Addressed almost all technical and cosmetic concerns concerns. Except putting reference of OpenCLOptions in Sema due to const of TargetInfo. I think I'll think about that later. Also:

Hi! Great to see the interest in OpenCL C 3.0!

So if I understand it well you are suggesting to perform a check for every parsed macro definition that would identify whether the macro has a name matching what is provided in -cl-ext=? Then if the name matches it would check whether the macro should be defined or not?

Perhaps if you give me an example it would help to understand

Yes, in general this approach looks good to me conceptually. I have two suggestions:

What did you think in mind regarding activation of features for SPIR?

Addressed all concerns except replacing __opencl_c_int64 definition into header. The reason for this as follows: this macro should be predefined regardless if clang includes default header or not.

I guess targets like SPIR will be supporting all features by default?

Looks good to me, thanks for the note.

Anastasia, Sven, thanks for the review! Anastasia, it seems that I don't have write access yet. Would you mind landing this change on behalf of me? Thanks!

In D88300#2302796, @svenvh wrote:

LGTM! I'd suggest waiting a bit before committing this though, to give people time to catch up on the RFC.