[patch] Lno branch merge part 3 -- ssa form updating improvements

[Zdenek Dvorak]

Hello,

> > Yes; the method is not really much different from what
> > rewrite_ssa_into_ssa does. The exceptions are that
> > rewrite_ssa_into_ssa searches for new definitions by scanning all the
> > statements (making it possibly a bit slower), and that it works for
> > multiple definitions at a time (making it possibly a bit faster, and
> > much easier to use then direct incremental algorithm).
> > 
> Then let's keep them separate.  They are conceptually different and we
> need the abstraction of being able to insert new SSA definitions.

you may use rewrite_ssa_into_ssa for this, as well as incremental
updating and often in an easier way.  So I don't really see what you
protest against (so far you have provided no reason except for your
personal dislike of the concept, sorry).

> So
> far, I see no compelling reasons why we should make rewrite_into_ssa any
> more complicated than it already is.

I do not touch rewrite_into_ssa at all (I just share some parts to avoid code
duplication).

> The patch is very intrusive in that respect and it will be difficult to
> maintain.  We will now have two SSA renaming algorithms, each slightly
> different yet similar.

If you check the incremental updating algorithm, you will see that it
also uses basically the same SSA renaming algorithm as well, so you
won't avoid this.

> Am I missing anything?  You are resisting the idea of having a separate
> name insertion utility, but I don't really understand why.

Because it is harder to use as I argumented (and also because the rest
of the lno-branch depends on this patch, and I don't really have time to
rewrite it and test it just for your pleasure just now).

Zdenek