[llvm-dev] [GSoC] Supporting Efficiently the Shift-vector Instructions of the Connex Vector Processor
Alex Susu via llvm-dev
llvm-dev at lists.llvm.org
Sun Apr 28 15:56:16 PDT 2019
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
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 .
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
> On Mon, Apr 8, 2019 at 7:53 PM Andrei Popa via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> 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:
>> Thank you,
>> Andrei Popa
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
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