[LLVMdev] Complex load patterns and token factors

[Hal Finkel]

On Sun, 24 Jun 2012 10:18:00 +0100
Tim Northover <t.p.northover at gmail.com> wrote:

> > I also had to include II.canFoldAsLoad to make this work for me. As
> > is the case with other "simple" loads in the PowerPC backend,
> > canFoldAsLoad is set but mayLoad is not (is this wrong)?
> 
> Hmm. So far we've got: mayLoad, mayStore, canFoldAsLoad and
> hasUnmodeledSideEffects as candidates.
> 
> Looking at Target.td, I see that I missed hasCtrlDep which seems to be
> exactly what we're looking for, though it doesn't appear to actually
> be used for *anything* at the moment. I'm not sure how I missed it
> before.
> 
> Unless anyone comes up with a better idea (or just a reason why this
> idea is bad) I think I'll send a patch making the predicate just
> hasCtrlDep to llvm-commits later, and change my instructions so they
> set that flag when needed. It's less friendly than checking all of the
> others, but what if someone has a mayLoad instruction they don't want
> to chain (for some bizarre reason)?

If it is not being used, maybe we should change it to be
doesNotNeedChain? I am not sure what kind of load does not need to be
chained (prefetch?), but I'd prefer to keep the system friendly if at
all possible. They'll be fewer bugs that way.

Thanks again,
Hal

> 
> Tim.



-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory