OpenMP and OpenACC Offload
Every portability layer covered so far in this folder still asks for a rewrite: HIP wants CUDA calls translated, SYCL wants kernels re-expressed as lambdas passed to a queue. Directive-based offload takes a different bet — annotate the loop nest you already have, keep one source file that still compiles and runs correctly on the CPU with the annotations ignored, and get working GPU code without restructuring the algorithm. That pitch is genuinely attractive for porting a large, already-correct codebase; it is a worse fit for the few kernels where every last percent of throughput matters, and this page is honest about where that line falls.