db0f754c5a
Summary: Currently, we build a single `libomptarget.devicertl.a` which is a fatbinary. It is a host object file that contains the embedded archive files for both the NVIDIA and AMDGPU targets. This was done primarily as a convenience due to naming conflicts. Now that the clang driver for the GPU targets can appropriate link via the per-target runtime-dir, we can just make two separate static libraries and remove the indirection. This patch creates two new static libraries that get installed into ``` /lib/amdgcn-amd-amdhsa/libomp.a /lib/nvptx64-nvidia-cuda/libomp.a ``` for AMDGPU and NVPTX respectively. The link job created by the linker wrapper now simply needs to do `-lomp` and it will search those directories and link those static libraries. This requires far less special handling. This patch is a precursor to changing the build system entirely to be a runtimes based one. Soon this target will be a standard `add_library` and done through the GPU runtime targets. NOTE that this actually does remove an additional optimization step. Previously we merged all of the files into a single bitcode object and forcibly internalized some definitions. This, instead, just treats them like a normal static library. This may possibly affect performance for some files, but I think it's better overall to use static library semantics because it allows us to have an 'include-what-you-use' relationship with the library. Performance testing will be required. If we really need the merged blob then we can simply pack that into a new static library.
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.
For OpenMP offload users, the project is ready and fully usable. The final API design is still under development. 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