It simply doesn’t scale. You can only superoptimize very short runs of code, nowhere anywhere close to even smaller code bases, let alone big ones.

It scales well enough. You can apparently run Souper on SQLite in 24 hours with a beefy machine, according to a talk I recently attended, by one of the developers.

That’s a cool data point, thanks! Though mind that it is a superoptimizer on LLVM bitcode, not on machine code itself, avoiding all the combinatorial explosion of register allocations and probably a bunch of more, but I don’t know enough about the program.