[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 Ben Gamari <ben@…>):

 In [changeset:"665f8b0c778b3a5dac4696f81da0cea88b101ea9/ghc" 665f8b0/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="665f8b0c778b3a5dac4696f81da0cea88b101ea9"
 hadrian: eliminate most of the remaining big rule enumerations

 Following what was done to Rules.Library some time ago and to
 Rules.Compile recently (D5412), this patch moves more rules away from
 the "enumerate a lot of contexts and generate one rule for each" style
 and instead uses the "parse data from file path to recover context"
 approach. In fact, the only rules left to convert seem to be the ones
 from Rules.Generate.

 This effectively decreases the pauses described in #15938 further as
 well as the amount of allocations and GC that we do, unsurprisingly.
 Nowhere as drastically as D5412, though.

 Test Plan: perform full build and generate docs

 Reviewers: snowleopard, bgamari

 Reviewed By: snowleopard

 Subscribers: rwbarton, carter

 GHC Trac Issues: #15938

 Differential Revision: https://phabricator.haskell.org/D5422
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15938#comment:39>
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