efacdfc235
The GPU vendors currently provide bitcode files for their device runtime. These files need to be handled specially as they are not built to be linked in with a standard `llvm-link` call or through LTO linking. This patch adds an alternative to use the existing clang handling of these libraries that does the necessary magic to make this work. We do this by causing the LTO backend to emit bitcode before running the backend. We then pass this through to clang which uses the existing support which has been fixed to support this by D152391. The backend will then be run with the merged module. This patch adds the `--builtin-bitcode=<triple>=file.bc` to specify a single file, or just `--clang-backend` to let the toolchain handle its defaults (currently nothing for NVPTX and the ROCm device libs for AMDGPU). This may have a performance impact due to running the optimizations again, we could potentially disable optimizations in LTO and only do the linking if this is an issue. This should allow us to resolve issues when relying on the `linker-wrapper` to do a late linking that may depend on vendor libraries. Depends on D152391 Reviewed By: JonChesterfield Differential Revision: https://reviews.llvm.org/D152442
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