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

[Sander de Smalen via llvm-commits]

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@@ -8074,14 +8102,20 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
                                  PStateSM, false);
   }
 
+  if ((RequiresLazySave && !CalleeAttrs.preservesZA()) || ToggleZA)
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sdesmalen-arm wrote:

Not something for this patch, but I think the combination of 'lazy-save + preserving ZA' is no longer a supported combination with the new attributes, since `__arm_preserves("za")` means the function uses a shared-ZA interface, and will therefore not use the lazy-save mechanism. We can simplify this further in a future patch.

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