80525dfcde
Through the new `-foffload-via-llvm` flag, CUDA kernels can now be lowered to the LLVM/Offload API. On the Clang side, this is simply done by using the OpenMP offload toolchain and emitting calls to `llvm*` functions to orchestrate the kernel launch rather than `cuda*` functions. These `llvm*` functions are implemented on top of the existing LLVM/Offload API. As we are about to redefine the Offload API, this wil help us in the design process as a second offload language. We do not support any CUDA APIs yet, however, we could: https://www.osti.gov/servlets/purl/1892137 For proper host execution we need to resurrect/rebase https://tianshilei.me/wp-content/uploads/2021/12/llpp-2021.pdf (which was designed for debugging). ``` ❯❯❯ cat test.cu extern "C" { void *llvm_omp_target_alloc_shared(size_t Size, int DeviceNum); void llvm_omp_target_free_shared(void *DevicePtr, int DeviceNum); } __global__ void square(int *A) { *A = 42; } int main(int argc, char **argv) { int DevNo = 0; int *Ptr = reinterpret_cast<int *>(llvm_omp_target_alloc_shared(4, DevNo)); *Ptr = 7; printf("Ptr %p, *Ptr %i\n", Ptr, *Ptr); square<<<1, 1>>>(Ptr); printf("Ptr %p, *Ptr %i\n", Ptr, *Ptr); llvm_omp_target_free_shared(Ptr, DevNo); } ❯❯❯ clang++ test.cu -O3 -o test123 -foffload-via-llvm --offload-arch=native ❯❯❯ llvm-objdump --offloading test123 test123: file format elf64-x86-64 OFFLOADING IMAGE [0]: kind elf arch gfx90a triple amdgcn-amd-amdhsa producer openmp ❯❯❯ LIBOMPTARGET_INFO=16 ./test123 Ptr 0x155448ac8000, *Ptr 7 Ptr 0x155448ac8000, *Ptr 42 ```
The LLVM/Offload Subproject
The Offload subproject aims at providing tooling, runtimes, and APIs that allow users to execute code on accelerators or other "co-processors" that may or may not match the architecture of their "host". In the long run, all kinds of targets are in scope of this effort, including but not limited to: CPUs, GPUs, FPGAs, AI/ML accelerators, distributed resources, etc.
The project is just starting and the design is still not ironed out. More content will show up here and on our webpage soon. In the meantime people are encouraged to participate in our meetings (see below) and check our development board as well as the discussions on Discourse.
Meetings
Every second Wednesday, 7:00 - 8:00am PT, starting Jan 24, 2024. Alternates with the OpenMP in LLVM meeting. invite.ics Meeting Minutes and Agenda