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Submitted by Kazu Yamamoto on glasgow-haskell-users.

This program

import System.IO

n :: Int
n = 10000

main :: IO ()
main = withFile "/dev/null" WriteMode $ \h ->
    hPutStr h . foldr1 (++) . replicate n . replicate n $ 'a'

runs much more slowly with the current 7.0 branch than with either 7.0.1 or HEAD.

He also reported that the program runs faster interpreted with runghc than when compiled. I think this is due to #917 (full-laziness), so that's a separate issue. THe regression reported in this ticket is in compiled performance relative to 7.0.1 and HEAD.

I don't see any obvious differences in the simplified output, so the difference could be in library code. I'm using libraries compiled with -O2 in all cases.

Trac metadata

Trac field	Value
Version	7.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
Test case
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