[llvm] [AArch64][SME] Save VG for unwind info when changing streaming-mode (PR #83301)

[Kerry McLaughlin via llvm-commits]

kmclaughlin-arm wrote:

> On additional concern I just realized looking at the patch again: I don't think we can use cntd in non-streaming mode on targets without SVE. (See #86743 for more discussion of SME without SVE.)

If the target doesn't have SVE, I don't think there is a need to save VG even in functions which have streaming-mode changes. I've added a helper to AArch64MachineFunctionInfo which will ensure we only spill VG if both hasSVE and hasStreamingModeChanges are true.


https://github.com/llvm/llvm-project/pull/83301