GHC Panic on import with 'OPTIONS_GHC -fobject-code -O'

I get

> :l Test.hs
[1 of 1] Compiling Main             ( Test.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.2 for x86_64-apple-darwin):
	floatExpr tick break<11>()

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

with Test.hs:

{-# OPTIONS_GHC -fobject-code -O #-}

import Control.Exception (assert)
import Data.Char (ord)

f :: String -> String
f s = assert (all (`elem` letters) s) $ (letters!!) <$> (ix <$> s)
    where
        ix ch = (ord ch - ord 'A')
        letters = ['A'..'Z']

OSX 10.11, GHC 7.10.2; uad-core 64-bit haswell; Homebrew GHC

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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