[GHC] #12191: 7% allocation regression in Haddock performance tests

[GHC]

#12191: 7% allocation regression in Haddock performance tests
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  niteria
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10482            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Bartosz Nitka <niteria@…>):

 In [changeset:"123062946dfdbcfc24abd468e24e358118b8e2eb/ghc"
 12306294/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="123062946dfdbcfc24abd468e24e358118b8e2eb"
 Make checkFamInstConsistency less expensive

 Doing canonicalization on every comparison turned
 out to be very expensive.

 Caching the canonicalization through the smart `modulePair` constructor
 gives `8%` reduction in allocations on `haddock.compiler` and
 `8.5%` reduction in allocations on `haddock.Cabal`.
 Possibly other things as well, but it's really visible in Haddock.

 Test Plan: ./validate

 Reviewers: jstolarek, simonpj, austin, simonmar, bgamari

 Reviewed By: simonpj, simonmar

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2350

 GHC Trac Issues: #12191
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12191#comment:12>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler