[llvm] [AMDGPU] Don't fix the scavenge slot at offset 0 (PR #79136)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> This means that we need to fully handle access by incrementing SP and decrementing after. That was broken at some point. Do we still hit the PEI logic to keep the scavenging slot as close to the incoming SP as possible?

allocateScavengingFrameIndexesNearIncomingSP is overridden, so that should take care of it. I'm also not really seeing any case where we actually make use of the emergency stack slot now?

https://github.com/llvm/llvm-project/pull/79136