[llvm] [llvm-calc-occupancy] Add an AMDGPU occupancy calculator tool (PR #208727)

[via llvm-commits]

michaelselehov wrote:

Sorry for the breakage — the branch predated #209848, which removed `AMDGPU::IsaInfo::getAddressableNumSGPRs()` in favor of the TargetParser version. One-line follow-up fix switching to `GCNSubtarget::getAddressableNumSGPRs()` is on its way.

https://github.com/llvm/llvm-project/pull/208727