Is this name still correct? Was it ever?

It seems to do optimization and assembly.

There used to be just assemble(C) which takes the compiler and and does all the optimization and assembly. I split out assemble_code_unit (which takes just the c->u and not the whole c) and does most of what used to be in assemble(). So the name was always incorrect (assemble() called the optimizer). I think the reason it was done like this is that assemble() gets called from a number of places in the compiler (lambda, class, module, etc). So it was convenient to have one function that does opt+assemble and returns a code object.

We can rename assemble() and assemble_code_unit(). Any suggestions what to call it? something like instr_sequence_to_code_object()?