How to add RVE to the LLVM

[liang1232018]

Now I’m doing something about rve. it seems like rve is not supported in llvm upstream. How can I add the rve to the LLVM backend? I have try to learn the source code,but it seems really hard to find the specific position to add rve. Did there have some useful examples or some specific patches which were in the repositories that I can learn or imitate? thanks If the llvm could support the rve someday is great! :-)

[liang1232018]

@asb