FWIW, I have made a quick attempt at removing the f->f_lasti assignment
in the few places where it could be removed, but it didn't make a
difference on my machine. The problem being that there are very few
places where it is legitimate to remove the assignment (even a call to
Py_DECREF can invoke arbitrary external code through destructors, so
even a very simple opcode such as POP_TOP needs the f->f_lasti assignment).

Another approach would be to create agregate opcodes, e.g.
BINARY_ADD_FAST would combine LOAD_FAST and BINARY_ADD. That's
orthogonal to the current issue though.