Use ShouldOutputSplitLighting() for material abstraction

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Deferred.shader

                 Outputs outputs;
 
             #ifdef OUTPUT_SPLIT_LIGHTING
-                if (HasFeatureFlag(bsdfData.materialFeatures, MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING))
+                if (_EnableSubsurfaceScattering != 0 && ShouldOutputSplitLighting(bsdfData))
                 {
                     outputs.specularLighting = float4(specularLighting, 1.0);
                     outputs.diffuseLighting  = TagLightingForSSS(diffuseLighting);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/Deferred.compute

     float3 specularLighting;
     LightLoop(V, posInput, preLightData, bsdfData, bakeLightingData, featureFlags, diffuseLighting, specularLighting);
 
-    if (HasFeatureFlag(bsdfData.materialFeatures, MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING))
+    if (_EnableSubsurfaceScattering != 0 && ShouldOutputSplitLighting(bsdfData))
     {
         specularLightingUAV[pixelCoord] = float4(specularLighting, 1.0);
         diffuseLightingUAV[pixelCoord]  = TagLightingForSSS(diffuseLighting);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.hlsl

     /* 26 */ LIGHT_FEATURE_MASK_FLAGS_OPAQUE | MATERIAL_FEATURE_MASK_FLAGS, // Catch all case with MATERIAL_FEATURE_MASK_FLAGS is needed in case we disable material classification
 };
 
+// Additional bits set in 'bsdfData.materialFeatures' to save registers and simplify feature tracking.
 #define MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING         ((MATERIAL_FEATURE_MASK_FLAGS + 1) << 0)
 #define MATERIAL_FEATURE_FLAGS_SSS_TEXTURING_MODE_OFFSET FastLog2((MATERIAL_FEATURE_MASK_FLAGS + 1) << 1) // 2 bits
 #define MATERIAL_FEATURE_FLAGS_TRANSMISSION_MODE_THIN            ((MATERIAL_FEATURE_MASK_FLAGS + 1) << 3)
     bsdfData.diffusionProfile = diffusionProfile;
     bsdfData.fresnel0 = _TransmissionTintsAndFresnel0[diffusionProfile].a;
     bsdfData.subsurfaceMask = subsurfaceMask;
-    bsdfData.materialFeatures |= (_EnableSubsurfaceScattering != 0) ? MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING : 0;
+    bsdfData.materialFeatures |= MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING;
     bsdfData.materialFeatures |= GetSubsurfaceScatteringTexturingMode(bsdfData.diffusionProfile) << MATERIAL_FEATURE_FLAGS_SSS_TEXTURING_MODE_OFFSET;
 }
 
 // Subsurface Scattering functions
 //-----------------------------------------------------------------------------
 
-bool PixelHasSubsurfaceScattering(BSDFData bsdfData)
+bool ShouldOutputSplitLighting(BSDFData bsdfData)
-    // bsdfData.subsurfaceMask != 0 allow if sss is enabled for this pixels (i.e like per pixels feature) as in deferred case MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING alone is not sufficient
-    // but keep testing MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING for forward case
-    return bsdfData.diffusionProfile != DIFFUSION_PROFILE_NEUTRAL_ID && bsdfData.subsurfaceMask != 0 && HasFeatureFlag(bsdfData.materialFeatures, MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING);
+    return HasFeatureFlag(bsdfData.materialFeatures, MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING);
 }
 
 //-----------------------------------------------------------------------------

ScriptableRenderPipeline/HDRenderPipeline/HDRP/ShaderPass/ShaderPassForward.hlsl

         LightLoop(V, posInput, preLightData, bsdfData, bakeLightingData, featureFlags, diffuseLighting, specularLighting);
 
 #ifdef OUTPUT_SPLIT_LIGHTING
-        if (HasFeatureFlag(bsdfData.materialFeatures, MATERIAL_FEATURE_FLAGS_SSS_OUTPUT_SPLIT_LIGHTING))
+        if (_EnableSubsurfaceScattering != 0 && ShouldOutputSplitLighting(bsdfData))
         {
             outColor = float4(specularLighting, 1.0);
             outDiffuseLighting = float4(TagLightingForSSS(diffuseLighting), 1.0);