Re: Graph colouring and local register allocation

Pertti Kellomdki <pertti.kellomaki@tut.fi> writes:


> So what are the trade-offs for ILP vs. non-ILP register
> allocation? It is pretty clear that you don't want to
> introduce unnecessary dependences in you code by register
> reuse in the ILP case, but is there more than that to it?


Actually, register reuse is not a problem on most OOO architectures,
as they use register renaming at runtime to avoid this kind of
dependencies. And on processors that do dynamic runtime scheduling,
compile-time scheduling is less important than avoiding spills: The
processor can to some extent schedule around a bad compile-time
schedule, but it can't undo a spill.


If you work with processors that have little or no runtime scheduling
but lots of registers (Itanium, Cell, etc.), then compile-time
scheduling becomes more important than register allocation.


Torben

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