[GHC] #5916: runST isn't free

[GHC]

#5916: runST isn't free
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    Reporter:  tibbe             |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  Compiler          |     Version:  7.4.1           
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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Comment(by simonpj):

 Conclusion: inline `runSTRep`, but very late. The comments suggest this is
 difficult. Perhaps we could arrange it so full laziness (which is what
 causes the wrong let floating according to the comment) happens before the
 last inliner phase. But this feels a bit brittle still, we have to be
 really careful so any optimizations we run won't result in things becoming
 shared CAFs.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5916#comment:6>
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