Checking equal variable

Hello. I'm newbie for LLVM.

What I'm trying to do is to check the usage of certain variable in the program.

In order to do that, Iterating the program, what do I need to check?
For example, when checking operands used in any functions, what do I
need to test?

I'm newbie for LLVM and compiler as well, so I need some help. If the
question is so naive, sorry for it.

Thanks