Hi, when trying to compile a ghc HEAD on LLVM ARM, I end up getting an exception: ghc-stage1: panic! (the 'impossible' happened) (GHC version 7.9.20140911 for arm-apple-ios): globalRegMaybe After some digging I found that a new call to globalRegMaybe was introduced here: http://git.haskell.org/ghc.git/blob/HEAD:/compiler/cmm/CmmSink.hs#l231 on 2014-04-29 in commit: http://git.haskell.org/ghc.git/commitdiff/83a003fcaec93dbfd5b46837f2bf335341... In a similar timeframe (since 2014-05-02) /include/CodeGen.Platform.hs was changed: http://git.haskell.org/ghc.git/blobdiff/b0534f78a73f972e279eed4447a5687bd6a8... introducing a set of new ifdef/elif/endif pairs. Especially for MACHREGS_NO_REGS, namely: -#endif globalRegMaybe _ = Nothing +#elif MACHREGS_NO_REGS +globalRegMaybe _ = Nothing +#else +globalRegMaybe = panic "globalRegMaybe not defined for this platform" +#endif ARM.hs (http://git.haskell.org/ghc.git/blob/23892440032fcab8a6a753916d506857674169ec...) however, has: #define MACHREGS_NO_REGS 0 #define MACHREGS_arm 1 where MACHREGS_arm 1 has no effect on the subsequently imported CodeGen.Platform.hs. Therefore I propose that a change to ARM.hs is made to set MACHREGS_NO_REGS to 1. Cheers, Moritz