Enable SSA at -O0

[Robert Dewar]

Richard Guenther wrote:

> Uh, well.  We are going to merge 5 branches, SSA at -O0 is a minor
> thing.  I don't see why you are so concerned about its effects?
> Also most of the benefits, like enabling some extra warnings at -O0,
> consistent asm constraint processing, getting rid of unneccessary
> code can be done in short time.

My biggest concern is that this may degrade debugging. We have
done quite a number on -O1 debuggability, and I am quite concerned
about this issue. if we can really be sure that there is zero or
positive impact on debugging and no other negatives, I have no
objection.
> 
> But well I'll stop trying to argue here, as obviously my priorities
> do not match yours.
> 
> Thanks,
> Richard.