Correctly split AO to not affect emissive in forward

com.unity.render-pipelines.high-definition/HDRP/Material/Lit/Lit.hlsl

     // RT3 - 11f:11f:10f
     // In deferred we encode emissive color with bakeDiffuseLighting. We don't have the room to store emissiveColor.
     // It mean that any futher process that affect bakeDiffuseLighting will also affect emissiveColor, like SSAO for example.
-    outGBuffer3 = float4(builtinData.bakeDiffuseLighting + builtinData.emissiveColor, 0.0);
-
+    // Also if we don't have the room to store AO, then we apply it at this time on bakeDiffuseLighting which will cause a double occlusion with SSAO
+    outGBuffer3 = float4(builtinData.bakeDiffuseLighting + builtinData.emissiveColor, 0.0);
+#else
+    outGBuffer3 = float4(builtinData.bakeDiffuseLighting * surfaceData.ambientOcclusion + builtinData.emissiveColor, 0.0);
 #endif
 
 #ifdef SHADOWS_SHADOWMASK
     GBufferType2 inGBuffer2 = LOAD_TEXTURE2D(_GBufferTexture2, positionSS);
 
     // BuiltinData
-    builtinData.bakeDiffuseLighting = LOAD_TEXTURE2D(_GBufferTexture3, positionSS).rgb;  // This also contain emissive
+    builtinData.bakeDiffuseLighting = LOAD_TEXTURE2D(_GBufferTexture3, positionSS).rgb;  // This also contain emissive (and * AO if no lightlayers)
 
     // Avoid to introduce a new variant for light layer as it is already long to compile
     if (_EnableLightLayers)
     }
 
     // Premultiply bake diffuse lighting information with DisneyDiffuse pre-integration
-    return builtinData.bakeDiffuseLighting * preLightData.diffuseFGD * surfaceData.ambientOcclusion * bsdfData.diffuseColor;
+    return builtinData.bakeDiffuseLighting * preLightData.diffuseFGD * bsdfData.diffuseColor;
 }
 
 //-----------------------------------------------------------------------------

com.unity.render-pipelines.high-definition/HDRP/Material/MaterialEvaluation.hlsl

 
 void ApplyAmbientOcclusionFactor(AmbientOcclusionFactor aoFactor, inout BuiltinData builtinData, inout AggregateLighting lighting)
 {
-    // Note: in case of deferred Lit, builtinData.bakeDiffuseLighting contain indirect diffuse + emissive,
-    // so Ambient occlusion is multiply by emissive which is incorrect but we accept the tradeoff
+    // Note: in case of deferred Lit, builtinData.bakeDiffuseLighting contain indirect diffuse * surfaceData.ambientOcclusion + emissive,
+    // so emissive is affected by SSAO and we get a double darkening from SSAO and from AO which is incorrect but we accept the tradeoff
     builtinData.bakeDiffuseLighting *= aoFactor.indirectAmbientOcclusion;
     lighting.indirect.specularReflected *= aoFactor.indirectSpecularOcclusion;
     lighting.direct.diffuse *= aoFactor.directAmbientOcclusion;

com.unity.render-pipelines.high-definition/HDRP/Material/StackLit/StackLit.hlsl

 
     // Premultiply bake diffuse lighting information
     // preLightData.diffuseEnergy will be 1,1,1 if no vlayering or no VLAYERED_DIFFUSE_ENERGY_HACKED_TERM
-    return builtinData.bakeDiffuseLighting * preLightData.diffuseFGD * preLightData.diffuseEnergy * surfaceData.ambientOcclusion * bsdfData.diffuseColor;
+    return builtinData.bakeDiffuseLighting * preLightData.diffuseFGD * preLightData.diffuseEnergy * bsdfData.diffuseColor;
 }