[llvm] [AArch64] Refactor @plt, @gotpcrel, and @AUTH to use parseDataExpr (PR #134202)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I submitted issue #132569 and created this PR to address the syntax issues in `AArch64AsmParser` and reduce its dependence on the parsing workarounds found in `llvm/lib/MC/MCParser/AsmParser.cpp`. Currently, in data directives, `@specifier` is only utilized by -fexperimental-relative-c++-abi-vtables and PAuth.

I propose introducing a breaking change to eliminate future dependencies on `@specifier`. RISC-V made the breaking change. GNU Assembler doesn't support `@specifier` in data directives for either AArch64 or RISC-V.

While I’d prefer for Mach-O to phase out `@specifier` in data directives, I recognize that it’s used in Mach-O’s instruction operands and may already be part of some shipped arm64e syntax. That said, I strongly believe ELF would benefit from completely removing `@` to streamline its implementation.

https://github.com/llvm/llvm-project/pull/134202