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GHCi panic when trying to avoid GHC_OPTIONS -O warning

    • Closed Issue created by ChaiTRex @trac-ChaiTRex

    Following the advice on an answer to "How can I load optimized code in GHCI?", I get a GHCi panic. Running ghc Luhn succeeds just fine. On running ghci Luhn, I get:

    $ ghci Luhn
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Luhn             ( Luhn.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.3 for x86_64-unknown-linux):
	floatExpr tick break<15>()

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

    Contents of Luhn.hs:

    {-# OPTIONS_GHC -fobject-code -O3 #-}

module Luhn (checkLuhn) where

import Data.Bits  (shiftL)
import Data.Char  (digitToInt)
import Data.List  (foldl')

-- Quickly gets a list of digits from a nonnegative Integer
-- Gives error for negative inputs
-- Uses GMP's show for greatly-improved speed over GMP's div and mod
toDigits :: Integer -> [Int]
{-# INLINE toDigits #-}
toDigits = map digitToInt . show

-- Quickly gets the same result as iteratively getting the digit sum of a nonnegative Int until the digit sum is only one digit long
-- Gives an erroneous value for negative inputs
repeatedDigitSum :: Int -> Int
{-# INLINE repeatedDigitSum #-}
repeatedDigitSum n = (n - 1) `rem` 9 + 1

-- Gets the Luhn sum, which is zero for valid inputs, of a list of digits
-- Uses Data.Bits.shiftL to quickly double
luhnSum :: [Int] -> Int
{-# INLINE luhnSum #-}
luhnSum = fromInteger . flip rem 10 . foldl' (+) 0 . zipWith ($) (cycle [toInteger, toInteger . repeatedDigitSum . flip shiftL 1])

-- Checks whether a nonnegative Integer passes the Luhn algorithm
-- Negative inputs are False, since the Luhn algorithm is intended for unsigned inputs
checkLuhn :: Integer -> Bool
{-# INLINABLE checkLuhn #-}
checkLuhn n = (n >= 0) && ((== 0) . luhnSum . reverse . toDigits) n

    Strangely, ghci -fobject-code -O3 Luhn works just great, so apparently it's not a problem with the switches?

    ghc --version:

    The Glorious Glasgow Haskell Compilation System, version 7.10.3

    Ubuntu (and presumably Debian) package information:

    ghc:
  Installed: 7.10.3-7
  Candidate: 7.10.3-7
  Version table:
 *** 7.10.3-7 500
        500 http://mirror.atlantic.net/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status
    Edited
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