[shadowofneptune]

Right now Rust often limits what it does to what is supported by LLVM. An example is the become statement. This is a reserved keyword which will eventually act as a jump to a function without saving a return address, the current stack frame becomes a new one. This is tricky since things like deconstructors need to still work. It is only recently that LLVM supported this well, and Clang did it first. Separate implementations and having a standard or some other form of communicatiom between implementers can help with these delays.

EDIT: Clang's version is the attribute 'musttail,' if anyone is interested.