[GHC] #15938: Hadrian's recompilation check is extremely slow

[GHC]

#15938: Hadrian's recompilation check is extremely slow
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Build System      |              Version:  8.6.2
  (Hadrian)                          |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Thankfully, while things get quite bad in half-built trees (as seen in
 comment:16), they appear to get better once the build has finished (as
 suggested by mpickering in comment:1). After finishing the build the no-op
 rebuild time is around 15 seconds. Still bad, but at least it's not 45
 seconds

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:18>
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