[cfe-dev] Problem building llvm and clang 7.0.0

[Andrea Bocci via cfe-dev]

Hi Jonas,
I have a related question: is it possible to build the nvidia OpenMP
support with clang itself, instead of nvcc ?

I am trying to build clang 7 (r339664) with support for CUDA 9.2.148, using
gcc 8.1, on a CentOS 7.5 system.

It builds fine if I leave out OpenMP support:

$ cmake $BASE/llvm-project/llvm -G Ninja \
  -DLLVM_TARGETS_TO_BUILD:STRING="X86;NVPTX" \
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;compiler-rt;lld" \
  -DCMAKE_BUILD_TYPE:STRING=Release \
  -DCMAKE_INSTALL_PREFIX:PATH="$BASE/install-r339664" \
  -DLLVM_LIBDIR_SUFFIX:STRING=64 \
  -DBUILD_SHARED_LIBS:BOOL=ON \
  -DLLVM_ENABLE_EH:BOOL=ON \
  -DLLVM_ENABLE_PIC:BOOL=ON \
  -DLLVM_ENABLE_RTTI:BOOL=ON
...
-- Targeting X86
-- Targeting NVPTX
...
-- Clang version: 7.0.0
-- Performing Test CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG
-- Performing Test CXX_SUPPORTS_NO_NESTED_ANON_TYPES_FLAG - Failed
-- LLD version: 7.0.0
-- Configuring done
-- Generating done
-- Build files have been written to: /data/user/fwyzard/llvm/build-r339664


$ ninja
...
[3874/3875] Linking CXX executable bin/llvm-readobj
[3875/3875] Generating ../../bin/llvm-readelf


If I try to include OpenMP support, it correctly finds the CUDA
installation (and libelf / libffi with some help):

$ cmake $BASE/llvm-project/llvm -G Ninja \
  -DLLVM_TARGETS_TO_BUILD:STRING="X86;NVPTX" \
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;compiler-rt;lld;openmp" \
  -DLIBOMPTARGET_DEP_LIBELF_INCLUDE_DIR:PATH="$GCC_ROOT/include" \
  -DLIBOMPTARGET_DEP_LIBELF_LIBRARIES:PATH="$GCC_ROOT/lib/libelf.so" \
  -DLIBOMPTARGET_DEP_LIBFFI_INCLUDE_DIR:PATH="$LIBFFI_ROOT/include" \
  -DLIBOMPTARGET_DEP_LIBFFI_LIBRARIES:PATH="$LIBFFI_ROOT/lib64/libffi.so" \
  -DCMAKE_BUILD_TYPE:STRING=Release \
  -DCMAKE_INSTALL_PREFIX:PATH="$BASE/install-r339664" \
  -DLLVM_LIBDIR_SUFFIX:STRING=64 \
  -DBUILD_SHARED_LIBS:BOOL=ON \
  -DLLVM_ENABLE_EH:BOOL=ON \
  -DLLVM_ENABLE_PIC:BOOL=ON \
  -DLLVM_ENABLE_RTTI:BOOL=ON
...
-- Targeting X86
-- Targeting NVPTX
...
-- Found LIBOMPTARGET_DEP_LIBELF:
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/gcc/8.1.0/lib/libelf.so
-- Found LIBOMPTARGET_DEP_LIBFFI:
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/libffi/3.2.1/lib64/libffi.so
-- LIBOMPTARGET: Building offloading runtime library libomptarget.
-- LIBOMPTARGET: Not building aarch64 offloading plugin: machine not found
in the system.
-- LIBOMPTARGET: Building CUDA offloading 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: Building x86_64 offloading plugin.
-- LIBOMPTARGET: Building CUDA offloading device RTL.
-- Clang version: 7.0.0
-- LLD version: 7.0.0
-- Configuring done
-- Generating done
-- Build files have been written to: /data/user/fwyzard/llvm/build-r339664

but then it fails because CUDA 9.2 does not support gcc 8:

ninja
...
[780/3744] Building NVCC (Device) object
projects/openmp/libomptarget/deviceRTLs/nvptx/CMakeFiles/omptarget-nvptx.dir/src/omptarget-nvptx_generated_cancel.cu.o
FAILED:
projects/openmp/libomptarget/deviceRTLs/nvptx/CMakeFiles/omptarget-nvptx.dir/src/omptarget-nvptx_generated_cancel.cu.o
cd
/data/user/fwyzard/llvm/build-r339664/projects/openmp/libomptarget/deviceRTLs/nvptx/CMakeFiles/omptarget-nvptx.dir/src
&&
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/cmake/3.11.1/bin/cmake
-E make_directory /data/user/fwyzard/llvm/b
In file included from
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/cuda/9.2.148/include/host_config.h:50,
                 from
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/cuda/9.2.148/include/cuda_runtime.h:78,
                 from <command-line>:
/data/user/fwyzard/llvm/build/slc7_amd64_gcc810.llvm/slc7_amd64_gcc810/external/cuda/9.2.148/include/crt/host_config.h:119:2:
error: #error -- unsupported GNU version! gcc versions later than 7 are not
supported!
 #error -- unsupported GNU version! gcc versions later than 7 are not
supported!

and so on.


Is it possible to build openmp with offload capabilities, using the
just-built clang 7 itself as the compiler ?


Ciao,
.Andrea
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