[GHC] #12356: StaticPointers support in GHCi

[GHC]

#12356: StaticPointers support in GHCi
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        Reporter:  bgamari           |                Owner:
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            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:  #12000, #9878     |  Differential Rev(s):  Phab:D2504
       Wiki Page:                    |
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Comment (by bgamari):

 One particularly hairy problem that arises here is that of breakpoint
 ticks interacting with FloatOut. Currently we disallow any floating
 through breakpoint ticks. However, static pointer support requires that we
 float out static expressions to the top level. I can see two options here,

  1. Allow floating of `StaticPtr` values through breakpoints as a special
 case.
  2. Disable breakpoint production while `-XStaticPointers` is enabled.

 Given that (1) may give rise to some rather surprising behavior in the
 face of recursive groups (e.g. a recursive group with one `StaticPtr` and
 a bunch of other bindings; the whole group will need to be floated,
 killing breakpoint support for all floated code), I suspect that (2) is
 the only sensible option.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12356#comment:6>
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