[GHC] #12415: Fancy BinIface encoding for tuples is broken for constraint tuples

[GHC]

#12415: Fancy BinIface encoding for tuples is broken for constraint tuples
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12357            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Simon and I have been doing a lot of thinking about how best to fix this:
 here is the current story.

 It looks like we can get rid of the entirely tuple serialization since
 tuples (and indeed all other wired-in things) are known-key and are
 therefore already serialized efficiently with the existing known-key logic
 in `BinIface`. I've gone ahead and removed this codepath in Phab:D2467.

 However, Phab:D2467 still leaves some room for improvement as we have an
 extremely large number of tuple and sum names in `knownKeyNames` and hence
 the name cache unnecessarily. These can in principle be removed (and
 indeed this was what lead me to this ticket to begin with). However, as
 this is largely an orthogonal matter I'll be tracking it in #

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12415#comment:5>
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