[GHC] #16379: JuicyPixels build panics on s390x ghc-8.4.4

[GHC]

#16379: JuicyPixels build panics on s390x ghc-8.4.4
-------------------------------------+-------------------------------------
           Reporter:  juhpetersen    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.4.4
           Keywords:                 |  Operating System:  Linux
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 When I try to build JuicyPixels on Fedora s390x Linux with ghc-8.4.4
 I get a compiler panic:

 {{{
 [ 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.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16379>
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