sizetype, bitsizetype and DECL_FIELD_BITPOS

[Richard Kenner]

    > Yes.  VAR is clearly bitsizetype and OFFSET is supposed to be sizetype
    > and there's no conversion.

    size_binop is supposed to convert to sizetype.

In which cases?  Surely it can't convert both of its args unconditionally to
sizetype since it's called to do an EXACT_DIV_EXPR of a bitsizetype value by
BITS_PER_UNIT.  That division has to be in bitsizetype.  And in that case the
BITS_PER_UNIT also needs to be bitsizetype, while it's currently sizetype.
Moreover, in a number of cases, the WITH_RECORD_EXPR that's being made is
also the wrong type (sizetype instead of bitsizetype).

I'm certainly willing to fix this all up, but I'd like to try to get a
concensus as to what to fix it up *to*.  I'd really like to better understand
the reason for adding all this in the first place since it seems like it'll
be quite a lot of trouble to get this to work properly and I'm not convinced
it's worth it and it wouldn't be simpler just to back this all out and try to
find another way to fix the original problem (which I don't have a complete
explanation of yet).