[GHC] #12115: CoreLint error in safe program

[GHC]

#12115: CoreLint error in safe program
-------------------------------------+-------------------------------------
        Reporter:  osa1              |                Owner:
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  codegen/should_compile/T12115
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by thomie):

 This patch is causing the following panic in `tcrun051` (on Linux):
 {{{
 [1 of 1] Compiling Main             ( tcrun051.hs, tcrun051.o )
 7907    ghc: panic! (the 'impossible' happened)
 7908      (GHC version 8.1.20160527 for x86_64-unknown-linux):
 7909            unboxed tuple PrimRep
 7910
 7911    Please report this as a GHC bug:
 http://www.haskell.org/ghc/reportabug
 7912
 7913
 7914    *** unexpected failure for tcrun051(normal)
 7915
 }}}

 tcrun051.hs:
 {{{#!hs
 {-# LANGUAGE UnboxedTuples #-}

 module Main where

 -- Tests unboxed tuple slow calls

 {-# NOINLINE g #-}
 g :: Int -> (# Int, Int #) -> Int -> (# Int, (# Int #) #) -> (# #) -> Int
 g a (# b, c #) d (# e, (# f #) #) (# #) = a + b + c + d + e + f

 {-# NOINLINE h #-}
 h :: (Int -> (# Int, Int #) -> Int -> (# Int, (# Int #) #) -> (# #) ->
 Int) -> (Int, Int)
 h g = (g5, g5')
   where
     -- Apply all the arguments at once
     g5' = g 1 (# 2, 3 #) 4 (# 5, (# 6 #) #) (# #)

     -- Try to force argument-at-a-time application as a stress-test
     g1 = g 1
     g2 = g1 `seq` g1 (# 2, 3 #)
     g3 = g2 `seq` g2 4
     g4 = g3 `seq` g3 (# 5, (# 6 #) #)
     g5 = g4 `seq` g4 (# #)


 main = print $ h g
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12115#comment:4>
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