Cannot build a debug version of LLVM due to libopenmptarget problem

unterumarmung · May 24, 2023, 9:47pm

Hi

I configure the project with such command:

cmake \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_INSTALL_PREFIX=$INSTALLDIR \
  -DCMAKE_CXX_STANDARD=17 \
  -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
  -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$LD_LIBRARY_PATH" \
  -DFLANG_ENABLE_WERROR=ON \
  -DLLVM_ENABLE_ASSERTIONS=ON \
  -DLLVM_TARGETS_TO_BUILD=host \
  -DLLVM_LIT_ARGS=-v \
  -DLLVM_ENABLE_PROJECTS="clang;mlir;flang;openmp" \
  -DLLVM_ENABLE_RUNTIMES="compiler-rt" \
  ../llvm-project/llvm

And I get the following problem:

[ 78%] Internalizing LLVM bitcode libomptarget-amdgpu-gfx700.bc
/bin/sh: 1: ../../../../bin/opt: Permission denied
make[2]: *** [projects/openmp/libomptarget/DeviceRTL/CMakeFiles/omptarget-amdgpu-gfx700-bc.dir/build.make:80: projects/openmp/libomptarget/DeviceRTL/internalized_libomptarget-amdgpu-gfx700.bc] Error 126
make[1]: *** [CMakeFiles/Makefile2:32863: projects/openmp/libomptarget/DeviceRTL/CMakeFiles/omptarget-amdgpu-gfx700-bc.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs...

It is weird that the build is dependent on the installed opt tool rather than on the one that was built. ../../../../ in my case goes to /.
I do not have such problem with the release build
I have enough space on the disk and resources in general - not the greatest setup but enough to build LLVM.

So, maybe someone knows what the problem could be? Any information is appreciated, thanks.

jplehr · May 25, 2023, 8:42am

Hi,

we typically enable openmp as part of the -DLLVM_ENABLE_RUNTIMES rather than the -DLLVM_ENABLE_PROJECTS.
My understanding is that the main difference is that for the runtime builds, it will pick-up the freshly built clang.
Potentially give that a try.

unterumarmung · May 25, 2023, 8:59am

we typically enable openmp as part of the -DLLVM_ENABLE_RUNTIMES rather than the -DLLVM_ENABLE_PROJECTS

The CMake command I used is based on this one: Getting Started — The Flang Compiler
So, maybe it should be fixed somehow?
-DLLVM_ENABLE_RUNTIMES="compiler-rt;openmp" - is this the correct way to enable OpenMP Runtime?

My understanding is that the main difference is that for the runtime builds, it will pick-up the freshly built clang.

Yet, the problem is not with clang. At least it seems so from the build logs. But maybe it’ll also pick up the fresh opt this way

I’ll definitely try it, thanks!

jplehr · May 25, 2023, 9:56pm

Thanks for pointing out the Flang Getting started guide as the source. That potentially should be changed.

The (almost) same question seemed to also come up here with the same answer.

tschuett · May 26, 2023, 8:36am

I would open an issue with a link to this thread.

unterumarmung · May 29, 2023, 10:22pm

github.com/llvm/llvm-project

Improvement Request: Clarification on Building OpenMP - `-DLLVM_ENABLE_PROJECTS` or `-DLLVM_ENABLE_RUNTIMES`

opened 10:21PM - 29 May 23 UTC

unterumarmung

openmp flang

I would like to suggest a clarification regarding the appropriate method for bui…lding OpenMP within LLVM. Based on the discussions in the following topics: - [**Discourse:** Cannot build a debug version of LLVM due to libopenmptarget problem](https://discourse.llvm.org/t/cannot-build-a-debug-version-of-llvm-due-to-libopenmptarget-problem/70851) - [**Discourse:** OpenMP project or runtime?](https://discourse.llvm.org/t/openmp-project-or-runtime/70886) It is recommended that OpenMP be built as a runtime, as it relies on freshly-built Clang and LLVM tools. However, I have come across three instances where it is suggested to be built as a project. - [Getting Started — The Flang Compiler](https://flang.llvm.org/docs/GettingStarted.html#building-flang-in-tree) - https://github.com/llvm/llvm-project/blob/main/clang/utils/analyzer/entrypoint.py#L56 - https://github.com/llvm/llvm-project/blob/main/llvm/utils/release/build_llvm_release.bat#L155 To avoid confusion and ensure consistency, it would be beneficial to update the relevant documentation and scripts to reflect the recommended approach of building OpenMP as a runtime. Thank you for your attention to this matter.

kiranchandramohan · May 30, 2023, 8:28am

Does that mean, we will have to build clang if we need the OpenMP runtime? This will create an indirect dependence on clang if the requirement is to use OpenMP with flang.

tschuett · May 30, 2023, 8:34am

-DLLVM_ENABLE_RUNTIMES=openmp
will automatically build a fresh Clang and then will build openmp with the fresh Clang.

jplehr · May 30, 2023, 8:39am

As far as I know, the only portion that requires the most up-to-date version of Clang is the DeviceRTL for libomptarget.
I believe though that @jhuber6 would be a much better person to answer this question.

tschuett · May 30, 2023, 8:49am

From the other thread:

Even for OpenMP, the build of libomp and libomptarget are different. For libomp , project build uses the compiler to build LLVM, while runtime build uses the in-tree clang. For libomptarget , in-tree clang is always used.

unterumarmung · May 30, 2023, 8:54am

I guess, they should be built separately then, if they have such differences…