[GHC] #12990: Partially applied constructors with unpacked fields simplified badly

[GHC]

#12990: Partially applied constructors with unpacked fields simplified badly
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        Reporter:  dfeuer            |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Inlining
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  D2891
       Wiki Page:                    |
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Comment (by David Feuer <David.Feuer@…>):

 In [changeset:"2be364ac8cf2f5cd3b50503e8b26f51eb46101e5/ghc"
 2be364ac/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2be364ac8cf2f5cd3b50503e8b26f51eb46101e5"
 Inline partially-applied wrappers

 Suppose we have

 ```
 data Node a = Node2 !Int a a | Node3 !Int a a a
 instance Traversable Node where
   traverse f (Node2 s x y) = Node2 s <$> f x <*> f y
   ...

 ```

 Since `Node2` is partially applied, we wouldn't inline its
 wrapper.  The result was that we'd box up the `Int#` to put
 the box in the closure passed to `fmap`. We now allow the wrapper
 to inline when partially applied, so GHC stores the `Int#`
 directly in the closure.

 Reviewers: rwbarton, mpickering, simonpj, austin, bgamari

 Reviewed By: simonpj, bgamari

 Subscribers: mpickering, thomie

 Differential Revision: https://phabricator.haskell.org/D2891

 GHC Trac Issues: #12990
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12990#comment:10>
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