If a class inherits from NSObject and has an implementation, then we
can assume that ivar offsets won't need to be updated by the runtime.
This allows us to index into the object using a constant value and
avoid loading from the ivar offset variable.
This patch was adapted from one written by Pete Cooper.
rdar://problem/10132568
Differential revision: https://reviews.llvm.org/D56802
llvm-svn: 351461
Erik Pilkington