Data flow equations to determine value dependencies
Well, it seems that this can be reduced to the Reaching Definition problem, who's equations are:

$REACH_{in}(S) = \bigcup_{p \in pred(S)} REACH_{out}(p)$ 

$REACH_{out}(S) = GEN(S) \cup (REACH_{in}(S) - KILL(S))$

$GEN[d: y \rightarrow f(x_1, .., x_n)] = {d}$ 

$KILL[d: y \rightarrow f(x_1, .., x_n)] =DEFS(y) - {d}$