[GHC] #13695: Highly nested UNPACKed data causes panic

[GHC]

#13695: Highly nested UNPACKed data causes panic
----------------------------------------+---------------------------------
           Reporter:  ryanreich         |             Owner:  (none)
               Type:  bug               |            Status:  new
           Priority:  normal            |         Milestone:
          Component:  Compiler          |           Version:  8.2.1-rc2
           Keywords:                    |  Operating System:  Linux
       Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
          Test Case:                    |        Blocked By:
           Blocking:                    |   Related Tickets:  3990
Differential Rev(s):                    |         Wiki Page:
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 See attached source files.  I get the following error:

 {{{
 [3 of 3] Compiling Data.BigWord     ( src/Data/BigWord.hs, .stack-
 work/dist/x86_64-linux/Cabal-2.0.0.0/build/Data/BigWord.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.0.20170505 for x86_64-unknown-linux):
         urk! lookup local fingerprint
   D:R:DoubleWordDoubleWord2
   [cESifd :-> (BigWord2, acd0b93ce6ccc191df910f3c0527af52),
    cESife :-> (BigWord3, c2394bb5a6246cea8260b764c4645609),
    cESiqK :-> (BigWord4, dfeb99d5c409e91fe7084935101bb1a8),
    cESiqT :-> (R:DoubleWordDoubleWord3,
                00000000000000000000000000000000),
    cESiqV :-> (D:R:DoubleWordDoubleWord4,
                00000000000000000000000000000000),
    cESir1 :-> (D:R:BigWord4, 7d2736129b3a85c7e71bc1954bb41ec0),
    dESiqK :-> (BigWord4, d51a0117843c625086a534a6e4b47d85),
    iESiqK :-> (BigWord4, 139d5d98471af07fbafb30541b5ec225),
    iESiqX :-> ($WBigWord4, df51c2cc8c85fdd30898a16f2568c91a)]
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1134:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in
 ghc:Outputable
         pprPanic, called at compiler/iface/MkIface.hs:508:37 in
 ghc:MkIface

 }}}

 I need to use ghc-8.2.1 because it seems to be the earliest version that
 contains the fixes in [https://ghc.haskell.org/trac/ghc/ticket/3990],
 without which the UNPACKs will be ignored.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13695>
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