[cfe-dev] [llvm-dev] [Openmp-dev] RFC: Proposing an LLVM subproject for parallelism runtime and support libraries

C Bergström via cfe-dev cfe-dev at lists.llvm.org
Mon Apr 25 10:51:51 PDT 2016

Speaking from 1st hand experience -

The off-the-cuff high level benefits
1) Better interopt of different programming models - For example what
if someone wants to mix SE+OMP(4). Having the same runtime on the
backend should make this a lot easier. (Maybe this particular example
may never happen, but I hope you get what I'm talking about)
2) Less duplication of effort for common things.
3) Easier time for new programming models

By ignoring the current technical issues it's just playing
kick-the-can for someone less intimate with SE or OMP.

I hate to pushback on SE for this general requirement, but it seems
like the right time to do it. If not now - At which point does it make
My real honest motivation here is for Google and Intel to join
together on this. I believe SE will be much better long term if major
stakeholders are aligned.

How many disjoint and fragmented programming models do "we" really
need.. (I don't think SE falls into this category, but if we have a
PHI and Intel backend.. why can't it be used)

On Tue, Apr 26, 2016 at 1:38 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
> On Mon, Apr 25, 2016 at 12:14 PM C Bergström <cbergstrom at pathscale.com>
> wrote:
>> I can't comment on all the things not directly used by llvm community,
>> but I feel pretty strongly that
>> 1) An independent project like liboffload should exist ; which
>> 2) Projects like SE and OpenMP should both be using it ; and further
>> 3) SE shouldn't just do their own thing because they haven't figured
>> out how to make it work with other projects that already have some
>> overlapping behaviour
>> ---------
>> If my points above are invalid - can someone clarify that SE and the
>> "stuff" in OpenMP-llvm doesn't actually overlap in functionality.
> It isn't that any of these points are invalid, it's just that I don't think
> we know how or if these projects have a useful overlap to extract and keep
> separate. That was the whole point of my email suggesting that we shouldn't
> try to force some hypothetical refactoring that we don't even know will work
> to happen. Several serious technical challenges have been raised with doing
> this refactoring, so its not just avoiding it for the sake of avoiding it.
> Even if/when these issues are sorted out and it is feasible to refactor
> things to have a common layer, it still isn't clear whether the overlap is
> actually that useful. I think we're over analyzing and designing this when
> we don't even have the code in place to see if there is an interesting
> problem to solve here.

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