[cfe-dev] [RFC] Unified offloading option for CUDA/HIP/OpenMP

[Alexey Bataev via cfe-dev]

Why do we need “kind” here? We know the kind already, if -fopenmp is used - kind is omp, if .hip is compiled - kind is hip. 
Adding arch also does not look good. We may need to pass some extra params. Better to have something like `-offload=target1,target2,... -offload-target1=“-march xxx -opt1” -offload-target2=“-march yyy -opt2 -opt3” ...`. 

Best regards,
Alexey Bataev

> 12 дек. 2020 г., в 09:11, Liu, Yaxun (Sam) <Yaxun.Liu at amd.com> написал(а):
> 
> [AMD Public Use]
> 
> Currently CUDA/HIP and OpenMP has different offloading options, e.g.
> 
> clang++  -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx900 test.cpp
> 
> clang++ -offload-arch=gfx906 test.hip
> 
> Our users request to have a concise way to specify offloading options for OpenMP. Ideally, one option to convey offloading kind, offloading triple, and offloading device arch.
> 
> On the other hand, there are some limitations of the current offloading option for CUDA/HIP:
> 
> 1. It does not specify offloading kind whereas relies on file type to infer offloading kind. If input file is not CUDA/HIP source code (e.g. bundled LLVM bit code), there needs a way to specify offloading kind.
> 
> 2. It does not specify offloading target triple whereas relies on device arch to infer target triple. As HIP is ported to different targets, there needs a way to specify offloading target triple.
> 
> In summary, a unified offloading option is preferred, which conveys offloading kind, offloading target triple and offloading device arch.
> 
> I would like to propose to either have a new option or extend the existing -offload-arch option for that, in the format kind-triple-arch, e.g.
> 
> -offload=omp-amd-gfx900
> 
> -offload=hip-amd-gfx906
> 
> Whereas kind and triple can be abbreviations for conciseness, e.g. omp expands to openmp, amd expands to amdgcn-amd-amdhsa. Arch can be omitted, in which case clang will use the default arch for the triple.
> 
> Your feedbacks are welcome.
> 
> Thanks.
> 
> Sam
>