Find all killers to the specified variable definition.

        :param ProgramVariable var_def: The variable definition.
        :param bool simplified_graph: True if we want to search in the simplified graph, False otherwise.
        :return: A collection of all killers to the specified variable definition.
        :rtype: list

def find_killers(self, var_def, simplified_graph=True):
        """
        Find all killers to the specified variable definition.

        :param ProgramVariable var_def: The variable definition.
        :param bool simplified_graph: True if we want to search in the simplified graph, False otherwise.
        :return: A collection of all killers to the specified variable definition.
        :rtype: list
        """

        if simplified_graph:
            graph = self.simplified_data_graph
        else:
            graph = self.data_graph

        if var_def not in graph:
            return []

        killers = []
        out_edges = graph.out_edges(var_def, data=True)
        for _, dst, data in out_edges:
            if 'type' in data and data['type'] == 'kill':
                killers.append(dst)

        return killers