--- Comment #101 from Walter Bright <> 2011-04-14 
14:46:52 PDT ---
(In reply to comment #96)
> Anyway, this problem is taking care of in the implementation by nfxjfg,

His bitmap implementation consists of two bitmaps, one for all pointers and the
other for the subset that are ambiguous. There is one bit for each PTRSIZE

Although that works, the difficulty with it is the potentially large amount of
static data this requires:

1. ambiguous pointers are pretty rare, so the second bitmap will be largely 0
2. non-pointer fields still consume space in the bitmaps
3. static arrays are fully fleshed out, so a large static array will have a
correspondingly large bitmap
4. large static arrays embedded in a struct with another pointer in them will
be fully fleshed out, even if there are no pointers in the array
5. there's no provision for reusing bitmaps for types embedded in aggregate
types, everything is repeated

This also applies at compile time, where one byte per pointer size for every
type is allocated.

I think the static size is important - take a look at the .map file of a
typical D app, and there's a lot of space consumed by the typeinfo data.

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