Mysterious behavior with s8vector and -specialize?

Diego via Chicken-users <[email protected]> Tue, 18 Nov 2025 03:51:32 +0000

Newsgroups	gmane.lisp.scheme.chicken
Message-ID	<72Wj7ifYwx9i7BetKSDTIE-dDUKk_C1pBMP0cdRbo77AP3ZAU0uL5YG3KquKA5Nb0wPR4lxVc_JankHyy0N_wb30PpcGROOEqpNz_MIC35U=@pm.me>

I was testing SRFI-160 with CHICKEN 6 and found some interesting behavior. I bisected the individual -O3 optimizations to debug the behavior, and found -specialize might be the culprit?

Attached is a minimal reproduction example (or at least, as minimal as I could get it). Surprisingly, this behavior only seems to occur with an s8vector; all the other specialized vector types behave as expected as far as I can tell (e.g. replacing s8 with u8 in the example makes the behavior go away).

When I compile it with:

csc test.scm -optimize-leaf-routines -inline -lfa2 -local -inline-global

Then run the "test" program, I see:

0
(move-memory! #s8(1 2 3 4 5) #s8(-16 98 -108 -80 -70 127 0 0 16 0) 5 0 0)
5
(move-memory! #s8(1 2 3 4 5) #s8(1 2 3 4 5 127 0 0 16 0) 5 0 5)
#s8(1 2 3 4 5 1 2 3 4 5)

When I add -specialize to the same command line above, I instead see:

0
(move-memory! #s8(1 2 3 4 5) #s8(-48 -64 -31 -59 -112 127 0 0 16 27) 5 0 0)
2
(move-memory! #s8(1 2 3 4 5) #s8(1 2 3 4 5 127 0 0 16 27) 5 0 2)
#s8(1 2 1 2 3 4 5 0 16 27)

What could be going on here?

Thanks,
Diego

test.scm (text/x-scheme, 1.4 KB)

(module test ()
  (import (scheme base)
          (scheme case-lambda)
          (chicken memory)
          (chicken number-vector)
          (chicken fixnum)
          (chicken base))
  (define (len-sum vecs)
    (if (null? vecs)
        0
        (fx+ (s8vector-length (car vecs))
             (len-sum (cdr vecs)))))

  (define s8vector-copy!
    (case-lambda
      ((to at from)
       (move-memory! from to (fx* 1 (s8vector-length from)) 0 (fx* at 1)))
      ((to at from start)
       (move-memory! from to (fx* 1 (s8vector-length from)) (fx* start 1) (fx* at 1)))
      ((to at from start end)
       (chicken.base#print `(move-memory! ,from ,to
                                          ,(fx* 1 (fx- end start))
                                          ,(fx* start 1)
                                          ,(fx* at 1)))
       (move-memory! from to
                     (fx* 1 (fx- end start))
                     (fx* start 1)
                     (fx* at 1)))))

  (define (s8vector-concatenate vecs)
    (let ((v (make-s8vector (len-sum vecs))))
      (let loop ((vecs vecs) (at 0))
        (unless (null? vecs)
          (let ((vec (car vecs)))
            (print at)
            (s8vector-copy! v at vec 0 (s8vector-length vec))
            (loop (cdr vecs) (fx+ at (s8vector-length vec)))))
        v)))

  (define s5 (s8vector 1 2 3 4 5))
  (print (s8vector-concatenate (list s5 s5))))