[tree-ssa] Lazy updating of stmt operands

[Zdenek Dvorak]

Hello,

> I suspect the loop optimizations are going to fall into the same
> category as CCP in that they are going to be interested in the immediate
> uses of only a partial subset of variables most of the time. I think its
> far more efficient to calculate those when you need them/know what they
> are, and possibly maintain just those def->uses.

hardly; you still must scan all statements to find the uses, so I don't
see where you would want to get the extra efficiency.

Zdenek