question about memory dependence analysis for local structure

Hi,

   I want to do a def-use analysis for fields of local structure. I have tried to use memory dependence analysis to look for depending load/store for a given load from a field of a local structure. I noticed that memory dependence analysis returns a lot of unkown result. I add some print inside the code of memory dependence analysis, and I find that memory dependence analysis got some problems during phi translation. I feel the problem is that the operands of phi are structure, but my input pointer for memory dependence analysis is the address of one field of the structure.

   Do I use memory dependence analysis in a wrong way? Does llvm have some other built-in analysis for field of local structure?

   Thanks a lot!

   Best,

                                                                                       Linhai