llvm dev - Apr 2019 - [GSoC] Supporting Efficiently the Shift-vector Instructions of the Connex Vector Processor

Hello,

I am applying for Google Summer of Code with a project related to LLVM and
Connex SIMD processor and I would appreciate some feedback on the proposal.
The proposal can be found here:
https://docs.google.com/document/d/1pBRbW8pU9GV8zWCJQrILhynNEBpGXJKtev1j7ekXfqs/edit?usp=sharing

Thank you,
Andrei Popa

Hello Andrei,

You proposal seems to be centered on improvements of out-of-tree
backend entirely and therefore is not entirely clear what are the
benefits of this project to the LLVM project making the project
slightly outside the scope of LLVM GSoC.

Probably it would make sense to restructure the proposal in such way
that it would be clear how the work that is supposed to be done over
the summer will benefit e.g. other backends that we already having in
the repository. After all, the vector instructions do exist in many
architectures.

On Mon, Apr 8, 2019 at 7:53 PM Andrei Popa via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hello,
>
> I am applying for Google Summer of Code with a project related to LLVM and
Connex SIMD processor and I would appreciate some feedback on the proposal.
> The proposal can be found here:
>
https://docs.google.com/document/d/1pBRbW8pU9GV8zWCJQrILhynNEBpGXJKtev1j7ekXfqs/edit?usp=sharing
>
> Thank you,
> Andrei Popa
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


-- 
With best regards, Anton Korobeynikov
Department of Statistical Modelling, Saint Petersburg State University

Hello, Anton,
     I'd like to add a small reply regarding this GSoC project that I would
like to mentor
and I discussed also with Andrei.
     A good part of our GSoC project is indeed related to this Connex back end
that it's
not yet part of the LLVM source repository - an important thing proposed in the
project is
that we plan to perform efficient realignment for this Connex vector processor.

     I looked a bit in LLVM and I see that support for realignment of misaligned
vector
memory accesses is not implemented in the LoopVectorize pass (see 
lib/Transforms/Vectorize/LoadStoreVectorizer.cpp) nor in any back end (folder
lib/Target).
Please correct me if I'm wrong.
     But realignment is an interesting technique useful for many SIMD and (wide)
vector
processors - there are still SIMD processors today that either have performance
issues or
simply can't perform misaligned accesses, and for wide vector processors
with many lanes
this problem is equally important and even more complex. People have already
addressed in
a platform-independent way realignment of misaligned vector memory accesses -
see, for
example for GCC a paper of Nuzman and Henderson ("Multi-platform
Auto-vectorization", CGO
2006,
https://www.researchgate.net/publication/4231612_Multi-platform_auto-vectorization).
     It would be interesting to address this issue of realignment of misaligned
vector
memory accesses in LLVM - this seems to be already well supported in GCC.

     Please note also our Connex vector processor back end has been reviewed and
we should
be accepted as experimental (also because it has a few "exotic"
features) - see, if
interested, https://reviews.llvm.org/D60052 .

   Best regards,
     Alex


On 4/9/2019 1:38 PM, Anton Korobeynikov via llvm-dev
wrote:
> Hello Andrei,
>
> You proposal seems to be centered on improvements of out-of-tree
> backend entirely and therefore is not entirely clear what are the
> benefits of this project to the LLVM project making the project
> slightly outside the scope of LLVM GSoC.
>
> Probably it would make sense to restructure the proposal in such way
> that it would be clear how the work that is supposed to be done over
> the summer will benefit e.g. other backends that we already having in
> the repository. After all, the vector instructions do exist in many
> architectures.
>
> On Mon, Apr 8, 2019 at 7:53 PM Andrei Popa via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> Hello,
>>
>> I am applying for Google Summer of Code with a project related to LLVM
and Connex SIMD processor and I would appreciate some feedback on the proposal.
>> The proposal can be found here:
>>
https://docs.google.com/document/d/1pBRbW8pU9GV8zWCJQrILhynNEBpGXJKtev1j7ekXfqs/edit?usp=sharing
>>
>> Thank you,
>> Andrei Popa
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>