[GHC] #8742: Reuse scavenge_small_bitmap

[GHC]

#8742: Reuse scavenge_small_bitmap
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        Reporter:  Tarrasch          |            Owner:
            Type:  task              |           Status:  patch
        Priority:  lowest            |        Milestone:  7.10.1
       Component:  Runtime System    |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Tarrasch):

 Ok. I stumbled upon the same exact set of issues with non-matching types
 for `Compact.c`. It seems like at differenct places `StgWord`, `W_` and
 `nat` is used. And again `scavenge_PAP_payload` gets passed
 `StgHalfWord`s.

 If I were to unify these to use the same type for the variable `size`,
 which should it be? I would myself just go for `StgWord` since if you look
 at the `bitmap` variable, it's usually of type `StgWord`, and usually the
 equation is that `size == BITMAP_SIZE(bitmap) == ((bitmap) &
 BITMAP_SIZE_MASK)`.

 Am I over-thinking this? I just think that with these series of patches we
 get these two nice benefits:

   1. A consistent use of the types (or is there any good reason they
 differ so much?)
   2. We can safely apply two patches that would remove a total of 30 lines
 of code. Without worrying that we loose performance since the `.o` files
 can be checked to be exact matches.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8742#comment:10>
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