[PATCH] D68388: [PR41008][OpenCL] Add OpenCL C compatibility mode to C++ for OpenCL

Fri Nov 22 05:38:14 PST 2019

kpet added a comment.

Thanks for the feedback.

> I think we should use -fpermissive rather than adding similar flag to Clang.

Could you point me at a use of `-fpermissive` for a similar case? Also it seems `-fpermissive` is not mentioned in the Clang manual or the help text. Am I missing something?

> At the end we might end up with other cases where we need similar mechanism it doesn't make sense to add a flag for each case.

Completely agree and that was one of the reasons I decided to add a generic flag like this. I felt that compatibility with existing OpenCL C source was an important enough use-case to warrant adding a flag for it especially since, as you say, we expect such a flag could be useful to control several bits of behaviour.

> Also I am not sure that what you are doing here is really enabling OpenCL C compatibility mode that would imply to me that restrict is expected to behave in C++ mode as it was in C but is it really the case?

Isn't restrict mainly an optimisation feature? That's certainly my reading of 6.7.3-7 in the C99 spec:

> The intended use of the restrict qualifier (like the register storage class) is to promote
> optimization, and deleting all instances of the qualifier from all preprocessing translation
> units composing a conforming program does not change its meaning (i.e., observable
> behavior).

The main goal here is to be able to consume existing OpenCL C source without modifications. I thought that enabling existing behaviour for `restrict`/`__restrict` that may result in additional optimisations was more useful than just discarding `restrict`, which would be a valid way of achieving compatibility. Is there something specific that worries you?

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