[WIP][Attributor] Look through indirect calls

[jdoerfert]

Summary

Through the new Attributor::checkForAllCallees we can look through
indirect calls and visit all potential callees.

NOTE: This is a work in progress patch without much testing.

[arsenm]

llvm/lib/Transforms/IPO/Attributor.cpp

1015

Why the compare to 1 for a bool?

[jdoerfert]

llvm/lib/Transforms/IPO/Attributor.cpp

1015

If we have more than 1 potential callee we don't know if it is a "must" callee anymore. I haven't thought enough about this to be sure we need or don't need it but there is the possibility we want to distinguish callees that may be called here from the one that certainly is.

[arsenm]

ping, what is the status of this?