[GHC] #14626: No need to enter a scrutinised value

[GHC]

#14626: No need to enter a scrutinised value
-------------------------------------+-------------------------------------
        Reporter:  heisenbug         |                Owner:  heisenbug
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:  performance
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13861            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by heisenbug):

 Replying to [comment:19 heisenbug]:
 > Replying to [comment:18 heisenbug]:
 > > [snippety]
 >
 > Now, maybe the `Binary` instance breaks the invariant that the `n_occ`
 field is strict?

 Actually it seems to be
 {{{#!hs
 -- | Assumes that the 'Name' is a non-binding one. See
 -- 'IfaceSyn.putIfaceTopBndr' and 'IfaceSyn.getIfaceTopBndr' for
 serializing
 -- binding 'Name's. See 'UserData' for the rationale for this distinction.
 instance Binary Name where
    put_ bh name =
       case getUserData bh of
         UserData{ ud_put_nonbinding_name = put_name } -> put_name bh name

    get bh =
       case getUserData bh of
         UserData { ud_get_name = get_name } -> get_name bh
 }}}
 which breaks the contract. Let's see what `getUserData` does...

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14626#comment:20>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler