[GHC] #14152: Float exit paths out of recursive functions

[GHC]

#14152: Float exit paths out of recursive functions
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        Reporter:  nomeata           |                Owner:  (none)
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14137 #10918     |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Joachim, I've just been looking at `Exitify.hs` in pursuit of #15005.
 It's not easy going.

 Could you add some careful Notes?   For example, here are the things I
 stumbled over immediately:

 * In the top-level `exitifyProgram` I think we make no attempt to exitify
 top level recursive functions.  That's fine, but say so.

 * Then in `go` of `exitifyProgram` I think we are looking at the RHS of a
 top-level function, and applying `goBind` to every binding within it.
 (NB: `goBind` calls `go` to deal with the RHS of the bindings; I'd be
 inlined do that in `go` so that `goBind` gets the post-exitify bindings.)

 * Mysteriously we do not exitify the RHS of a case alternative (`goAlts`).
 This exception seems highly mysterious, possibly a bug?

 * Then for recursive join-point bindings, we apply `exitify` to them
 (after having recursively processed the RHSs).

 * There is some magic in `go` in `exitify` to pick out the ones we want to
 exitify. Explaining these conditions in a note would be good

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14152#comment:33>
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