So, how exactly do you check your compiler's behavior? Given: 1) There are various optimizations that may kick in or not depending on UB. 2) The cleverness of

So, how exactly do you check your compiler's behavior? Given: 1) There are various optimizations that may kick in or not depending on UB. 2) The cleverness of the optimizer may and does(!) change between versions. 3) There's no "-warn-on-optimizer-changes" flag for any compiler. Do you think it's realistic to compare compiler output whenever you upgrade your compiler? Do you think it's realistic for 1M SLoC projects? If not, do you take a statistical approach with random sampling? If so, I'd be very interested. If not... what exactly are you sure of and how?