[cfe-dev] [llvm-dev] Clang driver for OpenMP target offloading

[Simone Atzeni via cfe-dev]

Hi Jonas,

thanks for the answer.
For now I can use the "--save-temps" flag to keep my investigation.

Do you know what's the timeline for integrating offloading for NVidia GPUs
upstream?
I remember seeing a big patch for integrating OpenMP target generation in
the clang driver and I thought it was already accepted and committed, but I
might be wrong.

Thanks.
Simone


On Wed, Dec 27, 2017 at 1:10 AM, Jonas Hahnfeld <hahnjo at hahnjo.de> wrote:

> Hi Simone,
>
> you are more likely to get answers to frontend questions asking on
> cfe-dev. However, your output shows that you are using clang-ykt which
> isn't supported upstream so this is not the right place for your questions.
> Nevertheless, I'll answer some because the same "problem" will arise with
> (upstream) trunk.
>
> Am 2017-12-26 23:37, schrieb Simone Atzeni via llvm-dev:
>
>> Hi,
>>
>> I am having some trouble to understand how the clang driver works for
>> OpenMP offloading.
>>
>> For example, if I run the following command (with the -v flag):
>>
>> clang -v -g -fopenmp offloading_success.c -o offloading_success
>>
>> I can see the invocations that clang does and if I run those command
>> one by one I can successfully compile my program.
>>
>
> Just to clarify: This will compile but will fallback to run on the host
> because the arguments don't specify which device to compile for.
>
> Now, if I do the same but with the offloading option, as in the
>> following command:
>>
>> clang -v -g -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda
>> offloading_success.c -o offloading_success
>>
>> the command works, compiles correctly, and when I run the program, it
>> successfully run on the device.
>>
>
> (which would not be the case for upstream trunk yet...)
>
> However, if I show the invocations with "-v" and try to run the
>> commands one by one it does not work and in particular I get an error
>> with the last command which is the linking part with "ld".
>> The error i get is the following:
>>
>> /usr/bin/ld: cannot open linker script file
>> /tmp/offloading_success-2b4739.lk [1]: No such file or directory
>>
>> Where is this ".lk" file generated? Is there a missing commands in the
>> invocations?
>>
>
> The linker script is generated by Clang's driver (both in clang-ykt and
> trunk) and is deleted after its usage which is the default for temporary
> files. If you want to inspect the intermediate files, I suggest adding
> --save-temps which will dump a bunch of files to the current directory.
> (AFAIK this will result in more files than generated by default so that
> developers have more intermediate steps to look at.)
>
> Cheers,
> Jonas
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20180104/4d04f6e9/attachment.html>