Thanks, but iOS supports neither CUDA, OpenCL, Vulkan nor TBB. It's only Metal and higher-level frameworks like Core Image for GPU, and vImage for SIMD image manipulation.
You can use MoltenVK to run Vulkan via Metal (https://github.com/KhronosGroup/MoltenVK). Apparently performance is quite good for regular 3D rendering, compute support is officially listed, but I'm not at all sure what performance is like.