[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 simonpj):

 >  If we exclude tuple type representations from the known key list then
 they will be loaded from GHC/Tuple.hi with the wrong unique

 I don't understand. Isn't that what `-- Note [Symbol table representation
 of names]`
  is all about? What gets loaded with the wrong key?

 >     Add a special encoding to the symbol table format for type rep
 names. However, it seems odd to add special encodings in the interface
 file format for such a narrow case

 Not really.  We already have
 {{{
 --   A tuple name:
 --    x is the tuple sort (00b ==> boxed, 01b ==> unboxed, 10b ==>
 constraint)
 --    y is the thing (00b ==> tycon, 01b ==> datacon, 10b ==> datacon
 worker)
 --    z is the arity
 }}}
 Data con workers seems similarly specialised.  It's just an encoding for a
 large family.  Maybe 11b for rep-name?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12357#comment:27>
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