panic when compiling SHA

Fri Dec 27 01:47:33 UTC 2013

On Thu, Dec 26, 2013 at 8:37 PM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:
> When I tried to build the SHA library with GHC head on on 32bit Linux,
> GHC head got panic. GHC 7.4.2 can build SHA on the same machine.
>
> [1 of 1] Compiling Data.Digest.Pure.SHA ( Data/Digest/Pure/SHA.hs, dist/dist-sandbox-ef3aaa11/build/Data/Digest/Pure/SHA.o )
> ghc: panic! (the 'impossible' happened)
>   (GHC version 7.7.20131202 for i386-unknown-linux):
>         regSpill: out of spill slots!
>        regs to spill = 1129
>        slots left    = 677

I ran into this a while ago.  Turns out it’s a known bug[0], but it
seems like it’s been hard to reproduce.  FWIW, I also hit it on 32bit
Linux.  You can probably work around it with `-fno-regs-graph`.

[0]: <https://ghc.haskell.org/trac/ghc/ticket/5361>