Re: #16379: JuicyPixels build panics on s390x ghc-8.4.4

#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
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  Other
 Type of failure:  Compile-time      |            Test Case:
  crash or panic                     |
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by juhpetersen:

Old description:

> 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.

New description:

 When I try to build JuicyPixels 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.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16379#comment:2>