#5920: stack overflow in strict function depending on return type
------------------------------+---------------------------------------------
Reporter: ben0x539 | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.4.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Runtime crash | Testcase:
Blockedby: | Blocking:
Related: |
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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 `seq`s 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.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5920>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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