Just some minor nits; the bulk of this is above my pay grade. :)
Here and line 34, extraneous whitespace. (Weird spacing throughout, honestly, but that's clang-format for you.)
Here and throughout, FYI, the code is not ADL-proof, which means it'll have this problem:
(1) It kinda looks like __pattern_sort (pstl/include/pstl/internal/algorithm_impl.h line 2198) can call this with __xe == __xs. But maybe I'm wrong.
I have re-run clang-format on the code. Not sure what else to do about it.
Good point. I've tried to fix this everywhere, in the same way that the OpenMP backend fixes it.
Good catch, thank you!
Is there a reason you use ::std here instead of std?
This isn't ADL-proof.
Also not ADL-proof
These comments seem weird to me.