[GHC] #5642: Deriving Generic of a big type takes a long time and lots of space

[GHC]

#5642: Deriving Generic of a big type takes a long time and lots of space
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        Reporter:  basvandijk        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.3
      Resolution:                    |             Keywords:  deriving-
                                     |  perf, Generics
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:  T5642
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2304
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"34010dbe77ac405da6c671c3feb3573d0d025379/ghc" 34010db/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="34010dbe77ac405da6c671c3feb3573d0d025379"
 Derive the Generic instance in perf/compiler/T5642

 Summary:
 For some inexplicable reason, the `Generic` instance in
 `perf/compiler/T5642` is written out entirely by hand. This is not only
 strange, since Trac #5642 is about derived `Generic` instances, but it
 also
 annoying to maintain, since it requires manually changing a bunch of code
 whenever the algorithm behind `deriving Generic` changes. (See D2304 for a
 recent example of this.)

 It seems more sensible to just derive the `Generic` instance. It shifts
 the
 goalposts of what allocations we're measuring a bit, since we no longer
 have
 to parse a large amount of code (and as a knock-on effect, the allocations
 go
 down a bit). But I think this program is morally equivalent to what we
 were
 benchmarking before, so it's not too unreasonable to change.

 Test Plan: make test TEST=T5642

 Reviewers: austin, thomie, bgamari

 Reviewed By: bgamari

 Differential Revision: https://phabricator.haskell.org/D2511

 GHC Trac Issues: #5642
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5642#comment:48>
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