[llvm] [AArch64] Fix return address auth in swiftasync epilogues (PR #189484)

[Oliver Hunt via llvm-commits]

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ojhunt wrote:

If this is only reasonably used in epilogues a reasonable solution here would be to rename the function to indicate that that is the intended use. That's safer than a more generic sounding name wrapping code that is making a non-generic assumption.

Alternatively we could take the impl wrapper approach, e.g

```cpp
void emitPACSymOffsetIntoRegImpl(All, The, Flags, You, Could, Ever, Want) { ... }
void emitEpiloguePACSymOffset(...) { ... emitPACSymOffsetIntoRegImpl(........) }
void emitProloguePACSymOffset(...) { ... emitPACSymOffsetIntoRegImpl(........) }
void emitGeneralPurposePACSymOffsetThingy(...) { ... emitPACSymOffsetIntoRegImpl(........) }
// And of course, for especially logical code
void emitPrologPACSymOffset(...) { ... emitPACSymOffsetIntoRegImpl(........) }
```


https://github.com/llvm/llvm-project/pull/189484