Commit: 10a25b655af60ca097177058be9ee2cfb2bf4597
Author: Sergey Sharybin
Date:   Mon Oct 24 16:56:41 2016 +0200
Branches: master
https://developer.blender.org/rB10a25b655af60ca097177058be9ee2cfb2bf4597

Cycles: Add AVX2 path to subsurface triangle intersection

Similar to regular triangle intersection case. Gives about 3% speedup rendering
SSS object on my desktop,

Question: how to avoid such a code duplication in a nice way without speed loss?

===================================================================

M       intern/cycles/kernel/geom/geom_triangle_intersect.h

===================================================================

diff --git a/intern/cycles/kernel/geom/geom_triangle_intersect.h 
b/intern/cycles/kernel/geom/geom_triangle_intersect.h
index b505bd5..8d17e12 100644
--- a/intern/cycles/kernel/geom/geom_triangle_intersect.h
+++ b/intern/cycles/kernel/geom/geom_triangle_intersect.h
@@ -269,6 +269,67 @@ ccl_device_inline void triangle_intersect_subsurface(
        const float4 tri_a = kernel_tex_fetch(__prim_tri_verts, tri_vindex+0),
                     tri_b = kernel_tex_fetch(__prim_tri_verts, tri_vindex+1),
                     tri_c = kernel_tex_fetch(__prim_tri_verts, tri_vindex+2);
+
+#if defined(__KERNEL_AVX2__)
+       const avxf avxf_P(P.m128, P.m128);
+
+       const avxf tri_ab = kernel_tex_fetch_avxf(__prim_tri_verts, tri_vindex 
+ 0);
+       const avxf tri_bc = kernel_tex_fetch_avxf(__prim_tri_verts, tri_vindex 
+ 1);
+
+       const avxf AB = tri_ab - avxf_P;
+       const avxf BC = tri_bc - avxf_P;
+
+       const __m256i permuteMask = _mm256_set_epi32(0x3, kz, ky, kx, 0x3, kz, 
ky, kx);
+
+       const avxf AB_k = shuffle(AB, permuteMask);
+       const avxf BC_k = shuffle(BC, permuteMask);
+
+       /* Akz, Akz, Bkz, Bkz, Bkz, Bkz, Ckz, Ckz */
+       const avxf ABBC_kz = shuffle<2>(AB_k, BC_k);
+
+       /* Akx, Aky, Bkx, Bky, Bkx,Bky, Ckx, Cky */
+       const avxf ABBC_kxy = shuffle<0,1,0,1>(AB_k, BC_k);
+
+       const avxf Sxy(Sy, Sx, Sy, Sx);
+
+       /* Ax, Ay, Bx, By, Bx, By, Cx, Cy */
+       const avxf ABBC_xy = nmadd(ABBC_kz, Sxy, ABBC_kxy);
+
+       float ABBC_kz_array[8];
+       _mm256_storeu_ps((float*)&ABBC_kz_array, ABBC_kz);
+
+       const float A_kz = ABBC_kz_array[0];
+       const float B_kz = ABBC_kz_array[2];
+       const float C_kz = ABBC_kz_array[6];
+
+       /* By, Bx, Cy, Cx, By, Bx, Ay, Ax */
+       const avxf BCBA_yx = permute<3,2,7,6,3,2,1,0>(ABBC_xy);
+
+       const avxf negMask(0,0,0,0,0x80000000, 0x80000000, 0x80000000, 
0x80000000);
+
+       /* W           U                             V
+        * (AxBy-AyBx) (BxCy-ByCx) XX XX (BxBy-ByBx) (CxAy-CyAx) XX XX
+        */
+       const avxf WUxxxxVxx_neg = _mm256_hsub_ps(ABBC_xy * BCBA_yx, negMask /* 
Dont care */);
+
+       const avxf WUVWnegWUVW = permute<0,1,5,0,0,1,5,0>(WUxxxxVxx_neg) ^ 
negMask;
+
+       /* Calculate scaled barycentric coordinates. */
+       float WUVW_array[4];
+       _mm_storeu_ps((float*)&WUVW_array, _mm256_castps256_ps128 
(WUVWnegWUVW));
+
+       const float W = WUVW_array[0];
+       const float U = WUVW_array[1];
+       const float V = WUVW_array[2];
+
+       const int WUVW_mask = 0x7 & _mm256_movemask_ps(WUVWnegWUVW);
+       const int WUVW_zero = 0x7 & 
_mm256_movemask_ps(_mm256_cmp_ps(WUVWnegWUVW,
+                                                      _mm256_setzero_ps(), 0));
+
+       if(!((WUVW_mask == 7) || (WUVW_mask == 0)) && ((WUVW_mask | WUVW_zero) 
!= 7)) {
+               return;
+       }
+#else
        const float3 A = make_float3(tri_a.x - P.x, tri_a.y - P.y, tri_a.z - 
P.z);
        const float3 B = make_float3(tri_b.x - P.x, tri_b.y - P.y, tri_b.z - 
P.z);
        const float3 C = make_float3(tri_c.x - P.x, tri_c.y - P.y, tri_c.z - 
P.z);
@@ -295,6 +356,7 @@ ccl_device_inline void triangle_intersect_subsurface(
        {
                return;
        }
+#endif
 
        /* Calculate determinant. */
        float det = U + V + W;

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