[GHC] #11545: Strictness signature blowup

5 Feb 2016

      #11545: Strictness signature blowup
-------------------------------------+-------------------------------------
           Reporter:  jscholl        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The following code takes a lot of memory (556MB) to compile:

 {{{#!hs
 data A = A A A A A A deriving (Eq)
 }}}

 More {{{A}}}s result in more memory consumption during compilation. Using
 {{{ghc -O A.hs -v -dverbose-core2core -c -ddump-simpl +RTS -s}}} it seems
 like the strictness signatures of (==) and (/=) blow up quite a bit.

 A less silly example could be the following:
 {{{#!hs
 data QuadTree a = QuadTree !Int [a] (QuadTree a) (QuadTree a) (QuadTree a)
 (QuadTree a)

 foldQuadTree :: (a -> b -> b) -> Int -> b -> QuadTree a -> b
 foldQuadTree f maxSize = go
     where
         go z (QuadTree size elems t1 t2 t3 t4)
             | size <= maxSize = foldr f z elems
             | otherwise       = go (go (go (go z t4) t3) t2) t1

 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11545
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