[SYCL] linking sycl gives missing __cpu_model

[airlied]

On Fedora 28 + gcc 8.2.1

CMakeFiles/sycl.dir/source/detail/device_info.cpp.o: In function cl::sycl::detail::get_native_vector_width(unsigned long)': device_info.cpp:(.text._ZN2cl4sycl6detail23get_native_vector_widthEm+0x3): undefined reference to __cpu_model'

I can fix this by manually adding -lgcc to the end of the c++ linker line, but that probably means something has gone wrong elsewhere, just mentioning here in case anyone else hits it.

[bader]

Hi Dave, thanks for reporting this issue. We have seen the sample problem with Ubuntu and implemented a workaround in CMake files here: https://github.com/intel/llvm/blob/sycl/sycl/CMakeLists.txt#L102
I think we should look at this problem more carefully and implement a more robust solution.

[kusma]

I'm seeing the same problem as well on Fedora 29 + gcc 8.2.1.

[keryell]

It works out of the box on Ubuntu 18.10 & g++ 8.2.0 at least...

[airlied]

There's probably no harm in expanding the workaround to always just link -lgcc on gcc.