[PATCH] D126398: [Clang] Introduce `-dl` option to perform offload device linking

Wed May 25 11:08:24 PDT 2022

tra added a comment.

> Currently, we infer the usage of the device linker by the user
> specifying an offloading toolchain, e.g. (--offload-arch=...) or
> (-fopenmp-targets=...), but this shouldn't be strictly necessary.

Yup. Whether we want to perform device link or not is orthogonal to those options.

> This patch introduces a new option -dl to tell the driver to use the
> offloading linker instead. So a compilation flow can now look like this,
>
> clang foo.cu --offload-new-driver -fgpu-rdc --offload-arch=sm_70 -c
> clang foo.o -dl -lcudart

It's an essential feature, as we do want to be able to produce libraries with host object files, but with fully linked GPU executables.
Naming, as usual, is hard. I would prefer a more explicit `--offload-link` which would be in line with other --offload* options we have by now. 
`-dl` is cryptic for uninitiated and is uncomfortably close to commonly used `-ldl`. If it gets mistyped as `-ld`, it would lead to a legitimate but unrelated error about missing `libd`. Or it might silently succeed linking with `libd` without actually doing any device linking.

> I was considering if this could be merged into the -fuse-ld option,
> but becuse the device linker wraps over the users linker it would
> conflict with that. In the future it's possible to merge this into lld
> completely or gold via a plugin. Let me know what you think for this.

Repository:
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https://reviews.llvm.org/D126398