[llvm] [AArch64][SME2] Preserve ZT0 state around function calls (PR #78321)

[Sander de Smalen via llvm-commits]

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@@ -7664,6 +7666,35 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
     });
   }
 
+  SDValue ZTFrameIdx;
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  bool PreserveZT0 = CallerAttrs.requiresPreservingZT0(CalleeAttrs);
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sdesmalen-arm wrote:

nit:
```suggestion
  bool ShouldPreserveZT0 = CallerAttrs.requiresPreservingZT0(CalleeAttrs);
```

To avoid confusion with `preserves("zt0")`

https://github.com/llvm/llvm-project/pull/78321