Add AVX2 version of ConvolveVertically

src/opts/SkBitmapFilter_opts.h

Index: src/opts/SkBitmapFilter_opts.h
diff --git a/src/opts/SkBitmapFilter_opts.h b/src/opts/SkBitmapFilter_opts.h
index f22b5c2368050681f6979fe08dfaeeec8405c6ca..9238f419afcc92b75b68bcca804a59803032e170 100644
--- a/src/opts/SkBitmapFilter_opts.h
+++ b/src/opts/SkBitmapFilter_opts.h
@@ -11,14 +11,118 @@
 #include "SkConvolver.h"
 
 #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
-    #include <emmintrin.h>
+    #include <immintrin.h>
 #elif defined(SK_ARM_HAS_NEON)
     #include <arm_neon.h>
 #endif
 
 namespace SK_OPTS_NS {
 
-#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
+#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_AVX2
+
+    static SK_ALWAYS_INLINE
+    void compute_coefficient_row(SkConvolutionFilter1D::ConvolutionFixed filterValue, const unsigned char* sourceDataRows,
+                               __m256i* accum01, __m256i* accum23, __m256i* accum45, __m256i* accum67) {
+        __m256i coefs = _mm256_set1_epi16(filterValue);
+        __m256i pixels = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(sourceDataRows));
+        __m256i zero = _mm256_setzero_si256();
+
+        // [16] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+        __m256i pixels_0123_16bit = _mm256_unpacklo_epi8(pixels, zero);
+
+        __m256i scaled_0123_hi = _mm256_mulhi_epi16(pixels_0123_16bit, coefs),
+                scaled_0123_lo = _mm256_mullo_epi16(pixels_0123_16bit, coefs);
+
+        // [32] c*a1 c*b1 c*g1 c*r1 c*a0 c*b0 c*g0 c*r0
+        *accum01 = _mm256_add_epi32(*accum01, _mm256_unpacklo_epi16(scaled_0123_lo, scaled_0123_hi));
+        // [32] c*a3 c*b3 c*g3 c*r3 c*a2 c*b2 c*g2 c*r2
+        *accum23 = _mm256_add_epi32(*accum23, _mm256_unpackhi_epi16(scaled_0123_lo, scaled_0123_hi));
+
+        // [16] a7 b7 g7 r7 a6 b6 g6 r6 a5 b5 g5 r5 a4 b4 g4 r4
+        __m256i pixels_4567_16bit = _mm256_unpackhi_epi8(pixels, zero);
+
+        __m256i scaled_4567_hi = _mm256_mulhi_epi16(pixels_4567_16bit, coefs),
+                scaled_4567_lo = _mm256_mullo_epi16(pixels_4567_16bit, coefs);
+
+        // [32] c*a5 c*b5 c*g5 c*r5 c*a4 c*b4 c*g4 c*r4
+        *accum45 = _mm256_add_epi32(*accum45, _mm256_unpacklo_epi16(scaled_4567_lo, scaled_4567_hi));
+        // [32] c*a7 c*b7 c*g7 c*r7 c*a6 c*b6 c*g6 c*r6
+        *accum67 = _mm256_add_epi32(*accum67, _mm256_unpackhi_epi16(scaled_4567_lo, scaled_4567_hi));
+    }
+
+    template<bool hasAlpha>
+    void ConvolveVertically(const SkConvolutionFilter1D::ConvolutionFixed* filterValues,
+                            int filterLength,
+                            unsigned char* const * sourceDataRows,
+                            int pixelWidth,
+                            unsigned char* outRow) {
+        // Output eight pixels per iteration (32 bytes).
+        for (int outX = 0; outX < pixelWidth; outX += 8) {
+            // Accumulated result for each pixel. 32 bits per RGBA channel.
+            __m256i accum01 = _mm256_setzero_si256();
+            __m256i accum23 = _mm256_setzero_si256();
+            __m256i accum45 = _mm256_setzero_si256();
+            __m256i accum67 = _mm256_setzero_si256();
+
+            // Convolve with 4 filter coefficient per iteration.
+            int length = filterLength & ~3;
+            for (int filterY = 0; filterY < length; filterY += 4) {
+                compute_coefficient_row(filterValues[filterY + 0], sourceDataRows[filterY + 0] + outX * 4, &accum01, &accum23, &accum45, &accum67);
