data structure analysis

Hello,

In the poolalloc module, the
DSAA::getModRefInfo(CallSite,Value*,unsigned) function in
DataStructureAA.cpp uses the top-down graph of the caller, but the the
bottom-up graph of the callee to compute the caller-callee node
mapping which it uses to answer mod/ref queries. There is a comment in
the code that says:

  "// Get the graphs for the callee and caller. Note that we want the BU graph
  // for the callee because we don't want all caller's effects incorporated!"

Why is it that we don't want the caller's effects to be incorporated?

Thanks.

Suhabe