[llvm] [AMDGPU] Add intrinsic readanylane (PR #115696)

[via llvm-commits]

ruiling wrote:

> The first part "if x is uniform" means that it is uniform at the place where it is used, not at the place where it is defined. In your example that means that all the dark red cells must have the same value (42) but other green cells could be different.

I would say let's say it clearly that readanylane is defined only if the input is uniform when defined and at the use of readanylane call. We really want the intrinsic to be not convergent to allow related middle-end optimizations.

btw, I think for the existing uniformity analysis, we can say that: "if a value is uniform at use, then it should be uniform at define", right? We only have the case that a value is defined uniform but divergent at its use currently.


https://github.com/llvm/llvm-project/pull/115696