Variable Expansion Optimization

[Zdenek Dvorak]

Hello,

> >1) The loop unrolling as a separate optimization should be done on
> >   rtl level, to avoid unnecessary compile-time overheads (optimizing
> >   the unrolled loop bodies separately is rarely useful and usually
> >   just a waste of time).  For reasons mentioned by Sebastian (possible
> >   loss of information during unrolling, mostly), I believe the right
> >   place for the unrolling optimization would be after the loop-aware
> >   scheduling passes (SMS), and before rest of scheduling passes and
> >   register allocation.
> 
> Well, SMS could overlap more insns if the loop is unrolled before SMS.

as I understood, unrolling is a part of SMS; why this should be the
case?

Zdenek

> OTOH, SMS generates register-moves (in the absence of rotating registers),
> which could be eliminated by further unrolling - after or as a final step
> of SMS.