Richard Kenner
Sun Feb 20 11:50:00 GMT 2000

    In the C++ front-end, BINFO_OFFSET always has type sizetype, to the
    best of my knowledge.  However, we often need to subtract one
    BINFO_OFFSET from another, and that often yields negative values.  (In
    other words, we ask the question: how far is it from this sub-object
    to this other sub-object?)

That sounds like a common enough idiom to justify a size_diffop, which
takes two operands that are either both sizetype or both bitsize type
and returns an object of ssizetype or sbitsizetype.

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