bug#39997: High CPU load and no return value with 3.0.0

[Roel Janssen <roel@gnu.org>]

On Wed, 2020-03-11 at 12:07 +0100, Ludovic Courtès wrote:
> Hi,
> 
> Roel Janssen <roel@gnu.org> skribis:
> 
> > When I use the "md5" module from guile-lib (release 0.2.6.1)
> > together
> > with the following snippet in Guile 3.0.0, it never returns, while
> > on
> > Guile 2.2.6, it returns the MD5 sum of the input string:
> > ---
> > (use-modules (md5))
> > 
> > (define (md5-from-string input)
> >   (call-with-input-string input md5))
> > 
> > (define (random-ascii length)
> >   "Returns a random string of ASCII characters of length LENGTH."
> >   (list->string
> >    (map (lambda _ (integer->char (+ (random 95) 32)))
> >         (iota length))))
> > 
> > (display
> >  (md5-from-string
> >   (random-ascii 32)))
> > ---
> > 
> > Could you point me in the right direction for finding the problem?
> 
> The Guix package has this patch:
> 
>         '(begin
>            ;; Work around miscompilation on Guile 3.0.0 at -O2:
>            ;; <https://bugs.gnu.org/39251>;.
>            (substitute* "src/md5.scm"
>              (("\\(define f-ash ash\\)")
>               "(define f-ash (@ (guile) ash))\n")
>              (("\\(define f-add \\+\\)")
>               "(define f-add (@ (guile) +))\n"))
>            #t)
> 
> It’s very likely that you’re hitting this problem.

Yes!  Thanks for sharing this fix.
I applied the same changes to my code and now I don't encounter the bug
anymore.

I tested the patched code with both guile-2.2 and guile-3.0.  Do you
know whether this will also work with guile-2.0?  (I'd like to keep
things compatible with guile-2.0 for a few more years).

Kind regards,
Roel Janssen