panic in GHC when building QuickCheck with optimization

When building QuickCheck, I get:

cdsmith@devtools:~/tmp/QuickCheck$ runhaskell Setup build
Preprocessing library QuickCheck-2.0...
Building QuickCheck-2.0...
Glasgow Haskell Compiler, Version 6.7.20070529, for Haskell 98, compiled by GHC                                                                                                                            version 6.7.20070529
Using package config file: /usr/local/lib/ghc-6.7.20070529/package.conf
wired-in package base mapped to base-2.1
wired-in package rts mapped to rts-1.0
wired-in package haskell98 mapped to haskell98-1.0
wired-in package template-haskell mapped to template-haskell-0.1
Hsc static flags: -static
*** Chasing dependencies:
Chasing modules from: Test.QuickCheck,Test.QuickCheck.Arbitrary,Test.QuickCheck.                                                                                                                           Function,Test.QuickCheck.Gen,Test.QuickCheck.Monadic,Test.QuickCheck.Property,Te                                                                                                                           st.QuickCheck.Test,Test.QuickCheck.Exception,Test.QuickCheck.Text
Stable obj: []
Stable BCO: []
Ready for upsweep
  [NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:28:15 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Gen,
         ms_imps = [Control.Monad.Reader, Control.Monad, System.Random]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Arbitrary,
         ms_imps = [Control.Monad, Data.List, System.Random, Data.Ratio,
                    Data.Char, Test.QuickCheck.Gen]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:39 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Exception,
         ms_imps = [Control.Exception]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:39 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Text,
         ms_imps = [Data.IORef, System.IO]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Property,
         ms_imps = [System.IO, Data.IORef, Control.Concurrent,
                    Test.QuickCheck.Exception, Test.QuickCheck.Text,
                    Test.QuickCheck.Arbitrary, Test.QuickCheck.Gen]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Test,
         ms_imps = [Data.List, Data.Char, System.Random,
                    Test.QuickCheck.Exception, Test.QuickCheck.Text,
                    Test.QuickCheck.Property, Test.QuickCheck.Gen]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Monadic,
         ms_imps = [System.IO.Unsafe, Control.Monad.ST, Control.Monad,
                    Test.QuickCheck.Arbitrary, Test.QuickCheck.Property,
                    Test.QuickCheck.Gen]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck.Function,
         ms_imps = [System.IO.Unsafe, Data.List, Data.IORef,
                    Test.QuickCheck.Property, Test.QuickCheck.Arbitrary,
                    Test.QuickCheck.Gen]
         ms_srcimps = []
      },
   NONREC
      ModSummary {
         ms_hs_date = Fri Jun  1 10:11:40 MDT 2007
         ms_mod = QuickCheck-2.0:Test.QuickCheck,
         ms_imps = [Test.QuickCheck.Test, Test.QuickCheck.Property,
                    Test.QuickCheck.Arbitrary, Test.QuickCheck.Gen]
         ms_srcimps = []
      }]
compile: input file Test/QuickCheck/Gen.hs
Created temporary directory: /tmp/ghc2049_0
*** Checking old interface for QuickCheck-2.0:Test.QuickCheck.Gen:
[1 of 9] Compiling Test.QuickCheck.Gen ( Test/QuickCheck/Gen.hs, dist/build/Test                                                                                                                           /QuickCheck/Gen.o )
*** Parser:
*** Renamer/typechecker:
*** Desugar:
    Result size = 1180
*** Simplify:
    Result size = 803
    Result size = 789
    Result size = 789
*** Specialise:
*** Deleting temp files:
Deleting: /tmp/ghc2049_0/ghc2049_0.s
Warning: deleting non-existent /tmp/ghc2049_0/ghc2049_0.s
*** Deleting temp dirs:
Deleting: /tmp/ghc2049_0
ghc-6.7.20070529: panic! (the 'impossible' happened)
  (GHC version 6.7.20070529 for i386-unknown-linux):
        my_zipEqual
    []
    [random-1.0:System.Random.$f6{v r2X} [gid]]
    QuickCheck-2.0:Test.QuickCheck.Gen.choose{v r6H} [lid] [Just base:GHC.Base.I                                                                                                                           nt{(w) tc 3J}]
    \ (@ a{tv asq} [sk] :: base:GHC.Prim.*{(w) tc 34d}) ->
      (a_sIo{v} [lid] @ a{tv asq} [sk])
      `cast` (<pred>random-1.0:System.Random.Random{tc r33}
                      a{tv asq} [sk]
              -> (a{tv asq} [sk], a{tv asq} [sk])
              -> base:GHC.Prim.sym{(w) tc 34v}
                   ((QuickCheck-2.0:Test.QuickCheck.Gen.:CoGen{tc rfI})
                      a{tv asq} [sk])
              :: <pred>(random-1.0:System.Random.Random{tc r33}
                          a{tv asq} [sk]) =>
                       (a{tv asq} [sk], a{tv asq} [sk])
                       -> random-1.0:System.Random.StdGen{tc r35}
                       -> base:GHC.Base.Int{(w) tc 3J}
                       -> a{tv asq} [sk]
                         ~
                       (random-1.0:System.Random.Random{tc r33} a{tv asq} [sk])                                                                                                                            =>
                       (a{tv asq} [sk], a{tv asq} [sk])
                       -> <nt>QuickCheck-2.0:Test.QuickCheck.Gen.Gen{tc r76}
                            a{tv asq} [sk])

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

If I build with -Onot, the error does not occur.

cdsmith@devtools:~/tmp/QuickCheck$ uname -a
Linux devtools 2.4.27-2-k7 #1 Tue Aug 16 17:30:14 JST 2005 i686 GNU/Linux

The error occurs in:

-- | Generates a random element in the given inclusive range.
choose :: Random a => (a,a) -> Gen a
choose rng = MkGen (\r _ -> let (x,_) = randomR rng r in x)

The GHC version is one that I pulled from darcs head on the 29th of May. It does have one local modification, but in an unrelated part of the compiler (the GHCi banner patch I sent to the cvs-ghc list on 6/1/2007)

Trac metadata

Trac field	Value
Version	6.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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