[PATCH] Improve debugging output when there is a null function pointer in the IR dump.

[Philip Reames]

LGTM, this seems like a strict improvement.

However, is this the best reporting we could give?  From what I can gather, null function means either an indirect call or the external function node in the callgraph.   Given the purpose of this pass, would simply skipping the null node entirely be clearer?

http://reviews.llvm.org/D4262