$ ghc -O3 -Wall --make -threaded -rtsopts -fspec-constr-count=50 autotune.hs
...
$ ./autotune +RTS -N -hT -RTS
...
autotune: internal error: heapCensus, unknown object: -538405951
    (GHC version 7.0.3 for x86_64_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

The unknown object number varies between program runs, and I got a segmentation fault too in one test.

I didn't manage to provoke a crash with each of -N or -hT alone, but the combination seems problematic.

I compiled ghc-7.0.3 from source with INTEGER_LIBRARY=integer-simple (so I can use hmpfr); my code uses hmpfr, parallel, ad, Vec, and possibly some other things from hackage too - I can try to make a simple test case at some point, or attach the code as-is if it would be useful.