zfs kernel panic, known incompatibilities with clang & CPUTYPE/COPTFLAGS?

Hi,

I try to update from a pre-clang world (r242511M) to "now" (r251618M).
The resulting kernel boots, but while starting some jails (with ezjail
from ports, so fairly late in the boot process) I get a kernel panic
(IIRC zfs trying to access page 0).

Before I try to get some time to debug this, I would like to know if
there are some known incompatibilities with my make.conf settings. With
gcc I used successfully this:
---snip---
COPTFLAGS= -O2 -pipe
CPUTYPE?=core2
---snip---

With those settings I first did a buildworld, then a buildkernel with
the r251618 sources.

Are there some known issues with those settings? If yes, any suggestions
what I should use instead? If not, would it be beneficial to try with
different settings (which ones)?

Bye,
Alexander.

-- 
http://www.Leidinger.net    Alexander _at_ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild _at_ FreeBSD.org  : PGP ID = 72077137