Traditionally, the graph fuser in PyTorch has been operating on a per-Block basis. This is inherited (at least it used to a few weeks ago) by the CustomFuseGraph.
PyTorch TVM (and probably also glow) are interested in fusing across blocks, e.g. to also fuse control flow nodes. This is why PyTorch TVM has switched away from CustomFuseGraph 12. Personally, I would expect that custom fusion mechanism will be folded back into PyTorch when the picture of what users need there becomes clearer (just like CustomFuseGraph was introduced when one thought that one could also make good use of that, I think I recall that originally we thought that the CustomFuseGraph might already work for PyTorch TVM).
Best regards
Thomas