SCC mis-accounting

The profiles sometimes charges to the wrong account. In this example:

foo :: (() -> () -> [()] -> [()]) -> () -> [()] -> [()]
foo k =
  \_ xs -> concatMap ($ [head xs]) [bar]
 where
  bar =
    let k' = k undefined undefined
    in  \xs ->
          let k'' = [k' xs]
          in  (() : (foldr1 (>>) k''))

k = foo (\_ -> k)
--k a = foo (\_ -> k) a
r = k undefined [] !! 4000
main = print r

almost all of the time, allocations, and heap retention are charged to k. However, if you use the commented definition of k, the changes switch to foo, as expected. This can be tested by running

ghc --make -prof -auto-all Logic.hs && ./a.out +RTS -hc && hp2ps -c a.out.hp

and watching the pretty graph change.

This is using ghc 6.4.1 from Debian unstable. More background at http://haskell.org/pipermail/haskell-cafe/2006-February/014139.html

Trac metadata

Trac field	Value
Version	6.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Profiling
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown