YAMP: ivopts vs sizetype

[DJ Delorie]

> I don't think you can tell that, but maybe look into tree-ssa-address.c where
> it asks the target for costs via building some rtx-en.

Ok, here's something... I adjusted my address_cost hook to figure
costs of offsets more accurately, and even though it only tests
"offset" vs "no offset", it does seem to prefer the working case (no
offset, vs negative offset) more.  Not sure how many tests it will
fix, but it fixes at least the one I reported.  On to testing...