Added debug message to ObjCARC when we transform an objc_autoreleaseReturnValue => objc_autorelease due to its operand not being used as a return value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171669 91177308-0d34-0410-b5e6-96231b3b80d8
Added debug message in ObjCARC when we remove a no-op cast which has only special semantic meaning in the frontend and thus in the optimizer can be deleted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171670 91177308-0d34-0410-b5e6-96231b3b80d8
Documentation: add clang 3.0 + libstdc++ 4.7.x as a known bad combination that
is actually used by a few Linux distributions


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171671 91177308-0d34-0410-b5e6-96231b3b80d8
Added 2x Debug statements to ObjCARC that log when we handle the two undefined pointer-to-weak-pointer is NULL cases by replacing the given call inst with an undefined value.

The reason that there are two cases is that the first case handles the unary cases and the second the binary cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171672 91177308-0d34-0410-b5e6-96231b3b80d8