[AbstractCallSite] Look though constant cast expression when checking for callee use
Summary: That makes AbstractCallSite::isCallee(const Use *) behavior consistent with AbstractCallSite constructor.
Reviewers: jdoerfert
Reviewed By: jdoerfert
Subscribers: mgorny, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79188