[LLVMdev] SIV tests in LoopDependence Analysis, Sanjoy's patch

[Hal Finkel]

On Mon, 14 May 2012 13:54:19 -0700
Preston Briggs <preston.briggs at gmail.com> wrote:

> On Mon, May 14, 2012 at 1:30 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> 
> > Can you explain this comment:
> > > With minor algebra, this test can also be used for things like
> > > [c1 + a1*i + a2*j][c2].
> 
> It's really too simple to deserve mention...
> Given a subscript pair, [c1 + a1*i + a2*j] and [c2], we can test for
> dependence using the RDIV test by rewriting as [c1 + a1*i] and [c2 -
> a2*j].
> 
> > I this look good, but, as you say below, we also need to work on the
> > top-level infrastructure. It will be hard to validate and evaluate
> > this code without a framework in which to use it.
> 
> Yep. I've written a simple framework to do tests on my own, but it
> needs to be extended to be more generally useful.
> 
> > One thing that I would like to mention is that 'use' here should
> > also include user feedback. This means being able to pass
> > information back to the frontends about which loops are being
> > effectively analyzed, and for loops that are not, why not.
> 
> Absolutely. I've been thinking in terms of passing info back to the
> programmer (see
> https://sites.google.com/site/parallelizationforllvm/feedback). It's a
> very interesting problem and one where I think there are real research
> possibilities.

Do you think that we should do this by adding metadata, or should we
establish some kind of separate feedback channel? Metadata would make
it more useful for writing regression tests (perhaps), but a separate
feedback channel might be more useful for the front ends. Maybe we
should have a separate feedback channel that, lacking any other
consumer, writes out metadata?

 -Hal

> 
> Preston



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