That's a fair point (and worth documenting as part of the library), but I'd be much more likely to implement pow(x, x) carefully than switch to a different language or compiler.
I appreciate the library approach and I basically agree with you. If anything, I wanted to point out that a normal general language is so general that adding differentiation into it would be highly costly - just this feature would require that every loop and every conditional return be watched (relative to pow(x,x), an even more challenging example is the Newton's method implementation of a continuous function using a loop).
An alternative would be creating a general purpose language just for this feature - an interesting though rather specialized project.
An alternative would be creating a general purpose language just for this feature - an interesting though rather specialized project.