[LLVMdev] questions about getAnalysisUsage

[songlh]

Hi,

   I notice that there are several different methods called inside 
getAnalysisUsage(). The parameters of addRequiredID and addPreservedID 
are passID. What is the difference between Required and Preserved? There 
are also function named addRequired<PassName>() called. What is the 
difference between addRequired<PassName>() and addRequiredID(PassID)?

   Thanks a lot!

   Best,

                                                           Linhai