[PATCH] Fix optimization regression in constant folder

[Richard Kenner]

> I don't think that's good enough.  If we can't specify this better, then
> I suspect that, over time, it's going to break, and people will
> eventually just rip it out.  

I think we CAN specific it better, but it's just not that easy.

> That begs the question: why aren't they signed

I think because you run into problems in corner cases in C if size_t and
sizetype don't have the same precision and signedness or, more precisely,
if you can't encode a value that's a valid result of size_t in sizetype.