https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97553
--- Comment #5 from Eyal Rozenberg <eyalroz at technion dot ac.il> --- (In reply to Jakub Jelinek from comment #4) > Depends on what you mean by properly. -O3 can be used with sanitization, > but expecting the code to be optimized the same way as without sanitization > is wrong, it is more important to catch as many bugs as possible, and the > runtime instrumentation slows things down anyway. The sanitization is not > meant to be used for production code, only when debugging it. I wonder, then, if some kind of notice isn't called for when -O3 and UBsan are used together.