[LLVMdev] Order of optimization: modulo scheduling & register allocation

[greened at obbligato.org]

Jakob Stoklund Olesen <stoklund at 2pi.dk> writes:

>     If modulo scheduling happens before more code is introduced, how
>     do we know that we still have an optimal schedule?  Is there
>     another scheduling stage during later optimization?

I think in general that a modulo scheduler will have to mark a
scheduled block to be untouched by other things.  There are too
many strange things that can happen in-between the scheduler
and actual asm emission.

> There is a post-RA scheduling pass. It is only used when compiling for
> in-order CPUs. Out-of-order CPUs usually don't care.

There are any number of reasons to do scheuling for out-of-order
machines.

                           -David