[SYCL][libdevice]: Use g++ driver mode (instead of CC mode) for sycl sources #15885
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…sources This is the technically correct thing to do, and fixes a warning with the Intel C++ compiler, as it warns when CC mode is used for linking C++ sources.
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| set(install_dest_bc lib${LLVM_LIBDIR_SUFFIX}) | ||
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| set(clang $<TARGET_FILE:clang>) | ||
| set(clangxx $<TARGET_FILE:clang> --driver-mode=g++) |
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I think the right place to add compiler options is to extend compile_opts variable. If I understand the problem correctly, the option we need to set is rather -x c++.
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If I understand the problem correctly, the option we need to set is rather -x c++
That's not case, -x c++ is already implicitly set based on the file extension. ICX is specifically looking for the name it is invoked as (argv[0]), which set it's driver mode.
Since clang++ is not a full CMake target (but a symlink) we can't do $<TARGET_FILE:clang++>, but the "driver mode" can also be set explicitly via the option as I did here. This is also why I included the option as part of the variable for the the tool "executable"; In my thinking we're invoking clang++, but can't spell it exactly as such.
I don't mind moving the option to compile_opts though if that's preferred.
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I think this falls more to the compilation/offload tools or driver than to SYCL RT.
@mdtoguchi , @AlexeySachkov , @asudarsa , what are your thoughts on this?
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I somewhat agree and in-fact my initial reaction was fixing icx to not issue this warning for this case. We're passing it -fsycl-device so the host c++ runtime libs are irrelevant. I will revisit that patch, but I believe its not completely wrong to suggest that clang++ be used for C++ sources, so we might apply this too.
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The use of clang --driver-mode=g++ does tell the driver to work as the C++ compiler but from what I understand, the diagnostic that is emitted is happening when we are using -fsycl-device-only. The diagnostic is a link specific diagnostic and since we aren't really doing a host link step with -fsycl-device-only we can probably address the diagnostic emission with a modification to the compiler driver to be a bit smarter when emitting this diagnostic.
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This is the technically correct thing to do, and fixes a warning with the Intel C++ compiler, as it warns when CC mode is used for linking C++ sources.