https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83126
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Tom de Vries from comment #4) > (In reply to rguent...@suse.de from comment #3) > > > This is the usual "you should not repeat analysis during transform" issue. > > The vectorizer gets around this by caching relevant scalar evolution > > but obviously that's difficult if using generic stuff like > > canonicalize_loop_ivs ... > > I wonder if it makes sense to add an interface to scalar_evolution_info to > update the instantiated_below field for existing entries. So, before the > loop versioning, the loop preheader is bb10, but after loop versioning, it's > bb15. If we update the instantiated_below field from 10 to 15, the cached > scalar evolution info can still be used. I don't see how this is a sound API that can be used without too much possibility to shoot yourself in the foot ;) I _think_ that eventually the bug is fixed if you move the update_ssa after versioning to after canonicalize_loop_ivs which should have a similar effect than what you propose. GRAPHITE relies on defered update_ssa as well to maintain "compatible" SCEV analysis results.
