https://blog.wongcw.com/2018/10/20/%e4%b8%89%e5%b9%b4%e8%bf%87%e5%8e%bb%e4%ba%86-llvm%e4%bb%8d%e7%84%b6%e6%b2%a1%e6%9c%89%e5%ae%8c%e6%88%90%e5%bc%80%e6%ba%90%e8%ae%b8%e5%8f%af%e8%af%81%e7%9a%84%e6%9b%b4%e6%8d%a2/