On the ghc-7.10 branch, PPC.Regs has duplicate exports (see below). The offending lines are fReg, sp, r3, r4, r27, r28, r30, r0, sp, r3, r4, r27, r28, r30, tmpReg, and indeed there are duplicates. Why? git branch -v * ghc-7.10 e22d7dc nativeGen PPC: fix > 16 bit offsets in stack handling master f17992a [behind 1397] Updaete perf numbers for 32-bit machines wip/T10527 eb66575 Use lazy substitution in simplCast wip/T10527-2 9e4908b Add an ambient Id substitution to Subst Simon compiler/nativeGen/PPC/Regs.hs:41:13: Warning: 'sp' is exported by 'sp' and 'sp' compiler/nativeGen/PPC/Regs.hs:41:17: Warning: 'r3' is exported by 'r3' and 'r3' compiler/nativeGen/PPC/Regs.hs:41:21: Warning: 'r4' is exported by 'r4' and 'r4'