Meinersbur wrote:
> I think it is because COMPILE_LANGUAGE:CXX does not work for sources where
> the language has been set to CUDA. Since CUDA may be C or C++ sources, it
> would also be wrong to add them to COMPILE_LANGUAGE:CUDA.
>
> I do not think cmake has a way to specify flags to be passed to host
> compilers ([from this cmake
> issue](https://gitlab.kitware.com/cmake/cmake/-/issues/25911)).
>
> Maybe you could define those flags in some functions that could be used both
> here to set COMPILE_LANGUAGE:CXX flags and in `AddFlangRTOffload` to add
> these flags to the `CUDA_COMPILE_OPTIONS`.
I think you are right, the generator-expression only applies to C++. I added it
to avoid applying those switches to C files. I didn't have CUDA in mind, and
neither I think llvm_add_library had[^1]. Overriding the `LANGUAGE` source file
property is something I would not recommend.
For `nvcc`, the documented switch to disable exceptions seems to be
`--no-exceptions`. Options can be forwarded to the host compiler using
`-Xcompiler`. I updated this PR to use these options. Please check those
options.
Windows targets might not be supported for now, but I think still need to be
thought of. Using Clang to compile with experimental CUDA support seemed to
habe been intended at some point, but currently fails (on main) with
```
/home/meinersbur/src/llvm-project-flangrt/flang-rt/../flang/include/flang/Runtime/freestanding-tools.h:91:5:
error: non-void function 'memmove' should return a value [-Wreturn-type]
91 | return;
| ^
```
and other errors.
If I read the CMake issue Kitware correctly, Kitware consideres `-Xcompiler` to
be nvcc-specific and didn't want generalize this for all compilers[^2].
[^1]: The code that applies these compile switches has the comment `# Update
target props, since all sources are C++.` Using the file extension might have
been a workaround before generator expression were available in CMake. It was
added in 2014.
[^2]: If it was up to me, I would rather add `target_device_compile_options`
than `target_host_compile`, because the host (respectively the target that we
are cross-compiling to; "host" is ambiguous here) is the level that all the
compilers and linkers work on. Only the device/auxiliary code is different from
other CMake-supported-languages.
https://github.com/llvm/llvm-project/pull/110217
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