[GHC] #1600: Optimisation: CPR the results of IO

[GHC]

#1600: Optimisation: CPR the results of IO
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        Reporter:  simonmar          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler          |              Version:  6.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #8598             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonmar):

 > (I had stage=2 in build.mk. I removed it and typed make. Is it not
 sufficient to cause a full build?).

 make won't necessarily rebuild your libraries, due to GHC's recompilation
 avoidance.  It knows about changes in the source code and the flags, but
 it doesn't know about changes in GHC itself.  So when I'm making
 measurements like this, I always delete the library object files manually:

 ```
 find libraries/*/dist-install | grep 'o$' | xargs rm
 ```

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:61>
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