[Openmp-dev] offloading to Nvidia GPUs

[Jonas Hahnfeld via Openmp-dev]

Hi,

the answer is the same as in October: (upstream) Clang 5 doesn't fully 
support offloading to GPUs. Trunk's support has progressed since then 
but AFAIK still isn't able to link applications at the moment.

Regards,
Jonas

Am 2017-12-18 16:11, schrieb Eichstaedt, Jan R via Openmp-dev:
> Hello,
> 
> in addition to my previous mail:
> I saw in this year's October archive, that Gabriele Jost has been
> running into similar issue. Do you know if and how it has been
> resolved for him?
> 
> Further, I tried out the clang-ykt git repo, and compiled in the same
> fashion as I did with v5, which worked fine for some small test-cases.
> This is why I am still quite surprised I ran into the mentioned
> compile issue with v5. That said, I assume you merged the clang-ykt
> branch into the v5 branch?
> The problem with the clang-ykt branch for me however is, that I run
> into some mysterious linking errors when compiling our major
> framework.
> 
> Would you be able to kindly shed some light on this issue?
> Thanks and kind regards,
> Jan
> 
> -------------------------
> 
> FROM: Eichstaedt, Jan R
> SENT: 14 December 2017 11:39:00
> TO: Gheorghe-Teod Bercea
> CC: via Openmp-dev
> SUBJECT: Re: [Openmp-dev] offloading to Nvidia GPUs
> 
> Hello,
> 
> both your suggestions of adding the compile flags
>     -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_35
> 
>     -Xopenmp-target -march=sm_35
> 
> still give me exactly the same error message.
> 
> Do you have any other suggestions?
> 
> Cheers,
> Jan
> 
> -------------------------
> 
> FROM: Gheorghe-Teod Bercea <Gheorghe-Teod.Bercea at ibm.com>
> SENT: 13 December 2017 18:30:00
> TO: Eichstaedt, Jan R
> CC: via Openmp-dev
> SUBJECT: Re: [Openmp-dev] offloading to Nvidia GPUs
> 
> Hi,
> 
> Yes there is:
> 
> -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_35
> 
> You may also run into the problem that target offloading is not yet
> fully supported.
> 
> Hope this helps!
> 
> Thanks,
> 
> --Doru
> 
> From:        "Eichstaedt, Jan R via Openmp-dev"
> <openmp-dev at lists.llvm.org>
> To:        via Openmp-dev <openmp-dev at lists.llvm.org>
> Date:        12/13/2017 01:11 PM
> Subject:        [Openmp-dev] offloading to Nvidia GPUs
> Sent by:        "Openmp-dev" <openmp-dev-bounces at lists.llvm.org>
> 
> -------------------------
> 
> Hello,
> 
> I am using llvm and clang version 5.0.0 together with the openmp
> project of that version on Ubuntu 16.04.
> I try to compile a simple program involving a _#pragma omp target
> teams distribute parallel for _statement to offload to a Nvidia-GPU
> using the following flags:
> -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda
> --cuda-path=/usr/local/cuda/ --cuda-gpu-arch=sm_35
> 
> However, the compilation fails, with the following being the first
> assertion that is triggered:
> clang++:
> [...]/llvm-5.0.0.src/tools/clang/lib/Driver/ToolChains/Cuda.cpp:346:
> virtual void
> clang::driver::toolchains::CudaToolChain::addClangTargetOptions(const
> llvm::opt::ArgList&, llvm::opt::ArgStringList&,
> clang::driver::Action::OffloadKind) const: Assertion `!GpuArch.empty()
> && "Must have an explicit GPU arch."' failed.
> 
> Is there a way to pass the GPU architecture differently? Or is target
> offloading not fully supported in v5.0.0 yet and I might better use
> the clang-ykt project? Or have I overlooked something else completely?
> 
> Thanks for any help you can offer.
> 
> Cheers,
> Jan
> 
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