Optimize the computation of 'NdotL' during importance sampling

Assets/ScriptableRenderLoop/ShaderLibrary/ImageBasedLighting.hlsl

 
 void ImportanceSampleCosDir(float2   u,
                             float3x3 localToWorld,
-                        out float3   L)
+                        out float3   L,
+                        out float    NdotL)
 {
     // Cosine sampling - ref: http://www.rorydriscoll.com/2009/01/07/better-sampling/
     float cosTheta = sqrt(saturate(1.0 - u.x));
-    L = SphericalToCartesian(phi, sinTheta, cosTheta);
-    L = mul(L, localToWorld);
+    float3 localL = SphericalToCartesian(phi, sinTheta, cosTheta);
+
+    NdotL = localL.z;
+
+    L = mul(localL, localToWorld);
 }
 
 void ImportanceSampleGGXDir(float2   u,
                         out float3   L,
+                        out float    NdotL,
                         out float    NdotH,
                         out float    VdotH,
                             bool     VeqN = false)
         VdotH  = saturate(dot(localV, localH));
     }
 
-    // Compute { L = reflect(-localV, localH) }
-    L = -localV + 2.0 * VdotH * localH;
+    // Compute { localL = reflect(-localV, localH) }
+    float3 localL = -localV + 2.0 * VdotH * localH;
-    L = mul(L, localToWorld);
+    NdotL = localL.z;
+
+    L = mul(localL, localToWorld);
 }
 
 // ref: http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_notes_v3.pdf p26
                          out float    NdotL,
                          out float    weightOverPdf)
 {
-    ImportanceSampleCosDir(u, localToWorld, L);
-
-    NdotL = saturate(dot(localToWorld[2], L));
+    ImportanceSampleCosDir(u, localToWorld, L, NdotL);
 
     // Importance sampling weight for each sample
     // pdf = N.L / PI
                      out float    NdotL,
                      out float    weightOverPdf)
 {
-    float3 H;
-    float  NdotH;
-    ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotH, VdotH);
-
-    NdotL = saturate(dot(localToWorld[2], L));
+    float NdotH;
+    ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotL, NdotH, VdotH);
 
     // Importance sampling weight for each sample
     // pdf = D(H) * (N.H) / (4 * (L.H))
         u.x = lerp(u.x, 0.0, bias);
 
         float3 L;
-        float  NdotH, VdotH;
-        ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotH, VdotH, true);
-
-        float NdotL = saturate(dot(N, L));
+        float  NdotL, NdotH, VdotH;
+        ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotL, NdotH, VdotH, true);
 
         float mipLevel;