[GHC] #7309: The Ix instance for (,) leaks space in range

[GHC]

#7309: The Ix instance for (,) leaks space in range
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    Reporter:  nomeata            |       Owner:                         
        Type:  bug                |      Status:  new                    
    Priority:  normal             |   Milestone:                         
   Component:  libraries (other)  |     Version:  7.6.1                  
    Keywords:                     |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple   |     Failure:  Runtime performance bug
  Difficulty:  Unknown            |    Testcase:                         
   Blockedby:                     |    Blocking:                         
     Related:                     |  
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Comment(by nomeata):

 Would #7206 really help here? After all, the problematic code is
 polymophic, so there is not a concrete ```range``` that could be inlined
 to a ```cheapBuild```.

 In code where the tuple-```range``` is inlined and the concrete
 ```range``` functions of the element types are known (as in the second
 example in the stack exchange question), things already work out nicely as
 the foldr/builder fusion actually kicks in.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7309#comment:2>
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