Function reaches 

fn reaches<'gcx>(
    gcx: Gcx<'gcx>,
    bases: &'gcx [ContractId],
    fid: FunctionId,
    hit: impl FnMut(&'gcx Expr<'gcx>) -> bool,
) -> bool

True if hit matches an expression in fid’s body or, transitively, in the body of any internal function it calls.