Control Dependencies for Loops

This definition of control dependence is fairly typical, right?


    DEP(x,y) iff !POST-DOM(y,x)
                        and there exists a path P=<x,...,y> such that
                                  for all z in P (except x,y), POST-DOM(y,z)


Consider the following loop:


    while (E) do S;


and the corresponding CFG:


        [START]
              |
              v
            [E]<-+
              | |
              v |
        +-<?> |
        | | |
        | v |
        | [S] |
        | | |
        | +---+
        v
    [END]


The above definition specifies that DEP(<?>,[E]) and DEP(<?>,[S]). But it
seems like I should only be concerned with the dependencies within a
single iteration, so why have DEP(<?>,[E]) at all? Is it only an artifact
of the definition? If I change the definition so that backedges are not
permitted in P, do I shoot myself?


Thanks - John
--
hagerman@ece.cmu.edu
--

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