length [Integer] is twice as slow but length [Int] is 10 times faster

Compared to 7.6.3 length in 7.8.1-rc1 has a performance regression:

 ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.20140130
bash-3.2$ ghc -O2 LengthIntegerList.hs
[1 of 1] Compiling Main             ( LengthIntegerList.hs, LengthIntegerList.o )
Linking LengthIntegerList ...
bash-3.2$ time ./LengthIntegerList
1073741824

real	0m45.344s
user	0m44.230s
sys	0m0.494s
bash-3.2$ /usr/bin/ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.6.3
bash-3.2$ /usr/bin/ghc -O2 LengthIntegerList.hs
[1 of 1] Compiling Main             ( LengthIntegerList.hs, LengthIntegerList.o )
Linking LengthIntegerList ...
bash-3.2$ time ./LengthIntegerList
1073741824

real	0m22.769s
user	0m22.042s
sys	0m0.385s
bash-3.2$ cat LengthIntegerList.hs
{-# OPTIONS_GHC -Wall #-}

module Main where

main :: IO()
main = print $ length [1..(2^(30::Int)::Integer)]

thus length of [Integer] is twice as slow in rc1 but length of [Int] is 10 times faster:

 ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.20140130
bash-3.2$ ghc -O2 LengthIntList.hs
[1 of 1] Compiling Main             ( LengthIntList.hs, LengthIntList.o )
Linking LengthIntList ...
bash-3.2$ time ./LengthIntList
1073741824

real	0m0.723s
user	0m0.693s
sys	0m0.003s
bash-3.2$ /usr/bin/ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.6.3
bash-3.2$ /usr/bin/ghc -O2 LengthIntList.hs
[1 of 1] Compiling Main             ( LengthIntList.hs, LengthIntList.o )
Linking LengthIntList ...
bash-3.2$ time ./LengthIntList
1073741824

real	0m11.805s
user	0m10.900s
sys	0m0.351s
bash-3.2$ cat LengthIntList.hs
{-# OPTIONS_GHC -Wall #-}


module Main where

main :: IO()
main = print $ length [1..(2^(30::Int)::Int)]

Trac metadata

Trac field	Value
Version	7.8.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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