[llvm] [AArch64][SME] Support `aarch64-split-sve-objects` with VLAs/realignment (PR #163816)

[Benjamin Maxwell via llvm-commits]

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@@ -1308,6 +1307,26 @@ AArch64EpilogueEmitter::AArch64EpilogueEmitter(MachineFunction &MF,
   SEHEpilogueStartI = MBB.end();
 }
 
+void AArch64EpilogueEmitter::moveSPBelowFP(MachineBasicBlock::iterator MBBI,
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MacDue wrote:

I don't think `deallocateStackSpace` is a good name for this function, as that sounds very general, and that's not really what this code does. This function takes a negative offset (which is normally allocating) and moves the SP to the `FP+Offset`. 

I called this `moveSPBelowFP` as that's what this does, it moves the stack pointer to the FP+Offset, while ensuring nothing in the range FP to FP+Offset is (temporarily) deallocated.

https://github.com/llvm/llvm-project/pull/163816