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Re: register allocation vs. scheduling and other stuff
- From: tm_gccmail at mail dot kloo dot net
- To: Brad Lucier <lucier at math dot purdue dot edu>
- Cc: tm <tm at mail dot kloo dot net>, gcc at gcc dot gnu dot org
- Date: Mon, 6 Jan 2003 16:40:53 -0800 (PST)
- Subject: Re: register allocation vs. scheduling and other stuff
On Mon, 6 Jan 2003, Brad Lucier wrote:
> > >Since we will have a new register allocator for 3.4 that is based on
> > >graph coloring, perhaps one could add a new flag
> > >
> > >--fuse-all-registers
> > >
> > >that would not try to use the *minimum* number of colors to color an
> > >interference graph, but, if the minimum number is less than the actual
> > >number of available registers, it could use the actual numbers of
> > >registers to color the graph, perhaps guided by liveness information.
> >
> > This is a kludgy solution IMHO.
>
> OK, the special flag might be a kludge.
>
> And it's a known problem after all.
>
> The point I was trying to make that got lost in all the verbiage is
> that one might want to try to teach the register allocator a bit
> about scheduling rather than trying to teach the scheduler a bit about
> register allocation.
This makes sense to me too. Scheduler modifications to estimate register
pressure are dependent on the register allocation algorithm (and
possibly sensitive to small tweaks in the register allocator) whereas
register allocator modifications to reduce register pressure are not
dependent on the scheduling algorithm.
Toshi