'Build a Data Flow Grah (DFG) for every basic block of a CFG
The DFGs are available in the dict self.dfgs where the key
is a basic block addr and the value a DFG.
:param cfg: A CFG used to get all the basic blocks
:param annocfg: An AnnotatedCFG built from a backward slice used to only build the DFG on the whitelisted statements'

def __init__(self, cfg=None, annocfg=None):

    if (cfg is None):
        self._cfg = self.project.analyses.CFGAccurate()
    else:
        self._cfg = cfg
    self._annocfg = annocfg
    self.dfgs = self._construct()
