[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):  Phab:D2400
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by bgamari):

 > > Data con workers seems similarly specialised. It's just an encoding
 for a large family. Maybe 11b for rep-name?

 > Fair enough. Alright; I'll move ahead with this option then.

 On second thought, this is actually not entirely trivial; to see why,
 consider what happens when you are writing out the interface file of
 `GHC.Tuple`. Under the proposal, you would need to somehow recognize type
 representations (which are plain value-level bindings) which belong to a
 tuple type and encode them with the special symbol table encoding.

 Indeed we already do this for encoding `TyCon` names and it's not hard:
 just look for `TyCon`s with `algTcRhs = TupleTyCon {}` (as is done by
 `tyConTuple_maybe`). However, distinguishing a value level binding as a
 tuple's type rep is not as easy. I can think of two options neither being
 terribly nice,

  1. Build a `Map TypeRepName TupleSort` and check it for every symbol that
 we write to the symbol table (yuck)
  2. Add a constructor to `IdDetails` to encode the fact that the binding
 is the typerep of a tuple

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12357#comment:29>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler