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When I try to build JuicyPixels-3.2.9.5 on Fedora s390x Linux, ghc-8.4.4 panics:

[ 9 of 30] Compiling Codec.Picture.ColorQuant ( src/Codec/Picture/ColorQuant.hs, dist/build/Codec/Picture/ColorQuant.o )
BUILDSTDERR: src/Codec/Picture/ColorQuant.hs:123:26: warning: [-Woverflowed-literals]
BUILDSTDERR:     Literal 256 is out of the GHC.Word.Word8 range 0..255
BUILDSTDERR:     |
BUILDSTDERR: 123 |       (PixelRGB8 (r .&. (256 - dr)) (g .&. (256 - dg)) (b .&. (256 - db)))
BUILDSTDERR:     |                          ^^^
BUILDSTDERR: src/Codec/Picture/ColorQuant.hs:123:45: warning: [-Woverflowed-literals]
BUILDSTDERR:     Literal 256 is out of the GHC.Word.Word8 range 0..255
BUILDSTDERR:     |
BUILDSTDERR: 123 |       (PixelRGB8 (r .&. (256 - dr)) (g .&. (256 - dg)) (b .&. (256 - db)))
BUILDSTDERR:     |                                             ^^^
BUILDSTDERR: src/Codec/Picture/ColorQuant.hs:123:64: warning: [-Woverflowed-literals]
BUILDSTDERR:     Literal 256 is out of the GHC.Word.Word8 range 0..255
BUILDSTDERR:     |
BUILDSTDERR: 123 |       (PixelRGB8 (r .&. (256 - dr)) (g .&. (256 - dg)) (b .&. (256 - db)))
BUILDSTDERR:     |                                                                ^^^
BUILDSTDERR: ghc: panic! (the 'impossible' happened)
BUILDSTDERR:   (GHC version 8.4.4 for s390x-ibm-linux):
BUILDSTDERR: 	pprStatics: float
BUILDSTDERR:   F32
BUILDSTDERR:   F32
BUILDSTDERR:   I32
BUILDSTDERR:   Call stack:
BUILDSTDERR:       CallStack (from HasCallStack):
BUILDSTDERR:         callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
BUILDSTDERR:         pprPanic, called at compiler/cmm/PprC.hs:525:5 in ghc:PprC
BUILDSTDERR: Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

I would test on ghc-8.6.3 too, but I haven't been able to build ghc-8.6 yet on s390x (unregisterized on unregisterized): see issue 15913.