[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:  patch
        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):  Phab:D2400,
       Wiki Page:                    |  Phab:D2414
-------------------------------------+-------------------------------------

Comment (by bgamari):

 Sadly I mentioned the wrong commit in the commit message. Here is the
 merged commit for Phab:D2414,

 In [changeset:"9513fe6bdeafd35ca1a04e17b5f94732516766aa/ghc" 9513fe6/ghc]:
 {{{
 Clean up interaction between name cache and built-in syntax

 This cleans up various aspects of the handling of built-in syntax in the
 original name cache (hopefully resulting in a nice reduction in compiler
 allocations),

   * Remove tuple types from original name cache: There is really no
     reason for these to be in the name cache since we already handle
     them specially in interface files to ensure that we can resolve them
     directly to Names, avoiding extraneous name cache lookups.

   * Sadly it's not possible to remove all traces of tuples from the
     name cache, however. Namely we need to keep the tuple type
     representations in since otherwise they would need to be wired-in

   * Remove the special cases for (:), [], and (##) in isBuiltInOcc_maybe
     and rename it to isTupleOcc_maybe

   * Split lookupOrigNameCache into two variants,

      * lookupOrigNameCache': Merely looks up an OccName in the original
        name cache, making no attempt to resolve tuples

      * lookupOrigNameCache: Like the above but handles tuples as well.
        This is given the un-primed name since it does the "obvious"
        thing from the perspective of an API user, who knows nothing of
        our special treatment of tuples.

 Arriving at this design took a significant amount of iteration. The
 trail of debris leading here can be found in #11357.

 Thanks to ezyang and Simon for all of their help in coming to this
 solution.

 Test Plan: Validate

 Reviewers: goldfire, simonpj, austin

 Reviewed By: simonpj

 Subscribers: thomie, ezyang

 Differential Revision: https://phabricator.haskell.org/D2414

 GHC Trac Issues: #11357
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12357#comment:35>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler