[cfe-dev] Can't compile simple OpenMP code with clang 5.0.0

[Johannes Doerfert via cfe-dev]

Hi Marcus,

On 12/22/20 2:57 PM, Marcus Johnson via cfe-dev wrote:
> Another thing:
>
> Clang can be compiled without OpenMP support, which removes the omp.h header, libomp.dylib, and tablegen isn’t even run for OpenMP pragmas.
>
> Your Clang distribution needs to be compiled with OpenMP support for it to work at all.

As far as I can tell, LLVM/Clang doesn't have the ability to disable 
OpenMP support.
This might have been different in the past, or in some derived 
compilers, but I would
assume the clang would have emitted an error upon encountering 
`-fopenmp` then.

~ Johannes


>> On Dec 22, 2020, at 12:55 PM, Marcus Johnson <MarcusLJohnson1991 at gmail.com> wrote:
>>
>> 
>> Why are you using such an old version of Clang?
>>
>> Clang the compiler needs to be built with support for parsing OpenMP pragmas.
>>
>> It’s not just the header and runtime you need to successfully compile with OpenMP
>>
>>>> On Dec 22, 2020, at 11:57 AM, Керим Хемраев via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>>>
>>> 
>>> Hi,
>>>   
>>> I’m struggling with compiling simple OpenMP program with clang 5.0.0.
>>> Here is the code (foo.cxx):
>>>   
>>> #include "omp.h"
>>> #include <stdio.h>
>>>   
>>> int main(void) {
>>>    #pragma omp parallel
>>>    printf("thread %d\n", omp_get_thread_num());
>>> }
>>>   
>>> As I use clang as part of xeus-cling my clang installation is inside conda packages:
>>> $ which clang
>>> /home/tasik/miniconda3/envs/cling/bin/clang
>>>   
>>> As this clang package does’t have omp.h I provide additional directories to find omp.h and libomp.so
>>> To compile the code I use the command:
>>> $ clang -fopenmp -I/home/../usr/lib/llvm-10/include/openmp/ -L/home/../usr/lib/llvm-10/lib foo.cxx
>>>   
>>> And I get errors:
>>> /usr/bin/ld: cannot find /lib64/libpthread.so.0
>>> /usr/bin/ld: cannot find /usr/lib64/libpthread_nonshared.a
>>> clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
>>>   
>>> I really need some help to undertand how to work with clang 5.0.0 OpenMP
>>> And I think that it is difficult to update clang’s version as xeus-cling requires mentioned 5.0.0 version...
>>>   
>>>   
>>> With respect,
>>> kerim
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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