[llvm] [NVPTX] Add support for atomic add for bf16 type (PR #89586)

[Adrian Kuegel via llvm-commits]

akuegel wrote:

@Artem-B Do you know someone we could ask who is a floating point expert?
Note that in my previous change where I added support for f16 type, I also didn't handle the case with ftz mode. So do I need to revert that previous patch?

https://github.com/llvm/llvm-project/pull/89586