[llvm] [AMDGPU] Save/Restore SCC bit across waterfall loop. (PR #68363)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Also should fix this in the generalized waterfall handling in AMDGPURegBankSelect for GlobalISel

Surely GlobalISel Just Works because it is emitting real instructions that clobber SCC, so the register allocator can see exactly what's going on?

https://github.com/llvm/llvm-project/pull/68363