[llvm] [AArch64][PAC] Introduce AArch64::PAC pseudo instruction (PR #146488)

[Daniil Kovalev via llvm-commits]

================
@@ -3079,6 +3079,76 @@ AArch64TargetLowering::EmitGetSMESaveSize(MachineInstr &MI,
   return BB;
 }
 
+// Helper function to find the instruction that defined a virtual register.
+// If unable to find such instruction, returns nullptr.
+static MachineInstr *stripVRegCopies(const MachineRegisterInfo &MRI,
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kovdan01 wrote:

Nit

```suggestion
static const MachineInstr *stripVRegCopies(const MachineRegisterInfo &MRI,
```

https://github.com/llvm/llvm-project/pull/146488