Questions about BB number changes

Hi, All,

Thanks for your answer ahead of time.

I plug in an new pass into LLVM to insert one line of code to each BB for printing current BB number.
I insert this pass in the Instrumentation phase. But after code generation, I found the total number of BB
is different with the number shown in Assembly code.
For example, when I traverse all BBs during the instrumentation phase, there are 30000. But after
code generation, there are 30100 BBs. For small scale of programs, there is no such issue. Can you
tell me which of the succeeding phases changes the BB number ? How can I deal with this ?