[clang] [llvm] AMDGPU: Add llvm.amdgcn.s.wait.event intrinsic (PR #180170)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> We have things like `__builtin_readcyclecounter` that lowers to something different every time the HW team changes the clock interface, was wondering if we could just do something similar but I don't know the full context here.

It's way too hardware specific 

https://github.com/llvm/llvm-project/pull/180170