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

[GHC]

#15938: Hadrian's recompilation check is extremely slow
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  alpmestan
            Type:  bug               |               Status:  patch
        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):  Phab:D5412,
       Wiki Page:                    |  Phab:D5422
-------------------------------------+-------------------------------------

Comment (by alpmestan):

 Both D5412 and D5422 have landed on master. When I now resume builds that
 I stopped while building base (`_build/stage1/libraries/base/*`), hadrian
 gets back to work pretty quickly on my machine, never above 5 seconds for
 sure, and it seems to me it's back on track within 2-3 seconds in general
 now.

 Is this acceptable? Can we consider this problem solved and close the
 ticket?

 (We might want to get rid of the only big rule enumeration we have left --
 the ones for generated files, `Rules.Generate` -- but I'd say it's not
 worth the trouble right now. The impact would quite likely be minor, while
 requiring some non trivial effort.)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:40>
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