[llvm] [LLVM] New NoDivergenceSource function attribute (PR #111832)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> That interpretation of `inreg` is AMDGPU-specific and it only applies to arguments. This is about whether (the return value of) a call is considered always divergent vs only divergent if some of its arguments are.

Oh, I see. It's a replacement for the SourceOfDivergence searchable table, rather than an annotation of the return value 

https://github.com/llvm/llvm-project/pull/111832