Not sure what a "superoptimizer" would look like in this context. For a reference, I know for sure that this https://github.com/giaf/blasfeo (which beats Intel MKL) was coded entirely by hand.
There is more and more effort in the automatic development of high-performance linear algebra kernels.
But based on my experience, it would certainly be a big challenge to have a tool able to exploit the subtle differences in the assembly languages of different architectures, if the aim is to match or even exceed an expert-crafted assembly kernel.
Anyway, that's surely a very promising active research direction.
Anyway, that's surely a very promising active research direction.