[GHC] #12437: 20% regression in max_bytes_used for T1969

[GHC]

#12437: 20% regression in max_bytes_used for T1969
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        Reporter:  simonmar          |                Owner:  osa1
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       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:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 I'm experimenting with some changes to fix this without bumping any
 numbers, so I may leave this unfixed for a little bit more if that's OK?
 Otherwise let me know and I'll bump the number.

 (Unfortunately even if I fix this, in a few commits it'll be broken again,
 this time because of `peak_megabytes_allocated`. Apparently it has been
 increasing for a long time and now we have 1MB left before it needs
 bumping again.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12437#comment:9>
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