[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:  alpmestan
            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 NeilMitchell):

 I just added a feature to Shake HEAD when running in diagnostic mode
 {{{-VVV}}} prints out the number of actions, rules and user rules:

 {{{
 % Number of actions = 0
 % Number of builtin rules = 20 [OracleQ Generator,OracleQ
 ModuleFiles,OracleQ
 PackageConfigurationKey,FilesQ,FileQ,GetDirectoryFilesQ,OracleQ
 WindowsPath,OracleQ DirectoryContents,OracleQ KeyValue,OracleQ
 LookupInPath,OracleQ KeyValues,OracleQ
 ContextDataKey,DoesDirectoryExistQ,AlwaysRerunQ,GetDirectoryContentsQ,OracleQ
 (ArgsHash Context Builder),DoesFileExistQ,GetDirectoryDirsQ,OracleQ
 PackageDataKey,GetEnvQ]
 % Number of user rule types = 2
 % Number of user rules = 36790
 }}}

 The number of user rules at 36K is way higher than Shake can deal with
 nicely. I see one for every directory (e.g.
 {{{_build/stage3/libraries/containers/build/cmm}}},
 {{{_build/stage3/libraries/containers/build/c}}},
 {{{_build/stage3/libraries/containers/build/s}}}) cross product with every
 extension (e.g. {{{.l_o}}}, {{{.thr_debug_o}}}, {{{.thr_dyn_o}}}).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:29>
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