[llvm] [AMDGPU] Cgscc amdgpu attributor (PR #179719)

[Yoonseo Choi via llvm-commits]

yoonseoch wrote:

> > Even some callees -> kernels require that. For example, whether a kernel uses Y or Z dimension workgroups is an information gets propagated from leaves to kernel.
> 
> Yes, but that does not require whole world visibility. That only requires knowing everything the kernel will call

I guess the question is if information about a caller not a part of the SCC of the callee is needed when callee's SCC is processed. 
My observation of the ADMGPUAttributor.cpp is that only two attributes AAAMDAttributes and AAAMDGPUMinAGPRAlloc do NOT call `getAAFor()` upon a caller function in its `updateImpl()`.  Other 5 or so attributes do call.  Shilei meant one attribute among those 5 attributes? 

https://github.com/llvm/llvm-project/pull/179719