CAF isn't floated

In the following code, pattern isn't floated, and the execution time is 20x slower than it should be:

import Text.Regex.TDFA (Regex, makeRegex, match)

main :: IO ()
main = do
    entries <- map parseFilename . lines <$> getContents
    let check (Right (_, t)) = last t == 'Z'
        check _ = False
    print $ all check entries

parseFilename :: String -> Either String (String, String)
parseFilename fn = case (pattern `match` fn :: [[String]]) of
    [[_, full, _, time]] -> Right $ (full, time)
    _ -> Left fn
  where
    pattern :: Regex
    pattern = makeRegex
        "^\\./duplicity-(full|inc|new)(-signatures)?\\.\
        \([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]T[0-9][0-9][0-9][0-9][0-9][0-9]Z)\\."

Curiously, it is floated when profiling is enabled, so the profiled program ends up being 7x faster than the unprofiled one.

I can float the code manually (by taking out where and unindenting) and the program then runs at an acceptable speed.

I get the same behaviour with 8.0.2, 8.2.1 and 8.2.2 but 7.10.3 is OK. I don't think the OS and architecture makes a difference, but for the record I'm on various flavours of 64-bit Linux.

Test input data is here

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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