[GHC] #13331: Worker/wrapper can lead to sharing failure

[GHC]

#13331: Worker/wrapper can lead to sharing failure
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by dfeuer):

 Actually, I just discovered that we don't even need pointer equality to
 reproduce!

 {{{#!hs
 naiveInsert1 :: Ord k => k -> a -> Map k a -> Map k a
 naiveInsert1 kx0 = go kx0
   where
     --go :: Ord k => k -> a -> Map k a -> Map k a
     go !kx x Tip = singleton kx0 x
     go !kx x t@(Bin sz ky y l r) =
         case compare kx ky of
             LT -> balanceL ky y l' r
                where !l' = go kx x l
             GT -> balanceR ky y l r'
                where !r' = go kx x r
             EQ -> Bin sz kx0 x l r

 {-# INLINABLE naiveInsert1 #-}
 }}}

 and

 {{{#!hs
 naiveInsert2 :: Ord k => k -> a -> Map k a -> Map k a
 naiveInsert2 = go
   where
     go :: Ord k => k -> a -> Map k a -> Map k a
     go !kx x Tip = singleton kx x
     go !kx x t@(Bin sz ky y l r) =
         case compare kx ky of
             LT -> balanceL ky y l' r
                where !l' = go kx x l
             GT -> balanceR ky y l r'
                where !r' = go kx x r
             EQ -> Bin sz kx x l r

 {-# INLINABLE naiveInsert2 #-}
 }}}

 both demonstrate the same problem.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13331#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler