yxsamliu wrote:
> > I am afraid this will break all existing CUDA/HIP programs since they
> > expect to be able to parse the builtins for both host and device targets.
> > In the spirit of single source, the compiler sees the entire code for all
> > targets, including host target and all device targets. It is supposed to
> > have AST for all host and device targets. Ideally, it should generate a
> > heterogeneous IR that is for all host and device targets, and eventually
> > generate a heterogeneous executable that includes everything. That would
> > make some optimizations across host and device IR possible. It is just due
> > to current limitation of LLVM/Clang, we generate and process IR separately
> > for each host and device target.
> > I think at least during parsing/sema/AST clang could and should see code
> > and AST for both host and device, since that helps avoid inconsistency
> > between host and device. Therefore it is necessary to see builtins for both
> > host and device. Clang only needs to make sure they are only emitted for
> > the supported target.
>
> This is/was my concern. However, upon thinking further, as long as we
> RECOGNIZE/Parse/etc the builtins, it is OK I think if we report
> "!__has_builtin".
>
> That is:
>
> ```
> void foo() {
> #if __has_builtin(__builtin_x86_thing)
> __builtin_x86_thing();
> #else
> __builtin_x86_thing(); // woops, not has_builtin!
> #endif
> }
> ```
>
> NEEDS to still work, even if the `__has_builtin` answer is 'no'.
If declarations are still there. Only making changes to `__has_builtin`, the
risk of breaking existing code is low.
https://github.com/llvm/llvm-project/pull/121839
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