Unboxed sums-related panic: getUnboxedSumName 513

Originally reported here. You'll need these two files:

-- Testing.hs
{-# LANGUAGE UnboxedSums #-}

module Testing where

func :: s -> (# Bool | Bool #)
func _ = (# True | #)

-- Bug.hs
{-# LANGUAGE UnboxedSums #-}

module Main where

import Testing

main :: IO ()
main = print $ func 1

And you must compile them like so (the -c and -O2 flags are important):

$ ghc -O2 -c Testing.hs 
$ ghc -O2 -c Bug.hs
ghc: panic! (the 'impossible' happened)
  (GHC version 8.2.1 for x86_64-unknown-linux):
        getUnboxedSumName
  513
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/prelude/KnownUniques.hs:104:5 in ghc:KnownUniques

Reproducible with GHC 8.2.1 and HEAD.

Trac metadata

Trac field	Value
Version	8.2.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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