[llvm] [AMDGPU] Prefer lower total register usage in regions with spilling (PR #71882)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

> is it possible to make the patch to choose the default value of `ExcessVGPRWeight` such that the original behavior of unpatched code could be preserved? 

Unfortunately, it is not possible in the current formulation. The new weighted-cost logic is inconsistent with the unpatched tiered-comparisons logic; mainly because the weight-cost formula does not include all of the terms (e.g. tuple pressure). 

https://github.com/llvm/llvm-project/pull/71882