[llvm] [NVPTX] Stop using 16-bit CAS instructions from PTX (PR #120220)

[Artem Belevich via llvm-commits]

Artem-B wrote:

> On the flipside, this degrades codegen for 16-bit cmpxchg: https://godbolt.org/z/rMbfc33dz

Interesting. One thing I notice that 32-bit cmpxchg loop does issue a `YIELD` on each iteration, while `atom.cas.b16` does not.
Is `YIELD` required to guarantee forward progress?

E.g. if the atomic var is constantly changed by some other CM, and we're unlucky to have cmpxchg failing on the time, will 32-bit version allow other threads in a warp to progress, while the 16-bit one would keep them stuck?


https://github.com/llvm/llvm-project/pull/120220