[llvm-dev] [RFC] Polly Status and Integration

[C Bergström via llvm-dev]

On Wed, Sep 13, 2017 at 8:05 PM, Hal Finkel <hfinkel at anl.gov> wrote:

>
> On 09/13/2017 06:53 AM, C Bergström wrote:
>
>
>
> On Wed, Sep 13, 2017 at 7:43 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>>
>> On 09/13/2017 02:16 AM, C Bergström wrote:
>>
>> A completely non-technical point, but what's the current "polly" license?
>> Does integrating that code conflict in any way with the work being done to
>> relicense llvm?
>>
>>
>> Good question. I discussed this explicitly with Tobias, and his general
>> feeling is that relicensing isl again would be doable if necessary (we
>> already did this once, to an MIT license, in order to enable better LLVM
>> integration).
>>
>>
>> Does adding polly expose any additional legal risks? Some people from
>> Reservoir labs have explicitly stated to me that some of their patents
>> target polyhedral optimizations. You should almost certainly review their
>> portfolio or contact them.
>>
>> If at some point someone wants to add real loop optimizations - will
>> there be a conflict?
>>
>>
>> Can you define "real loop optimizations"?
>>
>
> I think most readers here will understand what I mean. I can go find
> specific chapters of textbooks if it's unclear. Maybe the word "real" could
> be replaced with traditional, well tested, industry standard or something
> else. (ok I'll stop being snarky)
>
>
> That's what I thought you meant. No, I believe there's not a conflict. In
> fact, this will provide infrastructure to make this easier. While you can
> handle a bunch of these as one problem using this kind of framework, you
> don't need to do so.
>


By this I think you either mean A) the polly stuff will provide a better
analysis pass or B) the llvm side will have a better analysis pass, correct?

If you mean A, then that's cool. I was unaware that poly had an interface
and could be used like this. The cost model aspect is very important. I'm
mildly curious how it builds this.

(correct me if I'm wrong please) It's my lay understanding that poly
optimizations are an either or and do not generally play well with
tradtional methods. More specifically, after poly things are "messed up"
and it would be difficult to do another (traditional type) transformation
that it missed. Since llvm doesn't have or doesn't do the traditional side
very well, this is less a concern though.
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