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1.. _omp100:2.. _omp_no_external_caller_in_target_region:3 4Potentially unknown OpenMP target region caller `[OMP100]`5==========================================================6 7A function remark that indicates the function, when compiled for a GPU, is8potentially called from outside the translation unit. Note that a remark is9only issued if we tried to perform an optimization which would require us to10know all callers on the GPU.11 12To facilitate OpenMP semantics on GPUs we provide a runtime mechanism through13which the code that makes up the body of a parallel region is shared with the14threads in the team. Generally we use the address of the outlined parallel15region to identify the code that needs to be executed. If we know all target16regions that reach the parallel region we can avoid this function pointer17passing scheme and often improve the register usage on the GPU. However, If a18parallel region on the GPU is in a function with external linkage we may not19know all callers statically. If there are outside callers within target20regions, this remark is to be ignored. If there are no such callers, users can21modify the linkage and thereby help optimization with a `static` or22`__attribute__((internal))` function annotation. If changing the linkage is23impossible, e.g., because there are outside callers on the host, one can split24the function into an external visible interface which is not compiled for25the target and an internal implementation which is compiled for the target26and should be called from within the target region.27