),
+                       vs20_5 = _mm512_setzero_ps(), vs21_5 = _mm512_setzero_ps(),
+                       vs22_5 = _mm512_setzero_ps(), vs23_5 = _mm512_setzero_ps();
+
+                for (; k <= vecsize - 16; k += 16, rptr += 16)
+                {
+                    __m512 w0 = _mm512_loadu_ps(wptr0 + k);
+                    __m512 w1 = _mm512_loadu_ps(wptr1 + k);
+                    __m512 w2 = _mm512_loadu_ps(wptr2 + k);
+                    __m512 r0 = _mm512_loadu_ps(rptr);
+
+                    vs00_5 = _mm512_fmadd_ps(w0, r0, vs00_5);
+                    vs10_5 = _mm512_fmadd_ps(w1, r0, vs10_5);
+                    vs20_5 = _mm512_fmadd_ps(w2, r0, vs20_5);
+
+                    r0 = _mm512_loadu_ps(rptr + vecsize_aligned);
+                    vs01_5 = _mm512_fmadd_ps(w0, r0, vs01_5);
+                    vs11_5 = _mm512_fmadd_ps(w1, r0, vs11_5);
+                    vs21_5 = _mm512_fmadd_ps(w2, r0, vs21_5);
+
+                    r0 = _mm512_loadu_ps(rptr + vecsize_aligned*2);
+                    vs02_5 = _mm512_fmadd_ps(w0, r0, vs02_5);
+                    vs12_5 = _mm512_fmadd_ps(w1, r0, vs12_5);
+                    vs22_5 = _mm512_fmadd_ps(w2, r0, vs22_5);
+
+                    r0 = _mm512_loadu_ps(rptr + vecsize_aligned*3);
+                    vs03_5 = _mm512_fmadd_ps(w0, r0, vs03_5);
+                    vs13_5 = _mm512_fmadd_ps(w1, r0, vs13_5);
+                    vs23_5 = _mm512_fmadd_ps(w2, r0, vs23_5);
+                }
+                /*
+                 * now fold the 512 bit accumulator vectors into 256 bit vectors so that the AVX2 code can finish
+                 * the tail of the vector
+                 */
+                vs00 = _mm256_add_ps( _mm512_extractf32x8_ps(vs00_5, 0), _mm512_extractf32x8_ps(vs00_5, 1));
+                vs10 = _mm256_add_ps( _mm512_extractf32x8_ps(vs10_5, 0), _mm512_extractf32x8_ps(vs10_5, 1));
+                vs20 = _mm256_add_ps( _mm512_extractf32x8_ps(vs20_5, 0), _mm512_extractf32x8_ps(vs20_5, 1));
+
+                vs01 = _mm256_add_ps( _mm512_extractf32x8_ps(vs01_5, 0), _mm512_extractf32x8_ps(vs01_5, 1));
+                vs11 = _mm256_add_ps( _mm512_extractf32x8_ps(vs11_5, 0), _mm512_extractf32x8_ps(vs11_5, 1));
+                vs21 = _mm256_add_ps( _mm512_extractf32x8_ps(vs21_5, 0), _mm512_extractf32x8_ps(vs21_5, 1));
+
+                vs02 = _mm256_add_ps( _mm512_extractf32x8_ps(vs02_5, 0), _mm512_extractf32x8_ps(vs02_5, 1));
+                vs12 = _mm256_add_ps( _mm512_extractf32x8_ps(vs12_5, 0), _mm512_extractf32x8_ps(vs12_5, 1));
+                vs22 = _mm256_add_ps( _mm512_extractf32x8_ps(vs22_5, 0), _mm512_extractf32x8_ps(vs22_5, 1));
+
+                vs03 = _mm256_add_ps( _mm512_extractf32x8_ps(vs03_5, 0), _mm512_extractf32x8_ps(vs03_5, 1));
+                vs13 = _mm256_add_ps( _mm512_extractf32x8_ps(vs13_5, 0), _mm512_extractf32x8_ps(vs13_5, 1));
+                vs23 = _mm256_add_ps( _mm512_extractf32x8_ps(vs23_5, 0), _mm512_extractf32x8_ps(vs23_5, 1));
+            }
+#endif
+
+            for (; k < vecsize; k += 8, rptr += 8 )
             {
                 __m256 w0 = _mm256_load_ps(wptr0 + k);
                 __m256 w1 = _mm256_load_ps(wptr1 + k);