[GHC] #10260: last uses too much space with optimizations disabled

[GHC]

#10260: last uses too much space with optimizations disabled
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        Reporter:  rwbarton          |                   Owner:  nomeata
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:
       Component:  Core Libraries    |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D847
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Comment (by nomeata):

 Ah, right, the template is stored before this happens; good.

 What is our motivation to eta-expand PAPs? In this case, it is to allow
 for RULES to fire. Is it not likely that in order for RULES to fire, we
 might have to eta-expand beyond a coercion? So it does not gain a lot in
 robustness.

 I’m inclined to wait for more than just this example to give this a shot,
 after all, implementing the heuristics (“if it is a PAP, and there is a
 chance to eta-expand, but only up to the next coercion...”) does not
 really make the code simpler...

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10260#comment:14>
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