[clang] [AArch64] Add support for the __{inc|add}x18{byte|word|dword|qword intrinsics (PR #117752)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic requested changes to this pull request.

Sorry, just spotted an issue: I don't think you're emitting the operations in the correct order.  You need to emit both arguments before you read the register or load the value.

If you have some non-trivial operation like a call in one of the arguments, you don't want that call to happen in the middle of the operation.  MSVC appears to emit the arguments before touching x18.

https://github.com/llvm/llvm-project/pull/117752