Cycles: BVH-related SSE optimization

Several ideas here:

- Optimize calculation of near_{x,y,z} in a way that does not require
  3 if() statements per update, which avoids negative effect of wrong
  branch prediction.

- Optimization of direction clamping for BVH.

- Optimization of point/direction transform.

Brings ~1.5% speedup again depending on a scene (unfortunately, this
speedup can't be sum across all previous commits because speedup of
each of the changes varies from scene to scene, but it still seems to
be nice solid speedup of few percent on Linux and bigger speedup was
reported on Windows).

Once again ,thanks Maxym for inspiration!

Still TODO: We have multiple places where we need to calculate near
x,y,z indices in BVH, for now it's only done for main BVH traversal.
Will try to move this calculation to an utility function and see if
that can be easily re-used across all the BVH flavors.

1 files changed, 18 insertions, 1 deletions

diff --git a/intern/cycles/kernel/geom/geom_object.h b/intern/cycles/kernel/geom/geom_object.h
index c2ec774362a..0e0932512e9 100644
--- a/intern/cycles/kernel/geom/geom_object.h
+++ b/intern/cycles/kernel/geom/geom_object.h
@@ -376,15 +376,32 @@ ccl_device float3 particle_angular_velocity(KernelGlobals *kg, int particle)
 ccl_device_inline float3 bvh_clamp_direction(float3 dir)
 {
 	/* clamp absolute values by exp2f(-80.0f) to avoid division by zero when calculating inverse direction */
-	float ooeps = 8.271806E-25f;
+#if defined(__KERNEL_SSE__) && defined(__KERNEL_SSE2__)
+	const ssef oopes(8.271806E-25f,8.271806E-25f,8.271806E-25f,0.0f);
+	const ssef mask = _mm_cmpgt_ps(fabs(dir),oopes);
+	const ssef signdir = signmsk(dir.m128) | oopes;
+#  ifndef __KERNEL_AVX__
+	ssef res = mask & dir;
+	res = _mm_or_ps(res,_mm_andnot_ps(mask, signdir));
+#  else
+	ssef res = _mm_blendv_ps(signdir,dir,mask);
+#  endif
+	return float3(res);
+#else  /* __KERNEL_SSE__ && __KERNEL_SSE2__ */
+	const float ooeps = 8.271806E-25f;
 	return make_float3((fabsf(dir.x) > ooeps)? dir.x: copysignf(ooeps, dir.x),
 	                   (fabsf(dir.y) > ooeps)? dir.y: copysignf(ooeps, dir.y),
 	                   (fabsf(dir.z) > ooeps)? dir.z: copysignf(ooeps, dir.z));
+#endif  /* __KERNEL_SSE__ && __KERNEL_SSE2__ */
 }
 
 ccl_device_inline float3 bvh_inverse_direction(float3 dir)
 {
+#ifdef __KERNEL_SSE__
+	return rcp(dir);
+#else
 	return 1.0f / dir;
+#endif
 }
 
 /* Transform ray into object space to enter static object in BVH */