[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        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           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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 In make mode, GHC keeps a lot of in-memory data structures about modules
 it has built and interface files it has read. These data structures are
 long-lived and immutable (at least, per module/mutually recursive module
 group/package), so they may be candidates for storing in compact regions
 to reduce the work done by the GC.

 Potential problem: if we rely heavily on lazy evaluation in these
 structures for the purpose of avoiding work that will never be needed,
 then we can't store them in a compact region (since the contents of a
 compact region must be fully evaluated).

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