Prepare RISC-V OpenMP ToolChain

In "Cross Compile to Target Platform" in Deep Learning Benchmark, you can use either method as follows to enable the openmp feature on RISC-V.

Directly Download

You can download "build-omp-shared-rv" from this link and place it under ${LLVM_MLIR_BUILD_DIR}/../ to get environment variable RISCV_OMP_SHARED ready. See the following steps:

$ cd ${LLVM_MLIR_BUILD_DIR}/../
$ wget --no-check-certificate 'https://docs.google.com/uc?export=download&id=1XEsAhOcMioN9gdufuyO9OrHIdR0UtHh2' -O build-omp-shared-rv.tar.gz`
$ tar -xzf build-omp-shared-rv.tar.gz
$ export RISCV_OMP_SHARED=${LLVM_MLIR_BUILD_DIR}/../build-omp-shared-rv/libomp.so

Build From Source Code

In the step "Build Local LLVM/MLIR" in Environment Setup Guide for MLIR and RVV Testing and Experiments, the configuration -DLLVM_ENABLE_PROJECTS="mlir;clang;openmp" only help build OpenMP on X86. If you want to build OpenMP on RV from source code, you need to make the following changes:

STEP ONE: Modify the corresponding part in llvm/openmp/runtime/src/CMakeLists.txt like this:

libomp_get_libflags(LIBOMP_CONFIGURED_LIBFLAGS)
# Build libomp library. Add LLVMSupport dependency if building in-tree with libomptarget profiling enabled.
if(OPENMP_STANDALONE_BUILD OR (NOT OPENMP_ENABLE_LIBOMP_PROFILING))
add_library(omp ${LIBOMP_LIBRARY_KIND} ${LIBOMP_SOURCE_FILES})
target_compile_options(omp PRIVATE ${CMAKE_C_FLAGS}) # new added
# Linking command will include libraries in LIBOMP_CONFIGURED_LIBFLAGS
target_link_libraries(omp ${LIBOMP_CONFIGURED_LIBFLAGS} ${LIBOMP_DL_LIBS})

STEP TWO: Use the following configuration to cross compile openmp with clang.

cmake -G Ninja ../llvm \
    -DLLVM_ENABLE_PROJECTS="clang;openmp" \
    -DLLVM_TARGETS_TO_BUILD="RISCV" \
    -DCMAKE_SYSTEM_NAME=Linux \
    -DCMAKE_VERBOSE_MAKEFILE=ON \
    -DCMAKE_C_COMPILER=${BUILD_LOCAL_LLVM_DIR}/bin/clang \
    -DCMAKE_CXX_COMPILER=${BUILD_LOCAL_LLVM_DIR}/bin/clang++ \
    -DCMAKE_C_FLAGS="--target=riscv64-unknown-linux-gnu --sysroot=${RISCV_GNU_TOOLCHAIN_SYSROOT_DIR} --gcc-toolchain=${BUILD_RISCV_GNU_TOOLCHAIN_DIR}" \
    -DCMAKE_CXX_FLAGS="--target=riscv64-unknown-linux-gnu --sysroot=${RISCV_GNU_TOOLCHAIN_SYSROOT_DIR} --gcc-toolchain=${BUILD_RISCV_GNU_TOOLCHAIN_DIR}" \
    -DLLVM_TABLEGEN=${BUILD_LOCAL_LLVM_DIR}/bin/llvm-tblgen \
    -DCLANG_TABLEGEN=${BUILD_LOCAL_LLVM_DIR}/bin/clang-tblgen \
    -DLLVM_DEFAULT_TARGET_TRIPLE=riscv64-unknown-linux-gnu \
    -DLLVM_TARGET_ARCH=RISCV64 \
    -DCMAKE_BUILD_TYPE=Release \
    -DOPENMP_ENABLE_LIBOMPTARGET=Off \
	-DLIBOMP_ARCH=riscv64 \
	-DLIBOMP_ENABLE_SHARED=On

ninja  clang lli omp