The main change is avoid storage of redundant data in the subdivision
draw cache, mainly by replacing reverse lookup from subdivided edge to
coarse edge. This way loops are structured as iteration over coarse
edges instead of iteration over subdivided edges with optional behavior
for vertices with matching base mesh faces. With that inversion the
information in the draw cache is trivial (or duplicated from an array
in `MeshRenderData`), so it's all removed, except for the subdivided
loose edge positions. That array is also shrunk though, by not
duplicating positions in between each subdivided edge. Its calculation
is more efficient for the same reason too.
Overall, besides code simplification, the effect should be lower
overhead with loose edges with GPU subdivision. Admittedly this isn't
a very important use case, but it's part of a general refactor trying
to use better data oriented design in this area (#116901).
Pull Request: https://projects.blender.org/blender/blender/pulls/122071
d93b27a12e