[cfg-branch] unroll-new cleanups

[Zdenek Dvorak]

> > Hello.
> > 
> > > > To be able to handle overflow, we must at least ensure that number of unrolling
> > > > is a power of 2.
> > > 
> > > Why?
> > 
> > Consider
> > 
> > for (i=1;i!=0;i++)
> >   do_something ();
> > 
> > if you unroll this (say) 3 times, in which copy will it exit? It depends on
> > what is range of i's type modulo 3; perhaps it can be handled somehow, but it
> > is much easier to unroll it with number of unrollings being power of two, when
> > we use the fact that this number is always 0.
> 
> Is this corect
>   If I will set number of unrollings to 4, and we unroll the "usual way"
>
> for (i=1;i!=0;i+=4)
> {
>   do_something ();
>   do_something ();
>   do_something ();
>   do_something ();
> }
> 
> it will never get to zero...

But we do not unroll it this way, of course. What we currently do
(after lot of simplifying) is

do_something ();
do_something ();
do_something ();
i=4;
for (;i!=0;i+=4)
 {
   do_something ();
   do_something ();
   do_something ();
   do_something ();
 }

> I think we should compute that the loop has 0xff iterations (lets count in
> unsigned chars) and unroll by something that divides 255, lets say 5 times.

This makes no sense to me, sorry. Could you explain more precisely?

Zdenek