This commit: 278eb28 introduced a workaround for functions special-casing aarch64 due to an upstream LLVM issue. That issue was closed some time ago, but (according to the comment) that couldn't be removed all the time that rustc supported LLVM versions which wouldn't contain that fix. As rustc now requires LLVM 21 (which is post-fix, I think), could that special-casing now be removed?
Happy to try and help where possible, though I'm no LLVM expert. I have used the intrinsics directly without issue, although "works on my machine" is clearly not the standard.