//===----------------------------------------------------------------------===//
//                        CallGraph Class Enhancements
//===----------------------------------------------------------------------===//

8/18/2004

The problem is that the current implementation of the CallGraph class is about
as stupid as it gets.  It currently assumes that all indirect call sites call
call any address taken function.  More agressive analysis could obviously do
better than this, and we want all of our CallGraphSCC passes to be able to take
advantage of this extra precision.

On the other hand, we don't want to force the clients to use a particular
implementation of this, as there is no globally "right" implementation that
makes sense in all circumstances.

//===----------------------------------------------------------------------===//
//   The solution
//

The solution to this is to just perform some minor surgery on the CallGraph
class, splitting it into an analysis interface (like AliasAnalysis) and a
default implementation.  Unlike the alias analysis class, the actual
representation of the call graph is common across all implementations of the
call graph class (e.g. the use of CallGraphNode), so no accessors need to be
virtual or anything like that.

Implementing the CallGraph class as an analysis interface would allow other
implementations (e.g. a DSA based one) to be trivially plugged in, and all
clients of the CallGraph would automatically use the result.