[LTO] Symbole can't be removed by linker

Hi everyone,

I just ran the example from https://llvm.org/docs/LinkTimeOptimization.html#example-of-link-time-optimization , and on my machine clang 12.0.0 , foo4 can’t be removed.

So, Under what conditions will foo4 be removed?

Thanks,
酷酷的哀殿