[GHC] #14693: Computing imp_finst can take up significant amount of time

[GHC]

#14693: Computing imp_finst can take up significant amount of time
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        Reporter:  niteria           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  phab:D4369
       Wiki Page:                    |
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Comment (by Bartosz Nitka <niteria@…>):

 In [changeset:"d2511e3b61563ed3fc2c9aec2c90a4156373a24c/ghc" d2511e3/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="d2511e3b61563ed3fc2c9aec2c90a4156373a24c"
 Compute the union of imp_finsts on the side

 I've explained most of the rationale in a new Note.
 I'd happily add a test for this, but the difference is only
 visible in run time, allocations remain more or less the same.

 FWIW running `generateModules` from #14693 with DEPTH=16, WIDTH=30
 finishes in `23s` before, and `11s` after.

 Test Plan: ./validate

 Reviewers: simonpj, simonmar, bgamari

 Reviewed By: simonpj

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #14693

 Differential Revision: https://phabricator.haskell.org/D4369
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14693#comment:5>
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