It is still possible to free a bit more memory by detecting buildin images which are not used by shaders, but that's not going to improve memory usage that much to bother about this now. Such change brings peak memory usage from 4.1GB to 3.4GB when rendering 01_01_01_D layout scene from the Gooseberry project. Mainly because of freeing memory used by rather huge environment map in the viewport. Reviewers: campbellbarton, juicyfruit Subscribers: eyecandy Differential Revision: https://developer.blender.org/D1215