'Request the assignment of the next available stack variable
for block *outgoing_block* with target name *phiname*.'

def request_outgoing(self, outgoing_block, phiname, stack_index):

    if (phiname in self.outgoing_phis):
        return
    if (stack_index < self.stack_offset):
        assert self.incoming_blocks
        for ib in self.incoming_blocks:
            ib.request_outgoing(self, phiname, stack_index)
    else:
        varname = self.stack[(stack_index - self.stack_offset)]
        self.outgoing_phis[phiname] = varname
