Does jax.grad involves jaxpr conversion? If so, how?

[riven314]

For more context of this question, it actually extends from another discussion happened here:

I noticed unlike other function transformations (e.g. jax.vmap, jax.jit), jax.grad is traced by concrete tracer because it has to handle the case of value-based control flow, e.g.:

import jax

def f(x):
  if x < 0:
    return 0.0
  return x ** 2

print(jax.grad(f)(1.0))

Meanwhile, I learned from the above discussion that jaxpr has to be converted by abstract tracer. It leads me to wonder:

1. whether jax.grad transformation involves jaxpr?
2. if so, how jaxpr is produced in this case given jax.grad is traced by a concrete tracer instead of an abstract tracer?