https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72488
--- Comment #7 from Jeffrey A. Law <law at redhat dot com> --- I poked at this a bit yesterday (given the irreducible loops I've got some concerns that jump threading might be involved). Whatever is going on, it is highly sensitive to just about any codegen changes. I've identified 3 separate patches from August that can make the bug go latent. Arggh.
