No? The CPU doesn't have undefined behaviour, thus any code running on it doesn't have undefined behaviour either. There are certain operations whose result is

No? The CPU doesn't have undefined behaviour, thus any code running on it doesn't have undefined behaviour either. There are certain operations whose result is not defined in certain states, I think on Intel some SSE operations had undefined results, but even then the same order of operations will lead to the same result. C/C++ compilers generally let you turn off almost all possible undefined behaviour assumptions. I think the only one you can't turn off is the assumption that a pointer to an object is properly aligned, which is understandable - if every pointer had to be checked for alignment before every access, it would ruin performance. In general I would be much happier if I could assert to the compiler that my data fits certain parameters and it would optimise based on these explicit assertions rather than on implicit assumptions (undefined behaviour). Those assertions could be turned off in the final build if we determine they actually impact performance, but I expect I'd be able to keep them on all the time.