Hahnfeld added a comment.
In https://reviews.llvm.org/D50845#1202973, @ABataev wrote:
> > So ideally I think Clang should determine which functions are really
> > `declare target` (either explicit or implicit) and only run semantical
> > analysis on them. If a function is then found to be "broken" it's perfectly
> > desirable to error back to the user.
>
> It is not possible for OpenMP because we support implicit declare target
> functions. Clang cannot identify whether the function is going to be used on
> the device or not during sema analysis.
You are right, we can't do this during device compilation because we don't have
an AST before Sema.
However I'm currently thinking about the following:
1. Identify explicit and implicit `declare target` functions during host Sema
and CodeGen.
2. Attach meta-data for all of them to LLVM IR `.bc` which is passed via
`-fopenmp-host-ir-file-path`. I think we already do something similar for
outlined `target` regions?
3. During device Sema query that meta-data so Clang knows when a function will
be called from within a `target` region. Skip analysis of functions that are
not needed for the device, just as CUDA does.
4. Check that we don't need functions that weren't marked in 2. That's to catch
users doing something like:
#pragma omp target
{
#ifdef __NVPTX__
target_func()
#endif
}
For now that's just an idea, I didn't start implementing any of this yet. Do
you think that could work?
Repository:
rC Clang
https://reviews.llvm.org/D50845
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