[GHC] #12896: Consider using compact regions in GHC itself to reduce GC overhead

[GHC]

#12896: Consider using compact regions in GHC itself to reduce GC overhead
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        Reporter:  rwbarton          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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 simonmar):

 I actually tried using it for interface files, but it won't work (yet).
 We can't compact pinned memory, and FastString is implemented in terms of
 ByteString, which is backed by pinned memory.  Perhaps we ought to
 special-case this somehow, because compacting things involving ByteString
 would be really useful - it would be possible but we have to adjust the
 address stored in the ByteString when we copy it.  (or fix ByteString to
 use unpinned memory, which we want to do anyway, but that's harder).

 Also I'm not 100% sure that there aren't functions buried somewhere in
 ModIface, which also can't be compacted.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12896#comment:2>
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