Call function *fn* with *args*:
            name = fn(args...)

def call(self, fn, args, name='', cconv=None, tail=False, fastmath=()):
        """
        Call function *fn* with *args*:
            name = fn(args...)
        """
        inst = instructions.CallInstr(self.block, fn, args, name=name,
                                      cconv=cconv, tail=tail, fastmath=fastmath)
        self._insert(inst)
        return inst