[llvm] [WIP][AMDGPU] combine uniform AMDGPU lane Intrinsics (PR #116953)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > If `speculatable_use()` depends on the uniformity of its argument, then shouldn't it be marked convergent? Clearly it has cross-thread semantics and should not be moved in the control flow.
> 
> No, it could be anything, like a simple `add`. The transitive users may be convergent, but I don't think it really matters. I think there would need to be some kind of convergent operation inserted here to maintain the use position

If it was a simple `add` then hoisting it would not break anything. So there is no problem.

https://github.com/llvm/llvm-project/pull/116953