[PATCH] Remove bogus TYPE_IS_SIZETYPE special-casing in extract_muldiv_1

[Richard Kenner]

Let me jump in on this a little bit, since much of the code in this area
was originally written by me.

> Are all sizetype (sub-)expressions always of value in that range?
> What do we do about the fact that sizetype is unsigned, so -x always
> overflows for x != 0?  Thus, do we need to disable all a - b -> a +
> -b kind of foldings for sizetypes? (we don't)

The basic idea is that an overflow of sizetype is either:

(1) Detected at a higher level (e.g., testing for maximum sizes of objects) or;
(2) Is an undetected error and hence the result of such overflow is undefined.

What this means from a practical point of view (but indeed a bit hard
to define from a formal point of view) is that the normal addition and
subtraction operations (on a 2's complement machines, which all are
now) will "do the right thing" in all cases so we can perform all
those sorts of folding operations.