[llvm] [AMDGPU] Introduce "amdgpu-sw-lower-lds" pass to lower LDS accesses. (PR #87265)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Which runtime are you talking about? The firmware or trap handler? And where are they going to place the pointer? Or are you even considering a new architected or reserved register to hold it and a new ABI?

Presumably the implicit kernel arguments, and whatever is setting that up. It's essentially a partner to the queue pointer, which also is in the implicit kernargs 

https://github.com/llvm/llvm-project/pull/87265