With -O or up, but not with -fno-strictness, the following program terminates with a stack overflow:

goInt :: Integer -> Integer -> Int
goInt 500 250000 = 0
goInt   x 250000 = goInt (x+1) 1
goInt   x      y = goInt x     (y+1)

main = do 
  print $ goInt 1 1

In contrast, the following program runs just fine even though the differences should not impact strictness:

import Debug.Trace

goInteger  :: Integer -> Integer -> Integer
goInteger  500 250000 = 0
goInteger    x 250000 = goInteger (x+1) 1
goInteger    x      y = goInteger x     (y+1)

goIntTrace :: Integer -> Integer -> Int
goIntTrace 500 250000 = 0
goIntTrace   x 250000 = goIntTrace (x+1) 1
goIntTrace   x      y = (if y < 0 then trace "" else id) goIntTrace x (y+1)

main = do
  print $ goInteger 1 1
  print $ goIntTrace 1 1

goInteger does not overflow the stack even though it only differs in the type of the return value.

goIntTrace does not overflow the stack even though goInt is already strict in y. Trying to make goInt "stricter" via seqs or bangs instead does not seem to have the same effect without the threat of IO.

The behavior could be reproduced on at least ghc 7.0.1 and 7.4.1, linux x86_64.