(once-only ((n-tail `(block-info
(component-tail
(block-component ,n-first)))))
`(do ((,block-var (block-info ,n-first)
(ir2-block-next ,block-var)))
((or (eq ,block-var ,n-tail)
(once-only ((n-tail `(block-info
(component-tail
(block-component ,n-first)))))
`(do ((,block-var (block-info ,n-first)
(ir2-block-next ,block-var)))
((or (eq ,block-var ,n-tail)