+                compute_coefficient_row(filterValues[filterY + 1], sourceDataRows[filterY + 1] + outX * 4, &accum01, &accum23, &accum45, &accum67);
+                compute_coefficient_row(filterValues[filterY + 2], sourceDataRows[filterY + 2] + outX * 4, &accum01, &accum23, &accum45, &accum67);
+                compute_coefficient_row(filterValues[filterY + 3], sourceDataRows[filterY + 3] + outX * 4, &accum01, &accum23, &accum45, &accum67);
+            }
+            for (int filterY = length; filterY < filterLength; filterY++) {
+                compute_coefficient_row(filterValues[filterY], sourceDataRows[filterY] + outX * 4, &accum01, &accum23, &accum45, &accum67);
+            }
+
+            // Shift right for fixed point implementation.
+            accum01 = _mm256_srai_epi32(accum01, SkConvolutionFilter1D::kShiftBits);
+            accum23 = _mm256_srai_epi32(accum23, SkConvolutionFilter1D::kShiftBits);
+            accum45 = _mm256_srai_epi32(accum45, SkConvolutionFilter1D::kShiftBits);
+            accum67 = _mm256_srai_epi32(accum67, SkConvolutionFilter1D::kShiftBits);
+
+            // Packing 32 bits |accum| to 16 bits per channel (signed saturation).
+            // [16] a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+            __m256i accum_0123 = _mm256_packs_epi32(accum01, accum23);
+
+            // Packing 32 bits |accum| to 16 bits per channel (signed saturation).
+            // [16] a7 b7 g7 r7 a6 b6 g6 r6 a5 b5 g5 r5 a4 b4 g4 r4
+            __m256i accum_4567 = _mm256_packs_epi32(accum45, accum67);
+
+            // Packing 16 bits |accum| to 8 bits per channel (unsigned saturation).
+            //  [8] a7 b7 g7 r7 a6 b6 g6 r6 a5 b5 g5 r5 a4 b4 g4 r4 a3 b3 g3 r3 a2 b2 g2 r2 a1 b1 g1 r1 a0 b0 g0 r0
+            __m256i accum = _mm256_packus_epi16(accum_0123, accum_4567);
+
+            if (hasAlpha) {
+                // Make sure the value of alpha channel is always larger than maximum
+                // value of color channels.
+                // If alpha is less than r, g, or b, set it to their max.
+                __m256i max_rg  = _mm256_max_epu8( accum, _mm256_srli_epi32(accum,  8));
+                __m256i max_rgb = _mm256_max_epu8(max_rg, _mm256_srli_epi32(accum, 16));
+                accum = _mm256_max_epu8(accum, _mm256_slli_epi32(max_rgb, 24));
+            } else {
+                // Force opaque.
+                accum = _mm256_or_si256(accum, _mm256_set1_epi32(0xff000000));
+            }
+
+            // Store the convolution result (32 bytes) and advance the pixel pointers.
+            // During the last iteration, when pixels left are less than 8, store them one at a time.
+            if (outX + 8 <= pixelWidth) {
+                _mm256_storeu_si256(reinterpret_cast<__m256i *>(outRow), accum);
+                outRow += 32;
+            } else {
+                for (int i = outX; i < pixelWidth; i++) {
+                    *(reinterpret_cast<int*>(outRow)) = _mm_cvtsi128_si32(_mm256_castsi256_si128(accum));
+                    __m256i rotate = _mm256_setr_epi32(1, 2, 3, 4, 5, 6, 7, 0);
+                    accum = _mm256_permutevar8x32_epi32(accum, rotate);
+                    outRow += 4;
+                }
+            }
+        }
+    }
+
+#elif SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
 
     static SK_ALWAYS_INLINE void AccumRemainder(const unsigned char* pixelsLeft,
             const SkConvolutionFilter1D::ConvolutionFixed* filterValues, __m128i& accum, int r) {