[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)                          |
      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:                    |
-------------------------------------+-------------------------------------
Changes (by snowleopard):

 * cc: NeilMitchell (added)


Comment:

 Thank for reporting. 45 seconds of doing nothing sounds strange, I'm not
 sure how/why this happened. Is this something you can reliably reproduce
 by `Ctrl-C`'ing the full build in the middle of building `libraries/base`?

 Zero build currently takes around 7 seconds on my machine. Neil was
 optimistic that we'll be able to substantially improve this, so I'm
 tagging him too.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler