GHC panic encountered for unlifted let bindings

The following code block makes GHC panic:

{-# LANGUAGE BangPatterns #-}
module GhcPanic where

import GHC.Ptr
import Foreign 

-- Occurred in a really low-level bytestring decoder implementation.
{-# INLINE byteStringSlice #-}
byteStringSlice len = \fpbuf ip0 ipe s0 ->
    let ip1p@(Ptr ip1) = Ptr ip0 `plusPtr` len
    -- Note that the panic goes away if we use a bang-pattern as follows
    -- let !ip1p@(Ptr ip1) = Ptr ip0 `plusPtr` len
    in  ip1p

The panic output is

ghc-7.4.1 GhcPanic.hs                                                           
[1 of 1] Compiling GhcPanic         ( GhcPanic.hs, GhcPanic.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.1 for x86_64-unknown-linux):
        dsLet: unlifted
    AbsBinds
    [( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )]
    []
    [( ip1p{v acI} [lid] :: forall ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ).
                            base:GHC.Ptr.Ptr{tc 33A}
                              ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ) ) <= ( ip1p{v acK} [lid] :: base:GHC.Ptr.Ptr{tc 33A}
                                                                                                                  ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ) )
       /\(@ ( t{tv acW} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )).
       (<>) @ ( t{tv acW} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ),
     ( ip1{v acJ} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33} ) <= ( ip1{v acP} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33} )
       (<>)
       @ (ghc-prim:GHC.Prim.Any{(w) tc 31N}
            ghc-prim:GHC.Prim.*{(w) tc 34d})]
      ( ip1p{v acI} [lid] :: forall ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ).
                             base:GHC.Ptr.Ptr{tc 33A}
                               ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ) )
        :: forall ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ).
           base:GHC.Ptr.Ptr{tc 33A}
             ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )
      [LclId]
      ( ip1{v acJ} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33} )
        :: ghc-prim:GHC.Prim.Addr#{(w) tc 33}
      [LclId]
      {GhcPanic.hs:10:9-46}
      {GhcPanic.hs:10:9-22}
      {GhcPanic.hs:10:9-12}
      ( ip1p{v acK} [lid] :: base:GHC.Ptr.Ptr{tc 33A}
                               ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ) )@({GhcPanic.hs:10:15-21}
                                                                                        {GhcPanic.hs:10:15-17}
                                                                                        base:GHC.Ptr.Ptr{d r3C}{EvBinds{}} ((( ip1{v acP} [lid] :: ghc-prim:GHC.Prim.Addr#{(w) tc 33} )
                                                                                                                               :: ghc-prim:GHC.Prim.Addr#{(w) tc 33})))
        = {GhcPanic.hs:10:26-46}
          {GhcPanic.hs:10:34-42}
          (base:GHC.Ptr.plusPtr{v r3E})
          @ (ghc-prim:GHC.Prim.Any{(w) tc 31N}
               ghc-prim:GHC.Prim.*{(w) tc 34d})
          @ ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )
            ((base:GHC.Ptr.Ptr{v r39})
             @ (ghc-prim:GHC.Prim.Any{(w) tc 31N}
                  ghc-prim:GHC.Prim.*{(w) tc 34d})
               ip0{v acF})
            len{v acD}
    EvBinds{}
    ( ip1p{v acI} [lid] :: forall ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ).
                           base:GHC.Ptr.Ptr{tc 33A}
                             ( t{tv acU} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ) )
      @ ( t{tv ad5} [sk] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )

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

It might be that its an instance of #4498 (closed).

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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