[llvm] [AArch64] Disable Pre-RA Scheduler for Neoverse V2 (PR #127784)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

This should fix the crash. There were some interesting things going on: despite the machine scheduler being disabled, there was scheduling for register pressure going on for the SelectionDAG. The reason was that the default scheduling policy was set to Hybrid, which causes this. If the MachineScheduler is disabled, this now chances the default sched policy to Source.
This is behaviour that we want. 

There is something to fix for the combination "disabled MIScheduler + Hybrid SelectionDAG scheduling" but I can't trigger that (with options); I do have a fix, but can't add a test. 

Anyway, with this fix, I will take these next steps:
- I need to rerun perf numbers,
- I will see if I can create a reproducer that isn't too big for the code that starts spilling.  


https://github.com/llvm/llvm-project/pull/127784