Factoring algorithms on rtl ?

[Joern Rennecke]

> 
> > Gábor Lóki wrote:
> > >The attached patch finds those basic blocks of which the first insns
> > >are indentical, and factor out them into the end of parent basic blocks.
> > >This is done only if it has no side effects and the count of original
> > >insns - marked for factoring - is greater than the count of parent basic
> > >blocks.
> > 
> > This seems to be the same optmization as cross-jumping, except that 
> > cross-jumping only handles the suffix case, and you are trying to handle 
> > both prefix and suffix cases.

While my if-convert code handles just the complete equivalence case, but
allows for local registers and an input register.  I've started it rewriting
it so that it scans from the end of the block so that the code can be
shared with crossjumping...