[GHC] #13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC 8.2

[GHC]

#13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC
8.2
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        Reporter:  hvr               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      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):
       Wiki Page:                    |
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Comment (by simonpj):

 Great work.  There is definitely a space leak here and it should not be to
 hard to find.  Some ideas

 * In `CoreLint.lintSingleBinding` you'll find a series of tests.  If you
 comment then out one by one, you'll find when the space leak comes back.
 That test must be forcing the offending bit of `IdInfo`.

 * Does the leak happen when you use `-dshow-passes`?  That shows the size
 of eac intermediate, and `exprSize` is deliberately strict (see
 `CoreStats.bndrSize`).

   You could try making `CoreSeq.megaSeqidInfo` actually force the
 unfolding info (currently commented out) and see if that helps.  (I'm not
 sure WHY it is commented out, incidentally.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13426#comment:7>
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