[tree-ssa] Fix problem with loop notes emitted by targets

[Jan Hubicka]

> Hello,
> 
> > > some targets (s390, maybe other) produce loops when expanding
> > > builtins; this causes problems as create_loop_notes does not like
> > > the notes created by them.  This patch makes the functions that expand
> > > loops work without creating the notes.  It also removes
> > > NOTE_INSN_LOOP_CONT, since it is not produced anywhere.
> > 
> > There are some parts of loop.c that rely on presence of LOOP_CONT (such
> > as dbra code) If we want to save them, we can simply emit LOOP_CONT note
> > at the beggining of latch basic block (or more aggressivly a superblock).
> 
> we currently don't produce these notes at all on tree-ssa branch anyway,
> so it does not seem to be a big problem; especially since I hope to get
> rid of the whole loop.c soon.
That would be best of course :)  I think we ought to start killing loop
pass slowly now.  What about removing unroller for start?

I would be curious tought how much of problem not emitting the
LOOP_CONT notes contribute to the current perfomrance regression
relative to mainline...

Honza
> 
> Zdenek