If we enable accelerated CPU, wouldn't we also need to install LLVM first? Or does it also work with Apple clang?

(And are there even Mac packages for LLVM? Compiling it in CI could take forever..)

Guess it should work, but will be a similar situation as with ROCm... versioning is quite different for Apple clang...

Meaning it probably won't work then :P I guess then the question is whether we want to support Apple clang with accelerated cpu to the extent that we test it in CI..

yeah, that's your decision, I guess.. 😇
at least brew should cover your upstream LLVM needs :) brew install llvm

@normallytangent note the difference: OMP_CXX_FLAGS vs OpenMP_CXX_FLAGS where the first one is consumed when configuring the hipSYCL build (not the tests), setting the default for syclcc which is then automatically used for building the tests.
OpenMP_CXX_FLAGS are unused by hipSYCL.

Thank you so much! I was so confused why the flags used during building hipsycl were not being used by when building the tests. If I understand correctly, I need to give both the OMP_CXX_FLAGS and OpenMP_CXX_FLAGS. One for cmake to find the libomp package, and the latter for configuring hipSYCL

Looking at https://github.com/illuhad/hipSYCL/blob/develop/src/runtime/CMakeLists.txt#L181, I think hipSYCL indeed uses the FindOpenMP module? So yeah, those OpenMP_ variables will likely have an effect on whether or not that find_package is happy. Might be that setting OpenMP_CXX_INCLUDE_DIR would be what you'd want to do then? (cf. https://cmake.org/cmake/help/latest/module/FindOpenMP.html, https://github.com/Kitware/CMake/blob/master/Modules/FindOpenMP.cmake)

On a slightly related note (seeing your last commit): I would guess it might make sense to add OMP_CXX_FLAGS_EXTRA (and similarly for *_LINK_* and the other backends) options to hipSYCL's main CMakeLists.txt that are just appended to their respective OMP_CXX_FLAGS? (so that one doesn't have to override the full commandline, e.g. messing up the boost include paths)

@fodinabor I had originally added OpenMP_CXX_INCLUDE_DIR. Later I removed it, when I started passing the path via -I flag to OpenMP_CXX_FLAGS. This commit had built successfully. I've since been unable to reproduce it when I reduce the number of CMAKE options. Another solution probably would be to export LDFLAGS and CPPFLAGS for libomp but I didn't really try it on the CI.

Thanks for the idea about how to append those flags, I was actually finding a way to do just this, but from the user's point of view.

Mhh.. how about providing OMP_ROOT as such -DOpenMP_ROOT=$OMP_ROOT to the hipSYCL build? (alternatively -DCMAKE_PREFIX_PATH=$OMP_ROOT might also work...?)
Maybe that still needs -DCMAKE_CXX_FLAGS=-I$OMP_ROOT/include for the tests though..?
Is that maybe sufficient?

Setting OMP_CXX_FLAGS as currently is, seems brittle (with the boost issue..), but with the _EXTRA thing you could do -DOMP_CXX_FLAGS_EXTRA=-I$OMP_ROOT/include.