[llvm-dev] Trying to build clang-13 for openmp target offload

[Michael Kruse via llvm-dev]

Hi,

If using LLVM_ENABLE_PROJECTS=clang;openmp (or
LLVM_ENABLE_PROJECTS=clang and LLVM_ENABLE_RUNTIMES=openmp),
libomptarget should pick-up in-tree clang itself. The relevant change
(ofr LLVM_ENABLE_PROJECTS=clang;openmp) is
https://reviews.llvm.org/D101265, which I just checked landed in the
release of clang 13. Are you maybe using a pre-release version of
clang 13?

In any case, you should be able to explicitly set the clang for the
device RTL using -DLIBOMPTARGET_NVPTX_CUDA_COMPILER=... Just compile
clang first, then re-configure using the
DLIBOMPTARGET_NVPTX_CUDA_COMPILER set to the clang executable you just
build.

Note that this just changed for clang-14 which uses the clang found in
LLVM_TOOLS_BINARY_DIR.

Michael


Am Fr., 22. Okt. 2021 um 18:16 Uhr schrieb Jost, Gabriele
(ARC-TNC)[Supersmith] via llvm-dev <llvm-dev at lists.llvm.org>:
>
> Hello,
>
> I am trying to build clang-13 with support for OpenMP target offload to Nvidia GPUS.
>
> I can build clang, but it stubbornly refuses to build the openmpRTL, I get this in the cmake output:
>
>
>
> - Could NOT find LIBOMPTARGET_DEP_VEO (missing: LIBOMPTARGET_DEP_VEO_LIBRARIES LIBOMPTARGET_DEP_VEOSINFO_LIBRARIES LIBOMPTARGET_DEP_V
>
> EO_INCLUDE_DIRS)
>
> -- LIBOMPTARGET: Building offloading runtime library libomptarget.
>
> -- LIBOMPTARGET: Not building aarch64 offloading plugin: machine not found in the system.
>
> -- LIBOMPTARGET: Building AMDGPU plugin for dlopened libhsa
>
> -- LIBOMPTARGET: Not generating amdgcn test targets as amdgpu-arch is not found
>
> -- LIBOMPTARGET: Building CUDA offloading plugin.
>
> -- LIBOMPTARGET: Building CUDA plugin linked against libcuda
>
> -- LIBOMPTARGET: Enable tests using CUDA plugin
>
> -- LIBOMPTARGET: Not building PPC64 offloading plugin: machine not found in the system.
>
> -- LIBOMPTARGET: Not building PPC64le offloading plugin: machine not found in the system.
>
> -- LIBOMPTARGET: Not building nec-aurora plugin: libveo or libveosinfo not found.
>
> -- LIBOMPTARGET: Not building x86_64 offloading plugin: libffi dependency not found.
>
> -- LIBOMPTARGET: Building AMDGCN device RTL. Using clang from in-tree build
>
> -- LIBOMPTARGET: Not building NVPTX deviceRTL: clang not found
>
> -- LIBOMPTARGET: Not building NVPTX deviceRTL: clang not found
>
> -- LIBOMPTARGET: Building the llvm-omp-device-info tool
>
>
>
> So, it wants an existig clang. I already have a clang built, I tried to use the old clang rather than gcc, but that lead to other errors.
>
> The AMDGCM RTL is built using the in-tree clang. Is there a way to do the same for nvptx?
>
>
>
> I has also tried a 2-step approach, building the deviceRTL seperately, but then it complaints about some previously built tools.
>
>
>
> Have you encountered such a situation before and can maybe provide some guidance?
>
>
>
> Here is the cmake I am using:
>
> CMAKE_OPTIONS="\
>
>     -DLLVM_ENABLE_PROJECTS=clang \
>
>     -DLLVM_ENABLE_RUNTIMES=openmp;compiler-rt \
>
>     -DLLVM_TARGETS_TO_BUILD=X86;NVPTX \
>
>     -DCMAKE_LIBRARY_PATH='${LD_LIBRARY_PATH};/lib64;${CUDA_PATH}/lib64/stubs' \
>
>     -DLIBOMPTARGET_DEP_LIBELF_LIBRARIES:FILEPATH=/usr/lib64/libelf.so.1 \
>
>     -DLIBOMPTARGET_DEP_LIBELF_INCLUDE_DIR=/usr/include \
>
>     -DLIBOMPTARGET_DEP_LIBFFI_INCLUDE_DIR=/usr/include:${CLANG}/extra-includes \
>
>     -DFFI_INCLUDE_DIR:PATH=/usr/include \
>
>     -DLIBOMPTARGET_DEP_LIBFFI_LIBRARIES=${CLANG}/extra-libs/libffi.so \
>
>     -DCMAKE_C_COMPILER=gcc\
>
>     -DCMAKE_CXX_COMPILER=g++ \
>
>     -DLLVM_ENABLE_BACKTRACES=ON \
>
>     -DLLVM_ENABLE_WERROR=OFF \
>
>     -DLLVM_ENABLE_RTTI=ON \
>
>     -DLIBOMP_FORTRAN_MODULES=ON \
>
>     -DOPENMP_ENABLE_LIBOMPTARGET=ON \
>
>     -DLIBOMPTARGET_NVPTX_COMPUTE_CAPABILITIES=35,60,70 \
>
>     -DCLANG_OPENMP_NVPTX_DEFAULT_ARCH=sm_${COMPUTE_CAPABILITY}"
>
>
>
>
>
> Gabriele Jost
>
>
>
> ************************************************************************
>
> Gabriele Jost       NASA Ames Research Center
>
> Email: Gabriele.Jost at nasa.gov      Mail Stop 258-6
>
> Work Phone: (650) 604-0468         Bldg. 258, Rm. 232-4
>
> Scientific & HPC Application           P.O. Box 1
>
> Development/Optimization            Moffett Field, CA 94035-0001
>
> ************************************************************************
>
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