Cling and OpenMP

[Ahmidou_Lyazidi]

Hi,
What would be the procedure to get Clang’s OpenMP working with the cling interpreter (on windows)?
I’m currently doing it this way and call my program with the -fopenmp option:

    typedef int(*myFunc_t)();

    const char* myFuncCode =
        R"(
        #include "omp.h"
        #include "stdio.h" 
        #include "vector"
        extern "C" int myFunc(){

        int a, b, c;
        std::vector<float> aa(100);
        std::vector<float> bb(100);
        #pragma omp parallel for
        for (int i = 0; i < aa.size(); i+=3) {
            aa[i] = sqrt(2.0 * float(i));
            aa[i+1] = sqrt(2.0 * float(i));
            aa[i+2] = sqrt(2.0 * float(i));
            printf("thread %d\n", omp_get_thread_num());
        }
    })";

    myFunc_t myFuncP = (myFunc_t)interp.compileFunction("myFunc", myFuncCode);

and I’m getting this error:

IncrementalExecutor::executeFunction: symbol '__kmpc_fork_call' unresolved while linking symbol 'myFunc'!
You are probably missing the definition of __kmpc_fork_call
Maybe you need to load the corresponding shared library?

Thanks!!

[Axel]

You’ll probably have to build cling linking against the mp libraries.

We have no experience with OpenMP and cling. I’m happy to receive patches that add support for OpenMP to cling.

[wlav]

Not sure why you think building cling itself with openmp would make it work, unless it is then build with the Clang it is being built/linked against.

I’m not familiar with Windows, but presume it has the same issue as would appear on Linux: the symbols missing are from Clang’s (Intel’s) OpenMP run-time, as that is what Cling (or LLVM, rather) generates code for. Any previously linked OpenMP run-time would be the system one (on Linux/gcc that would be gomp, for example), if the system compiler was used to build Cling.

So, get the OpenMP run-time for llvm (http://openmp.llvm.org/) and explicitly load libiomp5.so with the Windows equivalent of dlopen with RTLD_GLOBAL and you should be good to go. (There should be no problems unless Cling uses OpenMP internally, which AFAIK it doesn’t.)

[Axel]

Yeah but then that’s incompatible with the rest of the OpenMP libs the OP might use which is why we advocate having consistent build- and runtime. Anyway, thanks for the pointers, Wim!