Panic on type inference with vectorised parallel arrays

{-# LANGUAGE CPP #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE ParallelArrays #-}
module Y where

import Data.Array.Parallel

#ifndef BUG
func :: Bool -> [: [: a :] :]
#endif
func True = [: [: :] :]
func False = [: j | j <- func True :]

Result of ghc --make -fvectorise Y.hs:

[1 of 1] Compiling Y                ( C:\tmp\Y.hs, C:\tmp\Y.o )
exprType TYPE [:a{tv b} [tv]:]
exprType TYPE a{tv b} [tv]
exprType TYPE [:a{tv b} [tv]:]
exprType TYPE a{tv b} [tv]
exprType TYPE [:a{tv b} [tv]:]
exprType TYPE a{tv b} [tv]
exprType TYPE [:a{tv b} [tv]:]
exprType TYPE a{tv b} [tv]
Warning: vectorisation failure: identityConv: quantified type changes under vectorisation
  Could NOT call vectorised from original version Y.func

Result of ghc --make -fvectorise -DBUG Y.hs:

[1 of 1] Compiling Y                ( C:\tmp\Y.hs, C:\tmp\Y.o )
exprType TYPE [:t{tv a30W} [tv]:]
exprType TYPE t{tv a30W} [tv]
exprType TYPE [:t{tv a30W} [tv]:]
exprType TYPE t{tv a30W} [tv]
exprType TYPE [:t{tv a30W} [tv]:]
exprType TYPE t{tv a30W} [tv]
exprType TYPE [:t{tv a30W} [tv]:]
exprType TYPE t{tv a30W} [tv]
Warning: vectorisation failure: identityConv: quantified type changes under vectorisation
  Could NOT call vectorised from original version func
exprType TYPE t{tv a30W} [tv]
Warning: vectorisation failure: identityConv: quantified type changes under vectorisation
  Could NOT call vectorised from original version Y.func
ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.1 for x86_64-unknown-mingw32):
        nameModule func1{v r3ap}

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

And so I did.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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