assert failed in head build

Last nights (Sep 13 EST) build of cvs HEAD on i386-unknown-openbsd
died in the stage3 build with the following output:

-- Don

 
/home/dons/ghc/cvs/nightly/i386-unknown-openbsd/stage2/ghc/compiler/ghc-inplace
-H16m -O -fvia-C -keep-hc-file  -istage1/utils  -istage1/basicTypes  -istage1/
types  -istage1/hsSyn  -istage1/prelude  -istage1/rename  -istage1/typecheck
- istage1/deSugar  -istage1/coreSyn  -istage1/specialise  -istage1/simplCore
-is tage1/stranal  -istage1/stgSyn  -istage1/simplStg  -istage1/codeGen
-istage1/a bsCSyn  -istage1/main  -istage1/profiling  -istage1/parser
-istage1/cprAnalysi s  -istage1/compMan  -istage1/ndpFlatten  -istage1/cbits
-istage1/nativeGen  - istage1/ghci -DGHCI -package haskell-src -package unix
-package readline  -cpp -fglasgow-exts -Rghc-timing -I. -IcodeGen -InativeGen
-Iparser -recomp -O -dcor e-lint -H24m -fvia-C -keep-hc-file  -H16M '-#include
"hschooks.h"'    -c simplC ore/Simplify.lhs -o stage1/simplCore/Simplify.o
-ohi stage1/simplCore/Simplify .hi

ghc-6.3: panic! (the `impossible' happened, GHC version 6.3):
        ASSERT failed! file simplCore/Simplify.lhs line 548
[lvl_sgIH S :: GHCziBase.Bool {- tc 3c -}
 Str: DmdType
 lvl_sgIH = CoreUtils.exprIsDupable {- v r1lq -}
              @ CoreSyn.CoreBndr {- tc r1QO -} mzuresult {- v a4LH -}]

Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.


<<ghc: 465015772 bytes, 412 GCs, 6196763/12742672 avg/max bytes residency (7
sa mples), 33M in use, 0.00 INIT (0.00 elapsed), 2.48 MUT (2.63 elapsed), 1.30
GC (1.33 elapsed) :ghc>>
gmake[1]: *** [stage1/simplCore/Simplify.o] Error 1
gmake: *** [all] Error 1