[llvm] [AMDGPU] Make SGPR occupancy the exact inverse of getMaxNumSGPRs (PR #201342)

[Patrick Simmons via llvm-commits]

linuxrocks123 wrote:

@michaelselehov the function 'getSGPRBudgetPerWave` describes itself as a single source of truth shared by `getMinNumSGPRs()` / `getMaxNumSGPRs()` and "the occupancy inverse" which I assume means `getOccupancyWithNumSGPRs`, but `getOccupancyWithNumSGPRs` never seems to call `getSGPRBudgetPerWave`.

I think that either the code is incorrect or the comment is confusingly worded.

https://github.com/llvm/llvm-project/pull/201342