Small example:

% cat rec.ml
let[@zero_alloc] rec f x = 1 + g (x * 2)
and[@zero_alloc] g x = 2 + f (x - 3)

let bar x = x + 1
% cat rec.mli
val bar : int -> int

(If we want to go ahead with something like this, @Gbury should look at the dataflow-related part of this PR to make sure it matches the specification above.)

As said some time ago on slack: the current code seems okay (for the data flow part at least), but it's not great to run the whole data_flow analysis twice. Instead I'd prefer if only the reachability analysis part of the flow analysis was run twice.

@gretay-js what should we do with this?