[llvm] [AMDGPU] When allocating VGPRs, VGPR spills are not part of the prologue (PR #109439)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

@alex-t might have a smaller test case for this. He had the same observation and proposed the same patch.

https://github.com/llvm/llvm-project/pull/109439