[GHC] #5567: LLVM: Improve alias analysis / performance

[GHC]

#5567: LLVM: Improve alias analysis / performance
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    Reporter:  dterei            |       Owner:  dterei                 
        Type:  task              |      Status:  new                    
    Priority:  normal            |   Component:  Compiler (LLVM)        
     Version:                    |    Keywords:                         
    Testcase:                    |   Blockedby:                         
          Os:  Unknown/Multiple  |    Blocking:                         
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
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 * LLVM doesn't generate as good as code as we feel it should in many
 situations
  * Why?
     * We've often felt its a alias anlysis issue.
     * I'm a little more doubtful of that than others (I feel its part of
 the bigger problem, not the whole thing).
     * I think there may be some register allocation / instruction
 selection / live range splitting issue going on.
  * We could also do with looking at what optimisation passes we should run
 and in what order...

 Here is some work Max did on the alias issue, his results for nofib
 weren't good:

 http://blog.omega-prime.co.uk/?p=135

 So this ticket is just a high level ticket about figuring out and
 improving the performance of LLVM backend.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5567>
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