[llvm] [RISCV] Allow spilling to unused Zcmp Stack (PR #125959)

[Craig Topper via llvm-commits]

topperc wrote:

> :/ I will try to get my head around the V-specific parts of framelowering, it could be that we're allocating specific frame indexes for vector registers which end up overlapping with push/pop.

In the example we have there five 4-byte frame locations and one RVV location. The five 4-byte frame locations should be near SP. The RVV frame location should be laid out between those and the callee saved registers. When accessing the RVV area, we added 16 to SP. I think that makes RVV and one of the scalar frame locations overlap since the scalar locations take up 20 bytes. We need to pad the local area to 32 bytes.

https://github.com/llvm/llvm-project/pull/125959