[CM] [PATCH] s7: fix stale opt1_lambda cache for a thunk parameter in recursion

[jinser]

Deal all,

Found an s7 bug at commit 915300e: an immediate lambda application
whose argument
closes over the caller's parameter loops forever

  (define (f form)
    ((lambda (recurse) (recurse))
     (lambda () (if (pair? form) (f (car form)) form))))
  (f '(a))    ; expected 'a, actually never terminates

For better debugging, I made a repro that output correct or wrong
message instead of loops forever

(define *calls* 0)
(define *limit* 20)

(define (guard! who)
  (set! *calls* (+ *calls* 1))
  (when (> *calls* *limit*)
    (error (string-append "s7 bug: unbounded re-invocation in " who))))

(define f (lambda (form)
            (guard! "f")
            ((lambda (recurse) (recurse))
             (lambda () (if (pair? form) (f (car form)) form)))))

(display "bug-pattern: ") (display (f '(a))) (newline)
(display "calls (expected 2): ") (display *calls*) (newline)
(display "done") (newline)

And s7 got "s7 bug: unbounded re-invocation in f", while Guile and
Chez got the correct answer "2".


I've attached a patch that is trying to fix the issue. I found the
issue caused by the closure_is_* fast-path shortcut.
I hope I handled it correctly and that it helps.

-- 
regards,
Jinser Kafka.
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