[GHC] #12357: Increasing maximum constraint tuple size significantly blows up compiler allocations

[GHC]

#12357: Increasing maximum constraint tuple size significantly blows up compiler
allocations
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      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):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"f53d761df9762232b54ec57a950d301011cd21f8/ghc" f53d761/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="f53d761df9762232b54ec57a950d301011cd21f8"
 TysWiredIn: Use UniqFM lookup for built-in OccNames

 Previously we would unpack the OccName into a String, then pattern match
 against this string. Due to the implementation of `unpackFS`, this
 actually unpacks the entire contents, even though we often only need to
 look at the first few characters.

 Here we take another approach: build a UniqFM with the known built-in
 OccNames, allowing us to use `FastString`'s hash-based comparison
 instead.

 Reviewers: simonpj, austin, simonmar

 Reviewed By: simonmar

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2385

 GHC Trac Issues: #12357
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12357#comment:18>
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