Summary:
This verification may fail after certain transformations due to
BasicAA's fragility. Added a small explanation and a testcase that
triggers the assert in checkClobberSanity (before its removal).
Addresses PR40509.
Reviewers: george.burgess.iv
Subscribers: sanjoy, jlebar, llvm-commits, Prazek
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D57973
llvm-svn: 353739