[cfe-dev] [RFC] Unified offloading option for CUDA/HIP/OpenMP (original) (raw)

Doerfert, Johannes via cfe-dev cfe-dev at lists.llvm.org
Mon Dec 14 12:20:55 PST 2020

Hi Sam, thanks for driving this, I really like the idea!

Here are some thoughts:

Make the "kind" optional if it can be deduced, as Alexey noted. So   -offload=amd-gfx900 should work fine if we have an -x c and -fopenmp set. Error out if it is ambiguous.

Allow multiple -offload occurrences.

Keep the support of the old ways for now as well.

Allow to pass the kind + triple + arch as first part of the new -offload flag and any options as a second part, so:  -offload=hip-amd-gfx906 works but also does  -offload="amd-gfx906 -fvectorize" -x hip as well as  -offload="amd -march=gfx906 -fno-vectorize" -fopenmp This will make it way easier to use.

I hope some of these make some sense :)

~ Johannes

On 12/12/20 8:11 AM, Liu, Yaxun (Sam) wrote:

[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

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