[GHC] #13255: aws package fails to build with master

[GHC]

#13255: aws package fails to build with master
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 I've managed the problem to isolate this smaller example:

 {{{#!hs
 module Bug where

 -------------------------------------------------------------------------------
 import qualified Data.ByteString.Base64       as Base64
 import qualified Data.ByteString.Char8        as B
 import qualified Data.Set                     as S
 import qualified Data.Text                    as T
 import qualified Data.Text.Encoding           as T

 data DValue
     = DBinary B.ByteString
     | DBool Bool
     | DBoolSet (S.Set Bool)

 -------------------------------------------------------------------------------
 class DynSize a where
     dynSize :: a -> Int

 instance DynSize DValue where
     dynSize (DBool _) = 8
     dynSize (DBoolSet s) = sum $ map (dynSize . DBool) $ S.toList s
     dynSize (DBinary bs) = T.length . T.decodeUtf8 $ Base64.encode bs
 }}}

 You'll need to run `cabal install base64-bytestring text --enable-library-
 profiling` beforehand. Then you can reproduce it like so:

 {{{
 $ ~/Software/ghc3/inplace/bin/ghc-stage2 -O2 -prof -fforce-recomp Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.1.20170213 for x86_64-unknown-linux):
         completeCall
   $wloop_length_s87d
   Stop[BoringCtxt] Int# -> Int# -> Int
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1197:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1201:37 in
 ghc:Outputable
         pprPanic, called at compiler/simplCore/Simplify.hs:1598:9 in
 ghc:Simplify
 CallStack (from -prof):
   SimplCore.SimplTopBinds (compiler/simplCore/SimplCore.hs:729:29-64)
   SimplCore.Simplify (compiler/simplCore/SimplCore.hs:426:40-55)
   HscMain.Core2Core (compiler/main/HscMain.hs:1170:7-42)
   HscMain.hscSimplify' (compiler/main/HscMain.hs:(1167,1)-(1170,42))
   HscMain.finish (compiler/main/HscMain.hs:(728,1)-(740,20))
   HscMain.hscIncrementalCompile
 (compiler/main/HscMain.hs:(639,1)-(694,32))
   GhcMake.upsweep_mod.compile_it
 (compiler/main/GhcMake.hs:(1380,13)-(1382,66))
   GhcMake.upsweep_mod (compiler/main/GhcMake.hs:(1328,1)-(1482,49))
   GhcMake.upsweep.upsweep' (compiler/main/GhcMake.hs:(1197,3)-(1296,91))
   GhcMake.upsweep (compiler/main/GhcMake.hs:(1189,1)-(1296,91))
   GhcMake.load'.upsweep_fn (compiler/main/GhcMake.hs:(351,9)-(352,41))
   GhcMake.load'.checkHowMuch (compiler/main/GhcMake.hs:(233,9)-(235,27))
   GhcMake.load' (compiler/main/GhcMake.hs:(210,1)-(439,38))
   GhcMake.load (compiler/main/GhcMake.hs:(202,1)-(204,44))
   GHC.withCleanupSession (compiler/main/GHC.hs:(450,1)-(459,37))
   GHC.runGhc (compiler/main/GHC.hs:(425,1)-(430,26))
   GHC.defaultErrorHandler (compiler/main/GHC.hs:(365,1)-(397,7))

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13255#comment:9>
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