[GHC] #13479: Core Lint issues during slowtest

[GHC]

#13479: Core Lint issues during slowtest
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        Reporter:  bgamari           |                Owner:  nomeata
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10181            |  Differential Rev(s):  Phab:D3390
       Wiki Page:                    |
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Comment (by nomeata):

 > I’ll add a note, and not set the call arity annotation.
 >
 > (Although it is debatable whether the simplifier is really innocent. The
 annotation is *true* even on join points; it is the simplifier that is
 stubbornly (but with good reason) refusing to eta-expand the join point!)

 I have a patch that does this, but I don’t like it. The Call Arity
 analysis uses the `idCallArity` fields internally as well (in particular
 `callArityRecEnv` reads it), and if I don’t set the Call Arity annotation,
 then things can go wrong. Some refactoring of the analysis could avoid
 this, of course, but given that the call arity annotation is not *wrong*
 on join points, I do not see the advantage of special-casing join-points
 here.

 Also zapping the call arity information in the simplifier is the right
 thing to do in any case. So the current state of affair seems fine with
 me.

 I did add a Note, though.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13479#comment:16>
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