[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 bgamari):

 Indeed something catastrophic is happening here; this can be plainly seen
 in the `+RTS -h` profiles I attached above. These were produced by
 building two GHC trees, one bootstrapping with 8.2 and another with 8.0.2,
 taking the `DynFlags` command line from the stage1 build, and adding
 `-fforce-recomp -v +RTS -h >log 2>&1` to it. Clearly we have a significant
 amount of leakage.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13426#comment:5>
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