[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
-------------------------------------+-------------------------------------
        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):  Phab:D3399,
       Wiki Page:                    |  Phab:D3400
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Changes (by simonpj):

 * status:  closed => new
 * owner:  rwbarton => (none)
 * resolution:  fixed =>


Comment:

 Ben, I'm puzzled here.  This commit seems to implement comment:15 (in
 `rebuildCase`) but not comment:11 and its antecedents.  How does your
 commit relate to Reid's work on this ticket?

 And did this one change cure the leak?  Reid thinks not?

 I'd like to work through comment:19 too.

 Moreover, presumably the commit you did make (in `rebuildCase`) presumably
 does help something substantially, or you would not have done it (esp
 given its equivocal effect on other perf tests).  But neither the commit
 message, nor (more importantly) the comment in the code, says what!
 `DynFlags` perhaps?  Please say, so that someone wondering if they can now
 take it out knows what they have to test against.

 I'm re-opening pending resolving some of these mysteries.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13426#comment:24>
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