[Openmp-dev] Using OpenMP target offloading in llvm-8.0.0

[Stephane Genaud via Openmp-dev]

Thanks for the quick answer.

> On 14 Nov 2019, at 02:23, Doerfert, Johannes <jdoerfert at anl.gov> wrote:
> 
> This looks like a bug in 8.0 that is fixed in trunk.
> You have a `target teams distribute`, right?
> 
> Can you put an empty target region before that and see if it helps.

Yes, indeed the weird error message disappears after inserting a parallel target region,
that is, the following code works.

#include <omp.h>
#include <stdio.h>
int a[100];

int main() {

  printf("* number of devices: %d\n",omp_get_num_devices());
#pragma omp target
{
}

#pragma omp target teams distribute parallel for
  for(int i=0; i<100; i++)
        a[i]++;
  return 0;
}

> 
> Cheers,
>  Johannes
> 
> P.S.
> This is the right place to ask these questions
> 
> ________________________________________
> From: Openmp-dev <openmp-dev-bounces at lists.llvm.org> on behalf of Stephane Genaud via Openmp-dev <openmp-dev at lists.llvm.org>
> Sent: Wednesday, November 13, 2019 08:30
> To: openmp-dev at lists.llvm.org
> Subject: [Openmp-dev] Using OpenMP target offloading in llvm-8.0.0
> 
> 
> 
> 
> Hello,
> 
> i came across this message on the list and found no better place to ask for help on a similar problem.
> I am just experimenting offloading to x86_64 code from a x86_64 host system (ubuntu 18.04).
> I have the packages:
> - libomp-8-dev , containing among others :
>   /usr/lib/llvm-8/lib/libomptarget.so
>   /usr/lib/llvm-8/lib/libgomp.so
>   /usr/lib/llvm-8/lib/libiomp5.so
>   /usr/lib/llvm-8/lib/libomp.so
> - clang-8
> 
> I compiled the same offload.c program as the one given in the referenced mail.
> 
> My first try was :
> $ clang-8 -g -fopenmp -fopenmp-targets=x86_64-pc-linux-gnu offload.c
> 
> which did produce a binary a.out,  but this one fails with the cryptic error message:
> $ export LD_LIBRARY_PATH=/usr/lib/llvm-8/lib/
> $ ./a.out
> Libomptarget fatal error 1: default offloading policy must switched to mandatory or disabled
> 
> Second try, after reading some of the hints was
> $ clang-8 -g -I//usr/lib/llvm-8/include/ -L/usr/lib/llvm-8/lib -Xopenmp-target -march=x86-64 -fopenmp -fopenmp-targets=x86_64-pc-linux-gnu offload.c
> 
> which resulted in the same error.
> By the way, i have no clue why -Xopenmp-target -march=x86-64 would be required, which quite seem redundant with -fopenmp_targets.
> 
> I went to see the source code at
> https://github.com/llvm-mirror/openmp/blob/master/libomptarget/src/interface.cpp  line:56
> but still can’t figure out what makes libomptarget unhappy.
> In case this is related to ‘device’, i tested omp_get_default_device() which returns 1.
> 
> Any help would be appreciated.
> Thanks.
> 
> 
>> Hi,
> 
>> When trying to use openmp target offloading with llvm I get the following error
>> *$ cat offload.cpp*
>>> #include <omp.h>
>>> int main() {
>>> #pragma omp target teams distribute parallel for
>>> for(int i=0; i<100; i++);
>>> return 0;
>>> }
>>> *$ clang++ -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda
>>> --cuda-path=$CUDA_TOOLKIT_ROOT_DIR offload.cpp -o offload*
>>> *$ ./offload*
>>> Libomptarget fatal error 1: default offloading policy must switched to
>>> mandatory or disabled
>>> *$*
>> I have llvm-8.0.0 installed in my system at LLVM_PATH. I downloaded openmp-8.0.0 source from the llvm download page. To build openmp I used the following command: $ mkdir build && cd build > $ cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=$LLVM_PATH
>>> -DCMAKE_C_COMPILER=$LLVM_PATH/bin/clang -DCMAKE_CXX_COMPILER= $LLVM_PATH/bin/clang++
>>> -DLIBOMPTARGET_NVPTX_COMPUTE_CAPABILITIES=35,60,70 ..
>>> $ make && make install
>>> $
>> OpenMP got built without giving any error. But when trying to use target offloading with OpenMP I get the above mentioned fatal error. I tried this on 3 different machines, with same result. -- Thank You. Regards, Alok
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