[jcranmer]

So asm! is basically the same functionality, except it's been stripped down to features that are more easily verified for correctness, and some of the syntax has been tweaked to be more understandable. The original asm! macro just passed everything through to the LLVM inline asm construct in raw form, and was renamed llvm_asm! to allow people to keep compatibility while the cleaned-up version of asm! was worked on.

I think the biggest missing features are the more exotic, non-register constraints, but some of the reasons those are omitted are because of unclear coordination between Rust code and the assembly language string.