[GHC] #9221: (super!) linear slowdown of parallel builds on 40 core machine

[GHC]

#9221: (super!) linear slowdown of parallel builds on 40 core machine
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        Reporter:  carter            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.8.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #910, #8224       |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by slyfox):

 As -feaged-blackholing helps for this case how would one find
 out statistics of closures needlessly computed multiple times?

 One of 'unsafeDupable' examples that might be heavyweight
 when done multiple times:
 http://git.haskell.org/ghc.git/blob/HEAD:/libraries/base/GHC/Fingerprint.hs#l45

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9221#comment:50>
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