[GHC] #13104: runRW# ruins join points

[GHC]

#13104: runRW# ruins join points
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        Reporter:  lukemaurer        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
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:                    |
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Comment (by nomeata):

 >  That would be horribly ad-hoc. We need a better way.

 *shrug* no more than the the one-shot hack we had for `build` before we
 came up with a proper analysis that could figure out that information. I
 guess the difference here is that we don’t expect random user-defined
 functions to have this property.

 The discussion of eta-expanding the argument of `runRW#` has been
 interrupted by comment:4, we should consider that thought again. Maybe one
 of the variants in comment:1 nail it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13104#comment:10>
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