https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61757
--- Comment #32 from Jeffrey A. Law <law at redhat dot com> --- No, we don't have that information available in any reasonable form. That's one of the things I need to investigate. One of the possibilities is to flip things on their side a bit. The old code started recording equivalences it might need to invalidate when it traversed the backedge. Part of the problem with that scheme is some of the equivalences were already recorded by tree-ssa-dom.c, independent of the threading bits. We didn't have a way to find or invalidate those equivalences. One of the things I want to look at is whether or not we can start recording when we process a PHI with arguments that are the targets of backedges. I haven't prototyped any code around that and I'm not sure if we'll have a reasonable separation between DOM and the threading code, but that's the first thing I want to look at once I deal with Teresa's changes.
