Implications of returning "false" after modifying a Module

I wrote a simple pass that inserts an instruction ( $result = add i32, i32 $op1, i32 $op2 ) right before the branch instruction in all basic blocks. This is effectively dead code since it doesn’t have any dependents. The pass then returns “false” even when the module is modified, and the resulting .bc file has the instructions that were inserted by the pass.

Why didn’t opt raise any warnings about the pass returning “false”, even when the module was modified? Are there instances where this check isn’t performed?