Problem with inserting a function call after certain x86 instructions

Hi all,
I am writing a pass subclassing the MachineFunctionPass and doing the instrumentation in runOnMachineFunction(). But I do not know how to insert a function call. In my work, I write a special function for a program to be compiled and I need to insert this function after certain instructions whose destination register is esp. In X86InstrInfo.cpp, there are two kinds of call may be useful, namely X86::CALL32r and X86::CALL32m. And in X86InstrInfo.td, there are three, namely call32i, call32m and CallImmAddr. But I do not know how to use them to insert my special function. Besides, I can not find LEAVE instruction in X86InstrInfo.cpp though it is found in X86InstrInfo.td. Should I use it in form of X86::LEAVE? I would appreciate it if anyone could help me.