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

[GHC]

#15938: Hadrian's recompilation check is extremely slow
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.8.1
          Component:  Build System   |           Version:  8.6.2
  (Hadrian)                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I just Ctrl-C'd hadrian while it was building `libraries/base`, having
 noticed that I forgot to start it with `-j`. I then immediately restarted
 it and noticed that Hadrian needed to think for 45 seconds before it
 started even a single build. This is orders of magnitude worse than `make`
 so something must be wrong.

 I'm setting this at high priority since 45 seconds is longer than many
 complete `make` rebuilds.

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