[patches] flow based jump pass take 2

[Jan Hubicka]

> > At the moment I am shooting for corectness of the patch.  There are some dark
> > sides, such as USE and CLOBBER expressions.  Old jump pass takes a lot of
> > care to move them when restructuring flowgraph.  I simply zap them and I am
> > not sure this is good idea.
> 
> Careful here -- I don't think jump was completely correct
> either.  I can't remember specifics at the moment; just a
> feeling.
Yes, I am trying to be curefull.
Basically I don't change use/clobbers before reload, I consider them
as an instructions.
After reload I zap them. reorg is possible candidate for problems,
I will try to investigate that beast but it is all greek for me.

Honza
> 
> 
> r~