[Cocci] continue statement of death?

[David Young <dyoung@netbsd.org>]

Today I built and installed Coccinelle 1.0.7 on NetBSD.

I am processing this fragment of NetBSD kernel code, `tbr_timeout.c`,

| /*
|  * tbr_timeout goes through the interface list, and kicks the drivers
|  * if necessary.
|  */
| static void
| tbr_timeout(void *arg)
| {
|         struct ifnet *ifp;
|         int active, s;
| 
|         active = 0;
|         s = splnet();
|         for (ifp = TAILQ_FIRST(&ifnet); ifp; ifp = TAILQ_NEXT(ifp, if_list)) {
|                 if (!TBR_IS_ENABLED(&ifp->if_snd))
| #if 1
|                         continue;
| #endif
|                 active++;
|                 if (!IFQ_IS_EMPTY(&ifp->if_snd) && ifp->if_start != NULL)
|                         (*ifp->if_start)(ifp);
|         }
|         splx(s);
|         if (active > 0)
|                 CALLOUT_RESET(&tbr_callout, 1, tbr_timeout, NULL);
|         else
|                 tbr_timer = 0;  /* don't need tbr_timer anymore */
| }
| 

using this semantic patch, `tailq.spatch`,

| @@
| identifier I, N;
| expression H;
| statement S;
| iterator name TAILQ_FOREACH;
| @@
| 
| - for (I = TAILQ_FIRST(H); I != NULL; I = TAILQ_NEXT(I, N)) S
| + TAILQ_FOREACH(I, H, N) S

I find that if the condition in the `#if` directive is 1, then `spatch
--sp-file tailq.spatch -o tbr_timeout.spatch tbr_timeout.c` runs for
a few minutes before running out of memory. `spatch` prints this
mysterious message when it starts:

     (ONCE) already tagged but only removed, so safe

If I turn the condition to 0, however, spatch instantaneously prints the
result with the `for (...)` clause turned to `TAILQ_FOREACH(...)`, as
expected.  I don't see the mysterious `(ONCE) ...` message.

Any ideas why `continue;` is troublesome to spatch?

Dave

-- 
David Young
dyoung@pobox.com    Urbana, IL    (217) 721-9981
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