[llvm] [AMDGPU] Strengthen preload intrinsics to noundef and nonnull (PR #92801)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Ok, so, implicit argument pointer can reasonably be null, and I'd think library code could reasonably check for implicit arguments being/not being there to avoid crashes or something like that.

The usage inference isn't smart enough to figure this out, and the attributes as defined don't give you the power to express this anyway. So I'm not sure it's worth trying to maintain this.

I do think it's a good idea to split the kernarg and implicitarg cases into a separate PR though. The other cases feel more straightforward 

https://github.com/llvm/llvm-project/pull/92801