Stack overflow when compiling with optimizations

[EyalLotem]

This program:

import Control.Exception (evaluate)

main :: IO ()
main = do
  let smap = concat . replicate 300 $ concat [" ", replicate 2027 '#', " \n"]
  evaluate $ fst (stringReader 1 smap)

stringReader :: Int -> String -> ((), String)
stringReader 1 ('\r':'\n':_) = ((), "")
stringReader _ ('\n':cs) = stringReader 1 cs -- unix
stringReader x (_:cs) = stringReader x cs
stringReader _ _ = ((), "")

Causes a stack overflow when compiled with -O2, and no problem when compiled without optimizations.

[EyalLotem]

Note that "smap" is not the culprit (it has the same result when reading smap from a file via readFile).

stringReader is the culprit.

If the argument order to stringReader is flipped, the stack overflow goes away.

[simonpj]

Happily this is already fixed; it's a dup of #5920 and #5997.

Simon