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

[GHC]

#12357: Increasing maximum constraint tuple size significantly blows up compiler
allocations
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        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):  Phab:D2400
       Wiki Page:                    |
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Comment (by bgamari):

 Hmm, while purusing I stumbled upon this comment in `TysWiredIn`,
 {{{
 wiredInTyCons = [ unitTyCon     -- Not treated like other tuples, because
                                 -- it's defined in GHC.Base, and there's
 only
                                 -- one of it.  We put it in wiredInTyCons
 so
                                 -- that it'll pre-populate the name cache,
 so
                                 -- the special case in lookupOrigNameCache
                                 -- doesn't need to look out for it
                 , ...
 }}}

 Which could be interpreted to imply that `wiredInTyCons`, not
 `allKnownKeyTyCons`, should be used to initialize the original name cache.
 Was this intentional or just me reading too much into the language?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12357#comment:24>
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