Algorithm

The C-Breeze framework is implemented by the dataflow methods on each AST node class. Each dataflow method implements the dataflow semantics of the particular C language construct of the node. For example, the following code shows the dataflow method for the ifelseNode (note that this is only the forward case):

void ifelseNode::dataflow(FlowVal * v, FlowProblem & fp)
{
  if (fp.forward()) {
    fp.flow_ifelse(v, this, FlowProblem::Entry);

    if (expr())
      expr()->dataflow(v, fp);
    FlowVal * fv = v->clone();
    if (true_br())
      true_br()->dataflow(v, fp);
    if (false_br())
      false_br()->dataflow(fv, fp);
    v->meet(fv);
    delete fv;

    fp.flow_ifelse(v, this, FlowProblem::Exit);
  }
}

The method flow_ifelse is the transfer function that you define. Note that many constructs have a no-op transfer function, which is the default. The transfer function is called before the construct is processed (the ``entry'' point) and after the construct is processed (the ``exit'' point). The transfer function needs to distinguish between these two cases so that it does not accidentally exert it's effects twice.

After calling the entry transfer function, the method calls dataflow on the conditional expression. The two branches of the if-else are modeled by cloning the flow value and passing the two independent values through the true and false branches separately. The two different control paths may yield different resulting flow values, so the meet method of FlowVal is called to reconcile them. Finally, the transfer function is called again.

The top-most call to dataflow should be made on a procNode (although this is not strictly necessary, it makes the most sense). When the call returns, one pass of the analysis over the procedure is complete. The framework repeats passes until the flow values no longer change. It than makes one more pass over the procedure to allow the resulting dataflow information to be used or stored.