[LLVMdev] addRequired vs addRequiredTransitive

[Ryan M. Lefever]

I am having a hard time figuring out the difference between addRequired
and addRequiredTransitive.  Could someone please clarify the difference?
  Let's say I have a function pass P1 that relies on a function pass P2.
P1 computes some sort of analysis on a function F and P2 uses that
analysis when it processes F.  Does that mean that I should use
addRequiredTransitive?

Thanks,
Ryan