Performance regression (involving sum, map, enumFromThenTo)

This program's performance suffers when compiled with 7.10, compared to 7.8:

main = print $ sum $ map bitcount [0, 4 .. 2^24-1 ]

bitcount :: Int -> Int
bitcount x =
  if x > 0 then let (d,m) = divMod x 2 in bitcount d + m else 0

See discussion in this thread: https://mail.haskell.org/pipermail/haskell-cafe/2015-December/122485.html

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture