[GHC] #4951: Performance regression 7.0.1 -> 7.0.1.20110201

[GHC]

#4951: Performance regression 7.0.1 -> 7.0.1.20110201
---------------------------------+------------------------------------------
    Reporter:  simonmar          |        Owner:                         
        Type:  bug               |       Status:  merge                  
    Priority:  highest           |    Milestone:  7.0.2                  
   Component:  Compiler          |      Version:  7.0.1                  
    Keywords:                    |     Testcase:                         
   Blockedby:                    |   Difficulty:                         
          Os:  Unknown/Multiple  |     Blocking:                         
Architecture:  Unknown/Multiple  |      Failure:  Runtime performance bug
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Changes (by simonmar):

  * status:  new => merge


Comment:

 The difference turned out to be in the inner loop of `hPutStr`, nothing to
 do with fusion as we first thought.

 Simon and I have verified that merging

 {{{
 Tue Dec 21 16:58:00 GMT 2010  simonpj at microsoft.com
   * Add a simple arity analyser
 }}}

 from HEAD into stable (it pulls in 2 dependencies) fixes the problem.

 I'll do a nofib run with this change and compare against 7.0.1.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4951#comment:1>
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