[llvm] [X86Backend] Use GetExternalSymbolSymbol for MO_ExternalSymbol. (PR #133352)

[weiwei chen via llvm-commits]

weiweichen wrote:

> If we are going to make changes here, I'd like to try to ensure consistency across targets. And that whatever API usage rule you want to impose for the sake of your out-of-tree code actually makes sense; if there's a general rule we should follow for creating MCSymbols from the AsmPrinter, we should document it and make sure we consistently follow it.

This is very good point!

I did some "grep" and found out that actually most backends are already using `AsmPrinter` to create `MCSymbol` for `MO_ExternalSymbol`.

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/AArch64/AArch64MCInstLower.cpp#L366-L367

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/ARC/ARCMCInstLower.cpp#L47-L48

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/BPF/BPFMCInstLower.cpp#L71-L72

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/Lanai/LanaiMCInstLower.cpp#L118-L119

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/Mips/MipsMCInstLower.cpp#L146-L147

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/PowerPC/PPCMCInstLower.cpp#L49-L50

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/XCore/XCoreMCInstLower.cpp#L49-L50

https://github.com/llvm/llvm-project/blob/3e742b517a0606bfed329dfcb8c34c614ed73ea7/llvm/lib/Target/Xtensa/XtensaAsmPrinter.cpp#L244-L245

With only one except (in addition to X86) for M68k backend. Adding the change for M68k backend as well. Is there another place to document this other than comments in the code?

https://github.com/llvm/llvm-project/pull/133352