I think the parent meant (global (optimisation flags)), not ((global optimisation) flags). Of course, some optimisations don't rely on UB, the difference betwee

I think the parent meant (global (optimisation flags)), not ((global optimisation) flags). Of course, some optimisations don't rely on UB, the difference between the unoptimised and optimised code won't be entirely based on UB (a more reasonable comparison for one single type of UB would be passing -fwrapv vs. not, to stop the compiler thinking signed integers never wrap).