[PATCH] D84364: [CUDA][HIP] Defer all diagnostics for host device functions

[Yaxun Liu via Phabricator via cfe-commits]

yaxunl added a comment.

In D84364#2168036 <https://reviews.llvm.org/D84364#2168036>, @tra wrote:

> One side effect of this change is that we'll probably stop producing diagnostics for the code that is known to be wrong, but happens to be unused.
>
> E.g.
>
>   __host__ __device__ static void hd() {
>      no_such_type_t t;
>   }
>
>
> We obviously can never compile this function on either side of the compilation and clang currently does diagnose it on both sides.
>  However, if all diagnostics in HD functions are postponed until codegen, this error will go unreported.
>
> What if I have a syntax error in a HD function? I'd still want it to be diagnosed. 
>  It's going to be interesting to see how it affects parsing subsequent code. 
>  E.g https://godbolt.org/z/1vfPcc -- clang complains about the error in `innocent` due to an error in `hd`. If all diags issues in `hd` are postponed and the user only sees `error: function definition is not allowed here`, it will be rather confusing, because the `innocent` itself is perfectly fine.


A diagnostic will be deferred only if clang successfully parsed a function declaration and the current context is a function declaration.

In the above situation, clang fails to parse the function and the current context is not a function, therefore the error is emitted immediately, like before.

I have added a lit test for such situation.

> Also, this patch may need more eyes on it. I'm sure there are more corner cases we may need to think about. 
>  E.g. how would it affect SFINAE? Will it allow some things to succeed where they would've failed previously? If so, is it always the right thing to do?

We only defer diagnostics happen inside a host device function. My guess is that SFINAE will work as before since it happens not in a function scope, therefore it is not deferred. I will add some tests.


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https://reviews.llvm.org/D84364